Method for Suppressing Torque Ripple of Permanent Magnet Motor Based on Hybrid System Theory

Abstract

The present invention provides a method for suppressing torque ripple of a permanent magnet motor based on the theory of hybrid systems. The commutation moment of the motor is determined by Hall signals and the control strategy is switched. PI-PWM control is adopted during non-commutation periods, and model predictive control is adopted during commutation periods: a hybrid logical dynamic model is established, the current at the next moment is predicted according to the continuously conducting phase current, and then a cost function is established based on the reference current and the current at the next moment. A set of control sequences that minimize the cost function are solved, and the control sequences are the states of the switching tubes. The states of the switching tubes are applied to the motor drive system to achieve suppression of torque ripple of a square-wave drive permanent magnet motor. By introducing the theory of hybrid systems to establish a hybrid logical dynamic model as a prediction model, the present invention reduces the commutation torque ripple while avoiding the complexity of the control algorithm.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent magnet motor control, and particularly relates to a method for suppressing torque ripple of a square-wave driven permanent magnet motor based on the theory of hybrid systems. Background Art

[0002] As a physical energy storage technology widely mentioned in recent years, flywheel energy storage has advantages such as high efficiency and long life. The square-wave driven permanent magnet motor is small in size, light in weight, high in power density, and strong in overload capacity, and is one of the ideal choices for the core drive motor of the flywheel energy storage device. The flywheel energy storage technology has high requirements for operation accuracy and rotation accuracy. However, during commutation of the square-wave driven permanent magnet motor, the current change rate of the conducting phase and the turning-off phase windings is different, which will cause fluctuations in the current of the continuously conducting phase. Since the commutation torque depends on the current of the continuously conducting phase, commutation torque ripple will be generated. The commutation torque ripple will cause vibration and noise, and at the same time seriously limit the flywheel energy storage efficiency. Therefore, suppressing the commutation torque ripple is particularly important.

[0003] The drive system of the square-wave driven permanent magnet motor contains both discrete event variables such as the on-off of electronic switch devices and continuous time variables such as inductor current, and is a hybrid system in which discrete events drive the evolution of continuous states. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the present invention provides a method for suppressing torque ripple of a square-wave driven permanent magnet motor based on the theory of hybrid systems, which suppresses the commutation torque ripple of the square-wave driven permanent magnet motor, describes the drive system with a unified model, and avoids the complexity of the control algorithm.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A method for suppressing torque ripple of a square-wave driven permanent magnet motor based on the theory of hybrid systems is specifically as follows:

[0007] During non-commutation of the motor, PI-PWM control is adopted;

[0008] During commutation of the motor, model predictive control is adopted: a hybrid logical dynamic model is established, and according to the current i non of the continuously conducting phase, the current i non at the next moment is predicted. Then, according to the reference current i * and the current i non (k + 1), a cost function is established, and a set of control sequences that minimize the cost function are solved. The control sequences are the states of the switching tubes, and the states of the switching tubes are applied to the motor drive system to achieve suppression of the torque ripple of the square-wave driven permanent magnet motor;

[0009] The hybrid logical dynamic model is:

[0010]

[0011] where: i a 、i b 、i c are the phase currents of the stator three-phase windings, R is the resistance of the stator three-phase windings, L is the inductance of the stator three-phase windings, z1, z2, z3 are auxiliary continuous variables, I is the identity matrix, T s is the sampling time, e a 、e b 、e c are the back electromotive forces.

[0012] Furthermore, the cost function is:

[0013]

[0014] where: Q1, Q2, Q3, Q4 are introduced weight coefficients, u(k) is the discrete input at time k, u * is the reference trajectory of the discrete input, δ(k + 1) is the auxiliary logic variable at time k + 1, δ * is the reference trajectory of the auxiliary logic variable, z(k + 1) is the auxiliary continuous variable at time k + 1, z * is the reference trajectory of the auxiliary continuous variable, i non (k + 1) is the predicted current at time k + 1, i * is the reference current, and T is the prediction time domain.

[0015] Even further, the constraint conditions of the cost function are mixed-integer linear inequalities and a mixed logical dynamic model.

