Method for controlling a multi-level inverter circuit and grid-connected inverter

Abstract

The application discloses a control method of a multi-level inverter circuit and a grid-connected inverter. The multi-level inverter circuit can include a plurality of controllable switching tubes, three-phase bridge arm voltages formed on the plurality of switching tubes are mutually 120 degrees out of phase, and the control method can include detecting that a modulation ratio of a modulation signal decreases to less than or equal to a preset threshold, injecting a triple-frequency component into the modulation signal to change turn-on and turn-off time of different switching tubes in the plurality of switching tubes, so that a switching tube with large loss is reduced in on-time or reduced in switching times in one signal period of the modulation signal, a switching tube with small loss is increased in on-time or increased in switching times in one switching period, and the three-phase bridge arm voltages respectively contain the triple-frequency component. According to the embodiment of the application, the loss distribution of the switching tubes in the multi-level inverter circuit can be changed, the loss of each switching tube can be balanced, and the cost can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronics and new energy power supply, and particularly relates to a control method of a multi-level inverter circuit and a grid-connected inverter. BACKGROUND

[0002] Low voltage ride through (LVRT) refers to, when a voltage drop of a grid-connected point of a photovoltaic power station is caused by an accident or a disturbance of a power system, the photovoltaic power station can ensure not to be disconnected from the grid within a certain voltage drop range and time interval, to avoid the expansion of the power grid fault, and meanwhile the photovoltaic grid-connected inverter needs to be able to output certain active power and reactive power to support the recovery of the power grid, so as to pass through the low voltage time (region). During the power grid fault, the voltage difference between the internal bus voltage of the grid-connected converter and the grid voltage will increase, the modulation ratio during the low voltage ride through is reduced, which leads to the increase of the converter loss and the high transient temperature rise, which will affect the reliability of the converter. SUMMARY

[0003] Embodiments of the present application provide a control method of a multi-level inverter circuit and a grid-connected inverter. Embodiments of the present application can adjust the loss distribution of multiple switching tubes in the multi-level inverter circuit, can balance the losses of the switching tubes, and reduce the cost.

[0004] In a first aspect, embodiments of the present application provide a control method of a multi-level inverter circuit. The control method can control a multi-level inverter circuit for converting direct current and alternating current between a direct current source and an alternating current grid through a modulation signal. The multi-level inverter circuit can include multiple switching tubes, and three-phase bridge arm voltages formed on the multiple switching tubes are mutually 120 degrees out of phase. The modulation signal is used to control the turn-on and turn-off control of the multiple switching tubes respectively. The control method can include, when the modulation ratio of the modulation signal is detected to be reduced to less than or equal to a preset threshold, injecting a triple-frequency component into the modulation signal to change the turn-on and turn-off time of different switching tubes in the multiple switching tubes, so that a switching tube with a first loss has reduced turn-on time or reduced switching times in one signal period of the modulation signal, and a switching tube with a second loss has increased turn-on time or increased switching times in one switching period, and the three-phase bridge arm voltages respectively contain the triple-frequency component; and the first loss is greater than the second loss.

[0005] The control method of the multi-level inverter circuit provided by the embodiments of the present application can make the multi-level inverter circuit inject a triple-frequency component into the modulation signal during low voltage ride through, and then control the multiple switching tubes in the multi-level inverter circuit. In this way, the loss distribution of the multiple switching tubes in the multi-level inverter circuit can be adjusted, the losses of the switching tubes can be balanced, the cost can be reduced, and the reliability of the grid-connected inverter can be ensured.

[0006] In one possible implementation, the multiple switching transistors may include a first switching transistor, a second switching transistor, a third switching transistor, and a fourth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and a second switching transistor. The second switching transistor is electrically connected between the first and third switching transistors. The fourth switching transistor is electrically connected between the third switching transistor and a second terminal of the DC source. The node between the first and second switching transistors is electrically connected to the cathode of a first diode. The anode of the first diode is electrically connected to the cathode of the second diode. The anode of the second diode is electrically connected to the node between the third and fourth switching transistors. The control method may further include injecting a third harmonic component into the modulation signal to reduce the on-time or switching frequency of the second and third switching transistors within one signal cycle of the modulation signal, and to increase the on-time or switching frequency of the first and fourth switching transistors within one switching cycle. This approach can adjust the loss distribution of the multiple switching transistors in the multi-level inverter circuit, balance the losses of each switching transistor, reduce costs, and ensure the reliability of the grid-connected inverter.

[0007] In one possible implementation, the multiple switches may include a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch. The first switch is electrically connected between a first terminal of the DC source and a second switch; the second switch is electrically connected between the first and third switches; the fourth switch is electrically connected between the third switch and a second terminal of the DC source; the fifth switch is electrically connected between the node between the first and second switches and the sixth switch; and the sixth switch is electrically connected between the node between the third and fourth switches and the fifth switch. The control method may further include injecting a third harmonic component into the modulation signal to reduce the on-time or switching frequency of the second, third, fifth, and sixth switches within one signal cycle of the modulation signal, and to increase the on-time or switching frequency of the first and fourth switches within one switching cycle. This approach can adjust the loss distribution of the multiple switches in the multi-level inverter circuit, balance the losses of each switch, reduce costs, and ensure the reliability of the grid-connected inverter.

[0008] In one possible implementation, the multiple switching transistors may include a first switching transistor, a second switching transistor, a third switching transistor, and a fourth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and the fourth switching transistor; the fourth switching transistor is electrically connected between the first switching transistor and a second terminal of the DC source; the second switching transistor is electrically connected between the node between the first and fourth switching transistors and the third switching transistor; the third switching transistor is electrically connected between the capacitor module and the second switching transistor; and the capacitor module is electrically connected between the first and second terminals of the DC source. The control method may further include injecting a third harmonic component into the modulation signal to reduce the on-time or switching frequency of the second and third switching transistors within one signal cycle of the modulation signal, and to increase the on-time or switching frequency of the first and fourth switching transistors within one switching cycle. This approach can adjust the loss distribution of multiple switching transistors in the multi-level inverter circuit, balance the losses of each switching transistor, reduce costs, and ensure the reliability of the grid-connected inverter.

[0009] In one possible implementation, the control method may further include: acquiring the electrical parameters of the AC power grid, calculating the common-mode injection quantity based on the AC power grid electrical parameters, controlling the magnitude of the common-mode injection quantity, and outputting a third harmonic component. The third harmonic component is injected into a modulation signal, and the modulation signal with the injected third harmonic component is used to control the multi-level inverter circuit. Based on this design, after obtaining the modulation signal with the injected third harmonic component, this modulation signal is used to control multiple switching transistors in the multi-level inverter circuit. This can balance the losses of each switching transistor and avoid transient temperature rise that reduces the reliability of the grid-connected inverter.

[0010] In one possible implementation, the modulation signal includes an A-phase modulation signal, a B-phase modulation signal, and a C-phase modulation signal;

[0011] The formula for calculating the common mode injection amount is:

[0012]

[0013] Where, ucmv is the calculated common-mode injection quantity, k1 is the amplitude parameter, k2 is the positive-sequence voltage coefficient of the AC power grid, k3 is the negative-sequence voltage coefficient of the AC power grid, and V p V is the positive sequence voltage value of the AC power grid. n This refers to the negative sequence voltage value of the AC power grid. The voltage frequency of the AC power grid is [missing information]. The common-mode injection quantity ucmv and the A-phase modulation signal U aThe phase difference. The required common-mode injection amount can be calculated using the above formula. After limiting the common-mode injection amount, a third harmonic component is obtained. By injecting the third harmonic component into the modulation signal, the turn-on and turn-off times of different switches among the multiple switches can be changed, thereby balancing the losses of each switch and ensuring the stability of the grid-connected inverter.

[0014] In one possible implementation, controlling the magnitude of the common-mode injection and outputting the third harmonic component includes: if the amplitude of the common-mode injection is greater than a first threshold, then the third harmonic component is equal to the first threshold; if the amplitude of the common-mode injection is less than a second threshold, then the third harmonic component is equal to the second threshold; and if the amplitude of the common-mode injection is greater than the second threshold and less than the first threshold, then the third harmonic component is equal to the common-mode injection. The third harmonic component finally injected into the modulation signal can be obtained through the above calculation formula. This design can balance the losses of each switch and ensure the stability of the grid-connected inverter.

[0015] In one possible implementation, the modulation signal includes an A-phase modulation signal U. a B-phase modulation signal U b and C-phase modulation signal U c The formula for calculating the first threshold is: uup = 1 – max (U a U b U c Where uup is the first threshold, max (U a U b U c ) is the A-phase modulation signal U a The B-phase modulation signal U b and the C-phase modulation signal U c The largest of the components. The third harmonic component can be obtained using the above calculation formula. This design can balance the losses of each switch and ensure the stability of the grid-connected inverter.

[0016] In one possible implementation, the modulation signal includes an A-phase modulation signal U. a B-phase modulation signal U b and C-phase modulation signal U c The formula for calculating the second threshold is: udn = -1 – min (U a U b U c Where udn is the second threshold, min (U a U b U c) is the A-phase modulation signal U a The B-phase modulation signal U b and the C-phase modulation signal U c The smallest of the components. The third harmonic component injected into the modulation signal can be obtained through the above calculation formula. This design can balance the losses of each switch and ensure the stability of the grid-connected inverter.

