Inverter and wave-transmitting control method

Abstract

The present application provides an inverter and a wave-transmitting control method. The inverter comprises: a primary side circuit, a transformer, a secondary side circuit, and a controller. The controller is configured to: in response to an absolute value of an alternating-current voltage outputted by a filter circuit changing from a value greater than an absolute value of a preset voltage threshold value to a value less than or equal to the absolute value of the preset voltage threshold value, control the inverter to switch from a first working mode to a second working mode, so that among four switch transistors comprised in a bridge arm, at least one switch transistor is turned on, and at most three switch transistors are turned on. The solution provided by the present application can ensure that a follow current path is present in a current of a secondary side winding of the transformer, and avoid the occurrence of shoot through of a secondary side switch transistor, thereby eliminating the risk of damage to the switch transistors caused by inaccurate polarity judgment of the alternating-current voltage.

Description

Inverter and wave generation control method

[0001] This application claims priority to the Chinese patent application with application number 202311055318.5 filed with the State Intellectual Property Office of China on August 18, 2023, and priority to the Chinese patent application with the invention name “A kind of inverter and wave control method”, all contents of which are incorporated by reference into this application. Technical Field

[0002] The embodiments of the present application relate to the field of electric power technology, and in particular to an inverter and a wave generation control method. Background Art

[0003] For various converters that use bidirectional switches as half-bridge arms on the secondary side for grid connection, the port voltage is sampled to control the output voltage and power. Since there is a single or multiple filtering circuits between the port voltage and the bidirectional switch, there is a phase and amplitude difference between the AC voltage at the output port and the output voltage of the bidirectional switch. Therefore, it is impossible to accurately determine the polarity of the output voltage of the bidirectional switch based on the detected AC voltage at the output port. On the other hand, when the AC voltage at the output port is relatively small, the polarity of the output voltage of the bidirectional switch may be misjudged. Once the polarity of the output voltage of the bidirectional switch is misjudged, the controller may turn both bidirectional switches off or on during the switching process, resulting in no freewheeling path for the current in the secondary winding of the transformer or a direct current flow in the switch tube of the secondary circuit, causing damage to the switch tube.

[0004] Summary of the Invention

[0005] The present application provides an inverter and a wave generation control method, which can ensure that the current of the secondary winding of the transformer has a freewheeling path and avoid the problem of direct conduction of the switch tube of the secondary circuit, thereby eliminating the risk of damage to the switch tube.

[0006] In a first aspect, an inverter is provided, comprising: a primary circuit for converting direct current (DC) into alternating current (AC); a transformer for stepping up or down the AC output by the primary circuit; and a secondary circuit for converting the frequency of the stepped-up or stepped-down AC power and filtering the frequency-converted AC power. The secondary circuit comprises a half-bridge circuit and a filter circuit. The half-bridge circuit includes a bridge arm and at least two capacitors, the two capacitors being connected in series and in parallel with the bridge arm. The bridge arm comprises an upper half-bridge arm and a lower half-bridge arm. The connection point between the upper half-bridge arm and the lower half-bridge arm is connected to one end of a secondary winding of the transformer, and the connection point between the two capacitors is connected to the other end of the secondary winding of the transformer. The upper half-bridge arm and the lower half-bridge arm each include a set of switching transistors, each set of switching transistors including two switching transistors each including a parallel freewheeling diode, the two parallel freewheeling diodes in each set of switching transistors having opposite freewheeling directions. The filter circuit is connected to the half-bridge circuit and outputs an AC voltage. A controller is configured to control the on and off of the switching transistors in the bridge arm. The inverter includes a first operating mode and a second operating mode. In the first operating mode, three of the four switching tubes in the bridge arm are turned on, and the remaining switch is turned off. In the second operating mode, both switching tubes in the upper half of the bridge arm are turned on and both switching tubes in the lower half of the bridge arm are turned off, or both switching tubes in the upper half of the bridge arm are turned off and both switching tubes in the lower half of the bridge arm are turned on. The controller is further configured to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, control the inverter to switch from the first operating mode to the second operating mode, so that at least one of the four switching tubes included in the bridge arm is turned on and at most three of the switching tubes are turned on.

[0007] In an embodiment of the present application, since the controller changes the absolute value of the AC voltage output by the filter circuit from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the inverter is controlled to switch from the first operating mode to the second operating mode, so that at least one of the four switching tubes included in the bridge arm is turned on, so that the current of the secondary winding of the transformer has a freewheeling path at any time, and at most three of the four switching tubes included in the bridge arm are turned on, and the secondary side switch tube will not be directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0008] In some possible designs, the controller is used to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and two of the three switching tubes turned on in the first operating mode are the same as the two target switching tubes turned on in the second operating mode to be switched, turn off the switching tubes other than the target switching tubes among the three switching tubes turned on in the first operating mode.

[0009] In the embodiment of the present application, before and after the controller switches the switch tubes, the freewheeling paths for the current in the secondary winding of the transformer are reduced from three to two. Although one freewheeling path is missing, a freewheeling path still exists. Furthermore, in the embodiment of the present application, the controller directly turns off the three switch tubes that are turned on in the first operating mode, excluding the target switch tube. This reduces the number of turned-on switch tubes from three to two, preventing the secondary switch tube from being directly turned on. This eliminates the risk of switch tube damage caused by inaccurate AC voltage polarity determination.

[0010] In some possible designs, the controller is configured to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switching tubes turned on in the first operating mode is the same as a target switching tube turned on in the second operating mode to be switched, first turn off the switching tube in the bidirectional current path of the half-bridge circuit in the first operating mode whose freewheeling direction is opposite to the current direction of the unidirectional current path of the half-bridge circuit in the first operating mode, then turn on the non-conducting switching tube in the unidirectional current path, and then turn off the switching tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half-bridge arm or the lower half-bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half-bridge arm or the lower half-bridge arm through which the current flows is turned on.

[0011] In an embodiment of the present application, in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, and in the case where only one of the three switching tubes turned on in the first operating mode is the same as a target switching tube turned on in the second operating mode to be switched, the controller switches the states of the switching tubes in steps. During the process of the controller switching the states of the switching tubes, since at least one switching tube is in the on state, a freewheeling path always exists for the current in the secondary winding of the transformer. Furthermore, during the process of the controller switching the states of the switching tubes, the controller sequentially turns the switching tubes on or off. At any given moment, only some of the four switching tubes included in the bridge arm are in the on state, thereby avoiding the situation where the switches are directly connected, thereby eliminating the risk of damage to the switches due to inaccurate judgment of the polarity of the AC voltage.

[0012] In some possible designs, the controller is configured to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, only one of the three switching tubes turned on in the first operating mode is the same as a target switching tube turned on in the second operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first operating mode, first simultaneously turn off the two switching tubes in the bidirectional current path of the half-bridge circuit in the first operating mode, and then turn on the non-conducting switching tube in the unidirectional current path of the half-bridge circuit in the first operating mode. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half-bridge arm or the lower half-bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half-bridge arm or the lower half-bridge arm through which the current flows is turned on.

[0013] In the embodiment of the present application, if one of the three switching transistors turned on in the first operating mode is the same as a target switching transistor turned on in the second operating mode to be switched, the controller switches the state of the switching transistor based on the direction of the current flowing through the secondary winding of the transformer. In particular, if the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path, the number of controller actions is reduced.

[0014] In some possible designs, the controller is configured to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, and only one of the three switching tubes turned on in the first operating mode is the same as a target switching tube turned on in the second operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first operating mode, first turn off the switching tube in the bidirectional current path whose freewheeling direction is opposite to the current direction of the unidirectional current path, then turn on the non-conducting switching tube in the unidirectional current path, and then turn off the switching tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0015] In an embodiment of the present application, when one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, the controller switches the state of the switch tube in combination with the direction of the current flowing through the secondary winding of the transformer. When the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path, the controller switches the state of the switch tube in steps. During the process of the controller switching the state of the switch tube, since at least one switch tube is in the on state, the current of the secondary winding of the transformer always has a freewheeling path. Moreover, during the process of the controller switching the state of the switch tube, the switch tube is turned on or off in sequence. At any time, only some of the four switch tubes included in the bridge arm are in the on state, avoiding the situation where the switch tube is directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0016] In some possible designs, the controller is also used to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, control the inverter to switch from the second operating mode to the first operating mode, so that at least one of the four switching tubes included in the bridge arm is turned on and at most three switching tubes are turned on.

[0017] In an embodiment of the present application, since the controller controls the inverter to switch from the second operating mode to the first operating mode in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, at least one of the four switching tubes included in the bridge arm is turned on, so that the current of the secondary winding of the transformer has a freewheeling path at any time, and at most three of the four switching tubes included in the bridge arm are turned on, and the secondary switch tube will not be directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0018] In some possible designs, the controller is used to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold and when the two switching tubes turned on in the second operating mode are the same as two of the three target switching tubes turned on in the first operating mode to be switched, turn on the switching tubes among the target switching tubes except the two switching tubes that are already turned on.

[0019] In this embodiment of the present application, before and after the controller switches the switch, the current in the secondary winding of the transformer has an additional freewheeling path, ensuring that the current always has a freewheeling path. Furthermore, in this embodiment of the present application, the controller turns on the target switch tubes in addition to the two already turned-on switch tubes, increasing the number of turned-on switch tubes from two to three. This prevents the secondary switch tube from being directly turned on, thereby eliminating the risk of switch tube damage caused by inaccurate AC voltage polarity judgment.

[0020] In some possible designs, the controller is configured to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold and when only one of the two switching tubes turned on in the second operating mode is the same as one of the three target switching tubes turned on in the first operating mode to be switched, first turn on the switch tube in the bidirectional current path of the half-bridge circuit in the first operating mode to be switched, whose freewheeling direction is the same as the current direction of the unidirectional current path of the half-bridge circuit in the first operating mode to be switched, then turn off the switch tube that is not in the unidirectional current path, and then turn on the non-conducting switch tube in the bidirectional current path. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switches of the upper half-bridge arm or the lower half-bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switches of the upper half-bridge arm or the lower half-bridge arm through which the current flows is turned on.

[0021] In an embodiment of the present application, in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, and when only one of the two switching tubes turned on in the second operating mode is the same as one of the three target switching tubes turned on in the first operating mode to be switched, the controller turns the switching tubes on or off in steps. During the process of the controller switching the states of the switching tubes, since at least one switching tube is in the on state, a freewheeling path always exists for the current in the secondary winding of the transformer. Furthermore, during the process of the controller switching the states of the switching tubes, the controller turns the switching tubes on or off sequentially, so that at any given moment, only some of the four switching tubes included in the bridge arm are in the on state, thereby avoiding the situation where the switches are directly turned on, thereby eliminating the risk of damage to the switching tubes due to inaccurate judgment of the polarity of the AC voltage.

[0022] In some possible designs, the controller is configured to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, and only one of the two switching transistors turned on in the second operating mode is the same as one of the three target switching transistors turned on in the first operating mode to be switched, and if the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first operating mode, first turn off the switching transistors that are not in the target switching transistors in the unidirectional current path of the half-bridge circuit in the first operating mode, and then simultaneously turn on the non-conducting switching transistors in the bidirectional current path of the half-bridge circuit in the first operating mode. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching transistors in the upper half-bridge arm or the lower half-bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching transistors in the upper half-bridge arm or the lower half-bridge arm through which the current flows is turned on.

[0023] In the embodiment of the present application, when one of the two switching transistors turned on in the second operating mode is the same switching transistor turned on in the first operating mode to be switched, the controller switches the state of the switching transistor based on the current direction of the secondary winding of the transformer. In particular, when the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first operating mode to be switched, the number of controller actions is reduced.

[0024] In some possible designs, the controller is configured to: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, and only one of the two switching transistors turned on in the second operating mode is the same as one of the three target switching transistors turned on in the first operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first operating mode, first turn on the switching transistors in the bidirectional current path whose freewheeling direction is the same as the current direction in the unidirectional current path, then turn off the switching transistors in the unidirectional current path that are not the target switching transistors, and then turn on the non-conducting switching transistors in the bidirectional current path. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching transistors in the upper half bridge arm or the lower half bridge arm through which the current flows are both turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching transistors in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0025] In an embodiment of the present application, when one of the two switch tubes turned on in the second working mode is the same as the target switch tube turned on in the first working mode to be switched, the controller switches the state of the switch tube in combination with the current direction of the secondary winding of the transformer. When the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first working mode, the controller turns on or off the switch tube in steps. During the process of the controller switching the state of the switch tube, since at least one switch tube is in the on state, the current of the secondary winding of the transformer always has a freewheeling path. Moreover, during the process of the controller switching the state of the switch tube, the controller turns on or off the switch tube in sequence. At any time, only some of the four switch tubes included in the bridge arm are in the on state, avoiding the situation where the switch tube is directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0026] In some possible designs, the controller is used to control other switching tubes to start executing switching actions of changing the on-off states after the switching action of controlling the switching tube to change the on-off state is completed.

[0027] In some possible designs, the anodes of the two diodes connected in parallel of the two switch tubes included in each group of switch tubes are connected, or the cathodes of the two diodes connected in parallel of the two switch tubes included in each group of switch tubes are connected.

[0028] In a second aspect, an inverter is provided, comprising: a primary circuit for converting direct current (DC) into alternating current (AC); a transformer for stepping up or down the AC output by the primary circuit; and a secondary circuit for converting the frequency of the stepped-up or stepped-down AC power and filtering the frequency-converted AC power. The secondary circuit comprises a half-bridge circuit and a filter circuit. The half-bridge circuit includes a bridge arm and at least two capacitors, the two capacitors being connected in series and in parallel with the bridge arm. The bridge arm comprises an upper half-bridge arm and a lower half-bridge arm. The connection point of the upper half-bridge arm and the lower half-bridge arm is connected to one end of the secondary winding of the transformer, and the connection point of the two capacitors is connected to the other end of the secondary winding of the transformer. The upper half-bridge arm and the lower half-bridge arm each include a set of switching transistors, each set of switching transistors including two switching transistors each including a parallel freewheeling diode, the two parallel freewheeling diodes in each set of switching transistors having opposite freewheeling directions. The filter circuit is connected to the half-bridge circuit and outputs an AC voltage. A controller is configured to control the switching transistors of the bridge arm to be turned on and off. The inverter includes a first operating mode (positive voltage operating mode) and a first operating mode (negative voltage operating mode). In both the positive voltage operating mode and the negative voltage operating mode, three of the four switching tubes in the bridge arm are turned on, and the remaining switching tube is turned off. The controller is configured to, in response to the AC voltage output by the filter circuit changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, control the inverter to switch from the first operating mode (positive voltage operating mode) to the first operating mode (negative voltage operating mode), so that at least one switching tube and at most three switching tubes of the four switching tubes in the bridge arm are turned on.

[0029] In an embodiment of the present application, the controller controls the inverter to switch from a positive voltage operating mode to a negative voltage operating mode in response to the AC voltage output by the filter circuit being greater than a preset positive voltage threshold and being converted to less than a preset negative voltage threshold, so that at least one of the four switching tubes included in the bridge arm is turned on, so that the current of the secondary winding of the transformer has a freewheeling path at any time, and a maximum of three of the four switching tubes included in the bridge arm are controlled to be turned on, and the secondary switch tube will not be directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0030] In some possible designs, the controller is configured to: in response to the AC voltage output by the filter circuit changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, and the path of the bidirectional current path of the half-bridge circuit in the positive voltage operating mode is the same as the path of the bidirectional current path of the half-bridge circuit in the negative voltage operating mode to be switched, first turn off the switch tubes that are not the target switch tubes among the three switch tubes that are turned on in the positive voltage operating mode, and then turn on the switch tubes that are not turned on among the target switch tubes, so as to control the inverter to switch from the positive voltage operating mode to the negative voltage operating mode, where the target switch tube is the switch tube that is turned on in the negative voltage operating mode. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switches of the upper half-bridge arm or the lower half-bridge arm through which the current flows are turned on.

