Common-mode voltage elimination and midpoint voltage cooperative control method and device, and electronic equipment

Abstract

This invention discloses a common-mode voltage cancellation and midpoint voltage coordinated control method, device, and electronic equipment for controlling an even-array three-phase three-level NPC converter sharing a common midpoint. The method uses a dual three-phase three-level NPC converter as the smallest control unit. First, it determines the dynamic carrier phase-shift modulation mode based on two sets of three-phase modulation waves to cancel out the common-mode voltage transitions generated by the two sets of three phases. Then, it obtains the total target average midpoint current based on the shared midpoint voltage feedback and distributes it to each control unit. Next, it calculates the zero-sequence voltage reference value for each control unit based on the modulation wave and the output phase current, and superimposes zero-sequence voltages of equal magnitude but opposite polarity onto the two sets of three-phase modulation waves to obtain a corrected modulation wave. Finally, based on the corrected modulation wave, it generates PWM drive signals for each phase according to the dynamic carrier phase-shift modulation mode, achieving total common-mode voltage cancellation and midpoint voltage balance. This method is suitable for coordinated control scenarios involving multiple dual three-phase control units.

Description

Technical Field

[0001] This application relates to the field of modulation and control technology of multiphase multilevel converters, specifically to a common-mode voltage elimination and neutral point voltage coordinated control method and device, and electronic equipment, for an even-array three-phase three-level NPC converter with a shared neutral point. Background Technology

[0002] Even-array three-phase three-level NPC converters with a shared neutral point consist of multiple three-phase units, combining the technical characteristics of multiphase systems and three-level NPC topologies. They offer advantages such as high output quality, low device voltage stress, large power capacity, and high reliability, making them promising for high-performance AC power conversion applications. Among these, the dual three-phase three-level NPC converter represents the basic configuration of even-array three-phase three-level NPC converters with a shared neutral point and serves as a crucial foundation for studying the modulation and control of such systems.

[0003] In the operation of an even-array three-phase three-level NPC converter sharing a common midpoint, common-mode voltage suppression and midpoint voltage balance are two key issues that need to be addressed. On the one hand, common-mode voltage can generate shaft voltage in the motor drive system and further induce shaft current, which can easily lead to bearing electrolytic corrosion and affect the reliability of system operation. On the other hand, the midpoint voltage on the DC side of the three-level NPC topology is easily affected by switching states and phase current distribution, resulting in uneven voltage distribution on devices and increased output voltage distortion, thus affecting the stable operation of the system. For an even-array three-phase three-level NPC system composed of multiple dual three-phase control units sharing a common DC side midpoint, the midpoint voltage fluctuation is also affected by the combined influence of the midpoint current distribution relationship of each control unit, making its control problem even more complex.

[0004] Extensive research has been conducted on the common-mode voltage suppression problem in dual three-phase two-level systems. Alcaide et al. proposed a method to reduce common-mode voltage and current by applying a specific phase shift between the two inverter modulation strategies in dual three-phase voltage source inverters. Furthermore, Shen et al. proposed a modulation method for eliminating common-mode voltage in a six-phase system powered by dual two-level inverters by shifting the PWM signal using a cyclic sequence. On the other hand, considerable research has also been conducted on the midpoint voltage balance and common-mode voltage suppression problems of three-level NPC converters. Vu et al. proposed a virtual space vector modulation method that can simultaneously achieve common-mode voltage elimination and midpoint voltage balance in a three-level NPC inverter; subsequently, Xia et al. proposed a three-level NPC modulation strategy that balances active midpoint voltage balance and common-mode voltage suppression.

[0005] However, the even-array three-phase three-level NPC converter with a shared neutral point is not simply a superposition of multiple dual three-phase systems and a three-level NPC topology. When the dual three-phase three-level NPC converter is used as the smallest control unit, a clear coupling relationship exists between common-mode voltage elimination and neutral-point voltage balance: achieving common-mode voltage elimination imposes constraints on the modulation relationship of the two sets of three phases within the control unit, thus compressing the degree of freedom in neutral-point voltage regulation; conversely, neutral-point voltage regulation affects the common-mode voltage elimination effect. When this approach is further extended to even-array three-phase three-level NPC systems with a shared neutral point, especially when multiple dual three-phase control units share the DC-side neutral point, it is also necessary to coordinate the neutral-point current distribution relationship between the control units from the perspective of the entire system to balance common-mode voltage elimination and neutral-point voltage balance.

[0006] Currently, there is relatively little research on the coordinated control of common-mode voltage elimination and neutral-point voltage balance in dual three-phase three-level NPC converters. Lu et al. proposed a modulation method that balances neutral-point voltage fluctuation suppression and common-mode voltage elimination in dual three-phase three-level systems. However, its neutral-point voltage balance control is mainly based on a dual-modulation wave strategy, which is implemented separately for each group of three-phase units. It does not fully utilize the characteristics of the dual three-phase system from the perspective of unified control of the DC side of the dual three-phase three-level system. At the same time, this method also introduces high switching losses, thus its versatility is still limited. For the further extended even-group three-phase three-level NPC system with a shared neutral point, existing methods still lack a unified and effective solution in terms of multi-control unit coordination, neutral-point current distribution, and integrated control of common-mode voltage elimination and neutral-point voltage balance.

[0007] Therefore, existing technologies still lack a unified solution for even-array three-phase three-level NPC converters with a common neutral point that can balance common-mode voltage elimination and neutral point voltage balance, and is applicable to the coordinated control of multiple dual three-phase control units. Summary of the Invention

[0008] In view of this, this application provides a common-mode voltage elimination and midpoint voltage coordinated control method, apparatus, and electronic device for an even-numbered three-phase three-level NPC converter sharing a common midpoint, wherein a dual three-phase three-level NPC converter is used as the smallest control unit. The method first uses dynamic carrier phase-shift modulation based on the modulation waves of the two sets of three phases within each dual three-phase control unit to cancel out the common-mode voltage transitions generated by one set of three phases with the reverse common-mode voltage transitions generated by the other set of three phases. Then, feedback adjustment is performed based on the shared midpoint voltage to obtain the total target average midpoint current, which is then weighted and distributed to each dual three-phase control unit. Further, a zero-sequence voltage reference value is obtained by combining the modulation waves and output phase currents of each control unit, and zero-sequence voltages of equal magnitude but opposite polarity are superimposed on the modulation waves of the two sets of three phases within the control unit to obtain a corrected modulation wave. Finally, based on the corrected modulation wave, a PWM drive signal is generated according to the dynamic carrier phase-shift modulation method, thereby achieving total common-mode voltage elimination and midpoint voltage balance under the coordinated action of multiple dual three-phase control units. This method requires no additional hardware and can improve system reliability and output performance.

[0009] According to a first aspect of the embodiments of this application, a common-mode voltage elimination and neutral-point voltage coordinated control method is provided, the method being used for the control of an even-array three-phase three-level NPC converter sharing a common neutral point, comprising: Within each control cycle, the modulation waves of each group of three phases of the even-numbered three-phase three-level NPC converter with the common neutral point are acquired, and the output phase current and common neutral point voltage of each group of three phases are collected. Each pair of three phases constitutes a dual three-phase control unit. Based on the modulation waves of the two sets of three phases in each of the dual three-phase control units, a dynamic carrier phase-shifting modulation method is adopted to make the common-mode voltage transition generated by one set of three phases in each of the dual three-phase control units cancel each other out with the reverse common-mode voltage transition generated by the other set of three phases. Feedback adjustment is performed on the common midpoint voltage to obtain the total target average midpoint current, and the current is distributed according to the weighting coefficients corresponding to each of the dual three-phase control units to obtain the target average midpoint current corresponding to each of the dual three-phase control units. Based on the modulation waves of the two sets of three corresponding phases in each of the dual three-phase control units and the corresponding output phase currents, the zero-sequence voltage reference value of each of the dual three-phase control units is obtained so that the deviation between the average midpoint current of each of the dual three-phase control units and the corresponding target average midpoint current is zero or minimized. Based on the zero-sequence voltage reference value of each of the dual three-phase control units, zero-sequence voltages of equal magnitude and opposite polarity are superimposed onto the two sets of three corresponding modulation waves in each of the dual three-phase control units to obtain the two sets of three corresponding corrected modulation waves in each of the dual three-phase control units. Based on the corrected modulation waves, PWM drive signals for each phase are generated according to the dynamic carrier phase-shift modulation method, and the PWM drive signals are applied to the even-numbered three-phase three-level NPC converter at the common midpoint.