[0017] Secondly, embodiments of this application also provide a grid-connected inverter. The converter system includes a controller and multiple switching transistors. The controller can control the multiple switching transistors, which are connected between a DC source and an AC grid for DC-AC conversion, via a modulation signal. Three-phase bridge arm voltages with a 120-degree phase shift are formed on the multiple switching transistors. The controller can also, when detecting that the modulation ratio of the modulation signal decreases to less than or equal to a preset threshold, inject a third harmonic component into the modulation signal to change the turn-on and turn-off times of different switching transistors. This causes the switching transistors with first losses to have a reduced on-time or fewer switching cycles within one signal cycle of the modulation signal, while the switching transistors with second losses have an increased on-time or more switching cycles within one switching cycle. The three-phase bridge arm voltages each contain the third harmonic component, where the first loss is greater than the second loss. The grid-connected inverter provided in this application embodiment enables the multilevel inverter circuit to inject a third harmonic component into the modulation signal during low voltage ride-through, thereby controlling multiple switching transistors in the multilevel inverter circuit. This allows for adjustment of the loss distribution of multiple switching transistors in the multilevel inverter circuit, balancing the losses of each switching transistor, reducing costs, and ensuring the reliability of the grid-connected inverter.

[0018] In one possible implementation, the multiple switches may include a first switch, a second switch, a third switch, and a fourth switch. The first switch is electrically connected between a first terminal of the DC source and a second switch. The second switch is electrically connected between the first and third switches. The fourth switch is electrically connected between the third switch and a second terminal of the DC source. The node between the first and second switches is electrically connected to the cathode of a first diode. The anode of the first diode is electrically connected to the cathode of the second diode. The anode of the second diode is electrically connected to the node between the third and fourth switches. The controller can also be used to: reduce the on-time or switching frequency of the second and third switches within one signal cycle of the modulation signal by injecting a third harmonic component into the modulation signal, and increase the on-time or switching frequency of the first and fourth switches within one switching cycle. This approach can adjust the loss distribution of multiple switches in the multi-level inverter circuit, balance the losses of each switch, reduce costs, and ensure the reliability of the grid-connected inverter.

[0019] In one possible implementation, the multiple switches may include a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch. The first switch is electrically connected between a first terminal of the DC source and a second switch; the second switch is electrically connected between the first and third switches; the fourth switch is electrically connected between the third switch and a second terminal of the DC source; the fifth switch is electrically connected between the node between the first and second switches and the sixth switch; and the sixth switch is electrically connected between the node between the third and fourth switches and the fifth switch. The controller can also be used to: reduce the on-time or switching frequency of the second, third, fifth, and sixth switches within one signal cycle of the modulation signal by injecting a third harmonic component into the modulation signal, and increase the on-time or switching frequency of the first and fourth switches within one switching cycle. This approach can adjust the loss distribution of multiple switches in the multi-level inverter circuit, balance the losses of each switch, reduce costs, and ensure the reliability of the grid-connected inverter.

[0020] In one possible implementation, the multiple switching transistors may include a first switching transistor, a second switching transistor, a third switching transistor, and a fourth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and the fourth switching transistor; the fourth switching transistor is electrically connected between the first switching transistor and a second terminal of the DC source; the second switching transistor is electrically connected between the node between the first and fourth switching transistors and the third switching transistor; the third switching transistor is electrically connected between the capacitor module and the second switching transistor; and the capacitor module is electrically connected between the first and second terminals of the DC source. The controller can also be used to: reduce the on-time or switching frequency of the second and third switching transistors within one signal cycle of the modulation signal by injecting a third harmonic component into the modulation signal, and increase the on-time or switching frequency of the first and fourth switching transistors within one switching cycle. This approach can adjust the loss distribution of multiple switching transistors in the multi-level inverter circuit, balance the losses of each switching transistor, reduce costs, and ensure the reliability of the grid-connected inverter.

[0021] In one possible implementation, the controller can also be used to: acquire the electrical parameters of the AC grid, calculate the common-mode injection quantity based on the AC grid's electrical parameters, control the magnitude of the common-mode injection quantity, and output a third harmonic component. The third harmonic component is injected into a modulation signal, and this modulation signal with the injected third harmonic component is used to control multiple switching transistors. Based on this design, after obtaining the modulation signal with the injected third harmonic component, this modulation signal is used to control multiple switching transistors in the multi-level inverter circuit. This can balance the losses of each switching transistor and avoid transient temperature rise that reduces the reliability of the grid-connected inverter.

[0022] In one possible implementation, the modulation signal includes an A-phase modulation signal, a B-phase modulation signal, and a C-phase modulation signal;

[0023] The formula for calculating the common mode injection amount is:

[0024]

[0025] Where, ucmv is the calculated common-mode injection quantity, k1 is the amplitude parameter, k2 is the positive-sequence voltage coefficient of the AC power grid, k3 is the negative-sequence voltage coefficient of the AC power grid, and V p V is the positive sequence voltage value of the AC power grid. n This refers to the negative sequence voltage value of the AC power grid. The voltage frequency of the AC power grid is [missing information]. The common-mode injection quantity ucmv and the A-phase modulation signal U a The phase difference. The required common-mode injection amount can be calculated using the above formula. After limiting the common-mode injection amount, a third harmonic component is obtained. By injecting the third harmonic component into the modulation signal, the turn-on and turn-off times of different switches among the multiple switches can be changed, thereby balancing the losses of each switch and ensuring the stability of the grid-connected inverter.

[0026] In one possible implementation, controlling the magnitude of the common-mode injection and outputting the third harmonic component includes: if the amplitude of the common-mode injection is greater than a first threshold, then the third harmonic component is equal to the first threshold; if the amplitude of the common-mode injection is less than a second threshold, then the third harmonic component is equal to the second threshold; and if the amplitude of the common-mode injection is greater than the second threshold and less than the first threshold, then the third harmonic component is equal to the common-mode injection. The third harmonic component finally injected into the modulation signal can be obtained through the above calculation formula. This design can balance the losses of each switch and ensure the stability of the grid-connected inverter.

[0027] In one possible implementation, the modulation signal includes an A-phase modulation signal U. a B-phase modulation signal U b and C-phase modulation signal U c The formula for calculating the first threshold is: uup = 1 – max (U a U b U c Where uup is the first threshold, max (U a U b U c ) is the A-phase modulation signal U a The B-phase modulation signal Ub and the C-phase modulation signal U c The largest of the components. The third harmonic component can be obtained using the above calculation formula. This design can balance the losses of each switch and ensure the stability of the grid-connected inverter.

[0028] In one possible implementation, the modulation signal includes an A-phase modulation signal U. a B-phase modulation signal U b and C-phase modulation signal U c The formula for calculating the second threshold is: udn = -1 – min (U a U b U c Where udn is the second threshold, min (U a U b U c ) is the A-phase modulation signal U a The B-phase modulation signal U b and the C-phase modulation signal U c The smallest of the components. The third harmonic component injected into the modulation signal can be obtained through the above calculation formula. This design can balance the losses of each switch and ensure the stability of the grid-connected inverter.

[0029] The control method and grid-connected inverter circuit provided in this application embodiment can inject a third harmonic component into the modulation signal during low voltage ride-through, thereby controlling multiple switching transistors in the multilevel inverter circuit. This can adjust the loss distribution of multiple switching transistors in the multilevel inverter circuit, balance the losses of each switching transistor, reduce costs, and ensure the reliability of the grid-connected inverter. Attached Figure Description

[0030] Figure 1 This is an application environment diagram of the grid-connected inverter according to an embodiment of this application.

[0031] Figure 2 This is a schematic diagram of the switching network structure according to an embodiment of this application.

[0032] Figure 3 This is another schematic diagram of the switching network in an embodiment of this application.

[0033] Figure 4 This is another schematic diagram of the switching network in an embodiment of this application.

[0034] Figure 5 This is another schematic diagram of the switching network in an embodiment of this application.

[0035] Figure 6 This is a schematic diagram of the modulation drive of a switch in a switching network.

[0036] Figure 7 This is a schematic diagram of the drive modulation of the A-phase switch module.

[0037] Figure 8 This is a flowchart of a control method for a multilevel inverter circuit according to an embodiment of this application.

[0038] Figure 9 This is another flowchart illustrating the control method of the multilevel inverter circuit according to an embodiment of this application.

[0039] Figure 10 The waveform of the three-phase modulated wave after injecting a third harmonic component in the embodiment of this application.

[0040] Figure 11 This is a schematic diagram of the drive modulation of the A-phase switch module after injecting a third harmonic component in an embodiment of this application.

[0041] Figure 12 This is a schematic diagram of switching losses according to one embodiment of this application.

[0042] Figure 13 This is a schematic diagram of switching losses in another embodiment of this application.

[0043] Figure 14 This is a schematic diagram of the controller structure according to an embodiment of this application.

[0044] Figure 15 This is another schematic diagram of the controller according to an embodiment of this application.

[0045] Figure 16 This is a structural diagram of the grid-connected inverter according to an embodiment of this application. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0047] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have a component that is centrally located. When a component is considered to be "set" on another component, it can be directly set on the other component or may also have a component that is centrally located.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0049] This application provides a control method for a multi-level inverter circuit. During low-voltage ride-through (i.e., when the modulation ratio of the modulation signal decreases to less than or equal to a preset threshold), a third harmonic component is injected into the modulation signal to alter the turn-on and turn-off times of different switching transistors among a plurality of switching transistors. For example, the modulation signal can reduce the on-time or switching frequency of high-loss switching transistors within one signal cycle of the modulation signal, while increasing the on-time or switching frequency of low-loss switching transistors within one switching cycle. This adjusts the loss distribution of the switching transistors in the multi-level inverter circuit, thereby balancing the losses of each switching transistor, widening the inverter's operating range, and reducing hardware costs. Embodiments of this application can also provide corresponding grid-connected inverters. Detailed descriptions are provided below using specific embodiments.