[0031] In an embodiment of the present application, in response to the AC voltage output by the filter circuit changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, and the path of the bidirectional current path of the half-bridge circuit in the positive voltage operating mode is the same as the path of the bidirectional current path of the half-bridge circuit in the negative voltage operating mode to be switched, the controller operates to switch the states of the switches twice. During the process of switching the states of the switches, the controller ensures that at least one switch is in the on state, thereby always providing a freewheeling path for the current in the secondary winding of the transformer. Furthermore, during the process of switching the switches, the controller sequentially turns the switches on or off, so that at any given moment, only some of the four switches included in the bridge arm are in the on state, thereby avoiding the situation where the switches are directly connected, thereby eliminating the risk of damage to the switches due to inaccurate judgment of the polarity of the AC voltage.

[0032] In some possible designs, the controller is used to: in response to the AC voltage output by the filter circuit changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold and the path of the bidirectional current path of the half-bridge circuit in the positive voltage working mode is different from the path of the bidirectional current path of the half-bridge circuit in the negative voltage working mode to be switched, first turn off the switch tube in the bidirectional current path of the half-bridge circuit in the positive voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer, then turn on the non-conducting switch tube in the unidirectional current path of the half-bridge circuit in the positive voltage working mode, then turn off the other conductive switch tube in the bidirectional current path of the half-bridge circuit in the positive voltage working mode, and finally turn on the switch tube in the bidirectional current path of the half-bridge circuit in the positive voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer. In a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0033] In the embodiment of the present application, when the bidirectional current paths of the positive voltage operating mode and the negative voltage operating mode to be switched differ, the controller switches the states of the switches four times. During these switching steps, the controller ensures that at least one switch remains in the on state, thereby ensuring a continuous freewheeling path for the current in the secondary winding of the transformer. Furthermore, during these switching steps, the controller sequentially turns the switches on and off. At any given moment, only some of the four switches in the bridge arm are in the on state, preventing the switches from being bypassed and eliminating the risk of damage due to inaccurate AC voltage polarity determination.

[0034] In some possible designs, the controller is configured to: in response to the AC voltage output by the filter circuit changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, and the path of the bidirectional current path of the half-bridge circuit in the positive voltage operating mode is different from the path of the bidirectional current path of the half-bridge circuit in the negative voltage operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path of the half-bridge circuit in the positive voltage operating mode, first turn off the switches other than the target switch in the bidirectional current path of the half-bridge circuit in the positive voltage operating mode, and then turn on the switches that are not conducting in the unidirectional current path of the half-bridge circuit in the positive voltage operating mode, the target switch being the switch conducting in the negative voltage operating mode. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switches of the upper half-bridge arm or the lower half-bridge arm through which the current flows are conducting; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switches of the upper half-bridge arm or the lower half-bridge arm through which the current flows is conducting.

[0035] In the embodiment of the present application, when the bidirectional current path in the positive voltage operating mode differs from the bidirectional current path in the negative voltage operating mode to be switched, the controller switches the state of the switch tube based on the current direction of the secondary winding of the transformer. In particular, when the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the initial operating mode to be switched, the number of controller actions is reduced.

[0036] In some possible designs, the controller is used to: in response to the AC voltage output by the filter circuit changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold and the path of the bidirectional current path of the half-bridge circuit in the positive voltage working mode is different from the path of the bidirectional current path of the half-bridge circuit in the negative voltage working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the current direction in the unidirectional current path of the half-bridge circuit in the positive voltage working mode, first turn off the switch tube in the bidirectional current path of the half-bridge circuit in the positive voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer, then turn on the switch tube in the unidirectional current path of the half-bridge circuit in the positive voltage working mode that is not turned on, then turn off another switch tube in the bidirectional current path of the half-bridge circuit in the positive voltage working mode that is turned on, and finally turn on the switch tube in the bidirectional current path of the half-bridge circuit in the positive voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer. In a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0037] In an embodiment of the present application, when the path of the bidirectional current path of the half-bridge circuit in the positive voltage working mode is different from the path of the bidirectional current path of the half-bridge circuit in the negative voltage working mode to be switched, the controller switches the state of the switch tube in combination with the current direction of the secondary winding of the transformer. When the direction of the current flowing through the secondary winding of the transformer is opposite to the current direction in the unidirectional current path of the half-bridge circuit in the initial working mode, the controller turns on or off the switch tube in steps. During the process of the controller switching the state of the switch tube, it is ensured that at least one switch tube is in the on state. Therefore, there is always a freewheeling path for the current of the secondary winding of the transformer. Moreover, during the process of the controller switching the switch tube, the switch tube is turned on or off in sequence. At any time, only some of the four switch tubes included in the bridge arm are in the on state, avoiding the situation where the switch tube is directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0038] In some possible designs, the controller is also used to: in response to the AC voltage output by the filter circuit changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold, control the inverter to switch from the negative voltage working mode of the first working mode to the positive voltage working mode of the first working mode, so that at least one of the four switching tubes included in the bridge arm is turned on and at most three switching tubes are turned on.

[0039] In an embodiment of the present application, in response to the AC voltage output by the filter circuit being less than a preset positive voltage threshold and being converted to greater than a preset negative voltage threshold, the controller controls the inverter to switch from a negative voltage operating mode to a positive voltage operating mode, so that at least one of the four switching tubes included in the bridge arm is turned on, so that the current of the secondary winding of the transformer has a freewheeling path at any time, and a maximum of three of the four switching tubes included in the bridge arm are controlled to be turned on, and the secondary switch tube will not be directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0040] In some possible designs, the controller is used to: in response to the AC voltage output by the filter circuit changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold and the path of the bidirectional current path of the half-bridge circuit in the negative voltage working mode is the same as the path of the bidirectional current path of the half-bridge circuit in the positive voltage working mode to be switched, first turn off the switch tube that does not belong to the target switch tube among the three switch tubes that are turned on in the negative voltage working mode, and then turn on the switch tube that is not turned on in the target switch tube to control the inverter to switch from the negative voltage working mode to the positive voltage working mode, and the target switch tube is the switch tube that is turned on in the positive voltage working mode; in the bidirectional current path, the current flowing through the secondary winding of the transformer includes two directions, and the two switch tubes of the upper half-bridge arm or the lower half-bridge arm through which the current flows are both turned on.

[0041] In the embodiment of the present application, when the bidirectional current paths of the negative voltage operating mode and the positive voltage operating mode to be switched are identical, the controller switches the states of the switches twice. During this process, the controller ensures that at least one switch is in the on state, thus ensuring that a freewheeling path exists for the current in the secondary winding of the transformer. Furthermore, during this process, the controller sequentially switches the switches on and off. At any given moment, only some of the four switches in the bridge arm are in the on state, preventing the switches from being bypassed and eliminating the risk of damage to the switches due to inaccurate AC voltage polarity determination.

[0042] In some possible designs, the controller is used to: in response to the AC voltage output by the filter circuit changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold and the path of the bidirectional current path of the half-bridge circuit in the negative voltage working mode is different from the path of the bidirectional current path of the half-bridge circuit in the positive voltage working mode to be switched, first turn off the switch tube in the bidirectional current path of the half-bridge circuit in the negative voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer, then turn on the non-conducting switch tube in the unidirectional current path of the half-bridge circuit in the negative voltage working mode, then turn off the other conductive switch tube in the bidirectional current path of the half-bridge circuit in the negative voltage working mode, and finally turn on the switch tube in the bidirectional current path of the half-bridge circuit in the negative voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer. In a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0043] In the embodiment of the present application, when the bidirectional current paths of the negative voltage operating mode and the positive voltage operating mode to be switched differ, the controller switches the states of the switches four times. During these switching steps, the controller ensures that at least one switch remains in the on state, thereby ensuring that a freewheeling path exists for the current in the secondary winding of the transformer. Furthermore, during these switching steps, the controller sequentially turns the switches on and off. At any given moment, only some of the four switches in the bridge arm are in the on state, preventing the switches from being bypassed and eliminating the risk of damage due to inaccurate AC voltage polarity determination.

[0044] In some possible designs, the controller is configured to: in response to the AC voltage output by the filter circuit changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold, and the path of the bidirectional current path of the half-bridge circuit in the negative voltage operating mode is different from the path of the bidirectional current path of the half-bridge circuit in the positive voltage operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path of the half-bridge circuit in the negative voltage operating mode, first turn off the switches other than the target switch in the bidirectional current path of the half-bridge circuit in the negative voltage operating mode, and then turn on the non-conducting switches in the unidirectional current path of the half-bridge circuit in the negative voltage operating mode, where the target switch is the switch that is conductive in the positive voltage operating mode. In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switches of the upper half-bridge arm or the lower half-bridge arm through which the current flows are conductive; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switches of the upper half-bridge arm or the lower half-bridge arm through which the current flows is conductive.

[0045] In the embodiments of the present application, when the bidirectional current path in the negative voltage operating mode differs from the bidirectional current path in the positive voltage operating mode to be switched, the controller switches the state of the switch tube based on the current direction of the transformer's secondary winding. In particular, when the direction of the current flowing through the transformer's secondary winding is the same as the direction of the current in the unidirectional current path in the initial operating mode to be switched, the number of controller actions is reduced.

[0046] In some possible designs, the controller is used to: in response to the AC voltage output by the filter circuit changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold and the path of the bidirectional current path of the half-bridge circuit in the negative voltage working mode is different from the path of the bidirectional current path of the half-bridge circuit in the positive voltage working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the current direction in the unidirectional current path of the half-bridge circuit in the negative voltage working mode, first turn off the switch tube in the bidirectional current path of the half-bridge circuit in the negative voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer, then turn on the switch tube in the unidirectional current path of the half-bridge circuit in the negative voltage working mode that is not turned on, then turn off another switch tube in the bidirectional current path of the half-bridge circuit in the negative voltage working mode that is turned on, and finally turn on the switch tube in the bidirectional current path of the half-bridge circuit in the negative voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer. In a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0047] In the embodiment of the present application, when the path of the bidirectional current path in the negative voltage working mode is different from the path of the bidirectional current path in the positive voltage working mode to be switched, the controller switches the state of the switch tube in combination with the current direction of the secondary winding of the transformer. When the direction of the current flowing through the secondary winding of the transformer is opposite to the current direction in the unidirectional current path of the half-bridge circuit in the negative voltage working mode, the controller turns on or off the switch tube in steps. In the process of the controller switching the state of the switch tube, it is ensured that at least one switch tube is in the on state. Therefore, there is always a freewheeling path for the current of the secondary winding of the transformer. Moreover, in the process of the controller switching the switch tube, the switch tube is turned on or off in sequence. At any time, only some of the four switch tubes included in the bridge arm are in the on state, avoiding the situation where the switch tube is directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0048] In some possible designs, the controller is used to control other switching tubes to start executing switching actions of changing the on-off states after the switching action of controlling the switching tube to change the on-off state is completed.

[0049] In some possible designs, the anodes of the two diodes connected in parallel of the two switch tubes included in each group of switch tubes are connected, or the cathodes of the two diodes connected in parallel of the two switch tubes included in each group of switch tubes are connected.

[0050] In a third aspect, a wave generation control method is provided, which is applied to an inverter. The method includes: in a first working mode, controlling three of the four switch tubes in the bridge arm of the inverter to be turned on and the remaining switch tube to be turned off, wherein the secondary circuit of the inverter includes a half-bridge circuit and a filter circuit, the half-bridge circuit includes a bridge arm, the bridge arm includes an upper half-bridge arm and a lower half-bridge arm, the upper half-bridge arm and the lower half-bridge arm each include a group of switch tubes, each group of switch tubes includes two switch tubes each including a parallel freewheeling diode, and each group of switch tubes includes two parallel freewheeling diodes. The freewheeling direction of the tube is opposite; in the second working mode, the two switch tubes in the upper half bridge arm are controlled to be turned on and the two switch tubes in the lower half bridge arm are controlled to be turned off, or, the two switch tubes in the upper half bridge arm are controlled to be turned off and the two switch tubes in the lower half bridge arm are controlled to be turned on; in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the secondary circuit is controlled to switch from the first working mode to the second working mode, so that at least one switch tube among the four switch tubes is turned on and at most three switch tubes are turned on.

[0051] In some possible designs, in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the secondary circuit is controlled to switch from the first operating mode to the second operating mode, including: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and when two of the three switching tubes turned on in the first operating mode are the same as the two target switching tubes turned on in the second operating mode to be switched, the switching tubes other than the target switching tubes among the three switching tubes are turned off to control the secondary circuit to switch from the first operating mode to the second operating mode.

[0052] In some possible designs, in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the secondary circuit is controlled to switch from the first operating mode to the second operating mode, including: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and when only one of the three switch tubes turned on in the first operating mode is the same as a target switch tube turned on in the second operating mode to be switched, first turning off the switch tube in the bidirectional current path of the half-bridge circuit in the first operating mode whose freewheeling direction is opposite to the current direction of the unidirectional current path of the half-bridge circuit in the first operating mode, then turning on the switch tube in the unidirectional current path that is not turned on, and then turning off the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, so as to control the secondary circuit to switch from the first operating mode to the second operating mode. In a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0053] In some possible designs, in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the secondary circuit is controlled to switch from the first operating mode to the second operating mode, including: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first operating mode is the same as a target switch tube turned on in the second operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first operating mode, first simultaneously turn off the two switch tubes in the bidirectional current path of the half-bridge circuit in the first operating mode, and then turn on the switch tube that is not turned on in the unidirectional current path of the half-bridge circuit in the first operating mode, so as to control the secondary circuit to switch from the first operating mode to the second operating mode. In a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0054] In some possible designs, in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, controlling the secondary circuit to switch from the first operating mode to the second operating mode includes: in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first operating mode is the same as a target switch tube turned on in the second operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first operating mode, first turning off the switch tube in the bidirectional current path whose freewheeling direction is opposite to the current direction of the unidirectional current path, then turning on the switch tube in the unidirectional current path that is not turned on, and then turning off the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, so as to control the secondary circuit to switch from the first operating mode to the second operating mode. In a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0055] For the beneficial effects of the third aspect, please refer to the relevant content of the first aspect above and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG1A is a schematic diagram of a scenario applicable to this application.

[0057] FIG1B is a schematic diagram of a topology of an inverter.

[0058] FIG2 is a schematic diagram of an inverter provided in an embodiment of the present application.

[0059] FIG3 is a schematic diagram of another inverter provided in an embodiment of the present application.

[0060] FIG4 is a schematic diagram of partitioning the AC voltage output by the filter circuit according to an embodiment of the present application.

[0061] FIG5 and FIG6 are schematic diagrams of a current loop with an AC voltage in a P region and an O region, respectively, provided in an embodiment of the present application.

[0062] 7 and 8 are schematic diagrams of another current loop with an AC voltage in a P region and an O region, respectively, provided in an embodiment of the present application.

[0063] FIG9 and FIG10 are schematic diagrams of a current loop with an AC voltage in an N region and an O region, respectively, provided in an embodiment of the present application.

[0064] 11 and 12 are schematic diagrams of another current loop with an AC voltage in an N region and an O region, respectively, provided in an embodiment of the present application.

[0065] 13 and 14 are schematic diagrams of another current loop with an AC voltage in a P region and an O region, respectively, provided in an embodiment of the present application.

[0066] 15 and 16 are schematic diagrams of another current loop with an AC voltage in the P region and the O region, respectively, provided in an embodiment of the present application.

[0067] 17 and 18 are schematic diagrams of another current loop with an AC voltage in the N region and the O region, respectively, provided in an embodiment of the present application.

[0068] 19 and 20 are schematic diagrams of another current loop in which the AC voltage is in the N region and the O region, respectively, provided in an embodiment of the present application.

