Three-phase permanent magnet synchronous motor driving system and control method thereof

Abstract

The invention relates to the technical field of motor driving control, and discloses a three-phase permanent magnet synchronous motor driving system and a control method thereof. Aiming at the problems of output current quality reduction and calculation burden increase when the existing limited control set model prediction control is combined with the switching state PWM to control the inverter, the method comprises the following steps: establishing a leakage current mathematical model, adopting limited switching state dead-beat prediction leakage current control, and combining switching state prediction and a virtual voltage vector. Common-mode voltage and leakage current are reduced, current THD is reduced, calculation amount is reduced, virtual voltage vectors are generated through software, cost is reduced, and an economical and efficient control scheme is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of motor drive control, and in particular to a three-phase permanent magnet synchronous motor drive system and a control method thereof. Background Art

[0002] Permanent magnet synchronous motor (PMSM) is widely used in electric vehicles, industrial automation and household appliances due to its high efficiency and high power density. However, in the PMSM drive system, the high-frequency pulse width modulation (PWM) signal generated by the inverter will cause the generation of common mode voltage (CMV), which will cause leakage current problems. Leakage current not only affects the safety and reliability of the system, but also causes the increase of total harmonic distortion (THD) of the current, thereby reducing the operating performance of the motor.

[0003] In order to solve the leakage current problem, researchers have proposed a variety of PWM modulation techniques, such as active zero-state PWM (AZS-PWM), switch-state PWM, and near-state PWM (NS-PWM). Among them, switch-state PWM reduces leakage current by fixing the common mode voltage (CMV), showing good results. However, the traditional finite control set model predictive control (FCS-MPC) method can reduce leakage current when using a limited number of voltage vectors, but it will increase the total harmonic distortion (THD) of the output current and affect the current quality.

[0004] In the prior art, the finite control set model predictive control (FCS-MPC) combined with the switch state PWM method is widely used in inverter control. This method reduces leakage current by fixing the common mode voltage using a finite number of voltage vectors (usually odd or even vectors). Specifically, the switch state PWM selects a specific voltage vector to keep the common mode voltage at a constant value, thereby effectively reducing leakage current.

[0005] However, this approach has a significant disadvantage: due to the use of a limited number of voltage vectors, although the common-mode voltage is controlled, the output current quality of the inverter is reduced, which is manifested as an increase in current THD. For example, when using an odd number of vectors to fix the CMV, the current THD may increase to 7.5%. In addition, although the introduction of virtual voltage vectors can increase the number of switching states and improve the current quality, it will also increase the computational burden, resulting in the processor requiring more computing resources. Summary of the invention

[0006] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a three-phase permanent magnet synchronous motor drive system and a control method thereof, so as to solve the problem that when the finite control set model predictive control combined with the switch state PWM method is used to control the inverter in the prior art, although the common mode voltage can be controlled to reduce the leakage current, the output current quality will be reduced and the introduction of a virtual voltage vector will increase the calculation burden.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a three-phase permanent magnet synchronous motor drive system control method, the method comprising: The current state of the three-phase inverter is obtained through the controller, and the current value of the next control cycle is predicted based on the dynamic circuit equation; Construct a discretized prediction model to generate a voltage vector set based on the synthesis rules of physical voltage vectors and virtual voltage vectors; Combined with the current value of the next control cycle predicted based on the dynamic circuit equation, a multi-cycle current prediction is performed on each voltage vector in the voltage vector set to obtain a predicted current value; A cost function is defined, and a candidate voltage vector sequence is screened from a voltage vector set in combination with a current tracking error; Based on the deadbeat control principle, the optimal voltage vector is selected from the candidate voltage vector sequence according to the difference between the reference current and the predicted current; The optimal voltage vector is applied to the three-phase inverter to drive the permanent magnet synchronous motor to operate.

[0008] Preferably, in a possible implementation manner of the first aspect, the dynamic circuit equation is:

[0009] in, is the current value, is the predicted current value at the next moment, is the current voltage vector, is the control period, and It is the filter resistor and inductor.

[0010] Preferably, in a possible implementation manner of the first aspect, the voltage vector set includes 3 physical voltage vectors and 6 virtual voltage vectors, the physical voltage vectors are odd-numbered vectors, and the common-mode voltage values ​​of the voltage vectors are constrained to be , is the DC bus voltage.