[0050] The control method for the multi-level inverter circuit in this application can be applied to power electronic converters. The power grid supplying the multi-level inverter circuit can be, but is not limited to, a three-phase power grid. Three-phase power grids are currently the main power supply method used in power systems, and this application's embodiments can be applied to power systems such as three-phase power grids. For ease of description, this application's embodiments use a three-phase power grid as an example for detailed explanation, but this does not constitute a limitation of this application.

[0051] like Figure 1 As shown, in one embodiment of this application, a multilevel inverter circuit 200 is connected between a DC source 100 and an AC power grid 300. The multilevel inverter circuit 200 includes a switching network 210, a filter 220 connected to the switching network 210, and a controller 230 connected to the switching network 210. The controller 230 can also be connected to the AC power grid 300 to obtain the electrical parameters of the AC power grid 300.

[0052] It is understood that the DC source 100 can be any power source that provides DC current, including batteries and solar photovoltaic panels. In some scenarios, the filter 220 described above can be a three-phase filter.

[0053] The input terminal of the switch network 210 is connected to the output terminal of the DC source 100, and is used to convert the DC power from the DC source 100 into a multi-level AC output. For example, the switch network 210 can convert the DC power from the DC source 100 into a three-level AC output. The filter 220 is used to convert the multi-level AC output of the switch network 210 into AC power with a sine wave or a cosine wave for transmission to the AC power grid 300.

[0054] The multilevel inverter circuit 200 may include multiple controllable switching transistors, and the controller 230 can control the on and off states of the switches in the multilevel inverter circuit 200. For example, the controller 230 can control the multiple switching transistors that perform DC-AC conversion between the DC source 100 and the AC power grid 300 using a modulation signal. The controller 230 can acquire the electrical parameters required for control, such as output voltage and output current.

[0055] Please refer to the following: Figure 2 , Figure 2 A schematic diagram of a switch network 210 provided for one embodiment of this application.

[0056] In this embodiment, the switch network 210 may include multiple controllable switches.

[0057] The switch network 210 can adopt a diode-clamped three-level topology. Specifically, the switch network 210 may include an A-phase switch module 212 and a capacitor module 218.

[0058] The capacitor module 218 may include capacitor C1 and capacitor C2. The first terminal of capacitor C1 is electrically connected to the DC output terminal Vbus+, the second terminal of capacitor C1 is electrically connected to the first terminal of capacitor C2, and the second terminal of capacitor C2 is electrically connected to the DC output terminal Vbus-.

[0059] The A-phase switch module 212 may include multiple controllable switching transistors. Specifically, the A-phase switch module 212 may include switching transistors Q11, Q12, Q13, Q14, diode D1, and diode D2.

[0060] The first terminal of the switching transistor Q11 can be connected to the controller 230, the second terminal of the switching transistor Q11 can be electrically connected to the DC output terminal Vbus+, and the third terminal of the switching transistor Q11 can be electrically connected to the cathode of the diode D1. It can be understood that the first terminal of the switching transistor Q11 can serve as the control terminal of the switching transistor Q11. The controller 230 can output a signal to the first terminal of the switching transistor Q11 to control the state of the switching transistor Q1. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q11 to control the switching transistor Q1 to be turned on or off.

[0061] The first terminal of the switching transistor Q12 can be connected to the controller 230. The second terminal of the switching transistor Q12 can be electrically connected to the third terminal of the switching transistor Q11 and the cathode of the diode D1. The third terminal of the switching transistor Q12 can be electrically connected to the second terminal of the switching transistor Q13. It can be understood that the first terminal of the switching transistor Q12 can serve as the control terminal of the switching transistor Q12. The controller 230 can output a signal to the first terminal of the switching transistor Q12 to control the state of the switching transistor Q12. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q12 to control the switching transistor Q12 to be turned on or off.

[0062] The first terminal of the switching transistor Q13 can be connected to the controller 230, the second terminal of the switching transistor Q13 can be electrically connected to the third terminal of the switching transistor Q12, and the third terminal of the switching transistor Q13 can be electrically connected to the anode of the diode D2. It can be understood that the first terminal of the switching transistor Q13 can serve as the control terminal of the switching transistor Q13, and the controller 230 can output a signal to the first terminal of the switching transistor Q13 to control the state of the switching transistor Q13. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q13 to control the switching transistor Q13 to be turned on or off.

[0063] The first terminal of the switching transistor Q14 can be connected to the controller 230. The second terminal of the switching transistor Q14 can be electrically connected to the third terminal of the switching transistor Q13 and the anode of the diode D2. The third terminal of the switching transistor Q14 can be electrically connected to the DC output terminal Vbus-. It can be understood that the first terminal of the switching transistor Q14 can serve as the control terminal of the switching transistor Q14. The controller 230 can output a signal to the first terminal of the switching transistor Q14 to control the state of the switching transistor Q14. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q14 to control the switching transistor Q14 to be turned on or off.

[0064] It is understood that in this embodiment, the anode of diode D1 is electrically connected to the cathode of diode D2. The node between the anode of diode D1 and the cathode of diode D2 can be electrically connected to node N between the second terminal of capacitor C1 and the first terminal of capacitor C2.

[0065] In this embodiment, the node between the third terminal of switch Q12 and the second terminal of switch Q13 can output the first phase voltage U. u Give filter 220.

[0066] Understandable. Figure 2 The switch network 210 only shows the A-phase switch module. In other scenarios, the switch network 210 may also include a B-phase switch module and a C-phase switch module. The B-phase switch module and the C-phase switch module have the same structure as the A-phase switch module 212.

[0067] It is understood that the switching transistors Q11, Q12, Q13, and Q14 can all be any one of metal-oxide-semiconductor field-effect transistors, insulated-gate bipolar transistors, thyristors, bipolar power transistors, or wide-bandgap semiconductor field-effect transistors.

[0068] Please refer to the following: Figure 3 , Figure 3 A schematic diagram of a switch network 210 provided for another embodiment of this application.

[0069] and Figure 2 The difference between the switch network 210 shown in the embodiment is that, in this embodiment, as... Figure 3 As shown, the switch network 210 can adopt an active clamp three-level topology.

[0070] Compared to Figure 2 In this embodiment, the A-phase switch module 212 may further include switch Q15 and switch Q16.

[0071] like Figure 3 As shown, the first terminal of switch Q15 can be connected to the controller 230. The second terminal of switch Q15 can be electrically connected to the third terminals of switch Q11 and switch Q12. The third terminal of switch Q15 can be electrically connected to the second terminal of switch Q16 and node N between capacitor C1 and capacitor C2. The first terminal of switch Q15 can serve as the control terminal of switch Q15. The controller 230 can output a signal to the first terminal of switch Q15 to control the state of switch Q15. For example, the controller 230 can output a signal to the first terminal of switch Q15 to control switch Q15 to be turned on or off.

[0072] The first terminal of switch Q16 can be connected to the controller 230. The third terminal of switch Q16 can be electrically connected to the third terminal of switch Q13 and the second terminal of switch Q14. The second terminal of switch Q16 can be electrically connected to node N between capacitor C1 and capacitor C2. The first terminal of switch Q16 can serve as the control terminal of switch Q16. The controller 230 can output a signal to the first terminal of switch Q16 to control the state of switch Q16. For example, the controller 230 can output a signal to the first terminal of switch Q16 to control switch Q16 to be turned on or off.

[0073] In this embodiment, the node between the third terminal of switch Q12 and the second terminal of switch Q13 can output the first phase voltage U. u Give filter 220.

[0074] Understandable. Figure 3 The switch network 210 only shows the A-phase switch module. In other scenarios, the switch network 210 may also include a B-phase switch module and a C-phase switch module. The B-phase switch module and the C-phase switch module have the same structure as the A-phase switch module 212.

[0075] Please refer to the following: Figure 4 , Figure 4 A schematic diagram of a switch network 210 provided for another embodiment of this application.

[0076] and Figure 2 The difference between the switch network 210 shown in the embodiment is that, in this embodiment, as... Figure 4 As shown, the switch network 210 can adopt a T-type three-level topology.

[0077] Compared to Figure 2 In this embodiment, the A-phase switch module 212 may further include switch transistors Q11, Q12, Q13, and Q14.

[0078] The first terminal of the switch Q11 can be connected to the controller 230, the second terminal of the switch Q11 can be electrically connected to the DC output terminal Vbus+, and the third terminal of the switch Q11 can be electrically connected to the second terminal of the switch Q4. It can be understood that the first terminal of the switch Q11 can serve as the control terminal of the switch Q11, and the controller 230 can output a signal to the first terminal of the switch Q11 to control the state of the switch Q11.

[0079] The first terminal of the switch Q12 can be connected to the controller 230, the second terminal of the switch Q12 can be electrically connected to the second terminal of the switch Q13, and the third terminal of the switch Q12 can be electrically connected to node N between the second terminal of capacitor C1 and the first terminal of capacitor C2. It can be understood that the first terminal of the switch Q12 can serve as the control terminal of the switch Q12, and the controller 230 can output a signal to the first terminal of the switch Q12 to control the state of the switch Q12.

