Three-level converter control method, controller, system, medium and product

Abstract

The invention discloses a three-level converter control method, a controller, a system, a medium and a product, and relates to the technical field of three-phase three-level converter control, and the method comprises the steps: obtaining the current operation parameters of a three-phase four-wire three-level converter; wherein the current operation parameters of the three-phase four-wire system three-level converter comprise a current three-phase current value of an alternating current side and a current midpoint voltage value of a direct current side, and the current midpoint voltage value is a voltage value of a common connection point of a first bus capacitor of the direct current side and a second bus capacitor of the direct current side; determining a modulation compensation value of the three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value; updating the three-phase modulation wave based on the modulation compensation value to obtain an updated three-phase modulation wave; and carrying out modulation wave generation based on the updated three-phase modulation wave to generate a driving signal so as to control the three-phase four-wire system three-level converter to work. According to the invention, neutral-point voltage balance control of the three-phase four-wire three-level converter can be realized.

Description

Technical Field

[0001] The present application relates to the technical field of three-phase three-level converter control, and in particular to a three-level converter control method, controller, system, medium and product. Background Art

[0002] In the related art, the control method for the DC bus midpoint voltage balance of the three-phase three-level converter topology can generally collect the changes in the DC side bus midpoint voltage of the converter, and then directly act on the opening and closing control of the switch tube in the three-phase three-level converter through loop control.

[0003] However, the above method is usually applicable to three-phase three-wire three-level converters. For three-phase four-wire three-level converters, due to the influence of the common-mode current loop, grid-side current harmonics are easily introduced. If the above control method is still used, the control effect is not good. Therefore, it is necessary to find a midpoint voltage balance control method suitable for three-phase four-wire three-level converters. Summary of the invention

[0004] The main purpose of the present application is to provide a three-level converter control method, controller, system, medium and product, aiming to solve the technical problem that the three-level converter midpoint voltage balance control method in the related art has poor control effect on the three-phase four-wire three-level converter.

[0005] To achieve the above object, the present application proposes a three-level converter control method, the three-level converter control method comprising:

[0006] Obtaining current operating parameters of the three-phase four-wire three-level converter; wherein the current operating parameters of the three-phase four-wire three-level converter include a current three-phase current value of the AC side of the three-phase four-wire three-level converter and a current midpoint voltage value of the DC side of the three-phase four-wire three-level converter, and the current midpoint voltage value is a voltage value of a common point of a first bus capacitor on the DC side and a second bus capacitor on the DC side;

[0007] Determine the modulation compensation value of the three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value;

[0008] Update the three-phase modulation wave based on the modulation compensation value to obtain an updated three-phase modulation wave;

[0009] The updated three-phase modulation wave is modulated and a drive signal is generated to control the operation of the three-phase four-wire three-level converter.

[0010] In one embodiment, before the step of updating the three-phase modulation wave based on the modulation compensation value to obtain the updated three-phase modulation wave, the method further includes:

[0011] Acquire a first voltage value across the first bus capacitor and a second voltage value across the second bus capacitor;

[0012] Perform proportional-integral regulation based on the difference between the first voltage value and the second voltage value to obtain a feedback regulation value;

[0013] The steps of updating the three-phase modulation wave based on the modulation compensation value and obtaining the updated three-phase modulation wave include:

[0014] The three-phase modulation wave is updated based on the modulation compensation value and the feedback adjustment value to obtain an updated three-phase modulation wave.

[0015] In one embodiment, the step of updating the three-phase modulation wave based on the modulation compensation value and the feedback adjustment value to obtain the updated three-phase modulation wave includes:

[0016] In v A ×I LA ×sign(v A )+v B ×I LB ×sign(v B )+v C ×I LC ×sign(v C )>0, based on v X ′=v X +v0+PI out Obtaining an updated three-phase modulation wave;

[0017] In v A ×I LA ×sign(v A )+v B ×I LB ×sign(v B )+v C ×I LC ×sign(v C )<0, based on v X ′=v X +v0-PI out Obtaining an updated three-phase modulation wave;

[0018] Among them, v X ' is the updated three-phase modulation wave, v X is a three-phase modulation wave, X∈(A,B,C), v0 is the modulation compensation value, PI out is the feedback adjustment value, I LA is the current A phase current value on the AC side, I LB is the current B-phase current value on the AC side, I LCis the current C-phase current value on the AC side, sign() indicates the direction of the modulation wave, sign()=1 indicates the positive half cycle of the modulation wave, and sign()=-1 indicates the negative half cycle of the modulation wave.

[0019] In one embodiment, the step of determining the modulation compensation value of the three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value includes:

[0020] Based on the current three-phase current value and the current midpoint voltage value, the modulation compensation value is determined using formula 1; formula 1 is:

[0021]

[0022] Where, v0 is the modulation compensation value, Vdc is the voltage value of the DC bus power supply connected to the three-phase four-wire three-level converter, C P is the capacitance value of the first bus capacitor, C N is the capacitance value of the second bus capacitor, Ts is the switching period, v A is the A phase modulation wave voltage, v B is the B phase modulation wave voltage, v C is the C phase modulation wave voltage, I LA is the current A phase current value on the AC side, I LB is the current B-phase current value on the AC side, I LC is the current C-phase current value on the AC side, sign() indicates the direction of the modulation wave, sign()=1 indicates the positive half cycle of the modulation wave, and sign()=-1 indicates the negative half cycle of the modulation wave.