[0011] Preferably, in a possible implementation manner of the first aspect, the synthesis method of the virtual voltage vector is: dividing the control period into three time periods, applying different physical voltage vectors in each time period, and using the formula Generate a virtual voltage vector where , and are three physical voltage vectors.

[0012] Preferably, in a possible implementation manner of the first aspect, during the synthesis of the virtual voltage vector, the optimization of the application sequence is performed by calculating the current ripple surface Implementation, where , , They are the ripple components in three time periods respectively.

[0013] Preferably, in a possible implementation manner of the first aspect, the multi-cycle current prediction is:

[0014] in, is the predicted current value at the second moment in the future, is the predicted current value at the next moment, is the voltage vector at the next moment, is the control period, and It is the filter resistor and inductor.

[0015] Preferably, in a possible implementation manner of the first aspect, the cost function is:

[0016] in, is the candidate voltage vector sequence, is the reference current.

[0017] Preferably, in a possible implementation manner of the first aspect, calculation of the optimal voltage vector satisfies:

[0018] in, is the optimal voltage vector.

[0019] In a second aspect, the present invention provides a three-phase permanent magnet synchronous motor drive system, the system comprising: Three-phase inverter: used to convert DC power into AC power to drive a three-phase permanent magnet synchronous motor; Controller: used to obtain the current state of the three-phase inverter and predict the future current state, define the cost function, and select the optimal voltage vector based on the deadbeat control to act on the three-phase inverter; Filter: used to reduce harmonic distortion, smooth output current and stabilize common-mode voltage; Permanent magnet synchronous motor: used to receive AC power generated by a three-phase inverter.

[0020] The beneficial effect of the present invention is that by combining switch state predictive control and virtual voltage vector, the method effectively reduces the common mode voltage, thereby significantly reducing the leakage current. At the same time, by optimizing the voltage vector selection, the total harmonic distortion of the line current is reduced, significantly improving the current quality.

[0021] Compared with the traditional method that needs to evaluate all virtual vectors, the present invention only needs to evaluate ten candidate voltage vectors by defining a voltage-based cost function, which greatly reduces the amount of calculation while maintaining high control accuracy and dynamic response.

[0022] The virtual voltage vector is generated by software without changing the hardware topology, which reduces the implementation cost and improves the flexibility and adaptability of the system.

[0023] In summary, the present invention provides an economical and efficient control solution for controlling an inverter in a system that supplies energy to a permanent magnet synchronous motor based on a photovoltaic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A leakage current path diagram in a permanent magnet synchronous motor drive system is provided for this application.

[0026] Figure 2 A relationship diagram of voltage vector and common mode voltage is provided for this application.

[0027] Figure 3 A synthesis method diagram of a virtual voltage vector is provided for this application.

[0028] Figure 4 A synthetic virtual voltage vector diagram is provided for this application.

[0029] Figure 5 A system block diagram of finite switch state deadbeat control is provided for this application.

[0030] Figure 6 A simulation waveform diagram of finite switching state deadbeat control in a permanent magnet synchronous motor drive system is provided for this application. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Embodiment 1: The present invention provides a three-phase permanent magnet synchronous motor drive control method, including establishing a mathematical model of leakage current, proposing a finite switching state deadbeat prediction leakage current control and a virtual voltage vector synthesis method.

[0033] 1. Establishing a mathematical model of leakage current like Figure 1 As shown, the common mode voltage CMV refers to the potential difference between the motor neutral point (n) and the midpoint of the DC bus in the permanent magnet synchronous motor. The relationship between the common mode voltage CMV and the phase voltage is described by the following formula:

[0034] in, They are the potentials of the three-phase inverter and the midpoint o of the DC bus respectively.

[0035] The leakage current is driven by the common mode voltage, and the equivalent impedance of its path is determined by the filter parameters. and is the resistance and inductance of the grid-connected filter. To calculate the frequency The equivalent impedance of the leakage current path when is expressed by the following formula:

[0036]

[0037] in is the capacitor, is the comprehensive equivalent impedance.

[0038] (II) Propose a finite switching state deadbeat predictive leakage current control like Figure 2 As shown in FIG. 1 , in a three-phase inverter, the value and waveform of the common-mode voltage present a switching cycle that is not constant. Among them, the odd vector, the even vector, and the zero vector each correspond to a different value. Figure 2 The influence of even vectors and odd vectors can be seen in the figure. They cause the common mode voltage waveform to be and Changes in level occur.

