A potential control method for the midpoint of a DC busbar of an inverter and related components thereof

Abstract

The present invention discloses a potential control method for the midpoint of a DC bus of an inverter and its related components, which relate to the technical field of inverters, obtaining a first voltage of a first DC bus capacitor and a second voltage of a second DC bus capacitor; judging whether the absolute value of the difference between the first voltage and the second voltage is greater than a preset fluctuation threshold; if so, controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold. In this way, the present application utilizes the existing structure of the flying capacitor three-level boost circuit and the software control method to achieve the potential balance of the midpoint of the DC bus of the inverter, the control method is simple, the economy is good, and the output performance of the inverter circuit will not be affected.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to a potential control method for a midpoint of a DC bus of an inverter and related components thereof. Background Art

[0002] Please refer to Figure 1 , Figure 1 The figure is a schematic diagram of the structure of a photovoltaic inverter in the related technology. A photovoltaic inverter is usually composed of a boost circuit, a DC bus capacitor and an inverter circuit connected in sequence. At present, the boost circuit of a photovoltaic inverter with a system voltage of 1500V on the market usually adopts a flying capacitor three-level boost topology, and the inverter circuit usually adopts a three-level topology. In a photovoltaic inverter with a three-level topology, the DC bus midpoint ( Figure 1 The potential fluctuation of the DC bus (point O in the middle) is its inherent disadvantage. As long as the current at the midpoint is not zero, the potential at the midpoint will change. Excessive potential fluctuation at the DC bus midpoint will increase the voltage stress of the switch tube in the inverter circuit, shorten the life of the DC bus capacitor, cause the waveform of the voltage and current output by the inverter circuit to be distorted, and increase the harmonic content.

[0003] In order to suppress the potential fluctuation of the DC bus midpoint, two methods are usually used in the relevant technology: one method is to change the modulation output of the inverter circuit through software control to control the potential balance of the midpoint. This method will be coupled with the control of the inverter current while the software controls the inverter circuit, thereby affecting other control targets such as current harmonics and DC components, reducing the inverter output performance. The other method is to use additional hardware circuits ( Figure 1 The potential of the midpoint can be controlled by using the three points (Bus+, O, and Bus-), but this method will increase the equipment cost and make the control method complicated. Summary of the invention

[0004] The purpose of the present invention is to provide a potential control method for the midpoint of the DC bus of an inverter and its related components, which can realize the potential balance of the midpoint of the DC bus of the inverter by combining the existing structure of the flying capacitor three-level boost circuit with software control, and the control method is simple and economical, and at the same time, the output performance of the inverter circuit will not be affected. The specific scheme is as follows:

[0005] In a first aspect, the present application discloses a potential control method for a midpoint of a DC bus of an inverter, wherein the boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control method for the midpoint of a DC bus of the inverter comprises:

[0006] Acquire a first voltage of the first DC bus capacitor and a second voltage of the second DC bus capacitor;

[0007] Determining whether an absolute value of a difference between the first voltage and the second voltage is greater than a preset fluctuation threshold;

[0008] If so, controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold;

[0009] Among them, the preset stability threshold is not greater than the preset fluctuation threshold, the target voltage is a value between the first voltage and the second voltage; the first end of the first DC bus capacitor is connected to the positive DC bus, the second end is connected to the first end of the second DC bus capacitor, and the second end of the second DC bus capacitor is connected to the negative DC bus.

[0010] Optionally, the first switch tube is a switch tube connected to the DC positive terminal through a reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0011] Controlling a first switch tube and a second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, comprising:

[0012] Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0013] determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0014] superimposing the adjusted duty cycle onto the first duty cycle, and generating a first driving signal for the first switch tube based on the superimposed duty cycle;

[0015] The first switch tube is controlled based on the first drive signal, the second switch tube is controlled based on the second original drive signal, and the step of determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor is returned until the voltage of the flying capacitor is reduced to the target voltage.

[0016] Optionally, the first switch tube is a switch tube connected to the DC positive terminal through a reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0017] Controlling a first switch tube and a second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, comprising:

[0018] Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0019] determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0020] Reducing the second duty cycle by the adjusted duty cycle, and generating a second drive signal for the second switch tube based on the reduced duty cycle;

[0021] The first switch tube is controlled based on the first original drive signal, the second switch tube is controlled based on the second drive signal, and the step of determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor is returned until the voltage of the flying capacitor drops to the target voltage.

[0022] Optionally, the first switch tube is a switch tube connected to the DC positive terminal through a reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0023] Controlling a first switch tube and a second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, comprising:

[0024] Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0025] determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0026] superimposing the adjusted duty cycle onto the first duty cycle, and generating a first driving signal for the first switch tube based on the superimposed duty cycle;

[0027] Reducing the second duty cycle by the adjusted duty cycle, and generating a second drive signal for the second switch tube based on the reduced duty cycle;

[0028] The first switch tube is controlled based on the first drive signal, the second switch tube is controlled based on the second drive signal, and the step of determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor is returned until the voltage of the flying capacitor drops to the target voltage.

[0029] Optionally, determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor includes:

[0030] Acquire the current voltage of the flying capacitor and the target voltage;

[0031] Determine a difference between a current voltage of the flying capacitor and the target voltage;

[0032] The difference is subjected to a proportional-integral operation to obtain the adjustment duty cycle.

[0033] Optionally, the target voltage is an arithmetic mean of the first voltage and the second voltage.

[0034] Optionally, after controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold, the method further includes:

[0035] Acquire a current first voltage of the first DC bus capacitor and a current second voltage of the second DC bus capacitor;

[0036] The target voltage of the flying capacitor is set to a second target voltage, where the second target voltage is greater than or equal to a maximum value of the current first voltage and the current second voltage.