[0080] The first terminal of the switch Q13 can be connected to the controller 230, and the third terminal of the switch Q13 can be electrically connected to the third terminal of the switch Q11 and the second terminal of the switch Q14. It can be understood that the first terminal of the switch Q13 can serve as the control terminal of the switch Q13, and the controller 230 can output a signal to the first terminal of the switch Q13 to control the state of the switch Q13.

[0081] The first terminal of the switching transistor Q14 can be connected to the controller 230, and the third terminal of the switching transistor Q14 can be electrically connected to the DC output terminal Vbus-. It can be understood that the first terminal of the switching transistor Q14 can serve as the control terminal of the switching transistor Q14, and the controller 230 can output a signal to the first terminal of the switching transistor Q14 to control the state of the switching transistor Q14.

[0082] In this embodiment, the node between the third terminal of switch Q11 and the second terminal of switch Q14 can output the first phase voltage U. u Give filter 220.

[0083] Figure 4 The switch network 210 only shows the A-phase switch module. In other scenarios, the switch network 210 may also include a B-phase switch module and a C-phase switch module. The B-phase switch module and the C-phase switch module have the same structure as the A-phase switch module 212.

[0084] Please refer to the following: Figure 5 , Figure 5 A schematic diagram of a switch network 210 provided for another embodiment of this application.

[0085] and Figure 2 The difference between the switch network 210 shown in the embodiment is that, in this embodiment, the switch network 210 may also include a B-phase switch module 214 and a C-phase switch module 216.

[0086] The B-phase switch module 214 may include switch transistors Q21, Q22, Q23, and Q24, diode D3, and diode D4.

[0087] The first terminal of the switching transistor Q21 can be connected to the controller 230, the second terminal of the switching transistor Q21 can be electrically connected to the DC output terminal Vbus+, and the third terminal of the switching transistor Q21 can be electrically connected to the cathode of the diode D3. It can be understood that the first terminal of the switching transistor Q21 can serve as the control terminal of the switching transistor Q21. The controller 230 can output a signal to the first terminal of the switching transistor Q21 to control the state of the switching transistor Q21. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q21 to control the switch Q21 to be turned on or off.

[0088] The first terminal of the switching transistor Q22 can be connected to the controller 230. The second terminal of the switching transistor Q22 can be electrically connected to the third terminal of the switching transistor Q21 and the cathode of the diode D3. The third terminal of the switching transistor Q22 can be electrically connected to the second terminal of the switching transistor Q23. It can be understood that the first terminal of the switching transistor Q22 can serve as the control terminal of the switching transistor Q22. The controller 230 can output a signal to the first terminal of the switching transistor Q22 to control the state of the switching transistor Q22. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q22 to control the switching transistor Q22 to be turned on or off.

[0089] The first terminal of the switch Q23 can be connected to the controller 230, the second terminal of the switch Q23 can be electrically connected to the third terminal of the switch Q22, and the third terminal of the switch Q23 can be electrically connected to the anode of the diode D4. It can be understood that the first terminal of the switch Q23 can serve as the control terminal of the switch Q23, and the controller 230 can output a signal to the first terminal of the switch Q23 to control the state of the switch Q23. For example, the controller 230 can output a signal to the first terminal of the switch Q23 to control the switch Q23 to be turned on or off.

[0090] The first terminal of the switching transistor Q24 can be connected to the controller 230. The second terminal of the switching transistor Q24 can be electrically connected to the third terminal of the switching transistor Q23 and the anode of the diode D4. The third terminal of the switching transistor Q24 can be electrically connected to the DC output terminal Vbus-. It can be understood that the first terminal of the switching transistor Q24 can serve as the control terminal of the switching transistor Q24. The controller 230 can output a signal to the first terminal of the switching transistor Q24 to control the state of the switching transistor Q24. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q24 to control the switching transistor Q24 to be turned on or off.

[0091] The node between the anode of diode D3 and the cathode of diode D4 can be electrically connected to the node between the second terminal of capacitor C1 and the first terminal of capacitor C2.

[0092] In this embodiment, the node between the third terminal of switch Q22 and the second terminal of switch Q23 can output the second phase voltage U. v Give filter 220.

[0093] It is understood that the switching transistors Q21, Q22, Q23, and Q24 can all be any one of metal-oxide-semiconductor field-effect transistors, insulated-gate bipolar transistors, thyristors, bipolar power transistors, or wide-bandgap semiconductor field-effect transistors.

[0094] The C-phase switch module 216 may include switch transistors Q31, Q32, Q33, and Q34, diode D5, and diode D6.

[0095] The first terminal of the switching transistor Q31 can be connected to the controller 230, the second terminal of the switching transistor Q31 can be electrically connected to the DC output terminal Vbus+, and the third terminal of the switching transistor Q31 can be electrically connected to the cathode of the diode D5. It can be understood that the first terminal of the switching transistor Q31 can serve as the control terminal of the switching transistor Q31. The controller 230 can output a signal to the first terminal of the switching transistor Q31 to control the state of the switching transistor Q31. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q31 to control the switching transistor Q31 to be turned on or off.

[0096] The first terminal of the switching transistor Q32 can be connected to the controller 230. The second terminal of the switching transistor Q32 can be electrically connected to the third terminal of the switching transistor Q31 and the cathode of the diode D5. The third terminal of the switching transistor Q32 can be electrically connected to the second terminal of the switching transistor Q33. It can be understood that the first terminal of the switching transistor Q32 can serve as its control terminal. The controller 230 can output a signal to the first terminal of the switching transistor Q32 to control the state of the switching transistor Q32. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q32 to control the switching transistor Q32 to be turned on or off.

[0097] The first terminal of the switch Q33 can be connected to the controller 230, the second terminal of the switch Q33 can be electrically connected to the third terminal of the switch Q32, and the third terminal of the switch Q33 can be electrically connected to the anode of the diode D6. It can be understood that the first terminal of the switch Q33 can serve as the control terminal of the switch Q33, and the controller 230 can output a signal to the first terminal of the switch Q33 to control the state of the switch Q33. For example, the controller 230 can output a signal to the first terminal of the switch Q33 to control the switch Q33 to be turned on or off.

[0098] The first terminal of the switching transistor Q34 can be connected to the controller 230. The second terminal of the switching transistor Q34 can be electrically connected to the third terminal of the switching transistor Q33 and the anode of the diode D6. The third terminal of the switching transistor Q34 can be electrically connected to the DC output terminal Vbus-. It can be understood that the first terminal of the switching transistor Q34 can serve as its control terminal. The controller 230 can output a signal to the first terminal of the switching transistor Q34 to control its state. For example, the controller 230 can output a signal to the first terminal of the switching transistor Q34 to control the switching transistor Q34 to be turned on or off.

[0099] The node P4 between the anode of diode D5 and the cathode of diode D6 can be electrically connected to the node between the second terminal of capacitor C1 and the first terminal of capacitor C2.

[0100] In this embodiment, the node between the third terminal of the switching transistor Q32 and the second terminal of the switching transistor Q33 can output a third-phase voltage U. w Give filter 220.

[0101] It is understood that three-phase bridge arm voltages with a 120-degree phase shift are formed on the multiple switching transistors in the multi-level inverter circuit 200. The three-phase bridge arm voltages include the first phase voltage U. u Second phase voltage U v Third phase voltage U w For example, the first phase voltage U u With the second phase voltage U v They are 120 degrees out of phase. The first phase voltage U... u With the third phase voltage U w They are 120 degrees out of phase. The second phase voltage U v With the third phase voltage U w They are 120 degrees apart.

[0102] It is understood that the controller 230 can output drive signals to the A-phase switch module, the B-phase switch module, and the C-phase switch module.

[0103] It is understood that the switching transistors Q31, Q32, Q33, and Q34 can all be any one of metal-oxide-semiconductor field-effect transistors, insulated-gate bipolar transistors, thyristors, bipolar power transistors, or wide-bandgap semiconductor field-effect transistors.

[0104] Please see Figure 6 This is a schematic diagram of the modulation drive of the multi-level inverter circuit. The modulation unit can modulate the three-phase modulation signal U... a U b U c With triangular carrier U tr The comparison is performed, and a drive signal is output to the A-phase switch module 212, B-phase switch module 214 and C-phase switch module 216 in the multi-level inverter circuit according to the comparison result, so as to control the multiple switching transistors in the multi-level inverter circuit 200.

[0105] The following example illustrates the modulation drive of the A-phase switch module.

[0106] like Figure 7 As shown, when the modulation signal U a When the value is greater than 0, the modulation unit 232 will output a drive signal to control the high-frequency complementary conduction of the switching transistors Q11 and Q13, and control the switching transistor Q12 to remain on while the switching transistor Q14 remains off. When the modulation wave U a Greater than the triangular carrier U tr When the modulation unit 232 controls the switching transistor Q11 to turn on, the modulation wave U... a Smaller than the triangular carrier U tr When this happens, the modulation unit 232 will control the switching transistor Q11 to turn off.

[0107] When the modulation signal U a When the value is less than 0, the modulation unit 232 will output a drive signal, which can control the high-frequency complementary conduction of the switching transistors Q14 and Q12, and control the switching transistor Q13 to remain on while the switching transistor Q11 remains off. When the modulation signal U a Smaller than the triangular carrier U tr When the modulation unit 232 controls the switching transistor Q14 to turn on, the modulation signal U... a Greater than the triangular carrier U tr When this happens, the modulation unit 232 will control the switching transistor Q14 to turn off.

