Micro inverter and control method thereof

Abstract

The invention discloses a micro inverter and a control method thereof, and belongs to the technical field of inverters. The method comprises the following steps: when the output voltage of the micro inverter is changed from a preset voltage range to a position outside the preset voltage range, controlling a secondary side bridge arm to be switched from a first type of working state in a first working mode to a second type of working state in a second working mode; at most two switch tubes are conducted at the same moment in the first working mode, and at most three switch tubes are conducted at the same moment in the second working mode; the resonant current between the transformer and the secondary side bridge arm in the first working mode and the second working mode always has a follow current path; when the output voltage is changed from the outside of the preset voltage range to the inside of the preset voltage range, the secondary side bridge arm is controlled to be switched from the second type of working state to the first type of working state; wherein in the switching process between the first type of working state and the second type of working state, only one switching tube is controlled to change the on-off state. According to the embodiment of the invention, the operation reliability of the micro inverter can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular, to a micro-inverter and a control method thereof. Background Art

[0002] A micro photovoltaic grid-connected inverter, hereinafter referred to as a micro-inverter, is a power conversion unit based on an independent photovoltaic module, which can modularize the power conversion process and achieve maximum power point tracking for a single module. Since each single module is connected by a DC-AC converter that performs maximum power point tracking and system integration, the system composed of micro-inverters can exhibit higher reliability, and the failure of any inverter module can be treated as an individual fault without affecting the overall system. The secondary bridge arm of the micro-inverter includes at least two groups of bidirectional switches, which are respectively connected to different output terminals of the micro-inverter. The switching of the bidirectional switches needs to be judged according to the polarity of the voltage at the output terminal of the micro-inverter. However, whether software or hardware switching is used, there is a certain delay. When the grid voltage undergoes a zero-crossing stage or fluctuates and undergoes a polarity inversion at a relatively high voltage, due to sampling delay or inaccurate polarity judgment, the bidirectional switch tubes may not have time to make real-time adjustments, resulting in a direct connection of the bridge arm between the two output terminals, causing a sharp rise in the bridge arm current and burning out the bidirectional switch tubes. Therefore, the operation reliability of the micro-inverter in the related art is poor. Summary of the Invention

[0003] The present invention provides a micro-inverter and a control method thereof to improve the operation reliability of the micro-inverter.

[0004] In a first aspect, an embodiment of the present invention provides a control method for a micro-inverter. The micro-inverter includes: a transformer and a secondary bridge arm; the secondary bridge arm includes four switch tubes connected in series between two output terminals of the micro-inverter, wherein any two adjacent switch tubes have opposite directions, and the connection node between the middle two switch tubes is connected to the secondary winding of the transformer as an intermediate node;

[0005] The control method of the micro-inverter includes:

[0006] When the output voltage of the micro-inverter changes from within a preset voltage range to outside the preset voltage range, controlling the working state of the secondary bridge arm to switch from a first type of working state in a first working mode to a second type of working state in a second working mode; wherein, the output voltage is the voltage difference between the two output terminals of the micro-inverter, and the preset voltage range is the voltage range between a negative voltage threshold and a positive voltage threshold; at most two switch tubes are turned on at the same time in the first working mode, and at most three switch tubes are turned on at the same time in the second working mode; there is always a freewheeling path for the resonant current between the transformer and the secondary bridge arm in both the first working mode and the second working mode;

[0007] When the output voltage changes from outside the preset voltage range to within the preset voltage range, control the operating state of the secondary side bridge arm to switch from the second type of operating state to the first type of operating state;

[0008] Wherein, in the first type of operating state, two of the switching tubes between the intermediate node and one of the output terminals are turned on, and the other two switching tubes are turned off; in the second type of operating state, three of the switching tubes are turned on, and the other switching tube is turned off; during the switching process between the first type of operating state and the second type of operating state, only control one of the switching tubes to change its on / off state.

[0009] Optionally, the two output terminals include a first output terminal and a second output terminal, and the output voltage is the voltage difference between the first output terminal and the second output terminal; the four switching tubes include a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube connected in series between the first output terminal and the second output terminal in sequence; the first type of operating state includes: a first operating state and a second operating state; in the first operating state, the first switching tube and the second switching tube are turned on, and the other switching tubes are turned off; in the second operating state, the third switching tube and the fourth switching tube are turned on, and the other switching tubes are turned off; the second type of operating state includes: a third operating state, a fourth operating state, a fifth operating state, and a sixth operating state; in the third operating state, the first switching tube is turned off, and the other switching tubes are turned on; in the fourth operating state, the third switching tube is turned off, and the other switching tubes are turned on; in the fifth operating state, the second switching tube is turned off, and the other switching tubes are turned on; in the sixth operating state, the fourth switching tube is turned off, and the other switching tubes are turned on;

[0010] The control method of the micro-inverter includes:

[0011] In the first operating mode, according to the positive / negative of the output voltage and the level of the pulse control signal, control the secondary side bridge arm to operate in the first operating state or the second operating state;

[0012] In the second operating mode, when the output voltage is positive, control the secondary side bridge arm to operate in the third operating state or the fourth operating state according to the level of the pulse control signal; when the output voltage is negative, control the secondary side bridge arm to operate in the fifth operating state or the sixth operating state according to the level of the pulse control signal;

[0013] During the switching process between the first type of working state and the second type of working state, according to the change of the output voltage, control the working state of the secondary side bridge arm to switch between the first working state and the fourth working state or the sixth working state, or switch between the second working state and the third working state or the fifth working state.

[0014] Optionally, if the secondary side bridge arm is currently working in the first working state, when the output voltage is positive and rises above the positive voltage threshold, control the secondary side bridge arm to switch to the fourth working state; when the output voltage is negative and drops below the negative voltage threshold, control the secondary side bridge arm to switch to the sixth working state;

[0015] If the secondary side bridge arm is currently working in the second working state, when the output voltage is positive and rises above the positive voltage threshold, control the secondary side bridge arm to switch to the third working state; when the output voltage is negative and drops below the negative voltage threshold, control the secondary side bridge arm to switch to the fifth working state;

[0016] If the secondary side bridge arm is currently working in the third working state or the fifth working state, when the output voltage changes from outside the preset voltage range to within the preset voltage range, control the secondary side bridge arm to switch to the second working state;

[0017] If the secondary side bridge arm is currently working in the fourth working state or the sixth working state, when the output voltage changes from outside the preset voltage range to within the preset voltage range, control the secondary side bridge arm to switch to the first working state.

[0018] Optionally, the first working mode further includes:

[0019] When the resonant current is within the preset current range, control the secondary side bridge arm to maintain the current first type of working state; wherein, the preset current range is the current range between the negative current threshold and the positive current threshold;

[0020] When the resonant current is outside the preset current range, when the positive and negative of the output voltage changes or the level of the pulse control signal changes, according to the direction of the resonant current, control the working state of the secondary side bridge arm to switch from the current first type of working state to another first type of working state through three first type of transition states; wherein, during the switching process, only one of the switching tubes is controlled to change the on-off state compared with the previous working state; in the first type of transition state, at most one of the switching tubes between the intermediate node and any one of the output terminals is conducting at the same time;

[0021] The second operating mode further includes: when the level of the pulse control signal changes, controlling the operating state of the secondary side bridge arm to switch from the current second type of operating state through a second type of transition state to another second type of transition state corresponding to the positive or negative of the current output voltage; wherein, during the switching process, only one of the switching tubes is controlled to change its on / off state compared to the previous operating state; in the second type of transition state, one of the switching tubes is conducting between the intermediate node and any one of the output terminals at the same moment.

[0022] Optionally, each of the first type of operating states and each of the second type of operating states are maintained for at least a preset conduction maintenance time;

[0023] Each of the first type of transition states and each of the second type of transition states are maintained for at least a preset dead time.