[0016] Even further, the mixed-integer linear inequality is:

[0017]

[0018] where: δ i is the introduced auxiliary logic variable, f(x) is a linear function, L is the maximum value of f(x), s1 - s6 are the states of the switching transistors, is the negation variable of the state of the switching transistor, is the negation variable of the three-phase auxiliary logic variables δ a 、δ b 、δ c , and i = 1, 2, 3.

[0019] Even further, the auxiliary logic variable δ = [δ a , δ b , δ c; Taking the current flowing into the winding as positive and the current flowing out of the winding as negative, it can be expressed by logical variables as:

[0020] Furthermore, the states of the switching tubes include conduction and cutoff, and the change between conduction and cutoff corresponds to a control transition; the current flowing into the stator three-phase winding is positive and the current flowing out of the stator three-phase winding is negative, corresponding to a condition transition, and the working mode of the inverter drive circuit is determined by the control transition and the condition transition.

[0021] Even further, for the switching tube states of the A-phase bridge arm:

[0022] When the switching tube of the upper bridge arm is cutoff and the switching tube of the lower bridge arm is conducting, and at the same time the current flows into the stator three-phase winding, the drive system operates in Mode 1;

[0023] When the switching tube of the upper bridge arm is conducting and the switching tube of the lower bridge arm is cutoff, and at the same time the current flows into the stator three-phase winding, the drive system operates in Mode 2;

[0024] When the switching tubes of both the upper and lower bridge arms are cutoff, and the lower bridge arm conducts through the anti-parallel diode while the current flows into the stator three-phase winding, the drive system operates in Mode 3;

[0025] When the switching tube of the upper bridge arm is cutoff and the switching tube of the lower bridge arm is conducting, and at the same time the current flows out of the stator three-phase winding, the drive system operates in Mode 4;

[0026] When the switching tube of the upper bridge arm is conducting and the switching tube of the lower bridge arm is cutoff, and at the same time the current flows out of the stator three-phase winding, the drive system operates in Mode 5;

[0027] When the switching tubes of both the upper and lower bridge arms are cutoff, and the upper bridge arm conducts through the anti-parallel diode while the current flows out of the stator three-phase winding, the drive system operates in Mode 6.

[0028] Even further, according to the event transition and the working mode, analyze all the value cases of the three-phase winding terminal voltages U ag 、U bg 、U cg and list the truth table, and obtain the three-phase winding terminal voltages by the truth table method:

[0029]

[0030] Where: s1 - s6 are the states of the switching tubes, is the non-variable of the switching tube state, V dc is the DC bus voltage, is the non-variable of the three-phase auxiliary logic variables δ a 、δ b 、δ c .

[0031] Furthermore, the switching of the control method is carried out according to the commutation moment. Specifically:

[0032] When the rising edge or falling edge of the Hall signal is detected, at this time the flag signal V = 1, and the current is at the commutation moment, switch to model predictive control;

[0033] When the current of the turned-off phase is detected to drop to 0, at this time the flag signal V = 0, the commutation has ended and entered the non-commutation moment with two-phase conduction, switch to PI-PWM control.

[0034] Furthermore, during commutation, the relationship between the commutation torque and the continuous conduction current of the square-wave drive permanent magnet motor is:

[0035] T e = e non i non / ω

[0036] Where: i non is the continuous conduction phase current, e non is the back electromotive force of the continuous conduction phase, and ω is the motor speed.

[0037] The beneficial effects of the present invention are:

[0038] (1) The commutation torque of the square-wave drive permanent magnet motor depends on the continuous conduction phase current. The present invention detects the commutation moment of the motor according to the rising edge and falling edge of the Hall signal. During commutation, model predictive control is adopted to establish a prediction model of the continuous conduction phase current and a cost function to solve the switching tube state acting on the motor drive system. During non-commutation, PI-PWM control is adopted. The control scheme of the present invention not only suppresses the commutation torque ripple but also avoids complex control algorithms;

[0039] (2) The present invention conducts hybrid logical dynamic modeling on the square-wave drive permanent magnet motor and uses the established model as the prediction model of the continuous conduction phase current at the next moment. Compared with the traditional current prediction model that depends on the switching function model, this model accurately predicts the continuous conduction phase current and effectively reduces the commutation torque ripple;