[0023] In one embodiment, before the step of determining the modulation compensation value of the three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value, the method further includes:

[0024] Acquire current operating parameters of the AC power supply; wherein the AC power supply is connected to the AC side, and the current operating parameters of the AC power supply include a current three-phase AC source current value and a current three-phase AC source voltage value;

[0025] Determine a reference current value based on a current three-phase AC source current value and a current three-phase AC source voltage value;

[0026] Based on the reference current value and the current three-phase current value, a three-phase modulation wave is determined.

[0027] In one embodiment, the modulation method for modulating the updated three-phase modulation wave includes SPWM modulation and SVPWM modulation.

[0028] In addition, to achieve the above objectives, the present application also proposes a controller, which includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the three-level converter control method as described above.

[0029] In addition, to achieve the above objectives, the present application also proposes a three-level converter control system, the three-level converter control system comprising:

[0030] A controller such as the one described above;

[0031] The three-level converter is a three-phase four-wire three-level converter connected to the controller.

[0032] In addition, to achieve the above-mentioned purpose, the present application also proposes a storage medium, which is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the three-level converter control method as described above are implemented.

[0033] In addition, to achieve the above-mentioned purpose, the present application also proposes a computer program product, which includes a computer program. When the computer program is executed by a processor, the steps of the three-level converter control method as described above are implemented.

[0034] One or more technical solutions proposed in this application have at least the following technical effects:

[0035] The three-level converter control method proposed in the present application can obtain the current operating parameters of the three-phase four-wire three-level converter (including the current three-phase current value on the AC side of the three-phase four-wire three-level converter and the current midpoint voltage value on the DC side of the three-phase four-wire three-level converter, etc.); thus, the modulation compensation value corresponding to the three-phase modulation wave at the current moment can be determined according to the real-time feedback of the current operating parameters, so that the three-phase modulation wave can be updated by the modulation compensation value, and the updated three-phase modulation wave can be used for modulation and emitting waves to generate a drive signal to control the operation of the three-phase four-wire three-level converter. The present application uses the current operating parameters of the three-phase four-wire three-level converter to adjust the modulation waveform in real time to compensate and correct the voltage imbalance on the DC side bus capacitor, maintain the balance of the midpoint voltage, and enable the converter to work more stably and symmetrically, thereby also reducing the harmonic components in the current. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 A schematic diagram of a flow chart provided for a first embodiment of a three-level converter control method of the present application;

[0039] Figure 2 It is a circuit structure diagram of a three-phase three-level NPC converter;

[0040] Figure 3 It is a circuit structure diagram of a three-phase three-level ANPC converter;

[0041] Figure 4 Schematic diagram of the circuit structure of a three-phase three-level Vienna converter;

[0042] Figure 5 Schematic diagram of the circuit structure of a three-phase T-type three-level converter;

[0043] Figure 6 is a schematic diagram of the structure of an example three-phase four-wire three-level converter;

[0044] Figure 7 It is the schematic diagram of SPWM modulation;

[0045] Figure 8 This is a schematic diagram of PWM modulation zero state;

[0046] Fig. 9 To obtain a simulation waveform diagram using a midpoint voltage balance algorithm in the related art;

[0047] Fig.10 This is a simulation waveform diagram obtained by using the three-level converter control method provided in Example 1 of the present application;

[0048] Fig.11 is a control principle diagram of an exemplary three-level converter control system;

[0049] Fig.12 Schematic diagram of the controller structure of the hardware operating environment involved in the three-level converter control method in the embodiment of the present application.

[0050] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0051] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0052] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0053] The main solution of the embodiment of the present application is: obtaining the current operating parameters of the three-phase four-wire three-level converter; wherein the current operating parameters of the three-phase four-wire three-level converter include the current three-phase current value of the AC side of the three-phase four-wire three-level converter and the current midpoint voltage value of the DC side of the three-phase four-wire three-level converter, and the current midpoint voltage value is the voltage value of the common connection point of the first bus capacitor on the DC side and the second bus capacitor on the DC side; based on the current three-phase current value and the current midpoint voltage value, determining the modulation compensation value of the three-phase modulation wave; updating the three-phase modulation wave based on the modulation compensation value to obtain the updated three-phase modulation wave; modulating and transmitting the wave based on the updated three-phase modulation wave to generate a drive signal to control the operation of the three-phase four-wire three-level converter.

[0054] The bus midpoint voltage fluctuation of the three-phase three-level converter topology is mainly caused by the inconsistency of the DC side capacitor and the switch tube parameters, the unbalanced load, and the different effects of the switch state on the midpoint voltage. In essence, in each switching cycle, when current flows through the midpoint, the upper and lower bus capacitors on the DC side have opposite charging and discharging processes, and the midpoint voltage fluctuates at this time. The midpoint voltage fluctuation will cause multiple hazards to the entire system: the output side increases low-order harmonics, reduces efficiency, and affects output performance; the power device is subjected to unbalanced voltage, which affects the normal operation of the device or even destroys it, and reduces the life of the DC side capacitor. Therefore, the problem of midpoint voltage fluctuation is an important issue directly related to system safety and output performance, and needs to be properly resolved.

