Zero vector starting SVPWM midpoint voltage balancing method and related components

Abstract

The present application discloses a zero-vector-starting SVPWM midpoint voltage balancing method and related components, the method comprising: obtaining a preset unbalance margin factor K and a DC side voltage U of the three-level inverter; dc ; Calculate the midpoint voltage unbalance value U of the three-level inverter dc_dev ; when U dc_dev Greater than K×U dc When the zero-sequence voltage U of the SVPWM is corrected at the peak value of the triangle carrier, the zero-vector starts zero ; when U dc_dev Less than ‑K×U dc When the zero-sequence voltage U of the zero-vector starting SVPWM is corrected at the zero point of the triangle carrier zero ;Change U zero The three-phase original modulation wave of the three-level inverter is injected. When the midpoint voltage imbalance value is positive or negative, the present application realizes midpoint voltage balance control by correcting the zero-sequence voltage, thereby improving the reliability of the three-level NPC inverter under the action of zero-vector starting SVPWM based on carrier; and in the midpoint voltage balance control process, the present application can significantly reduce the three-phase current THD, thereby improving the output harmonic performance of the three-level NPC inverter.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to a zero-vector starting SVPWM midpoint voltage balancing method and related components. Background Art

[0002] The three-level neutral point clamped (NPC) inverter is the most commonly used three-level inverter. Its main circuit topology is as follows: Figure 1 Due to the advantages of low device voltage stress, simple structure and control, and easy bidirectional energy flow, three-level inverters have been widely used in photovoltaic and wind power generation, variable frequency speed regulation, metallurgical mining and other fields.

[0003] Space Vector Pulse Width Modulation (SVPWM) is a commonly used pulse width modulation strategy for three-level converters. The three levels of output from high to low of the three-level NPC inverter are defined as P, O, and N. The space vector of the three-level NPC inverter can be summarized as Figure 2 Among them, each space vector can be classified into zero vector, P-type small vector, N-type small vector, medium vector and large vector according to the amplitude, and the P-type small vector and N-type small vector at the same position are redundant small vectors. The specific classification of each space vector is shown in Table 1.

[0004] Table 1 Types of voltage space vectors for three-level converters

[0005]

[0006] SVPWM can be divided into small vector starting SVPWM and zero vector starting SVPWM according to whether the first vector in each sampling period is a small vector or a zero vector. The literature "Research on Pulse Width Modulation and Field Oriented Control of High Power Three-Level Inverter" (Yin Zhenggang, [D]. Beijing: University of Chinese Academy of Sciences, 2012: 87-89) points out that in the low modulation ratio area below 0.3, compared with small vector starting SVPWM, zero vector starting SVPWM will not produce narrow pulses, can produce arbitrarily small line voltage values ​​and has better harmonic performance. Therefore, in order to achieve the best control effect, the three-level NPC inverter should use zero vector starting SVPWM as the pulse width modulation strategy in the low modulation ratio area.

[0007] In the process of implementing zero-vector-start SVPWM, it is necessary to calculate the action time of each space vector and determine the sector area where the reference voltage is located. The steps are cumbersome, the calculations are complex, and there are calculation errors, which is not conducive to engineering applications. In order to more conveniently implement zero-vector-start SVPWM, the patent "Zero-vector-start SVPWM control method based on carrier" (Ge Qiongxuan. [P]. Invention Patent, 2020, CN201811265431.5) proposes a zero-vector-start SVPWM based on carrier by deriving the zero-sequence voltage and triangular carrier of zero-vector-start SVPWM. While retaining the advantages of zero-vector-start SVPWM, this method simplifies the system calculation amount, does not require sector judgment and rotation coordinate transformation, and improves the calculation efficiency and calculation accuracy of the system.

[0008] When the midpoint voltage of a three-level NPC inverter is unbalanced, low-order harmonics will be generated in the output voltage, and the switching devices will be subjected to excessive voltage, endangering the safe operation of the three-level NPC inverter. Therefore, measures must be taken to control the midpoint voltage balance. The literature "Research on the Midpoint Potential Control Strategy of Three-Level ANPC Converter" (Zhang Bo. [J]. New Technology of Electrical Engineering and Energy, 2016, 35(8): 1-7.) points out that the two redundant small vectors in the same position have opposite effects on the midpoint voltage, so the midpoint voltage balance can be controlled by reallocating the action time of the two redundant small vectors. However, there is no redundant small vector in a zero-vector starting SVPWM within a sampling period, and it is impossible to use the existing method of reallocating the action time of the redundant small vector to control the midpoint voltage balance.

[0009] In view of the problem that the traditional midpoint voltage balancing method is not applicable to zero-vector starting SVPWM, the patent "A midpoint potential balancing control method for zero-vector starting SVPWM" proposes a midpoint voltage balancing method applicable to zero-vector starting SVPWM by adjusting the duty cycle of the small vector with a longer action time among the two non-redundant small vectors. Under the action of zero-vector starting SVPWM, this method can effectively control the midpoint voltage to restore balance, thereby improving the reliability of the three-level NPC inverter. However, this method will cause an increase in current harmonics, and this method requires the use of a PI controller and the judgment of the current direction and phase angle area during the balance control process. The steps are complicated and will reduce the output harmonic performance of the three-level NPC inverter. In addition, since the implementation process of zero-vector starting SVPWM and zero-vector starting SVPWM based on carrier are not the same, this method is only designed for zero-vector starting SVPWM and is not applicable to zero-vector starting SVPWM based on carrier.