[0024] Optionally, the first type of transition states include: a first transition state, a second transition state, a third transition state, a fourth transition state, a fifth transition state, and a sixth transition state; in the first transition state, the third switching tube is conducting and the other switching tubes are off; in the second transition state, the second switching tube and the third switching tube are conducting and the other switching tubes are off; in the third transition state, the second switching tube is conducting and the other switching tubes are off; in the fourth transition state, the first switching tube is conducting and the other switching tubes are off; in the fifth transition state, the first switching tube and the fourth switching tube are conducting and the other switching tubes are off; in the sixth transition state, the fourth switching tube is conducting and the other switching tubes are off;

[0025] Controlling the operating state of the secondary side bridge arm to switch from the current first type of operating state through three first type of transition states to another first type of operating state according to the direction of the resonant current, includes:

[0026] When the resonant current flows from the transformer to the secondary side bridge arm, when the resonant current is outside the preset current range and the positive or negative of the output voltage changes or the level of the pulse control signal changes, if the secondary side bridge arm is currently operating in the first operating state, then control the secondary side bridge arm to sequentially pass through the third transition state, the second transition state, and the first transition state to switch to the second operating state; if the secondary side bridge arm is currently operating in the second operating state, then control the secondary side bridge arm to sequentially pass through the first transition state, the second transition state, and the third transition state to switch to the first operating state;

[0027] When the resonant current flows from the secondary side bridge arm to the transformer, when the resonant current is outside the preset current range and there is a positive or negative change in the output voltage or a change in the level of the pulse control signal, if the secondary side bridge arm is currently operating in the first operating state, control the secondary side bridge arm to sequentially switch to the second operating state through the fourth transition state, the fifth transition state, and the sixth transition state; if the secondary side bridge arm is currently operating in the second operating state, control the secondary side bridge arm to sequentially switch to the first operating state through the sixth transition state, the fifth transition state, and the fourth transition state.

[0028] Optionally, the control method of the micro-inverter further includes:

[0029] When receiving the effective level of the enable signal, control the secondary side bridge arm to operate in the first type of operating state; wherein, the effective level of the enable signal is used to control the startup of the micro-inverter;

[0030] When receiving the non-effective level of the enable signal, control all the switching tubes in the secondary side bridge arm to turn off; wherein, the non-effective level of the enable signal is used to control the shutdown of the micro-inverter.

[0031] Optionally, the two output terminals include a first output terminal and a second output terminal, and the output voltage is the voltage difference between the first output terminal and the second output terminal; the four switching tubes include a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube that are sequentially connected in series between the first output terminal and the second output terminal; the first type of operating state includes: a first operating state and a second operating state; in the first operating state, the first switching tube and the second switching tube are turned on, and the other switching tubes are turned off; in the second operating state, the third switching tube and the fourth switching tube are turned on, and the other switching tubes are turned off;

[0032] When receiving the effective level of the enable signal, controlling the secondary side bridge arm to operate in the first type of operating state includes: when receiving the effective level of the enable signal:

[0033] If the exclusive NOR result of the voltage polarity identifier and the pulse control signal is 1, control the secondary side bridge arm to operate in the first operating state; wherein, the voltage polarity identifier is 1 when the output voltage is positive, and the voltage polarity identifier is 0 when the output voltage is negative;

[0034] If the exclusive NOR result of the voltage polarity identifier and the pulse control signal is 0, control the secondary side bridge arm to operate in the second operating state.

[0035] Optionally, when receiving the invalid level of the enable signal, controlling each of the switching tubes in the secondary bridge arm to turn off, including: when receiving the invalid level of the enable signal:

[0036] If the secondary bridge arm operates in the second operating state, then by changing the on-off state of one switching tube, switching the operating state of the secondary bridge arm to the first operating state, and executing the first operating mode until the resonant current enters a preset current range, controlling each of the switching tubes in the secondary bridge arm to turn off; wherein, the preset current range is the current range between the negative current threshold and the positive current threshold;

[0037] If the secondary bridge arm operates in the first operating mode, then continue to execute the first operating mode until the resonant current enters a preset current range, controlling each of the switching tubes in the secondary bridge arm to turn off.

[0038] In a second aspect, an embodiment of the present invention further provides a micro-inverter, including: a primary bridge arm, a transformer, a secondary bridge arm, and a controller;

[0039] The primary bridge arm is respectively connected to the input end of the micro-inverter and the primary winding of the transformer. The secondary bridge arm includes four switching tubes connected in series between the two output ends of the micro-inverter. Among them, any two adjacent switching tubes have opposite directions, and the connection node between the middle two switching tubes is used as the middle node to connect the secondary winding of the transformer; the controller is connected to the primary bridge arm and the control poles of each of the switching tubes; the controller is configured to execute the control method of the micro-inverter provided in any embodiment of the present invention.

[0040] In the control method of the micro-inverter provided by the embodiment of the present invention, the first operating mode is adopted when the output voltage is within a preset voltage range, which is equivalent to controlling as few switching tubes as possible to conduct within the range where it is easy to make mistakes in judging the positive and negative polarities of the output voltage, so as to avoid the direct connection of the secondary bridge arm caused by the wrong judgment of the voltage polarity and prevent the switching tubes in the secondary bridge arm from being burned out by large current. The second operating mode is adopted when the output voltage is outside the preset voltage range, which is equivalent to minimizing the actions of the switching tubes when the positive and negative polarities of the output voltage can be accurately judged, simplifying the control logic and reducing the switching loss. Moreover, during the switching process between the first operating state and the second operating state, only one switching tube is controlled to change the on-off state, and the operating mode can be switched in the most convenient way, avoiding the delay and operating state fluctuations caused by the actions of more switching tubes, and reducing the mode switching time and switching loss. In summary, the embodiment of the present invention can effectively improve the operation reliability of the micro-inverter.

[0041] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0043] Figure 1 is a schematic structural diagram of a micro-inverter provided by an embodiment of the present invention;

[0044] Figure 2 is a schematic flowchart of a control method of a micro-inverter provided by an embodiment of the present invention;

[0045] Figure 3 is a schematic timing diagram when switching between a first working mode and a second working mode provided by an embodiment of the present invention;

[0046] Figure 4 is a schematic timing diagram of a first working mode provided by an embodiment of the present invention;

[0047] Figure 5 is a schematic timing diagram when the voltage polarity of the second working mode is positive provided by an embodiment of the present invention;

[0048] Figure 6 is a schematic timing diagram when the voltage polarity of the second working mode is negative provided by an embodiment of the present invention;

[0049] Figure 7 is a schematic startup timing diagram provided by an embodiment of the present invention;

[0050] Figure 8 is a schematic shutdown timing diagram provided by an embodiment of the present invention;

[0051] Figure 9 is a schematic timing diagram of the operation of the secondary side bridge arm provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] To enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0053] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion.

[0054] The embodiment of the present invention provides a control method for a micro-inverter to improve the operation reliability of the micro-inverter. To facilitate the explanation of this control method, the topology of the micro-inverter will be briefly described below. Figure 1 is a schematic structural diagram of a micro-inverter provided by an embodiment of the present invention. Refer to Figure 1 , the micro-inverter 100 can be a single-stage micro-inverter, and its topology includes a primary bridge arm 10, a transformer 20 (such as a high-frequency transformer), and a secondary bridge arm 30. Among them, the input end of the primary bridge arm 10 is connected to an input voltage VIN, which is, for example, a DC voltage provided by a photovoltaic module. The output end of the primary bridge arm 10 is connected to the primary winding of the transformer 20; the primary bridge arm 10 can include multiple switching tubes, and the input end of the primary bridge arm 10 can also be connected to an input capacitor Cin. The secondary winding of the transformer 20 can be connected to a resonant inductor Lr, which can be an independently provided inductor or composed of the leakage inductance of the transformer 20. Figure 1 The excitation inductance Lm of the transformer 20 is also equivalently drawn in according to the characteristics of the transformer 20. The secondary bridge arm 30 is respectively connected to the secondary winding of the transformer 20 and the two output ends of the micro-inverter 100; the two output ends of the micro-inverter 100 are, for example, a first output end L1 and a second output end L2 respectively, and the voltage difference between the two output ends is the output voltage of the micro-inverter 100, which can specifically be the voltage of the first output end L1 minus the voltage of the second output end L2; the two output ends of the micro-inverter 100 can be connected to the power grid, and the output voltage is an AC voltage; an output capacitor Cout is also connected between the two output ends of the micro-inverter 100.