[0055] In the related art, the control method for the DC bus midpoint voltage balance of the three-phase three-level converter topology can generally collect the changes in the DC side bus midpoint voltage of the converter, and then directly act on the opening and closing control of the switch tube in the three-phase three-level converter through loop control.

[0056] However, the above method is usually applicable to three-phase three-wire three-level converters. For three-phase four-wire three-level converters, due to the influence of the common-mode current loop, grid-side current harmonics are easily introduced. If the above control method is still used, the control effect is not good. Therefore, it is necessary to find a midpoint voltage balance control method suitable for three-phase four-wire three-level converters.

[0057] The present application provides a solution that can determine the modulation compensation value of the modulation waveform in real time through the current operating parameters such as the current three-phase current value and the current midpoint voltage value of the three-phase four-wire three-level converter. The modulation waveform can be compensated by the modulation compensation value to correct the imbalance of the DC side capacitor voltage. By maintaining the balance of the midpoint voltage, it is ensured that the converter can operate more stably and symmetrically, and the harmonic components in the current can also be reduced.

[0058] It should be noted that the execution subject of this embodiment may be a computing service device with data processing, network communication and program running functions, such as a tablet computer, a personal computer, etc., or an electronic device capable of realizing the above functions, etc. The controller is taken as an example to illustrate this embodiment and the following embodiments.

[0059] Based on this, the embodiment of the present application provides a three-level converter control method, referring to Figure 1 , Figure 1 This is a flow chart of Embodiment 1 of the three-level converter control method of the present application.

[0060] In this embodiment, the three-level converter control method may include steps S100 to S400:

[0061] Step S100, obtaining current operating parameters of a three-phase four-wire three-level converter.

[0062] Among them, the current operating parameters of the three-phase four-wire three-level converter include the current three-phase current value of the AC side of the three-phase four-wire three-level converter and the current midpoint voltage value of the DC side of the three-phase four-wire three-level converter. The current midpoint voltage value is the voltage value of the common connection point of the first bus capacitor on the DC side and the second bus capacitor on the DC side.

[0063] Step S200, determining the modulation compensation value of the three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value.

[0064] Step S300, updating the three-phase modulation wave based on the modulation compensation value to obtain an updated three-phase modulation wave.

[0065] Step S400, modulating and transmitting the wave based on the updated three-phase modulation wave to generate a driving signal to control the operation of the three-phase four-wire three-level converter.

[0066] It should be noted that the three-level converter control method in this embodiment is applicable to a three-phase four-wire three-level converter; the three-phase four-wire three-level converter may include a three-phase switch bridge arm, a first bus capacitor, a second bus capacitor and an LC filter; wherein, the first port on the DC side of the three-phase switch bridge arm is connected to one end of the first bus capacitor, the second port on the DC side of the three-phase switch bridge arm is respectively connected to the other end of the first bus capacitor and one end of the second bus capacitor, the second port on the DC side of the three-phase switch bridge arm is the common connection point of the midpoints of the three bridge arms, the third port on the DC side of the three-phase switch bridge arm is connected to the other end of the second bus capacitor, the three AC side ports of the three-phase switch bridge arm are all connected to the LC filter, and the common connection point of the capacitor of the LC filter is connected to the common connection point of the first bus capacitor and the second bus capacitor; one end of the first bus capacitor and the other end of the second bus capacitor are connected to the DC bus power supply, and the LC filter is also connected to the AC power supply.

[0067] like Figures 2 to 5 The following are circuit diagrams of four common three-phase three-wire three-level converters; Figure 2 It is the circuit structure diagram of three-phase three-level NPC converter. Figure 3 The circuit structure diagram of the three-phase three-level ANPC converter is shown in Figure 1. Figure 4 It is the circuit structure diagram of the three-phase three-level Vienna converter. Figure 5 The circuit structure diagram of the three-phase T-type three-level converter is shown in FIG. 1 . The topological structures of the three-phase switch bridge arms of the above four three-phase three-wire three-level converters are slightly different, and the other structures are similar. The three-phase four-wire three-level converter in this embodiment is an improved three-level converter obtained by connecting the capacitor common point of the filter on the AC side of the three-phase three-wire three-level converter to the neutral point on the DC side of the converter based on the common three-phase three-wire three-level converter.

[0068] For ease of understanding, based on Figure 6 The structural diagram of the three-phase four-wire three-level converter shown in FIG. 1 illustrates the three-level converter control method in this embodiment. Figure 6 As shown, the LC filter includes an inductor L A1 ~L C1 、Inductance Lf A1 ~Lf C1 and capacitor C A ~C C ; Among them, the inductance L A1 ~L C1 One end of the inductor L is connected to the three AC side ports of the three-phase switch bridge arm. A1 ~L C1 The other end corresponds to the capacitor C A ~C C One end and the inductor LfA1 ~Lf C1 One end of the capacitor C A ~C C The other end of the capacitor C A ~C C The common point N' is connected to the first bus capacitor C P and the second bus capacitor C N The common point O. Inductance Lf A1 ~Lf C1 The other end corresponds to the three-phase E A ~E C In the control process of the three-phase four-wire three-level converter, real-time sampling can be performed through devices such as current sensors and voltage sensors to obtain the current three-phase current value output on the AC side of the three-phase switch bridge arm and the current midpoint voltage value on the DC side of the three-phase switch bridge arm; the midpoint voltage value can be used to determine the voltage balance state. If the midpoint voltage is unbalanced, it may cause harmonic distortion or unstable control.

