Soft start control circuit

Abstract

The invention discloses a soft start control circuit, and relates to the technical field of power electronics. The soft start control circuit is used for being connected between an alternating current power grid and a direct current bus of an inverter and comprises a soft start controller, a first capacitor, a second capacitor, a rectifier bridge and a circuit control element, and the circuit control element comprises a current limiting circuit, a power switch circuit and a zero line power switch. The soft start controller can adjust the on-off state of the circuit control element based on the voltage conditions of the first capacitor, the second capacitor and the direct current bus, and can transmit electric energy to the first capacitor, the second capacitor and the direct current bus through the current limiting circuit with the current limiting function so as to slowly charge the first capacitor and the second capacitor. Or the direct-current bus is connected to the alternating-current power grid through the power switch circuit, so that the direct-current bus is boosted, and the inverter can safely perform grid-connected operation. According to the technical scheme, the soft start efficiency of the inverter can be remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a soft start control circuit. Background Art

[0002] At present, string-based small and medium-sized off-grid photovoltaic inverters are connected to the AC grid or AC load through AC side relays. When the power system is only powered by AC, when the inverter is started, it is necessary to pull in the AC side relay so that the AC grid can provide support voltage to the DC bus to achieve grid-connected state, realize reactive power compensation and voltage regulation functions of the inverter system, or charge the energy storage battery. When the inverter is started, since there is no voltage in the DC bus of the inverter, and the supporting capacitor capacity of the inverter system is generally above millifarads, directly pulling in the AC relay will cause the impact current to damage the rectifier power device in the inverter and the relay contacts to stick. Therefore, before starting the inverter, it is generally necessary to connect a soft start circuit to the AC switch device of the inverter to achieve the purpose of slowly charging the DC bus capacitor with a small current.

[0003] The existing soft start circuit is generally composed of a soft start relay and a soft start resistor. By closing the soft start relay, the grid voltage passes through the soft start circuit, and the DC bus capacitor is charged by the inverter power freewheeling diode uncontrolled rectification method. When the amplitude of the DC bus voltage reaches the preset standard, the soft start process is judged to be completed. At this time, the AC side relay can be attracted to achieve the grid connection of the inverter. However, in the actual soft start process, the AC grid provides a support voltage for the DC bus through the soft start circuit with a large impedance, so that the speed at which the DC bus reaches the bus voltage required for grid connection is too slow, resulting in low efficiency of the inverter soft start. Summary of the invention

[0004] In view of this, the present application provides a soft start control circuit, the main purpose of which is to solve the technical problem of low efficiency of current inverter soft start.

[0005] According to a first aspect of the present invention, there is provided a soft start control circuit, which is used to be connected between an AC power grid and a DC bus of an inverter, wherein the soft start control circuit comprises a soft start controller, a first capacitor, a second capacitor, a rectifier bridge and a circuit control element, wherein the circuit control element comprises a current limiting circuit, a power switch circuit and a neutral line power switch;

[0006] The first capacitor and the second capacitor are connected in series between the positive terminal and the negative terminal of the rectifier bridge, the positive terminal and the negative terminal of the rectifier bridge are also connected to the positive terminal and the negative terminal of the DC bus respectively, the first end of the zero line power switch is connected between the first capacitor and the second capacitor, and the second end of the zero line power switch is connected to the neutral line of the AC power grid;

[0007] The first end of the current limiting circuit and the first end of the power switch circuit are connected to the voltage output end of the AC power grid, and the second end of the current limiting circuit and the second end of the power switch circuit are connected to the voltage input end of the rectifier bridge, wherein the impedance of the current limiting circuit is greater than the impedance of the power switch circuit;

[0008] The soft start controller is used to monitor the bus voltage of the DC bus and the capacitor voltages of the first capacitor and the second capacitor in response to a soft start execution signal, and control each circuit control element to be turned on or off based on the bus voltage and the capacitor voltage.

