Low leakage current and low current ripple vector modulation method for coupled three-level inverter

Abstract

This invention provides a low leakage current and low current ripple vector modulation method for coupled three-level inverters. It utilizes a low common-mode voltage vector to fundamentally reduce leakage current. Building upon this reduction, it further considers the common-mode voltage variation frequency to further decrease leakage current. In the low-modulation mode, a zero vector and two small low common-mode vectors are combined; in the high-modulation mode, two large vectors and one medium vector are combined, reducing ripple and minimizing switching losses. Simultaneously, the sequence is selected based on the midpoint potential, and midpoint voltage balance is achieved by switching between two pairs of designed leakage current sequences and two pairs of ripple reduction sequences. This invention effectively suppresses leakage current and reduces ripple while providing a certain degree of midpoint voltage balance, thereby improving the reliability and economy of non-isolated inverters in the photovoltaic field.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-level inverter control, and in particular relates to a low leakage current and low current ripple vector modulation method for coupling a three-level inverter. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, as the capacity of new energy access to the power grid has increased year by year, compared with traditional power generation methods, new energy power generation has been widely used due to its advantages such as cleanliness and pollution-free. Among them, photovoltaic power generation technology is even more widely used. In photovoltaic power generation systems, the cost, efficiency, volume, and output effect of power electronic converters are important considerations. At present, non-isolated grid-connected inverters are widely used in photovoltaic grid-connected systems. They have abandoned the isolation transformer and achieved indicators such as simple structure, small volume, and high efficiency; but this leads to a current connection between the grid grounding point and the photovoltaic array, forming a common mode loop between the earth and the photovoltaic components, thereby generating leakage current. High-frequency leakage current can cause problems such as grid current distortion and electromagnetic interference. According to the German VDE-0126-1-1 standard, the leakage current peak should not be higher than 300mA.

[0004] The non-isolated converter has achieved simple structure, small size, high efficiency and other indicators. On this basis, considering the cost and the leakage current problem caused by the non-isolated converter, the new coupled three-level inverter proposed based on the existing one solves the high-frequency leakage current problem. The traditional three-level topology requires 12 switching elements, while the coupled inverter topology only requires 10, which significantly reduces the cost. However, the coupled three-level inverter still has the problem of midpoint voltage balance. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a low leakage current and low current ripple vector modulation method for coupling a three-level inverter. The present invention can suppress low leakage current and reduce ripple and has a certain midpoint voltage balancing ability, thereby improving the reliability and economy of non-isolated inverters in the photovoltaic field.

[0006] According to some embodiments, the present invention adopts the following technical solutions:

[0007] A low leakage current and low current ripple vector modulation method for coupled three-level inverters comprises the following steps:

[0008] Determine whether a reference voltage vector has a sector;

[0009] Determining a low leakage current or low current ripple sequence according to a low common mode voltage vector in the sector, so that a switching frequency of the common mode voltage is reduced or a current ripple is reduced;

[0010] Determine whether the midpoint voltage of each sub-sector in the sector exceeds the set upper limit. If not, do not perform midpoint voltage balance control and use the nearest optimal vector. If yes, perform midpoint voltage balance control, switch the low leakage current sequence and the low current ripple sequence for the corresponding sub-sector, calculate the action time of each vector, and generate a corresponding control signal.

[0011] As an optional implementation, there are six sectors in total, which are obtained by evenly dividing the sectors according to the space vector diagram of the coupled three-level inverter.

[0012] As an optional implementation, each vector is divided into a large vector, a small vector and a zero vector according to the distance from the vector to the vector OOO. Each sector is divided into a low leakage part close to the vector OOO, a low current ripple part far from the vector OOO and two common parts in the middle according to the locations of the large vector, the small vector and the zero vector.

[0013] As an optional implementation, the low leakage part and different common parts of each sector are combined to form two low leakage current sequences, and the low current ripple part and different common parts are combined to form two low current ripple sequences.

[0014] As an optional implementation, in each sub-sector, a large vector, a small vector, and a zero vector are used to synthesize a reference voltage vector; or a corresponding vector is selected based on the proximity principle to achieve low ripple; or a low leakage current sequence and a low current ripple sequence are shared, and the balance of the midpoint voltage is achieved by switching between the two.