[0069] In order to eliminate the influence of harmonics and achieve voltage balance, the modulation compensation value of the three-phase modulation wave can be determined based on the current three-phase current value and the current midpoint voltage value, and the waveform shape of the three-phase modulation wave can be adjusted according to the modulation compensation value. The addition of the modulation compensation value will adjust its waveform shape in each cycle of the three-phase modulation wave, so that the amplitude, frequency and even phase of the waveform of the three-phase modulation wave can be appropriately corrected and updated according to the current three-phase current value and the current midpoint voltage value measured in real time. The updated three-phase modulation wave is overlapped with the carrier used for modulating the wave, and a drive signal can be generated. The drive signal drives the switch tube in the three-phase switch bridge arm to turn on or off, thereby controlling the operation of the three-phase four-wire three-level converter to minimize harmonic distortion; wherein, the modulation method for modulating the updated three-phase modulation wave can include SPWM modulation and SVPWM modulation. In a feasible implementation, step S200 can specifically include determining the modulation compensation value based on the current three-phase current value and the current midpoint voltage value using calculation formula 1; calculation formula 1 is:

[0070]

[0071] Where, v0 is the modulation compensation value, Vdc is the voltage value of the DC bus power supply connected to the three-phase four-wire three-level converter, C P is the capacitance value of the first bus capacitor, C N is the capacitance value of the second bus capacitor, Ts is the switching period, v A is the A phase modulation wave voltage, v B is the B phase modulation wave voltage, v C is the C phase modulation wave voltage, I LAis the current A phase current value on the AC side, I LB is the current B-phase current value on the AC side, I LC is the current C-phase current value on the AC side, sign() indicates the direction of the modulation wave, sign()=1 indicates the positive half cycle of the modulation wave, and sign()=-1 indicates the negative half cycle of the modulation wave.

[0072] Combine the following Figure 6 The above calculation formula 1 is explained. Figure 6 The circuit structure shown can be obtained as follows:

[0073]

[0074] Among them, I p is the current flowing through the first bus capacitor C P The current, I n is the current flowing through the second bus capacitor C N The current, I pn is the current flowing into the midpoint of the DC busbar, I no is the common mode current flowing into the middle point of the DC bus, Vdc is the voltage value of the DC bus power supply, V o It is the voltage value of the midpoint of the DC bus relative to the low-voltage end of the DC bus.

[0075] Assuming that the current in the circuit does not change within a switching cycle Ts, the above expression shows that the change value of the DC bus midpoint voltage within a switching cycle Ts is Since the current of the three-phase switch bridge arm (i.e. the current I flowing into the midpoint of the DC bus) pn ) and common mode current I no The first bus capacitor C flowing into the DC bus P and the second bus capacitor C N , which will cause the midpoint potential of the DC side bus to change. Therefore, the problem of midpoint potential imbalance of the three-phase four-wire three-level converter can be solved by analyzing the corresponding midpoint current.

[0076] Further, by analyzing the current I pn The relationship between the duty cycle and the modulation compensation value is used to determine the specific modulation compensation value. The following takes the SPWM modulation method as an example for quantitative derivation. Figure 7 It is a schematic diagram of SPWM modulation, such as Figure 7 As shown, v X is a three-phase modulation wave, X∈(A,B,C), and the positive half cycle of the modulation wave is represented by sign(v X )=1; the negative half cycle of the modulation wave is represented by sign(v X )=-1; Figure 8 As shown, Figure 8It is a schematic diagram of PWM modulation zero state; where T 0X is the total time of zero-state voltage action in one switching cycle, that is, at T 0x Invalid drive signals are output during the time. Figure 8 In the case where the carrier amplitude is 1, Assume that the currents flowing into the midpoint of the DC busbar in a certain switching cycle are:

[0077] I pn1 =(1-|v A |)×I LA +(1-|v B |)×I LB +(1-|v C |)×I LC ;

[0078] I no1 =I LA +I LB +I LC -I gA -I gB -I gC ;

[0079] Among them, I gA ,I gB and I gC are the three-phase current values ​​of the AC power supply, I gA +I gB +I gC =0; at this time, the voltage value of the DC bus midpoint relative to the DC bus low voltage end is expressed as V o1 In order to control the midpoint voltage on the DC bus side to achieve balance, the zero-sequence component of the modulation wave (i.e. the aforementioned modulation compensation value) can be superimposed on the three-phase modulation wave. The zero-sequence component is recorded as v0, v X ′=v X +v0.

[0080] In a switching cycle Ts, the currents flowing into the midpoint of the DC busbar after superimposing v0 are:

[0081] I pn2 =(1-|v A ′|)×I LA ′+(1-|v B ′|)×I LB ′+(1-|v C ′|)×I LC ′;

[0082] I no2 =I LA ′+I LB ′+I LC ′;

[0083] At this time, the voltage value of the DC bus midpoint relative to the DC bus low voltage end is expressed as V o2 , I LA ′、I LB ′ and I LC ' are the A-phase current value, B-phase current value and C-phase current value of the corresponding AC side output respectively. The expression of the DC side bus midpoint voltage change value within a switching cycle Ts obtained above is: It can be seen that after superimposing the modulation compensation value, Since the midpoint voltage needs to be balanced, And v A +v0 positive and negative and v A ' is the same, so the following calculation formula can be derived:

[0084]

[0085] After obtaining the parameters of relevant circuit components such as the first bus capacitor and the second bus capacitor of the three-phase four-wire three-level converter, and the current operating parameters of the three-phase four-wire three-level converter (including the current three-phase current value on the AC side and the current midpoint voltage value on the DC side), the above calculation formula 1 is substituted to calculate the corresponding modulation compensation value v0, and then v0 is superimposed on the three-phase modulation wave for modulation and wave generation, and a driving signal can be obtained to drive and control the three-phase switch bridge arm to achieve the DC bus side midpoint voltage balance control.