[0055] The secondary bridge arm 30 includes four switching tubes connected in series between the two output terminals of the micro-inverter. Among them, any two adjacent switching tubes are in opposite directions, and the connection node between the middle two switching tubes serves as the middle node P and is connected to the secondary winding of the transformer 20. It can be understood that two adjacent switching tubes in opposite directions can form a pair of top-to-bottom switching tubes, and the directions of their body diodes are opposite. For example, the anodes or cathodes of the two body diodes are connected to each other. Exemplarily, the four switching tubes of the secondary bridge arm 30 include a first switching tube QH1, a second switching tube QL1, a third switching tube QL2, and a fourth switching tube QH2 that are connected in series in sequence between the first output terminal L1 and the second output terminal L2. The connection node between the second switching tube QL1 and the third switching tube QL2 is the middle node P, and this middle node P can be connected to one end of the secondary winding of the transformer 20 through the resonant inductor Lr; the body diode in the first transistor QH1, for example, has its cathode connected to the first output terminal L1. The micro-inverter 100 may further include: a first capacitor C1 connected between the other end of the secondary winding of the transformer 20 and the first output terminal L1; a second capacitor C2 connected between the other end of the secondary winding of the transformer 20 and the second output terminal L2. The first capacitor C1 and the second capacitor C2 and the secondary bridge arm 30 form a half-bridge structure.

[0056] During the operation of the micro-inverter 100, a resonant current is will appear on the resonant inductor Lr between the transformer 20 and the secondary bridge arm 30. The direction (or polarity) of the resonant current is can be specified as follows: the direction of the resonant current is refers to its transmission direction between the transformer 20 and the secondary bridge arm 30, with the direction of the resonant current is flowing from the transformer 20 to the secondary bridge arm 30 being positive and flowing from the secondary bridge arm 30 to the transformer 20 being negative. The micro-inverter 100 may further include a controller for controlling the on-off states of the switching tubes in the primary bridge arm 10 and the secondary bridge arm 30. For example, the controller can generate control signals for the switching tubes in the secondary bridge arm 30 according to the pulse control signals output by the modulation module; the pulse control signals are used to control the phase-shift angles of the secondary switching tubes, and the pulse control signals can specifically be high-frequency pulse signals with a duty cycle of 50%.

[0057] The control method of the micro-inverter will be described below. This control method mainly involves the on-off control strategy of the switching tubes in the secondary bridge arm 30, which can ensure that the secondary bridge arm 30 will not have a through situation at any time, and there is a freewheeling path for the resonant current is at any time.

[0058] Figure 2 is a schematic flowchart of a control method of a micro-inverter provided by an embodiment of the present invention. Refer to Figure 2 and the control method of this micro-inverter includes:

[0059] S110. When the output voltage of the micro-inverter changes from within the preset voltage range to outside the preset voltage range, control the operating state of the secondary side bridge arm to switch from the first type of operating state in the first operating mode to the second type of operating state in the second operating mode.

[0060] Wherein, the preset voltage range is the voltage range between the negative voltage threshold and the positive voltage threshold; the output voltage being within the preset voltage range means that the output voltage is greater than or equal to the negative voltage threshold and less than or equal to the positive voltage threshold; the output voltage being outside the preset voltage range means that the output voltage is greater than the positive voltage threshold or less than the negative voltage threshold. The absolute values of the positive and negative voltage thresholds can be the same or different, and can be specifically set according to actual requirements.

[0061] In the first operating mode, at most two switching tubes in the secondary side bridge arm 30 are conducting at the same time, and at least two switching tubes with opposite directions are turned off, thereby avoiding the occurrence of through conduction in the secondary side bridge arm and preventing the switching tubes from being burned out due to overcurrent. In the second operating mode, at most three switching tubes are conducting at the same time. In the second operating mode, specifically, according to the polarity (or positive and negative) of the output voltage, two switching tubes with the same direction in the secondary side bridge arm 30 can be controlled to be always conducting, and the other two switching tubes can be controlled to conduct alternately, so as to reduce the switching loss and control complexity. In both the first operating mode and the second operating mode, there is always a freewheeling path for the resonant current is between the transformer 20 and the secondary side bridge arm 30, so as to avoid the loss of the freewheeling path and prevent the switching tubes in the secondary side bridge arm 30 from being damaged due to overvoltage.

[0062] By adopting the first operating mode when the output voltage is within the preset voltage range, it is equivalent to controlling as few switching tubes as possible to conduct when the absolute value of the output voltage is relatively low, thereby avoiding through conduction of the bridge arm caused by incorrect voltage polarity judgment and improving the circuit safety. By adopting the second operating mode when the output voltage is outside the preset voltage range, it is equivalent to minimizing the switching times of the switching tubes when the absolute value of the output voltage is relatively high. Since the voltage polarity can be accurately judged when the absolute value of the output voltage is relatively high, it can ensure the avoidance of through conduction of the bridge arm. In this case, the simplification of the control logic and the reduction of the switching loss can be mainly considered.

[0063] S120. When the output voltage changes from outside the preset voltage range to within the preset voltage range, control the operating state of the secondary side bridge arm to switch from the second type of operating state to the first type of operating state.

[0064] Among them, the path between the intermediate node P and any output terminal is denoted as a branch of the secondary side bridge arm. Then, two switching tubes with opposite directions are connected in series between the intermediate node P and an output terminal in a branch. In the first type of operating state in the first operating mode, the two switching tubes between the intermediate node P and one of the output terminals are turned on, and the other two switching tubes are turned off. In the first type of operating state, the resonant current is can flow through the turned-on branch. In the second type of operating state in the second operating mode, three switching tubes are turned on and the other switching tube is turned off. For example, both switching tubes in one branch are turned on, and one switching tube with the freewheeling direction of the body diode in the other branch opposite to the direction of the resonant current is is turned off, and the other switching tube is turned on. Then, in the second type of operating state, the resonant current is can flow through the fully turned-on branch, and the turned-off switching tube can prevent the resonant current is from flowing through the branch where the switching tube is located, thereby avoiding direct connection of the secondary side bridge arm 30.

[0065] During the switching process between the first type of operating state and the second type of operating state, only one switching tube is controlled to change its on-off state to achieve the mode switching in the most convenient way, reducing the mode switching time and switching loss. For example, when switching from the first type of operating state to the second type of operating state, the two switching tubes in the turned-on branch can be controlled to remain turned on, and the switching tube with the freewheeling direction of the body diode in the other branch the same as the direction of the resonant current is can be controlled to turn on. Conversely, when switching from the second type of operating state to the first type of operating state, the two switching tubes in the turned-on branch can be controlled to remain turned on, and the turned-on switching tube in the other branch can be controlled to turn off.

[0066] In the control method of the micro-inverter provided by the embodiment of the present invention, the first operating mode is adopted when the output voltage is within the preset voltage range, which is equivalent to controlling as few switching tubes as possible to turn on within the range where it is easy to make mistakes in judging the positive and negative polarities of the output voltage, thereby avoiding direct connection of the secondary side bridge arm due to incorrect voltage polarity judgment and preventing the switching tubes in the secondary side bridge arm from being burned out by large current. The second operating mode is adopted when the output voltage is outside the preset voltage range, which is equivalent to minimizing the actions of the switching tubes when the positive and negative polarities of the output voltage can be accurately judged, simplifying the control logic and reducing the switching loss. Moreover, during the switching process between the first type of operating state and the second type of operating state, only one switching tube is controlled to change its on-off state, and the operating mode can be switched in the most convenient way, avoiding the delay and working state fluctuation caused by the actions of more switching tubes, and reducing the mode switching time and switching loss. In summary, the embodiment of the present invention can effectively improve the operation reliability of the micro-inverter.

[0067] The following combines Figure 1 the circuit structure in

[0068] SeeFigure 1 For Figure 1 , the two output terminals of the micro-inverter 100 include a first output terminal L1 and a second output terminal L2, and the output voltage is the voltage difference between the first output terminal L1 and the second output terminal L2; the four switching tubes include a first switching tube QH1, a second switching tube QL1, a third switching tube QL2, and a fourth switching tube QH2 that are connected in series between the first output terminal L1 and the second output terminal L2 in sequence.