[0015] As an optional implementation, the specific process of switching the corresponding sub-sector between the low leakage current sequence and the low current ripple sequence includes: the low modulation system is switched through the low leakage current sequence, the common part of the high modulation system is switched through the low leakage current sequence and the low current ripple sequence; the independent part of the high modulation system is switched through the low current ripple sequence.

[0016] As an optional implementation, during the switching between the low leakage current sequence and the low current ripple sequence for the corresponding sub-sector, the large vector and the zero vector do not affect the midpoint balance, and the two low leakage current sequences are switched according to the different effects of the small vector on the midpoint voltage balance.

[0017] As an optional implementation, during the switching between the low leakage current sequence and the low current ripple sequence for the corresponding sub-sector, when the midpoint voltage is greater than zero, a P-type small vector is used, and when the midpoint voltage is less than zero, an N-type small vector is used.

[0018] As an optional implementation, the action time of each vector is calculated according to the volt-second balance principle.

[0019] A low leakage current and low current ripple vector modulation system coupled to a three-level inverter, comprising:

[0020] A sector determination module, configured to determine a sector where a reference voltage vector appears;

[0021] A switch sequence selection module, configured to determine a low leakage current or low current ripple sequence in the sector according to a low common mode voltage vector, so as to reduce a switching frequency of the common mode voltage or reduce a current ripple;

[0022] The sub-sector sequence switching module is configured to determine whether the midpoint voltage of each sub-sector in the sector exceeds the set upper limit. If not, midpoint voltage balance control is not performed and the nearest optimal vector is used; if yes, midpoint voltage balance control is performed, and the corresponding sub-sector is switched between a low leakage current sequence and a low current ripple sequence, and the action time of each vector is calculated to generate a corresponding control signal.

[0023] An electronic device comprises a memory and a processor, and computer instructions stored in the memory and executed on the processor. When the computer instructions are executed by the processor, the steps in the above method are completed.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention replaces the traditional three-level inverter with a coupled three-level inverter, and the number of switches is reduced from 12 to 10, which significantly reduces the cost; the low leakage current peak is essentially reduced, not only by applying a low common-mode vector to reduce the common-mode voltage amplitude, but also by adopting a five-segment sequence to reduce the common-mode voltage switching frequency, and the low leakage current peak of the low-mode system is controlled within 150mA, and the low leakage current of the high-mode system is basically within 300mA.

[0026] The present invention realizes the balance of midpoint potential by reasonably selecting the switch sequence. The low modulation system is switched through the low leakage current sequence, the common part of the high modulation system is switched through the low leakage current sequence and the low current ripple sequence; the independent part of the high modulation system is switched through the low current ripple sequence.

[0027] The present invention reasonably designs a switch sequence according to the common mode voltage amplitude of a voltage vector, thereby achieving low common mode voltage and low leakage current, and improving electromagnetic interference and other problems.

[0028] The present invention reduces ripple in the high modulation area, uses only a five-segment sequence, and fixes the switching frequency, thereby reducing switching losses; at the same time, the current ripple THD is reduced compared to the existing coupled three-level inverter modulation method, which is beneficial to reducing the filter volume and cost.

[0029] The present invention proposes for the first time that under certain modulation degrees, there is a situation where the common mode voltage change rate is equal. In this case, the effect of low leakage current is the best, and low leakage current spikes will not appear due to too short switching time.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0032] Figure 1 It is a system diagram of coupled three-level photovoltaic inverter;

[0033] Figure 2 (a) is the space vector diagram of 21 coupled three-level vectors; (b) is the space vector diagram of 13 coupled three-level low common mode vectors;

[0034] Figure 3 is a schematic diagram of each sub-sector of the first sector;

[0035] FIG4( a ) is a schematic diagram of the space vector of low leakage current sequence 1;

[0036] FIG4( b ) is a schematic diagram of the space vector of low leakage current sequence 2;

[0037] Figure 4(c) is a schematic diagram of the space vector of low current ripple sequence 1;

[0038] Figure 4(d) is a schematic diagram of the space vector of low current ripple sequence 2;

[0039] Figure 5 (a) is a schematic diagram of a low leakage current sequence 1 of the first sub-sector, (b) is a schematic diagram of a low leakage current sequence 2 of the second sub-sector, (c) is a schematic diagram of a low current ripple sequence 1 of the third sub-sector, and (d) is a schematic diagram of a low current ripple sequence 2 of the fourth sub-sector;