[0039] Switch state predictive control extends traditional model predictive control by incorporating switch state information into the control algorithm. This real-time data from the switch node can improve the control accuracy and response speed of the system. This embodiment examines the odd vector as a finite input set.

[0040] The implementation steps of deadbeat predictive control of switch states include: (1) State estimation State estimation mainly models the system based on the current state or voltage vector of the current state in the system, obtains the dynamic circuit equation, and uses these data to predict the future state of the system. The current is predicted using the following formula:

[0041] in, is the current value, is the predicted current value at the next moment, is the current voltage vector, is the control period, and It is the filter resistor and inductor.

[0042] (2) Prediction model Due to the limited number of switching vectors and the lack of zero vectors, the generated current contains high ripple and distortion. Virtual vectors are used to increase the number of switches without changing the inverter topology.

[0043]

[0044] in , and are three odd physical voltage vectors (this embodiment uses , and ), these three physical voltage vectors are placed in the control interval They are applied separately to obtain a synthetic virtual vector.

[0045] By introducing a virtual voltage vector and increasing the switching state, the control quality of the system can be improved. Multi-cycle current prediction is performed based on the following formula:

[0046] in, is the predicted current value at the second moment in the future, is the predicted current value at the next moment, is the voltage vector at the next moment, is the control period, and It is the filter resistor and inductor.

[0047] The model is predicted and optimized based on feasible switching vectors at one or more future moments. The optimization result takes into account multiple factors, such as current tracking, common-mode voltage control, and current distortion. The candidate voltage vector sequence is screened through the cost function and applied to the next control moment. The calculation result provides candidate optimal voltage vectors for zero-beat control.

[0048] (3) Design of control law The control requirement is expressed in a formula by defining a cost function to obtain the minimum value. The cost function for the inverter has the following components:

[0049] in, is the reference current, is the predicted current at the second moment in the future.

[0050] (4) Deadbeat control Deadbeat control is based on a discretized mathematical model and calculates the optimal voltage vector through an analytical formula to ensure that the current accurately tracks the reference value at the next sampling moment.

[0051]

[0052] in, It is the optimal voltage vector, which is applied to the current control moment to ensure that the current can accurately track the reference value in the next time period (k+1 moment).

[0053] 3. Virtual vector synthesis method In a three-phase inverter, there are usually seven basic voltage vectors, including six effective vectors and one zero vector. In this embodiment, in order to optimize the control effect, especially to reduce the common-mode voltage and current distortion, a virtual voltage vector is synthesized to increase the selection range of the control input. The virtual vector is generated by splitting and applying different physical voltage vectors in one control cycle. In this embodiment, odd-numbered vectors are combined to generate a new virtual vector.

[0054] like Figure 3 As shown, the synthetic virtual vector first divides the control cycle into three time periods, and a different physical voltage vector is applied to each time period. This voltage vector is derived from the odd vector , and By selecting from the three time periods and applying different odd vectors, a new virtual vector can be synthesized.

[0055] like Figure 4 Of the nine vectors shown, three are physical vectors and the remaining six are synthesized virtual vectors.

[0056] However, when selecting a virtual vector, the application order needs to be considered. For example, if n = 113 is the optimal vector, then a choice needs to be made from the sequences 113, 131, or 311. The method used in this embodiment uses a ripple-based cost function. Figure 4 The corrugated surface defined by considering the three-part vector synthesis is presented.

[0057] First, calculate the slope of the current due to the applied vector:

[0058]

[0059]

[0060] The surface ripple is realized as shown in the following formula:

[0061] in,

[0062]

[0063]

[0064] in,

[0065]

[0066]

[0067] in, , , , and They are the current current value, the predicted current value at the beginning of the next control cycle, the predicted current value at the first third of the next control cycle, the predicted current value at the second third of the next control cycle, and the predicted current value at the beginning of the second control cycle in the future.

[0068] Finally, the minimum hanging surface ripple Perform sequence optimization, where There are three possible vector sequences.

[0069] Figure 5 Figure 2 is the system block diagram of the proposed finite switching state deadbeat control.

[0070] Embodiment 2: The present invention provides a three-phase permanent magnet synchronous motor drive system, including a three-phase inverter, a controller, a filter and a permanent magnet synchronous motor.

[0071] Three-phase inverter: used to convert direct current into alternating current to drive permanent magnet synchronous motor.