[0040] (3) The present invention can accurately detect the commutation moment by detecting the rising edge and falling edge of the Hall signal, better control the inverter during commutation, and can suppress the commutation torque ripple of the square-wave drive permanent magnet motor in the full speed range without the need to distinguish between low-speed and high-speed operating states;

[0041] (4) By establishing a hybrid logical dynamic model, the present invention includes both control transitions and conditional transitions, and can fully describe the operating state of the inverter, while the traditional inverter switching function model only considers the control transitions in the inverter and does not consider the conditional transitions related to continuous state variables. Description of the Drawings

[0042] Figure 1 This is the schematic diagram of torque ripple suppression for the square - wave - driven permanent - magnet motor described in the present invention;

[0043] Fig. 2(a) is the waveform diagram of current and torque of the square - wave - driven permanent - magnet motor described in the present invention when the current change rates of the turn - off phase and the turn - on phase are equal and the current of the non - commutation phase is constant;

[0044] Fig. 2(b) is the waveform diagram of current and torque of the square - wave - driven permanent - magnet motor described in the present invention when the current change rate of the turn - on phase is greater than that of the turn - off phase and the non - commutation phase current is convex downward;

[0045] Fig. 2(c) is the waveform diagram of current and torque of the square - wave - driven permanent - magnet motor described in the present invention when the current change rate of the turn - off phase is greater than that of the turn - on phase and the non - commutation phase current is convex upward;

[0046] Figure 3 This is the control flow chart of the square - wave - driven permanent - magnet motor described in the present invention;

[0047] Figure 4 This is the equivalent circuit diagram of the inverter and the motor described in the present invention;

[0048] Fig. 5(a) is a schematic diagram of the first working mode of the drive circuit described in the present invention;

[0049] Fig. 5(b) is a schematic diagram of the second working mode of the drive circuit described in the present invention;

[0050] Fig. 5(c) is a schematic diagram of the third working mode of the drive circuit described in the present invention;

[0051] Fig. 5(d) is a schematic diagram of the fourth working mode of the drive circuit described in the present invention;

[0052] Fig. 5(e) is a schematic diagram of the fifth working mode of the drive circuit described in the present invention;

[0053] Fig. 5(f) is a schematic diagram of the sixth working mode of the drive circuit described in the present invention. Detailed Embodiments

[0054] The present invention will be further described below in conjunction with the drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0055] As Figure 1 shown, a method for suppressing torque ripple of a square - wave - driven permanent - magnet motor based on the theory of hybrid systems in the present invention is as follows: The motor adopts a double - closed - loop control strategy: the speed loop adopts PI control, and the current loop adopts model - predictive control and PI control; In the speed loop, the rotor position and speed information are calculated according to the Hall signals, and the speed ω and the set reference speed ω* is fed back to the speed regulator, and a reference current i is output through the speed regulator * , where the structure of the speed regulator and the process of outputting the reference current based on the rotational speed are both prior arts;

[0056] As Figure 3 shown, the rising edge and falling edge of the Hall signal are detected, and a flag signal V is returned. The control strategy is switched through the flag signal V. When the rising edge or falling edge of the Hall signal is detected, at this time V = 1, indicating that the current is at the commutation moment, and the model predictive control based on the hybrid system theory is switched to. When the current of the turned-off phase drops to 0, at this time V = 0, indicating that the commutation has ended and entered the non-commutation moment with two-phase conduction, and the PI-PWM control is switched to;

[0057] The Hall signal and the commutation sequence are shown in Table 1. During the non-commutation period, the PI-PWM control is adopted (the specific process of the PI-PWM control is the prior art), and the reference current i * and the feedback actual current i abc are input into the current PI regulator. A set of control sequences u(0) (switching tube states) are output by the current PI regulator and act on the motor drive system. The structure of the current PI regulator and the process of outputting the control sequence based on the current are both prior arts; During the commutation period, the model predictive control is adopted. A mixed logical dynamic (MLD) model is established as the prediction model of the continuous conduction phase current i non , and the current i non at the next moment is predicted * (k + 1). Then, a cost function is established according to the reference current i non (k + 1) and the predicted current i