[0069] Figure 3 It is a timing diagram when switching between a first working mode and a second working mode provided by an embodiment of the present invention. Figure 3 In Figure 3 , the working states of the secondary side bridge arm are represented by solid-line boxes. Among them, any switching tube = 0 means that the switching tube is turned off, that is, the control electrode of the switching tube receives a cut-off level; any switching tube = 1 means that the switching tube is turned on, that is, the control electrode of the switching tube receives a conduction level. The first type of working state is in the red dotted-line box, and the second type of working state is in the black dotted-line box. The upper black dotted-line box is the two second type of working states adopted in the second working mode when the output voltage is positive, and the lower black dotted-line box is the two second type of working states adopted in the second working mode when the output voltage is negative. See Figure 3 Specifically, the first type of working state includes: a first working state S11 and a second working state S12. In the first working state S11, the first switching tube QH1 and the second switching tube QL1 are turned on, and other switching tubes are turned off; in the second working state S12, the third switching tube QL2 and the fourth switching tube QH2 are turned on, and other switching tubes are turned off. The second type of working state includes: a third working state S23, a fourth working state S24, a fifth working state S25, and a sixth working state S26; in the third working state S23, the first switching tube QH1 is turned off, and other switching tubes are turned on; in the fourth working state S24, the third switching tube QL2 is turned off, and other switching tubes are turned on; in the fifth working state S25, the second switching tube QL1 is turned off, and other switching tubes are turned on; in the sixth working state S26, the fourth switching tube QH2 is turned off, and other switching tubes are turned on.

[0070] Specifically, the control method of the micro-inverter includes:

[0071] In the first working mode, according to the positive or negative of the output voltage and the level of the pulse control signal, control the secondary side bridge arm to work in the first working state S11 or the second working state S12.

[0072] In the second working mode, when the output voltage is positive, control the secondary side bridge arm to work in the third working state S23 or the fourth working state S24 according to the level of the pulse control signal; when the output voltage is negative, control the secondary side bridge arm to work in the fifth working state S25 or the sixth working state S26 according to the level of the pulse control signal.

[0073] In the switching process between the first working state and the second working state, the working state of the secondary bridge arm is controlled to switch between the first working state S11 and the fourth working state S24 or the sixth working state S26 according to the change of the output voltage (see Figure 3 or, switching between the second working state S12 and the third working state S23 or the fifth working state S25 (see Figure 3 on the right).

[0074] Figure 3 The symbols in each switching condition are explained as follows: p and U n is the output voltage threshold judgment mark, U p =1 indicates that the output voltage is greater than the positive voltage threshold, U p =0 means the output voltage is less than or equal to the positive voltage threshold, U n =1 means the output voltage is less than the negative voltage threshold, U n =0 indicates that the output voltage is greater than or equal to the negative voltage threshold. t indicates time; t on is the preset conduction maintenance time. EN is the enable signal, which is the switch state control signal provided externally to the controller; when EN=1, the micro-inverter is controlled to start (turn on), and when EN=0, the micro-inverter is controlled to shut down. It can be understood that during the normal operation of the micro-inverter, EN=1 is maintained; once EN=0, the micro-inverter needs to be controlled to shut down; for example, EN=0 will be controlled when it needs to be shut down or protection is triggered.

[0075] See also Figure 3 , the switching process and specific conditions between the first working state and the second working state are as follows:

[0076] If the secondary bridge arm is currently operating in the first operating state S11, when the output voltage is positive and increases to be greater than the positive voltage threshold, that is, t>=t on , U p =1,U n =0, EN = 1, the secondary bridge arm is controlled to switch to the fourth working state S24; when the output voltage is negative and drops below the negative voltage threshold, that is, t> = t on , U p =0,U n =1, EN=1, the secondary bridge arm is controlled to switch to the sixth working state S26.

[0077] If the secondary bridge arm is currently operating in the second operating state S12, when the output voltage is positive and increases to be greater than the positive voltage threshold, that is, t>=t on , U p =1,U nWhen =0 and EN=1, control the secondary side bridge arm to switch to the third working state S23; when the output voltage is negative and drops below the negative voltage threshold, that is, when t>=t on , U p =0, U n =1, and EN=1, control the secondary side bridge arm to switch to the fifth working state S25.

[0078] If the secondary side bridge arm is currently working in the third working state S23 or the fifth working state S25, when the output voltage changes from outside the preset voltage range to within the preset voltage range, control the secondary side bridge arm to switch to the second working state S12. Specifically, if it is currently working in the third working state S23, when t>=t on , (U p =0, U n =0)||(U p =0, U n =1)||(U p =1, U n =1), control the secondary side bridge arm to switch to the second working state S12; where, (U p =0, U n =0)||(U p =0, U n =1)||(U p =1, U n =1) represents various situations where the output voltage deviates from the condition of (U p =1, U n =0). If it is currently working in the fifth working state S25, when t>=t on , (U p =0, U n =0)||(U p =1, U n =0)||(U p =1, U n =1), control the secondary side bridge arm to switch to the second working state S12; where, (U p =0, U n =0)||(U p =1, U n =0)||(U p =1, U n =1) represents various situations where the output voltage deviates from the condition of (U p =0, U n =1).

[0079] If the secondary side bridge arm is currently operating in the fourth operating state S24 or the sixth operating state S26, when the output voltage changes from outside the preset voltage range to within the preset voltage range, control the secondary side bridge arm to switch to the first operating state S11. Specifically, if it is currently operating in the fourth operating state S24, when t >= t on , (U p = 0, U n = 0) || (U p = 0, U n = 1) || (U p = 1, U n = 1), control the secondary side bridge arm to switch to the first operating state S11. If it is currently operating in the sixth operating state S26, when t >= t on , (U p = 0, U n = 0) || (U p = 1, U n = 0) || (U p = 1, U n = 1), control the secondary side bridge arm to switch to the first operating state S11.

[0080] Among them, each first - type operating state and each second - type operating state are maintained for at least a preset conduction maintenance time t on , that is, when switching to any one of the first to sixth operating states, it is necessary to maintain at least the preset conduction maintenance time t on before allowing switching to other operating states. As Figure 3 shown, the switching conditions between operating states all include t >= t on , and when t < t on , the current operating state needs to be maintained. In this way, continuous switching of the switching tube can be avoided.

[0081] It can be understood that in the various figures of this application, in the switching conditions between different states, a comma represents the meaning of "and", that is, if the condition is "A, B", then it is necessary to simultaneously satisfy A and B to perform the state switching corresponding to this condition.

[0082] It should be noted that under normal operating conditions, in the second operating mode, it is not possible to directly switch between the positive output voltage and the negative output voltage. It is necessary to first switch to the first operating mode, for example, switch to the first - type operating state, and then switch to the second - type operating state under the other output voltage polarity.

[0083] The above - mentioned embodiments have described the timing of state switching between the first operating mode and the second operating mode. Next, the timing of state switching within the first operating mode and within the second operating mode will be described.

[0084] In one implementation, optionally, the first operating mode further includes:

[0085] 1) When the resonant current is within the preset current range, control the secondary side bridge arm to maintain the current first type of operating state.

[0086] Among them, the preset current range is the current range between the negative current threshold and the positive current threshold. The output current being within the preset current range means that the output current is greater than or equal to the negative current threshold and less than or equal to the positive current threshold; the output current being outside the preset current range means that the output current is greater than the positive current threshold or less than the negative current threshold. The absolute values of the positive and negative current thresholds can be the same or different, and can be specifically set according to actual requirements.

[0087] Specifically, when the output voltage is within the preset voltage range and the resonant current is also within the preset current range, when the voltage of the pulse control signal jumps, keep each switching tube in the current switching state without acting until the resonant current changes beyond the preset current range or the output voltage exceeds the preset voltage range.

[0088] 2) When the absolute value of the resonant current is greater than the current threshold, when the positive and negative of the output voltage change or the level of the pulse control signal changes, according to the direction of the resonant current, control the operating state of the secondary side bridge arm to switch from the current first type of operating state to another first type of operating state through three first type of transition states.