[0069] FIG21 is a schematic diagram showing the location of an inductor current sampling and zero-crossing detection circuit provided in an embodiment of the present application.

[0070] FIG22 is a schematic diagram of an inductor current sampling and zero-crossing detection circuit provided in an embodiment of the present application.

[0071] FIG23 is a schematic diagram of another inductor current sampling and zero-crossing detection circuit provided in an embodiment of the present application.

[0072] 24 to 27 are schematic diagrams of another current loop with an AC voltage in the P region and the O region provided by an embodiment of the present application.

[0073] 28 to 31 are schematic diagrams of another current loop with an AC voltage in the P region and the O region provided by an embodiment of the present application.

[0074] 32 to 35 are schematic diagrams of another current loop in which the AC voltage is in the N region and the O region provided in an embodiment of the present application.

[0075] 36 to 39 are schematic diagrams of another current loop in which the AC voltage is in the N region and the O region, provided in an embodiment of the present application.

[0076] 40 to 43 are schematic diagrams of another current loop with an AC voltage in the P region and the N region provided by an embodiment of the present application.

[0077] 44 to 47 are schematic diagrams of another current loop in which an AC voltage is in a P region and an N region, provided in an embodiment of the present application.

[0078] 48 to 51 are schematic diagrams of another current loop with an AC voltage in the P region and the N region provided by an embodiment of the present application.

[0079] 52 to 55 are schematic diagrams of another current loop in which an AC voltage is in a P region and an N region, provided in an embodiment of the present application.

[0080] Figure 56 is another schematic diagram of a half-bridge circuit in an inverter provided in an embodiment of the present application.

[0081] Figure 57 is a schematic diagram of a wave control method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0082] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0083] Figure 1A is a schematic diagram of a scenario applicable to this application. Referring to Figure 1A , photovoltaic modules convert solar energy into direct current (DC) through the photovoltaic effect. An inverter converts this DC into alternating current (AC) before feeding it into the grid or supplying power to a load. The inverter can also convert DC power from an energy storage system into AC before feeding it into the grid or supplying power to a load.

[0084] Figure 1B is a schematic diagram of the inverter topology. The primary side (i.e., the dotted box ①) is composed of an H-bridge, the middle dotted box ② is a transformer, Ls represents the transformer leakage inductance or the inductance connected in series with the transformer, and the secondary side (i.e., the dotted box ③) is a half-bridge circuit consisting of four switching tubes (including S5, S6, S7, and S8) and two bridge arm capacitors (including Cs1 and Cs2) connected to the output filter (i.e., the dotted box ④). Among them, S8 and S6 in the half-bridge circuit form a bidirectional switch, and S5 and S7 form a bidirectional switch.

[0085] During the positive half cycle of the AC voltage Vac, S5 and S8 switch, while S6 and S7 remain connected. During the negative half cycle of the AC voltage, S6 and S7 switch, while S5 and S8 remain connected. The current technical problems are as follows:

[0086] For the inverter circuit of FIG1B , on the one hand, in order to control the output voltage and power, the output port voltage Vac is sampled. Due to the presence of one or more filtering circuits between the output port current voltage Vac and the voltage V87 across the switches S8-S7, there is a phase and amplitude difference between the output port AC voltage Vac and the voltage V87 across the switches S8-S7. Therefore, it is impossible to accurately determine the polarity of the output voltage V87 of the bidirectional switch based on the detected output port AC voltage Vac. On the other hand, since both the upper and lower bridge arms of the secondary side comprise two bidirectional switches, when the output port voltage Vac is relatively low, the polarity of the voltage V87 across the switches S8-S7 may be incorrectly determined. If the polarity of the output voltage V87 of the switches S8-S7 is incorrectly determined, the controller may switch both bidirectional switches off or on during the switching process, resulting in a loss of a freewheeling path for the current in the inductor Ls or a direct current flow through the switches in the secondary circuit, causing damage to the switches.

[0087] The present application provides an inverter that can ensure that the inductor current has a freewheeling path and avoid the problem of shoot-through in the secondary side switch tube, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0088] FIG2 and FIG3 are schematic diagrams of two inverters provided in embodiments of the present application.

[0089] 2 , the inverter in the embodiment of the present application specifically includes a primary circuit 310, a transformer 320, a secondary circuit 330, and a controller 340. The inverter provided in the embodiment of the present application is specifically applicable to a single-stage isolated inverter topology.

[0090] One end of the primary circuit 310 is connected to a DC voltage Vdc, and the other end is connected to the primary winding of a transformer 320. The primary circuit 310 is configured to convert the input DC voltage Vdc into a high-frequency AC rectangular wave signal. Referring to Figure 3 , the primary circuit 310 can also be configured to consist of multiple submodules connected in series or in parallel, each of which can be a half-bridge circuit or a full-bridge circuit.

[0091] Transformer 320 is used to step up or down the AC power output by primary circuit 310. Transformer 320 can be designed with a secondary leakage inductance equal to Ls. Alternatively, referring to Figures 2 and 3, transformer 320 can be designed with a very low leakage inductance, with a separate inductive element Ls connected in series. This embodiment of the present application uses a separate series inductor Ls as an example.

[0092] In an embodiment of the present application, the secondary circuit 330 includes a half-bridge circuit 331 and a filter circuit 332. The half-bridge circuit 331 includes a bridge arm and at least two capacitors. The two capacitors are connected in series and in parallel with the bridge arm. The bridge arm includes an upper half-bridge arm and a lower bridge arm. The connection point of the upper half-bridge arm and the lower half-bridge arm is connected to one end of the secondary winding of the transformer 320 through an inductive device, and the connection point of the two capacitors is connected to the other end of the secondary winding of the transformer 320. The upper half-bridge arm and the lower half-bridge arm each include a group of switching tubes. The two switching tubes included in each group of switching tubes each include a parallel freewheeling diode. The freewheeling directions of the two parallel freewheeling diodes in each group of switching tubes are opposite. The filter circuit 332 is connected to the half-bridge circuit 331 and outputs an AC voltage.

[0093] In the embodiment of the present application, the inverter includes a first operating mode and a second operating mode. In the first operating mode, three of the four switches in the bridge arm are turned on, and the remaining switch is turned off. In the second operating mode, both switches in the upper half of the bridge arm are turned on and both switches in the lower half of the bridge arm are turned off, or both switches in the upper half of the bridge arm are turned off and both switches in the lower half of the bridge arm are turned on.

[0094] The controller 340 is also used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, control the inverter to switch from the first operating mode to the second operating mode, so that at least one of the four switching tubes included in the bridge arm is turned on and at most three switching tubes are turned on.

[0095] In the embodiment of the present application, the preset voltage threshold includes a preset positive voltage threshold and a preset negative voltage threshold. If the value of the AC voltage output by the filter circuit 332 is greater than the preset positive voltage threshold or the value of the AC voltage output by the filter circuit 332 is less than or equal to the preset negative voltage threshold, the inverter operates in the first operating mode. If the value of the AC voltage output by the filter circuit 332 is greater than or equal to the preset negative voltage threshold and less than or equal to the preset positive voltage threshold, the inverter operates in the second operating mode.

[0096] The absolute values ​​of the preset positive voltage threshold and the preset negative voltage threshold may be equal or different. The absolute values ​​of the preset positive voltage threshold and the preset negative voltage threshold are both less than the maximum positive voltage output by the filter circuit 332. The preset positive voltage threshold and the preset negative voltage threshold may be fixed values ​​or variable values.

[0097] In the embodiments of the present application, the primary circuit 310 may be an H-bridge circuit, such as a half-bridge circuit, a full-bridge circuit, or other circuit capable of converting direct current into high-frequency alternating current. The primary circuit may include multiple H-bridge circuits, such as multiple half-bridge circuits connected in series or in parallel, or a half-bridge circuit and a full-bridge circuit connected in series or in parallel, without limitation.

[0098] In the embodiment of the present application, the upper half bridge arm and the lower half bridge arm of the half-bridge circuit 331 each include two switching tubes, and the two switching tubes included in each bridge arm constitute a bidirectional switch. The switching tube in the embodiment of the present application can specifically be a metal-oxide-semiconductor field-effect transistor (MOSFET), or an insulated gate bipolar transistor (IGBT) or a gallium nitride (GaN) high electron mobility transistor (HEMT), etc. Specifically, the upper half bridge arm or the lower half bridge arm can be composed of two discrete switching tubes, or can be composed of a module integrating two switching tubes, or can be composed of a monolithic bidirectional (conducting or blocking) device (such as a monolithic bidirectional GaN device). For example, the upper half bridge arm includes a switch tube S8 and a switch tube S6 connected in series, and the lower half bridge arm includes a switch tube S5 and a switch tube S7 connected in series.

[0099] Each switch tube in the embodiment of the present application includes a parallel freewheeling diode, which can be called a body diode.

[0100] In the embodiment of the present application, the filter circuit 332 may be a single-stage or multi-stage circuit. One side of the filter circuit 332 is connected to the half-bridge circuit 331 , and the other side 332 of the filter circuit is connected to the AC power supply.

[0101] In an embodiment of the present application, controller 340 can obtain the AC voltage output by filter circuit 332. In one implementation, the filter circuit is a single-stage circuit, and controller 340 obtains the AC voltage output by the single-stage circuit. In another implementation, the filter circuit is a multi-stage circuit, and controller 340 obtains the AC voltage output by any circuit in the multi-stage circuit. Controller 340 compares the AC voltage output by filter circuit 332 with a preset positive voltage threshold and a preset negative voltage threshold, and controls the operating mode of the inverter based on the comparison results.

[0102] For example, assuming the preset positive voltage threshold is 20V and the preset negative voltage threshold is -20V, if the voltage output by the filter circuit 332 is 220V, which is greater than the preset positive voltage threshold of 20V, the controller 340 controls the inverter to operate in the positive voltage operating mode of the first operating mode. If the voltage output by the filter circuit 332 is -220V, which is less than the preset negative voltage threshold of -20V, the controller 340 controls the inverter to operate in the negative voltage operating mode of the first operating mode. If the voltage output by the filter circuit 332 is 10V, which is less than the preset positive voltage threshold of 20V and greater than the preset negative voltage threshold of -20V, the controller 340 controls the inverter to operate in the second operating mode.

[0103] In some implementations, the AC voltage output by the filter circuit 332 can be divided into zones, as shown in FIG4 . If the AC voltage is greater than or equal to a preset positive voltage threshold (the preset positive voltage threshold is VgH in the figure), the AC voltage is in the P zone; if the AC voltage is less than or equal to a preset negative voltage threshold (the preset negative voltage threshold is VgL in the figure), the AC voltage is in the N zone; if the AC voltage is greater than the preset negative voltage threshold and less than the preset positive voltage threshold, the AC voltage is in the O zone. For voltages in the P or N zones, the controller 340 controls the inverter to operate in the first operating mode; for voltages in the O zone, the controller 340 controls the inverter to operate in the second operating mode.

[0104] The difference between the first working mode and the second working mode lies in the different states of the switch tube, where the states of the switch tube include an on state and an off state.

[0105] Specifically, the controller 340 controls the inverter to operate in a first operating mode, and the controller 340 controls three of the four switching tubes included in the bridge arm to be turned on, and the remaining switching tube to be turned off. In the first operating mode, the loop formed by the transformer, the turned-on switching tube, and the two capacitors includes multiple loops, and the inductor current is a current loop among these multiple current loops at any time. The controller 340 controls the inverter to operate in a second operating mode, and the controller 340 controls the two switching tubes included in the upper half bridge arm to be turned on and the two switching tubes included in the lower half bridge arm to be turned off, or the two switching tubes included in the upper half bridge arm to be turned off and the two switching tubes included in the lower half bridge arm to be turned on. In the second operating mode, the loop formed by the transformer, the turned-on switching tube, and the two capacitors includes only one loop.

[0106] It should be noted that if the AC voltage is in the P region or N region, the controller 340 will not control the inverter to operate in the second working mode. This is because the switching frequency of the switch tube is high when operating in the second working mode, which can easily cause damage to the switch tube.

[0107] In an embodiment of the present application, since the controller changes the absolute value of the AC voltage output by the filter circuit from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the inverter is controlled to switch from the first operating mode to the second operating mode, so that at least one of the four switching tubes included in the bridge arm is turned on, so that the current of the secondary winding of the transformer has a freewheeling path at any time, and at most three of the four switching tubes included in the bridge arm are turned on, and the secondary side switch tube will not be directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0108] As mentioned above, the AC voltage output by the filter circuit 332 can be divided into zones, such as P zone, O zone, and N zone. In some cases, due to external factors or other reasons, the AC voltage output by the filter circuit 332 may fluctuate, causing the AC voltage to shift from one zone to another. The controller 340 adopts appropriate strategies based on different situations, as detailed below.

[0109] In one embodiment, the controller 340 is used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and two of the three switch tubes turned on in the first working mode are the same as the two target switch tubes turned on in the second working mode to be switched, turn off the switch tubes other than the target switch tubes among the three switch tubes turned on in the first working mode, so as to control the inverter to switch from the first working mode to the second working mode.

[0110] In the embodiment of the present application, the inverter switches from the first operating mode to the second operating mode in two situations: that is, the AC voltage enters the O region from the P region, or the AC voltage enters the O region from the N region. The following uses the transformer series inductor Ls as an example to illustrate the different situations.

[0111] Case 1: AC voltage enters O region from P region

[0112] (1) In the first operating mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on and the other switching tube included in the lower half bridge arm is turned off. Switching to the second operating mode, the two switching tubes included in the upper half bridge arm are turned on and the two switching tubes included in the lower half bridge arm are turned off.

[0113] FIG5 and FIG6 are schematic diagrams of a current loop with an AC voltage in a P region and an O region, respectively, provided in an embodiment of the present application.

[0114] 5(a) and 5(b), the upper bridge arm includes S8, S6 and the lower bridge arm includes S7, which is turned on, and the lower bridge arm includes S5. Referring to FIG6, the upper bridge arm includes S8, S6 and the lower bridge arm includes S7, S5 which is turned off.

[0115] Referring to Figure 5(a), the current flowing through inductor Ls can have two directions. If the transformer's dotted end (i.e., the end indicated by the black dot on the transformer in the figure) is positive, the current flows from the positive pole of the transformer's secondary winding (i.e., the dotted end of the transformer), passes through switch S6, switch S8, filter capacitor Cx1, and bridge arm capacitor Cs2, and returns to the negative pole of the transformer's secondary winding. If the transformer's dotted end is negative, the current flows from the positive pole of the transformer's secondary winding (i.e., the non-dotted end of the transformer), passes through bridge arm capacitor Cs2, filter capacitor Cx1, switch S8, and switch S6, and returns to the negative pole of the transformer's secondary winding.

[0116] Referring to (b) in Figure 5, the current flowing through the inductor Ls has only one direction. At this time, the same-name terminal of the transformer is the negative pole. The current flows out from the positive pole of the secondary winding of the transformer (that is, the non-same-name terminal of the transformer), passes through the bridge arm capacitor Cs1, the filter capacitor Cx1, S7, and the freewheeling diode on S5 and returns to the negative pole of the secondary winding of the transformer.

[0117] As shown in FIG6 , the current flowing through the inductor Ls also has two directions. The current path is similar to that in FIG5 (a), and will not be described in detail.

[0118] If the current path shown in FIG5 is to be switched to the current path shown in FIG6 , since two of the three switch tubes turned on in the first working mode (i.e., S6 and S8) are the same as the target switch tube, in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 can directly turn off S7.

[0119] In the embodiment of the present application, before the controller 340 turns off S7, the current can form a loop through S6, S8, Cx1, and Cs2, as well as through the freewheeling diodes on Cs1, Cx1, S7, and S5. Even after S7 is turned off, the current can still form a loop through S6, S8, Cx1, and Cs2, which is equivalent to reducing the freewheeling path for the inductor current and does not affect the freewheeling path of the inductor current.