[0010] Therefore, how to provide a solution to the above technical problems is a problem that those skilled in the art need to solve. Summary of the invention

[0011] In view of this, the object of the present invention is to provide a zero-vector-starting SVPWM midpoint voltage balancing method, device, equipment and storage medium to improve the reliability of the three-level NPC inverter under the zero-vector-starting SVPWM based on the carrier and the output harmonic performance in the midpoint voltage balancing control process. The specific scheme is as follows:

[0012] A zero vector starting SVPWM midpoint voltage balancing method, comprising: obtaining a preset unbalance margin factor K and a DC side voltage U of the three-level inverter dc According to the three-level inverter DC side voltage U dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ; when U dc_dev Greater than K×U dc When U dc_dev Less than -K×U dc When the zero-sequence voltage of the zero vector starting SVPWM is corrected at the zero point of the triangle carrier, U zero The three-phase original modulation wave is injected into the three-level inverter.

[0013] Preferably, the DC side voltage U of the three-level inverter dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev , including: Calculate U using the following formula dc_dev :

[0014] U dc_dev =U dc -2U neu

[0015] Where U dc is the DC side voltage of the three-level inverter, U neu is the DC side midpoint voltage of the three-level inverter.

[0016] Preferably, the zero-sequence voltage of the zero-vector starting SVPWM is corrected at the peak value of the triangle carrier, including: if the direction of the triangle carrier in the current sampling period is the descending direction, and the direction of the triangle carrier in the previous sampling period is the ascending direction, U zero Corrected to (U min +U max -1) / 2; if the triangle carrier direction is rising in the current sampling period, and the triangle carrier direction is falling in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep Uzero unchanged; among them, U min is the minimum value of the three-phase original modulation wave, U max is the maximum value of the three-phase original modulation wave.

[0017] Preferably, the zero-sequence voltage of the zero vector starting SVPWM is corrected at the zero point of the triangle carrier, comprising: if the direction of the triangle carrier in the current sampling period is the rising direction, and the direction of the triangle carrier in the previous sampling period is the falling direction, U zero Corrected to -(U min +U max +1) / 2; if the triangle carrier direction is in the descending direction in the current sampling period, and the triangle carrier direction is in the ascending direction in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero unchanged; among them, U min is the minimum value of the three-phase original modulation wave, U max is the maximum value of the three-phase original modulation wave.

[0018] Preferably, the DC side voltage U of the three-level inverter dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev Afterwards, the method also includes: assigning values ​​to the triangular carrier direction flag Tcflag in the current sampling cycle and the triangular carrier direction flag Tcflag_pre in the previous sampling cycle based on the following steps: before assigning values ​​to Tcflag in the current sampling cycle, set Tcflag_pre=Tcflag; if the triangular carrier is in the rising direction in the current sampling cycle, assign Tcflag a value of 1; if the triangular carrier is in the falling direction in the current sampling cycle, assign Tcflag a value of -1.

[0019] Preferably, U zero Before injecting the three-phase original modulation wave into the three-level inverter, the method further comprises: when U dc_dev In-K×U dc With K×U dc When between 1 and 2, the three-phase level state of SVPWM output is set according to the zero vector starting state. zero : When the three-phase level state is OPO, set U zero =(U min +U max -1) / 2; when the three-phase level state is ONO, set U zero =-(U min +U max +1) / 2.

[0020] Preferably, the zero The three-phase original modulation wave injected into the three-level inverter includes: based on the following method: zero The three-phase original modulation wave injected into the three-level inverter is:

[0021]

[0022] Among them, U 1a is the original modulation wave of phase A, U 2a To inject U zero The A-phase modulation wave after that, U 1b is the original modulation wave of phase B, U 2b To inject U zero The B-phase modulation wave after that, U 1c is the original modulation wave of phase C, U 2c To inject U zero The C-phase modulation wave after that.

[0023] Correspondingly, the present application also discloses a zero-vector starting SVPWM midpoint voltage balancing device, comprising: an acquisition module for acquiring a preset unbalance margin factor K and a DC side voltage U of the three-level inverter. dc ; A calculation module for calculating the DC side voltage U of the three-level inverter dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ; The first correction module is used when U dc_dev Greater than K×U dc When U dc_dev Less than -K×U dc When the zero-sequence voltage of the zero vector starting SVPWM is corrected at the zero point of the triangle carrier, the injection module is used to inject U zero The three-phase original modulation wave is injected into the three-level inverter.

[0024] Correspondingly, the present application also discloses a zero-vector starting SVPWM midpoint voltage balancing device, comprising: a memory for storing a computer program; a processor for implementing the steps of the zero-vector starting SVPWM midpoint voltage balancing method as described in any one of the above items when executing the computer program.

[0025] Correspondingly, the present application also discloses a readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the zero-vector starting SVPWM midpoint voltage balancing method as described in any one of the above items are implemented.