[0089] Among them, this step is equivalent to determining the action sequence of the switching tubes according to the direction of the resonant current when the switching condition is met. During the switching process, each operating state controls only one switching tube to change its on-off state compared with the previous operating state; in the first type of transition state, at most one switching tube conducts between the intermediate node and any output terminal at the same time. In the first type of transition state, the resonant current can flow through the body diode of one conducting switching tube and another off-switching tube in one of the branches.

[0090] The following combines Figure 4 , and specifically describes the operating state switching timing in the first operating mode. Figure 4 In, I p and I n are the resonant current threshold judgment identifiers. Taking the direction of the resonant current flowing to the secondary side bridge arm as positive, I p =1 indicates that when the resonant current flows to the secondary side bridge arm and is greater than the positive current threshold, I n =1 indicates that the resonant current flows to the transformer and is less than the negative current threshold; when the resonant current is between the positive and negative current thresholds, I p =0, I n= 0. gp is the voltage polarity identifier, or the power frequency positive and negative half - cycle judgment signal. When gp = 1, it means the circuit is working in the positive half - cycle of the power frequency (the output voltage is positive); when gp = 0, it means the circuit is working in the negative half - cycle of the power frequency (the output voltage is negative). PWM is the pulse control signal, which can be provided by the modulation module and is used to control the phase - shift angle of each switch tube on the secondary side. The pulse control signal can specifically be a pulse signal with a duty cycle of 50%, and 0 and 1 appear alternately. ⊙ is the exclusive - NOR symbol. When PWM⊙gp, if the levels of PWM and gp are the same, the output is 1; if the levels are different, the output is 0. t d represents the preset dead - time.

[0091] Specifically, the first - type transition states include: the first transition state S31, the second transition state S32, the third transition state S33, the fourth transition state S34, the fifth transition state S35, and the sixth transition state S36. In the first transition state S31, the third switch tube QL2 is turned on, and other switch tubes are turned off; in the second transition state S32, the second switch tube QL1 and the third switch tube QL2 are turned on, and other switch tubes are turned off; in the third transition state S33, the second switch tube QL1 is turned on, and other switch tubes are turned off; in the fourth transition state S34, the first switch tube QH1 is turned on, and other switch tubes are turned off; in the fifth transition state S35, the first switch tube QH1 and the fourth switch tube QH2 are turned on, and other switch tubes are turned off; in the sixth transition state S36, the fourth switch tube QH2 is turned on, and other switch tubes are turned off.

[0092] See Figure 4 , when the resonant current is within the preset current range and PWM⊙gp = 0, the second working state S12 can be executed; when the resonant current is within the preset current range and PWM⊙gp = 1, the first working state S11 can be executed.

[0093] When the resonant current reaches outside the preset current range, when there is a positive - negative change in the output voltage or a change in the level of the pulse control signal, that is, when the result of PWM⊙gp changes, the working state of the secondary - side bridge arm can be controlled to switch from the current first - type working state to another first - type working state through three first - type transition states according to the direction of the resonant current, specifically as follows:

[0094] When the resonant current flows from the transformer to the secondary - side bridge arm, when the resonant current is outside the preset current range (corresponding to the condition I p = 1, I n = 0), and there is a positive - negative change in the output voltage or a change in the level of the pulse control signal, if the secondary - side bridge arm is currently working in the first working state S11, then control the secondary - side bridge arm to sequentially pass through the third transition state S33, the second transition state S32, and the first transition state S31 and switch to the second working state S12. That is to say, when the conditions I p = 1, I n= 0, when (PWM⊙gp = 0), that is, when the pulse control signal for controlling the upper branch to disconnect comes, the first switch QH1 is controlled to turn off, the third switch QL2 is controlled to turn on, the second switch QL1 is controlled to turn off, and the fourth switch QH2 is controlled to turn on. If the secondary bridge arm is currently operating in the second operating state S12, then the secondary bridge arm is controlled to switch to the first operating state S11 through the first transition state S31, the second transition state S32, and the third transition state S33 in sequence. That is to say, when satisfying I p = 1, I n = 0, when (PWM⊙gp = 1), that is, when the pulse control signal for controlling the lower branch to disconnect comes, the fourth switch QH2 is controlled to turn off, the second switch QL1 is controlled to turn on, the third switch QL2 is controlled to turn off, and the first switch QH1 is controlled to turn on.

[0095] When the resonant current flows from the secondary bridge arm to the transformer, when the resonant current is outside the preset current range (corresponding to the condition I p = 0, I n = 1), and when the positive and negative of the output voltage changes or the level of the pulse control signal changes, if the secondary bridge arm is currently operating in the first operating state S11, then the secondary bridge arm is controlled to switch to the second operating state S12 through the fourth transition state S34, the fifth transition state S35, and the sixth transition state S36 in sequence. That is to say, when satisfying I p = 0, I n = 1, when (PWM⊙gp = 0), that is, when the pulse control signal for controlling the upper branch to disconnect comes, the second switch QL1 is controlled to turn off, the fourth switch QH2 is controlled to turn on, the first switch QH1 is controlled to turn off, and the third switch QL2 is controlled to turn on. If the secondary bridge arm is currently operating in the second operating state S12, then the secondary bridge arm is controlled to switch to the first operating state S11 through the sixth transition state S36, the fifth transition state S35, and the fourth transition state S34 in sequence. That is to say, when satisfying I p = 0, I n = 1, when (PWM⊙gp = 1), that is, when the pulse control signal for controlling the lower branch to disconnect comes, the third switch QL2 is controlled to turn off, the first switch QH1 is controlled to turn on, the fourth switch QH2 is controlled to turn off, and the second switch QL1 is controlled to turn on.

[0096] It can be understood that Figure 4 All the condition restrictions of t >= t on are still to avoid continuous switch switching; all the condition restrictions of EN = 1 are to ensure that the secondary bridge arm is controlled when the micro-inverter is in the normal operating state. It should be noted that during the process of switching from one first type of operating state to another first type of operating state, each time a working state is switched, it is necessary to satisfy t >= t d, to ensure that after the switching action of each first - type transition state is completed, the next working state is switched. Therefore, this switching process takes 3t d . Also, during the process of switching from one first - type working state to another first - type working state, each time a working state is switched, the condition that the PWM⊙gp result remains unchanged needs to be met, so as to avoid situations such as voltage polarity switching during the switching process, which may lead to the loss of the free - wheeling path of the resonant current and prevent the switching tube from bearing over - voltage.

[0097] Based on the above embodiments, optionally, the values of the positive and negative current thresholds are related to the slope of the resonant current. For example, it is necessary to ensure that within the 3t d duration experienced by the branch switching under the maximum slope of the resonant current, the resonant current does not reverse its polarity (i.e., change direction), to avoid the loss of the resonant - current free - wheeling loop and prevent the switching tube from experiencing over - voltage. Exemplarily, the absolute value of any current threshold is positively correlated with the amplitude of the output voltage.

[0098] In one embodiment, optionally, the second working mode further includes: when the level of the pulse control signal changes, controlling the working state of the secondary - side bridge arm to switch from the current second - type working state through a second - type transition state to another second - type transition state corresponding to the positive and negative conditions of the current output voltage. During the switching process, only one switching tube changes its on - off state compared with the previous working state; in the second - type transition state, there is one switching tube conducting between the intermediate node and any output terminal at the same time.

[0099] Next, in combination with Figure 5 and Figure 6 , the switching timing sequence of the working state in the second working mode will be specifically described. Figure 5 shows the control process when the output voltage is positive, Figure 6 shows the control process when the output voltage is negative.

[0100] Referring to Figure 5 , the second - type transition state includes the seventh transition state S47, where the second switching tube QL1 and the fourth switching tube QH2 are conducting, and other switching tubes are off. When the output voltage is greater than the positive voltage threshold (U p = 1, U nWhen PWM = 0), the second switching transistor QL1 and the fourth switching transistor QH2 are kept constantly on, and the first switching transistor QH1 and the third switching transistor QL2 are alternately turned on according to the pulse control signal, for example, alternately turned on with a 50% duty cycle. If the initial state is the third operating state S23, then when PWM = 1, it switches to the fourth operating state S24 through the seventh transition state S47, that is, the third switching transistor QL2 is turned off and the first switching transistor QH1 is turned on in sequence. If the initial state is the fourth operating state S24, then when PWM = 0, it switches to the third operating state S23 through the seventh transition state S47, that is, the first switching transistor QH1 is turned off and the third switching transistor QL2 is turned on in sequence.