[0072] Controller: Implements finite switch state deadbeat control, including a state acquisition module for acquiring the current working state of the system; a prediction model module for predicting future current states and optimizing based on feasible switch states; and a control law design module for designing control laws and defining cost functions to select the optimal voltage vector to control the minimum error of the system.

[0073] Filter: It reduces harmonic distortion, smoothes output current, and stabilizes common-mode voltage.

[0074] Permanent magnet synchronous motor: The receiver of energy in the system, accepting the AC power generated by the front-end inverter as input.

[0075] Embodiment 3: The present invention provides a simulation of finite switching state deadbeat control in a permanent magnet synchronous motor drive system. The simulated waveform is as follows: Figure 6 shown.

[0076] The main simulation parameters include: , , , , A 150W permanent magnet synchronous motor is used in the simulation. The main parameters of the permanent magnet synchronous motor are: rated voltage 24V, rated speed 3000r / min, rated torque 0.5N·m, rated power 150W, rated phase current 6.7A, rated phase resistance 0.18Ω, rated phase inductance 0.0025H, permanent magnet generates flux 0.016Wb, and pole pair number 2 (star connection).

[0077] Depend on Figure 6 It can be seen from the simulation results that the finite switch state model predictive control introduced in the present invention has a good effect in the permanent magnet synchronous motor drive system, which can effectively reduce the leakage current and current distortion to ensure the safe operation of the system.

[0078] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A three-phase permanent magnet synchronous motor drive system control method, characterized in that: The method comprises: The current state of the three-phase inverter is obtained through the controller, and the current value of the next control cycle is predicted based on the dynamic circuit equation; Construct a discretized prediction model to generate a voltage vector set based on the synthesis rules of physical voltage vectors and virtual voltage vectors; Combined with the current value of the next control cycle predicted based on the dynamic circuit equation, a multi-cycle current prediction is performed on each voltage vector in the voltage vector set to obtain a predicted current value; A cost function is defined, and a candidate voltage vector sequence is screened from a voltage vector set in combination with a current tracking error; Based on the deadbeat control principle, the optimal voltage vector is selected from the candidate voltage vector sequence according to the difference between the reference current and the predicted current; The optimal voltage vector is applied to the three-phase inverter to drive the permanent magnet synchronous motor to operate.

2. The three-phase permanent magnet synchronous motor drive system control method according to claim 1, characterized in that: The dynamic circuit equation is: in, is the current value, is the predicted current value at the next moment, is the current voltage vector, is the control period, and It is the filter resistor and inductor.

3. The three-phase permanent magnet synchronous motor drive system control method according to claim 1, characterized in that: The voltage vector set includes 3 physical voltage vectors and 6 virtual voltage vectors. The physical voltage vectors are odd-numbered vectors. The common-mode voltage values ​​of the voltage vectors are constrained to be , is the DC bus voltage.

4. The three-phase permanent magnet synchronous motor drive system control method according to claim 3, characterized in that: The synthesis method of the virtual voltage vector is: divide the control cycle into three time periods, apply different physical voltage vectors in each time period, and use the formula Generate a virtual voltage vector where , and are three physical voltage vectors.

5. The three-phase permanent magnet synchronous motor drive system control method according to claim 4, characterized in that: During the synthesis of the virtual voltage vector, the optimization of the application sequence is performed by calculating the current ripple surface Implementation, where , , They are the ripple components in three time periods respectively.

6. The three-phase permanent magnet synchronous motor drive system control method according to claim 1, characterized in that: The multi-cycle current prediction is: in, is the predicted current value at the second moment in the future, is the predicted current value at the next moment, is the voltage vector at the next moment, is the control period, and It is the filter resistor and inductor.

7. The three-phase permanent magnet synchronous motor drive system control method according to claim 6, characterized in that: The cost function is: in, is the candidate voltage vector sequence, is the reference current.

8. The three-phase permanent magnet synchronous motor drive system control method according to claim 7, characterized in that: The calculation of the optimal voltage vector satisfies: in, is the optimal voltage vector.

9. A three-phase permanent magnet synchronous motor drive system, characterized in that: The system comprises: Three-phase inverter: used to convert DC power into AC power to drive a three-phase permanent magnet synchronous motor; Controller: used to obtain the current state of the three-phase inverter and predict the future current state, define the cost function, and select the optimal voltage vector based on the deadbeat control to act on the three-phase inverter; Filter: used to reduce harmonic distortion, smooth output current and stabilize common-mode voltage; Permanent magnet synchronous motor: used to receive AC power generated by a three-phase inverter.

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