[0010] Optionally, based on the modulation waves of the two sets of three phases in each of the dual three-phase control units, a dynamic carrier phase-shift modulation method is adopted to cancel out the common-mode voltage transition generated by one set of three phases and the reverse common-mode voltage transition generated by the other set of three phases in each of the dual three-phase control units, including: Based on the extreme value distribution relationship of the modulation waves of the two sets of three corresponding to each of the dual three-phase control units, the sector corresponding to the control cycle and the sorting sequence of the six-phase pulses are determined. Based on the sign and amplitude of the modulation waves of the two sets of three corresponding to each of the dual three-phase control units, the effective range width of the six-phase pulse is determined, and the rising edge time and falling edge time of the six-phase pulse are determined sequentially according to the sorting sequence, so that the falling edge of the previous pulse in adjacent pulses coincides with the rising edge of the next pulse, and the six-phase pulses are connected end to end in the control cycle. One phase is selected as a continuous reference phase, and a uniform shift is applied to the rising and falling edges of the six-phase pulses with reference to the continuous reference phase. The timing sequence of the six-phase pulses under the dynamic carrier phase-shift modulation method is determined based on the rising and falling edge times of the translated six-phase pulses.

[0011] Optionally, the shared midpoint voltage is adjusted by feedback to obtain the total target average midpoint current, and then allocated according to the weighting coefficients corresponding to each of the dual three-phase control units to obtain the target average midpoint current corresponding to each of the dual three-phase control units, including: Based on the deviation between the common midpoint voltage and the given value of the common midpoint voltage, feedback adjustment is performed to obtain the total target average midpoint current; Based on the adjustment capability, operating status, or preset allocation rules of each dual-three-phase control unit, the weight coefficient corresponding to each dual-three-phase control unit is determined, wherein the sum of each weight coefficient is 1; Based on the weighting coefficients corresponding to each of the dual three-phase control units, the total target average midpoint current is allocated to obtain the target average midpoint current corresponding to each of the dual three-phase control units.

[0012] Optionally, based on the modulation waves corresponding to the two sets of three phases within each of the dual three-phase control units and the corresponding output phase currents, the zero-sequence voltage reference value of each dual three-phase control unit is determined, so that the deviation between the average midpoint current of each dual three-phase control unit and the corresponding target average midpoint current is zero or minimized, including: Based on the value constraints of the modified modulation wave obtained by superimposing the two sets of three-phase modulation waves in each of the dual three-phase control units with zero-sequence voltages of equal magnitude and opposite polarity, the feasible range of zero-sequence voltage for each of the dual three-phase control units is determined. If the feasible range of zero-sequence voltage of a certain dual three-phase control unit is empty, then the reference value of zero-sequence voltage of the dual three-phase control unit is taken as zero; if the feasible range of zero-sequence voltage of a certain dual three-phase control unit is not empty, then the upper and lower boundaries of the feasible range of zero-sequence voltage of the dual three-phase control unit and the zero-sequence voltage values ​​that cause the segmentation characteristics of the modified modulation wave corresponding to the two sets of three phases in the dual three-phase control unit to change are taken as candidate breakpoints. Based on the output phase currents of the two sets of three phases in the dual three-phase control unit, calculate the average midpoint current corresponding to each candidate breakpoint. When the average midpoint current corresponding to a candidate breakpoint is equal to the target average midpoint current corresponding to the dual three-phase control unit, the corresponding zero-sequence voltage is taken as the zero-sequence voltage reference value of the dual three-phase control unit. When the average midpoint current corresponding to adjacent candidate breakpoints is located on both sides of the target average midpoint current corresponding to the dual three-phase control unit, linear interpolation is used to obtain the zero-sequence voltage reference value of the dual three-phase control unit. When the average midpoint current corresponding to all candidate breakpoints is located on the same side of the target average midpoint current corresponding to the dual three-phase control unit, the zero-sequence voltage corresponding to the candidate breakpoint that minimizes the absolute value of the deviation between the average midpoint current and the target average midpoint current corresponding to the dual three-phase control unit is selected as the zero-sequence voltage reference value of the dual three-phase control unit.

[0013] According to a second aspect of the embodiments of this application, a quasi-cascade-free model predictive control device for a PWM rectifier is provided for controlling an even-array three-phase three-level NPC converter with a common midpoint, comprising: The sampling module is used to acquire the modulation waves of each group of three phases of the even-numbered three-phase three-level NPC converter with the common neutral point in each control cycle, and to collect the output phase current and common neutral point voltage of each group of three phases. Each pair of three phases constitutes a dual three-phase control unit. The dynamic carrier phase-shift modulation module is used to use dynamic carrier phase-shift modulation to make the common-mode voltage transition generated by one set of three phases in each of the dual three-phase control units cancel each other out with the reverse common-mode voltage transition generated by the other set of three phases, based on the modulation waves of the two sets of three phases in each dual three-phase control unit. The midpoint current distribution module is used to perform feedback adjustment on the common midpoint voltage to obtain the total target average midpoint current, and to distribute it according to the weight coefficients corresponding to each of the dual three-phase control units to obtain the target average midpoint current corresponding to each of the dual three-phase control units. The zero-sequence voltage acquisition module is used to obtain the zero-sequence voltage reference value of each of the two sets of three corresponding modulation waves and the corresponding output phase current in each of the two three-phase control units, so that the deviation between the average midpoint current of each of the two three-phase control units and the corresponding target average midpoint current is zero or minimal. The PWM generation and output module is used to superimpose equal-sized but opposite-polarity zero-sequence voltages onto two sets of three-corresponding modulation waves in each of the dual three-phase control units according to the zero-sequence voltage reference value of each dual three-phase control unit, to obtain two sets of three-corresponding corrected modulation waves in each dual three-phase control unit. Based on the corrected modulation waves, the module generates PWM drive signals for each phase according to the dynamic carrier phase-shift modulation method, and applies the PWM drive signals to the even-numbered three-phase three-level NPC converter with the common midpoint.

[0014] According to a third aspect of the embodiments of this application, an electronic device is provided, comprising: One or more processors; Memory, used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method as described in the first aspect.

[0015] According to a third aspect of the embodiments of this application, a computer-readable storage medium is provided, on which computer instructions are stored, which, when executed by a processor, implement the steps of the method as described in the first aspect.

[0016] The technical solutions provided by the embodiments of this application may include the following beneficial effects: As can be seen from the above embodiments, this application uses dynamic carrier phase-shift modulation in each dual three-phase control unit to cancel out the common-mode voltage transitions generated by the two sets of three phases, and achieves total system-level common-mode voltage elimination through the coordinated action of multiple dual three-phase control units. This helps to reduce the adverse effects of common-mode voltage on shaft voltage, shaft current, and bearing electro-corrosion. By using feedback adjustment based on the shared neutral point voltage to obtain the total target average neutral point current, and distributing it to each dual three-phase control unit according to weight, a coordinated distribution of the neutral point current for the entire system is achieved, which helps to enhance the neutral point voltage regulation capability under the condition of multiple control units sharing the neutral point. By injecting reverse zero-sequence voltage to obtain a corrected modulation wave, and generating a PWM drive signal based on the corrected modulation wave according to the dynamic carrier phase-shift modulation method, the neutral point voltage regulation does not destroy the common-mode voltage transition cancellation relationship. Therefore, it can achieve coordinated control of common-mode voltage elimination and neutral point voltage balance, suppress neutral point voltage fluctuations, and improve system reliability and output performance. At the same time, this application does not require additional hardware or increase the switching losses of power devices, and can give full play to the combined advantages of even-array three-phase systems and three-level NPC topologies, which has good engineering application value.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] Figure 1 This is a flowchart illustrating a common-mode voltage elimination and midpoint voltage coordinated control method according to an exemplary embodiment.

[0020] Figure 2 This is a structural topology diagram of the minimum control unit of the dual three-phase three-level NPC converter and the dual three-phase permanent magnet synchronous motor system with a phase shift of 30° in one embodiment of this application.

[0021] Figure 3 This is a diagram illustrating the common-mode voltage elimination and midpoint voltage coordinated control structure of a dual three-phase three-level NPC converter minimum control unit and a dual three-phase permanent magnet synchronous motor system with a 30° phase shift, according to one embodiment of this application.

