Modulation method and system for suppressing common-mode voltage and mid-point low-frequency oscillation of three-level inverter

Abstract

The invention discloses a modulation method and system for suppressing common-mode voltage and midpoint low-frequency oscillation of a three-level inverter, and the method comprises the steps: obtaining a reference voltage vector, and judging a sector where the reference voltage vector is located according to the division condition of a space sector; according to the space sector division condition and the position of the reference voltage vector, a synthetic virtual vector and a corresponding basic voltage vector are obtained, and the action sequence of the basic voltage vector is determined; based on the action sequence of the basic voltage vector, virtual vector action time is calculated according to volt-second balance, the virtual vector action time is distributed to the basic voltage vector action time, and a pulse width modulation signal is output to control the on-off of a power device of the inverter, so that the common-mode voltage of the three-level inverter is suppressed, and the three-level inverter is obtained. And safe and stable operation of the system is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of three-level inverters, and in particular to a modulation method and system for suppressing common-mode voltage and mid-point low-frequency oscillation of a three-level inverter. Background Art

[0002] In the context of rapid development of power semiconductors and large-scale access to distributed new energy, three-level inverters have a wide range of applications. With the continuous improvement of the computing power of digital signal processors, advanced PWM modulation technology suitable for three-level inverters has become a research hotspot. The current mainstream advanced PWM modulation technology is space vector pulse width modulation (Space Vector PWM, SVPWM). The basic principle is to generate a circular magnetic flux on the complex plane by controlling the on and off of the power devices of the three-level inverter, so that the load can work normally and output a stable waveform. The implementation steps are: calculate the reference voltage vector; determine the large sector (Sector A~F) and small sector (A1~F6) where the reference vector is located; select the basic voltage vector used to synthesize the reference voltage vector; determine the action order of the basic voltage vector; calculate the action time of the basic voltage vector; output PWM signal to control the on and off of the power device.

[0003] The existing scheme has the phenomenon of low-frequency oscillation of the midpoint potential of the three-level inverter, which leads to an increase in the low-order harmonics of the output current and an increase in the voltage stress of the power devices; the common-mode voltage is not suppressed, and the large leakage current generated in the photovoltaic grid-connected system causes electromagnetic interference and parasitic capacitance damage. Due to the low-frequency oscillation of the midpoint potential and the common-mode voltage problem, the conversion efficiency and system stability of the inverter are affected. These problems will cause the performance of the inverter to deteriorate under high load or long-term operation; the current research shows that when the DC bus voltage is 800V, the common-mode voltage amplitude of the SVPWM modulation method is about 267V, which indicates that the common-mode voltage amplitude has not been effectively suppressed. Summary of the invention

[0004] In view of the above existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a modulation method and system for suppressing the common-mode voltage and mid-point low-frequency oscillation of a three-level inverter to solve the obvious deficiencies of existing solutions in mid-point potential control and common-mode voltage suppression, which not only affects the performance and efficiency of the inverter, but may also cause electromagnetic interference and equipment damage.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a modulation method for suppressing common mode voltage and midpoint low frequency oscillation of a three-level inverter, comprising:

[0008] Obtaining a reference voltage vector, and determining a sector where the reference voltage vector is located according to a spatial sector division situation;

[0009] According to the spatial sector division and the position of the reference voltage vector, a synthetic virtual vector and a corresponding basic voltage vector are obtained, and the action order of the basic voltage vector is determined;

[0010] Based on the action sequence of the basic voltage vector, a virtual vector action time is calculated according to the volt-second balance, the virtual vector action time is allocated to the basic voltage vector action time, and a pulse width modulation signal is output to control the on and off of the power devices of the inverter.

[0011] As a preferred solution of the modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of the three-level inverter described in the present invention, the spatial sector division includes:

[0012] The spatial sectors are divided into large sectors of a first threshold, and each large sector is composed of small sectors of a second threshold.

[0013] As a preferred solution of the modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of the three-level inverter according to the present invention, the synthetic virtual vector includes:

[0014] The virtual small vector is synthesized from the adjacent basic small vector and the adjacent basic medium vector;

[0015] The adjacent mean vector is synthesized from the adjacent basic mean vectors;

[0016] The virtual zero vector is the basic zero vector itself;

[0017] The virtual large vector is the basic large vector itself.

[0018] As a preferred solution of the modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of the three-level inverter described in the present invention, it also includes:

[0019] During the switching cycle, the midpoint current corresponding to the three-level inverter is zero, so the value of the low-frequency oscillation of the midpoint potential is zero.