[0009] In an optional embodiment, the current limiting circuit includes a first current limiting circuit, a second current limiting circuit and a third current limiting circuit; the power switch circuit includes a first power switch, a second power switch and a third power switch; the voltage output end of the AC power grid includes an A-phase end, a B-phase end and a C-phase end; the voltage input end of the rectifier bridge includes an A-phase input end, a B-phase input end and a C-phase input end; the first end of the first current limiting circuit is connected in parallel with the first end of the first power switch and then connected to the A-phase input end of the rectifier bridge, and the second end of the first current limiting circuit is connected in parallel with the second end of the first power switch and then connected to the A-phase end of the AC power grid; the first end of the second current limiting circuit is connected in parallel with the first end of the second power switch and then connected to the B-phase input end of the AC power grid, and the second end of the second current limiting circuit is connected in parallel with the second end of the second power switch and then connected to the B-phase end of the AC power grid; the first end of the third current limiting circuit is connected in parallel with the first end of the third power switch and then connected to the C-phase input end of the rectifier bridge, and the second end of the third current limiting circuit is connected in parallel with the second end of the third power switch and then connected to the C-phase end of the AC power grid.

[0010] In an optional embodiment, the soft start controller monitors the bus voltage of the DC bus, the capacitor voltages of the first capacitor and the second capacitor in response to a soft start execution signal, and controls the way in which each of the circuit control elements is turned on or off based on the bus voltage and the capacitor voltage, including: the soft start controller controls the zero-line power switch, the first current limiting circuit, the second current limiting circuit, and the third current limiting circuit to be turned on in response to the soft start execution signal; monitors the capacitor voltage, and when the capacitor voltage reaches a capacitor voltage threshold, controls the zero-line power switch to be turned off, and after the zero-line power switch is in an off state, controls the first power switch, the second power switch, and the third power switch to be turned on; monitors the bus voltage, and when the bus voltage reaches a bus voltage threshold, controls the zero-line power switch to be turned on, and after the zero-line power switch is in an on state, controls the first current limiting circuit, the second current limiting circuit, and the third current limiting circuit to be turned off, so that the inverter is in a state where it can be connected to the AC power grid.

[0011] In an optional embodiment, the soft start controller controls the conduction of the neutral line power switch, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit in response to the soft start execution signal, including: the soft start controller disconnects each of the circuit control elements in response to the soft start execution signal; after a preset interval time, controls the conduction of the neutral line power switch, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit.

[0012] In an optional embodiment, the first current limiting circuit includes a first resistor and a first relay connected in series; the second current limiting circuit includes a second resistor and a second relay connected in series; the third current limiting circuit includes a third resistor and a third relay connected in series; the soft start controller is used to send a first timing drive signal to the first relay, the second relay and the third relay to control the first relay, the second relay and the third relay to be turned on or off.

[0013] In an optional embodiment, the rectifier bridge includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube; the connection end of the first end of the first switch tube, the first end of the second switch tube and the first end of the third switch tube connected in parallel serves as the positive end of the rectifier bridge, and the connection end of the first end of the fourth switch tube, the first end of the fifth switch tube and the first end of the sixth switch tube connected in parallel serves as the negative end of the rectifier bridge; the connection end of the second end of the first switch tube connected to the second end of the fourth switch tube serves as the C-phase input end of the rectifier bridge, the connection end of the second end of the second switch tube connected to the second end of the fifth switch tube serves as the B-phase input end of the rectifier bridge, and the connection end of the second end of the third switch tube connected to the second end of the sixth switch tube serves as the A-phase input end of the rectifier bridge.

[0014] In an optional embodiment, the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube and the sixth switch tube are respectively insulated gate bipolar transistor circuits; the insulated gate bipolar transistor circuit includes an insulated gate bipolar transistor and a diode; the collector terminal of the insulated gate bipolar transistor is connected to the cathode terminal of the diode, the emitter terminal of the insulated gate bipolar transistor is connected to the anode terminal of the diode, and the base terminal of the insulated gate bipolar transistor is used to receive an external control signal to control the insulated gate bipolar transistor to be turned on or off.

[0015] In an optional embodiment, the base terminal of the insulated gate bipolar transistor is connected to the soft start controller; the soft start controller is also used to control the on and off of each of the insulated gate bipolar transistors in the rectifier bridge.

[0016] In an optional embodiment, the soft start controller has a remote communication port; the soft start controller is used to connect to a remote host computer through the remote communication port to establish a communication connection with the host computer.

[0017] In an optional embodiment, the soft start controller is also used to issue a docking prompt message when the bus voltage reaches the bus voltage threshold and the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are in a disconnected state.