[0108] It is understood that the modulation drive of the B-phase switch module and the C-phase switch module is the same as that of the A-phase switch module, so it will not be described again here.

[0109] The control method for a multi-level inverter circuit provided in this application embodiment can calculate the third harmonic component and inject it into the original three-phase modulation signal U when the multi-level inverter circuit is in a low-voltage ride-through state. a U b U c This allows the modulated signal U after control to be... a U b U c The waveform changes, altering the loss distribution of the switching transistors in the switching network. This, in turn, balances the losses of each switching transistor, broadens the operating range of the grid-connected inverter, and reduces hardware costs.

[0110] Please see Figure 8 , Figure 8 This is a flowchart illustrating a control method for a multilevel inverter circuit according to an embodiment of this application. The control method can be executed by the controller 230. The control method can be used to control a multilevel inverter circuit that performs DC-AC conversion between a DC source and an AC grid using a modulation signal. The multilevel inverter circuit may include multiple switching transistors, and three-phase bridge arm voltages with 120-degree phase shifts can be formed on these transistors. The modulation signal is used to control the on and off states of the multiple switching transistors respectively. The control method for the multilevel inverter circuit may include the following steps:

[0111] Step S81: Obtain the modulation ratio of the modulation signal of the multi-level inverter circuit.

[0112] If applied in a three-phase power grid, the controller 230 can acquire the three-phase modulated wave, i.e., the A-phase modulated wave U. a B-phase modulated wave U b and C-phase modulated wave U c It can be understood that the three-phase modulation wave is the modulation signal used to control the multi-level inverter circuit.

[0113] It can be understood that the three-phase initial modulation signal is the initial modulation signal of each phase of the multi-level inverter circuit, such as the A-phase modulation signal, B-phase modulation signal and C-phase modulation signal mentioned above.

[0114] The modulation ratio of the three-phase initial modulation signal can be obtained by calculating the peak value of the three-phase initial modulation signal and the carrier peak value. The grid-connected inverter can control the voltage and current of the multi-level inverter circuit by adjusting the modulation signal; therefore, the modulation signal is dynamically changing. When the multi-level inverter circuit enters a stable operating state, the modulation signal repeats periodically. At this time, the peak value of the modulation signal can be considered a fixed value, and the modulation ratio of the modulation signal can be accurately obtained.

[0115] Step S82: Detect whether the modulation ratio of the modulated signal has decreased to less than or equal to a preset threshold. If the modulation ratio of the modulated signal is detected to have decreased to less than or equal to the preset threshold, proceed to step S83; otherwise, return to step S81.

[0116] It is understood that after obtaining the modulation ratio of the modulation signal, the controller 230 can compare the modulation ratio of the modulation signal with a preset threshold and determine whether to perform common mode calculation based on the comparison result.

[0117] For example, in one scenario, assuming a preset threshold of 0.8 and a modulation ratio of 0.9 or 1 (meaning the modulation ratio is greater than the preset threshold), the controller 230 will not inject common-mode power. In this case, the switching transistors in the multi-level inverter circuit do not need to undergo loss optimization.

[0118] In another scenario, assuming the preset threshold is 0.8, the modulation ratio of the modulation signal is 0.7 or 0.6, meaning the modulation ratio of the modulation signal is less than the preset threshold. Alternatively, the modulation ratio of the modulation signal is 0.8, meaning the modulation ratio of the modulation signal is equal to the preset threshold. This indicates that the modulation ratio of the modulation signal has decreased to less than or equal to the preset threshold, meaning the multilevel inverter circuit 200 has entered a low-voltage ride-through state. The controller 230 will then perform common-mode calculation, thereby adjusting the losses of multiple switching transistors in the multilevel inverter circuit 200.

[0119] Step S83: By injecting a third harmonic component into the modulation signal, the turn-on and turn-off times of different switching transistors in the multiple switching transistors of the multi-level inverter circuit are changed.

[0120] It is understood that in this embodiment, by injecting a third harmonic component into the modulation signal, the turn-on and turn-off times of different switches among the plurality of switches can be changed. This reduces the on-time or switching frequency of switches with high losses within one signal cycle of the modulation signal, while increasing the on-time or switching frequency of switches with low losses within one switching cycle. Furthermore, the three-phase bridge arm voltages each contain the third harmonic component. This alters the loss distribution of the switches. It is understood that the aforementioned three-phase bridge arm voltages including the third harmonic component can be as follows: Figure 5 The first phase voltage U mentioned in the text u Second phase voltage U v and the third phase voltage U w .

[0121] The following will illustrate the three different three-level topologies of switching networks (diode-clamped three-level topology, active-clamped three-level topology, and T-type three-level topology) with examples.

[0122] exist Figure 5 In the illustrated diode-clamped three-level topology, taking the control of the switching transistors in the A-phase switching module as an example, when the modulation ratio of the modulation signal is less than or equal to a preset threshold (i.e., entering a low-voltage ride-through state), the losses of switching transistors Q11 and Q14 are low, while the losses of switching transistors Q12, Q13, diodes D1 and D2 are high. When the modulation ratio of the modulation signal is detected to decrease to less than or equal to the preset threshold, the controller 230 can change the turn-on and turn-off times of different switching transistors in the A-phase switching module by injecting a third harmonic component into the modulation signal. For example, after injecting the third harmonic component into the modulation signal, the modulation signal can control the high-loss switching transistors Q12 and Q13 to reduce their on-time or switching frequency within one signal cycle of the modulation signal, and can control the low-loss switching transistors Q11 and Q14 to increase their on-time or switching frequency within one switching cycle. By inputting a suitable third harmonic component into the modulation signal, some of the losses in switching transistors Q12, Q13, diode D1, and diode D2 can be transferred to switching transistors Q11 and Q14. This balances the losses of each switching transistor in the A-phase switching module.

[0123] Taking the control of the switching transistors in the B-phase switching module as an example, transistors Q21 and Q24 have low losses, while transistors Q22, Q23, and diodes D3 and D4 have high losses. For example, after injecting a modulation signal with a third harmonic component, the modulation signal can control the high-loss transistors Q22 and Q23 to reduce their on-time or switching frequency within one signal cycle of the modulation signal, and can control the low-loss transistors Q21 and Q24 to increase their on-time or switching frequency within one switching cycle. Thus, by inputting a suitable third harmonic component into the modulation signal, some of the losses in transistors Q22, Q23, and diodes D3 and D4 can be transferred to transistors Q21 and Q24. This balances the losses of the various switching transistors in the B-phase switching module.

[0124] Taking the control of the switching transistors in the C-phase switching module as an example, transistors Q31 and Q34 have low losses, while transistors Q32, Q33, and diodes D5 and D6 have high losses. For example, after injecting a modulation signal with a third harmonic component, the modulation signal can control the high-loss transistors Q32 and Q33 to reduce their on-time or switching frequency within one signal cycle of the modulation signal, and can control the low-loss transistors Q31 and Q34 to increase their on-time or switching frequency within one switching cycle. Thus, by inputting a suitable third harmonic component into the modulation signal, some of the losses in transistors Q32, Q33, and diodes D5 and D6 can be transferred to transistors Q31 and Q34. This balances the losses of the various switching transistors in the C-phase switching module.

[0125] exist Figure 3In the illustrated active clamp three-level topology, taking the control of the switching transistors in the A-phase switching module as an example, when the modulation ratio of the modulation signal is less than or equal to a preset threshold (i.e., entering a low-voltage ride-through state), the losses of switching transistors Q11 and Q14 are low, while the losses of switching transistors Q12, Q13, Q15, and Q16 are high. When the modulation ratio of the modulation signal is detected to decrease to less than or equal to the preset threshold, the controller 230 can change the turn-on and turn-off times of different switching transistors in the A-phase switching module by injecting a third harmonic component into the modulation signal. For example, after injecting the third harmonic component into the modulation signal, the modulation signal can control the high-loss switching transistors Q12, Q13, Q15, and Q16 to reduce their on-time or switching frequency within one signal cycle of the modulation signal, and can control the low-loss switching transistors Q11 and Q14 to increase their on-time or switching frequency within one switching cycle. By inputting a suitable third harmonic component into the modulation signal, some of the losses in switches Q12, Q13, Q15, and Q16 can be transferred to switches Q11 and Q14. This balances the losses of each switch in the A-phase switching module.

[0126] It is understandable that the modulation principles of the B-phase and C-phase switching modules in the above active clamp three-level topology are the same as those of the A-phase switching module, and will not be elaborated here.

[0127] exist Figure 4 In the illustrated T-type three-level topology, taking the control of the switching transistors in the A-phase switching module as an example, when the modulation ratio of the modulation signal is less than or equal to a preset threshold (i.e., entering a low-voltage ride-through state), the losses of switching transistors Q11 and Q14 are low, while the losses of switching transistors Q12 and Q13 are high. When the modulation ratio of the modulation signal is detected to decrease to less than or equal to the preset threshold, the controller 230 can change the turn-on and turn-off times of different switching transistors among the multiple switching transistors in the A-phase switching module by injecting a third harmonic component into the modulation signal. For example, after injecting the third harmonic component into the modulation signal, the modulation signal can control the high-loss switching transistors Q12 and Q13 to reduce their on-time or switching frequency within one signal cycle of the modulation signal, and can control the low-loss switching transistors Q11 and Q14 to increase their on-time or switching frequency within one switching cycle. By inputting a suitable third harmonic component into the modulation signal, some of the losses in switching transistors Q12 and Q13 can be transferred to switching transistors Q11 and Q14. This can balance the losses of each switching transistor in the A-phase switching module.