[0120] (2) In the first operating mode, the two switch tubes included in the lower half bridge arm and one switch tube included in the upper half bridge arm are turned on, and the other switch tube included in the upper half bridge arm is turned off; and in the second operating mode, the two switch tubes included in the upper half bridge arm are turned off, and the two switch tubes included in the lower half bridge arm are turned on

[0121] 7 and 8 are schematic diagrams of another current loop with an AC voltage in a P region and an O region, respectively, provided in an embodiment of the present application.

[0122] Referring to (a) and (b) of Figure 7 , S5, S7, and S6 are on, and S8 is off. Referring to Figure 8 , S8 and S6 are off, and S7 and S5 are on.

[0123] Referring to (a) in Figure 7, the current flowing through the inductor Ls has only one direction. At this time, the same-name terminal of the transformer is the positive pole. The current flows out from the positive pole of the secondary winding of the transformer (that is, the same-name terminal of the transformer), passes through the freewheeling diodes on S6 and S8, Cx1, and Cs1, and returns to the negative pole of the secondary winding of the transformer.

[0124] Referring to Figure 7(b), the current flowing through inductor Ls can have two directions. If the transformer's dotted-terminal is positive, the current flows from the positive pole of the transformer's secondary winding (i.e., the dotted-terminal of the transformer), passes through S5, S7, Cx1, and Cs1, and returns to the negative pole of the transformer's secondary winding. If the transformer's dotted-terminal is negative, the current flows from the positive pole of the transformer's secondary winding (i.e., the non-dotted-terminal of the transformer), passes through Cs1, Cx1, S7, and S5, and returns to the negative pole of the transformer's secondary winding.

[0125] As shown in FIG8 , the current flowing through the inductor Ls also has two directions. The current path is similar to that in FIG7 ( b ), and thus will not be described in detail.

[0126] If the current path shown in FIG7 is to be switched to the current path shown in FIG8 , since two of the three switch tubes turned on in the first working mode (i.e., S5 and S7) are the same as the target switch tube, in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 can directly turn off S6 without affecting the freewheeling path of the inductor current.

[0127] Case 2: AC voltage enters O region from N region

[0128] (1) In the first working mode, the two switching tubes included in the upper half bridge arm and the one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off; and in the second working mode, the two switching tubes included in the upper half bridge arm are turned on, and the two switching tubes included in the lower half bridge arm are turned off.

[0129] FIG9 and FIG10 are schematic diagrams of a current loop with an AC voltage in an N region and an O region, respectively, provided in an embodiment of the present application.

[0130] Referring to (a) and (b) of Figure 9 , S8, S6, and S5 are on, and S7 is off. Referring to Figure 10 , S8 and S6 are on, and S7 and S5 are off.

[0131] The current loops in Figures 9(a) and 9(b) refer to the current loops in Figures 5(a) and 5(b) above. The difference is that the current in Figure 9(b) passes through the freewheeling diode on S7, while the current in Figure 5(b) passes through the freewheeling diode on S5. The current loop in Figure 10 is similar to that in Figure 9(a) and will not be described again.

[0132] If the current path shown in FIG9 is to be switched to the current path shown in FIG10 , since two of the three switch tubes turned on in the first working mode (i.e., S6 and S8) are the same as the target switch tube, in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 can directly turn off S5 without affecting the freewheeling path of the inductor current.

[0133] (2) In the first operating mode, the two switch tubes included in the lower half bridge arm and one switch tube included in the upper half bridge arm are turned on, and the other switch tube included in the upper half bridge arm is turned off; and in the second operating mode, the two switch tubes included in the upper half bridge arm are turned off, and the two switch tubes included in the lower half bridge arm are turned on

[0134] 11 and 12 are schematic diagrams of another current loop with an AC voltage in an N region and an O region, respectively, provided in an embodiment of the present application.

[0135] Referring to (a) and (b) of Figure 11 , S5, S7, and S8 are on, and S6 is off. Referring to Figure 12 , S8 and S6 are off, and S7 and S5 are on.

[0136] The current loops in Figures 11(a) and 11(b) refer to the current loops in Figures 7(a) and 7(b) above. The difference is that the current in Figure 11(a) passes through the freewheeling diode on S6, while the current in Figure 7(a) passes through the freewheeling diode on S8. The current loop in Figure 12 is similar to that in Figure 11(b).

[0137] If the current path shown in FIG11 is to be switched to the current path shown in FIG12 , since two of the three switch tubes turned on in the first working mode (i.e., S5 and S7) are the same as the target switch tube, in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 can directly turn off S8 without affecting the freewheeling path of the inductor current.

[0138] In the embodiment of the present application, since two of the three switching tubes turned on in the first operating mode are the same as the two target switching tubes turned on in the second operating mode to be switched, the controller turns off the switching tubes other than the target switching tubes among the three switching tubes turned on in the first operating mode. Before and after the controller switches the switching tubes, the freewheeling paths of the current in the secondary winding of the transformer are reduced from three to two. Although one freewheeling path is missing, the freewheeling path still exists. Moreover, in the embodiment of the present application, the controller directly turns off the switching tubes other than the target switching tube among the three switching tubes turned on in the first operating mode, and the number of switching tubes turned on is reduced from three to two. This prevents the secondary switching tube from being directly turned on, thereby eliminating the risk of damage to the switching tube due to inaccurate judgment of the polarity of the AC voltage.

[0139] In one embodiment, the controller 340 is used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, first turn off the switch tube in the bidirectional current path of the half-bridge circuit 331 in the first working mode whose freewheeling direction is opposite to the current direction of the unidirectional current path of the half-bridge circuit 331 in the first working mode, then turn on the switch tube that is not turned on in the unidirectional current path, and then turn off the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, so as to control the inverter to switch from the first working mode to the second working mode.

[0140] Among them, in the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and the two switching tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are both turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0141] Case 1: AC voltage enters O region from P region

[0142] (1) In the first working mode, the two switch tubes included in the upper half bridge arm and the one switch tube included in the lower half bridge arm are turned on, and the other switch tube included in the lower half bridge arm is turned off. In the second working mode, the two switch tubes included in the upper half bridge arm are turned off, and the two switch tubes included in the lower half bridge arm are turned on.

[0143] 13 and 14 are schematic diagrams of another current loop with an AC voltage in a P region and an O region, respectively, provided in an embodiment of the present application.

[0144] For the state and current path of the switch tube shown in (a) of Figure 13 and (b) of Figure 13 , please refer to the contents of (a) of Figure 5 and (b) of Figure 5 above; for the state and current path of the switch tube shown in Figure 14 , please refer to the contents of Figure 8 above; no further details will be given.

[0145] In conjunction with Figures 13 and 14 , the switches S6, S7, and S8 are turned on in the first operating mode, and the target switches S5 and S7 are turned on in the second operating mode to be switched. Of the three switches turned on in the first operating mode, only one switch (i.e., S7) is the same as the target switch. To switch from the current path shown in Figure 13 to the current path shown in Figure 14 , in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 first turns off the switch in the bidirectional current path whose freewheeling direction is opposite to that of the unidirectional current path, i.e., S8; then turns on the non-conducting switch in the unidirectional current path, i.e., S5; and finally turns off the switch in the bidirectional current path whose freewheeling direction is the same as that of the unidirectional current path, i.e., S6.

[0146] In the embodiment of the present application, the switches that are initially turned on are S6, S7, and S8. The controller 340 first turns off S8, so that S6 and S7 are in the on state. The inductor current forms a freewheeling path through the freewheeling diodes, Cx1, and Cs2 on S6 and S8, and the inductor current forms a freewheeling path through the freewheeling diodes on Cs1, Cx1, S7, and S5. After S8 is completely turned off, the controller 340 turns on S5, so that S5, S6, and S7 are in the on state. The current forms a freewheeling path through Cs1, Cx1, S7, and S5. The inductor current can also form a freewheeling path through the freewheeling diodes, Cx1, and Cs2 on S6 and S8. After S5 is completely turned on, the controller 340 turns off S6, so that S7 and S5 are in the on state. The current forms a freewheeling path through Cs1, Cx1, S7, and S5.

[0147] It is worth noting that since it takes a certain amount of time for a switch to switch between the on and off states, when the controller 340 controls the switching of the switch states, it must ensure that after each switching action of controlling the switch to change the on-off state is completed, that is, after the switch is fully turned on or off, it controls the next switch to start the switching action of changing the on-off state. In other words, before each switching action of the on-off state of a switch is performed, the on-off state switching action of the previous switch must be fully completed. The above-mentioned principle must be followed when the controller 340 controls the switching of the switch states below.

[0148] (2) In the first working mode, the two switch tubes included in the lower half bridge arm and the one switch tube included in the upper half bridge arm are turned on, and the other switch tube included in the upper half bridge arm is turned off. In the second working mode, the two switch tubes included in the upper half bridge arm are turned on, and the two switch tubes included in the lower half bridge arm are turned off.

[0149] 15 and 16 are schematic diagrams of another current loop with an AC voltage in the P region and the O region, respectively, provided in an embodiment of the present application.

[0150] The state and current path of the switch tube shown in (a) of FIG15 and (b) of FIG15 can refer to the contents of (a) of FIG7 and (b) of FIG7 above; the state and current path of the switch tube shown in FIG16 please refer to the contents of FIG6 above; no further details will be given.

[0151] In conjunction with Figures 15 and 16 , the switches S5, S6, and S7 are active in the first operating mode, and the target switches S6 and S8 are active in the second operating mode to be switched. Of the three active switches in the first operating mode, only S6 is identical to the target switch. To switch from the current path shown in Figure 15 to the current path shown in Figure 16 , in response to the absolute value of the AC voltage output by filter circuit 332 changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, controller 340 first turns off S5, then turns on S8, and then turns off S7. For the sake of brevity, the freewheeling path of the inductor current during this switching process will not be described in detail.

[0152] Case 2: AC voltage enters O region from N region

[0153] (1) In the first operating mode, the two switch tubes included in the upper half bridge arm and one switch tube included in the lower half bridge arm are turned on, and the other switch tube included in the lower half bridge arm is turned off; and, in the second operating mode, the two switch tubes included in the upper half bridge arm are turned off, and the two switch tubes included in the lower half bridge arm are turned on.

[0154] 17 and 18 are schematic diagrams of another current loop with an AC voltage in the N region and the O region, respectively, provided in an embodiment of the present application.

[0155] For the status and current loop of the switch tube shown in (a) of Figure 17 and (b) of Figure 17 , please refer to the contents of (a) of Figure 9 and (b) of Figure 9 above; for the status and current loop of the switch tube shown in Figure 18 , please refer to the contents of Figure 12 above; no further details will be given.

[0156] 17 and 18 , the switch tubes turned on in the first working mode are S5, S6, and S8, and the target switch tubes turned on in the second working mode to be switched are S5 and S7. Among the three switch tubes turned on in the first working mode, only S5 is the same as the target switch tube. If the current path shown in FIG17 is to be switched to the current path shown in FIG18 , in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 first turns off S6, then turns on S7, and then turns off S8.

[0157] (2) In the first operating mode, the two switching tubes included in the lower half bridge arm and the one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off; and, in the second operating mode, the two switching tubes included in the upper half bridge arm are turned on, and the two switching tubes included in the lower half bridge arm are turned off.

[0158] 19 and 20 are schematic diagrams of another current loop in which the AC voltage is in the N region and the O region, respectively, provided in an embodiment of the present application.

[0159] The states and current paths of the switch tubes shown in Figures 19(a) and 19(b) refer to the contents of Figures 11(a) and 11(b) above. The states and current paths of the switch tubes shown in Figure 20 refer to the contents of Figure 10 above; no further details will be given.

[0160] In combination with Figures 19 and 20, the switch tubes turned on in the first working mode are S5, S7, and S8, and the target switch tubes turned on in the second working mode to be switched are S6 and S8. Among the three switch tubes turned on in the first working mode, only S8 is the same as the target switch tube. If the current path shown in Figure 19 is to be switched to the current path shown in Figure 20, in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 first turns off S7, then turns on S6, and then turns off S5.

[0161] In summary, when controller 340 controls the switching of the switches, a freewheeling path for the inductor current always exists. Furthermore, at any given moment, only some of the four switches in the upper and lower bridge arms are in the on state, preventing shoot-through and eliminating the risk of switch damage.

[0162] It should be noted that, during the above switching process, the controller 340 cannot first turn off the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, which may cause damage to the switch tube.

[0163] Taking Figures 13 and 14 as an example, the switches S6, S7, and S8 are initially on, and the switches S7 and S5 are targeted for the target state. The switch S6 has the same freewheeling direction in the bidirectional current path as the unidirectional current path. If S6 is turned off first, the current flowing from the same-name end of the transformer's secondary winding cannot pass through the freewheeling diode on S6 due to the unidirectional conductivity of the diode. This leaves the inductor current without a freewheeling path, damaging the switch.

[0164] Furthermore, it should be noted that if only one of the three switching transistors turned on in the first operating mode is the same as the target switching transistor, the remaining non-conducting switching transistor in the target switching transistor cannot be directly turned on. If the remaining non-conducting switching transistor in the target switching transistor is blindly turned on, the switching transistor may be turned on directly, causing damage to the switching transistor.

[0165] Using Figures 13 and 14 as an example, in the first operating mode, S8, S6, and S7 are on, and S5 is off. In the second operating mode, the target switches to be turned on are S7 and S5. Of the switches turned on in the first operating mode, only S7 is the target switch. If S5 is turned on directly, the four switches S5, S6, S7, and S8 will be directly on, causing damage.

[0166] In an embodiment of the present application, if one of the three switching transistors turned on in the first operating mode is the same switching transistor turned on in the second operating mode to be switched, the controller switches the switch states in steps. During this process, at least one switching transistor is in the on state, thus ensuring a freewheeling path for the current in the secondary winding of the transformer. Furthermore, during this process, the controller sequentially switches the switching transistors on and off. At any given moment, only some of the four switching transistors in the bridge arm are in the on state, preventing the switch from being shot through and eliminating the risk of switch damage due to inaccurate AC voltage polarity determination.

[0167] The above description, in conjunction with Figures 13 to 20, describes the process by which the controller 340 controls the inverter to switch between the first operating mode and the second operating mode. The controller 340 needs to perform three steps during the switching process. In order to reduce the number of actions performed by the controller 340, the controller 340 can switch the state of the switch tube based on the direction of the current flowing through the secondary winding of the transformer. This application still takes the example of an inductor connected in series with the secondary winding of the transformer. Before that, a method for detecting the direction of the inductor current is briefly introduced.

[0168] Figure 21 is a schematic diagram illustrating the location of an inductor current sampling and zero-crossing detection circuit provided in an embodiment of the present application. The inductor current sampling and zero-crossing detection circuit can be located at any location where current flows, such as the location shown in Figure 21.

[0169] Figure 22 is a schematic diagram of an inductor current sampling and zero-crossing detection circuit provided by an embodiment of the present application. Zero_P is used to detect positive zero-crossings of the inductor current, and Zero_N is used to detect negative zero-crossings of the inductor current. For a specific strategy for determining the polarity of the inductor current, see Table 1.

[0170] Table 1

[0171] Referring to Table 1 above, when Zero_P = 1 and Zero_N = 0, the controller determines that the inductor current is positive; when Zero_P = 0 and Zero_N = 1, the controller determines that the inductor current is negative; and when Zero_P = 1 and Zero_N = 1, or Zero_P = 0 and Zero_N = 0, the inductor current is approximately 0. This embodiment of the present application mainly describes the case where the inductor current is positive or negative.

[0172] Figure 23 is a schematic diagram of another inductor current sampling and zero-crossing detection circuit provided by an embodiment of the present application. A high-speed analog-to-digital converter (ADC) is used to transmit the real-time sampled signal to the control IC, where a program is implemented to determine the current polarity. In Figure 23, this high-speed ADC can be a discrete ADC chip or an on-chip ADC peripheral integrated within the control IC.