[0101] See Figure 6 , the second type of transition state includes the eighth transition state S48, the second switching transistor QL1 and the fourth switching transistor QH2 are turned off, and other switching transistors are turned on. When the output voltage is less than the negative voltage threshold (U p = 0, U n = 1), the first switching transistor QH1 and the third switching transistor QL2 are kept constantly on, and the second switching transistor QL1 and the fourth switching transistor QH2 are alternately turned on according to the pulse control signal, for example, alternately turned on with a 50% duty cycle. If the initial state is the fifth operating state S25, then when PWM = 0, it switches to the sixth operating state S26 through the eighth transition state S48, that is, the fourth switching transistor QH2 is turned off and the second switching transistor QL1 is turned on in sequence. If the initial state is the sixth operating state S26, then when PWM = 1, it switches to the fifth operating state S25 through the eighth transition state S48, that is, the third switching transistor QL1 is turned off and the fourth switching transistor QH2 is turned on in sequence.

[0102] It can be understood that Figure 5 and Figure 6 all the condition restrictions where t >= t on are still for avoiding continuous switching of the switches; all the condition restrictions where EN = 1 are to ensure the control of the secondary side bridge arm when the micro-inverter is in the normal operating state. It should be noted that during the process of switching from one second type of operating state to another second type of operating state, each time a working state is switched, it is necessary to satisfy t >= t d to ensure that the switching action of each second type of transition state is completed before switching to the next working state. The following conditions related to t on and t d will not be repeated.

[0103] Based on the above embodiments, optionally, each first type of operating state and each second type of operating state are maintained for at least a preset conduction maintenance time to avoid continuous switching of the switching transistors. Specifically, see Figures 3 - 6 where any operating state needs to maintain the current operating state when t < t on .

[0104] Each first - type transition state and each second - type transition state are maintained for at least a preset dead - time to ensure that after the switching tube completes its operation, for example, after being fully turned on / off, the next working state is switched. Specifically, refer to Figures 4 - 6 In, any transition state needs to maintain the current transition state when t < t d .

[0105] In the above - mentioned embodiments, the normal working timing of the micro - inverter in the normal working state is described. Specifically, the first and second working modes, as well as the timing during the mode - switching, are described. In the first working mode, the switching state is judged according to the current switching - tube state, the polarity (direction) of the resonant current, the pulse - control signal PWM, and the voltage - polarity identifier gp. Specifically, in the first working mode, an absolute safety region is set, that is, when the resonant current is within the preset current range, the switching tubes of the secondary - side bridge arm are not allowed to operate within this region; after the current passes through zero and reaches outside the preset current range, the current polarity can be judged, and the correct switching - action sequence is made according to the direction of the resonant current to ensure that there is a free - wheeling path at any time, and at most two switching tubes of the secondary - side bridge arm are turned on at any time to prevent the bridge arm from short - circuiting. In the second working mode, the corresponding working state is selected according to the output - voltage polarity, and at most three switching tubes of the secondary - side bridge arm are turned on at any time. The switching condition between the first working mode and the second working mode is the current state and the output - voltage polarity (positive / negative), and only one switching tube operates each time between the above - mentioned each working state. The micro - inverter can be a matrix - type converter. The specific implementation scheme of the above - mentioned matrix - type converter control method based on timing can ensure that the secondary - side bridge - arm circuit does not short - circuit at any time, and there is a free - wheeling channel for the resonant current at any time, and the switching tubes of the bridge arm do not have over - voltage conditions.

[0106] The following gives an exemplary description of the timing when the micro - inverter is turned on and off, but it is not a limitation to the present invention.

[0107] In one embodiment, optionally, the control method of the micro - inverter further includes:

[0108] When receiving the effective level of the enable signal, control the secondary - side bridge arm to work in the first - type working state. Among them, the effective level of the enable signal can be expressed as EN = 1, which is used to control the startup of the micro - inverter;

[0109] When receiving the non - effective level of the enable signal, turn off all the switching tubes in the secondary - side bridge arm. Among them, the non - effective level of the enable signal can be expressed as EN = 0, which is used to control the shutdown of the micro - inverter. When shutdown or over - current protection is triggered, EN = 0 can be controlled.

[0110] Specifically, when receiving the effective level of the enable signal, controlling the secondary - side bridge arm to work in the first - type working state specifically includes:

[0111] When receiving the valid level of the enable signal:

[0112] If the exclusive-NOR result of the voltage polarity identification and the pulse control signal is 1, control the secondary side bridge arm to operate in the first operating state; wherein, when the output voltage is positive, the voltage polarity identification is 1, and when the output voltage is negative, the voltage polarity identification is 0.

[0113] If the exclusive-NOR result of the voltage polarity identification and the pulse control signal is 0, control the secondary side bridge arm to operate in the second operating state.

[0114] The start-up timing can be specifically referred to Figure 7 , when the circuit starts up, the initial current is very small, with I p = 0, I n = 0. When EN = 1, select the initial operating state of the secondary side bridge arm according to the pulse control signal PWM and the voltage polarity identification gp. The shutdown state S0 of the secondary side bridge arm is that all switching tubes are turned off. When PWM⊙gp = 0, enter the second operating state S12, and control the third switching tube QL2 and the fourth switching tube QH2 to conduct; when PWM⊙gp = 1, enter the first operating state S11, and control the first switching tube QH1 and the second switching tube QL1 to conduct.

[0115] Based on the above embodiments, when EN = 0, the correct turn-off sequence can be judged according to the current operating state of the secondary side bridge arm to quickly reduce the current and achieve safe shutdown.

[0116] Specifically, when receiving the non-valid level of the enable signal, control all the switching tubes in the secondary side bridge arm to turn off, including: when receiving the non-valid level of the enable signal:

[0117] If the secondary side bridge arm operates in the second type of operating state, switch the operating state of the secondary side bridge arm to the first type of operating state by changing the on-off state of one switching tube, and execute the first operating mode until the resonant current enters the preset current range, and then control all the switching tubes in the secondary side bridge arm to turn off.

[0118] If the secondary side bridge arm operates in the first operating mode, continue to execute the first operating mode until the resonant current enters the preset current range, and then control all the switching tubes in the secondary side bridge arm to turn off.

[0119] The shutdown timing can be specifically referred to Figure 8 , when the circuit receives the shutdown signal or triggers protection, EN = 0. At this time, it is necessary to judge the identification U p and U n , as well as the resonant current threshold judgment identification I p and I n to judge the corresponding shutdown sequence, so that the micro-inverter switches to the shutdown state S0 after the resonant current reaches within the preset current range in the first operating mode.

[0120] Specifically, when EN = 0, if the circuit is in the second working mode, for example, in the second type of working state, it will switch to the first type of working state, and then according to U p 、U n 、I p 、I n judge the shutdown sequence. Among them, in the third working state S23 and the fifth working state S25, if t >= t on , EN = 0, then switch to the second working state S12; in the fourth working state S24 and the sixth working state S26, if t >= t on , EN = 0, then switch to the first working state S11. It can be understood that if it is in the second working mode when EN = 0, regardless of U p and U n how, it will directly switch to the first working mode to execute the shutdown timing.

[0121] The shutdown timing in the first working mode is as follows:

[0122] If it is in the first working state S11 or the second working state S21 when EN = 0, and at this time I p = 0 and I n = 0, indicating that the resonant current is small and within the preset current range, all switching tubes can be directly turned off to achieve shutdown.