[0026] The present application discloses a zero vector starting SVPWM midpoint voltage balancing method, which is characterized by comprising: obtaining a preset unbalance margin factor K and a DC side voltage U of the three-level inverter. dc ; According to the three-level inverter DC side voltage U dc The unbalanced value of the midpoint voltage of the three-level inverter U is calculated by the midpoint voltage of the DC side of the three-level inverter. dc_dev ; when U dc_dev Greater than K×U dc When U dc_dev Less than -K×U dc When the zero-sequence voltage of the zero vector starting SVPWM is corrected at the zero point of the triangle carrier, U zero The three-phase original modulation wave of the three-level inverter is injected. When the midpoint voltage imbalance value is positive or negative, the present application realizes midpoint voltage balance control by correcting the zero-sequence voltage, thereby improving the reliability of the three-level NPC inverter under the action of zero-vector starting SVPWM based on carrier; and in the midpoint voltage balance control process, the present application can significantly reduce the three-phase current THD, thereby improving the output harmonic performance of the three-level NPC inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0028] Figure 1 It is a main circuit topology diagram of a three-level inverter in the prior art;

[0029] Figure 2 is a spatial vector diagram of a three-level inverter in the prior art;

[0030] Figure 3 It is a flow chart of a zero-vector-starting SVPWM midpoint voltage balancing method based on carrier wave implementation according to the first embodiment of the present invention;

[0031] Figure 4 It is a flow chart of a method for balancing the midpoint voltage of a zero-vector-started SVPWM based on a carrier wave according to a second embodiment of the present invention;

[0032] Figure 5 It is a schematic diagram of simulation experiment results of zero vector starting SVPWM without adding a midpoint voltage balancing method based on carrier wave implementation in the prior art;

[0033] Figure 6a , Figure 6b It is a schematic diagram of the simulation experiment results of the zero vector starting SVPWM using the patented method "A zero vector starting SVPWM midpoint potential balance control method";

[0034] Figure 7a , Figure 7b , Figure 8 It is a schematic diagram of simulation experiment results of the second embodiment of the present invention;

[0035] Fig. 9 It is a flow chart of a method for balancing the midpoint voltage of a zero-vector-started SVPWM based on carrier wave according to the third embodiment of the present invention;

[0036] Fig.10 It is a schematic diagram of simulation experimental results of the deviation of the midpoint voltage under the changing modulation ratio when the zero vector starting SVPWM modulation strategy based on carrier is adopted in the prior art;

[0037] Fig.11 It is a schematic diagram of the first simulation experiment result of the third embodiment of the present invention;

[0038] Fig.12 It is a schematic diagram of simulation experimental results of the deviation of the midpoint voltage under the changing fundamental frequency when the zero vector starting SVPWM modulation strategy based on carrier wave is adopted in the prior art;

[0039] Fig.13 It is a schematic diagram of the second simulation experiment result of the third embodiment of the present invention;

[0040] Fig.14 The structure distribution diagram of a zero-vector-started SVPWM midpoint voltage balancing device based on carrier wave implementation in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0042] The first embodiment of the present invention discloses a zero vector starting SVPWM midpoint voltage balancing method based on carrier wave implementation, see Figure 3 As shown, including:

[0043] S11: Obtaining a preset unbalance margin factor K and a DC side voltage U of the three-level inverter dc ;

[0044] In this step, the unbalance margin factor K is a parameter set in advance and can be selected according to actual working conditions.

[0045] S12: According to the DC side voltage U of the three-level inverter dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ;

[0046] S13: Judge U dc_dev Is it greater than K×U dc , if yes, go to step S14, if no, go to step S15;

[0047] S14: Correct the zero-sequence voltage U of the zero-vector starting SVPWM at the peak of the triangle carrier zero , and go to step S17

[0048] S15: Judge U dc_dev Is it less than -K×U dc , if yes, go to step S16, if no, go to step S17;

[0049] S16: Correct the zero-sequence voltage U of the zero-vector starting SVPWM at the zero point of the triangle carrier zero , and go to step S17;

[0050] S17: U zero The three-phase original modulation wave is injected into the three-level inverter.

[0051] It can be understood that if the midpoint voltage unbalance value is not greater than K×U dc or not less than -K×U dc , then the midpoint voltage is balanced at this time, and step S5 does not need to be executed. The original control strategy can be executed to control the three-level converter with the three-phase original modulation wave. The deviation threshold is a parameter set in advance and can be selected according to the actual working conditions.

[0052] Preferably, in step S12 of this embodiment, U can be calculated by the following formula: dc_dev :

[0053] U dc_dev =U dc -2U neu

[0054] Where U dc is the DC side voltage of the three-level inverter, U neu is the DC side midpoint voltage of the three-level inverter.

[0055] Preferably, in step S17 of this embodiment, U can be converted intozero The three-phase original modulation wave injected into the three-level inverter is:

[0056]

[0057] Among them, U 1a is the original modulation wave of phase A, U 2a To inject U zero The A-phase modulation wave after that, U 1b is the original modulation wave of phase B, U 2b To inject U zero The B-phase modulation wave after that, U 1c is the original modulation wave of phase C, U 2c To inject U zero The C-phase modulation wave after that.

[0058] In this embodiment, when the midpoint voltage imbalance value is positive or negative, the midpoint voltage balance control is achieved by correcting the zero-sequence voltage, thereby improving the reliability of the three-level NPC inverter under the action of zero-vector starting SVPWM based on the carrier; and in the process of midpoint voltage balance control, the present application can significantly reduce the three-phase current THD, thereby improving the output harmonic performance of the three-level NPC inverter.