[0018] The present invention provides a soft start control circuit, during soft start, when charging the bus capacitor, power is obtained from the AC power grid through a current limiting circuit with a large impedance that can play a current limiting function, and the bus capacitor is slowly charged. Further, when it is determined based on the voltage of the bus capacitor that the bus capacitor has been fully charged, the neutral line power switch is controlled to be disconnected, and the power switch circuit with a smaller impedance is controlled to be turned on, so that the AC power grid can quickly make the bus voltage of the DC bus reach the standard that can be connected to the grid, which can significantly improve the speed of the inverter soft start and the soft start efficiency of the inverter.

[0019] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0021] Figure 1 One of the structural schematic diagrams of a soft start control circuit provided by an embodiment of the present invention is shown;

[0022] Figure 2 A second structural schematic diagram of a soft start control circuit provided by an embodiment of the present invention is shown;

[0023] Figure 3 A timing diagram of a relay drive signal provided by an embodiment of the present invention is shown;

[0024] Figure 4 A schematic diagram of the structure of a current limiting circuit provided by an embodiment of the present invention is shown;

[0025] Figure 5 A schematic structural diagram of a rectifier bridge provided by an embodiment of the present invention is shown;

[0026] Figure 6 A schematic structural diagram of an insulated gate bipolar transistor circuit provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0028] In one embodiment, Figure 1As shown, a soft start control circuit is provided, which is used to be connected between an AC power grid and a DC bus of an inverter.

[0029] Specifically, the soft start control circuit includes a soft start controller, a first capacitor C1, a second capacitor C2, a rectifier bridge and a circuit control element. Among them, the first capacitor C1 and the second capacitor C2 serve as bus capacitors, and the rectifier bridge is a rectifier device that can convert the received alternating current into direct current. Further, the circuit control element includes a current limiting circuit, a power switching circuit and a neutral line power switch; here, the current limiting circuit is composed of a soft start resistor and a switching device so that the current limiting circuit has a current limiting function. Furthermore, the power switching circuit may also have a switching device, and the soft start controller can be connected to the current limiting circuit and the switching device in the power switching circuit, and the conduction and disconnection of the current limiting circuit and the power switching circuit are controlled by controlling the conduction and disconnection of the switching device.

[0030] Furthermore, the first capacitor C1 and the second capacitor C2 are connected in series between the positive terminal and the negative terminal of the rectifier bridge, and the positive terminal and the negative terminal of the rectifier bridge are also respectively connected to the positive terminal and the negative terminal of the DC bus, the first end of the zero-line power switch is connected between the first capacitor C1 and the second capacitor C2, and the second end of the zero-line power switch is connected to the neutral line N of the AC power grid.

[0031] Specifically, the first end of the first capacitor C1 is respectively connected to the positive terminal of the rectifier bridge and the positive terminal of the DC bus, the second end of the first capacitor C1 is respectively connected to the first end of the second capacitor C2 and the first end of the zero-line power switch, and the second end of the second capacitor C2 is respectively connected to the negative terminal of the DC bus and the negative terminal of the rectifier bridge.

[0032] Furthermore, the first end of the current limiting circuit and the first end of the power switching circuit are connected to the voltage output terminal E of the AC power grid, and the second end of the current limiting circuit and the second end of the power switching circuit are connected to the voltage input terminal of the rectifier bridge, wherein the impedance of the current limiting circuit is greater than the impedance of the power switching circuit.

[0033] Furthermore, the soft start controller is used to monitor the bus voltage of the DC bus, the capacitor voltages of the first capacitor C1 and the second capacitor C2 in response to a soft start execution signal, and control each of the circuit control elements to be turned on or off based on the bus voltage and the capacitor voltage.

[0034] Here, the soft start controller can be connected to a first voltage sensor set at the DC bus to obtain the bus voltage of the DC bus collected by the first voltage sensor; further, the soft start controller can be connected to a second voltage sensor set at the first capacitor C1 and a third voltage sensor set at the second capacitor C2 to respectively obtain the capacitor voltage of the first capacitor C1 and the capacitor voltage of the second capacitor C2 collected by the second voltage sensor and the third voltage sensor, where the capacitor voltage of the first capacitor C1 is equal to the capacitor voltage of the second capacitor C2.

[0035] Furthermore, when the relevant staff needs to soft-start the inverter, a soft-start execution signal can be sent to the soft-start controller through a computer terminal such as a controller, so that the soft-start controller controls the current limiting circuit to be turned on, and obtains power from the AC power grid through the current limiting circuit to slowly charge the first capacitor C1 and the second capacitor C2. Furthermore, when it is determined that the first capacitor C1 and the second capacitor C2 have been fully charged based on the capacitor voltage of the first capacitor C1 and the second capacitor C2, the neutral line power switch is controlled to be disconnected, and the power switch circuit with a smaller impedance is controlled to be turned on, so that the bus voltage of the DC bus reaches the standard that can be connected to the grid, and the inverter can be connected to the grid.