[0123] If it is in the second working state S21 when EN = 0, and I p = 1, I n = 0, then enter the first transition state S31, and then judge the appropriate discharge state according to the output voltage polarity; if it is in the first working state S11 when EN = 0, and I p = 1, I n = 0, then enter the third transition state S33, and then judge the appropriate discharge state according to the output voltage polarity. Among them, in the first transition state S31, if U p = 1, U n = 0, then the second switching tube QL1 needs to be turned on again and the third switching tube QL2 needs to be turned off, and enter the third transition state S33 through the second transition state S32 to make the resonant current decrease naturally; in the third transition state S33, if U p = 0, U n = 1, then it needs to enter the first transition state S31 through the second transition state S32 to make the resonant current decrease naturally. In the first transition state S31 and the third transition state S33, when I p = 0, judge that the resonant current is small enough, and all switching tubes can be turned off to achieve shutdown.

[0124] If it is in the second working state S21 when EN = 0, and I p = 0, In If EN = 1, it enters the sixth transition state S36, and then determines the appropriate discharge state according to the output voltage polarity; if EN = 0 and it is in the first working state S11, and there is I p = 0, I n = 1, it enters the fourth transition state S34, and then determines the appropriate discharge state according to the output voltage polarity. Among them, in the fourth transition state S34, if U p = 1, U n = 0, it needs to enter the sixth transition state S36 via the fifth transition state S35 to naturally reduce the resonant current; in the sixth transition state S36, if U p = 0, U n = 1, it needs to enter the fourth transition state S34 via the fifth transition state S35 to naturally reduce the resonant current. In the fourth transition state S34 and the sixth transition state S36, when I n = 0, it is determined that the resonant current is small enough, and all switching tubes can be turned off to achieve shutdown.

[0125] It can be understood that the second transition state S32 and the fifth transition state S35 only serve as intermediate states and need to transfer to other transition states to reduce the resonant current. Shutdown is not directly performed in the above two transition states.

[0126] In summary, the embodiments of the present invention can adopt state machine sequential logic to relatively simply implement the above functions such as various working modes, mode switching, startup, shutdown / protection, etc. Combining Figures 3 to 8 the timing can obtain Figure 9 as the complete control timing of the micro-inverter. Figure 9 The conditions 1 - 18 in

[0127] Condition 1: t >= t on , I p = 1, I n = 0, (PWM ⊙ gp = 1) || EN = 0;

[0128] Condition 2: t >= t d , (EN = 1, PWM ⊙ gp = 1) || [(U p = 1, U n = 0) && EN = 0];

[0129] Condition 3: t >= t d , (EN = 1, PWM ⊙ gp = 1) || [(U p = 1, U n = 0) && EN = 0];

[0130] Condition 4: t >= t d , EN = 1, (PWM ⊙ gp = 1);

[0131] Condition 5: t >= t on , I p = 1, I n = 0, (PWM ⊙ gp = 0) || EN = 0;

[0132] Condition 6: t >= t d , (EN = 1, PWM ⊙ gp = 0) || [(U p = 0, U n = 1) && EN = 0];

[0133] Condition 7: t >= t d , (EN = 1, PWM ⊙ gp = 0) || [(U p = 0, U n = 1) && EN = 0];

[0134] Condition 8: t >= t d , EN = 1, (PWM ⊙ gp = 0);

[0135] Condition 9: t >= t on , I p = 0, I n = 1, (PWM ⊙ gp = 1) || EN = 0;

[0136] Condition 10: t >= t d , (EN = 1, PWM ⊙ gp = 1) || [(U p = 0, U n = 1) && EN = 0];

[0137] Condition 11: t >= t d , (EN = 1, PWM ⊙ gp = 1) || [(U p = 0, U n = 1) && EN = 0];

[0138] Condition 12: t >= t d , EN = 1, (PWM ⊙ gp = 1);

[0139] Condition 13: t >= t on , I p = 0, I n = 1, (PWM ⊙ gp = 0) || EN = 0;

[0140] Condition 14: t >= t d , (EN = 1, PWM ⊙ gp = 0) || [(U p = 1, U n = 0) && EN = 0];

[0141] Condition 15: t >= td , (EN = 1, PWM⊙gp = 0) || [(U p = 1, U n = 0) && EN = 0];

[0142] Condition 16: t >= t d , EN = 1, (PWM⊙gp = 0);

[0143] Condition 17: t < t on || (I p = 0, I n = 0, EN = 1);

[0144] Condition 18: t < t on || (I p = 0, I n = 0, EN = 1).

[0145] In summary, the embodiment of the present invention provides a timing - based matrix converter control scheme for a single - stage micro - inverter, which is applicable to the secondary - side half - bridge bidirectional switch as shown in Figure 1 , and is also applicable to a full - bridge bidirectional switch (i.e., replacing the first capacitor C1 and the second capacitor C2 in Figure 1 with another bridge - arm structure identical to the secondary - side bridge arm 30, and any bridge arm of the full - bridge can be controlled by the above - mentioned control method), and is also applicable to a multi - path bidirectional switch circuit structure (i.e., the secondary - side bridge arm can include multiple branches respectively connected to multiple output terminals of the micro - inverter, and any two branches can be controlled by the above - mentioned control method). The shutdown timing of the micro - inverter can be achieved in the first working mode, or directly switched from the second working mode to the corresponding state of the first working mode to achieve shutdown. In practical applications, the above - mentioned scheme can be implemented by combining logic with relevant timing signals.

[0146] The embodiment of the present invention also provides a micro - inverter, which can be controlled by using the control method of the micro - inverter provided in any embodiment of the present invention and has corresponding beneficial effects. The micro - inverter may include: a primary - side bridge arm, a transformer, a secondary - side bridge arm, and a controller; the primary - side bridge arm is respectively connected to the input terminal of the micro - inverter and the primary - side winding of the transformer, the secondary - side bridge arm includes four switching tubes connected in series between the two output terminals of the micro - inverter, wherein any two adjacent switching tubes have opposite directions, and the connection node between the middle two switching tubes is used as the middle node to connect the secondary - side winding of the transformer; the controller is connected to the primary - side bridge arm and the control poles of each switching tube; the controller is used to execute the control method of the micro - inverter provided in any embodiment of the present invention.

[0147] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps recited in the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved, and no limitation is imposed herein.

[0148] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A control method for a micro-inverter, characterized in that, The micro-inverter includes: a transformer and a secondary side bridge arm; the secondary side bridge arm includes four switching tubes connected in series between two output terminals of the micro-inverter, wherein any two adjacent switching tubes have opposite directions, and a connection node between the middle two switching tubes is connected to the secondary winding of the transformer as an intermediate node; The control method of the micro-inverter includes: When the output voltage of the micro-inverter changes from within a preset voltage range to outside the preset voltage range, controlling the operating state of the secondary side bridge arm to switch from a first type of operating state in a first operating mode to a second type of operating state in a second operating mode; wherein, the output voltage is the voltage difference between the two output terminals of the micro-inverter, and the preset voltage range is the voltage range between a negative voltage threshold and a positive voltage threshold; at most two of the switching tubes are conducting at the same time in the first operating mode, and at most three of the switching tubes are conducting at the same time in the second operating mode; there is always a freewheeling path for the resonant current between the transformer and the secondary side bridge arm in both the first operating mode and the second operating mode; When the output voltage changes from outside the preset voltage range to within the preset voltage range, controlling the operating state of the secondary side bridge arm to switch from the second type of operating state to the first type of operating state; Wherein, in the first type of operating state, two of the switching tubes between the intermediate node and one of the output terminals are conducting, and the other two switching tubes are off; in the second type of operating state, three of the switching tubes are conducting, and the other switching tube is off; during the switching process between the first type of operating state and the second type of operating state, only one of the switching tubes is controlled to change its on-off state.