[0022] Figure 4 This is a schematic diagram of the six-phase pulse timing and total system modulus voltage before and after dynamic carrier phase-shift modulation in one embodiment of this application. (a) is a schematic diagram of the six-phase pulse timing and total system modulus voltage without timing reconstruction, and (b) is a schematic diagram of the six-phase pulse timing and total system modulus voltage after dynamic carrier phase-shift modulation.

[0023] Figure 5 This is a schematic diagram of zero-sequence voltage reference value calculation in one embodiment of the present application, wherein (a) is a schematic diagram of the feasible interval of zero-sequence voltage and the construction of candidate breakpoints, and (b) is a schematic diagram of the selection of average midpoint current and zero-sequence voltage reference value corresponding to candidate breakpoints.

[0024] Figure 6 This is a simulation waveform diagram of a sinusoidal pulse width modulation (SPWM) strategy under steady-state operating conditions (500 rpm) in one embodiment of this application, wherein (a) is... a Phase current and x (a) is the simulated waveform of the phase current, (b) is the simulated waveform of the total modulus voltage of the system, and (c) is the simulated waveform of the midpoint voltage.

[0025] Figure 7 This is a simulation waveform diagram of a common-mode voltage cancellation (CMVE) strategy under steady-state operating conditions (500 rpm) in one embodiment of this application, wherein (a) is... a Phase current and x (a) is the simulated waveform of the phase current, (b) is the simulated waveform of the total modulus voltage of the system, and (c) is the simulated waveform of the midpoint voltage.

[0026] Figure 8 The following is a simulation waveform diagram of the common-mode voltage elimination and midpoint voltage balance coordinated control (CMVE-NPP) strategy under steady-state conditions (500 rpm) in one embodiment of this application, wherein (a) is a Phase current and x (a) is the simulated waveform of the phase current, (b) is the simulated waveform of the total modulus voltage of the system, and (c) is the simulated waveform of the midpoint voltage.

[0027] Figure 9 The image shows a simulation waveform of a common-mode voltage cancellation (CMVE) strategy under dynamic operating conditions (-500 rpm to 500 rpm) in one embodiment of this application, wherein (a) is... a Phase current and x (a) is the simulated waveform of the phase current, (b) is the simulated waveform of the total modulus voltage of the system, and (c) is the simulated waveform of the midpoint voltage.

[0028] Figure 10 The image shows a simulation waveform of a common-mode voltage cancellation and midpoint voltage balance coordinated control (CMVE-NPP) strategy under dynamic operating conditions (-500 rpm to 500 rpm) in one embodiment of this application, wherein (a) is... a Phase current and x (a) is the simulated waveform of the phase current, (b) is the simulated waveform of the total modulus voltage of the system, and (c) is the simulated waveform of the midpoint voltage.

[0029] Figure 11 This is a block diagram illustrating a common-mode voltage elimination and midpoint voltage coordinated control device according to an exemplary embodiment. Detailed Implementation

[0030] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0031] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0032] Figure 1 This is a flowchart illustrating a common-mode voltage elimination and neutral-point voltage coordinated control method according to an exemplary embodiment. This method is used for controlling an even-array three-phase three-level NPC converter sharing a neutral point. It should be noted that this invention is applicable to the control of even-array three-phase three-level NPC converters sharing a neutral point, where every two groups of three phases constitute a dual three-phase control unit. The following description, in conjunction with the accompanying drawings, uses a dual three-phase three-level NPC converter as the smallest control unit. For an even-array three-phase three-level NPC converter sharing a neutral point, composed of multiple dual three-phase control units, the neutral-point current can be coordinated and distributed at the system level, and dynamic carrier phase-shift modulation and reverse zero-sequence voltage injection can be performed in each dual three-phase control unit, thereby achieving coordinated control of the entire system. Figure 2 This is a structural topology diagram of the minimum control unit of the dual three-phase three-level NPC converter and the dual three-phase permanent magnet synchronous motor system with a phase shift of 30° in one embodiment of this application. Figure 3 This diagram illustrates the common-mode voltage elimination and neutral-point voltage coordinated control structure of a dual three-phase three-level NPC converter minimum control unit and a dual three-phase permanent magnet synchronous motor system with a 30° phase shift, according to an embodiment of this application. The specific steps of the control method are as follows: S1: In each control cycle, the modulation waves of each group of three phases of the even-numbered three-phase three-level NPC converter with the common neutral point are acquired, and the output phase current and common neutral point voltage of each group of three phases are collected. Among them, each pair of three phases constitutes a dual three-phase control unit. Specifically, in this embodiment, a 30° phase-shifted dual three-phase permanent magnet synchronous motor is used as the load. A dual three-phase control unit and its corresponding dual three-phase three-level NPC converter are used as an example for illustration. The number of motor pole pairs... =4, phase resistance R =1Ω, phase inductance L =4mH, DC line voltage is 100V, switching frequency is 5kHz, DC bus capacitance = = C =1000uF; At the current control moment ( k (Time), acquire two sets of three-phase modulated waves , , , , , And collect the six-phase output phase currents corresponding to the dual three-phase control unit. , , , , , and shared midpoint voltage sampling value This serves as the input for subsequent common-mode voltage elimination and midpoint voltage coordinated control.

[0033] In this embodiment, the upper-level motor control adopts dual dq coordinate system current control, with the upper-level controller generating two sets of three-phase modulation waves. It should be noted that the focus of this application is on the common-mode voltage elimination and midpoint voltage coordinated control of the modulation layer. The dual dq coordinate system current control is merely one upper-level control method used in this embodiment and does not constitute a limitation on the scope of protection of this application. For even-numbered three-phase three-level NPC converters sharing a common midpoint, multiple dual three-phase control units can generate corresponding two sets of three-phase modulation waves respectively, and coordinate control can be performed at the system level.

[0034] S2: Based on the modulation waves of the two sets of three phases in each of the dual three-phase control units, a dynamic carrier phase-shift modulation method is adopted to make the common-mode voltage transition generated by one set of three phases in each of the dual three-phase control units cancel each other out with the reverse common-mode voltage transition generated by the other set of three phases; this step includes the following sub-steps: S21: Based on the extreme value distribution relationship of the modulation waves of the two sets of three corresponding to each of the dual three-phase control units, determine the sector corresponding to the control cycle and the sorting sequence of the six-phase pulses; Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter is used as an example for explanation. For a dual three-phase system with a phase shift of 30°, the two sets of three-phase modulation waves in its control unit under sinusoidal modulation can be expressed as: (1) in, , , It is the first set of three-phase modulation waves. , , It is the second set of three-phase modulation waves. m ∈(0,1) is the modulation ratio. ω It is the angular frequency. It should be noted that equation (1) is only used to illustrate the phase relationship of the two sets of three-phase modulation waves in this embodiment, and does not limit the specific generation method of the modulation wave in this application.

[0035] According to the two sets of three-phase modulation waves obtained in S1 within the dual three-phase control unit , , , , , Calculate the corresponding equivalent duty cycle. , , , , , The two satisfy the following relationship: (2) The equivalent duty cycle is used for sector determination and pulse sequencing of the current dual three-phase control unit, and is used to characterize the relative timing relationship of the two sets of three-phase modulation waves in the current switching cycle within the control unit.

[0036] The duty cycles of the two groups of three phases are sorted separately to obtain the maximum and minimum values ​​of the duty cycles of the first and second groups of three phases: (3) Further obtain the sector determination quantity at the current moment and for: (4) Combined with sector determination quantity , By identifying the phases corresponding to the extreme values ​​of the three-phase duty cycles in the two sets of three-phase circuits, the sector in which the dual three-phase control unit is located during the current switching cycle can be determined. After determining the current sector, the corresponding phase is selected as the anchor phase, and the six-phase pulses are sorted according to a preset cyclic sequence starting from the anchor phase. The anchor phases and sorting sequences corresponding to different sectors are shown in Table 1. A, B, and C represent the phases in the first set of three-phase circuits, respectively. a Mutually, b Mutually, cThe corresponding pulses, X, Y, and Z, represent the second group of three phases respectively. x Mutually, y Mutually, z The corresponding pulse. In this embodiment, a cyclic shift sequence based on AZBXCY is used.