[0036] The present invention provides a soft start control circuit, during soft start, when charging the bus capacitor, power is obtained from the AC power grid through a current limiting circuit that can play a current limiting function, and the bus capacitor is slowly charged. Further, when it is determined based on the voltage of the bus capacitor that the bus capacitor has been fully charged, the neutral line power switch is controlled to be disconnected, and the power switch circuit with a smaller impedance is controlled to be turned on, so that the AC power grid can quickly make the bus voltage of the DC bus reach the standard that can be connected to the grid, so that the inverter can be connected to the grid normally, which can significantly improve the speed of the inverter soft start and can significantly improve the soft start efficiency of the inverter.

[0037] In an optional embodiment, if Figure 2 As shown, the current limiting circuit includes a first current limiting circuit, a second current limiting circuit and a third current limiting circuit, and the first current limiting circuit, the second current limiting circuit and the third current limiting circuit respectively have the same or different impedances to play a current limiting role; further, the power switch circuit includes a first power switch, a second power switch and a third power switch; the AC power grid can be a power grid that outputs three-phase electricity, the inverter can be a three-phase four-wire inverter, and the voltage output end of the AC power grid includes an A-phase terminal A, a B-phase terminal B and a C-phase terminal C. Further, the voltage input end of the rectifier bridge includes an A-phase input end, a B-phase input end and a C-phase input end.

[0038] Further, the connection end after the first end of the first current limiting circuit is connected in parallel with the first end of the first power switch is connected to the A-phase input end of the rectifier bridge, and the connection end after the second end of the first current limiting circuit is connected in parallel with the second end of the first power switch is connected to the A-phase end A of the AC power grid; the connection end after the first end of the second current limiting circuit is connected in parallel with the first end of the second power switch is connected to the B-phase input end of the rectifier bridge, and the connection end after the second end of the second current limiting circuit is connected in parallel with the second end of the second power switch is connected to the B-phase end B of the AC power grid; the connection end after the first end of the third current limiting circuit is connected in parallel with the first end of the third power switch is connected to the C-phase input end of the rectifier bridge, and the connection end after the second end of the third current limiting circuit is connected in parallel with the second end of the third power switch is connected to the C-phase end C of the AC power grid.

[0039] Furthermore, the control end of the soft start controller can be connected to the controlled ends of the first current limiting circuit, the second current limiting circuit and the third current limiting circuit respectively. When the soft start controller sends a high-level signal to the controlled ends of the first current limiting circuit, the second current limiting circuit and the third current limiting circuit respectively, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are turned on. When the soft start controller does not send a high-level signal to the controlled ends of the first current limiting circuit, the second current limiting circuit and the third current limiting circuit, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are turned off.

[0040] Furthermore, the control end of the soft start controller can also be connected to the controlled ends of the first power switch, the second power switch, the third power switch and the neutral power switch respectively. When the soft start controller sends a high level signal to the controlled ends of the first power switch, the second power switch, the third power switch and the neutral power switch respectively, the first power switch, the second power switch, the third power switch and the neutral power switch are turned on. When the soft start controller does not send a high level signal to the controlled ends of the first power switch, the second power switch, the third power switch and the neutral power switch, the first power switch, the second power switch, the third power switch and the neutral power switch are disconnected. The embodiment provided by the present application can connect three-phase electricity to the soft start control circuit, so that the soft start control circuit can be applied to a three-phase four-wire inverter, enriching the application scenarios of the soft start control circuit.

[0041] In an optional embodiment, the soft start controller monitors the bus voltage of the DC bus and the capacitor voltages of the first capacitor and the second capacitor in response to the soft start execution signal, and controls each of the circuit control elements to be turned on or off based on the bus voltage and the capacitor voltage, including:

[0042] First, the soft start controller controls the neutral line power switch, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit to be turned on in response to the soft start execution signal; here, when the soft start controller receives the soft start execution signal, it can first send a low level signal to the controlled end of the first current limiting circuit, the second current limiting circuit, the third current limiting circuit, the first power switch, the second power switch, the third power switch and the neutral line power switch, so that the first current limiting circuit, the second current limiting circuit, the third current limiting circuit, the first power switch, the second power switch, the third power switch and the neutral line power switch are respectively in the disconnected state; then, a high level signal is sent to the controlled end of the neutral line power switch, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit, so that the neutral line power switch, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are turned on. At this time, the AC voltage charges the first capacitor C1 and the second capacitor C2 through the neutral line and the current limiting circuit, and the theoretical charging voltage can reach 2*Van*1.414, where Van is the effective value of the AC side phase voltage.