[0037] In a second aspect, the present application discloses a potential control system for a midpoint of a DC bus of an inverter, wherein the boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control system for the midpoint of the DC bus of the inverter comprises:

[0038] An acquisition module, used to acquire a first voltage of the first DC bus capacitor and a second voltage of the second DC bus capacitor;

[0039] A judging module, used to judge whether the absolute value of the difference between the first voltage and the second voltage is greater than a preset fluctuation threshold;

[0040] a control module, configured to control a first switch tube and a second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage if the absolute value of the difference between the first voltage and the second voltage is greater than a preset fluctuation threshold, so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold;

[0041] Among them, the preset stability threshold is not greater than the preset fluctuation threshold, the target voltage is a value between the first voltage and the second voltage; the first end of the first DC bus capacitor is connected to the positive DC bus, the second end is connected to the first end of the second DC bus capacitor, and the second end of the second DC bus capacitor is connected to the negative DC bus.

[0042] In a third aspect, the present application discloses a potential control device for a midpoint of a DC bus of an inverter, wherein the boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control device for a midpoint of a DC bus of the inverter comprises:

[0043] Memory, used to store computer programs;

[0044] A processor is used to execute the computer program to implement the steps of the potential control method of the DC bus midpoint of the inverter as described above.

[0045] In a fourth aspect, the present application discloses an inverter, including a potential control device at the midpoint of the DC bus of the inverter as described above, and also including a boost circuit, a DC bus capacitor and an inverter circuit connected in sequence, wherein the boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control device at the midpoint of the DC bus of the inverter is connected to the boost circuit.

[0046] The present application discloses a potential control method for a midpoint of a DC bus of an inverter and its related components. The inverter determines whether the absolute value of the difference between a first voltage and a second voltage is greater than a preset fluctuation threshold based on a first voltage and a second voltage to determine whether the potential of the midpoint of the DC bus is balanced. If the absolute value of the difference between the first voltage and the second voltage is greater than the preset fluctuation threshold, that is, the potential of the midpoint of the DC bus is unbalanced, the turn-on and turn-off time of the first switch tube and the second switch tube in the flying capacitor three-level boost circuit are controlled to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, so that the absolute value of the difference between the first voltage and the second voltage is less than the preset stability threshold to control the potential balance of the midpoint of the DC bus. As can be seen from the above, the present application utilizes the existing structure of the flying capacitor three-level boost circuit and software control to achieve the potential balance of the midpoint of the DC bus of the inverter. There is no need to add additional hardware circuits, the control method is simple, and the economy is good. At the same time, the power used for regulation depends on the power capacity of the flying capacitor three-level boost circuit. Usually, the power capacity of the flying capacitor three-level boost circuit is large, so the control effect is better than the method of software control of the inverter circuit. Moreover, there is no need for the inverter circuit to perform software midpoint potential balance control, and it will not be coupled with the control of the inverter circuit, so it will not affect the output performance of the inverter circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the prior art and the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0048] Figure 1 It is a structural schematic diagram of a photovoltaic inverter in the related art;

[0049] Figure 2 It is a flow chart of a potential control method of a DC bus midpoint of an inverter disclosed in the present invention;

[0050] Figure 3 A schematic diagram of a flying capacitor three-level boost circuit and a DC bus disclosed in the present invention;

[0051] Figure 4 A schematic diagram of original driving signals of a first switching tube and a second switching tube disclosed in the present invention;

[0052] Figure 5 A schematic diagram of a first driving signal of a first switching tube and a second original driving signal of a second switching tube disclosed in the present invention;

[0053] Figure 6 A schematic diagram of a first original driving signal of a first switching tube and a second driving signal of a second switching tube disclosed in the present invention;

[0054] Figure 7 A schematic diagram of a first driving signal of a first switching tube and a second driving signal of a second switching tube disclosed in the present invention;

[0055] Figure 8 A simulation waveform diagram of a DC bus midpoint potential adjustment function disclosed in the present invention;

[0056] Fig. 9 A schematic diagram of determining and adjusting a duty cycle disclosed in the present invention;

[0057] Fig.10 A schematic diagram of a specific method for adjusting duty cycle control disclosed in the present invention;

[0058] Fig.11 It is a structural schematic diagram of a potential control system of a DC bus midpoint of an inverter disclosed in the present invention;

[0059] Fig.12 The present invention is a structural diagram of an electronic device disclosed in the present invention. DETAILED DESCRIPTION

[0060] The core of the present invention is to provide a potential control method for the midpoint of the DC bus of an inverter and related components thereof, which can achieve the potential balance of the midpoint of the DC bus of the inverter by combining the existing structure of the flying capacitor three-level boost circuit and software control. The control method is simple and economical, and at the same time, it will not affect the output performance of the inverter circuit.

[0061] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] At present, in order to suppress the potential fluctuation of the DC bus midpoint, two methods are usually used in related technologies: one method is to change the modulation output of the inverter circuit through software control to control the potential balance of the midpoint. This method will be coupled with the control of the inverter current while the software controls the inverter circuit, thereby affecting other control targets such as current harmonics and DC components, reducing the inverter output performance. Another method is to use additional hardware circuits ( Figure 1 The potential of the midpoint is controlled by using a DC busbar (between Bus+, O, and Bus-), but this method increases the equipment cost and the control method is complicated. To this end, the present application provides a potential control scheme for the midpoint of the DC bus of an inverter to achieve potential balance at the midpoint of the DC bus of the inverter. The control method is simple and economical, and the output performance of the inverter circuit will not be affected.