[0037] Table 1: Anchoring phase and six-phase pulse arrangement sequence corresponding to different sectors;

[0038] S22: Based on the sign and amplitude of the modulation waves of the two sets of three corresponding to each of the dual three-phase control units, determine the effective range width of the six-phase pulse, and determine the rising edge time and falling edge time of the six-phase pulse in sequence according to the sorting sequence, so that the falling edge of the previous pulse in the adjacent pulse coincides with the rising edge of the next pulse, and the six-phase pulse is connected end to end in the control cycle. Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter is still used as an example for explanation. Based on the sign and amplitude of the modulation wave of each phase at the current control moment, the equivalent pulse action interval width for each phase used for dynamic carrier phase-shift modulation can be determined. The equivalent pulse action interval width of each phase can be expressed as: (5) in, i = a , b , c , x , y , z , For the switching period, is the period between the two switches. For simplicity, the equation is... This indicates the values ​​of the modulation waves for each phase corresponding to the current control moment. In the three-level pulse construction method used in this embodiment, when... When ≥0, the pulse action range corresponds to the positive level action range of that phase; when When the value is less than 0, the pulse action interval corresponds to the zero-level action interval of that phase, and the area outside the pulse action interval corresponds to the negative-level action interval. It should be noted that the six-phase pulse constructed in this step is an equivalent pulse for dynamic carrier phase-shift modulation, and its timing sequence is used to characterize the arrangement relationship of the action intervals of each phase level.

[0039] Based on the anchoring phase determined in step S21, the rising edge and falling edge times of the anchoring phase pulse are determined using a center alignment method. The rising edge and falling edge times are as follows: (6) in, The equivalent pulse action range width of the anchor phase. and These are the rising and falling edges of the anchoring phase pulse, respectively.

[0040] For the remaining phases in the sequence, the timing of each phase pulse is determined sequentially according to the principle of beginning-end connection. Specifically, the rising edge of the current phase is set to the falling edge of the previous phase, and its falling edge time is determined based on the equivalent pulse range width of the corresponding phase. When the falling edge time exceeds one switching cycle, a period modulo operation is performed to obtain the complete timing arrangement of the six phase pulses within the current switching cycle. Thus, the falling edge of the previous pulse coincides with the rising edge of the next pulse in adjacent pulses, and the six phase pulses are connected end-to-end within one switching cycle.

[0041] S23: Select one phase as a continuous reference phase, and apply a uniform shift to the rising and falling edges of the six-phase pulses with reference to the continuous reference phase. Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter will still be used as an example for explanation. Let the rising edge time and falling edge time of the six-phase pulse without uniform translation obtained in step S22 be respectively... , , i = a , b , c , x , y , z Let the continuous reference phase be... q ( q Can be a , b , c , x , y , z (any value), then the uniform shift amount of the current switching cycle. It can be represented as: (7) in, This refers to the rising edge time of the continuous reference phase after a uniform shift from the previous switching cycle. This refers to the rising edge time of the continuous reference phase before the uniform shift in the current switching cycle. By using the above shift amount, the rising edge time of the continuous reference phase in the current switching cycle can be kept continuous with the corresponding time in the previous switching cycle.

[0042] Applying the uniform shift amount to the rising and falling edges of the six-phase pulses before the uniform shift yields the rising and falling edges of the six-phase pulses after the uniform shift as follows: (8) Where, mod(· , ) indicates the switching cycle The modulo operation is used to map the shifted rising and falling edge times to the current switching cycle.

[0043] By performing the above unified translation process, the continuous reference phase can be kept continuous between adjacent switching cycles or during sector switching while maintaining the six-phase pulse sequence relationship unchanged, thereby avoiding abrupt changes in the six-phase pulse timing between adjacent control cycles or during sector switching.

[0044] S24: Determine the timing of the six-phase pulses under the dynamic carrier phase-shift modulation method based on the rising and falling edge times of the translated six-phase pulses.

[0045] Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter is still used as an example for explanation. Based on the rising and falling edges of the six-phase pulses obtained in step S23, the effective range of each phase's equivalent pulse within the current switching cycle can be determined; from the effective range of each phase pulse and its corresponding relationship, a complete timing arrangement of the six phases within the current switching cycle can be formed. Since steps S21 to S23 have constrained the ordering and unified shift of the six-phase pulses, at the current control time... k Within the corresponding switching cycle, for any time... t ∈[ k , ( k +1) The total modulo voltage of the control unit generated by the two sets of three-phase components within the dual three-phase control unit satisfies: (9) in, , , , , , This represents the instantaneous equivalent output level of the six-phase bridge arm within the current three-phase control unit during the current switching cycle, and is used to characterize the equivalent output state of the three-level NPC bridge arm. This represents the DC bus voltage. This indicates that at the current control moment... k Within the corresponding switching cycle, the common-mode voltage transition of one set of three-phase components and the reverse common-mode voltage transition of the other set of three-phase components within the dual three-phase control unit occur at any given time. t Real-time cancellation ensures that the total mode voltage of the dual three-phase control unit is always zero. For an even-numbered three-phase three-level NPC converter with a common midpoint, when each dual three-phase control unit satisfies the above common mode voltage elimination condition, the total mode voltage of the system can be eliminated through the coordinated action of multiple dual three-phase control units.

[0046] Figure 4 This is a schematic diagram showing the six-phase pulse timing and the total mode voltage of the system before and after dynamic carrier phase-shift modulation. Figure 4 (a) in the diagram shows the six-phase pulse timing and total system modulus voltage without timing reconstruction. Figure 4 Figure (b) shows the six-phase pulse timing and total system modulated voltage after dynamic carrier phase-shift modulation. It should be noted that... Figure 4 The middle vertical axis is shown a , b , c , x , y , z The waveforms represent the equivalent pulse timings for each phase. Their high and low levels are only used to indicate the effective pulse interval and edge timing, and do not represent the actual three-level voltage state of the NPC bridge arm output. Figure 4 It can be seen that without timing reconstruction, the timing arrangement of the two sets of three-phase pulses does not satisfy the common-mode voltage transition cancellation relationship, so the total system-wide common-mode voltage fluctuates significantly. After dynamic carrier phase-shift reconstruction, the six-phase pulses are rearranged according to the preset sorting sequence, so that the common-mode voltage transition generated by one set of three-phase pulses cancels out the reverse common-mode voltage transition generated by the other set of three-phase pulses, thereby eliminating the total system-wide common-mode voltage.

[0047] S3: Feedback adjustment is performed on the shared midpoint voltage to obtain the total target average midpoint current, and the current is distributed according to the weighting coefficients corresponding to each of the dual three-phase control units to obtain the target average midpoint current corresponding to each of the dual three-phase control units; this step includes the following sub-steps: S31: Based on the deviation between the common midpoint voltage and the given value of the common midpoint voltage, feedback adjustment is performed to obtain the total target average midpoint current; Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter is used as an example. Since this embodiment only includes one dual three-phase control unit, the total target average neutral point current of the even-array three-phase three-level NPC converter with a shared neutral point can be equivalent to the target average neutral point current corresponding to the dual three-phase control unit. For an even-array three-phase three-level NPC converter with a shared neutral point containing multiple dual three-phase control units, the total target average neutral point current needs to be allocated according to the weighting coefficients corresponding to each dual three-phase control unit.

[0048] Let the common midpoint voltage sampling value of the current switching cycle be... DC bus voltage is Therefore, the common midpoint voltage setpoint can be taken as half of the DC bus voltage, that is: (10) Therefore, the voltage deviation at the common midpoint is: (11) Feedback adjustment based on the midpoint voltage deviation generates the total target average midpoint current. When a proportional controller is used, the target average midpoint current can be expressed as: (12) in, The total target average neutral point current of the even-array three-phase three-level NPC converter with the shared neutral point is... This refers to the proportional controller coefficient.

[0049] When a proportional-integral controller is used, the target average midpoint current can be expressed as: (13) in, These are the integral controller coefficients.

[0050] In this embodiment, a proportional controller can be used to directly generate the total target average midpoint current based on the common midpoint voltage deviation, thereby reducing midpoint voltage fluctuations and offsets. It should be noted that the proportional controller is only one feedback control method used in this embodiment; a proportional-integral controller or other feedback control methods can also be used depending on the control requirements.

[0051] S32: Determine the weighting coefficient corresponding to each of the dual three-phase control units according to their adjustment capability, operating status or preset allocation rules, wherein the sum of the weighting coefficients is 1; Specifically, for the general case of an even-array three-phase three-level NPC converter sharing a common midpoint, let the system include... M The first dual three-phase control unit, the first r The weighting coefficients corresponding to each dual-three-phase control unit are denoted as follows: ,in r = 1,2,…, M Then the weighting coefficients corresponding to each dual-three-phase control unit satisfy: (14) The weighting coefficients can be determined based on the adjustment capability, operating status, or preset allocation rules of each dual-three-phase control unit under its current operating conditions.