[0040] Figure 6 (a) is a schematic diagram of midpoint balancing control of the first sub-sector, (b) is a schematic diagram of midpoint balancing control of the second sub-sector, (c) is a schematic diagram of midpoint balancing control of the third sub-sector, and (d) is a schematic diagram of midpoint balancing control of the fourth sub-sector;

[0041] Figure 7 A control flow diagram of a low leakage current and low current ripple modulation method;

[0042] FIG8( a ) is a diagram showing the simulation results of the output line voltage;

[0043] FIG8( b ) is a diagram showing the simulation results of the three-phase output current of the low-profile system;

[0044] FIG8(c) is a diagram showing the simulation results of the three-phase output current with a high modulation system;

[0045] FIG8( d ) is a diagram showing the simulation results of the midpoint voltage;

[0046] FIG8(e) is a diagram showing the simulation results of the common mode voltage of the low-profile system;

[0047] Figure 8(f) is a simulation result diagram of low leakage current amplitude in a low profile system;

[0048] FIG8( g ) is a diagram showing the simulation results of the common mode voltage with high modulation degree;

[0049] FIG8(h) is a diagram showing the simulation results of a high modulation system with low leakage current amplitude;

[0050] FIG8(i) is a diagram showing the simulation results of a low leakage current effective value of a low profile system;

[0051] FIG8(j) is a diagram showing the simulation results of the low leakage current effective value under high modulation;

[0052] Figure 8(k) is a diagram showing the FFT simulation results of the output current of the low-profile system;

[0053] FIG8(l) is a diagram showing the FFT simulation results of the output current with high modulation index;

[0054] FIG8(m) is a schematic diagram of the common mode voltage and low leakage current corresponding to the case where the common mode voltage switching frequency is equal;

[0055] FIG8(n) is a schematic diagram showing the common mode voltage and low leakage current corresponding to the case where the common mode voltage switching frequency is unequal. DETAILED DESCRIPTION

[0056] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0057] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0058] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0059] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0060] In one or more embodiments, the present invention discloses a coupled ten-switch three-level inverter, Figure 1 The topology diagram of the coupled ten-switch three-level inverter is shown in Figure 1. The first four switches are coupled, and the last six switches are A, B, and C three-phase outputs. Like the traditional three-level inverter, it can output three levels, namely 0. Among them, V dc is the DC side voltage amplitude. Here, the three levels are recorded as P, O, and N. However, due to the coupling of the first four switches, the three phases cannot output P, ​​O, and N states at the same time. Therefore, compared with the traditional three-level inverter topology, this topology lacks the middle vector, that is, there is no PON state. Figure 2 (a) is the space vector diagram of the coupled ten-switch three-level inverter, with each 60° being a sector, and a total of six sectors.

[0061] The embodiment of the present invention provides a modulation strategy for suppressing low leakage current peak and reducing current ripple and balancing midpoint voltage of a coupled three-level inverter. As in some disclosed embodiments, 13 space vectors are used. According to the distribution of the space vector diagram, the vectors are divided according to the distance from each vector to vector OOO, and can be divided into large vectors, small vectors, and zero vectors, that is, Figure 2 The vectors through which the three hexagons in (b) pass. Combined with the particularity of the coupled three-level, such as Figure 3 As shown, the present invention divides each sector into three parts under different modulation indices, namely: low leakage current part, low current ripple part and common part. Two different sequences are designed, namely low leakage current sequence and low current ripple sequence, and each sector has two low leakage current sequences and two low current ripple sequences. Figure 4 is a space vector diagram of the low leakage current sequence and low current ripple sequence of each sector, Figure 5 Schematic diagram of four sequences of each sub-sector of the first sector.

[0062] The common mode voltage is defined as the average value of the three-phase output voltages of the coupled three-level inverter.

[0063]

[0064] Among them, v CM is the common mode voltage amplitude, vAO 、v BO 、v CO They are the three-phase output voltages A, B, and C respectively.

[0065] According to the definition of common mode voltage, Figure 2 The common mode voltage amplitudes of the 13 vectors used in the present invention are also marked in (b). Since low common mode vectors are used, there are only three cases of amplitude, which are 0. In the figure, they are represented as [+], [0], [-].