2. The control method of the micro-inverter according to claim 1, characterized in that, The two output terminals include a first output terminal and a second output terminal, and the output voltage is the voltage difference between the first output terminal and the second output terminal; The four switching tubes include a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube connected in series between the first output terminal and the second output terminal in sequence; the first type of operating state includes: a first operating state and a second operating state; in the first operating state, the first switching tube and the second switching tube are conducting, and the other switching tubes are off; in the second operating state, the third switching tube and the fourth switching tube are conducting, and the other switching tubes are off; the second type of operating state includes: a third operating state, a fourth operating state, a fifth operating state, and a sixth operating state; in the third operating state, the first switching tube is off, and the other switching tubes are conducting; in the fourth operating state, the third switching tube is off, and the other switching tubes are conducting; in the fifth operating state, the second switching tube is off, and the other switching tubes are conducting; in the sixth operating state, the fourth switching tube is off, and the other switching tubes are conducting; The control method of the micro-inverter includes: In the first operating mode, according to the positive or negative of the output voltage and the level of the pulse control signal, controlling the secondary side bridge arm to operate in the first operating state or the second operating state; In the second operating mode, when the output voltage is positive, the secondary side bridge arm is controlled to operate in the third operating state or the fourth operating state according to the level of the pulse control signal; when the output voltage is negative, the secondary side bridge arm is controlled to operate in the fifth operating state or the sixth operating state according to the level of the pulse control signal; During the switching process between the first type of operating state and the second type of operating state, according to the change of the output voltage, the operating state of the secondary side bridge arm is controlled to switch between the first operating state and the fourth operating state or the sixth operating state, or, between the second operating state and the third operating state or the fifth operating state.

3. The control method of the micro-inverter according to claim 2, wherein If the secondary side bridge arm is currently operating in the first operating state, when the output voltage is positive and rises above the positive voltage threshold, the secondary side bridge arm is controlled to switch to the fourth operating state; when the output voltage is negative and drops below the negative voltage threshold, the secondary side bridge arm is controlled to switch to the sixth operating state; If the secondary side bridge arm is currently operating in the second operating state, when the output voltage is positive and rises above the positive voltage threshold, the secondary side bridge arm is controlled to switch to the third operating state; when the output voltage is negative and drops below the negative voltage threshold, the secondary side bridge arm is controlled to switch to the fifth operating state; If the secondary side bridge arm is currently operating in the third operating state or the fifth operating state, when the output voltage changes from outside the preset voltage range to within the preset voltage range, the secondary side bridge arm is controlled to switch to the second operating state; If the secondary side bridge arm is currently operating in the fourth operating state or the sixth operating state, when the output voltage changes from outside the preset voltage range to within the preset voltage range, the secondary side bridge arm is controlled to switch to the first operating state.

4. The control method of the micro-inverter according to claim 2, characterized in that, The first operating mode further includes: When the resonant current is within the preset current range, controlling the secondary side bridge arm to maintain the current first type of operating state; wherein, the preset current range is the current range between the negative current threshold and the positive current threshold; When the resonant current is outside the preset current range, when the positive and negative of the output voltage or the level of the pulse control signal changes, according to the direction of the resonant current, controlling the operating state of the secondary side bridge arm to switch from the current first type of operating state to another first type of operating state through three first type of transition states; wherein, during the switching process, only one of the switching tubes is controlled to change the on-off state compared with the previous operating state; in the first type of transition state, at most one of the switching tubes between the intermediate node and any one of the output terminals is conducting at the same time; The second working mode further includes: when the level of the pulse control signal changes, controlling the working state of the secondary side bridge arm to switch from the current second type of working state through a second type of transition state to another second type of transition state corresponding to the positive or negative situation of the current output voltage; wherein, during the switching process, only one of the switching tubes is controlled to change its on / off state compared with the previous working state; in the second type of transition state, one of the switching tubes is conducting between the intermediate node and any one of the output terminals at the same moment.

5. The control method of the micro-inverter according to claim 4, characterized in that, Each of the first type of working states and each of the second type of working states are maintained for at least a preset conduction maintaining time. Each of the first type of transition states and each of the second type of transition states are maintained for at least a preset dead time.

6. The control method of the micro-inverter according to claim 4, wherein, The first type of transition states include: a first transition state, a second transition state, a third transition state, a fourth transition state, a fifth transition state, and a sixth transition state; in the first transition state, the third switching tube is conducting and the other switching tubes are off; in the second transition state, the second switching tube and the third switching tube are conducting and the other switching tubes are off; in the third transition state, the second switching tube is conducting and the other switching tubes are off; in the fourth transition state, the first switching tube is conducting and the other switching tubes are off; in the fifth transition state, the first switching tube and the fourth switching tube are conducting and the other switching tubes are off; in the sixth transition state, the fourth switching tube is conducting and the other switching tubes are off. According to the direction of the resonant current, controlling the working state of the secondary side bridge arm to switch from the current first type of working state through three first type of transition states to another first type of working state, including: When the resonant current flows from the transformer to the secondary side bridge arm, when the resonant current is outside the preset current range, and the positive or negative of the output voltage changes or the level of the pulse control signal changes, if the secondary side bridge arm is currently working in the first working state, controlling the secondary side bridge arm to sequentially pass through the third transition state, the second transition state, and the first transition state and switch to the second working state; if the secondary side bridge arm is currently working in the second working state, controlling the secondary side bridge arm to sequentially pass through the first transition state, the second transition state, and the third transition state and switch to the first working state. When the resonant current flows from the secondary side bridge arm to the transformer, when the resonant current is outside the preset current range, and the positive or negative of the output voltage changes or the level of the pulse control signal changes, if the secondary side bridge arm is currently working in the first working state, controlling the secondary side bridge arm to sequentially pass through the fourth transition state, the fifth transition state, and the sixth transition state and switch to the second working state; if the secondary side bridge arm is currently working in the second working state, controlling the secondary side bridge arm to sequentially pass through the sixth transition state, the fifth transition state, and the fourth transition state and switch to the first working state.

7. The control method of the micro-inverter according to any one of claims 1-6, characterized in that, It further includes: When receiving the valid level of the enable signal, control the secondary side bridge arm to operate in the first type of operating state; wherein, the valid level of the enable signal is used to control the startup of the micro-inverter. When receiving the non-valid level of the enable signal, turn off all the switching tubes in the secondary side bridge arm; wherein, the non-valid level of the enable signal is used to control the shutdown of the micro-inverter.

8. The control method of the micro-inverter according to claim 7, wherein The two output terminals include a first output terminal and a second output terminal, and the output voltage is the voltage difference between the first output terminal and the second output terminal. The four switching tubes include a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube that are sequentially connected in series between the first output terminal and the second output terminal; the first type of operating state includes: a first operating state and a second operating state; in the first operating state, the first switching tube and the second switching tube are turned on, and the other switching tubes are turned off; in the second operating state, the third switching tube and the fourth switching tube are turned on, and the other switching tubes are turned off. When receiving the valid level of the enable signal, controlling the secondary side bridge arm to operate in the first type of operating state includes: when receiving the valid level of the enable signal: If the exclusive NOR result of the voltage polarity identifier and the pulse control signal is 1, control the secondary side bridge arm to operate in the first operating state; wherein, the voltage polarity identifier is 1 when the output voltage is positive, and the voltage polarity identifier is 0 when the output voltage is negative. If the exclusive NOR result of the voltage polarity identifier and the pulse control signal is 0, control the secondary side bridge arm to operate in the second operating state.

9. The control method of the micro-inverter according to claim 7, characterized in that, When receiving the non-valid level of the enable signal, controlling all the switching tubes in the secondary side bridge arm to turn off includes: when receiving the non-valid level of the enable signal: If the secondary side bridge arm is operating in the second type of operating state, change the on-off state of one switching tube to switch the operating state of the secondary side bridge arm to the first type of operating state, and execute the first operating mode until the resonant current enters the preset current range, then control all the switching tubes in the secondary side bridge arm to turn off; wherein, the preset current range is the current range between the negative current threshold and the positive current threshold. If the secondary side bridge arm is operating in the first operating mode, continue to execute the first operating mode until the resonant current enters the preset current range, then control all the switching tubes in the secondary side bridge arm to turn off.

10. A micro-inverter, characterized in that, Comprising: A primary side bridge arm, a transformer, a secondary side bridge arm, and a controller. The primary side bridge arm is respectively connected to the input terminal of the micro-inverter and the primary side winding of the transformer. The secondary side bridge arm includes four switching tubes connected in series between the two output terminals of the micro-inverter. Among them, any two adjacent switching tubes have opposite directions, and the connection node between the middle two switching tubes is used as the middle node to connect the secondary side winding of the transformer. The controller is connected to the primary side bridge arm and the control poles of all the switching tubes. The controller is used to execute the control method of the micro-inverter according to any one of claims 1-9.

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