[0059] The second embodiment of the present invention discloses a carrier-based zero-vector-start SVPWM midpoint voltage balancing method. The second embodiment is a further improvement of the first embodiment, and the improvement is that a specific method for correcting the zero-sequence voltage of the first embodiment is specifically provided, such as Figure 4 As shown, the following steps are included:

[0060] S21: Obtaining a preset unbalance margin factor K and a DC side voltage U of the three-level inverter dc ;

[0061] S22: According to the three-level inverter DC side voltage U dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ;

[0062] S23: Judge U dc_dev Is it greater than K×U dc , if yes, go to step S24, if no, go to step S27;

[0063] S24: Determine whether the condition "Tcflag = -1 and Tcflag_pre = 1" is met. If yes, proceed to step S25; if no, proceed to step S26;

[0064] S25: Correction of U at the peak of the triangle carrier zeroCorrected to (U min +U max -1) / 2, go to step S210;

[0065] S26: No zero Make corrections and go to step S211;

[0066] S27: Judgement U dc_dev Is it less than -K×U dc , if yes, go to step S28, if no, go to step S210;

[0067] S28: Determine whether the condition "Tcflag=1 and Tcflag_pre=-1" is met, if yes, go to step S29, if no, go to step S210;

[0068] S29: At the zero point of the triangle carrier, U zero Corrected to -(U min +U max +1) / 2, go to step S211;

[0069] S210: No zero Make corrections and go to step S211;

[0070] S211: U zero The three-phase original modulation wave is injected into the three-level inverter.

[0071] It should be noted that in step S24, U min is the minimum value of the three-phase original modulation wave, U max is the maximum value of the three-phase original modulation wave, Tcflag is the triangle carrier direction flag in the current sampling cycle, and Tcflag_pre is the triangle carrier direction flag in the previous sampling cycle. In this embodiment, the following method is used to assign values ​​to Tcflag and Tcflag_pre: before assigning values ​​to Tcflag in the current sampling cycle, let Tcflag_pre = Tcflag; if the triangle carrier is in the rising direction in the current sampling cycle, assign Tcflag to 1; if the triangle carrier is in the falling direction in the current sampling cycle, assign Tcflag to -1. In step S24, satisfying the condition of "Tcflag = -1 and Tcflag_pre = 1" means that the triangle carrier is in the falling direction in the current sampling cycle and the triangle carrier is in the rising direction in the previous sampling cycle. It can be understood that the key condition for correcting the zero-sequence voltage of the zero-vector starting SVPWM at the peak value of the triangle carrier is the direction of the triangle carrier in the current sampling cycle and the direction of the triangle carrier in the previous sampling cycle. Specifically, if the direction of the triangle carrier in the current sampling cycle is in the falling direction, and the direction of the triangle carrier in the previous sampling cycle is in the rising direction, Uzero Corrected to (U min +U max -1) / 2; if the triangle carrier direction is rising in the current sampling period, and the triangle carrier direction is falling in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero constant.

[0072] Similarly, step S28 is consistent with the principle of step S24, and also determines the direction of the triangle carrier in the current sampling cycle and the direction of the triangle carrier in the previous sampling cycle by assigning values ​​to Tcflag and Tcflag_pre. In step S28, satisfying the condition of "Tcflag = 1 and Tcflag_pre = -1" means that the triangle carrier in the current sampling cycle is in the rising direction and the triangle carrier in the previous sampling cycle is in the falling direction. It can be understood that the key condition for correcting the zero-sequence voltage of the zero-vector starting SVPWM at the zero point of the triangle carrier is the direction of the triangle carrier in the current sampling cycle and the direction of the triangle carrier in the previous sampling cycle. Specifically, if the direction of the triangle carrier in the current sampling cycle is in the rising direction and the direction of the triangle carrier in the previous sampling cycle is in the falling direction, U zero Corrected to -(U min +U max +1) / 2; if the triangle carrier direction is in the descending direction in the current sampling period, and the triangle carrier direction is in the ascending direction in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero constant

[0073] In this embodiment, the assignment method is used to determine the direction of the triangular carrier in the current sampling period and the direction of the triangular carrier in the previous sampling period. Those skilled in the art can determine the direction of the triangular carrier in the current sampling period and the direction of the triangular carrier in the previous sampling period based on different methods. Such implementation should not be considered to exceed the scope of the present invention.

[0074] In a specific embodiment, a three-level NPC inverter model is built with the help of PSIM software, and the effectiveness of the zero-vector starting SVPWM midpoint voltage balancing method based on carrier implementation of the present invention is verified by simulation. The simulation conditions of the embodiment are: the simulation step size is set to 2us, the DC side voltage is set to 5000V, the DC side capacitance is 16.2mF, the carrier frequency is set to 600Hz, the fundamental frequency is set to 15Hz, the modulation ratio is 0.2, and the output load is a 1.6Ω resistor in series with a 12.73mH inductor.

[0075] Figure 5The initial voltage of the upper bridge arm capacitor on the DC side of the embodiment is 3500V, the initial voltage of the lower bridge arm capacitor is 1500V, the midpoint voltage unbalance value, phase voltage, modulation wave and output current when the zero vector starting SVPWM implemented based on the carrier does not add the midpoint voltage balance method. Figure 4 It can be seen that when the zero-vector-start SVPWM based on carrier implementation does not add the midpoint voltage balancing method, the midpoint voltage imbalance value of the three-level NPC inverter will always exist. The unbalanced midpoint voltage will generate low-order harmonics in the output voltage and cause the switching devices to withstand excessive voltage, endangering the operation safety of the three-level NPC inverter.