[0043] Here, after the soft start controller receives the soft start execution signal, each of the circuit control elements can be disconnected, and after a preset interval time, the neutral line power switch, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are controlled to be turned on, and the subsequent control process is executed. Here, the length of the preset interval time can be determined according to actual conditions.

[0044] Then, the soft start controller monitors the capacitor voltage, and when the capacitor voltage reaches the capacitor voltage threshold, controls the zero line power switch to be disconnected, and after the zero line power switch is in the disconnected state, controls the first power switch, the second power switch and the third power switch to be turned on. Specifically, after a period of time, the capacitor voltage of the first capacitor C1 and the second capacitor C2 reaches the capacitor voltage threshold, and the bus capacitor is charged. The capacitor voltage threshold can be preset, and its value can be determined according to actual conditions. Further, after the bus capacitor is charged, the zero line power switch is controlled to be disconnected, and after the zero line power switch is switched from the on state to the off state, the first power switch, the second power switch and the third power switch are controlled to be turned on, so that the AC power grid no longer provides a support voltage for the DC bus through the soft start circuit with a larger impedance, which can effectively increase the speed at which the voltage of the DC bus reaches the bus voltage required for grid connection.

[0045] Finally, the soft start controller monitors the bus voltage, and when the bus voltage reaches the bus voltage threshold, controls the neutral power switch to conduct, and after the neutral power switch is in the conducting state, controls the first current limiting circuit, the second current limiting circuit and the third current limiting circuit to be disconnected, so that the inverter is in a state where it can be connected to the AC power grid. Specifically, the soft start controller can monitor the bus voltage of the DC bus, and when the bus voltage reaches the bus voltage threshold, controls the neutral power switch to conduct, wherein the bus voltage threshold can be preset, and its value can be determined according to actual conditions, and its value will not be significantly lower than the peak value of the AC power grid.

[0046] Furthermore, after the neutral power switch is switched from the off state to the on state, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are controlled to be disconnected to close the soft start relay so that the inverter is in a state where it can be connected to the AC power grid. At this time, the AC relay can be energized to achieve soft start of the inverter.

[0047] Further, such as Figure 3 As shown, in the above-mentioned soft start process, the soft start controller can control the conduction and disconnection of the first current limiting circuit, the second current limiting circuit and the third current limiting circuit by sending the first relay drive signal G1 to the first current limiting circuit, the second current limiting circuit and the third current limiting circuit; control the conduction and disconnection of the first power switch, the second power switch and the third power switch by sending the second relay drive signal G2 to the first power switch, the second power switch and the third power switch; and control the conduction and disconnection of the neutral line power switch by sending the third relay drive signal G3 to the neutral line power switch.

[0048] Furthermore, in the above-mentioned soft start process, the time period during which the soft start controller performs the control operation can be divided into a preparatory time period, a first time period, a second time period, a third time period, a fourth time period and a fifth time period. Figure 3 As shown, the preparation time period is between time point t0 and time point t1, the first time period is between time point t1 and time point t2, the second time period is between time point t2 and time point t3, the third time period is between time point t3 and time point t4, the fourth time period is between time point t4 and time point t5, and the fifth time period is after time point t5.

[0049] Specifically, Figure 3 As shown, between time point t0 and time point t1, the first relay drive signal G1, the second relay drive signal G2 and the third relay drive signal G3 are all low level signals, so that all circuit control elements remain in the disconnected state. The time length between time point t0 and time point t1 can be the above-mentioned preset interval time.

[0050] Furthermore, in the first time period, the first relay drive signal G1 and the third relay drive signal G3 are high level signals, and the second relay drive signal G2 is a low level signal. Here, the duration of the first time period can also be determined according to the capacities of the first capacitor and the second capacitor.

[0051] Further, at time t2, the capacitor voltages of the first capacitor and the second capacitor reach the capacitor voltage threshold, at which time the third relay drive signal G3 changes to a low level signal. The length of the second time period is the time required for the neutral line power switch to change from the on state to the off state.