[0020] As a preferred solution of the modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of the three-level inverter according to the present invention, the action sequence of the basic voltage vector includes:

[0021] Based on the principle of the nearest three vectors and the synthesis of virtual vectors, the basic vectors are selected, the number of switching times in each switching cycle is recorded, and the virtual vector synthesis type with the least number of switching times is selected.

[0022] As a preferred solution of the modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of the three-level inverter described in the present invention, it also includes:

[0023] The virtual vector synthesis rules for small sectors are exactly the same as those for large sectors, and only the basic vector selection is changed;

[0024] The wave transmission sequence is that the switching state of the voltage intermediate phase starts from N.

[0025] As a preferred solution of the modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of the three-level inverter described in the present invention, the basic voltage vector includes:

[0026] The basic voltage vectors greater than the third threshold are eliminated, and the common mode voltage amplitude is 0 or U dc The basic space vector of / 3 suppresses the common-mode voltage of the three-level inverter.

[0027] In a second aspect, the present invention provides a modulation system for suppressing common mode voltage and midpoint low frequency oscillation of a three-level inverter, comprising:

[0028] A division module, used for obtaining a reference voltage vector and determining the sector where the reference voltage vector is located according to the spatial sector division situation;

[0029] A sequence determination module, used to obtain a synthetic virtual vector and a corresponding basic voltage vector according to the spatial sector division and the position of the reference voltage vector, and determine the action sequence of the basic voltage vector;

[0030] The control module is used to calculate the virtual vector action time based on the action sequence of the basic voltage vector according to the volt-second balance, allocate the virtual vector action time to the basic voltage vector action time, and output a pulse width modulation signal to control the on and off of the power devices of the inverter.

[0031] In a third aspect, the present invention provides a computing device, comprising:

[0032] Memory and processor;

[0033] The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of the modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of the three-level inverter are implemented.

[0034] In a fourth aspect, the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the modulation method for suppressing the common-mode voltage and mid-point low-frequency oscillation of a three-level inverter.

[0035] Compared with the prior art, the present invention has the following beneficial effects: the present invention changes the spatial sector division method of the existing three-level inverter modulation method, introduces a virtual vector that does not affect the midpoint potential, effectively suppresses the low-frequency oscillation of the midpoint potential of the three-level inverter, and avoids unnecessary switching actions of power devices, thereby improving the conversion efficiency of the inverter. In the synthesis of virtual vectors, the basic vector with a large common-mode voltage is avoided, so that the common-mode voltage of the three-level inverter is suppressed, ensuring the safe and stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0037] Figure 1 A schematic diagram of the overall process logic of a modulation method for suppressing common-mode voltage and mid-point low-frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0038] Figure 2 A diagram of spatial sector division in a modulation method for suppressing common mode voltage and midpoint low frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0039] Figure 3 A first basic vector synthesis diagram of a small sector A1 in a modulation method for suppressing a common mode voltage and a midpoint low frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0040] Figure 4 A second basic vector synthesis diagram of a small sector A1 in a modulation method for suppressing a common mode voltage and a midpoint low frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0041] Figure 5 A third basic vector synthesis diagram of a small sector A1 in a modulation method for suppressing a common mode voltage and a midpoint low frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0042] Figure 6 A fourth basic vector synthesis diagram of a small sector A1 in a modulation method for suppressing a common mode voltage and a midpoint low frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0043] Figure 7 A waveform diagram of bus capacitor voltage of SVPWM strategy in a modulation method for suppressing common mode voltage and midpoint low-frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0044] Figure 8A waveform diagram of a common-mode voltage of SVPWM in a modulation method for suppressing a common-mode voltage and mid-point low-frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0045] Fig. 9 A waveform diagram of a DC bus capacitor voltage in a modulation method for suppressing a common-mode voltage and mid-point low-frequency oscillation of a three-level inverter according to an embodiment of the present invention;

[0046] Fig.10 This is a common mode voltage waveform diagram of a modulation method for suppressing common mode voltage and midpoint low frequency oscillation of a three-level inverter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0048] Example 1

[0049] Reference Figure 1-Figure 10 Tables 1 to 3 are an embodiment of the present invention, which provides a modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of a three-level inverter, including:

[0050] S100: Obtain a reference voltage vector, and determine the sector where the reference voltage vector is located according to the spatial sector division situation;

[0051] S200: obtaining a synthetic virtual vector and a corresponding basic voltage vector according to the spatial sector division and the position of the reference voltage vector, and determining the action order of the basic voltage vector;

[0052] S300: Calculate the virtual vector action time based on the action sequence of the basic voltage vector according to the volt-second balance, allocate the virtual vector action time to the basic voltage vector action time, and output a pulse width modulation signal to control the on and off of the power devices of the inverter.