[0076] Figure 6a , Figure 6b The simulation results of the embodiment when the initial voltage of the upper bridge arm capacitor on the DC side is 3500V and the initial voltage of the lower bridge arm capacitor is 1500V and the zero vector starting SVPWM midpoint voltage balance control method is used; wherein, Figure 6a is the unbalanced value of midpoint voltage, phase voltage and output current, Figure 6b is the THD of the three-phase output current during the midpoint voltage balance process. Figure 6a It can be seen that when the modulation strategy of the three-level NPC inverter is zero-vector starting SVPWM and the midpoint voltage is unbalanced, the midpoint voltage can be effectively controlled to restore balance by using the method proposed in the patent "A Zero-vector Starting SVPWM Midpoint Potential Balance Control Method". Figure 6b It is shown that this method will increase the THD of the three-phase current and reduce the output harmonic performance of the three-level NPC inverter. In addition, this method needs to use a PI controller in the balance control process and needs to judge the current direction and phase angle area, which makes the implementation steps complicated. In addition, this method is only applicable to zero-vector starting SVPWM and cannot be directly applied to zero-vector starting SVPWM based on carrier. Figure 5 , Figure 6a and Figure 6b The simulation results show that in order to improve the reliability of the three-level NPC inverter when using the zero-vector starting SVPWM based on the carrier and improve the output harmonic performance of the three-level NPC inverter during the midpoint voltage balancing process, it is necessary to design a midpoint voltage balancing method suitable for the zero-vector starting SVPWM based on the carrier.

[0077] Figure 7a , Figure 7b The initial voltage of the upper bridge arm capacitor of the DC side of the embodiment is 3500V, the initial voltage of the lower bridge arm capacitor is 1500V, the unbalance margin factor K is set to 0.05, and the simulation result when the midpoint voltage balancing method of the present invention is added to the zero vector starting SVPWM realized based on the carrier is shown in FIG. Figure 7a is the midpoint voltage unbalance value, phase voltage, modulation wave and output current, Figure 7bis the THD of the three-phase output current during the midpoint voltage balance process. Figure 7a It can be seen that when the midpoint voltage deviation value is 2000V and the unbalance margin factor K is 0.05, after adding the midpoint voltage balancing method of the present invention, the zero-sequence voltage is corrected to (U min +U max -1) / 2, the midpoint voltage unbalance value of the three-level NPC inverter can be effectively reduced to within 5% of the DC side voltage value. Therefore, the method of the present invention can achieve midpoint voltage balance control when the midpoint voltage unbalance value is positive. In addition, compared Figure 7b and Figure 6b It can be seen that the method of the present invention can significantly reduce the THD of the three-phase current while balancing the midpoint voltage, thereby improving the output harmonic performance of the three-level NPC inverter during the midpoint voltage balance control process.

[0078] Figure 8 In the embodiment, the initial voltage of the upper bridge arm capacitor on the DC side is 1500V, the initial voltage of the lower bridge arm capacitor is 3500V, the unbalance margin factor K is set to 0.03, and the midpoint voltage unbalance value, phase voltage, modulation wave and output current when the midpoint voltage balancing method of the present invention is added to the zero vector starting SVPWM realized based on the carrier are obtained. Figure 8 It can be seen that when the midpoint voltage deviation value is -2000V and the unbalance margin factor K is 0.03, the zero-vector starting SVPWM based on the carrier is corrected to -(U min +U max +1) / 2, the midpoint voltage unbalance value of the three-level NPC inverter can be reduced to within 3% of the DC side voltage value. Therefore, the method of the present invention can effectively realize midpoint voltage balance control when the midpoint voltage unbalance value is negative, thereby improving the reliability and safety of the three-level NPC inverter.

[0079] In this embodiment, when the midpoint voltage imbalance value is positive or negative, the midpoint voltage balance control is achieved by correcting the zero-sequence voltage, and a specific method for correcting the zero-sequence voltage is provided, thereby improving the reliability of the three-level NPC inverter under the action of the zero-vector starting SVPWM based on the carrier; and in the process of midpoint voltage balance control, the present application can significantly reduce the three-phase current THD, thereby improving the output harmonic performance of the three-level NPC inverter.