[0052] Furthermore, at time t3, the second relay drive signal G2 is converted into a high level signal, so that the first power switch, the second power switch and the third power switch are turned on. At this time, due to the existence of the modulation index M, the bus voltage of the DC bus only needs to be greater than 1.732*1.414*Van to complete the grid connection. After the grid connection, the bus voltage can be raised to the rated voltage value through the PFC circuit, where Van is the effective value of the AC side phase voltage.

[0053] Further, at time t4, the bus voltage reaches the bus voltage threshold, at which time the third relay drive signal G3 is converted into a high level signal, the neutral line power switch is energized, and no impact current is generated during the entire energization process. The length of the fourth time period is the time required for the neutral line power switch to change from an off state to an on state.

[0054] Furthermore, at time point t5, the first relay driving signal G1 is converted into a low level signal, so that the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are disconnected. At this time, the soft start process ends.

[0055] The embodiments provided in the present application can control the on and off states of each circuit control element in the soft start control circuit according to the states of the bus voltage and the capacitor voltage, which can significantly improve the soft start speed of the inverter and the soft start efficiency of the inverter.

[0056] In an optional embodiment, if Figure 4As shown, the first current limiting circuit includes a first resistor and a first relay connected in series; the second current limiting circuit includes a second resistor and a second relay connected in series; the third current limiting circuit includes a third resistor and a third relay connected in series; wherein the first resistor, the second resistor and the third resistor can be used as soft start resistors respectively to play a role in current limiting. Specifically, the first end of the first resistor is connected to the A-phase input end of the rectifier bridge, the second end of the first resistor is connected to the first end of the first relay, and the second end of the first relay is connected to the A-phase end of the AC power grid. Further, the first end of the second resistor is connected to the B-phase input end of the rectifier bridge, the second end of the second resistor is connected to the first end of the second relay, and the second end of the second relay is connected to the B-phase end of the AC power grid. Further, the first end of the third resistor is connected to the C-phase input end of the rectifier bridge, the second end of the third resistor is connected to the first end of the third relay, and the second end of the third relay is connected to the C-phase end of the AC power grid.

[0057] Furthermore, the soft start controller is used to send the first timing drive signal to the first relay, the second relay and the third relay to control the first relay, the second relay and the third relay to be turned on or off. The embodiment provided by the present application can play a role of current limiting through the first resistor, the second resistor and the third resistor, and can control whether to connect the current limiting circuit to the soft start control circuit by controlling the on and off states of the first relay, the second relay and the third relay, thereby improving the controllability of the soft start control circuit.

[0058] In an optional embodiment, if Figure 5 As shown, the rectifier bridge includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube.

[0059] Specifically, the connection end of the first end of the first switch tube, the first end of the second switch tube, and the first end of the third switch tube connected in parallel serves as the positive end of the rectifier bridge, and the connection end of the first end of the fourth switch tube, the first end of the fifth switch tube, and the first end of the sixth switch tube connected in parallel serves as the negative end of the rectifier bridge.

[0060] Furthermore, the connection end after the second end of the first switch tube is connected to the second end of the fourth switch tube serves as the C-phase input end of the rectifier bridge, the connection end after the second end of the second switch tube is connected to the second end of the fifth switch tube serves as the B-phase input end of the rectifier bridge, and the connection end after the second end of the third switch tube is connected to the second end of the sixth switch tube serves as the A-phase input end of the rectifier bridge.

[0061] The embodiment provided in the present application, by forming a rectifier bridge through multiple switch tubes, can convert AC power on the AC grid side into DC power on the DC bus side at a relatively low hardware cost, thereby reducing the hardware cost of the soft start control circuit.

[0062] In an optional embodiment, the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube and the sixth switch tube are insulated gate bipolar transistor circuits respectively; further, as Figure 6 As shown, the insulated gate bipolar transistor circuit includes an insulated gate bipolar transistor and a diode.

[0063] Specifically, the collector terminal of the insulated gate bipolar transistor is connected to the cathode terminal of the diode, the emitter terminal of the insulated gate bipolar transistor is connected to the anode terminal of the diode, and the base of the insulated gate bipolar transistor is used to receive an external control signal to control the insulated gate bipolar transistor to be turned on or off. The embodiment provided by the present application forms a switch tube by using an insulated gate bipolar transistor and a diode, and utilizes the good static and dynamic characteristics of the insulated gate bipolar transistor to improve the working performance of the switch tube, thereby improving the rectification capacity of the rectifier bridge.