[0086] See also Figures 9-10 , Fig. 9 To obtain the simulation waveform by using the midpoint voltage balance algorithm in the related technology; Fig. 9 It is not difficult to see that the use of the midpoint voltage balance control algorithm applicable to the three-phase three-wire three-level converter in the related art to control the three-phase four-wire three-level converter can improve the midpoint voltage balance to a certain extent, but from the midpoint voltage waveform ( Fig. 9 Middle U dc ) It can be seen that the midpoint voltage waveform has large fluctuations, and the voltage waveform of the AC power supply ( Fig. 9 Middle U gline ) and the current waveform of the AC power supply ( Fig. 9 Middle I g_abc ) also has certain harmonic interference, and the waveform is not smooth. Therefore, the midpoint voltage balance control algorithm suitable for three-phase three-wire three-level converter in the related technology is not effective in controlling the midpoint voltage balance of the improved three-phase four-wire three-level converter. Fig.10 is a simulation waveform obtained by using the three-level converter control method provided by this embodiment; Fig.10It is not difficult to see that the midpoint voltage waveform ( Fig.10 Middle U dc ), AC power supply voltage waveform ( Fig.10 Middle U gline ) and current waveform ( Fig.10 Middle I g_abc ) are effectively improved, so the control effect achieved by the three-level converter control method of this embodiment is better.

[0087] It is worth mentioning that in order to make the three-level converter control system more stable, in a feasible implementation manner, before step S300, steps A100 to A200 may be further included:

[0088] Step A100, obtaining a first voltage value across the first bus capacitor and a second voltage value across the second bus capacitor.

[0089] Step A200, performing proportional-integral regulation based on the difference between the first voltage value and the second voltage value to obtain a feedback regulation value.

[0090] In this implementation, step S300 may include updating the three-phase modulation wave based on the modulation compensation value and the feedback adjustment value to obtain an updated three-phase modulation wave.

[0091] Specifically, this embodiment adds a midpoint voltage balance loop on the basis of the aforementioned modulation compensation value, and introduces a feedback adjustment value when the modulation compensation value v0 is used as a feedforward quantity to compensate the three-phase modulation wave. Fig.11 is a control schematic diagram of an exemplary three-level converter control system, such as Fig.11 As shown in FIG. 1 , the K_AD module (data conversion module) and the PI regulator (proportional integral regulator) constitute a midpoint voltage balancing loop. Since the actual voltage value obtained is large, it is not convenient for the PI regulator to directly process it. The two K_AD modules can respectively obtain the first voltage value U corresponding to the first bus capacitor. P The second voltage value U corresponding to the second bus capacitance NThe numerical value is processed to convert the voltage value into a numerical range that can be processed by the PI regulator (proportional integral regulator). The difference between the first voltage value and the second voltage value is obtained. This difference is an important parameter in feedback control and can reflect the voltage imbalance degree of the two bus capacitors. The PI regulator is then used to adjust the difference. The PI regulator is a common feedback controller that combines the advantages of proportional control and integral control, and can effectively reduce the steady-state error of the system and improve the stability of the system; its proportional control part makes the output of the PI regulator proportional to the input signal (i.e., the voltage difference), that is, if the voltage difference increases, the corresponding output will also increase accordingly, thereby reducing the voltage difference; the integral control part makes the output of the PI regulator proportional to the accumulation (i.e., integration) of the input signal, that is, if the voltage difference persists, the corresponding output will continue to increase until the voltage difference is eliminated. In specific applications, the gain parameters of the proportional control part and the integral control part of the PI regulator can be adaptively adjusted according to the actual characteristics and performance parameters of the control system, and no specific restrictions are made here.