[0053] It should be noted that the present application changes the original sector division rule of the space vector diagram, introduces a virtual vector to synthesize the reference voltage vector, so that the average value of the midpoint current of the three-level inverter within a switching cycle is theoretically 0, thereby eliminating the low-frequency oscillation of the midpoint potential. In the process of defining the virtual vector, the basic voltage vector with a large common-mode voltage is avoided, thereby achieving effective suppression of the common-mode voltage of the three-level inverter.

[0054] In the embodiment of the present application, the above step S100 includes the following sub-steps A1-A3;

[0055] In A1: the spatial sectors are divided into large sectors of a first threshold, each large sector is composed of small sectors of a second threshold;

[0056] Specifically, in the present application, there are 6 large sectors with a first threshold, and each large sector is composed of 5 small sectors with a second threshold.

[0057] For example, Figure 2 The figure shows the spatial sector division. The large sectors are Sector A to Sector F, and the small sectors in the large sector A are A1 to A5.

[0058] It should be noted that by subdividing the sectors, the synthesis of the voltage vector can be more accurately controlled, thereby more accurately tracking the reference voltage vector and improving the modulation accuracy. By avoiding the use of basic voltage vectors with large common-mode voltages, especially the synthesis rules within small sectors, the common-mode voltage can be effectively suppressed, reducing the risk of electromagnetic interference and parasitic capacitance damage, reducing unnecessary switching actions, reducing the switching losses of power devices, and improving the conversion efficiency of the inverter. By reducing the low-frequency oscillation and common-mode voltage of the mid-point potential, the voltage stress of the power device can be reduced, the risk of device damage can be reduced, and the stability and reliability of the entire system can be enhanced.

[0059] In the embodiment of the present application, the basic voltage vector in the above step S200 includes the following sub-step B1;

[0060] In B1: the basic voltage vectors greater than the third threshold are eliminated, and the common mode voltage amplitude is 0 or U dc / 3 basic space vector, suppressing the common mode voltage of the three-level inverter;

[0061] Specifically, the present application abandons the common mode voltage being larger, that is, greater than the third threshold value U dc / 3 vector, only uses the common mode voltage amplitude of 0 or U dc / 3 basic space vector, the rules are shown in Table 1;

[0062] Table 1 Space vector of low common mode voltage amplitude

[0063]

[0064] It should be noted that by eliminating the common mode voltage greater than U dc The small vector of / 3 significantly reduces the common-mode voltage of the three-level inverter and the electromagnetic interference problem caused by the common-mode voltage. The reduced common-mode voltage reduces the electromagnetic interference of the inverter to the surrounding electronic equipment and improves the electromagnetic compatibility of the system. Reducing the common-mode voltage can reduce the noise in the system and improve the stability of the system.

[0065] In the embodiment of the present application, after completing step B1, the above step S200 synthesizing the virtual vector includes the following sub-steps B2-B6;

[0066] In B2: the virtual small vector is synthesized from the adjacent basic small vector and the adjacent basic medium vector;

[0067] In B3: the adjacent mean vector is synthesized from the adjacent basic mean vector;

[0068] In B4: the virtual zero vector is the basic zero vector itself;

[0069] In B5: the virtual large vector is the basic large vector itself;

[0070] In B6: During the switching period, the midpoint currents corresponding to the three-level inverters are all zero, so the value of the low-frequency oscillation of the midpoint potential is zero.

[0071] For example, taking large sector A as an example, large sector A involves a total of 6 virtual vectors, including 1 virtual zero vector, 2 virtual small vectors, 1 virtual medium vector, and 2 virtual large vectors. According to the virtual vector synthesis rule, it is expressed as:

[0072]

[0073] Among them, V S1 、V S2 is a virtual small vector, V Z is the virtual zero vector, V M is the virtual mean vector, V L1 、V L2 is a virtual large vector;

[0074] The midpoint currents corresponding to these six virtual vectors are all zero, so the value of the low-frequency oscillation of the midpoint potential is zero.