[0080] The third embodiment of the present invention discloses a zero vector starting SVPWM midpoint voltage balancing method based on carrier wave. The third embodiment is a further improvement of the second embodiment. The improvement is that when U zero Before injecting the three-phase original modulation wave into the three-level inverter, a new step is added: "When U dc_devIn-K×U dc With K×U dc When between 1 and 2, the three-phase level state of SVPWM output is set according to the zero vector starting state. zero ",like Fig. 9 As shown, the specific steps include:

[0081] S31: Obtaining a preset unbalance margin factor K and a DC side voltage U of the three-level inverter dc ;

[0082] S32: According to the three-level inverter DC side voltage U dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ;

[0083] S33: Judge U dc_dev Is it greater than K×U dc , if yes, go to step S34, if no, go to step S37;

[0084] S34: Determine whether the condition "Tcflag = -1 and Tcflag_pre = 1" is met. If yes, jump to step S35; if not, jump to step S36;

[0085] S35: Correction of U at the peak of the triangle carrier zero Corrected to (U min +U max -1) / 2, go to step S314;

[0086] S36: No zero Make corrections and jump to step S314;

[0087] S37: Judge U dc_dev Is it less than -K×U dc , if yes, go to step S38, if no, go to step S314;

[0088] S38: Determine whether the condition "Tcflag=1 and Tcflag_pre=-1" is met. If yes, go to step S39; if no, go to step S310;

[0089] S39: At the zero point of the triangle carrier, U zero Corrected to -(U min +U max +1) / 2, jump to step S313;

[0090] S310: No U zero Make corrections and jump to step S313;

[0091] S311: Determine whether the zero vector starting SVPWM output three-phase level state is OPO, if yes, jump to step S312, if no, jump to step S313;

[0092] S312: Setting U zero =(U min +U max -1) / 2;

[0093] S313: Setting U zero =-(U min +U max +1) / 2;

[0094] S314: U zero The three-phase original modulation wave is injected into the three-level inverter.

[0095] In a specific embodiment, a three-level NPC inverter model is built with the help of PSIM software, and the effectiveness of the zero-vector starting SVPWM midpoint voltage balancing method based on carrier implementation of the present invention is verified by simulation. The simulation conditions of the embodiment are: the simulation step size is set to 2us, the DC side voltage is set to 5000V, the DC side capacitance is 16.2mF, the carrier frequency is set to 600Hz, the fundamental frequency is set to 15Hz, the modulation ratio is 0.2, and the output load is a 1.6Ω resistor in series with a 12.73mH inductor (the basic conditions of the simulation experiment are the same as those of the second embodiment).

[0096] Fig.10 In the embodiment, the initial voltage of the upper bridge arm capacitor on the DC side is 3500V, the initial voltage of the lower bridge arm capacitor is 1500V, the modulation ratio varies from 0 to 0.3, and the midpoint voltage unbalance value, phase voltage, modulation wave and output current are obtained when the zero vector starting SVPWM implemented based on the carrier does not add the midpoint voltage balancing method. Fig.10 The results show that when the modulation strategy of the three-level NPC inverter is the zero-vector starting SVPWM based on carrier, if the midpoint voltage deviates under the changing modulation ratio, without adding the midpoint voltage balancing method, the midpoint voltage unbalance value of the three-level NPC inverter will always exist, endangering the operation safety of the three-level NPC inverter.

[0097] Fig.11 The initial voltage of the upper bridge arm capacitor of the DC side is 3500V, the initial voltage of the lower bridge arm capacitor is 1500V, the modulation ratio varies from 0 to 0.3, the unbalance margin factor K is set to 0.05, and the midpoint voltage unbalance value, phase voltage, modulation wave and output current when the midpoint voltage balancing method of the present invention is added to the zero vector starting SVPWM based on the carrier are compared. Fig.11 and Fig.10, setting the unbalance margin factor K to 0.05, after adding the midpoint voltage balancing method of the present invention to the zero vector starting SVPWM implemented based on the carrier, the midpoint voltage unbalance value of the three-level NPC inverter can be reduced to within 5% of the DC side voltage value under a variable modulation ratio. Therefore, the method of the present invention can effectively realize the midpoint voltage balance control under a variable modulation ratio.

[0098] Fig.12 In the embodiment, the initial voltage of the upper bridge arm capacitor on the DC side is 1500V, the initial voltage of the lower bridge arm capacitor is 3500V, the fundamental frequency varies from 5Hz to 25Hz, the midpoint voltage unbalance value, phase voltage, modulation wave and output current when the zero vector starting SVPWM implemented based on the carrier does not add the midpoint voltage balancing method. Fig.12 The results show that when the modulation strategy of the three-level NPC inverter is the zero-vector starting SVPWM based on carrier, if the midpoint voltage deviates under the changing fundamental frequency, without adding the midpoint voltage balancing method, the midpoint voltage unbalance value of the three-level NPC inverter will always exist, endangering the operation safety of the three-level NPC inverter.

[0099] Fig.13 In the embodiment, the initial voltage of the upper bridge arm capacitor on the DC side is 1500V, the initial voltage of the lower bridge arm capacitor is 3500V, the fundamental frequency changes from 5Hz to 25Hz, the unbalance margin factor K is set to 0.03, and the midpoint voltage unbalance value, phase voltage, modulation wave and output current when the midpoint voltage balancing method of the present invention is added to the zero vector starting SVPWM realized based on the carrier are compared. Fig.13 and Fig.12 , setting the unbalance margin factor K to 0.03, after adding the midpoint voltage balancing method of the present invention to the zero vector starting SVPWM implemented based on the carrier, the midpoint voltage unbalance value of the three-level NPC inverter can be reduced to within 3% of the DC side voltage value under the changing fundamental frequency. Therefore, the method of the present invention can effectively realize the midpoint voltage balance control under the changing fundamental frequency.

[0100] Further analysis Figure 7a , Figure 8 , Fig.11 and Fig.13 The method of the present invention completes the midpoint voltage balance control of the zero-vector starting SVPWM based on the carrier by correcting the zero-sequence voltage. In the balance control process, no PI controller is required and no current direction and phase angle area need to be determined. Therefore, the method of the present invention has the advantages of simple steps and easy implementation.