[0092] The PI regulator can calculate a feedback adjustment value based on the voltage difference, and at the same time superimpose the aforementioned modulation compensation value v0 as a feedforward quantity to compensate for the three-phase modulation wave and obtain an updated three-phase modulation wave. The waveform of the three-phase modulation wave is comprehensively adjusted and updated using the modulation compensation value and the feedback adjustment value. The modulation compensation value can dynamically respond to changes in the three-phase current and the midpoint voltage, while the feedback adjustment value can respond to the imbalance of the capacitor voltage. This dynamic combined control strategy can respond to changes in the system more quickly, adjust the modulation wave in time to maintain the balance of the midpoint voltage, and ensure the operating stability of the control system. In a feasible implementation, the three-phase modulation wave is updated based on the modulation compensation value and the feedback adjustment value to obtain an updated three-phase modulation wave. The steps may include: in v A ×I LA ×sign(v A )+v B ×I LB ×sign(v B )+v C ×I LC ×sign(v C )>0, based on v X ′=v X +v0+PI out Get the updated three-phase modulation wave; in v A ×I LA ×sign(v A )+v B ×I LB ×sign(v B )+v C ×I LC×sign(v C )<0, based on v X ′=v X +v0-PI out Obtain the updated three-phase modulation wave; wherein, v X ' is the updated three-phase modulation wave, v X is a three-phase modulation wave, X∈(A,B,C), v0 is the modulation compensation value, PI out is the feedback adjustment value. The given voltage of the above PI regulator is generally 0V, and the feedback value is U P -U N , the corresponding feedback output is PI out When v A ×I LA ×sign(v A )+v B ×I LB ×sign(v B )+v C ×I LC ×sign(v C )>0, the converter energy is transmitted to the grid, and the feedback adjustment value is determined as PI out , and add it together with the modulation compensation value v0 into the three-phase modulation wave to obtain the updated three-phase modulation wave; when v A ×I LA ×sign(v A )+v B ×I LB ×sign(v B )+v C ×I LC ×sign(v C )<0, the grid energy is transmitted to the converter, and the feedback adjustment value is determined as -PI out , together with the modulation compensation value v0, is superimposed into the three-phase modulation wave to obtain the corresponding updated three-phase modulation wave.

[0093] In addition, before step S200, steps B100 to B300 may be included for determining an initial three-phase modulation wave, so as to perform waveform adjustment update compensation based on the three-phase modulation wave and the aforementioned modulation compensation value and feedback adjustment value.

[0094] Step B100, obtaining current operating parameters of the AC power supply.

[0095] The AC power source is connected to the AC side, and the current operating parameters of the AC power source include a current three-phase AC source current value and a current three-phase AC source voltage value.

[0096] Step B200, determining a reference current value based on the current value of the three-phase AC source and the current value of the three-phase AC source voltage.

[0097] Step B300, determining a three-phase modulation wave based on a reference current value and a current three-phase current value.

[0098] For more information, see Fig.11 The control principle diagram shown can obtain the three-phase AC power supply E A ~E C The current three-phase AC source current value (i.e. I gA,gB,gC ) and the current three-phase AC source voltage value (i.e. U gA,gB,gC ), the voltage / power outer loop can calculate the reference current value according to the current three-phase AC source current value and the current three-phase AC source voltage value. The voltage / power outer loop is mainly responsible for controlling the overall performance of electric energy. It can adjust the control strategy according to the actual needs of the system (such as grid voltage, load demand, etc.) to maintain the overall stability of the system. Fig.11 The voltage / power outer loop shown can determine a reference current value Iref by comparing the actual current AC source voltage value with the target voltage value (reference voltage, etc.), as well as the current corresponding actual power with the set target power (reference power, etc.). The reference current value is Fig.11 The current control inner loop needs to track the target to ensure that the system output can meet expectations. The current control inner loop can compare the current three-phase current value I_sample (i.e. I LA,LB,LC ) and the reference current value Iref obtained by the voltage / power outer loop, calculate the required modulation waveform (i.e., the initial three-phase modulation wave). The above-mentioned voltage / power outer loop can usually be implemented using a PI regulator to adjust the voltage and power. The PI regulator can reduce the steady-state error. By adjusting the voltage / power outer loop by PI, an accurate reference current value can be generated for use by the current control inner loop. The current control inner loop usually uses pulse width modulation technology to generate a three-phase modulation wave. The generated three-phase modulation wave is superimposed with the aforementioned feedback adjustment value and modulation compensation value v0 to obtain an updated three-phase modulation wave. The updated three-phase modulation wave is overlapped with the preset carrier for modulation and emission, which can be used as a driving signal for driving the three-phase switch bridge arm. Among them, for SPWM modulation, the modulation compensation value v0 and the feedback adjustment value (PI out or-PI out ), and superimposed into the original three-phase modulation wave; for SVPWM modulation, the compensation value v0 needs to be converted into the corresponding zero vector action time, and then superimposed into the original algorithm for generating the three-phase modulation wave; that is, Fig.11As shown, in the three-level converter control method provided by this embodiment, the midpoint voltage balancing loop (including the K_AD module and PI regulator part shown in the figure), the modulation compensation value v0 as the feedforward quantity, and the dual-loop control subsystem (a control subsystem composed of a voltage / power outer loop and a current control inner loop) work together to achieve power flow control while realizing capacitor voltage balancing control on the DC bus side of the three-phase four-wire three-level converter.

[0099] It is not difficult to understand that the three-level converter control method provided in the embodiment of the present application can obtain the current operating parameters of the three-phase four-wire three-level converter (including the current three-phase current value on the AC side and the current midpoint voltage value on the DC side, etc.); thus, the modulation compensation value corresponding to the three-phase modulation wave at the current moment can be determined according to the real-time feedback of the current operating parameters, so that the three-phase modulation wave can be updated by the modulation compensation value, and the updated three-phase modulation wave is used for modulation and emitting waves to generate a drive signal to control the operation of the three-phase four-wire three-level converter. The present application uses the current operating parameters of the three-phase four-wire three-level converter to adjust the modulation waveform in real time to compensate and correct the imbalance of the capacitor voltage on the DC side, maintain the balance of the midpoint voltage, and enable the converter to work more stably and symmetrically, thereby also reducing the harmonic components in the current.