[0064] In an optional embodiment, the base of the insulated gate bipolar transistor is connected to the soft start controller; the soft start controller is also used to control the on and off of each of the insulated gate bipolar transistors in each of the rectifier bridges. The embodiment provided by the present application can control the working process of the rectifier bridge through the soft start controller, thereby improving the controllability of the soft start control circuit.

[0065] In an optional embodiment, the soft start controller has a remote communication port; here, the soft start controller is used to establish a communication connection with a remote host computer through the remote communication port. The host computer can be a computer device at a remote control center or other location, and the soft start controller can be connected to the host computer through cables such as optical fibers and buses to establish a communication connection between the host computer and the soft start controller. The embodiment provided by the present application enables relevant staff to remotely control the soft start controller through the host computer, thereby realizing remote control of the soft start control circuit, thereby improving the operational convenience of the soft start control circuit.

[0066] In an optional embodiment, the soft start controller is also used to send a docking prompt message when the bus voltage reaches the bus voltage threshold and the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are in a disconnected state. Here, when the bus voltage reaches the bus voltage threshold and the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are in a disconnected state, the AC side relay can be attracted to achieve the soft start of the inverter. At this time, the docking prompt message can be sent to the remote host computer so that the relevant staff can know that the inverter is in a state where soft start can be performed, and the inverter can be connected to the AC power grid to enable the inverter to enter a normal working state.

[0067] Furthermore, when the bus voltage reaches the bus voltage threshold and the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are in the disconnected state, the soft start controller can also directly control the AC side relay to be attracted to complete the soft start. The embodiment provided by the present application can send prompt information to relevant staff in a timely manner after the inverter is soft started and the inverter can be connected to the AC power grid, so that the relevant staff can perform further processing.

[0068] The soft start control circuit provided in the present application can control the AC soft start process of the three-phase four-wire inverter. By monitoring the bus voltage and the bus capacitor voltage, the conduction and disconnection of each switching element in the soft start control circuit are controlled, and then the charging process of the bus capacitor and the boost process of the DC bus are controlled. The soft start of the inverter can be completed when the DC bus voltage meets the conditions, which can effectively avoid the DC bus voltage being too much lower than the AC peak value after the inverter is soft-started, resulting in insufficient inverter voltage when connected to the grid. The DC bus voltage is boosted quickly, which effectively improves the efficiency of the inverter soft start.

[0069] The above serial numbers of this application are only for description and do not represent the advantages and disadvantages of the implementation scenarios. The above disclosure is only a few specific implementation scenarios of this application, but this application is not limited to them, and any changes that can be thought of by technicians in this field should fall within the scope of protection of this application.

Claims

1. A soft start control circuit, used to be connected between an AC power grid and a DC bus of an inverter, characterized in that: The soft start control circuit includes a soft start controller, a first capacitor, a second capacitor, a rectifier bridge and a circuit control element, and the circuit control element includes a current limiting circuit, a power switch circuit and a neutral line power switch; The first capacitor and the second capacitor are connected in series between the positive terminal and the negative terminal of the rectifier bridge, the positive terminal and the negative terminal of the rectifier bridge are also connected to the positive terminal and the negative terminal of the DC bus respectively, the first end of the zero line power switch is connected between the first capacitor and the second capacitor, and the second end of the zero line power switch is connected to the neutral line of the AC power grid; The first end of the current limiting circuit and the first end of the power switch circuit are connected to the voltage output end of the AC power grid, and the second end of the current limiting circuit and the second end of the power switch circuit are connected to the voltage input end of the rectifier bridge, wherein the impedance of the current limiting circuit is greater than the impedance of the power switch circuit; The soft start controller is used to monitor the bus voltage of the DC bus and the capacitor voltages of the first capacitor and the second capacitor in response to a soft start execution signal, and control each circuit control element to be turned on or off based on the bus voltage and the capacitor voltage.