[0101] The results of this embodiment verify the effectiveness of the zero-vector-start SVPWM midpoint voltage balancing method of the present invention based on carrier wave implementation. When the midpoint voltage imbalance value is positive or negative, when the modulation ratio and fundamental frequency are fixed or changed, the method of the present invention can achieve midpoint voltage balance control by correcting the zero-sequence voltage, which improves the safety and reliability of the three-level NPC inverter under the action of zero-vector-start SVPWM based on carrier wave implementation. In the midpoint voltage balance control process, the method of the present invention can significantly reduce the three-phase current THD, thereby improving the output harmonic performance of the three-level NPC inverter. In addition, the method of the present invention does not require a PI controller and does not require the judgment of the current direction and phase angle region, and it also has the advantages of simple steps and easy implementation.

[0102] Correspondingly, the embodiment of the present application also discloses a zero vector starting SVPWM midpoint voltage balancing device based on carrier wave implementation, see Fig.14 As shown, including:

[0103] The acquisition module 1 is used to obtain the preset unbalance margin factor K and the DC side voltage U of the three-level inverter. dc ;

[0104] Calculation module 2, used for calculating the DC side voltage U of the three-level inverter according to dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ;

[0105] The first correction module 3 is used when U dc_dev Greater than K×U dc When , the zero-sequence voltage of the zero-vector starting SVPWM is corrected at the peak of the triangle carrier;

[0106] The second correction module 4 is used when U dc_dev Less than -K×U dc When , the zero-sequence voltage of the zero-vector starting SVPWM is corrected at the zero point of the triangle carrier;

[0107] Injection module 5, used to inject U zero The three-phase original modulation wave is injected into the three-level inverter.

[0108] When the midpoint voltage imbalance value is positive or negative, the present application realizes midpoint voltage balance control by correcting the zero-sequence voltage, thereby improving the reliability of the three-level NPC inverter under the action of zero-vector starting SVPWM based on carrier; and, in the process of midpoint voltage balance control, the present application can significantly reduce the three-phase current THD, thereby improving the output harmonic performance of the three-level NPC inverter.

[0109] In some specific embodiments, the calculation module 2 is specifically used for:

[0110] The following formula is used to calculate U dc_dev :

[0111] U dc_dev =U dc -2U neu

[0112] Where U dc is the DC side voltage of the three-level inverter, U neu is the DC side midpoint voltage of the three-level inverter.

[0113] In some specific embodiments, the first correction module 3 is specifically used to: if the direction of the triangle carrier in the current sampling period is the descending direction, and the direction of the triangle carrier in the previous sampling period is the ascending direction, U zero Corrected to (U min +U max -1) / 2; if the triangle carrier direction is rising in the current sampling period, and the triangle carrier direction is falling in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero unchanged; among them, U min is the minimum value of the three-phase original modulation wave, U max is the maximum value of the three-phase original modulation wave.

[0114] In some specific embodiments, the second correction module 4 is specifically used to: if the direction of the triangle carrier in the current sampling period is the rising direction, and the direction of the triangle carrier in the previous sampling period is the falling direction, U zero Corrected to -(U min +U max +1) / 2; if the triangle carrier direction is in the descending direction in the current sampling period, and the triangle carrier direction is in the ascending direction in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero unchanged; among them, U min is the minimum value of the three-phase original modulation wave, U max is the maximum value of the three-phase original modulation wave.

[0115] In some specific embodiments, the zero-vector starting SVPWM midpoint voltage balancing device also includes an assignment module, which is used to assign a triangle carrier direction flag Tcflag in the current sampling cycle and a triangle carrier direction flag Tcflag_pre in the previous sampling cycle based on the following steps: before assigning Tcflag in the current sampling cycle, set Tcflag_pre=Tcflag; if the triangle carrier is in an ascending direction in the current sampling cycle, assign Tcflag a value of 1; if the triangle carrier is in a descending direction in the current sampling cycle, assign Tcflag a value of -1.

[0116] In some specific embodiments, the zero vector starting SVPWM midpoint voltage balancing device further includes a setting module, wherein the setting module is used to set the voltage balancing device to the zero vector starting SVPWM midpoint voltage balancing device. dc_dev In-K×U dc With K×U dc When between 1 and 2, the three-phase level state of SVPWM output is set according to the zero vector starting state. zero : When the three-phase level state is OPO, set U zero =(U min +U max -1) / 2; when the three-phase level state is ONO, set U zero =-(U min +U max +1) / 2.

[0117] Accordingly, the embodiment of the present application further discloses a zero-vector starting SVPWM midpoint voltage balancing device, comprising:

[0118] Memory for storing computer programs;

[0119] A processor is used to implement the steps of the zero-vector-started SVPWM midpoint voltage balancing method as described in any of the above embodiments when executing the computer program.

[0120] Correspondingly, an embodiment of the present application further discloses a readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the zero-vector starting SVPWM midpoint voltage balancing method as in any of the above embodiments are implemented.

[0121] For details about the zero-vector-starting SVPWM midpoint voltage balancing method, please refer to the relevant description in the above embodiment, which will not be repeated here.