[0063] See also Figure 2 As shown, Figure 2 The present invention discloses a flow chart of a method for controlling a potential of a midpoint of a DC bus of an inverter.

[0064] The boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control method of the midpoint of the DC bus of the inverter may include:

[0065] S11, obtaining a first voltage of a first DC bus capacitor and a second voltage of a second DC bus capacitor;

[0066] S12, determining whether the absolute value of the difference between the first voltage and the second voltage is greater than a preset fluctuation threshold, if so, proceeding to S13.

[0067] The inverter is usually composed of a boost circuit, a DC bus capacitor and an inverter circuit connected in sequence. The boost circuit in the inverter is a flying capacitor three-level boost circuit, see Figure 3 As shown, Figure 3The present invention discloses a flying capacitor three-level boost circuit and a DC bus schematic diagram, wherein the flying capacitor three-level boost circuit includes a reactor L, a flying capacitor Cfly, a first DC bus capacitor Cup, a second DC bus capacitor Cdn, a first switch tube Q1, a second switch tube Q2, a diode D1, a diode D2, a diode D3 and a diode D4, wherein the first DC bus capacitor Cup and the second DC bus capacitor Cdn are connected in series and bridged between the DC bus Bus+ and Bus-, the connection point O between the first DC bus capacitor Cup and the second DC bus capacitor Cdn is the midpoint of the DC bus, the first switch tube Q1 is connected to PV+ via the reactor L, and the second switch tube Q2 is connected to PV-.

[0068] In this embodiment, it is considered that the uneven distribution of the voltages of the first DC bus capacitor Cup and the second DC bus capacitor Cdn will lead to an unbalanced potential at the midpoint of the DC bus, thereby affecting the stability and safety of the system. Therefore, in order to detect whether the potential at the midpoint of the DC bus is balanced, the present application needs to first obtain the first voltage of the first DC bus capacitor Cup and the second voltage of the second DC bus capacitor Cdn, and then judge whether the potential at the midpoint of the DC bus is balanced by comparing the magnitude of the voltages at both ends of the first DC bus capacitor Cup and the second DC bus capacitor Cdn. If the absolute value of the difference between the voltages at both ends of the first DC bus capacitor Cup and the second DC bus capacitor Cdn is not greater than the preset fluctuation threshold, it indicates that the potential at the midpoint O of the DC bus is balanced; if the absolute value of the difference between the voltages at both ends of the first DC bus capacitor Cup and the second DC bus capacitor Cdn is greater than the preset fluctuation threshold, it indicates that the potential at the midpoint of the DC bus is unbalanced, and there may be a problem of uneven voltage distribution at both ends of the first DC bus capacitor Cup and the second DC bus capacitor Cdn. In this way, the problem of unbalanced potential at the midpoint of the DC bus can be discovered in time, and preparations can be made for subsequent processing.

[0069] S13, controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold;

[0070] Among them, the preset stability threshold is not greater than the preset fluctuation threshold, and the target voltage is a value between the first voltage and the second voltage; the first end of the first DC bus capacitor is connected to the positive DC bus, and the second end is connected to the first end of the second DC bus capacitor Cdn, and the second end of the second DC bus capacitor Cdn is connected to the negative DC bus.

[0071] In this embodiment, if the voltages across the first DC bus capacitor Cup and the second DC bus capacitor Cdn are unevenly distributed, the absolute value of the difference between the first voltage and the second voltage will be greater than the preset fluctuation threshold. In order to ensure the balance of the potential at the midpoint of the DC bus, to reduce the voltage stress of the switch tube in the inverter circuit and the harmonic content of the voltage and current output by the inverter circuit, and to improve the life of the DC bus capacitor, it is necessary to start the potential balance function at the midpoint of the DC bus.

[0072] When the inverter starts the potential balancing function of the midpoint of the DC bus, the inverter controls the on and off of the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to the target voltage. At this time, the current flowing through the midpoint O of the DC bus will change, so that the difference in voltage between the first DC bus capacitor Cup and the second DC bus capacitor Cdn is reduced. When the absolute value of the difference between the first voltage and the second voltage is less than the preset stability threshold, the potential balancing function of the DC bus midpoint is achieved. Specifically, the on and off time of the first switch tube and the second switch tube can be controlled by increasing the first duty cycle of the first original drive signal of the first switch tube and / or reducing the second duty cycle of the second original drive signal of the second switch tube to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to the target voltage, so that the absolute value of the difference between the first voltage and the second voltage is less than the preset stability threshold. The boost circuit in the inverter is a flying capacitor three-level boost circuit. See Figure 3 If the first switch tube Q1 is a switch tube connected to the DC positive terminal through the reactor, and the second switch tube is a switch tube connected to the DC negative terminal, according to the difference between the first voltage of the first DC bus capacitor Cup and the second voltage of the second DC bus capacitor Cdn, there will be two different charging and discharging processes to achieve the absolute value of the difference between the first voltage and the second voltage being less than the preset stability threshold.