[0173] In one embodiment, the controller 340 is used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first working mode, first simultaneously turn off the two switch tubes in the bidirectional current path of the half-bridge circuit 331 in the first working mode, and then turn on the non-conducting switch tube in the unidirectional current path of the half-bridge circuit 331 in the first working mode, so as to control the inverter to switch from the first working mode to the second working mode.

[0174] In one embodiment, the controller 340 is used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first working mode, first turn off the switch tube in the bidirectional current path whose freewheeling direction is opposite to the current direction of the unidirectional current path, then turn on the switch tube in the unidirectional current path that is not turned on, and then turn off the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, so as to control the inverter to switch from the first working mode to the second working mode.

[0175] In an embodiment of the present application, in a bidirectional current path, there are two directions of current flowing through the secondary winding of the transformer, and both of the two switch tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, there is only one direction of current flowing through the secondary winding, and only one of the two switch tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0176] In the embodiment of the present application, the controller 340 can switch the state of the switch tube in combination with the direction of the current of the secondary winding of the transformer. The following description will be made using the case where an inductor Ls is connected in series with the transformer.

[0177] Case 1: AC voltage enters O region from P region

[0178] (1) In the first operating mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on and the other switching tube included in the upper half bridge arm is turned off. Switching to the second operating mode, the two switching tubes included in the upper half bridge arm are turned on and the two switching tubes included in the lower half bridge arm are turned off.

[0179] Figures 24 and 26 are schematic diagrams of another current loop when the AC voltage is in the P region, provided in an embodiment of the present application, wherein the current direction shown in Figure 24 (including (a) in Figure 24 and (b) in Figure 24) is opposite to the current direction shown in Figure 26. Figures 25 and 27 are schematic diagrams of another current loop when the AC voltage is in the O region, provided in an embodiment of the present application, wherein the current direction shown in Figure 25 is opposite to the current direction shown in Figure 27.

[0180] Referring to Figures 24 and 26, when S5, S7, and S6 are on and S8 is off, the current forms a bidirectional current loop through S5, S7, Cx1, and Cs1. The current forms a unidirectional current loop through the freewheeling diodes on S6 and S8, Cx1, and Cs2. Referring to Figures 25 and 27, when S8 and S6 are on and S7 and S5 are off, the current forms a bidirectional current loop through S6, S8, Cx1, and Cs2.

[0181] In the embodiment of the present application, it is assumed that the direction of the current from left to right as shown in the figure is positive, and the direction from right to left is negative.

[0182] A. The current of inductor Ls is forward

[0183] If the current loop shown in FIG24 is to be switched to the current loop shown in FIG25 , since the current direction of the inductor Ls is the same as the current direction of the unidirectional current path (i.e., the current path shown in (a) in FIG24 ), in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 first simultaneously turns off the two switch tubes in the bidirectional current path in the first working mode, i.e., S5 and S7, and then turns on the non-conducting switch tube in the unidirectional current path, i.e., S8, after S5 and S7 are completely turned off.

[0184] Specifically, controller 340 first simultaneously turns off S5 and S7, leaving only S6 conductive. The current in inductor Ls forms a freewheeling path through the freewheeling diodes on S6 and S8, Cx1, and Cs2. After S5 and S7 are completely turned off, controller 340 turns on S8, turning both S6 and S8 conductive. The current in inductor Ls forms a freewheeling path through S6, S8, Cx1, and Cs2. In this process, controller 340 performs two actions, reducing the number of actions compared to a solution that does not determine the direction of the inductor current.

[0185] B. The inductor current is negative

[0186] If the current loop shown in FIG26 is to be switched to the current loop shown in FIG27 , since the current direction of the inductor Ls is opposite to the current direction of the unidirectional current path (i.e., the current path shown in (a) in FIG24 ), the action sequence of the controller 340 switching the switch tube can be referred to the contents of FIG15 and FIG16 related to switching from the P region to the O region, which will not be repeated here.

[0187] (2) In the first operating mode, the two switch tubes included in the upper half bridge arm and one switch tube included in the lower half bridge arm are turned on, and the other switch tube included in the lower half bridge arm is turned off; and in the second operating mode, the two switch tubes included in the upper half bridge arm are turned off, and the two switch tubes included in the lower half bridge arm are turned on

[0188] Figures 28 and 30 are schematic diagrams of another current loop when the AC voltage is in the P region, provided in an embodiment of the present application, wherein the current direction shown in Figure 28 is opposite to the current direction shown in Figure 30 (including (a) in Figure 30 and (b) in Figure 30). Figures 29 and 31 are schematic diagrams of another current loop when the AC voltage is in the O region, provided in an embodiment of the present application, wherein the current direction shown in Figure 29 is opposite to the current direction shown in Figure 31.

[0189] Referring to Figures 28 and 30, when S8, S6, and S7 are on and S5 is off, the current forms a bidirectional current loop through S6, S8, Cx1, and Cs2. The current forms a unidirectional current loop through the freewheeling diode on S5, S7, Cx1, and Cs1. Referring to Figures 29 and 31, when S8 and S6 are off and S7 and S5 are on, the current forms a bidirectional current loop through S5, S7, Cx1, and Cs1.

[0190] A. The inductor current is positive

[0191] If the current loop shown in FIG28 is to be switched to the current loop shown in FIG29 , the direction of the current in the inductor Ls is opposite to the current direction in the unidirectional current path (i.e., the current path shown in (a) in FIG30 ). For the action sequence of the controller 340 switching the switch tube, please refer to the contents of FIG13 and FIG14 related to switching from the P region to the O region, which will not be repeated here.

[0192] B. The inductor current is negative

[0193] To switch from the current loop shown in FIG30 to the current loop shown in FIG31 , since the direction of the current in inductor Ls is the same as that in the unidirectional current path, in response to the absolute value of the AC voltage output by filter circuit 332 changing from a value greater than a preset voltage threshold to a value less than or equal to the preset voltage threshold, controller 340 first simultaneously turns off S6 and S8, and then turns on S5 after S6 and S8 are completely turned off. For the sake of brevity, the freewheeling path of the inductor current during this switching process will not be described in detail.

[0194] Case 2: AC voltage enters O region from N region

[0195] (1) In the first operating mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off; and in the second operating mode, the two switching tubes included in the upper half bridge arm are turned on, and the two switching tubes included in the lower half bridge arm are turned off.

[0196] Figures 32 and 34 are schematic diagrams of another current loop when the AC voltage is in the N region, provided in accordance with an embodiment of the present application. The current direction shown in Figure 32 is opposite to that shown in Figure 34. Figures 33 and 35 are schematic diagrams of another current loop when the AC voltage is in the O region, provided in accordance with an embodiment of the present application. The current direction shown in Figure 33 is opposite to that shown in Figure 35.

[0197] Referring to Figures 32 and 34, when S5, S7, and S8 are on and S6 is off, the current forms a bidirectional current loop through S5, S7, Cx1, and Cs1. The current forms a unidirectional current loop through the freewheeling diode on S6, S8, Cx1, and Cs2. Referring to Figures 33 and 35, when S8 and S6 are on and S7 and S5 are off, the current forms a bidirectional current loop through S6, S8, Cx1, and Cs2.

[0198] A. The inductor current is positive

[0199] If the current loop shown in FIG34 is to be switched to the current loop shown in FIG35 , the direction of the current in the inductor Ls is opposite to the direction of the current in the unidirectional current path (i.e., the current path shown in (a) in FIG32 ). For the logical action of the controller 340 switching the switch tube, please refer to the above-mentioned contents related to FIG19 and FIG20 on switching from the N region to the O region, which will not be repeated here.

[0200] B. The inductor current is negative

[0201] If the current loop shown in Figure 32 is to be switched to the current loop shown in Figure 33, the direction of the current in the inductor Ls is the same as the current direction in the unidirectional current path (i.e., the current path shown in (a) in Figure 32). In response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 first turns off S5 and S7 at the same time, and then turns on S6 after S5 and S7 are completely turned off.

[0202] (2) In the first operating mode, the two switch tubes included in the upper half bridge arm and one switch tube included in the lower half bridge arm are turned on, and the other switch tube included in the lower half bridge arm is turned off; and in the second operating mode, the two switch tubes included in the upper half bridge arm are turned off, and the two switch tubes included in the lower half bridge arm are turned on

[0203] Figures 36 and 38 are schematic diagrams of another current loop when the AC voltage is in the N region, provided in embodiments of the present application. The current direction shown in Figure 36 is opposite to that shown in Figure 38. Figures 37 and 39 are schematic diagrams of another current loop when the AC voltage is in the O region, provided in embodiments of the present application. The current direction shown in Figure 37 is opposite to that shown in Figure 39.

[0204] Referring to Figures 36 and 38, when S8, S6, and S5 are on and S7 is off, the current forms a bidirectional current loop through S6, S8, Cx1, and Cs2. The current forms a unidirectional current loop through the freewheeling diodes on S5 and S7, Cx1, and Cs1. Referring to Figures 37 and 39, when S8 and S6 are off and S7 and S5 are on, the current forms a bidirectional current loop through S5, S7, Cx1, and Cs1.

[0205] A. The inductor current is positive

[0206] If the current loop shown in Figure 36 is to be switched to the current loop shown in Figure 37, the direction of the current in the inductor Ls is the same as the current direction in the unidirectional current path (i.e., the current path shown in (b) in Figure 36). In response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the controller 340 first turns off S6 and S8 at the same time, and then turns on S7 after S6 and S8 are completely turned off.

[0207] B. The inductor current is negative

[0208] If the current loop shown in FIG38 is to be switched to the current loop shown in FIG39 , the direction of the current in the inductor Ls is opposite to the direction of the current in the unidirectional current path (i.e., the current path shown in (b) in FIG36 ). For the logical action of the controller 340 switching the switch tube, please refer to the contents of FIG17 and FIG18 related to switching from the N region to the O region, which will not be repeated here.

[0209] In an embodiment of the present application, when one of the three switching tubes turned on in the first operating mode is the same as a target switching tube turned on in the second operating mode to be switched, the controller switches the state of the switching tube in combination with the direction of the current flowing through the secondary winding of the transformer. In particular, when the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path, the number of controller actions is reduced.

[0210] Based on this, the above has explained the relevant content of AC voltage entering the O region from the P region / N region. The following will introduce the content of AC voltage entering the P region / N region.

[0211] In one embodiment, the controller 340 is further used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, control the inverter to switch from the second operating mode to the first operating mode, so that at least one of the four switching tubes included in the bridge arm is turned on and at most three switching tubes are turned on.

[0212] For example, assuming the preset positive voltage threshold is 20V and the preset negative voltage threshold is -20V, if the filter circuit 332 converts the output voltage from 10V to 50V, the controller 340 controls the inverter to switch from the second operating mode to the first operating mode. During the inverter operating mode switching process, the controller controls at least one of the four switching tubes included in the bridge arm to be conductive, and at most three switching tubes to be conductive, so that the current in the secondary winding of the transformer has a freewheeling path at all times and avoids shoot-through in the secondary switching tubes.

[0213] In an embodiment of the present application, since the controller controls the inverter to switch from the second operating mode to the first operating mode in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, at least one of the four switching tubes included in the bridge arm is turned on, so that the current of the secondary winding of the transformer has a freewheeling path at any time, and at most three of the four switching tubes included in the bridge arm are turned on, and the secondary switch tube will not be directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0214] In one embodiment, the controller 340 is used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold and when the two switch tubes turned on in the second operating mode are the same as two of the three target switch tubes turned on in the first operating mode to be switched, turn on the switch tubes in the target switch tubes except the two switch tubes that are turned on, so as to control the inverter to switch from the second operating mode to the first operating mode.

[0215] Case 3: AC voltage enters P area from O area

[0216] (1) In the second working mode, the two switching tubes included in the upper half bridge arm are turned on and the two switching tubes included in the lower half bridge arm are turned off. Switching to the first working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0217] Referring to Figures 5 and 6 , the switches S6 and S8 are active in the second operating mode, and the target switches S6, S7, and S8 are active in the first operating mode to be switched. When the inverter switches from the second operating mode to the first operating mode, since the two active switches (i.e., S6 and S8) in the second operating mode are the same as the target switches, controller 340 can simply turn on S7 in response to the absolute value of the AC voltage output by filter circuit 332 changing from a value less than or equal to a preset voltage threshold to a value greater than the preset voltage threshold.

[0218] In the embodiment of the present application, before the controller 340 turns on S7, the current can form a loop through S6, S8, Cx1, and Cs2. Due to the conduction of S7, the current can also form a loop through the freewheeling diodes on Cs1, Cx1, S7, and S5, which is equivalent to adding an additional freewheeling path for the inductor current without affecting the freewheeling path of the inductor current.

[0219] (2) In the second working mode, the two switching tubes included in the upper half bridge arm are turned off, and the two switching tubes included in the lower half bridge arm are turned on. Switching to the first working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off.

[0220] Referring to Figures 7 and 8 above, the switches S5 and S7 are turned on in the second operating mode, and the target switches S5, S6, and S7 are turned on in the first operating mode to be switched. When the inverter switches from the second operating mode to the first operating mode, since the two switches (i.e., S5 and S7) turned on in the second operating mode are the same as the target switches, in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 can directly turn on S6. The reason is similar to that of (1) in Case 3 and will not be explained in detail.

[0221] Case 4: AC voltage enters N region from O region

[0222] (1) In the second working mode, the two switching tubes included in the upper half bridge arm are turned on, and the two switching tubes included in the lower half bridge arm are turned off. Switching to the first working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0223] Referring to Figures 9 and 10 above, the switches that are turned on in the second operating mode are S6 and S8, and the target switches that are turned on in the first operating mode to be switched are S5, S6, and S8. When the inverter switches from the second operating mode to the first operating mode, since the two switches that are turned on in the second operating mode (i.e., S6 and S8) are the same as the target switches, in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 can directly turn on S5. The reason is similar to that of (1) in Case 3 and will not be explained in detail.

[0224] (2) In the second working mode, the two switching tubes included in the upper half bridge arm are turned off, and the two switching tubes included in the lower half bridge arm are turned on. Switching to the first working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off.

[0225] Referring to Figures 11 and 12 above, the switches that are turned on in the second operating mode are S5 and S7, and the target switches that are turned on in the first operating mode to be switched are S5, S7, and S8. When the inverter switches from the second operating mode to the first operating mode, since the two switches that are turned on in the second operating mode (i.e., S5 and S7) are the same as the target switches, in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 can directly turn on S8. The reason is similar to that of (1) in Case 3 and will not be explained in detail.

[0226] In the embodiment of the present application, because the two switching tubes that are turned on in the second operating mode are the same as two of the three target switching tubes that are turned on in the first operating mode to be switched, the controller turns on the target switching tubes except for the two switching tubes that are already turned on. Before and after the controller switches the switching tubes, the current in the secondary winding of the transformer has an additional freewheeling path, and the freewheeling path always exists. Moreover, in the embodiment of the present application, the controller turns on the target switching tubes except for the two switching tubes that are already turned on, and the number of switching tubes turned on increases from two to three. This prevents the secondary switching tube from being directly turned on, thereby eliminating the risk of damage to the switching tube due to inaccurate judgment of the polarity of the AC voltage.

[0227] In one embodiment, the controller 340 is used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold and when only one of the two switch tubes turned on in the second working mode is the same as one of the three target switch tubes turned on in the first working mode to be switched, first turn on the switch tube in the bidirectional current path of the half-bridge circuit 331 in the first working mode to be switched, whose freewheeling direction is the same as the current direction of the unidirectional current path of the half-bridge circuit 331 in the first working mode, then turn off the switch tube in the unidirectional current path that does not belong to the target switch tube, and then turn on the switch tube that is not turned on in the bidirectional current path, so as to control the inverter to switch from the second working mode to the first working mode.