[0122] Among them, the zero-vector-starting SVPWM midpoint voltage balancing device and the readable storage medium described in this embodiment have the same technical effects as the zero-vector-starting SVPWM midpoint voltage balancing method described in the above embodiments, and will not be repeated here.

[0123] Finally, it should be noted that, in this article, 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 "include", "comprise" 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, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0124] The above is a detailed introduction to a zero-vector starting SVPWM midpoint voltage balancing method, system and related components provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A zero vector starting SVPWM midpoint voltage balancing method, characterized in that: include: Obtain the preset unbalance margin factor K and the DC side voltage U of the three-level inverter dc ; According to the three-level inverter DC side voltage U dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ; When U dc_dev Greater than K×U dc When the triangle carrier direction is in the descending direction in the current sampling period, and the triangle carrier direction is in the ascending direction in the previous sampling period, U zero Corrected to (U min +U max -1) / 2; if the triangle carrier direction is rising in the current sampling period, and the triangle carrier direction is falling in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero constant; When U dc_dev Less than -K×U dc When the triangle carrier direction is rising in the current sampling period and the triangle carrier direction is falling in the previous sampling period, U zero Corrected to -(U min +U max +1) / 2; if the triangle carrier direction is in the descending direction in the current sampling period, and the triangle carrier direction is in the ascending direction in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero unchanged; U min is the minimum value of the original three-phase modulation wave, U max is the maximum value of the three-phase original modulation wave; Will U zero The three-phase original modulation wave is injected into the three-level inverter.

2. The zero-vector-starting SVPWM midpoint voltage balancing method according to claim 1, characterized in that: The DC side voltage U of the three-level inverter dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ,include: The following formula is used to calculate U dc_dev : IN dc_dev =U dc -2U neu Where U dc is the DC side voltage of the three-level inverter, U neu is the DC side midpoint voltage of the three-level inverter.

3. The zero-vector-starting SVPWM midpoint voltage balancing method according to claim 1, characterized in that: The DC side voltage U of the three-level inverter dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev Afterwards, the method further comprises: The triangular carrier direction flag bit Tcflag in the current sampling period and the triangular carrier direction flag bit Tcflag_pre in the previous sampling period are assigned values ​​based on the following steps: Before assigning a value to Tcflag in the current sampling cycle, set Tcflag_pre = Tcflag; If the triangular carrier is in the rising direction in the current sampling period, Tcflag is assigned a value of 1; If the triangular carrier is in the descending direction in the current sampling period, Tcflag is assigned a value of -1.

4. The zero-vector-starting SVPWM midpoint voltage balancing method according to claim 1, characterized in that: Will U zero Before injecting the three-phase original modulation wave of the three-level inverter, the method further includes: When U dc_dev In-K×U dc With K×U dc When between 1 and 2, the three-phase level state of SVPWM output is set according to the zero vector starting state. zero : When the three-phase level state is OPO, set U zero =(U min +U max -1) / 2; When the three-phase level state is ONO, set U zero =-(U min +U max +1) / 2.

5. The zero-vector-starting SVPWM midpoint voltage balancing method according to claim 1, characterized in that: The U zero The three-phase original modulation wave injected into the three-level inverter includes: Based on the following method, U zero The three-phase original modulation wave injected into the three-level inverter is: Among them, U 1a is the original modulation wave of phase A, U 2a To inject U zero The A-phase modulation wave after that, U 1b is the original modulation wave of phase B, U 2b To inject U zero The B-phase modulation wave after that, U 1c is the original modulation wave of phase C, U 2c To inject U zero The C-phase modulation wave after that.

6. A zero vector starting SVPWM midpoint voltage balancing device, characterized in that: include: An acquisition module is used to obtain a preset unbalance margin factor K and a DC side voltage U of a three-level inverter. dc ; A calculation module is used to calculate the DC side voltage U of the three-level inverter according to the dc The midpoint voltage unbalance value U of the three-level inverter is calculated by using the midpoint voltage of the DC side of the three-level inverter. dc_dev ; The first correction module is used when U dc_dev Greater than K×U dc When the triangle carrier direction is in the descending direction in the current sampling period, and the triangle carrier direction is in the ascending direction in the previous sampling period, U zero Corrected to (U min +U max -1) / 2; if the triangle carrier direction is rising in the current sampling period, and the triangle carrier direction is falling in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero constant; The second correction module is used when U dc_dev Less than -K×U dc When the triangle carrier direction is rising in the current sampling period and the triangle carrier direction is falling in the previous sampling period, U zero Corrected to -(U min +U max +1) / 2; if the triangle carrier direction is in the descending direction in the current sampling period, and the triangle carrier direction is in the ascending direction in the previous sampling period, keep U zero If the direction of the triangle carrier in the current sampling period is the same as that in the previous sampling period, keep U zero unchanged; U min is the minimum value of the original three-phase modulation wave, U max is the maximum value of the three-phase original modulation wave; Injection module, used to inject U zero The three-phase original modulation wave is injected into the three-level inverter.

7. A zero vector starting SVPWM midpoint voltage balancing device, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the steps of the zero-vector-started SVPWM midpoint voltage balancing method as claimed in any one of claims 1 to 5 when executing the computer program.

8. A readable storage medium, characterized in that: The readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the zero-vector-started SVPWM midpoint voltage balancing method according to any one of claims 1 to 5 are implemented.

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