[0073] In the first specific embodiment, if the first voltage Uup of the first DC bus capacitor Cup is greater than the second voltage Udn of the second DC bus capacitor Cdn, and at this time the first voltage Uup is greater than the target voltage Ufly, and the target voltage is greater than the second voltage Udn, that is, when Uup > Ufly > Udn, Uup - Udn > 0. A preset fluctuation threshold ΔU1 > 0 can be set. If Uup - Udn > ΔU1, the potential balance function of the midpoint of the DC bus is started. When the first switch Q1 is turned on and the second switch Q2 is turned off, the current flowing in from the positive DC terminal PV+ sequentially passes through the reactor L and the first switch Q1. Since the first voltage Uup is greater than the target voltage Ufly, the current flows through the diode D3 and then into the midpoint O of the DC bus, charging the second DC bus capacitor Cdn and increasing the second voltage Udn of the second DC bus capacitor Cdn. When the second switch Q2 is turned on and the first switch Q1 is turned off, the current flowing in from the positive DC terminal sequentially passes through the reactor L, the diode D1, the flying capacitor Cfly and the second switch Q2 and then returns to the negative DC terminal PV-, which has no effect on the first voltage of the first DC bus capacitor Cup being greater than the second voltage of the second DC bus capacitor Cdn. By charging the second DC bus capacitor Cdn, the second voltage Udn of the second DC bus capacitor Cdn is increased, thereby realizing the potential balance of the midpoint of the DC bus.

[0074] In the second specific embodiment, if the first voltage Uup of the first DC bus capacitor Cup is less than the second voltage Udn of the second DC bus capacitor Cdn, and at this time the first voltage Uup is less than the target voltage Ufly, and the target voltage is less than the second voltage Udn, that is, when Uup < Ufly < Udn, Uup - Udn < 0. A preset fluctuation threshold ΔU2 < 0 can be set. If Uup - Udn < ΔU2, the potential balance function of the midpoint of the DC bus is started. When the first switch Q1 is turned off and the second switch Q2 is turned on, the current at the midpoint O of the DC bus will discharge through the diode D4, the resistor R and the second switch Q2 and then return to the negative DC terminal PV-, thereby reducing the second voltage of the second DC bus capacitor Cdn, and further realizing the potential balance of the midpoint of the DC bus.

[0075] It should be pointed out that the preset fluctuation threshold is used to identify whether the potential at the midpoint of the DC bus has abnormal fluctuations and changes beyond the normal range, and the preset stability threshold is used to ensure that the potential at the midpoint of the DC bus has restored to a balanced state. Even if the absolute value of the difference between the first voltage and the second voltage is detected again and changes within a certain range of the preset stability threshold, the potential at the midpoint of the DC bus will not be identified as being in an unbalanced state, thereby avoiding the situation where the first voltage and the second voltage are considered unstable under normal fluctuations, thereby ensuring the stability of the inverter operation. And when the target voltage is a value between the first voltage and the second voltage, it is ensured that the inverter can reduce the voltage of the flying capacitor Cfly to the target voltage to change the current flowing through the midpoint O of the DC bus, so that the absolute value of the difference between the first voltage and the second voltage is less than the preset stability threshold, thereby achieving the balancing function of the potential at the midpoint of the DC bus.

[0076] As can be seen from the above, the present application utilizes the existing structure of the flying capacitor three-level boost circuit and software control to achieve the potential balance of the midpoint of the DC bus of the inverter. There is no need to add additional hardware circuits, the control method is simple, and the economy is good. At the same time, the power used for regulation depends on the power capacity of the flying capacitor three-level boost circuit. Usually, the power capacity of the flying capacitor three-level boost circuit is large, so the control effect is better than the method of software control of the inverter circuit. Moreover, there is no need for the inverter circuit to perform software midpoint potential balance control, and it will not be coupled with the control of the inverter circuit, so it will not affect the output performance of the inverter circuit.

[0077] Based on the above embodiments:

[0078] As an optional embodiment, the first switch tube is a switch tube connected to the DC positive terminal through the reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0079] Controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage may include:

[0080] Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0081] determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0082] superimposing the adjusted duty cycle onto the first duty cycle, and generating a first driving signal for the first switch tube based on the superimposed duty cycle;

[0083] The first switch tube is controlled based on the first drive signal, the second switch tube is controlled based on the second original drive signal, and the step of determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor is returned until the voltage of the flying capacitor is reduced to the target voltage.

[0084] In this embodiment, the first duty cycle of the first original driving signal of the first switch tube Q1 and the second duty cycle of the second original driving signal of the second switch tube Q2 refer to Figure 4 As shown, Figure 4 The present invention discloses a schematic diagram of the original drive signal of the first switch tube Q1 and the second switch tube Q2. Because the on and off time of the first switch tube Q1 and the second switch tube Q2 are related to the duty cycle of the drive signals of the two, if the duty cycle of the first original drive signal of the first switch tube Q1 is increased, the on time of the first switch tube Q1 will increase, and the current flowing through the first switch tube Q1 to the flying capacitor Cfly will increase, thereby causing the voltage of the flying capacitor Cfly to decrease; conversely, if the duty cycle of the first original drive signal of the first switch tube Q1 is reduced, the on time of the first switch tube Q1 will decrease, and the current flowing through the first switch tube Q1 to the flying capacitor Cfly will decrease, thereby causing the voltage of the flying capacitor Cfly to increase. See Figure 5 As shown, Figure 5 A schematic diagram of a first drive signal of a first switch tube and a second original drive signal of a second switch tube disclosed in the present invention. For example, an adjustment duty ratio of Δt1 is added to the first duty ratio Duty1 of the first original drive signal PWM1 of the first switch tube Q1, and a first drive signal of the first switch tube Q1 is generated based on the superimposed duty ratio Duty1+Δt1, the first switch tube Q1 is controlled based on the first drive signal, the second switch tube Q2 is controlled based on the second original drive signal, and the step of determining the adjustment duty ratio based on the target voltage and the current voltage of the flying capacitor Cfly is returned until the voltage of the flying capacitor Cfly is reduced to the target voltage.

[0085] As can be seen from the above, this embodiment can increase the duty cycle of the first original driving signal of the first switch tube to increase the conduction time of the first switch tube, so that the current flowing from the first switch tube to the flying capacitor increases, thereby causing the voltage of the flying capacitor to drop to the target voltage, thereby achieving the potential balancing function of the midpoint of the DC bus.