[0052] When the topology parameters, operating status, and midpoint current regulation capability of each dual three-phase control unit are symmetrical, the weighting coefficient of each control unit can be determined by an equal-division method, i.e.: (15) In this embodiment, a dual three-phase control unit is used as an example for explanation. M= 1, therefore the weighting coefficient corresponding to this dual three-phase control unit is: (16) That is, in this embodiment, the total target average midpoint current is entirely allocated to the dual three-phase control unit. For an even array of three-phase three-level NPC converters composed of multiple dual three-phase control units, the weighting coefficients corresponding to each control unit can be determined in real time according to the above rules, so as to be used for the subsequent allocation of the total target average midpoint current among the dual three-phase control units.

[0053] S33: Based on the weighting coefficients corresponding to each of the dual three-phase control units, the total target average midpoint current is allocated to obtain the target average midpoint current corresponding to each of the dual three-phase control units.

[0054] Specifically, for the general case of an even-array three-phase three-level NPC converter sharing a common midpoint, the total target average midpoint current is obtained in step S31. In step S32, the weighting coefficients corresponding to each dual three-phase control unit are determined. After that, the r The target average midpoint current corresponding to each dual three-phase control unit can be expressed as: (17) in, For the first r The target average midpoint current corresponding to each dual three-phase control unit.

[0055] From equations (14) and (17), it can be seen that the sum of the target average midpoint currents of each dual three-phase control unit satisfies: (18) This ensures that each dual three-phase control unit still meets the overall requirements of the closed-loop regulation of the midpoint voltage in the entire system after the midpoint current is distributed.

[0056] In this embodiment, since the system contains only one dual three-phase control unit, that is M =1, and the corresponding weight coefficient =1, therefore we have: (19) That is, in this embodiment, the total target average midpoint current is fully allocated to the dual three-phase control unit, and the target average midpoint current corresponding to the dual three-phase control unit is equal to the total target average midpoint current.

[0057] The target average midpoint current corresponding to each dual three-phase control unit is used as the target quantity for selecting the subsequent zero-sequence voltage reference value. This is used to implement closed-loop regulation of the midpoint voltage of each dual three-phase control unit under the condition of meeting the common-mode voltage elimination requirement.

[0058] S4: Based on the modulation waves corresponding to the two sets of three phases in each of the dual three-phase control units and the corresponding output phase currents, calculate the zero-sequence voltage reference value for each of the dual three-phase control units, so that the deviation between the average midpoint current of each of the dual three-phase control units and the corresponding target average midpoint current is zero or minimized; this step includes the following sub-steps: S41: Based on the value constraints of the modified modulation wave obtained by superimposing the two sets of three-phase modulation waves in each of the dual three-phase control units with zero-sequence voltages of equal magnitude and opposite polarity, determine the feasible range of zero-sequence voltage for each of the dual three-phase control units. Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter is used as an example for explanation. Based on the dynamic carrier phase-shift modulation method described in step S2, which enables the common-mode voltage transitions generated by the two sets of three phases within the dual three-phase control unit to cancel each other out, to ensure that the common-mode voltage transition cancellation effect is not destroyed after zero-sequence voltage injection, it is assumed that zero-sequence voltage is injected into the first set of three phases and the second set of three phases respectively. and Then, at the modulation wave level, the total mode voltage constraint relationship corresponding to the dual three-phase control unit after injecting zero-sequence voltage is: (20) Since step S2 has already established the mutual cancellation relationship between the two sets of three-phase common-mode voltage transitions through dynamic carrier phase-shift modulation, in order to ensure that the zero-sequence voltage injection does not introduce new common-mode voltage components, the two sets of injected zero-sequence voltages should satisfy the following: (twenty one) in, To unify the zero-sequence adjustment amount for subsequent midpoint voltage regulation.

[0059] For the general case of an even-numbered three-phase three-level NPC converter with a common midpoint, each dual three-phase control unit can satisfy the reverse zero-sequence voltage injection relationship shown in equation (21), that is, the zero-sequence voltages of the two sets of three phases superimposed on the same dual three-phase control unit are equal in magnitude and opposite in polarity, thereby achieving the subsequent coordinated regulation of the midpoint voltage of the entire system while maintaining the common-mode voltage elimination requirements of each control unit.

[0060] After zero-sequence voltage injection, the corrected modulation waves of the first three-phase group and the second three-phase group are as follows: (twenty two) Because the corrected modulation wave after superimposing the zero-sequence voltage needs to meet the value range ∈[-1,1], i = a , b , c ,x , y , z Therefore, we have: (twenty three) Furthermore, the maximum and minimum values ​​of the first group of three-phase modulated waves are taken respectively. , The maximum and minimum values ​​of the second group of three-phase modulated waves are , Then the upper and lower boundaries of the feasible zero-sequence voltage interval of the dual three-phase control unit can be expressed as: (twenty four) when ≤ At that time, the feasible range of zero-sequence voltage for the dual three-phase control unit is [ , ];when > At that time, the feasible range of zero-sequence voltage for the dual three-phase control unit is empty.

[0061] S42: If the feasible range of zero-sequence voltage of a certain dual three-phase control unit is empty, then the reference value of zero-sequence voltage of the dual three-phase control unit is taken as zero; if the feasible range of zero-sequence voltage of a certain dual three-phase control unit is not empty, then the upper and lower boundaries of the feasible range of zero-sequence voltage of the dual three-phase control unit and the zero-sequence voltage values ​​that cause the segmentation characteristics of the modified modulation wave corresponding to the two sets of three phases in the dual three-phase control unit to change are taken as candidate breakpoints. Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter is still used as an example for explanation. From equation (22), it can be seen that when... > At this time, the feasible range of zero-sequence voltage for the dual three-phase control unit is empty, and the reference value of zero-sequence voltage for the dual three-phase control unit is taken. =0, and keep the original modulated wave unchanged; when ≤ When the zero-sequence voltage of the dual three-phase control unit is not empty, the reference value of the zero-sequence voltage is then obtained within this range.

[0062] When the feasible interval of zero-sequence voltage is not empty, it can be seen from equation (22) that the first group of three-phase modified modulation waves + , + , + The sign change points correspond to =− 、− 、− The second group of three-phase modified modulation waves - , - , - The sign change points correspond to = , , When the zero-sequence voltage passes through the aforementioned sign change point, the piecewise characteristics of the absolute value term of the modulated wave change, and therefore the expression of the average midpoint current with respect to the zero-sequence voltage will switch between adjacent sub-intervals.

[0063] Therefore, in this embodiment, the candidate breakpoint set can be represented as: (25) in, and Let - be the lower and upper boundaries of the feasible interval for zero-sequence voltage. 、− 、− , , , The zero-sequence voltage value that causes the corresponding modified modulation wave symbol to change.

[0064] Only those within the feasible range of zero-sequence voltage are retained. , The candidate breakpoints within the brackets are selected and sorted in ascending order to obtain the sorted candidate breakpoint sequence: (26) in, N The number of candidate breakpoints located within the feasible range of the zero-sequence voltage.

[0065] S43: Calculate the average midpoint current corresponding to each candidate breakpoint based on the output phase current of the two sets of three phases in the dual three-phase control unit. Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter will still be used as an example for explanation. The sorted candidate breakpoints will be... , ,…, Substituting these values ​​into equation (22) as zero-sequence voltage values, we can obtain the corrected modulation wave corresponding to each candidate breakpoint. For the first... j Candidate breakpoints The corresponding modified modulation wave is: (27) Combining the output phase currents of the two sets of three corresponding phases within the dual three-phase control unit , , , , , The first one can be calculated. j The average midpoint current corresponding to each candidate breakpoint is: (28) in, For the first j The candidate breakpoint corresponds to the first... i Phase-corrected modulated wave, Used to characterize the corresponding percentage of zero-level operation. For the first i Phase output phase current.

[0066] Since both sets of three-phase currents are Y-connected and the sum of the currents in each set is zero, the expression for the average midpoint current can also be expressed as: (29) Therefore, the average midpoint current corresponding to each candidate breakpoint can be obtained. , ,…, The average midpoint current corresponding to each candidate breakpoint is used to compare with the target average midpoint current corresponding to the dual three-phase control unit to determine the zero-sequence voltage reference value of the dual three-phase control unit.