[0228] Case 3: AC voltage enters P area from O area

[0229] (1) In the second working mode, the two switching tubes included in the upper half bridge arm are turned off, and the two switching tubes included in the lower half bridge arm are turned on. Switching to the first working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0230] With reference to Figures 13 and 14 , to switch from the current path shown in Figure 14 to the current path shown in Figure 13 , in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 first turns on the switch in the bidirectional current path in the first operating mode whose freewheeling direction is the same as that of the unidirectional current path, i.e., S6. It then turns off the switch in the unidirectional current path in the first operating mode that is not the target switch, i.e., S5. It then turns on the non-conducting switch in the bidirectional current path in the first operating mode, i.e., S8.

[0231] In the embodiment of the present application, the controller 340 first turns on S6, thereby turning on S5, S6, and S7. The inductor current forms a freewheeling path through Cs1, Cx1, S7, and S5. The current can also form a freewheeling path through the freewheeling diodes on S6 and S8, Cx1, and Cs2. After S6 is fully turned on, S5 is turned off, thereby turning on S6 and S7. The inductor current forms a freewheeling path through the freewheeling diodes on S6 and S8, Cx1, and Cs2. The inductor current can also form a freewheeling path through the freewheeling diodes on Cs1, Cx1, S7, and S5. After S5 is fully turned off, the controller 340 turns on S8, thereby turning on S6, S7, and S8. The freewheeling path of the inductor current is shown in Figure 13.

[0232] (2) In the second working mode, the two switching tubes included in the upper half bridge arm are turned on and the two switching tubes included in the lower half bridge arm are turned off. Switching to the first working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off.

[0233] 15 and 16 , if the current path shown in FIG. 16 is to be switched to the current path shown in FIG. 15 , in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 first turns on S7, then turns off S8, and finally turns on S5.

[0234] Case 4: AC voltage enters N region from O region

[0235] (1) In the second working mode, the two switching tubes included in the upper half bridge arm are turned off, and the two switching tubes included in the lower half bridge arm are turned on. Switching to the first working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0236] 17 and 18 , if the current path shown in FIG. 18 is to be switched to the current path shown in FIG. 17 , in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 first turns on S8, then turns off S7, and finally turns on S6.

[0237] (2) In the second working mode, the two switching tubes included in the upper half bridge arm are turned on, and the two switching tubes included in the lower half bridge arm are turned off. Switching to the first working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off.

[0238] 19 and 20 , if the current path shown in FIG. 20 is to be switched to the current path shown in FIG. 19 , in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 first turns on S5, then turns off S6, and finally turns on S7.

[0239] In an embodiment of the present application, when one of the two switching transistors turned on in the second operating mode is the same switching transistor turned on in the first operating mode to be switched, the controller turns the switching transistors on or off in steps. During the process of the controller switching the switching transistor states, at least one switching transistor is in the on state, so a freewheeling path for the current in the secondary winding of the transformer always exists. Furthermore, during the process of the controller switching the switching transistor states, the controller turns the switching transistors on or off sequentially. At any given moment, only some of the four switching transistors included in the bridge arm are in the on state, thus preventing the switch from being turned on straight through and eliminating the risk of switch damage due to inaccurate judgment of the AC voltage polarity.

[0240] The following describes the process of the controller 340 controlling the inverter to switch from the second operating mode to the first operating mode in conjunction with the current direction of the secondary winding of the transformer.

[0241] In one embodiment, the controller 340 is used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold and only one of the two switch tubes turned on in the second working mode is the same as one of the three target switch tubes turned on in the first working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first working mode, first turn off the switch tube that does not belong to the target switch tube in the unidirectional current path of the half-bridge circuit 331 in the first working mode, and then simultaneously turn on the switch tube that is not turned on in the bidirectional current path of the half-bridge circuit 331 in the first working mode, so as to control the inverter to switch from the second working mode to the first working mode.

[0242] In one embodiment, the controller 340 is used to: in response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to a preset voltage threshold to an absolute value greater than the preset voltage threshold and only one of the two switch tubes turned on in the second working mode is the same as one of the three target switch tubes turned on in the first working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first working mode, first turn on the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, then turn off the switch tube in the unidirectional current path that does not belong to the target switch tube, and then turn on the switch tube that is not turned on in the bidirectional current path, so as to control the inverter to switch from the second working mode to the first working mode.

[0243] In an embodiment of the present application, in a bidirectional current path, there are two directions of current flowing through the secondary winding of the transformer, and both of the two switch tubes in the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in a unidirectional current path, there is only one direction of current flowing through the secondary winding, and only one of the two switch tubes in the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0244] The following uses the transformer series inductance Ls as an example to explain different situations.

[0245] Case 3: AC voltage enters P area from O area

[0246] (1) In the second working mode, the two switching tubes included in the upper half bridge arm are turned on and the two switching tubes included in the lower half bridge arm are turned off. Switching to the first working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on and the other switching tube included in the upper half bridge arm is turned off.

[0247] A. When the inductor current is positive

[0248] Referring to Figures 24 and 25 , if the current path shown in Figure 25 is switched to the current path shown in Figure 24 , the direction of the inductor current is the same as that in the unidirectional current path in the first operating mode (i.e., the current path shown in Figure 24 (a)). In response to the absolute value of the AC voltage output by the filter circuit 332 changing from a value less than or equal to a preset voltage threshold to a value greater than the preset voltage threshold, the controller 340 first turns off the switch that is not the target switch in the unidirectional current path, i.e., S8. It then turns on the non-conducting switches in the bidirectional current path in the first operating mode, i.e., S5 and S7.

[0249] In this embodiment, controller 340 first turns off S8, leaving only S6 on. The inductor current forms a freewheeling path through the freewheeling diodes, Cx1, and Cs2 on S6 and S8. After S8 is completely turned off, S5 and S7 are turned on. At this point, S5, S6, and S7 are all on, and one freewheeling path for the inductor current is shown in Figure 24.

[0250] In this embodiment of the present application, if the inductor current direction is the same as the current direction in the unidirectional current path, controller 340 first turns off S8. After S8 is completely turned off, controller 340 simultaneously turns on S5 and S7. During this process, controller 340 performs two actions, which reduces the number of actions required by controller 340 compared to a solution that does not determine the inductor current direction.

[0251] B. When the inductor current is negative

[0252] If the current loop shown in FIG27 is to be switched to the current loop shown in FIG26 , the direction of the inductor current is opposite to the current direction in the unidirectional current path in the first working mode (i.e., the current path shown in (a) in FIG24 ). For the logical action of the controller 340 switching the switch tube, please refer to the contents of FIG15 and FIG16 related to switching from the O zone to the P zone, which will not be repeated here.

[0253] (2) In the second working mode, the two switching tubes included in the upper half bridge arm are turned off, and the two switching tubes included in the lower half bridge arm are turned on. Switching to the first working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0254] A. When the inductor current is positive

[0255] If the current path shown in FIG29 is to be switched to the current path shown in FIG28 , the logic action of the controller 340 switching the switch tube can be referred to the contents of FIG13 and FIG14 in the case of switching from the O region to the P region, which will not be repeated here.

[0256] B. When the inductor current is negative

[0257] 30 and 31 , if the current path shown in FIG. 31 is switched to the current path shown in FIG. 30 , at this time, the direction of the inductor current is the same as the current direction in the unidirectional current path in the first working mode (i.e., the current path shown in (b) in FIG. 30 ). In response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 first turns off S5 and then turns on S6 and S8.

[0258] Case 4: AC voltage enters N region from O region

[0259] (1) In the second working mode, the two switching tubes included in the upper half bridge arm are turned on, and the two switching tubes included in the lower half bridge arm are turned off. Switching to the first working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off.

[0260] A. When the inductor current is positive

[0261] 32 and 33 above, if the current path shown in FIG33 is to be switched to the current path shown in 32, the logic action of the controller 340 switching the switch tube can refer to the contents of FIG19 and FIG20 above regarding switching from the O region to the N region, which will not be repeated here.

[0262] B. When the inductor current is negative

[0263] 34 and 35 , if the current path shown in FIG35 is switched to the current path shown in FIG34 , at this time, the direction of the inductor current is the same as the current direction in the unidirectional current path in the first working mode (i.e., the current path shown in (a) in FIG32 ). In response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 first turns off S6 and then turns on S5 and S7 at the same time.

[0264] (2) In the second working mode, the two switching tubes included in the upper half bridge arm are turned off, and the two switching tubes included in the lower half bridge arm are turned on. Switching to the first working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0265] A. When the inductor current is positive

[0266] 36 and 37 , if the current path shown in FIG37 is switched to the current path shown in FIG36 , at this time, the direction of the inductor current is the same as the current direction in the unidirectional current path in the first working mode (i.e., the current path shown in (b) in FIG36 ). In response to the absolute value of the AC voltage output by the filter circuit 332 changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold, the controller 340 first turns off S7 and then turns on S6 and S8 at the same time.

[0267] B. When the inductor current is negative

[0268] Referring to Figures 38 and 39 above, if you want to switch from the current path shown in Figure 39 to the current path shown in 38, the logic action of the controller 340 switching the switch tube please refer to the above-mentioned Figures 17 and 18 related to switching from the O area to the N area, and no further details will be given.

[0269] In an embodiment of the present application, when one of the two switching tubes turned on in the second working mode is the same as the target switching tube turned on in the first working mode to be switched, the controller switches the state of the switching tube in combination with the current direction of the secondary winding of the transformer, especially when the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first working mode to be switched, the number of controller actions is reduced.

[0270] Based on this, the above description describes the switching of the AC voltage between the P / N region and the O region. In some cases, when the AC voltage is in the P / N region and the voltage peak is small, some interference may cause the polarity of the AC voltage to reverse, causing the inverter to switch between the positive voltage operating mode and the negative voltage operating mode included in the first operating mode.

[0271] In one embodiment, the controller 340 is used to control the inverter to switch from the positive voltage working mode of the first working mode to the negative voltage working mode of the first working mode in response to the AC voltage output by the filter circuit 332 changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, so that at least one switch tube among the four switch tubes included in the bridge arm is turned on and at most three switch tubes are turned on.

[0272] The controller 340 is also used to control the inverter 340 to switch from the negative voltage working mode of the first working mode to the positive voltage working mode of the first working mode in response to the AC voltage output by the filter circuit 332 changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold, so that at least one switch tube among the four switch tubes included in the bridge arm is turned on and at most three switch tubes are turned on.

[0273] For example, assuming the preset positive voltage threshold is 20V and the preset negative voltage threshold is -20V, if the filter circuit 332 converts the output voltage from 10V to -10V, the controller 340 controls the inverter to switch from the positive voltage operating mode of the first operating mode to the negative voltage operating mode of the first operating mode. During the process of switching the operating mode of the inverter, the controller controls at least one of the four switching tubes included in the bridge arm to be conductive, and at most three switching tubes to be conductive, so that the current of the secondary winding of the transformer has a freewheeling path at all times and the secondary switching tubes are prevented from shooting through.

[0274] Similarly, if the filter circuit 332 converts its output voltage from -10V to 10V, the controller 340 controls the inverter to switch from the negative voltage operating mode of the first operating mode to the positive voltage operating mode of the first operating mode. During the inverter operating mode switch, the controller controls at least one of the four switching transistors included in the bridge arm to be conductive, and at most three switching transistors to be conductive, thereby ensuring a freewheeling path for the current in the secondary winding of the transformer at all times and preventing shoot-through in the secondary switching transistors.

[0275] In an embodiment of the present application, the controller controls the inverter to switch from a positive voltage working mode to a negative voltage working mode in response to the AC voltage output by the filter circuit being greater than a preset positive voltage threshold and being converted to less than a preset negative voltage threshold; or, the controller controls the inverter to switch from a negative voltage working mode to a positive voltage working mode in response to the AC voltage output by the filter circuit being less than a preset negative voltage threshold and being converted to greater than a preset positive voltage threshold; so that at least one of the four switching tubes included in the bridge arm is turned on, so that the current of the secondary winding of the transformer has a freewheeling path at any time, and at most three of the four switching tubes included in the bridge arm are controlled to be turned on, and the secondary switch tube will not be directly turned on, thereby eliminating the risk of damage to the switch tube due to inaccurate judgment of the polarity of the AC voltage.

[0276] In one embodiment, the controller 340 is used to: in response to the AC voltage output by the filter circuit 332 changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold and the path of the bidirectional current path of the half-bridge circuit in the positive voltage working mode is the same as the path of the bidirectional current path of the half-bridge circuit in the negative voltage working mode to be switched, first turn off the switch tube that does not belong to the target switch tube among the three switch tubes that are turned on in the positive voltage working mode, and then turn on the switch tube that is not turned on in the target switch tube, so as to control the inverter to switch from the positive voltage working mode to the negative voltage working mode.

[0277] In one embodiment, the controller 340 is configured to: in response to the AC voltage output by the filter circuit 332 changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold and the path of the bidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode is different from the path of the bidirectional current path of the half-bridge circuit 331 in the negative voltage operating mode to be switched, first turn off the switch tube in the bidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode, in which the freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer; then turn on the switch tube in the unidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode that is not conducting; then turn off the other switch tube in the bidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode that is conducting; and finally turn on the switch tube in the bidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode, in which the freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer, so as to control the inverter to switch from the positive voltage operating mode to the negative voltage operating mode, where the target switch tube is the switch tube that is conducting in the negative voltage operating mode.

[0278] In a bidirectional current path, the current flows through the transformer's secondary winding in two directions, and both switches in the upper or lower bridge arm are turned on. In a unidirectional current path, the current flows through the secondary winding in only one direction, and only one of the two switches in the upper or lower bridge arm is turned on.

[0279] In the embodiment of the present application, the controller 340 can switch the state of the switch tube based on whether the paths of the bidirectional circuit paths of the initial operating mode and the target operating mode are consistent. See below for details. In this embodiment of the present application, the initial operating mode is a positive voltage operating mode, and the target operating mode is a negative voltage operating mode. In other words, in this embodiment of the present application, the controller 340 controls the inverter to switch from the positive voltage operating mode to the negative voltage operating mode.

[0280] Case 5: AC voltage switches from P region to N region

[0281] (1) In the initial working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off; when switching to the target working mode, the two switching tubes included in the upper half bridge arm are turned on, and the state of the switching tube included in the lower half bridge arm is opposite to the state of the switching tube in the initial working mode

[0282] Figures 40 and 42 are schematic diagrams of another current loop when the AC voltage is in the P region according to an embodiment of the present application, wherein the current direction shown in Figure 40 is opposite to the current direction shown in Figure 42. Figures 41 and 43 are schematic diagrams of another current loop when the AC voltage is in the N region according to an embodiment of the present application, wherein the current direction shown in Figure 41 is opposite to the current direction shown in Figure 43.

[0283] For the states and current loops of the switch tubes shown in FIG. 40 and FIG. 42 , please refer to the contents of FIG. 5 . For the states and current loops of the switch tubes shown in FIG. 41 and FIG. 43 , please refer to the contents of FIG. 9 . No further details will be given.

[0284] In the embodiment of the present application, the switches that are turned on in the initial operating mode are S6, S8, and S7, and the switches that are turned on in the target operating mode are S6, S8, and S5. Since the bidirectional current path in the initial operating mode is the same as the path of the bidirectional current path in the target operating mode to be switched, that is, both form a bidirectional current path through S6, S8, Cx1, and Cs2. Therefore, when switching from the initial operating mode to the target operating mode, in response to the AC voltage output by the filter circuit 332 changing from greater than the preset positive voltage threshold to less than the preset negative voltage threshold, the controller 340 turns off the switch that is not the target switch among the three switches that were turned on in the initial operating mode, namely, S7. As a result, S6 and S8 are in the on state, and the inductor current forms a freewheeling path through S6, S8, Cx1, and Cs2. After S7 is completely turned off, the controller 340 turns on the non-conducting switch tube in the target switch tube, that is, S5, so that S5, S6, and S8 are in the on state. In addition to forming a freewheeling path through S6, S8, Cx1, and Cs2, the inductor current also forms a freewheeling path through Cs1, Cx1, the freewheeling diode on S7, and S5.