[0075] It should be noted that by designing the midpoint currents corresponding to the six virtual vectors to be zero, the low-frequency oscillation of the midpoint potential is effectively eliminated, thereby reducing the low-order harmonic content of the inverter output. Since the low-frequency oscillation of the midpoint potential is eliminated, the waveform of the output current is smoother, which improves the power quality. By precisely controlling the synthesis of the voltage vector, unnecessary switching actions are reduced, thereby reducing switching losses and improving the efficiency of the inverter.

[0076] In the embodiment of the present application, the above step S200 may further include steps B7-B9 after completing steps B2-B6;

[0077] In B7: based on the principle of the nearest three vectors and the synthesis of virtual vectors, the basic vector is selected, the number of switching times in each switching cycle is recorded, and the virtual vector synthesis type with the least number of switching times is selected;

[0078] In B8: the virtual vector synthesis rule of the small sector is exactly the same as that of the large sector, and only the basic vector selection is changed;

[0079] In B9: the wave generation sequence is that the switching state of the voltage intermediate phase starts from N.

[0080] Specifically, since there are different synthesis methods for virtual small vectors, the selection of basic vectors needs to be analyzed;

[0081] For example, taking the case where the reference vector is located in the small sector A1 as an example, based on the principle of the nearest three vectors, the reference vector is composed of a virtual small vector V S1 、V S2 and virtual zero vector V Z There are four types of composition: Figure 3-Figure 6 As shown;

[0082] like Figure 3 As shown, under the action of the selected basic vector:

[0083] V S1 =(ONO+PON) / 2, V S2 =(OPO+PON) / 2;

[0084] The wave transmission sequence is ONO-OOO-PON-OOO-OPO-OOO-PON-OOO-ONO, and the number of switching times in one switching cycle is 12 times;

[0085] like Figure 4 As shown, under the action of the selected basic vector:

[0086] V S1 =(ONO+PON) / 2, V S2 =(POO+OPN) / 2;

[0087] The wave transmission sequence is ONO-OOO-POO-PON-OPN-PON-POO-OOO-ONO, and the number of switching times in one switching cycle is 10;

[0088] like Figure 5 As shown, under the action of the selected basic vector:

[0089] V S1 =(OON+PNO) / 2, V S2 =(OPO+PON) / 2;

[0090] The wave transmission sequence is PNO-PON-OON-OOO-OPO-OOO-OON-PON-PNO, and the number of switching times in one switching cycle is 10;

[0091] like Figure 6 As shown, under the action of the selected basic vector:

[0092] V S1 =(OON+PNO) / 2, V S2 =(POO+OPN) / 2;

[0093] The wave transmission sequence is PNO-POO-OOO-OON-OPN-OON-OOO-POO-PNO, and the number of switching times in one switching cycle is 8;

[0094] In order to reduce switching losses and increase the conversion efficiency of the three-level inverter, the virtual vector synthesis type with the least switching times should be selected;

[0095] The virtual vector expression is expressed as:

[0096]

[0097] According to the virtual vector expression, the synthetic virtual vectors and wave order of all small sectors in the large sector A are shown in Table 2;

[0098] Table 2 Synthetic virtual vectors and wave generation order of small sectors in large sector A1

[0099]

[0100] For large sectors B~F, the virtual vector synthesis rules of their small sectors are exactly the same as those of large sector A, and only the basic vector selection needs to be changed;

[0101] It should be noted that the main disadvantages of the existing solution are analyzed as follows. For a type of three-level inverter, the midpoint current is expressed as:

[0102] i np =d a,0 i a +d b,0 i b +d c,0 i c

[0103] Among them, i x (x=a,b,c) is the x-phase current, d x,0 (x=a,b,c) is the duty cycle of the x-phase modulation wave at 0 level. This value is related to the modulation wave voltage, and the relationship is as follows:

[0104] d x,0 =1-|m x |

[0105] Modulation wave voltage m x The instantaneous expression of is:

[0106]

[0107] The intermediate current is expressed as:

[0108]

[0109] Taking phase a as an example, |m x | is an even function symmetric about the y-axis. Perform Fourier series expansion on it. Let x = at, l = π / 2, f(x) = cos x, then the Fourier series coefficients are:

[0110]

[0111] Taking n = 0, 2, 4, the Fourier series is expressed as:

[0112]

[0113] Since the sum of the three cosine terms with a phase difference of 120° is 0 under fundamental conditions, the midpoint current is expressed as:

[0114]

[0115] in,

[0116]

[0117] The approximate expression of midpoint current is:

[0118]

[0119] When the upper and lower capacitances of the three-level inverter bus are both C, the midpoint potential is expressed as:

[0120]

[0121] Among them, I m To adjust the system, is the power factor angle.