[0066] Leakage current is defined as the rate of change of the common-mode voltage on the stray capacitance between the PV array and the ground.

[0067]

[0068] Among them, i cm is the leakage current amplitude, C pv is the stray capacitance value (stray capacitance exists between the photovoltaic array and the ground, generally 10-15nF / kW).

[0069] According to the definition of leakage current, the leakage current is determined by the common-mode voltage amplitude and the switching frequency of the common-mode voltage. Therefore, the present invention designs a switching sequence according to the common-mode voltage amplitude of the coupled three-level inverter. The low common-mode vector is used to reduce the common-mode voltage amplitude; a five-segment sequence is used and the sequence is reasonably designed according to 13 low common-mode voltage vectors to minimize the switching frequency of the common-mode voltage. As shown in Figures 4(a) and 4(b), in sub-sector 1, a large vector, a small vector, and a zero vector are used to synthesize a reference voltage vector; for example, the first sector can design two low leakage current sequences, namely OOO-POO-PPN and 000-OON-PNN. Figure 5 (a) and (b) show the low leakage current switching sequence of the first sector. In one switching cycle, the common mode voltage amplitude changes to The common mode voltage switches twice. According to the volt-second balance principle, the action time of each vector can be calculated:

[0070]

[0071] Among them, T OOO is the zero vector action time; T POO , T OON is the small vector action time; T PPN , T PNN is the action time of the large vector; T S is the switching period, V ref is the reference voltage vector amplitude, and θ is the reference voltage vector phase.

[0072] In sub-sector 4, two large vectors and one small vector are used to achieve low ripple without increasing the common-mode voltage amplitude and switching loss. Two large vectors and one small vector are selected according to the proximity principle. Figure 4 (c) and (d) are schematic diagrams of the space vectors of the low current ripple sequence of each sector. Figure 5 (c) and (d) are the low current ripple switching sequences of the first sector, which are POO-PNN-PPN and OON-PPN-PNN respectively. Since the coupled three-level inverter lacks the middle vector PON, the change of the common-mode voltage amplitude can only be According to the volt-second balance principle, the action time of the low current ripple sequence in the first sector is:

[0073]

[0074] In sub-sectors 2 and 3, the low leakage current sequence and the low current ripple sequence are shared, and the balance of the midpoint voltage is achieved by switching between the two.

[0075] Figure 6 The diagram is a switching diagram of the midpoint voltage balance sequence of each sub-sector. Since the midpoint voltage is coupled with the reduction of low leakage current and ripple, the present invention achieves midpoint balance without decoupling. Whether to balance the midpoint is determined by setting the midpoint voltage upper limit uplimit. When the midpoint voltage is higher than the upper limit, the midpoint voltage balance control is performed; when the midpoint voltage is lower than the upper limit, since the sequence designed by the present invention is a self-balancing sequence, the midpoint balance control may not be performed. Figure 6 (a) is the low leakage current part. The large vector and zero vector do not affect the midpoint balance. Therefore, according to the different effects of the small vectors POO and OON on the midpoint voltage balance, the low leakage current sequence 1 and 2 are switched. The midpoint voltage is defined as the difference between the upper and lower DC capacitors, that is, ΔU = V P -V N , where V P 、V N Represent the upper and lower capacitor voltages respectively. Figure 6 (b) and (c) are common parts. Figure 6 In (b), by switching the low leakage current sequence 1 and the low current ripple sequence 1; and Figure 6 In (c), the low leakage current sequence 2 and the low current ripple sequence 2 are switched. Figure 6 (d) is the low current ripple part, by switching the low current ripple sequences 1 and 2. As a result, each part can achieve midpoint voltage balance.

[0076] (1) When ΔU is greater than 0, a P-type small vector is used, that is, a low leakage current sequence 2 or a low current ripple sequence 1.

[0077] (2) When ΔU is less than 0, an N-type small vector is used, that is, a low leakage current sequence 1 or a low current ripple sequence 2.

[0078] When the reference voltage vector appears in the remaining five sectors, due to the symmetry of each sector, they can all be analyzed using a method similar to the first sector.