[0285] During the process of the controller 340 switching the states of the switches, the current of the inductor Ls always has a freewheeling path, and at any moment, the four switches S5, S6, S7, and S8 are not directly connected, eliminating the risk of damage to the switches.

[0286] (2) In the initial working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off; when switching to the target working mode, the two switching tubes included in the lower half bridge arm are turned on, and the state of the switching tube included in the upper half bridge arm is opposite to the state of the switching tube in the initial working mode

[0287] Figures 44 and 46 are schematic diagrams of another current loop when the AC voltage is in the P region according to an embodiment of the present application, wherein the current direction shown in Figure 44 is opposite to the current direction shown in Figure 46. Figures 45 and 47 are schematic diagrams of another current loop when the AC voltage is in the N region according to an embodiment of the present application, wherein the current direction shown in Figure 45 is opposite to the current direction shown in Figure 47.

[0288] For the states and current loops of the switch tubes shown in FIG44 and FIG46 , please refer to the contents of FIG7 above; for the states and current loops of the switch tubes shown in FIG45 and FIG47 , please refer to the contents of FIG11 above; no further details will be given.

[0289] In the embodiment of the present application, the switches S5, S7, and S6 are turned on in the initial operating mode, and the switches S5, S7, and S8 are turned on in the target operating mode. Because the bidirectional current path in the initial operating mode is the same as the bidirectional current path in the target operating mode to be switched, when switching from the initial operating mode to the target operating mode, in response to the AC voltage output by the filter circuit 332 changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, the controller 340 first turns off S6 and then turns on S8. For the sake of brevity, the freewheeling path of the inductor current during the switching process will not be described in detail.

[0290] (3) In the initial working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off; when switching to the target working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0291] Figures 48 and 50 are schematic diagrams of another current loop when the AC voltage is in the P region according to an embodiment of the present application, wherein the current direction shown in Figure 48 is opposite to the current direction shown in Figure 50. Figures 49 and 51 are schematic diagrams of another current loop when the AC voltage is in the N region according to an embodiment of the present application, wherein the current direction shown in Figure 49 is opposite to the current direction shown in Figure 51.

[0292] For the status of the switch tubes and the current path in Figures 48 and 50, please refer to the content of Figure 5 above; for the status of the switch tubes and the current path in Figures 49 and 51, please refer to the content of Figure 11 above, and no further details will be given.

[0293] In the embodiment of the present application, the switches S6, S8, and S7 are turned on in the initial operating mode, and the current forms a bidirectional current path through S6, S8, Cx1, and Cs2. In the target operating mode, the switches S5, S7, and S8 are turned on, and the current forms a bidirectional current path through S5, S7, Cx1, and Cs1. Because the bidirectional current paths formed in the two operating modes differ, in response to the AC voltage output by the filter circuit 332 changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, the controller 340 first turns off S8, then turns on S5, then turns off S6, and finally turns on S8.

[0294] (4) In the initial working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off; when switching to the target working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0295] Figures 52 and 54 are schematic diagrams of another current loop when the AC voltage is in the P region according to an embodiment of the present application, wherein the current direction shown in Figure 52 is opposite to the current direction shown in Figure 54. Figures 53 and 55 are schematic diagrams of another current loop when the AC voltage is in the N region according to an embodiment of the present application, wherein the current direction shown in Figure 53 is opposite to the current direction shown in Figure 55.

[0296] For the status of the switch tubes and the current path in Figures 52 and 54, please refer to the content of Figure 7 above; for the status of the switch tubes and the current path in Figures 53 and 55, please refer to the content of Figure 9 above, and no further details will be given.

[0297] In the embodiment of the present application, the switches S5, S7, and S6 are turned on in the initial operating mode, and the current forms a bidirectional current path through S5, S7, Cx1, and Cs1. In the target operating mode, the switches S6, S8, and S5 are turned on, and the current forms a bidirectional current path through S6, S8, Cx1, and Cs2. Because the bidirectional current paths formed in the two operating modes are different, in response to the AC voltage output by the filter circuit 332 changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, the controller 340 first turns off S5, then turns on S8, then turns off S7, and finally turns on S5.

[0298] In one embodiment, the controller 340 is used to: in response to the AC voltage output by the filter circuit 332 changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold and the path of the bidirectional current path of the half-bridge circuit 331 in the negative voltage working mode is the same as the path of the bidirectional current path of the half-bridge circuit 331 in the positive voltage working mode to be switched, first turn off the switch tube that does not belong to the target switch tube among the three switch tubes that are turned on in the negative voltage working mode, and then turn on the switch tube that is not turned on in the target switch tube, so as to control the inverter to switch from the negative voltage working mode to the positive voltage working mode, and the target switch tube is the switch tube that is turned on in the positive voltage working mode.

[0299] In one embodiment, the controller 340 is used to: in response to the AC voltage output by the filter circuit 332 changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold and the path of the bidirectional current path of the half-bridge circuit 331 in the negative voltage working mode is different from the path of the bidirectional current path of the half-bridge circuit 331 in the positive voltage working mode to be switched, first turn off the switch tube in the bidirectional current path of the half-bridge circuit 331 in the negative voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer, then turn on the switch tube in the unidirectional current path of the half-bridge circuit 331 in the negative voltage working mode that is not turned on, then turn off another switch tube in the bidirectional current path of the half-bridge circuit 331 in the negative voltage working mode that is turned on, and finally turn on the switch tube in the bidirectional current path of the half-bridge circuit 331 in the negative voltage working mode, whose freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer.

[0300] Among them, in the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and the two switching tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are both turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switching tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

[0301] In this embodiment of the present application, the controller 340 can switch the state of the switch tube based on whether the paths of the bidirectional circuit paths of the initial operating mode and the target operating mode are consistent. See below for details. In this embodiment of the present application, the initial operating mode is a negative voltage operating mode, and the target operating mode is a positive voltage operating mode. In other words, in this embodiment of the present application, the controller 340 controls the inverter to switch from the negative voltage operating mode to the positive voltage operating mode.

[0302] Case 6: AC voltage switches from N region to P region

[0303] (1) In the initial working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off; when switching to the target working mode, the two switching tubes included in the upper half bridge arm are turned on, and the state of the switching tube included in the lower half bridge arm is opposite to the state of the switching tube in the initial working mode

[0304] Referring to Figures 40 to 43 above, Figures 41 and 43 show the states of the switch tube in the initial working mode, while Figures 40 to 42 show the states of the switch tube in the target working mode.

[0305] In the embodiment of the present application, the switches S6, S8, and S5 are turned on in the initial operating mode, and the switches S6, S8, and S7 are turned on in the target operating mode. Because the bidirectional current path in the initial operating mode is the same as the bidirectional current path in the target operating mode to be switched, when switching from the initial operating mode to the target operating mode, in response to the AC voltage output by the filter circuit 332 changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold, the controller 340 first turns off S5 and then turns on S7.

[0306] (2) In the initial working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off; when switching to the target working mode, the two switching tubes included in the lower half bridge arm are turned on, and the state of the switching tube included in the upper half bridge arm is opposite to the state of the switching tube in the initial working mode

[0307] 44 to 47 , FIG45 and FIG47 show the states of the switch tube in the initial working mode, while FIG44 to FIG46 show the states of the switch tube in the target working mode.

[0308] In the embodiment of the present application, the switches S5, S7, and S8 are turned on in the initial operating mode, and the switches S5, S7, and S6 are turned on in the target operating mode. Because the bidirectional current path in the initial operating mode is the same as the bidirectional current path in the target operating mode to be switched, when switching from the initial operating mode to the target operating mode, in response to the AC voltage output by the filter circuit 332 changing from less than the preset negative voltage threshold to greater than the preset positive voltage threshold, the controller 340 first turns off S8 and then turns on S6.

[0309] (3) In the initial working mode, the two switching tubes included in the lower half bridge arm are turned on and one switching tube included in the upper half bridge arm is turned on, and the other switching tube included in the lower half bridge arm is turned off; when switching to the target working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0310] 48 to 51 , FIG49 and FIG51 show the states of the switch tube in the initial working mode, while FIG48 and FIG50 show the states of the switch tube in the target working mode.

[0311] In the embodiment of the present application, the switches S5, S7, and S8 are turned on in the initial operating mode, and the current forms a bidirectional current path through S5, S7, Cx1, and Cs1. In the target initial operating mode, the switches S6, S8, and S7 are turned on, and the current forms a bidirectional current path through S6, S8, Cx1, and Cs2. Because the bidirectional current paths formed in the two operating modes are different, in response to the AC voltage output by the filter circuit 332 changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold, the controller 340 first turns off S7, then turns on S6, then turns off S5, and finally turns on S7.

[0312] (4) In the initial working mode, the two switching tubes included in the lower half bridge arm and one switching tube included in the upper half bridge arm are turned on, and the other switching tube included in the upper half bridge arm is turned off; when switching to the target working mode, the two switching tubes included in the upper half bridge arm and one switching tube included in the lower half bridge arm are turned on, and the other switching tube included in the lower half bridge arm is turned off.

[0313] 52 to 55 , FIG53 and FIG55 show the state of the switch tube in the initial working mode, while FIG52 and FIG54 show the state of the switch tube in the target working mode.

[0314] In the embodiment of the present application, the switches S6, S8, and S5 are turned on in the initial operating mode, and the current forms a bidirectional current path through S6, S8, Cx1, and Cs2. In the target initial operating mode, the switches S5, S7, and S6 are turned on, and the current forms a bidirectional current path through S5, S7, Cx1, and Cs1. Because the bidirectional current paths formed in the two operating modes are different, in response to the AC voltage output by the filter circuit 332 changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold, the controller 340 first turns off S6, then turns on S7, then turns off S8, and finally turns on S6.

[0315] In the embodiments of the present application, the controller switches the states of the switches based on whether the bidirectional current paths of the initial operating mode and the target operating mode are identical. During this process, the controller ensures that at least one switch is in the on state, thus providing a continuous freewheeling path for the inductor current. Furthermore, during this switching process, the controller sequentially turns the switches on and off. At any given moment, only some of the four switches in the bridge arm are in the on state, preventing shoot-through and eliminating the risk of switch damage due to inaccurate AC voltage polarity determination.

[0316] In one embodiment, the controller 340 may switch from the positive voltage operation mode to the negative voltage operation mode in conjunction with the direction of the current flowing through the secondary winding of the transformer.

[0317] In one embodiment, the controller 340 is used to: in response to the AC voltage output by the filter circuit 332 changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold and the path of the bidirectional current path of the half-bridge circuit 331 in the positive voltage working mode is different from the path of the bidirectional current path of the half-bridge circuit 331 in the negative voltage working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the current direction in the unidirectional current path of the half-bridge circuit 331 in the positive voltage working mode, first turn off the switch tubes other than the target switch tube in the bidirectional current path of the half-bridge circuit 331 in the positive voltage working mode, and then turn on the switch tubes that are not turned on in the unidirectional current path of the half-bridge circuit 331 in the positive voltage working mode, where the target switch tube is the switch tube that is turned on in the negative voltage working mode.

[0318] In one embodiment, the controller 340 is configured to: in response to the AC voltage output by the filter circuit 332 changing from greater than a preset positive voltage threshold to less than a preset negative voltage threshold, and the path of the bidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode is different from the path of the bidirectional current path of the half-bridge circuit 331 in the negative voltage operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode, first turn off the switch tube in the bidirectional current path of the half-bridge circuit in the positive voltage operating mode, in which the freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer; then turn on the switch tube in the unidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode that is not turned on; then turn off another switch tube in the bidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode that is turned on; and finally turn on the switch tube in the bidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode, in which the freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer.

[0319] In the embodiment of the present application, in a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switches in the upper or lower half of the bridge arm through which the current flows are turned on. In a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switches in the upper or lower half of the bridge arm through which the current flows is turned on.

[0320] In the embodiment of the present application, the initial operating mode is the positive voltage operating mode, and the target operating mode is the negative voltage operating mode. In other words, in the embodiment of the present application, the controller 340 controls the inverter to switch from the positive voltage operating mode to the negative voltage operating mode.

[0321] Case 5: AC voltage switches from P region to N region

[0322] (1) Referring to Figures 48 to 51 above, the current direction in the unidirectional current path in the initial working mode is the current direction shown in (a) of Figure 50. If the direction of the current flowing through the inductor is the same as the current direction shown in (a) of Figure 50, in response to the AC voltage output by the filter circuit 332 changing from greater than the preset positive voltage threshold to less than the preset negative voltage threshold, the controller 340 turns off the switch tubes other than the target switch tube in the bidirectional current path in the initial working mode, that is, S6, so that S7 and S8 are in the on state, and the inductor current forms a freewheeling path through the freewheeling diodes on S6, S8, Cx1, and Cs2, and forms a freewheeling path through the freewheeling diodes on Cs1, Cx1, S7, and S5. After S6 is completely turned off, the controller 340 turns on the non-conducting switch tube in the unidirectional current path, that is, S5, so that S5, S7, and S8 are in the on state, and the inductor current forms a freewheeling path through the freewheeling diode on S6, S8, Cx1, and Cs2, and forms a freewheeling path through Cs1, Cx1, S7, and S5.

[0323] If the direction of the current flowing through the inductor is opposite to the current direction shown in (a) in Figure 50, the logical action of the controller 340 is similar to the logical action without combining the direction of the current flowing through the inductor. In response to the AC voltage output by the filter circuit 332 changing from greater than the preset positive voltage threshold to less than the preset negative voltage threshold, the controller 340 first turns off S8, then turns on S5, then turns off S6, and finally turns on S8.

[0324] (2) Referring to Figures 52 to 55 above, the current direction in the unidirectional current path in the initial working mode is the current direction shown in (a) of Figure 52. If the direction of the current flowing through the inductor is the same as the current direction shown in (a) of Figure 52, in response to the AC voltage output by the filter circuit 332 changing from greater than the preset positive voltage threshold to less than the preset negative voltage threshold, the controller 340 first turns off S7 and then turns on S8.

[0325] If the direction of the current flowing through the inductor is opposite to the current direction shown in (a) in Figure 52, the logical action of the controller 340 is similar to the logical action without combining the direction of the current flowing through the inductor. In response to the AC voltage output by the filter circuit 332 changing from greater than the preset positive voltage threshold to less than the preset negative voltage threshold, the controller 340 first turns off S5, then turns on S8, then turns off S7, and finally turns on S5.

[0326] In one embodiment, the controller 340 may switch from the negative voltage operation mode to the positive voltage operation mode in conjunction with the direction of the current flowing through the secondary winding of the transformer.

[0327] In one embodiment, the controller 340 is used to: in response to the AC voltage output by the filter circuit 332 changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold and the path of the bidirectional current path of the half-bridge circuit in the negative voltage working mode is different from the path of the bidirectional current path of the half-bridge circuit 331 in the positive voltage working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the current direction in the unidirectional current path of the half-bridge circuit 331 in the negative voltage working mode, first turn off the switch tubes other than the target switch tube in the bidirectional current path of the half-bridge circuit 331 in the negative voltage working mode, and then turn on the switch tubes that are not turned on in the unidirectional current path of the half-bridge circuit 331 in the negative voltage working mode, where the target switch tube is the switch tube that is turned on in the positive voltage working mode.