[0122] like Figure 7 The midpoint current shown in the figure has three times the power frequency oscillation. Under the action of integration, the midpoint potential also has three times the power frequency oscillation. The existing solution also does not have the ability to suppress common mode voltage.

[0123] The basic voltage vectors and corresponding common-mode voltages used in the SVPWM modulation method are shown in Table 3;

[0124] Table 3 SVPWM basic voltage vector and corresponding common mode voltage

[0125]

[0126] Since small vectors with large common-mode voltages such as ONN and PPO are used to synthesize the reference voltage vector, the amplitude of the common-mode voltage is U dc / 3, with DC bus voltage U dc =800V, build a simulation circuit in Matlab / Simulink, and get the common-mode voltage waveform of the SVPWM modulation method, as shown in Figure 8 As shown, the DC bus U dc =800V, the SVPWM common-mode voltage amplitude is about 267V, which fails to effectively suppress the common-mode voltage amplitude within U dc / 6.

[0127] like Fig. 9 As shown, the bus capacitor voltage waveform of the modulation method designed in the present application, the midpoint potential is the voltage difference between the capacitor under the bus and the capacitor on the bus, and the two waveforms show that the low-frequency oscillation of the midpoint potential is effectively suppressed. The suppression of the low-frequency oscillation of the midpoint potential helps to reduce the harmonic content in the inverter output and improve the power quality. Reducing the low-frequency oscillation of the midpoint potential can reduce the voltage stress on the power device and reduce the risk of device damage.

[0128] like Fig.10 As shown, the common-mode voltage waveform of the modulation method designed in the present application has a common-mode voltage amplitude of approximately 133V when the DC bus is 800V, thereby achieving effective suppression of the common-mode voltage. The effective suppression of the common-mode voltage reduces the electromagnetic interference of the inverter to the surrounding environment. For grid-connected inverters, effective control of the common-mode voltage helps to improve compatibility with the power grid, reduces the negative impact on the power grid, and helps to achieve a wider range of renewable energy grid connection.

[0129] It should also be noted that by discarding small vectors with large common-mode voltage, only vectors with common-mode voltage amplitude of 0 or U dc / 3 basic space vector significantly reduces the common-mode voltage, reduces the risk of electromagnetic interference and equipment damage, and by changing the sector division rule of the space vector diagram and introducing virtual vectors, the average value of the midpoint current in one switching cycle is made zero, which effectively suppresses the low-frequency oscillation of the midpoint potential, reduces unnecessary switching actions, and reduces the switching loss of power devices, thereby improving the conversion efficiency of the inverter, reducing the voltage stress of power devices, reducing the risk of device damage, and enhancing the stability and reliability of the entire system. It effectively suppresses the common-mode voltage, reduces the electromagnetic interference generated during the operation of the inverter, and helps to improve the electromagnetic compatibility of the entire system.

[0130] The above is a schematic scheme of a modulation method for suppressing the common mode voltage and midpoint low-frequency oscillation of a three-level inverter in this embodiment. It should be noted that the technical scheme of the modulation system for suppressing the common mode voltage and midpoint low-frequency oscillation of the three-level inverter and the technical scheme of the modulation method for suppressing the common mode voltage and midpoint low-frequency oscillation of the three-level inverter belong to the same conception, and the details of the technical scheme of the modulation system for suppressing the common mode voltage and midpoint low-frequency oscillation of the three-level inverter in this embodiment that are not described in detail can all be referred to the description of the technical scheme of the modulation method for suppressing the common mode voltage and midpoint low-frequency oscillation of the three-level inverter.

[0131] In this embodiment, the modulation system for suppressing the common mode voltage and midpoint low frequency oscillation of the three-level inverter includes:

[0132] A division module, used for obtaining a reference voltage vector and determining the sector where the reference voltage vector is located according to the spatial sector division situation;

[0133] A sequence determination module, used to obtain a synthetic virtual vector and a corresponding basic voltage vector according to the spatial sector division and the position of the reference voltage vector, and determine the action sequence of the basic voltage vector;

[0134] The control module is used to calculate the virtual vector action time based on the action sequence of the basic voltage vector according to the volt-second balance, allocate the virtual vector action time to the basic voltage vector action time, and output a pulse width modulation signal to control the on and off of the power devices of the inverter.