[0067] S44: When the average midpoint current corresponding to a candidate breakpoint is equal to the target average midpoint current corresponding to the dual three-phase control unit, the corresponding zero-sequence voltage is taken as the zero-sequence voltage reference value of the dual three-phase control unit; when the average midpoint current corresponding to adjacent candidate breakpoints is located on both sides of the target average midpoint current corresponding to the dual three-phase control unit, linear interpolation is used to obtain the zero-sequence voltage reference value of the dual three-phase control unit; when the average midpoint current corresponding to all candidate breakpoints is located on the same side of the target average midpoint current corresponding to the dual three-phase control unit, the zero-sequence voltage corresponding to the candidate breakpoint that minimizes the absolute value of the deviation between the average midpoint current and the target average midpoint current corresponding to the dual three-phase control unit is selected as the zero-sequence voltage reference value of the dual three-phase control unit.

[0068] Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter will still be used as an example for explanation. For the first... r A dual three-phase control unit, whose target average midpoint current is denoted as... In this embodiment, which includes only one dual three-phase control unit, there are... r = 1.

[0069] When the average midpoint current corresponding to a candidate breakpoint is equal to the target average midpoint current, the corresponding candidate breakpoint is taken as the zero-sequence voltage reference value. When the average midpoint currents corresponding to adjacent candidate breakpoints are located on both sides of the target average midpoint current, a zero-sequence voltage reference value is obtained between these adjacent candidate breakpoints using linear interpolation. Let the two adjacent candidate breakpoints be... and The corresponding average midpoint currents are respectively and Then the zero-sequence voltage reference value can be expressed as: (30) in, This is the zero-sequence voltage reference value. This represents the target average midpoint current corresponding to the dual three-phase control unit.

[0070] When the average midpoint current corresponding to all candidate breakpoints is on the same side as the target average midpoint current, it indicates that there is no zero-sequence voltage value within the current feasible range of zero-sequence voltage that makes the average midpoint current exactly equal to the target average midpoint current. At this time, the zero-sequence voltage corresponding to the candidate breakpoint that minimizes the absolute value of the deviation between the average midpoint current and the target average midpoint current is selected as the zero-sequence voltage reference value of the dual three-phase control unit.

[0071] For the general case of an even-array three-phase three-level NPC converter, the zero-sequence voltage reference value corresponding to each dual three-phase control unit can be obtained according to the above method.

[0072] Figure 5 This is a schematic diagram for calculating the zero-sequence voltage reference value, where, Figure 5 (a) in the diagram is a schematic diagram of the feasible interval of zero-sequence voltage and the construction of candidate breakpoints. Figure 5 (b) in the diagram shows the selection of reference values ​​for the average midpoint current and zero-sequence voltage corresponding to the candidate breakpoints. Figure 5 It can be seen that under any working condition k At this time, candidate breakpoints can be constructed and screened based on the feasible range of zero-sequence voltage. Then, the zero-sequence voltage reference value can be selected or interpolated based on the relationship between the average midpoint current corresponding to each candidate breakpoint and the target average midpoint current corresponding to the dual three-phase control unit.

[0073] S5: Based on the zero-sequence voltage reference value of each of the dual three-phase control units, zero-sequence voltages of equal magnitude and opposite polarity are superimposed onto the two sets of three corresponding modulation waves in each of the dual three-phase control units to obtain the two sets of three corresponding correction modulation waves in each of the dual three-phase control units. Based on the correction modulation waves, PWM drive signals for each phase are generated according to the dynamic carrier phase-shifting modulation method, and the PWM drive signals are applied to the even-numbered three-phase three-level NPC converter at the common midpoint.

[0074] Specifically, in this embodiment, the minimum control unit of a dual three-phase three-level NPC converter is used as an example for explanation. The zero-sequence voltage reference value obtained in step S44 is... If these are injected into the two sets of three-phase modulation waves in the dual three-phase control unit respectively, then the corrected modulation waves of the first set of three phases and the second set of three phases will be respectively (31) Since the feasible range of zero-sequence voltage has been determined in step S41 based on the value constraint of the modified modulation wave, and the reference value of zero-sequence voltage obtained in step S44 is within the feasible range, the modified modulation wave obtained after injecting the reference value of zero-sequence voltage still meets the allowable modulation range requirement.

[0075] For the general case of an even-array three-phase three-level NPC converter with a common midpoint, the zero-sequence voltage reference value corresponding to each dual three-phase control unit can be injected into its respective two sets of three-phase modulation waves in the manner described above to obtain the corrected modulation wave corresponding to each dual three-phase control unit.

[0076] Since the zero-sequence voltage reference value is injected as a common zero-sequence component within the same group of three phases, it will not change the relative magnitude relationship between the modulation waves of each phase within the same group of three phases. At the same time, since the zero-sequence voltages injected into the first group of three phases and the second group of three phases are equal in magnitude and opposite in polarity, it will not disrupt the mutual cancellation relationship of common-mode voltage transitions required by the dynamic carrier phase-shifting modulation method described in step S2.

[0077] Furthermore, based on the corrected modulation wave obtained by equation (31), the six-phase pulse timing is re-determined according to the dynamic carrier phase-shift modulation method described in steps S21 to S24. Specifically, the corrected modulation wave is used as the input of the dynamic carrier phase-shift modulation method to re-determine the corresponding equivalent duty cycle, sector, anchor phase, six-phase pulse sequence, equivalent pulse action interval width, and the rising and falling edge times after unified translation, thereby generating the six-phase equivalent pulse signal in the dual three-phase control unit.

[0078] Let the number of switches in the current switching cycle be... i Phase pulse signal is ,in i = a ,b , c , x , y , z In the three-level pulse construction method used in this embodiment, when the modulated wave is corrected... When ≥0, =1 corresponds to a positive voltage level. =0 corresponds to zero level; when When <0, =1 corresponds to zero level. =0 corresponds to a negative level. Therefore, the first... i The output state of the phase during the current switching cycle.

[0079] Furthermore, gate mapping is performed on the four switching devices of the three-level NPC bridge arm according to the output state of each phase. In this embodiment, the gate signals of the four power switching devices of each phase bridge arm from top to bottom represent the switching state of that phase bridge arm. i When the phase output is positive, the corresponding gate signal is [1 1 0 0]; when the first phase output is positive, the corresponding gate signal is [1 1 0 0]. i When the phase output is at zero level, the corresponding gate signal is [0 1 1 0]; when the first phase output is at zero level, the corresponding gate signal is [0 1 1 0]. i When the phase output is negative, the corresponding gate signal is [0 0 1 1]. Based on the above gate mapping relationship, PWM drive signals for each arm of the first group of three phases and the second group of three phases are generated respectively.

[0080] For the general case of an even-array three-phase three-level NPC converter, the PWM drive signal corresponding to each phase bridge arm can be generated by the modified modulation wave corresponding to each dual three-phase control unit according to the above method, thereby realizing the PWM drive of the entire system.

[0081] The PWM drive signal is output to the power switching device of the corresponding bridge arm, and the conduction and turn-off control of each bridge arm is completed within the current switching cycle, thereby realizing the voltage output regulation of the even-array three-phase three-level NPC converter with a common midpoint.

[0082] Under the action of the PWM drive signal, on the one hand, the common-mode voltage transitions generated by the corresponding phases of the two sets of three-phase converters cancel each other out, thereby achieving common-mode voltage elimination; on the other hand, the modified modulation wave is adjusted by the zero-sequence voltage reference value, so that the average midpoint current of the dual three-phase control unit tracks its corresponding target average midpoint current or minimizes the deviation between the two, thereby suppressing midpoint voltage fluctuations and offsets. For the general case of an even-array three-phase three-level NPC converter with a shared midpoint, each dual three-phase control unit outputs its corresponding PWM drive signal to the power switching device of its respective bridge arm to drive the entire even-array three-phase three-level NPC converter, thereby achieving system-level common-mode voltage elimination and coordinated control of midpoint voltage.