[0079] Figure 7 This is the control flow chart of the whole process mentioned above. Through sector judgment, low common mode vector is selected, switching sequence is designed, appropriate switching sequence is selected according to different modulation degrees, and then the switching sequence is switched according to the midpoint voltage. The action time of each vector is calculated to generate PWM signal.

[0080] The specific implementation steps are: preselecting a low common mode voltage vector; obtaining a three-phase output current value i by output current sampling; abc , after Park transformation, it is converted to the dq coordinate system, and the reference voltage in the αβ coordinate system is obtained through the PI controller through dq-αβ transformation; the sector judgment module includes large sector judgment and sub-sector judgment; due to the similarity of the sectors, the action time of the vectors in each sector is consistent. For the sake of simplicity of algorithm, they are all converted to the first sector; then judge the sub-sector part (low leakage current, low ripple, common part). Combined with the voltage difference between the upper and lower capacitors on the DC side, it is judged whether to perform midpoint balance control. When the absolute value is greater than the upper limit, midpoint balance control is not performed; when the absolute value is less than the upper limit, the difference is greater than the upper limit, and low leakage current sequence 2 and low ripple sequence 1 are selected; when the difference is less than the upper limit, low leakage current sequence 1 and low ripple sequence 2 are selected. Combined with the above-mentioned sector judgment, the sequence of each sub-sector is determined according to the sector to which it belongs. Finally, the action time of each vector is calculated to generate the corresponding control signal.

[0081] The above scheme uses a low common-mode voltage vector, which essentially reduces the low leakage current. On the basis of reducing the common-mode voltage, the frequency of change of the common-mode voltage is further considered to achieve the reduction of the low leakage current, and the low leakage current amplitude is within 300mA, meeting the standard. In the low-mode system, the zero vector and two low common-mode small vectors are used to synthesize, and the low leakage current amplitude is controlled within 150mA; in the high-mode system, two large vectors and one medium vector are used to synthesize. Under the premise that the low leakage current amplitude is within 300mA, the ripple is reduced at the same time, and the switching loss is small. At the same time, the sequence is selected according to the midpoint potential, and the midpoint voltage balance is achieved by switching the two pairs of low leakage current sequences and two pairs of low current ripple sequences designed.

[0082] In the simulation of the modulation method of the present invention, the DC power supply uses 100V DC power instead of the photovoltaic array DC power, and the grid side uses a fixed output resistor instead of the grid. The resistance is 8Ω, the fixed reference current amplitude is 3A and 5.5A, the AC side filter inductor uses 4.5mH, and the midpoint voltage balance uplimit is set to ±0.7V. In Figures 8(a) to (c), the line voltage is 3 levels and the current is sinusoidal, which is consistent with the output of the coupled three-level inverter. As shown in Figure 8(d), the midpoint balance is effectively controlled at 0.05s. In Figures 8(e) to (j), the common-mode voltage amplitude is controlled at 1 / 6 of the DC power supply voltage, and it can be seen that the common-mode voltage is only and 0, Switching between 0 and 0 achieves low common-mode voltage; at the same time, when the low-mode modulation is low, the low leakage current basically has no peaks and is effectively controlled within 150mA, and the effective value of the low leakage current is within 100mA. The amplitude of the low leakage current of the high modulation system is also basically controlled within 300mA, and the effective value is within 100mA. Figure 8 (k) and (1) are the output current THD. It can be seen that the high modulation current ripple is 1% smaller than the low modulation ripple, and the effect is better than the current output effect of the existing coupled three-level inverter. The above simulation results well verify the low leakage current and low current ripple modulation method proposed by the present invention, and at the same time have the ability to balance the midpoint voltage. In Figure 8 (m) and (n), when the common-mode voltage change rate is equal, the upper and lower amplitudes of the low leakage current are almost symmetrical, and only a large peak appears when switching between two switching cycles. When the change rate is unequal, multiple peaks will appear in the low leakage current. Therefore, in addition to zero common-mode voltage, to effectively reduce the low leakage current, it is necessary to control its change rate on the basis of reducing the common mode.