[0100] The present application provides a controller, which includes: at least one processor; and a memory that is communicatively connected to the at least one processor; wherein the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the three-level converter control method in the above-mentioned embodiment one.

[0101] Reference below Fig.12 , which shows a schematic diagram of the structure of a controller suitable for implementing the embodiment of the present application. The controller in the embodiment of the present application may include but is not limited to mobile terminals such as laptop computers, PDAs (Personal Digital Assistants), PADs (Portable Application Descriptions), etc., and fixed terminals such as desktop computers, etc. Fig.12 The controller shown is merely an example and should not bring any limitation to the functions and scope of use of the embodiments of the present application.

[0102] like Fig.12As shown, the controller may include a processing device 1001 (e.g., a central processing unit, a graphics processor, etc.), which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM: Read Only Memory) 1002 or a program loaded from a storage device 1003 to a random access memory (RAM: Random Access Memory) 1004. In RAM1004, various programs and data required for the operation of the controller are also stored. The processing device 1001, ROM1002, and RAM1004 are connected to each other through a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Generally, the following systems can be connected to the I / O interface 1006: an input device 1007 including, for example, a touch screen, a touch pad, a keyboard, a mouse, an image sensor, a microphone, an accelerometer, a gyroscope, etc.; an output device 1008 including, for example, a liquid crystal display (LCD: Liquid Crystal Display), a speaker, a vibrator, etc.; a storage device 1003 including, for example, a magnetic tape, a hard disk, etc.; and a communication device 1009. The communication device 1009 can allow the controller to communicate with other devices wirelessly or by wire to exchange data. Although the figure shows a controller with various systems, it should be understood that it is not required to implement or have all the systems shown. More or fewer systems can be implemented or have alternatively.

[0103] In particular, according to the embodiments disclosed in the present application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in the present application include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network through a communication device, or installed from a storage device 1003, or installed from a ROM 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the method of the embodiment disclosed in the present application are executed.

[0104] The controller provided by the present application adopts the three-level converter control method in the above embodiment, which can solve the technical problem that the three-level converter midpoint voltage balance control method in the related art has poor control effect on the three-phase four-wire three-level converter. Compared with the related art, the beneficial effects of the controller provided by the present application are the same as the beneficial effects of the three-level converter control method provided by the above embodiment, and the other technical features in the controller are the same as the features disclosed in the previous embodiment method, which will not be repeated here.

[0105] The present application also provides a three-level converter control system, which may include a controller and a three-level converter as described above; wherein the three-level converter is a three-phase four-wire three-level converter connected to the controller. The structure of the three-phase four-wire three-level converter can be partially described with reference to the foregoing embodiment, and will not be repeated here.

[0106] The beneficial effects of the three-level converter control system provided in the present application are the same as the beneficial effects of the three-level converter control method provided in the above embodiment, and other technical features of the three-level converter control system are the same as the features disclosed in the method of the previous embodiment, which will not be repeated here.

[0107] It should be understood that the various parts disclosed in this application can be implemented by hardware, software, firmware or a combination thereof. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0108] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0109] The present application provides a computer-readable storage medium having computer-readable program instructions (ie, computer programs) stored thereon, wherein the computer-readable program instructions are used to execute the three-level converter control method in the above-mentioned embodiment.

[0110] The computer-readable storage medium provided in the present application may be, for example, a USB flash drive, but is not limited to electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems or devices, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM: Random Access Memory), a read-only memory (ROM: Read Only Memory), an erasable programmable read-only memory (EPROM: Erasable Programmable Read Only Memory or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM: CD-Read Only Memory), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system or device. The program code contained on the computer-readable storage medium may be transmitted using any appropriate medium, including but not limited to: wires, optical cables, RF (Radio Frequency: Radio Frequency), etc., or any suitable combination of the above.

[0111] The computer-readable storage medium may be included in the controller; or may exist independently without being assembled into the controller.

[0112] The computer-readable storage medium carries one or more programs. When the one or more programs are executed by the controller, the controller: obtains the current operating parameters of the three-phase four-wire three-level converter; wherein the current operating parameters of the three-phase four-wire three-level converter include the current three-phase current value of the AC side of the three-phase four-wire three-level converter and the current midpoint voltage value of the DC side of the three-phase four-wire three-level converter, and the current midpoint voltage value is the voltage value of the common connection point of the first bus capacitor and the second bus capacitor on the DC side; determines the modulation compensation value of the three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value; updates the three-phase modulation wave based on the modulation compensation value to obtain the updated three-phase modulation wave; modulates and generates the wave based on the updated three-phase modulation wave to generate a drive signal to control the operation of the three-phase four-wire three-level converter.

[0113] Computer program code for performing the operations of the present application may be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0114] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present application. In this regard, each square box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the square box can also occur in a sequence different from that marked in the accompanying drawings. For example, two square boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each square box in the block diagram and / or flow chart, and the combination of the square boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0115] The modules involved in the embodiments described in this application may be implemented by software or hardware, wherein the name of the module does not constitute a limitation on the unit itself in some cases.

[0116] The readable storage medium provided in the present application is a computer-readable storage medium, which stores computer-readable program instructions (i.e., computer programs) for executing the above-mentioned three-level converter control method, and can solve the technical problem that the three-level converter midpoint voltage balance control method in the related art has poor control effect on the three-phase four-wire three-level converter. Compared with the related art, the beneficial effects of the computer-readable storage medium provided in the present application are the same as the beneficial effects of the three-level converter control method provided in the above-mentioned embodiment, and will not be repeated here.