[0086] As an optional embodiment, the first switch tube is a switch tube connected to the DC positive terminal through the reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0087] Controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage may include:

[0088] Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0089] determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0090] Reducing the second duty cycle by the adjusted duty cycle, and generating a second drive signal for the second switch tube based on the reduced duty cycle;

[0091] The first switch tube is controlled based on the first original drive signal, the second switch tube is controlled based on the second drive signal, and the step of determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor is returned until the voltage of the flying capacitor drops to the target voltage.

[0092] In this embodiment, because the on and off time of the first switch tube Q1 and the second switch tube Q2 are related to the duty cycle of the driving signals of the two, if the duty cycle of the second original driving signal of the second switch tube Q2 is reduced, the on time of the second switch tube Q2 will be reduced, and the current flowing through the second switch tube Q2 and the flying capacitor Cfly will be reduced, so that the voltage of the flying capacitor Cfly will decrease; conversely, if the duty cycle of the second original driving signal of the second switch tube Q2 is reduced, the on time of the second switch tube Q2 will be increased, and the current flowing through the second switch tube Q2 and the flying capacitor Cfly will increase, so that the voltage of the flying capacitor Cfly will increase. See Figure 6 As shown, Figure 6 A schematic diagram of a first original drive signal of a first switch tube and a second drive signal of a second switch tube disclosed in the present invention. For example, the duty cycle Δt2 is reduced based on the second duty cycle Duty2 of the second original drive signal PWM2 of the second switch tube Q2, and the second drive signal of the second switch tube Q2 is generated based on the reduced duty cycle Duty2-Δt2, the first switch tube Q1 is controlled based on the first original drive signal, the second switch tube Q2 is controlled based on the second drive signal, and the step of determining the duty cycle based on the target voltage and the current voltage of the flying capacitor Cfly is returned until the voltage of the flying capacitor Cfly is reduced to the target voltage.

[0093] As can be seen from the above, this embodiment can reduce the duty cycle of the second original driving signal of the second switch tube to reduce the conduction time of the second switch tube, so that the current flowing through the second switch tube and the flying capacitor is reduced, thereby reducing the voltage of the flying capacitor to the target voltage, thereby achieving the potential balancing function of the midpoint of the DC bus.

[0094] As an optional embodiment, the first switch tube is a switch tube connected to the DC positive terminal through the reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0095] Controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage may include:

[0096] Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0097] determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0098] superimposing the adjusted duty cycle onto the first duty cycle, and generating a first driving signal for the first switch tube based on the superimposed duty cycle;

[0099] Reducing the second duty cycle by the adjusted duty cycle, and generating a second drive signal for the second switch tube based on the reduced duty cycle;

[0100] The first switch tube is controlled based on the first drive signal, the second switch tube is controlled based on the second drive signal, and the step of determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor is returned until the voltage of the flying capacitor drops to the target voltage.

[0101] In this embodiment. Figure 7 As shown, Figure 7The present invention discloses a schematic diagram of a first drive signal of a first switch tube and a second drive signal of a second switch tube. For example, an adjustment duty ratio of Δt1 is added to the first duty ratio Duty1 of the first original drive signal PWM1 of the first switch tube, and the first drive signal of the first switch tube is generated based on the superimposed duty ratio Duty1+Δt1; the adjustment duty ratio Δt2 is reduced based on the second duty ratio Duty2 of the second original drive signal PWM2 of the second switch tube, and the second drive signal of the second switch tube is generated based on the reduced duty ratio Duty2-Δt2. The first switch tube is controlled based on the first drive signal, the second switch tube is controlled based on the second drive signal, and the step of determining the adjustment duty ratio based on the target voltage and the current voltage of the flying capacitor Cfly is returned until the voltage of the flying capacitor Cfly is reduced to the target voltage.

[0102] For further information, see Figure 8 As shown, Figure 8 A simulation waveform diagram of a DC bus midpoint potential adjustment function disclosed in the present invention, after the potential balance of the DC bus midpoint is enabled, as the voltage of the flying capacitor Cfly is gradually controlled to the target voltage, the first voltage of the first DC bus capacitor Cup and the second voltage of the second DC bus capacitor Cdn gradually approach each other, when the difference between the first voltage of the first DC bus capacitor Cup and the second voltage of the second DC bus capacitor Cdn is less than 3V, the second target voltage of the flying capacitor Cfly is set to be greater than or equal to the maximum value of the current first voltage and the current second voltage, and the potential balance function of the DC bus midpoint is turned off.

[0103] As can be seen from the above, this embodiment can increase the duty cycle of the first original driving signal of the first switch tube to increase the conduction time of the first switch tube and reduce the duty cycle of the second original driving signal of the second switch tube to reduce the conduction time of the second switch tube, so that the current flowing from the first switch tube to the flying capacitor increases while the current flowing through the second switch tube and the flying capacitor decreases, thereby accelerating the speed at which the voltage of the flying capacitor drops to the target voltage and improving the stability of the system.

[0104] As an optional embodiment, determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor may include:

[0105] Acquire the current voltage of the flying capacitor and the target voltage;

[0106] Determine a difference between a current voltage of the flying capacitor and the target voltage;

[0107] The difference is subjected to a proportional-integral operation to obtain the adjustment duty cycle.