[0128] It is understood that the modulation principles of the B-phase and C-phase switch modules in the above T-type clamped three-level topology are the same as those of the A-phase switch module, and will not be elaborated here.

[0129] Please see Figure 9 In some embodiments, the step of injecting a third harmonic component into the modulation signal to change the turn-on and turn-off times of different switches among the multiple switches in the multilevel inverter circuit may include the following steps:

[0130] Step S91: Obtain the electrical parameters of the AC power grid and calculate the common mode injection amount based on the electrical parameters of the AC power grid.

[0131] Based on the above Figure 1 Taking the scenario shown as an example, the controller 230 can acquire the electrical parameters of the AC power grid 300. The electrical parameters of the AC power grid 300 may include the positive sequence voltage value V of the AC power grid. p Negative sequence voltage value V n And voltage frequency, etc.

[0132] The controller 230 can calculate the common mode injection quantity ucmv based on the acquired electrical parameters of the AC power grid 300.

[0133] In one possible design, the formula (1) used by the controller 230 to calculate the common-mode injection amount based on the acquired electrical parameters of the AC power grid 300 is:

[0134] (1)

[0135] Where, ucmv is the calculated common-mode injection quantity, k1 is the amplitude parameter, k2 is the positive-sequence voltage coefficient of the AC power grid 300, k3 is the negative-sequence voltage coefficient of the AC power grid 300, and V p The positive sequence voltage value of the AC power grid is 300V, V n This is the negative sequence voltage value of the AC power grid at 300V. The voltage frequency of the AC power grid is 300 MHz. The common-mode injection quantity ucmv and the modulation signal U a The phase difference.

[0136] For example, in some specific application scenarios, K1 can be 1, K2 can be 0.8, and K3 can be 0.8. It can take the value 0. It should be noted that the above statements regarding K1, K2, K3, and... The value of is only one possible example, and this application does not make any specific limitation on it.

[0137] Step S92: Control the magnitude of the common-mode injection amount and output the third harmonic component.

[0138] It is understandable that the calculated common-mode injection quantity ucmv may fluctuate drastically, leading to significant differences in the output voltage of each phase in the multi-level inverter circuit 200. Therefore, to ensure that the calculated common-mode injection quantity ucmv does not fluctuate drastically, it is necessary to limit the calculated common-mode injection quantity ucmv. That is, the embodiments of this application control the magnitude of the calculated common-mode injection quantity ucmv to reduce or even avoid the above-mentioned situation.

[0139] In this embodiment, the common-mode injection quantity ucmv can be limited to output a third harmonic component ucmv_lmt.

[0140] As an example, the third harmonic component ucmv_lmt can be obtained using the following formula (2).

[0141] (2)

[0142] It is understandable that in the above formula (2), ucmv_lmt is the third harmonic component, uup is the first threshold, and udn is the second threshold.

[0143] When the common-mode injection quantity ucmv is greater than the first threshold uup, the third harmonic component ucmv_lmt = uup. When the common-mode injection quantity ucmv is less than the second threshold udn, the third harmonic component ucmv_lmt = udn. When the common-mode injection quantity ucmv is greater than the second threshold udn and less than the first threshold uup, the third harmonic component ucmv_lmt = ucmv.

[0144] As an example, the first threshold uup can be obtained using the following formula (3).

[0145] uup = 1 – max (U a U b U c (3)

[0146] In the above formula (3), max(U) a U b U c ) is the modulation signal U a Modulation signal U b and modulation signal U c The maximum value in. For example, suppose the modulated signal U a The modulated signal U is 0.5. b The modulated signal U is 0.3.c If the value is 0.7, then the first threshold uup is 0.3.

[0147] As an example, the second threshold udn can be obtained using the following formula (4).

[0148] udn = -1 – min (U a U b U c (4)

[0149] In the above formula (4), min(U a U b U c ) is the modulation signal U a Modulation signal U b and modulation signal U c The minimum value in the range. For example, suppose the modulated signal U... a The modulated signal U is 0.5. b The modulated signal U is 0.3. c If the value is 0.7, then the second threshold udn is -1.3.

[0150] As an example, if the modulated signal U a The modulated signal U is 0.5. b The modulated signal U is 0.3. c The common-mode injection quantity ucmv is 0.7, uup is 0.3, and udn is -1.3. If the common-mode injection quantity ucmv is -1.5, and ucmv is less than the second threshold udn, then the third harmonic component ucmv_lmt = udn. Assuming the common-mode injection quantity ucmv is 0.2, and ucmv is greater than the second threshold udn and less than the first threshold uup, then the third harmonic component ucmv_lmt = ucmv. If the common-mode injection quantity ucmv is 0.5, and ucmv is greater than the first threshold uup, then the third harmonic component ucmv_lmt = uup.

[0151] As can be seen from the above example, the controller 230 controls the magnitude of the common-mode injection quantity, that is, it limits the common-mode quantity ucmv and outputs the third harmonic component ucmv_lmt. This ensures that the calculated common-mode injection quantity ucmv will not change drastically.

[0152] Step S93: Inject the third harmonic component into the modulation signal, and use the modulation signal with the injected third harmonic component to control the multi-level inverter circuit.

[0153] In this embodiment, by injecting a third harmonic component into the modulation signal, the turn-on and turn-off times of different switches among the multiple switches in the multi-level inverter circuit are changed, so that the switch with high loss has a reduced conduction time or a reduced number of switching times in one signal cycle of the modulation signal, while the switch with low loss has an increased conduction time or an increased number of switching times in one switching cycle, and the three-phase bridge arm voltages respectively contain the third harmonic component.

[0154] For specific calculations, please refer to the following formula (5).

[0155] (5)

[0156] In formula (5) above, U a U b and U c These are the original A-phase modulation signal, B-phase modulation signal, and C-phase modulation signal, respectively. aout U bout and U cout These are the controlled A-phase modulation signal, B-phase modulation signal, and C-phase modulation signal, respectively.

[0157] like Figure 10 The diagram illustrates the injection of a third harmonic component into the modulation signal. After obtaining the third harmonic component ucmv_lmt, the controller 230 needs to further inject the third harmonic component into the modulation signal, for example, by injecting the initial modulation signal of each phase (modulation signal U) into the modulation signal. a Modulation signal U b and modulation signal U c The waveforms of each of the three harmonic components ucmv_lmt are superimposed one-to-one to obtain the modulation signal U. aout U bout and U cout .

[0158] It is understood that embodiments of this application may use a modulation signal with the injected third harmonic component to perform discontinuous pulse width modulation on the multilevel inverter circuit.

[0159] It is understandable that the A-phase modulation signal U, after being controlled, aout B-phase modulation signal U bout and C-phase modulation signal U cout Subsequently, the controller 230 can also control the A-phase modulation signal U aout B-phase modulation signal U bout and C-phase modulation signal U coutThe driving signal is modulated into the switching network 210 to drive the switching network 210 to output a multi-level signal to the filter 220, that is, the multi-level inverter circuit 200 can output a three-phase bridge arm voltage to the filter 220. The filter 220 can convert the multi-level signal into AC power input to the AC power grid 300.

[0160] In a more specific implementation, such as Figure 11 As shown, the controller 230 can control the A-phase modulation signal U aout After comparison with the carrier signal, a drive signal corresponding to the switching transistor in the A-phase switch module 212 is output, specifically used to modulate the controlled A-phase modulation signal U. aout The signal is modulated into a drive signal in phase A switch module 212 to drive phase A switch module 212 to operate.

[0161] Figure 11 Only the third harmonic component superimposed on the A-phase modulated signal U is shown. a The driving modulation process of the A-phase switch module 212 is taken as an example. It can be understood that the driving modulation process of the B-phase switch module 214 and the C-phase switch module can be the same as that of the A-phase switch module 212.

[0162] For example, the controller 230 can control the B-phase modulation signal U bout After comparison with the carrier signal, a drive signal corresponding to the switching device in the B-phase switch module 214 is output, specifically used to control the B-phase modulation signal U. bout The signal is modulated into a drive signal in the B-phase switch module 214 to drive the B-phase switch module 214 to operate. The controller 230 can control the C-phase modulation signal U. bout After comparison with the carrier signal, a drive signal corresponding to the switching device in the C-phase switch module 216 is output, specifically used to control the C-phase modulation signal U. bout The signal is modulated into a drive signal in the C-phase switch module 216 to drive the C-phase switch module 216 to operate.

[0163] The control method of the multi-level inverter circuit adopted in this application embodiment can change the turn-on and turn-off times of different switches by injecting a third harmonic component into the modulation signal during low voltage ride-through. This reduces the conduction time or switching frequency of the high-loss switch within one signal cycle of the modulation signal, while increasing the conduction time or switching frequency of the low-loss switch within one switching cycle. This balances the losses of each switch, broadens the operating range of the grid-connected inverter, reduces hardware costs, and avoids the problem of reduced reliability of the grid-connected inverter due to transient temperature rise.