[0328] In one embodiment, the controller 340 is configured to: in response to the AC voltage output by the filter circuit 332 changing from less than a preset negative voltage threshold to greater than a preset positive voltage threshold, and the path of the bidirectional current path of the half-bridge circuit 331 in the negative voltage operating mode is different from the path of the bidirectional current path of the half-bridge circuit 331 in the positive voltage operating mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path of the half-bridge circuit 331 in the negative voltage operating mode, first turn off the switch tube in the bidirectional current path of the half-bridge circuit 331 in the negative voltage operating mode, in which the freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer; then turn on the switch tube in the unidirectional current path of the half-bridge circuit 331 in the negative voltage operating mode that is not turned on; then turn off another switch tube in the bidirectional current path of the half-bridge circuit 331 in the negative voltage operating mode that is turned on; and finally turn on the switch tube in the bidirectional current path of the half-bridge circuit 331 in the negative voltage operating mode, in which the freewheeling direction is the same as the direction of the current flowing through the secondary winding of the transformer.

[0329] In the embodiment of the present application, in a bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both switches in the upper or lower half of the bridge arm through which the current flows are turned on. In a unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switches in the upper or lower half of the bridge arm through which the current flows is turned on.

[0330] In the embodiment of the present application, the initial operating mode is the positive voltage operating mode, and the target operating mode is the negative voltage operating mode. In other words, in the embodiment of the present application, the controller 340 controls the inverter to switch from the negative voltage operating mode to the positive voltage operating mode.

[0331] Case 6: AC voltage switches from N region to P region

[0332] (1) Referring to Figures 48 to 51 above, the current direction in the unidirectional current path in the initial operating mode is the current direction shown in (b) of Figure 51. If the direction of the current flowing through the inductor is the same as the current direction shown in (b) of Figure 51, in response to the AC voltage output by the filter circuit 332 changing from less than the preset negative voltage threshold to greater than the preset positive voltage threshold, the controller 340 first turns off S5 and then turns on S6 to control the inverter to switch from the initial operating mode to the target operating mode.

[0333] If the direction of the current flowing through the inductor is opposite to the current direction shown in (b) of Figure 51, the logical action of the controller 340 is similar to the logical action without combining the direction of the current flowing through the inductor. In response to the AC voltage output by the filter circuit 332 changing from less than the preset negative voltage threshold to greater than the preset positive voltage threshold, the controller 340 first turns off S7, then turns on S6, then turns off S5, and finally turns on S7 to control the inverter to switch from the initial operating mode to the target operating mode.

[0334] (2) Referring to Figures 52 to 55 above, the current direction in the unidirectional current path in the initial operating mode is the current direction shown in (b) of Figure 53. If the direction of the current flowing through the inductor is the same as the current direction shown in (b) of Figure 53, in response to the AC voltage output by the filter circuit 332 changing from less than the preset negative voltage threshold to greater than the preset positive voltage threshold, the controller 340 first turns off S8 and then turns on S7 to control the inverter to switch from the initial operating mode to the target operating mode.

[0335] If the direction of the current flowing through the inductor is opposite to the current direction shown in (b) in Figure 53, in response to the AC voltage output by the filter circuit 332 changing from less than the preset negative voltage threshold to greater than the preset positive voltage threshold, the controller 340 first turns off S6, then turns on S7, then turns off S8, and finally turns on S6 to control the inverter to switch from the initial operating mode to the target operating mode.

[0336] It should be noted that during the process of switching the switches by controller 340, controller 340 controls the other switches to begin switching their on / off states after completing the switching action of controlling the switches to change their on / off states. Furthermore, during the switching process, a freewheeling path for the inductor current always exists, which will not be further explained.

[0337] In the embodiments of the present application, if the bidirectional current path in the initial operating mode differs from the bidirectional current path in the target operating mode to be switched, the controller switches the state of the switch based on the current direction of the transformer's secondary winding. In particular, when the direction of the current flowing through the transformer's secondary winding is the same as the direction of the current in the unidirectional current path in the initial operating mode to be switched, the number of controller actions is reduced.

[0338] It should be noted that the switching tubes in the schematic diagrams shown in the above embodiments all have a common source, such as the source of S8 is connected to the source of S6, and the source of S7 is connected to the source of S5. In the embodiments of the present application, the switching tubes can also have a common drain, as shown in Figure 56. The drain of S8 shown in the figure is connected to the drain of S6, and the drain of S7 is connected to the drain of S5, without limitation. In other words, the freewheeling diode of S8 shown in Figure 56 is connected to the cathode of the freewheeling diode of S6, and the freewheeling diode of S7 is connected to the cathode of the freewheeling diode of S5.

[0339] Figure 57 is a schematic diagram of a wave control method provided by an embodiment of the present application. It should be understood that the description of the method embodiment corresponds to the description of the device embodiment. Therefore, for matters not described in detail, please refer to the method embodiment above and will not be repeated here.

[0340] The wave generation control method is applied to the inverter, and the wave generation control method includes steps S570 to S572:

[0341] S570, in the first working mode, controls three of the four switch tubes in the bridge arm of the inverter to be turned on, and the remaining switch tube to be turned off, wherein the secondary side circuit of the inverter includes a half-bridge circuit and a filter circuit, the half-bridge circuit includes a bridge arm, the bridge arm includes an upper half-bridge arm and a lower half-bridge arm, the upper half-bridge arm and the lower half-bridge arm each include a group of switch tubes, each group of switch tubes includes two switch tubes each including a parallel freewheeling diode, and the freewheeling directions of the two parallel freewheeling diodes in each group of switch tubes are opposite.

[0342] S571, in the second working mode, control both the switch tubes in the upper half bridge arm to be turned on and both the switch tubes in the lower half bridge arm to be turned off, or control both the switch tubes in the upper half bridge arm to be turned off and both the switch tubes in the lower half bridge arm to be turned on.

[0343] S572, in response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the secondary circuit is controlled to switch from the first operating mode to the second operating mode, so that at least one of the four switching tubes is turned on and at most three switching tubes are turned on.

[0344] In the above embodiments of the inverter, the controller is used to switch the state of the switch tube under different conditions and is still applicable to the above embodiments. For the sake of brevity, this application will not list them one by one.

[0345] An embodiment of the present application further provides a computer-readable storage medium storing computer instructions for implementing the method executed by the controller in the above method embodiment.

[0346] An embodiment of the present application further provides a computer program product comprising instructions, which, when executed by a computer, enables the computer to implement the method executed by the controller in the above method embodiment.

[0347] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. An inverter, characterized in that: include: A primary circuit, wherein the primary circuit is used to convert direct current into alternating current; A transformer, the transformer being used to step up or step down the alternating current output by the primary circuit; A secondary circuit, the secondary circuit is used to convert the frequency of the AC power after the voltage is stepped up or down and filter the AC power after the frequency conversion, the secondary circuit includes a half-bridge circuit and a filter circuit, the half-bridge circuit includes a bridge arm and at least two capacitors, the two capacitors are connected in series and connected in parallel with the bridge arm, the bridge arm includes an upper half-bridge arm and a lower half-bridge arm, the connection point of the upper half-bridge arm and the lower half-bridge arm is connected to one end of the secondary winding of the transformer, the connection point of the two capacitors is connected to the other end of the secondary winding of the transformer, the upper half-bridge arm and the lower half-bridge arm each include a group of switch tubes, the two switch tubes included in each group of the switch tubes respectively include a parallel freewheeling diode, the freewheeling directions of the two freewheeling diodes in parallel of each group of the switch tubes are opposite, and the filter circuit is connected to the half-bridge circuit and outputs an AC voltage; A controller, the controller is used to control the on and off of the switch tube of the bridge arm; The inverter includes a first working mode and a second working mode. In the first working mode, three of the four switch tubes in the bridge arm are turned on, and the remaining switch tube is turned off. In the second working mode, the two switch tubes in the upper half bridge arm are turned on and the two switch tubes in the lower half bridge arm are turned off, or the two switch tubes in the upper half bridge arm are turned off and the two switch tubes in the lower half bridge arm are turned on. The controller is also used for: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the inverter is controlled to switch from the first operating mode to the second operating mode, so that at least one switch tube among the four switch tubes included in the bridge arm is turned on and at most three switch tubes are turned on.

2. The inverter according to claim 1, characterized in that: The controller is used to: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and two of the three switch tubes turned on in the first operating mode are the same as the two target switch tubes turned on in the second operating mode to be switched, the switch tubes other than the target switch tubes among the three switch tubes turned on in the first operating mode are turned off to control the inverter to switch from the first operating mode to the second operating mode.

3. The inverter according to claim 1 or 2, characterized in that: The controller is used to: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, firstly turning off the switch tube whose freewheeling direction in the bidirectional current path of the half-bridge circuit in the first working mode is opposite to the current direction of the unidirectional current path of the half-bridge circuit in the first working mode, then turning on the switch tube that is not turned on in the unidirectional current path, and then turning off the switch tube whose freewheeling direction in the bidirectional current path is the same as the current direction of the unidirectional current path, so as to control the inverter to switch from the first working mode to the second working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

4. The inverter according to claim 1 or 2, characterized in that: The controller is used to: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first working mode, firstly turn off the two switch tubes in the bidirectional current path of the half-bridge circuit in the first working mode at the same time, and then turn on the switch tube that is not turned on in the unidirectional current path of the half-bridge circuit in the first working mode, so as to control the inverter to switch from the first working mode to the second working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

5. The inverter according to claim 1 or 2, characterized in that: The controller is used to: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first working mode, first turning off the switch tube in the bidirectional current path whose freewheeling direction is opposite to the current direction of the unidirectional current path, then turning on the switch tube that is not turned on in the unidirectional current path, and then turning off the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, so as to control the inverter to switch from the first working mode to the second working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

6. The inverter according to any one of claims 1 to 5, characterized in that: The controller is also used for: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold, the inverter is controlled to switch from the second operating mode to the first operating mode so that at least one of the four switching tubes included in the bridge arm is turned on and at most three switching tubes are turned on.

7. The inverter according to claim 6, characterized in that: The controller is used to: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold and the two switch tubes turned on in the second operating mode are the same as two switch tubes among the three target switch tubes turned on in the first operating mode to be switched, the switch tubes among the target switch tubes except the two switch tubes that are turned on are turned on to control the inverter to switch from the second operating mode to the first operating mode.

8. The inverter according to claim 6 or 7, characterized in that: The controller is used to: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold and only one of the two switch tubes turned on in the second working mode is the same as one of the three target switch tubes turned on in the first working mode to be switched, firstly turn on the switch tube whose freewheeling direction in the bidirectional current path of the half-bridge circuit in the first working mode to be switched is the same as the current direction of the unidirectional current path of the half-bridge circuit in the first working mode, then turn off the switch tube that does not belong to the target switch tube in the unidirectional current path, and then turn on the switch tube that is not turned on in the bidirectional current path, so as to control the inverter to switch from the second working mode to the first working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

9. The inverter according to claim 6 or 7, characterized in that: The controller is used to: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold and only one of the two switch tubes turned on in the second working mode is the same as one of the three target switch tubes turned on in the first working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first working mode, firstly turning off the switch tube that does not belong to the target switch tube in the unidirectional current path of the half-bridge circuit in the first working mode, and then turning on the switch tube that is not turned on in the bidirectional current path of the half-bridge circuit in the first working mode, so as to control the inverter to switch from the second working mode to the first working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

10. The inverter according to claim 6 or 7, characterized in that: The controller is used to: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value less than or equal to the preset voltage threshold to an absolute value greater than the preset voltage threshold, and only one of the two switch tubes turned on in the second working mode is the same as one of the three target switch tubes turned on in the first working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first working mode, first turn on the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, then turn off the switch tube in the unidirectional current path that does not belong to the target switch tube, and then turn on the switch tube that is not turned on in the bidirectional current path, so as to control the inverter to switch from the second working mode to the first working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

11. The inverter according to any one of claims 1 to 10, characterized in that: The controller is used to control other switch tubes to start executing the switching action of changing the on-off state after the switching action of controlling the switch tube to change the on-off state is completed.

12. The inverter according to any one of claims 1 to 11, characterized in that: The anodes of the two diodes connected in parallel of the two switch tubes included in each group of switch tubes are connected, or the cathodes of the two diodes connected in parallel of the two switch tubes included in each group of switch tubes are connected.

13. A wave generation control method, the wave generation control method being applied to an inverter, characterized in that: The wave control method comprises: In the first working mode, three of the four switch tubes in the bridge arm of the inverter are controlled to be turned on, and the remaining switch tube is turned off, wherein the secondary circuit of the inverter includes a half-bridge circuit and a filter circuit, the half-bridge circuit includes the bridge arm, the bridge arm includes an upper half bridge arm and a lower half bridge arm, the upper half bridge arm and the lower half bridge arm each include a group of switch tubes, the two switch tubes included in each group of the switch tubes respectively include a parallel freewheeling diode, and the freewheeling directions of the two parallel freewheeling diodes of each group of the switch tubes are opposite; In the second working mode, the two switch tubes in the upper half bridge arm are controlled to be turned on and the two switch tubes in the lower half bridge arm are controlled to be turned off, or the two switch tubes in the upper half bridge arm are controlled to be turned off and the two switch tubes in the lower half bridge arm are controlled to be turned on; In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, the secondary circuit is controlled to switch from a first operating mode to a second operating mode so that at least one of the four switching tubes is turned on and at most three switching tubes are turned on.

14. The wave control method according to claim 13, characterized in that: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, controlling the secondary circuit to switch from the first working mode to the second working mode includes: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and two of the three switch tubes turned on in the first operating mode are the same as the two target switch tubes turned on in the second operating mode to be switched, the switch tubes among the three switch tubes except the target switch tubes are turned off to control the secondary circuit to switch from the first operating mode to the second operating mode.

15. The wave control method according to claim 13 or 14, characterized in that: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, controlling the secondary circuit to switch from the first working mode to the second working mode includes: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, firstly turning off the switch tube whose freewheeling direction in the bidirectional current path of the half-bridge circuit in the first working mode is opposite to the current direction of the unidirectional current path of the half-bridge circuit in the first working mode, then turning on the switch tube that is not turned on in the unidirectional current path, and then turning off the switch tube whose freewheeling direction in the bidirectional current path is the same as the current direction of the unidirectional current path, so as to control the secondary circuit to switch from the first working mode to the second working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

16. The wave control method according to claim 13 or 14, characterized in that: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, controlling the secondary circuit to switch from the first working mode to the second working mode includes: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is the same as the direction of the current in the unidirectional current path in the first working mode, firstly turn off the two switch tubes in the bidirectional current path of the half-bridge circuit in the first working mode at the same time, and then turn on the switch tube that is not turned on in the unidirectional current path of the half-bridge circuit in the first working mode, so as to control the secondary circuit to switch from the first working mode to the second working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

17. The wave control method according to claim 13 or 14, characterized in that: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than a preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, controlling the secondary circuit to switch from the first working mode to the second working mode includes: In response to the absolute value of the AC voltage output by the filter circuit changing from an absolute value greater than the preset voltage threshold to an absolute value less than or equal to the preset voltage threshold, and only one of the three switch tubes turned on in the first working mode is the same as a target switch tube turned on in the second working mode to be switched, and the direction of the current flowing through the secondary winding of the transformer is opposite to the direction of the current in the unidirectional current path in the first working mode, first turn off the switch tube in the bidirectional current path whose freewheeling direction is opposite to the current direction of the unidirectional current path, then turn on the switch tube that is not turned on in the unidirectional current path, and then turn off the switch tube in the bidirectional current path whose freewheeling direction is the same as the current direction of the unidirectional current path, so as to control the secondary circuit to switch from the first working mode to the second working mode; In the bidirectional current path, the current flowing through the secondary winding of the transformer has two directions, and both of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows are turned on; in the unidirectional current path, the current flowing through the secondary winding has only one direction, and only one of the two switch tubes of the upper half bridge arm or the lower half bridge arm through which the current flows is turned on.

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