[0108] In this embodiment, in order to reduce the voltage of the flying capacitor Cfly to the target voltage, the adjustment duty cycle may be added to the first duty cycle and / or the adjustment duty cycle may be subtracted from the second duty cycle. The adjustment duty cycle needs to be determined first. Fig. 9 As shown, Fig. 9 This is a schematic diagram of determining an adjustable duty cycle disclosed in the present invention. Specifically, the current voltage and target voltage of the flying capacitor Cfly are obtained, and the current voltage and target voltage of the flying capacitor Cfly are used as sampling feedback values, and the difference between the current voltage of the flying capacitor Cfly and the target voltage is used as the input of the proportional-integral regulator. After proportional-integral calculation and limiting processing, the adjustable duty cycle Δt is output. Prevent the driving signal from being too large, causing the duty cycle of the driving signal to exceed a reasonable range, thereby affecting the normal operation of the inverter or even damaging the equipment. Then add the adjustable duty cycle Δt to the first duty cycle Duty1, and subtract the adjustable duty cycle Δt from the second duty cycle Duty2, and generate a corresponding driving signal with the adjusted duty cycle, see Fig.10 As shown, Fig.10 It is a schematic diagram of a specific method for adjusting duty cycle control disclosed in the present invention.

[0109] As can be seen from the above, this embodiment performs proportional integral operation on the difference between the current voltage of the flying capacitor and the target voltage to obtain the adjusted duty cycle. The integral link can perform error trimming to reduce the steady-state error, and can quickly respond to changes in input deviation, thereby improving the overall performance of the system.

[0110] As an optional embodiment, the target voltage is an arithmetic average of the first voltage and the second voltage.

[0111] In this embodiment, in order to speed up the charging and discharging of the midpoint of the DC bus so that the potential of the midpoint of the DC bus reaches a balance, the arithmetic mean of the first voltage and the second voltage can be set as the target voltage of the flying capacitor Cfly, and the voltage of the flying capacitor Cfly in the flying capacitor three-level boost circuit can be reduced to the arithmetic mean of the first voltage and the second voltage by controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit, so that the absolute value of the difference between the first voltage and the second voltage can be made less than a preset stability threshold more quickly.

[0112] As an optional embodiment, after controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold, the method may further include:

[0113] Acquire a current first voltage of the first DC bus capacitor and a current second voltage of the second DC bus capacitor;

[0114] The target voltage of the flying capacitor is set to a second target voltage, where the second target voltage is greater than or equal to a maximum value of the current first voltage and the current second voltage.

[0115] In this embodiment, considering that when the bus midpoint potential balancing function is turned on, current will flow through the diode D3 and the diode D4, and the diode D3 and the diode D4 will have a certain voltage drop when forward conducting, causing power loss, so when the absolute value of the difference between the first voltage and the second voltage is less than the preset stability threshold, the bus midpoint potential balancing function needs to be turned off. Specifically, the maximum value of the current first voltage of the first DC bus capacitor Cup and the current second voltage of the second DC bus capacitor Cdn is set to the second target voltage. At this time, the second target voltage is greater than the current first voltage and greater than the current second voltage. The DC bus midpoint O will no longer be charged or discharged through the flying capacitor Cfly, and the potential of the DC bus midpoint O reaches a balanced state, and the potential balancing function of the DC bus midpoint is turned off.

[0116] As can be seen from the above, in this embodiment, after the potential at the DC bus midpoint O reaches a balanced state, the balancing function of the potential at the DC bus midpoint is turned off, thereby reducing energy waste and having good economy.

[0117] Accordingly, see Fig.11 As shown, Fig.11 The present invention is a schematic diagram of a potential control system for a midpoint of a DC bus of an inverter disclosed in the present invention. The present invention also provides a potential control system for a midpoint of a DC bus of an inverter, wherein the boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control system for a midpoint of a DC bus of the inverter includes:

[0118] An acquisition module 11 is used to acquire a first voltage of a first DC bus capacitor Cup and a second voltage of a second DC bus capacitor Cdn;

[0119] A judging module 12, configured to judge whether an absolute value of a difference between the first voltage and the second voltage is greater than a preset fluctuation threshold;

[0120] A control module 13 is configured to control the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage if the absolute value of the difference between the first voltage and the second voltage is greater than a preset fluctuation threshold, so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold;

[0121] Among them, the preset stability threshold is not greater than the preset fluctuation threshold, the target voltage is a value between the first voltage and the second voltage; the first end of the first DC bus capacitor is connected to the positive DC bus, the second end is connected to the first end of the second DC bus capacitor, and the second end of the second DC bus capacitor is connected to the negative DC bus.

[0122] As can be seen from the above, the present application utilizes the existing structure of the flying capacitor three-level boost circuit and software control to achieve the potential balance of the midpoint of the DC bus of the inverter. There is no need to add additional hardware circuits, the control method is simple, and the economy is good. At the same time, the power used for regulation depends on the power capacity of the flying capacitor three-level boost circuit. Usually, the power capacity of the flying capacitor three-level boost circuit is large, so the control effect is better than the method of software control of the inverter circuit. Moreover, there is no need for the inverter circuit to perform software midpoint potential balance control, and it will not be coupled with the control of the inverter circuit, so it will not affect the output performance of the inverter circuit.

[0123] In some specific implementations, the first switch tube is a switch tube connected to the DC positive terminal through a reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0124] The control module 13 includes:

[0125] A first determining unit, configured to determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0126] a second determining unit, configured to determine an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0127] a first generating unit, configured to superimpose the adjusted duty cycle onto the first duty cycle, and generate a first driving signal for the first switch tube based on the superimposed duty cycle;

[0128] A first control unit is used to control the first switch tube based on the first drive signal, control the second switch tube based on the second original drive signal, and return to the step of determining the duty cycle adjustment based on the target voltage and the current voltage of the flying capacitor until the voltage of the flying capacitor is reduced to the target voltage.