[0083] Figure 6 The following is a simulation waveform diagram of the sinusoidal pulse width modulation (SPWM) strategy under steady-state operating conditions (500 rpm), where... Figure 6 (a) in the middle is a Phase current and x Simulated waveform of phase current. Figure 6 (b) in the figure is the simulated waveform of the total mode voltage of the system. Figure 6 (c) in the diagram shows the simulated waveform of the midpoint voltage. Figure 6 It is known that, under steady-state conditions, when using the sinusoidal pulse width modulation (SPWM) strategy, the maximum total common-mode voltage of the minimum control unit of the dual three-phase three-level NPC converter used in this embodiment can reach 1 / 3 of the DC bus voltage. Simultaneously, the midpoint voltage exhibits significant low-frequency fluctuations. Therefore, the traditional SPWM modulation method cannot reduce the system's common-mode voltage, nor can it achieve effective control of the midpoint voltage.

[0084] Figure 7 The following is a simulation waveform diagram of the common-mode voltage cancellation (CMVE) strategy under steady-state conditions (500 rpm). Figure 7 (a) in the middle is a Phase current and x Simulated waveform of phase current. Figure 7 (b) in the figure is the simulated waveform of the total mode voltage of the system. Figure 7 (c) in the diagram shows the simulated waveform of the midpoint voltage. Figure 7 As can be seen, under steady-state conditions, when the common-mode voltage cancellation (CMVE) strategy is adopted, the total common-mode voltage of the minimum control unit of the dual three-phase three-level NPC converter used in this embodiment is significantly reduced, with only slight fluctuations near 0. However, the midpoint voltage still exhibits significant low-frequency fluctuations, which disrupt the ideal common-mode voltage cancellation conditions, resulting in ineffective common-mode voltage cancellation. Therefore, while the common-mode voltage can be significantly reduced by employing the common-mode voltage cancellation (CMVE) strategy alone, it cannot achieve effective control of the midpoint voltage.

[0085] Figure 8 The following are simulation waveforms of the common-mode voltage cancellation and midpoint voltage balance coordinated control (CMVE-NPP) strategy under steady-state conditions (500 rpm). Figure 8 (a) in the middle is a Phase current and x Simulated waveform of phase current. Figure 8 (b) in the figure is the simulated waveform of the total mode voltage of the system. Figure 8 (c) in the diagram shows the simulated waveform of the midpoint voltage. Figure 8As can be seen, under steady-state conditions, when employing the Common Mode Voltage Elimination and Neutral Point Voltage Coordinated Control (CMVE-NPP) strategy, the total mode voltage of the minimum control unit of the dual three-phase three-level NPC converter used in this embodiment is essentially zero, and low-frequency fluctuations in the neutral point voltage are also effectively suppressed. Therefore, the Common Mode Voltage Elimination and Neutral Point Voltage Coordinated Control (CMVE-NPP) strategy can effectively balance the two control objectives of common mode voltage and neutral point voltage.

[0086] Figure 9 The simulation waveforms are shown below, illustrating the common-mode voltage cancellation (CMVE) strategy under dynamic operating conditions (-500 rpm to 500 rpm). Figure 9 (a) in the middle is a Phase current and x Simulated waveform of phase current. Figure 9 (b) in the figure is the simulated waveform of the total mode voltage of the system. Figure 9 (c) in the diagram shows the simulated waveform of the midpoint voltage. Figure 9 It is known that under the dynamic operating condition of low-speed zero crossing, when the common-mode voltage cancellation (CMVE) strategy is adopted, the midpoint voltage of the minimum control unit of the dual three-phase three-level NPC converter used in this embodiment will deviate significantly, resulting in increased output voltage distortion, a significant increase in common-mode voltage, and a deterioration in system stability.

[0087] Figure 10 The simulation waveforms are shown below, illustrating the combined common-mode voltage cancellation and midpoint voltage balance control (CMVE-NPP) strategy under dynamic operating conditions (-500 rpm to 500 rpm). Figure 10 (a) in the middle is a Phase current and x Simulated waveform of phase current. Figure 10 (b) in the figure is the simulated waveform of the total mode voltage of the system. Figure 10 (c) in the diagram shows the simulated waveform of the midpoint voltage. Figure 10 It can be seen that under the dynamic operating condition of low speed zero crossing, when the common mode voltage elimination and neutral point voltage coordinated control (CMVE-NPP) strategy is adopted, the minimum control unit of the dual three-phase three-level NPC converter used in this embodiment can still maintain the stability of the neutral point voltage and keep the total common mode voltage basically at 0.

[0088] In summary, this invention proposes a common-mode voltage elimination and neutral-point voltage coordinated control method for even-numbered three-phase three-level NPC converters sharing a common neutral point. This method acquires the modulation wave, output phase current, and common neutral-point voltage of each group of three phases within each control cycle, and forms a dual three-phase control unit with every two groups of three phases. Based on the extreme value distribution relationship and sector determination quantity of the two groups of three-phase modulation waves within each dual three-phase control unit, a dynamic carrier phase-shift modulation method is used to determine the six-phase pulse timing, so that the common-mode voltage transition generated by one group of three phases cancels out the reverse common-mode voltage transition generated by the other group of three phases, thereby achieving common-mode voltage elimination in each dual three-phase control unit. Furthermore, the overall system common-mode voltage elimination is achieved through the coordinated operation of multiple dual three-phase control units. Simultaneously, the common neutral-point voltage feedback is used to adjust the generation... The overall target average midpoint current is calculated and distributed according to the weighting coefficients corresponding to each dual three-phase control unit. Without disrupting the mutual cancellation relationship of common-mode voltage transitions, equal and opposite zero-sequence voltages are injected into the two sets of three phases within each dual three-phase control unit. The reference value of the zero-sequence voltage for each dual three-phase control unit is obtained by combining the feasible interval of the zero-sequence voltage, candidate breakpoint search, and linear interpolation. Finally, based on the corrected modulation wave after the injection of the zero-sequence voltage, PWM drive signals for each phase are generated according to the dynamic carrier phase-shift modulation method and applied to the even-array three-phase three-level NPC converter with the common midpoint. Based on the above method, coordinated control of common-mode voltage elimination and midpoint voltage balance can be achieved without adding additional hardware, improving system reliability and output performance.

[0089] Corresponding to the aforementioned embodiment of a common-mode voltage elimination and midpoint voltage coordinated control method, this application also provides an embodiment of a common-mode voltage elimination and midpoint voltage coordinated control device.

[0090] Figure 11 This is a block diagram illustrating a common-mode voltage cancellation and midpoint voltage coordinated control device according to an exemplary embodiment. (Refer to...) Figure 11 The device includes: Sampling module 1 is used to acquire the modulation waves of each group of three phases of the even-numbered three-phase three-level NPC converter with the common neutral point in each control cycle, and to collect the output phase current and common neutral point voltage of each group of three phases. Each pair of three phases constitutes a dual three-phase control unit. The dynamic carrier phase-shifting modulation module 2 is used to use dynamic carrier phase-shifting modulation to make the common-mode voltage transition generated by one set of three phases in each of the dual three-phase control units cancel each other out with the reverse common-mode voltage transition generated by the other set of three phases, based on the modulation waves of the two sets of three phases in each dual three-phase control unit. The midpoint current distribution module 3 is used to perform feedback adjustment on the common midpoint voltage to obtain the total target average midpoint current, and to distribute it according to the weight coefficients corresponding to each of the dual three-phase control units to obtain the target average midpoint current corresponding to each of the dual three-phase control units. The zero-sequence voltage acquisition module 4 is used to acquire the zero-sequence voltage reference value of each of the two sets of three corresponding modulation waves and the corresponding output phase current in each of the two three-phase control units, so that the deviation between the average midpoint current of each of the two three-phase control units and the corresponding target average midpoint current is zero or minimal. The PWM generation and output module 5 is used to superimpose zero-sequence voltages of equal magnitude and opposite polarity onto two sets of three-corresponding modulation waves in each of the dual three-phase control units according to the zero-sequence voltage reference value of each dual three-phase control unit, to obtain two sets of three-corresponding corrected modulation waves in each dual three-phase control unit, generate PWM drive signals for each phase according to the dynamic carrier phase shift modulation method based on the corrected modulation waves, and apply the PWM drive signals to the even-numbered three-phase three-level NPC converter with the common midpoint.

[0091] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0092] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to in the description of the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this application according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0093] Accordingly, this application also provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; and when the one or more programs are executed by the one or more processors, causing the one or more processors to implement a common-mode voltage elimination and midpoint voltage coordinated control method as described above.