[0164] For example, in a scenario such as Figure 12 As shown, during the 5% crossover period, a comparison chart of the losses of the switching transistors Q11, Q12 and diode D1 (or switching transistors Q21, Q22 and diode D3, or switching transistors Q31, Q32 and diode D5) using the embodiments of this application and those not using the embodiments of this application are presented.

[0165] from Figure 12 As can be seen from the above, by adopting the control method of the multi-level inverter circuit in the embodiments of this application, the loss of diode D1 (or diode D3 and diode D5) can be optimized by 83.6W, reducing the loss by about 49%.

[0166] For example, in another scenario, such as Figure 10 As shown, during the 20% crossover period, a comparison chart of the losses of the switching transistors Q11, Q12 and diode D1 (or switching transistors Q21, Q22 and diode D3, or switching transistors Q31, Q32 and diode D5) using the embodiments of this application and those not using the embodiments of this application are presented.

[0167] from Figure 13 As can be seen from the above, by adopting the control method of the multi-level inverter circuit in the embodiments of this application, the loss of diode D1 (or diode D3 and diode D5) can be optimized by 77.5W, reducing the loss by about 43%.

[0168] To facilitate better implementation of the control method for the multi-level inverter circuit provided in this application, this application also provides an apparatus based on the control method for the multi-level inverter circuit described above. The definitions of terms used are the same as in the control method for the multi-level inverter circuit described above, and specific implementation details can be found in the descriptions within the method embodiments.

[0169] Please see Figure 14 , Figure 14 This is a schematic diagram of a controller 230 in an embodiment of this application. The controller 230 can be used to execute... Figure 8 and Figure 9 For details, please refer to some or all of the steps of the control method for the multilevel inverter circuit described in [the document]. Figure 8 and Figure 9 The relevant description in the document.

[0170] The controller 230 may include an acquisition unit 231, a calculation unit 233, a limiting output unit 234, an injection unit 235, and a modulation unit 232, specifically as follows:

[0171] The acquisition unit 231 can also be used to acquire the modulation ratio of the modulation signal.

[0172] The acquisition unit 231 acquires the modulation wave and the electrical parameters of the AC power grid 300.

[0173] The calculation unit 233 is used to inject a third harmonic component into the modulation signal when the modulation ratio of the modulation signal is reduced to less than or equal to a preset threshold, so as to change the turn-on and turn-off times of different switches among the plurality of switches, so that the switch with high loss has a reduced conduction time or a reduced number of switching times in one signal cycle of the modulation signal, while the switch with low loss has an increased conduction time or an increased number of switching times in one switching cycle, and so that the three-phase bridge arm voltages respectively contain the third harmonic component.

[0174] Specifically, the calculation unit 233 is also used to calculate the common mode injection amount based on the electrical parameters of the AC power grid 300.

[0175] The limiting output unit 234 is used to control the magnitude of the common mode injection amount and output the third harmonic component.

[0176] The injection unit 235 is used to inject the third harmonic component into the modulation signal to obtain a modulation signal with the third harmonic component injected. The modulation unit 232 can use the modulation signal with the third harmonic component injected to control the multi-level inverter circuit.

[0177] Specifically, the calculation unit 233 can also calculate the common mode injection amount based on the electrical parameters of the AC power grid when the modulation ratio is less than the modulation ratio threshold.

[0178] In a three-phase power grid, the modulation signals include A-phase modulation signals, B-phase modulation signals, and C-phase modulation signals. The injection unit 235 is used to superimpose the third harmonic component onto the A-phase modulation signals, B-phase modulation signals, and C-phase modulation signals, respectively, to obtain the controlled A-phase modulation signals, B-phase modulation signals, and C-phase modulation signals.

[0179] The limiting output unit 234 is further configured to: if the amplitude of the common-mode injection is greater than a first threshold, then the third harmonic component is equal to the first threshold; if the amplitude of the common-mode injection is less than a second threshold, then the third harmonic component is equal to the second threshold; if the amplitude of the common-mode injection is greater than the second threshold and less than the first threshold, then the third harmonic component is equal to the common-mode injection.

[0180] It should be noted that the specific implementation can be found in the above method embodiments, and will not be repeated here.

[0181] Please see Figure 15The diagram shown is another structural schematic of the controller 230 provided in an embodiment of this application. In one embodiment, the controller 230 includes a memory 101 and at least one processor 102. Those skilled in the art should understand that... Figure 11 The structure of the controller 230 shown does not constitute a limitation of the embodiments of this application. The controller 230 may also include more or fewer other hardware or software than shown, or different component arrangements.

[0182] In some embodiments, the controller 230 includes a terminal capable of automatically performing numerical calculations and / or information processing according to pre-set or stored instructions. Its hardware includes, but is not limited to, microprocessors, application-specific integrated circuits (ASICs), programmable gate arrays (PGAs), digital processors, and embedded devices. In some embodiments, the memory 101 is used to store program code and various data. The memory 101 may include read-only memory (ROM), random access memory (RAM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), one-time programmable read-only memory (OTPROM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, disk storage, magnetic tape storage, or any other computer-readable medium capable of carrying or storing data.

[0183] In some embodiments, the at least one processor 102 may include an integrated circuit, such as a single-packaged integrated circuit or multiple integrated circuits with the same or different functions, including combinations of microprocessors, digital processing chips, graphics processors, and various control chips. The at least one processor 102 is the control unit of the controller, executing various functions of the controller 230 and processing data by running or executing programs or modules stored in the memory 101 and calling data stored in the memory 101. The integrated unit implemented as a software functional module can be stored in a computer-readable storage medium. The software functional module, stored in a storage medium, includes several instructions to cause a computer device (which may be a personal computer, terminal, or network device, etc.) or processor to execute portions of the methods described in the various embodiments of this application. The memory 101 stores program code, and the at least one processor 102 can call the program code stored in the memory 101 to execute related functions. In one embodiment of this application, the memory 101 stores multiple instructions, which are executed by the at least one processor 102 to implement the control method of the multi-level inverter circuit described above. Specifically, the implementation method of the above instructions by the at least one processor 102 can be referred to Figure 8 and Figure 9 The descriptions of the relevant steps in the corresponding embodiments are not repeated here.

[0184] Please refer to the following: Figure 16 , Figure 16 This is a schematic diagram of the grid-connected inverter 400 in the embodiments of this application.

[0185] It is understood that the grid-connected inverter 400 in this embodiment may include a controller 230 and a multi-level inverter circuit 200. The controller 230 can acquire the electrical parameters of the AC grid, calculate the common-mode injection amount based on the electrical parameters of the AC grid, control the magnitude of the common-mode injection amount to obtain the controlled third harmonic component, and inject the third harmonic component into the modulation signal.

[0186] The controller 230 may include an acquisition unit 231, a calculation unit 233, a limiting output unit 234, an injection unit 235, and a modulation unit 232.

[0187] The acquisition unit 231 acquires the modulation signal and the electrical parameters of the AC power grid 300. The calculation unit 233 calculates the common-mode injection amount based on the electrical parameters of the AC power grid 300 when the modulation ratio of the modulation signal is less than or equal to a preset threshold. The limiting output unit 234 controls the magnitude of the common-mode injection amount and outputs a third harmonic component. The injection unit 235 injects the third harmonic component into the modulation signal to obtain a modulation signal with the third harmonic component injected. The modulation unit 232 can use the modulation signal with the third harmonic component injected to control the multi-level inverter circuit.

[0188] It is understood that the specific implementation of the controller 230 can be found in the above embodiments, and will not be repeated here.

[0189] This application also provides a storage medium. The storage medium stores computer instructions, which, when executed on a controller, enable the controller to perform the control method for the multi-level inverter circuit provided in the foregoing embodiments.

[0190] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and modifications made to the above embodiments within the essential spirit and scope of this application shall fall within the scope of protection claimed in this application.

Claims

1. A control method for a multilevel inverter circuit, used to control a multilevel inverter circuit that performs DC-AC conversion between a DC source and an AC power grid via a modulation signal, characterized in that, The multi-level inverter circuit includes multiple switching transistors, and three-phase bridge arm voltages that are 120 degrees out of phase with each other are formed on the multiple switching transistors. The modulation signal is used to control the conduction and turn-off of the multiple switching transistors respectively. The control method includes: When the modulation ratio of the modulated signal is detected to decrease to less than or equal to a preset threshold; By injecting a third harmonic component into the modulation signal, the turn-on and turn-off times of different switches among the plurality of switches are changed, so that the switch with a first loss has a reduced on-time or a reduced number of switching times in one signal cycle of the modulation signal, while the switch with a second loss has an increased on-time or an increased number of switching times in one switching cycle, and the three-phase bridge arm voltages respectively contain the third harmonic component; wherein the first loss is greater than the second loss.

2. The control method according to claim 1, characterized in that, The plurality of switching transistors includes a first switching transistor, a second switching transistor, a third switching transistor, and a fourth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and the second switching transistor. The second switching transistor is electrically connected between the first switching transistor and the third switching transistor. The fourth switching transistor is electrically connected between the third switching transistor and a second terminal of the DC source. The node between the first switching transistor and the second switching transistor is electrically connected to the cathode of a first diode. The anode of the first diode is electrically connected to the cathode of the second diode. The anode of the second diode is electrically connected to the node between the third switching transistor and the fourth switching transistor. The control method further includes: By injecting the third harmonic component into the modulation signal, the conduction time or switching frequency of the second and third switches is reduced within one signal cycle of the modulation signal, while the conduction time or switching frequency of the first and fourth switches is increased within one switching cycle.