[0135] This embodiment further provides a computing device, which is applicable to suppressing modulation of common mode voltage and midpoint low frequency oscillation of a three-level inverter, and includes:

[0136] A memory and a processor; the memory is used to store computer executable instructions, and the processor is used to execute computer executable instructions to implement the modulation method for suppressing the common mode voltage and midpoint low-frequency oscillation of the three-level inverter as proposed in the above embodiment.

[0137] This embodiment further provides a storage medium having a computer program stored thereon, which, when executed by a processor, implements the modulation method for suppressing the common mode voltage and midpoint low-frequency oscillation of a three-level inverter as proposed in the above embodiment.

[0138] The storage medium proposed in this embodiment and the modulation method for suppressing the common-mode voltage and mid-point low-frequency oscillation of the three-level inverter proposed in the above embodiment belong to the same inventive concept. The technical details not described in detail in this embodiment can be referred to the above embodiment, and this embodiment has the same beneficial effects as the above embodiment.

[0139] Through the above description of the implementation methods, the technicians in the relevant field can clearly understand that the present invention can be implemented by means of software and necessary general hardware, and of course can also be implemented by hardware. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ReadOnly, Memory, ROM), random access memory (Random Access Memory, RAM), flash memory (FLASH), hard disk or optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform the methods of various embodiments of the present invention.

[0140] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A modulation method for suppressing common mode voltage and midpoint low frequency oscillation of a three-level inverter, characterized in that: include: Obtaining a reference voltage vector, and determining a sector where the reference voltage vector is located according to a spatial sector division situation; According to the spatial sector division and the position of the reference voltage vector, a synthetic virtual vector and a corresponding basic voltage vector are obtained, and the action order of the basic voltage vector is determined; Based on the action sequence of the basic voltage vector, a virtual vector action time is calculated according to the volt-second balance, the virtual vector action time is allocated to the basic voltage vector action time, and a pulse width modulation signal is output to control the on and off of the power devices of the inverter.

2. The modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of a three-level inverter according to claim 1, characterized in that: The spatial sector division includes: The spatial sectors are divided into large sectors of a first threshold, and each large sector is composed of small sectors of a second threshold.

3. The modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of a three-level inverter according to claim 2, characterized in that: The synthetic virtual vector includes: The virtual small vector is synthesized from the adjacent basic small vector and the adjacent basic medium vector; The adjacent mean vector is synthesized from the adjacent basic mean vectors; The virtual zero vector is the basic zero vector itself; The virtual large vector is the basic large vector itself.

4. The modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of a three-level inverter according to claim 1 or 3, characterized in that: Also includes: During the switching cycle, the midpoint current corresponding to the three-level inverter is zero, so the value of the low-frequency oscillation of the midpoint potential is zero.

5. The modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of a three-level inverter according to claim 4, characterized in that: The basic voltage vector action sequence includes: Based on the principle of the nearest three vectors and the synthesis of virtual vectors, the basic vectors are selected, the number of switching times in each switching cycle is recorded, and the virtual vector synthesis type with the least number of switching times is selected.

6. The modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of a three-level inverter according to claim 5, characterized in that: Also includes: The virtual vector synthesis rules for small sectors are exactly the same as those for large sectors, and only the basic vector selection is changed; The wave transmission sequence is that the switching state of the voltage intermediate phase starts from N.

7. The modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of a three-level inverter according to claim 6, characterized in that: The basic voltage vectors include: The basic voltage vectors greater than the third threshold are eliminated, and the common mode voltage amplitude is 0 or U dc The basic space vector of / 3 suppresses the common-mode voltage of the three-level inverter.

8. A system using the modulation method for suppressing the common mode voltage and midpoint low frequency oscillation of a three-level inverter as claimed in any one of claims 1 to 7, characterized in that: include: A division module, used for obtaining a reference voltage vector and determining the sector where the reference voltage vector is located according to the spatial sector division situation; A sequence determination module, used to obtain a synthetic virtual vector and a corresponding basic voltage vector according to the spatial sector division and the position of the reference voltage vector, and determine the action sequence of the basic voltage vector; The control module is used to calculate the virtual vector action time based on the action sequence of the basic voltage vector according to the volt-second balance, allocate the virtual vector action time to the basic voltage vector action time, and output a pulse width modulation signal to control the on and off of the power devices of the inverter.

9. An electronic device, comprising: Memory and processor; The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of the modulation method for suppressing the common mode voltage and mid-point low-frequency oscillation of a three-level inverter as described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the modulation method for suppressing the common-mode voltage and mid-point low-frequency oscillation of a three-level inverter as claimed in any one of claims 1 to 7.

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