[0083] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A low leakage current and low current ripple vector modulation method for coupled three-level inverters, characterized in that: The following steps are involved: Determine whether a reference voltage vector has a sector; Determining a low leakage current or low current ripple sequence according to a low common mode voltage vector in the sector, so that a switching frequency of the common mode voltage is reduced or a current ripple is reduced; Determine whether the midpoint voltage of each sub-sector in the sector exceeds the set upper limit. If not, do not perform midpoint voltage balance control and use the nearest optimal vector; if yes, perform midpoint voltage balance control, switch the low leakage current sequence and the low current ripple sequence for the corresponding sub-sector, calculate the action time of each vector, and generate a corresponding control signal; According to the distance from each vector to vector OOO, it is divided into large vector, small vector and zero vector. Each sector is divided into a low leakage part close to vector OOO, a low current ripple part far from vector OOO and two common parts in the middle according to the location of the large vector, small vector and zero vector. The low leakage part of each sector is combined with different common parts to form two low leakage current sequences, and the low current ripple part is combined with different common parts to form two low current ripple sequences; The specific process of switching the corresponding sub-sectors between the low leakage current sequence and the low current ripple sequence includes: the low regulation is switched through the low leakage current sequence, and the high regulation common part is switched through the low leakage current sequence and the low current ripple sequence; The high regulation independent parts are switched in sequence with low current ripple.

2. The low leakage current and low current ripple vector modulation method of coupled three-level inverter according to claim 1, characterized in that: There are six sectors in total, which are obtained by evenly dividing the sectors according to the space vector diagram of the coupled three-level inverter.

3. The low leakage current and low current ripple vector modulation method of the coupled three-level inverter according to claim 1, characterized in that In each sub-sector, a large vector, a small vector, and a zero vector are used to synthesize a reference voltage vector; or a corresponding vector is selected according to the proximity principle to achieve low ripple; or a low leakage current sequence and a low current ripple sequence are shared, and the balance of the midpoint voltage is achieved by switching between the two.

4. The low leakage current and low current ripple vector modulation method of coupled three-level inverter according to claim 1, characterized in that: During the switching between the low leakage current sequence and the low current ripple sequence for the corresponding sub-sector, the large vector and the zero vector do not affect the midpoint balance. The two low leakage current sequences are switched according to the different effects of the small vector on the midpoint voltage balance.

5. The low leakage current and low current ripple vector modulation method of coupled three-level inverter according to claim 1, characterized in that: In the process of switching the low leakage current sequence and the low current ripple sequence for the corresponding sub-sector, when the midpoint voltage is greater than zero, a P-type small vector is used, and when the midpoint voltage is less than zero, an N-type small vector is used.

6. The low leakage current and low current ripple vector modulation method of coupled three-level inverter according to claim 1, characterized in that: The action time of each vector is calculated according to the volt-second balance principle.

7. A low leakage current and low current ripple vector modulation system coupled with a three-level inverter, characterized in that: include: A sector determination module, configured to determine a sector where a reference voltage vector appears; A switch sequence selection module, configured to determine a low leakage current or low current ripple sequence in the sector according to a low common mode voltage vector, so as to reduce a switching frequency of the common mode voltage or reduce a current ripple; The sub-sector sequence switching module is configured to determine whether the midpoint voltage of each sub-sector in the sector exceeds a set upper limit. If not, midpoint voltage balance control is not performed and the nearest optimal vector is used; if yes, midpoint voltage balance control is performed, a low leakage current sequence and a low current ripple sequence are switched for the corresponding sub-sector, the action time of each vector is calculated, and a corresponding control signal is generated; According to the distance from each vector to vector OOO, it is divided into large vector, small vector and zero vector. Each sector is divided into a low leakage part close to vector OOO, a low current ripple part far from vector OOO and two common parts in the middle according to the location of the large vector, small vector and zero vector. The low leakage part of each sector is combined with different common parts to form two low leakage current sequences, and the low current ripple part is combined with different common parts to form two low current ripple sequences; The specific process of switching the corresponding sub-sectors between the low leakage current sequence and the low current ripple sequence includes: the low regulation is switched through the low leakage current sequence, and the high regulation common part is switched through the low leakage current sequence and the low current ripple sequence; The high regulation independent parts are switched in sequence with low current ripple.

8. An electronic device, characterized in that: The method comprises a memory and a processor, and computer instructions stored in the memory and executed on the processor, wherein when the computer instructions are executed by the processor, the steps in the method according to any one of claims 1 to 6 are completed.

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