3. The control method according to claim 1, characterized in that, The plurality of switching transistors includes a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a fifth switching transistor, and a sixth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and the second switching transistor. The second switching transistor is electrically connected between the first switching transistor and the third switching transistor. The fourth switching transistor is electrically connected between the third switching transistor and a second terminal of the DC source. The fifth switching transistor is electrically connected between the node between the first and second switching transistors and the sixth switching transistor. The sixth switching transistor is also electrically connected between the node between the third and fourth switching transistors and the fifth switching transistor. The control method further includes: By injecting the third harmonic component into the modulation signal, the conduction time or switching frequency of the second, third, fifth, and sixth switches is reduced within one signal cycle of the modulation signal, while the conduction time or switching frequency of the first and fourth switches is increased within one switching cycle.

4. The control method according to claim 1, characterized in that, The plurality of switching transistors includes a first switching transistor, a second switching transistor, a third switching transistor, and a fourth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and the fourth switching transistor. The fourth switching transistor is electrically connected between the first switching transistor and a second terminal of the DC source. The second switching transistor is electrically connected between the node between the first and fourth switching transistors and the third switching transistor. The third switching transistor is electrically connected between a capacitor module and the second switching transistor. The capacitor module is electrically connected between the first and second terminals of the DC source. The control method further includes: By injecting the third harmonic component into the modulation signal, the conduction time or switching frequency of the second and third switches is reduced within one signal cycle of the modulation signal, while the conduction time or switching frequency of the first and fourth switches is increased within one switching cycle.

5. The control method according to any one of claims 1-4, characterized in that, The control method further includes: Obtain the electrical parameters of the AC power grid; The common-mode injection quantity is calculated based on the electrical parameters of the AC power grid, and the magnitude of the common-mode injection quantity is controlled to output the third harmonic component; The third harmonic component is injected into the modulation signal, and the modulation signal with the injected third harmonic component is used to control the multilevel inverter circuit.

6. The control method according to claim 5, characterized in that, The modulation signal includes an A-phase modulation signal, a B-phase modulation signal, and a C-phase modulation signal; The formula for calculating the common mode injection amount is: Where, ucmv is the calculated common-mode injection quantity, k1 is the amplitude parameter, k2 is the positive-sequence voltage coefficient of the AC power grid, k3 is the negative-sequence voltage coefficient of the AC power grid, and V p V is the positive sequence voltage value of the AC power grid. n This refers to the negative sequence voltage value of the AC power grid. The voltage frequency of the AC power grid is [missing information]. The common-mode injection quantity ucmv and the A-phase modulation signal U a The phase difference.

7. The control method according to claim 5, characterized in that, The step of controlling the common-mode injection amount and outputting the third harmonic component includes: If the amplitude of the common-mode injection is greater than the first threshold, then the third harmonic component is equal to the first threshold. If the amplitude of the common-mode injection is less than the second threshold, then the third harmonic component is equal to the second threshold. If the amplitude of the common-mode injection is greater than the second threshold and less than the first threshold, the third harmonic component is equal to the common-mode injection.

8. The control method according to claim 7, characterized in that, The modulation signal includes phase A modulation signal U. a B-phase modulation signal U b and C-phase modulation signal U c ; The formula for calculating the first threshold is: uup = 1 – max (U a , U b , U c ); Where uup is the first threshold, max (U a U b U c ) is the A-phase modulation signal U a The B-phase modulation signal U b and the C-phase modulation signal U c The largest of them.

9. The control method according to claim 7, characterized in that, The modulation signal includes phase A modulation signal U. a B-phase modulation signal U b and C-phase modulation signal U c ; The formula for calculating the second threshold is: udn = -1 – min (U a , In b , In c ) Where udn is the second threshold, min (U a U b U c ) is the A-phase modulated wave U a The B-phase modulated wave U b and the C-phase modulated wave U c The smallest of them.

10. A grid-connected inverter, characterized in that, Includes the controller and multiple switching transistors; The controller is used to control the plurality of switching transistors that are connected between a DC source and an AC power grid to perform DC and AC conversion through a modulation signal; wherein, a three-phase bridge arm voltage with a 120-degree phase shift is formed on the plurality of switching transistors. The controller is further configured to, when detecting that the modulation ratio of the modulation signal has decreased to less than or equal to a preset threshold; By injecting a third harmonic component into the modulation signal, the turn-on and turn-off times of different switches among the plurality of switches are changed, so that the switch with a first loss has a reduced on-time or a reduced number of switching times in one signal cycle of the modulation signal, while the switch with a second loss has an increased on-time or an increased number of switching times in one switching cycle, and the three-phase bridge arm voltages respectively contain the third harmonic component; wherein the first loss is greater than the second loss.

11. The grid-connected inverter according to claim 10, characterized in that, The plurality of switching transistors includes a first switching transistor, a second switching transistor, a third switching transistor, and a fourth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and the second switching transistor. The second switching transistor is electrically connected between the first switching transistor and the third switching transistor. The fourth switching transistor is electrically connected between the third switching transistor and a second terminal of the DC source. The node between the first switching transistor and the second switching transistor is electrically connected to the cathode of a first diode. The anode of the first diode is electrically connected to the cathode of the second diode. The anode of the second diode is electrically connected to the node between the third switching transistor and the fourth switching transistor. The controller is further configured to: inject the third harmonic component into the modulation signal to reduce the on-time or switching frequency of the second and third switches within one signal cycle of the modulation signal, and to increase the on-time or switching frequency of the first and fourth switches within one switching cycle.

12. The grid-connected inverter according to claim 10, characterized in that, The plurality of switching transistors includes a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a fifth switching transistor, and a sixth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and the second switching transistor. The second switching transistor is electrically connected between the first switching transistor and the third switching transistor. The fourth switching transistor is electrically connected between the third switching transistor and a second terminal of the DC source. The fifth switching transistor is electrically connected between the node between the first switching transistor and the second switching transistor and the sixth switching transistor. The sixth switching transistor is also electrically connected between the node between the third switching transistor and the fourth switching transistor and the fifth switching transistor. The controller is further configured to: inject the third harmonic component into the modulation signal to reduce the on-time or switching frequency of the second, third, fifth, and sixth switches within one signal cycle of the modulation signal, and to increase the on-time or switching frequency of the first and fourth switches within one switching cycle.

13. The grid-connected inverter according to claim 10, characterized in that, The plurality of switching transistors includes a first switching transistor, a second switching transistor, a third switching transistor, and a fourth switching transistor. The first switching transistor is electrically connected between a first terminal of the DC source and the fourth switching transistor. The fourth switching transistor is electrically connected between the first switching transistor and a second terminal of the DC source. The second switching transistor is electrically connected between the node between the first and fourth switching transistors and the third switching transistor. The third switching transistor is electrically connected between the capacitor module and the second switching transistor. The capacitor module is electrically connected between the first and second terminals of the DC source. The controller is further configured to: inject the third harmonic component into the modulation signal to reduce the on-time or switching frequency of the second and third switches within one signal cycle of the modulation signal, and to increase the on-time or switching frequency of the first and fourth switches within one switching cycle.

14. The grid-connected inverter according to any one of claims 10-13, characterized in that, The controller is also used for: Obtain the electrical parameters of the AC power grid; The common-mode injection quantity is calculated based on the electrical parameters of the AC power grid, and the magnitude of the common-mode injection quantity is controlled to output the third harmonic component; The third harmonic component is injected into the modulation signal, and the modulation signal with the injected third harmonic component is used to control the plurality of switching transistors.

15. The grid-connected inverter according to claim 14, characterized in that, The modulation signal includes an A-phase modulation signal, a B-phase modulation signal, and a C-phase modulation signal; The formula used by the controller to calculate the common mode injection amount is: Where, ucmv is the calculated common-mode injection quantity, k1 is the amplitude parameter, k2 is the positive-sequence voltage coefficient of the AC power grid, k3 is the negative-sequence voltage coefficient of the AC power grid, and V p V is the positive sequence voltage value of the AC power grid. n This refers to the negative sequence voltage value of the AC power grid. The voltage frequency of the AC power grid is [missing information]. The common-mode injection quantity ucmv and the A-phase modulation signal U a The phase difference.

16. The grid-connected inverter according to claim 14, characterized in that, If the amplitude of the common-mode injection is greater than the first threshold, then the third harmonic component is equal to the first threshold. If the amplitude of the common-mode injection is less than the second threshold, then the third harmonic component is equal to the second threshold. If the amplitude of the common-mode injection is greater than the second threshold and less than the first threshold, the third harmonic component is equal to the common-mode injection.

17. The grid-connected inverter according to claim 16, characterized in that, The modulation signal includes phase A modulation signal U. a B-phase modulation signal U b and C-phase modulation signal U c ; The formula for calculating the first threshold is: uup = 1 – max (U a , U b , U c ); Where uup is the first threshold, max (U a U b U c ) is the A-phase modulation signal U a The B-phase modulation signal U b and the C-phase modulation signal U c The largest of them.

18. The grid-connected inverter according to claim 16, characterized in that, The modulation signal includes phase A modulation signal U. a B-phase modulation signal U b and C-phase modulation signal U c ; The formula for calculating the second threshold is: udn = -1 – min (U a , In b , In c ) Where udn is the second threshold, min (U a U b U c ) is the A-phase modulation signal U a The B-phase modulation signal U b and the C-phase modulation signal U c The smallest of them.

Images