[0129] In some specific implementations, the first switch tube is a switch tube connected to the DC positive terminal through a reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0130] The control module 13 includes:

[0131] A third determining unit, configured to determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0132] a fourth determining unit, configured to determine an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0133] a second generating unit, configured to reduce the second duty cycle by the adjusted duty cycle, and generate a second driving signal for the second switch tube based on the reduced duty cycle;

[0134] A second control unit is used to control the first switch tube based on the first original drive signal, control the second switch tube based on the second drive signal, and return to the step of determining the duty cycle adjustment based on the target voltage and the current voltage of the flying capacitor until the voltage of the flying capacitor is reduced to the target voltage.

[0135] In some specific implementations, the first switch tube is a switch tube connected to the DC positive terminal through a reactor, and the second switch tube is a switch tube connected to the DC negative terminal;

[0136] The control module 13 includes:

[0137] a fifth determining unit, configured to determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube;

[0138] a sixth determining unit, configured to determine an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor;

[0139] a third generating unit, configured to superimpose the adjusted duty cycle onto the first duty cycle, and generate a first driving signal for the first switch tube based on the superimposed duty cycle;

[0140] a fourth generating unit, configured to reduce the second duty cycle by the adjusted duty cycle, and generate a second driving signal for the second switch tube based on the reduced duty cycle;

[0141] A third control unit is used to control the first switch tube based on the first drive signal, control the second switch tube based on the second drive signal, and return to the step of determining the duty cycle adjustment based on the target voltage and the current voltage of the flying capacitor until the voltage of the flying capacitor drops to the target voltage.

[0142] In some specific implementations, the second determining unit, the fourth determining unit, and the sixth determining unit all include:

[0143] An acquisition unit, used for acquiring the current voltage of the flying capacitor and the target voltage;

[0144] a difference determination unit, configured to determine a difference between a current voltage of the flying capacitor and the target voltage;

[0145] The operation unit is used to perform proportional integral operation on the difference to obtain the adjustment duty cycle.

[0146] In some specific implementations, the target voltage is an arithmetic average of the first voltage and the second voltage.

[0147] In some specific implementations, the potential control system of the DC bus midpoint of the inverter further includes:

[0148] A voltage acquisition unit, used to acquire a current first voltage of the first DC bus capacitor and a current second voltage of the second DC bus capacitor;

[0149] A setting unit is configured to set the target voltage of the flying capacitor to a second target voltage, where the second target voltage is greater than or equal to a maximum value between the current first voltage and the current second voltage.

[0150] Furthermore, the present application also discloses an electronic device. Fig.12 This is a structural diagram of an electronic device disclosed in the present invention, and the content in the diagram cannot be regarded as any limitation on the scope of use of this application. The electronic device 20 may specifically include: at least one processor 21, at least one memory 22, a power supply 23, a communication interface 24, an input / output interface 25, and a communication bus 26. The memory 22 is used to store a computer program, which is loaded and executed by the processor 21 to implement the relevant steps in the DC voltage control of the inverter disclosed in any of the aforementioned embodiments. In addition, the electronic device 20 in this embodiment may specifically be an electronic computer.

[0151] In this embodiment, the power supply 23 is used to provide working voltage for each hardware device on the electronic device 20; the communication interface 24 can create a data transmission channel between the electronic device 20 and the external device, and the communication protocol it follows is any communication protocol that can be applied to the technical solution of the present application, and is not specifically limited here; the input and output interface 25 is used to obtain external input data or output data to the outside world, and its specific interface type can be selected according to specific application needs and is not specifically limited here.

[0152] In addition, the memory 22 as a carrier for storing resources may be a read-only memory, a random access memory, a disk or an optical disk, etc. The resources stored thereon may include an operating system 221, a computer program 222, etc., and the storage method may be temporary storage or permanent storage.

[0153] The operating system 221 is used to manage and control the hardware devices and computer program 222 on the electronic device 20, and can be Windows Server, Netware, Unix, Linux, etc. In addition to the computer program that can be used to complete the DC voltage control of the inverter performed by the electronic device 20 disclosed in any of the aforementioned embodiments, the computer program 222 can further include computer programs that can be used to complete other specific tasks.

[0154] It should be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0155] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0156] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the potential of a DC bus midpoint of an inverter, characterized in that: The boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control method of the midpoint of the DC bus of the inverter includes: Acquire a first voltage of the first DC bus capacitor and a second voltage of the second DC bus capacitor; Determining whether an absolute value of a difference between the first voltage and the second voltage is greater than a preset fluctuation threshold; If so, controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold; The preset stability threshold is not greater than the preset fluctuation threshold, and the target voltage is a value between the first voltage and the second voltage; a first end of the first DC bus capacitor is connected to the positive DC bus, and a second end of the first DC bus capacitor is connected to the first end of the second DC bus capacitor, and a second end of the second DC bus capacitor is connected to the negative DC bus; The first switch tube is a switch tube connected to the DC positive terminal through the reactor, and the second switch tube is a switch tube connected to the DC negative terminal; Controlling a first switch tube and a second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage, comprising: Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube; determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor; superimposing the adjusted duty cycle onto the first duty cycle, and generating a first driving signal for the first switch tube based on the superimposed duty cycle; Controlling the first switch tube based on the first drive signal, controlling the second switch tube based on the second original drive signal, and returning to the step of determining and adjusting the duty cycle based on the target voltage and the current voltage of the flying capacitor until the voltage of the flying capacitor decreases to the target voltage; Alternatively, controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage includes: Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube; determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor; Reducing the second duty cycle by the adjusted duty cycle, and generating a second drive signal for the second switch tube based on the reduced duty cycle; Controlling the first switch tube based on the first original drive signal, controlling the second switch tube based on the second drive signal, and returning to the step of determining and adjusting the duty cycle based on the target voltage and the current voltage of the flying capacitor until the voltage of the flying capacitor decreases to the target voltage; Alternatively, controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage includes: Determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube; determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor; superimposing the adjusted duty cycle onto the first duty cycle, and generating a first driving signal for the first switch tube based on the superimposed duty cycle; Reducing the second duty cycle by the adjusted duty cycle, and generating a second drive signal for the second switch tube based on the reduced duty cycle; The first switch tube is controlled based on the first drive signal, the second switch tube is controlled based on the second drive signal, and the step of determining the adjustment duty cycle based on the target voltage and the current voltage of the flying capacitor is returned until the voltage of the flying capacitor drops to the target voltage.