[0094] Accordingly, this application also provides a computer-readable storage medium storing computer instructions thereon, which, when executed by a processor, implement the common-mode voltage elimination and midpoint voltage coordinated control method described above.

[0095] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this application are indicated by the claims.

[0096] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for coordinated control of common-mode voltage elimination and midpoint voltage, characterized in that, The method is used for controlling an even-array three-phase three-level NPC converter with a shared neutral point. The method includes: Within each control cycle, the modulation waves of each group of three phases of the even-numbered three-phase three-level NPC converter with the common neutral point are acquired, and the output phase current and common neutral point voltage of each group of three phases are collected. Each pair of three phases constitutes a dual three-phase control unit. Based on the modulation waves of the two sets of three phases in each of the dual three-phase control units, a dynamic carrier phase-shifting modulation method is adopted to make the common-mode voltage transition generated by one set of three phases in each of the dual three-phase control units cancel each other out with the reverse common-mode voltage transition generated by the other set of three phases. Feedback adjustment is performed on the common midpoint voltage to obtain the total target average midpoint current, and the current is distributed according to the weighting coefficients corresponding to each of the dual three-phase control units to obtain the target average midpoint current corresponding to each of the dual three-phase control units. Based on the modulation waves of the two sets of three corresponding phases in each of the dual three-phase control units and the corresponding output phase currents, the zero-sequence voltage reference value of each of the dual three-phase control units is obtained so that the deviation between the average midpoint current of each of the dual three-phase control units and the corresponding target average midpoint current is zero or minimized. Based on the zero-sequence voltage reference value of each of the dual three-phase control units, zero-sequence voltages of equal magnitude and opposite polarity are superimposed onto the two sets of three corresponding modulation waves in each of the dual three-phase control units to obtain the two sets of three corresponding corrected modulation waves in each of the dual three-phase control units. Based on the corrected modulation waves, PWM drive signals for each phase are generated according to the dynamic carrier phase-shift modulation method, and the PWM drive signals are applied to the even-numbered three-phase three-level NPC converter at the common midpoint.

2. The common-mode voltage elimination and midpoint voltage coordinated control method according to claim 1, characterized in that, Based on the modulation waves corresponding to the two sets of three phases within each of the dual three-phase control units, a dynamic carrier phase-shift modulation method is adopted to cancel out the common-mode voltage transition generated by one set of three phases and the reverse common-mode voltage transition generated by the other set of three phases within each of the dual three-phase control units, including: Based on the extreme value distribution relationship of the modulation waves of the two sets of three corresponding to each of the dual three-phase control units, the sector corresponding to the control cycle and the sorting sequence of the six-phase pulses are determined. Based on the sign and amplitude of the modulation waves of the two sets of three corresponding to each of the dual three-phase control units, the effective range width of the six-phase pulse is determined, and the rising edge time and falling edge time of the six-phase pulse are determined sequentially according to the sorting sequence, so that the falling edge of the previous pulse in adjacent pulses coincides with the rising edge of the next pulse, and the six-phase pulses are connected end to end in the control cycle. One phase is selected as a continuous reference phase, and a uniform shift is applied to the rising and falling edges of the six-phase pulses with reference to the continuous reference phase. The timing sequence of the six-phase pulses under the dynamic carrier phase-shift modulation method is determined based on the rising and falling edge times of the translated six-phase pulses.

3. The common-mode voltage elimination and midpoint voltage coordinated control method according to claim 1, characterized in that, Feedback adjustment is performed on the shared midpoint voltage to obtain the total target average midpoint current, and the current is allocated according to the weighting coefficients corresponding to each of the dual three-phase control units to obtain the target average midpoint current corresponding to each of the dual three-phase control units, including: Based on the deviation between the common midpoint voltage and the given value of the common midpoint voltage, feedback adjustment is performed to obtain the total target average midpoint current; Based on the adjustment capability, operating status, or preset allocation rules of each dual-three-phase control unit, the weight coefficient corresponding to each dual-three-phase control unit is determined, wherein the sum of each weight coefficient is 1; Based on the weighting coefficients corresponding to each of the dual three-phase control units, the total target average midpoint current is allocated to obtain the target average midpoint current corresponding to each of the dual three-phase control units.

4. The common-mode voltage elimination and midpoint voltage coordinated control method according to claim 1, characterized in that, Based on the modulation waves corresponding to the two sets of three phases within each of the dual three-phase control units and the corresponding output phase currents, the zero-sequence voltage reference value of each of the dual three-phase control units is determined to ensure that the deviation between the average midpoint current of each of the dual three-phase control units and the corresponding target average midpoint current is zero or minimized, including: Based on the value constraints of the modified modulation wave obtained by superimposing the two sets of three-phase modulation waves in each of the dual three-phase control units with zero-sequence voltages of equal magnitude and opposite polarity, the feasible range of zero-sequence voltage for each of the dual three-phase control units is determined. If the feasible range of zero-sequence voltage of a certain dual three-phase control unit is empty, then the reference value of zero-sequence voltage of the dual three-phase control unit is taken as zero; if the feasible range of zero-sequence voltage of a certain dual three-phase control unit is not empty, then the upper and lower boundaries of the feasible range of zero-sequence voltage of the dual three-phase control unit and the zero-sequence voltage values ​​that cause the segmentation characteristics of the modified modulation wave corresponding to the two sets of three phases in the dual three-phase control unit to change are taken as candidate breakpoints. Based on the output phase currents of the two sets of three phases in the dual three-phase control unit, calculate the average midpoint current corresponding to each candidate breakpoint. When the average midpoint current corresponding to a candidate breakpoint is equal to the target average midpoint current corresponding to the dual three-phase control unit, the corresponding zero-sequence voltage is taken as the zero-sequence voltage reference value of the dual three-phase control unit. When the average midpoint current corresponding to adjacent candidate breakpoints is located on both sides of the target average midpoint current corresponding to the dual three-phase control unit, linear interpolation is used to obtain the zero-sequence voltage reference value of the dual three-phase control unit. When the average midpoint current corresponding to all candidate breakpoints is located on the same side of the target average midpoint current corresponding to the dual three-phase control unit, the zero-sequence voltage corresponding to the candidate breakpoint that minimizes the absolute value of the deviation between the average midpoint current and the target average midpoint current corresponding to the dual three-phase control unit is selected as the zero-sequence voltage reference value of the dual three-phase control unit.

5. A common-mode voltage elimination and midpoint voltage coordinated control device, characterized in that, Control of even-array three-phase three-level NPC converters with a shared neutral point includes: The sampling module is used to acquire the modulation waves of each group of three phases of the even-numbered three-phase three-level NPC converter with the common neutral point in each control cycle, and to collect the output phase current and common neutral point voltage of each group of three phases. Each pair of three phases constitutes a dual three-phase control unit. The dynamic carrier phase-shift modulation module is used to use dynamic carrier phase-shift modulation to make the common-mode voltage transition generated by one set of three phases in each of the dual three-phase control units cancel each other out with the reverse common-mode voltage transition generated by the other set of three phases, based on the modulation waves of the two sets of three phases in each dual three-phase control unit. The midpoint current distribution module is used to perform feedback adjustment on the common midpoint voltage to obtain the total target average midpoint current, and to distribute it according to the weight coefficients corresponding to each of the dual three-phase control units to obtain the target average midpoint current corresponding to each of the dual three-phase control units. The zero-sequence voltage acquisition module is used to obtain the zero-sequence voltage reference value of each of the two sets of three corresponding modulation waves and the corresponding output phase current in each of the two three-phase control units, so that the deviation between the average midpoint current of each of the two three-phase control units and the corresponding target average midpoint current is zero or minimal. The PWM generation and output module is used to superimpose equal-sized but opposite-polarity zero-sequence voltages onto two sets of three-corresponding modulation waves in each of the dual three-phase control units according to the zero-sequence voltage reference value of each dual three-phase control unit, to obtain two sets of three-corresponding corrected modulation waves in each dual three-phase control unit. Based on the corrected modulation waves, the module generates PWM drive signals for each phase according to the dynamic carrier phase-shift modulation method, and applies the PWM drive signals to the even-numbered three-phase three-level NPC converter with the common midpoint.

6. An electronic device, characterized in that, include: One or more processors; Memory, used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method as described in any one of claims 1-4.

7. A computer-readable storage medium storing computer instructions thereon, characterized in that, When the computer instructions are executed by the processor, they implement the steps of the method as described in any one of claims 1-4.

Images