2. The soft start control circuit according to claim 1, characterized in that: The current limiting circuit includes a first current limiting circuit, a second current limiting circuit and a third current limiting circuit; the power switch circuit includes a first power switch, a second power switch and a third power switch; the voltage output end of the AC power grid includes an A phase end, a B phase end and a C phase end; the voltage input end of the rectifier bridge includes an A phase input end, a B phase input end and a C phase input end; The first end of the first current limiting circuit is connected in parallel with the first end of the first power switch and then connected to the A-phase input end of the rectifier bridge, and the second end of the first current limiting circuit is connected in parallel with the second end of the first power switch and then connected to the A-phase end of the AC power grid; the first end of the second current limiting circuit is connected in parallel with the first end of the second power switch and then connected to the B-phase input end of the rectifier bridge, and the second end of the second current limiting circuit is connected in parallel with the second end of the second power switch and then connected to the B-phase end of the AC power grid; the first end of the third current limiting circuit is connected in parallel with the first end of the third power switch and then connected to the C-phase input end of the rectifier bridge, and the second end of the third current limiting circuit is connected in parallel with the second end of the third power switch and then connected to the C-phase end of the AC power grid.

3. The soft start control circuit according to claim 2, characterized in that: The soft start controller monitors the bus voltage of the DC bus and the capacitor voltages of the first capacitor and the second capacitor in response to the soft start execution signal, and controls the conduction or disconnection of each circuit control element based on the bus voltage and the capacitor voltage, including: The soft start controller controls the neutral line power switch, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit to be turned on in response to the soft start execution signal; monitoring the capacitor voltage, and when the capacitor voltage reaches a capacitor voltage threshold, controlling the neutral line power switch to be turned off, and after the neutral line power switch is in the off state, controlling the first power switch, the second power switch, and the third power switch to be turned on; The bus voltage is monitored, and when the bus voltage reaches a bus voltage threshold, the neutral line power switch is controlled to be turned on, and after the neutral line power switch is in the on state, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are controlled to be turned off, so that the inverter is in a state where it can be connected to the AC power grid.

4. The soft start control circuit according to claim 3, characterized in that: The soft start controller controls the conduction of the neutral line power switch, the first current limiting circuit, the second current limiting circuit, and the third current limiting circuit in response to the soft start execution signal, including: The soft start controller disconnects each of the circuit control elements in response to the soft start execution signal; After a preset interval time, the neutral line power switch, the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are controlled to be turned on.

5. The soft start control circuit according to claim 2, characterized in that: The first current limiting circuit includes a first resistor and a first relay connected in series; The second current limiting circuit includes a second resistor and a second relay connected in series; The third current limiting circuit comprises a third resistor and a third relay connected in series; The soft start controller is used to send a first timing drive signal to the first relay, the second relay and the third relay to control the first relay, the second relay and the third relay to be turned on or off.

6. The soft start control circuit according to claim 2, characterized in that: The rectifier bridge includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube; The first end of the first switch tube, the first end of the second switch tube, and the first end of the third switch tube are connected in parallel and connected at a connection end as the positive terminal of the rectifier bridge; the first end of the fourth switch tube, the first end of the fifth switch tube, and the first end of the sixth switch tube are connected in parallel and connected at a connection end as the negative terminal of the rectifier bridge; The connection end after the second end of the first switch tube is connected to the second end of the fourth switch tube serves as the C-phase input end of the rectifier bridge, the connection end after the second end of the second switch tube is connected to the second end of the fifth switch tube serves as the B-phase input end of the rectifier bridge, and the connection end after the second end of the third switch tube is connected to the second end of the sixth switch tube serves as the A-phase input end of the rectifier bridge.

7. The soft start control circuit according to claim 6, characterized in that: The first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube and the sixth switch tube are insulated gate bipolar transistor circuits respectively; The insulated gate bipolar transistor circuit includes an insulated gate bipolar transistor and a diode; The collector terminal of the insulated gate bipolar transistor is connected to the cathode terminal of the diode, the emitter terminal of the insulated gate bipolar transistor is connected to the anode terminal of the diode, and the base terminal of the insulated gate bipolar transistor is used to receive an external control signal to control the insulated gate bipolar transistor to be turned on or off.

8. The soft start control circuit according to claim 7, characterized in that: The base terminal of the insulated gate bipolar transistor is connected to the soft start controller; The soft start controller is also used to control the on and off of each of the insulated gate bipolar transistors in the rectifier bridge.

9. The soft start control circuit according to claim 1, characterized in that: The soft start controller has a remote communication port; The soft start controller is used to connect to a remote host computer through the remote communication port to establish a communication connection with the host computer.

10. The soft start control circuit according to claim 3, characterized in that: The soft start controller is also used to issue a docking prompt message when the bus voltage reaches the bus voltage threshold and the first current limiting circuit, the second current limiting circuit and the third current limiting circuit are in a disconnected state.

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