2. The method for controlling the potential of the DC bus midpoint of the inverter according to claim 1, characterized in that: Determining an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor includes: Acquire the current voltage of the flying capacitor and the target voltage; Determine a difference between a current voltage of the flying capacitor and the target voltage; The difference is subjected to a proportional-integral operation to obtain the adjustment duty cycle.

3. The method for controlling the potential of the DC bus midpoint of the inverter according to claim 1, characterized in that: The target voltage is an arithmetic average of the first voltage and the second voltage.

4. The method for controlling the potential of the DC bus midpoint of the inverter according to claim 1, characterized in that: After controlling the first switch tube and the second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold, the method further includes: Acquire a current first voltage of the first DC bus capacitor and a current second voltage of the second DC bus capacitor; The target voltage of the flying capacitor is set to a second target voltage, where the second target voltage is greater than or equal to a maximum value of the current first voltage and the current second voltage.

5. A potential control system for the midpoint of a DC bus of an inverter, characterized in that: The boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control system of the midpoint of the DC bus of the inverter includes: An acquisition module, used to acquire a first voltage of the first DC bus capacitor and a second voltage of the second DC bus capacitor; A judging module, used to judge whether the absolute value of the difference between the first voltage and the second voltage is greater than a preset fluctuation threshold; a control module, configured to control a first switch tube and a second switch tube in the flying capacitor three-level boost circuit to reduce the voltage of the flying capacitor in the flying capacitor three-level boost circuit to a target voltage if the absolute value of the difference between the first voltage and the second voltage is greater than a preset fluctuation threshold, so that the absolute value of the difference between the first voltage and the second voltage is less than a preset stability threshold; The preset stability threshold is not greater than the preset fluctuation threshold, and the target voltage is a value between the first voltage and the second voltage; a first end of the first DC bus capacitor is connected to the positive DC bus, and a second end of the first DC bus capacitor is connected to the first end of the second DC bus capacitor, and a second end of the second DC bus capacitor is connected to the negative DC bus; The first switch tube is a switch tube connected to the DC positive terminal through the reactor, and the second switch tube is a switch tube connected to the DC negative terminal; The control module includes: A first determining unit, configured to determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube; a second determining unit, configured to determine an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor; a first generating unit, configured to superimpose the adjusted duty cycle onto the first duty cycle, and generate a first driving signal for the first switch tube based on the superimposed duty cycle; a first control unit, configured to control the first switch tube based on the first drive signal, control the second switch tube based on the second original drive signal, and return to the step of determining the duty cycle adjustment based on the target voltage and the current voltage of the flying capacitor until the voltage of the flying capacitor decreases to the target voltage; Alternatively, the control module comprises: A third determining unit, configured to determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube; a fourth determining unit, configured to determine an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor; a second generating unit, configured to reduce the second duty cycle by the adjusted duty cycle, and generate a second driving signal for the second switch tube based on the reduced duty cycle; a second control unit, configured to control the first switch tube based on the first original drive signal, control the second switch tube based on the second drive signal, and return to the step of determining the duty cycle adjustment based on the target voltage and the current voltage of the flying capacitor until the voltage of the flying capacitor decreases to the target voltage; Alternatively, the control module comprises: a fifth determining unit, configured to determine a first duty cycle of a first original driving signal of the first switching tube and a second duty cycle of a second original driving signal of the second switching tube; a sixth determining unit, configured to determine an adjustment duty cycle based on the target voltage and a current voltage of the flying capacitor; a third generating unit, configured to superimpose the adjusted duty cycle onto the first duty cycle, and generate a first driving signal for the first switch tube based on the superimposed duty cycle; a fourth generating unit, configured to reduce the second duty cycle by the adjusted duty cycle, and generate a second driving signal for the second switch tube based on the reduced duty cycle; A third control unit is used to control the first switch tube based on the first drive signal, control the second switch tube based on the second drive signal, and return to the step of determining the duty cycle adjustment based on the target voltage and the current voltage of the flying capacitor until the voltage of the flying capacitor drops to the target voltage.

6. A potential control device for the midpoint of a DC bus of an inverter, characterized in that: The boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control device of the midpoint of the DC bus of the inverter includes: Memory, used to store computer programs; A processor is used to execute the computer program to implement the steps of the method for controlling the potential of the midpoint of the DC bus of the inverter according to any one of claims 1 to 4.

7. An inverter, characterized in that: The invention comprises a potential control device for the midpoint of the DC bus of the inverter as claimed in claim 6, and further comprises a boost circuit, a DC bus capacitor and an inverter circuit connected in sequence, wherein the boost circuit in the inverter is a flying capacitor three-level boost circuit, and the potential control device for the midpoint of the DC bus of the inverter is connected to the boost circuit.

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