[0117] The present application also provides a computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the steps of the three-level converter control method as described above are implemented.

[0118] The computer program product provided by the present application can solve the technical problem that the control method of the neutral point voltage balance of the three-level converter in the related art has poor control effect on the three-phase four-wire three-level converter. Compared with the related art, the beneficial effects of the computer program product provided by the present application are the same as the beneficial effects of the three-level converter control method provided by the above embodiment, and will not be repeated here.

[0119] The above descriptions are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A three-level converter control method, characterized in that: The three-level converter control method comprises: Acquire current operating parameters of a three-phase four-wire three-level converter; wherein the current operating parameters of the three-phase four-wire three-level converter include a current three-phase current value of an AC side of the three-phase four-wire three-level converter and a current midpoint voltage value of a DC side of the three-phase four-wire three-level converter, and the current midpoint voltage value is a voltage value of a common point of a first bus capacitor on the DC side and a second bus capacitor on the DC side; Determining a modulation compensation value of a three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value; Update the three-phase modulation wave based on the modulation compensation value to obtain an updated three-phase modulation wave; Modulation is performed based on the updated three-phase modulation wave to generate a drive signal to control the operation of the three-phase four-wire three-level converter.

2. The three-level converter control method according to claim 1, characterized in that: Before the step of updating the three-phase modulation wave based on the modulation compensation value to obtain an updated three-phase modulation wave, the method further includes: Acquire a first voltage value across the first bus capacitor and a second voltage value across the second bus capacitor; Perform proportional-integral regulation based on the difference between the first voltage value and the second voltage value to obtain a feedback regulation value; The step of updating the three-phase modulation wave based on the modulation compensation value to obtain an updated three-phase modulation wave comprises: The three-phase modulation wave is updated based on the modulation compensation value and the feedback adjustment value to obtain the updated three-phase modulation wave.

3. The three-level converter control method according to claim 2, characterized in that: The step of updating the three-phase modulation wave based on the modulation compensation value and the feedback adjustment value to obtain the updated three-phase modulation wave comprises: In v A ×I LA ×sign(v A )+v B ×I LB ×sign(v B )+v C ×I LC ×sign(v C )>0, based on v X ′=v X +v0+PI out Obtaining the updated three-phase modulation wave; In v A ×I LA ×sign(v A )+v B ×I LB ×sign(v B )+v C ×I LC ×sign(v C )<0, based on v X ′=v X +v0-PI out Obtaining the updated three-phase modulation wave; Among them, v X ' is the updated three-phase modulation wave, v X is a three-phase modulation wave, X∈(A,B,C), v0 is the modulation compensation value, PI out is the feedback adjustment value, I LA is the current A phase current value on the AC side, I LB is the current B-phase current value on the AC side, I LC is the current C-phase current value on the AC side, sign() indicates the direction of the modulation wave, sign()=1 indicates the positive half cycle of the modulation wave, and sign()=-1 indicates the negative half cycle of the modulation wave.

4. The three-level converter control method according to claim 1, characterized in that: The step of determining the modulation compensation value of the three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value comprises: Based on the current three-phase current value and the current midpoint voltage value, the modulation compensation value is determined using calculation formula 1; the calculation formula 1 is: Wherein, v0 is the modulation compensation value, Vdc is the voltage value of the DC bus power supply connected to the three-phase four-wire three-level converter, C P is the capacitance value of the first bus capacitor, C N is the capacitance value of the second bus capacitor, Ts is the switching period, v A is the A phase modulation wave voltage, v B is the B phase modulation wave voltage, v C is the C phase modulation wave voltage, I LA is the current A phase current value on the AC side, I LB is the current B-phase current value on the AC side, I LC is the current C-phase current value on the AC side, sign() indicates the direction of the modulation wave, sign()=1 indicates the positive half cycle of the modulation wave, and sign()=-1 indicates the negative half cycle of the modulation wave.

5. The three-level converter control method according to claim 1, characterized in that: Before the step of determining the modulation compensation value of the three-phase modulation wave based on the current three-phase current value and the current midpoint voltage value, the method further includes: Acquire current operating parameters of an AC power supply; wherein the AC power supply is connected to the AC side, and the current operating parameters of the AC power supply include a current three-phase AC source current value and a current three-phase AC source voltage value; Determining a reference current value based on the current three-phase AC source current value and the current three-phase AC source voltage value; The three-phase modulation wave is determined based on the reference current value and the current three-phase current value.

6. The three-level converter control method according to any one of claims 1 to 5, characterized in that: The modulation modes for modulating the updated three-phase modulation wave include SPWM modulation and SVPWM modulation.

7. A controller, characterized in that: The controller comprises: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the three-level converter control method according to any one of claims 1 to 6.

8. A three-level converter control system, characterized in that: The three-level converter control system comprises: The controller as claimed in claim 7; A three-level converter, wherein the three-level converter is a three-phase four-wire three-level converter, and is connected to the controller.

9. A storage medium, characterized in that: The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the three-level converter control method according to any one of claims 1 to 6 are implemented.

10. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the steps of the three-level converter control method according to any one of claims 1 to 6 are implemented.

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