[0058]

[0059] where: H, F are coefficient matrices, γ is a decision variable (including u(k), δ(k), z(k)), γ' is the transpose of γ, A ineq , b ineq are the coefficient matrix and vector of the inequality constraint in the MIQP problem, A eq , b eq ​is the coefficient matrix and vector of the equality constraints in the MIQP problem;

[0060] Table 1

[0061]

[0062] In the table: A, B, and C are the three-phase stator windings, and i a , i b , i c are the phase currents of the three-phase stator windings, and H a , H b , H c are the three-phase Hall signals;

[0063] As shown in Figures 2(a), (b), and (c) are the waveforms of the three-phase current and torque T e during commutation. During commutation, the different rates of change of the currents in the turned-off phase and the turned-on phase will cause fluctuations in the current of the continuously conducting phase. The commutation torque of the square-wave drive permanent magnet motor depends on the continuously conducting current. During commutation, the electromagnetic torque expression is T e = e non i non / ω, where i non is the continuously conducting phase current, e non is the back electromotive force of the continuously conducting phase, and ω is the motor speed; keeping the continuously conducting phase current constant can suppress the commutation torque ripple, and based on this, a model predictive control strategy is formulated, and a prediction model and a cost function are established according to the continuously conducting phase current;

[0064] The specific steps to establish the hybrid logical dynamic model are as follows:

[0065] Step (1), as Figure 4 shown is Figure 1 the equivalent circuit diagram of the inverter drive circuit and the motor in

[0066]

[0067]

[0068]

[0069] Among them: R is the resistance of the three-phase stator windings, L is the inductance of the three-phase stator windings, e a , e b , e c are the back electromotive forces, and U an , U bn , U cn are the phase voltages of the three-phase stator windings;

[0070] According to the circuit voltage balance equation, a state-space model of the continuous part of the circuit with the phase currents i a 、i b 、i c of the three-phase windings as state variables is established, as specifically shown in Equation (5):

[0071]

[0072] Figure 4 where s1 - s6 are the states of the switching tubes, V dc is the DC bus voltage, D1 - D6 are the anti-parallel diodes, and n is the neutral point of the motor.

[0073] Step (2): The system's transition from one event to another is called an event transition (such as a switch changing from on to off). Event transitions include control transitions and condition transitions, and events and event transitions can affect the system's working mode. Generally, it is considered that a change in the system's working mode caused by an externally applied control signal is called a control transition, and a change in the system's working mode caused by a state variable in the system reaching a certain threshold is called a condition transition. According to this method, all control transitions and condition transitions of the inverter drive system are determined, and then all working modes of the drive system (including the inverter drive circuit and the motor) are listed according to the control transitions and condition transitions. The specific method is as follows:

[0074] 1) The states of the switching tubes in the inverter drive circuit are determined by the control sequence. The switching tubes' change from on (off) to off (on) represents a control transition; defining the current flowing into the three-phase stator windings as positive and flowing out of the three-phase stator windings as negative, this event is determined by the state of the inverter drive circuit and is called a condition transition.

[0075] 2) Determine the working mode of the inverter drive circuit according to the control transition and condition transition. Taking the A-phase bridge arm of the switching tube as an example, Figures 5(a), (b), (c), (d), (e), and (f) show the schematic diagrams of the inverter drive circuit in different working modes; when the upper bridge arm is turned off (s1 = 0) and the lower bridge arm is turned on (s2 = 1) while the current flows into the stator three-phase windings, the drive system operates in Mode 1; when the upper bridge arm is turned on (s1 = 1) and the lower bridge arm is turned off (s2 = 0) while the current flows into the stator three-phase windings, the drive system operates in Mode 2; when both the upper and lower bridge arms are turned off (s1 = s2 = 0), the lower bridge arm conducts through the anti-parallel diode while the current flows into the stator three-phase windings, the drive system operates in Mode 3; when the upper bridge arm is turned off (s1 = 0) and the lower bridge arm is turned on (s2 = 1) while the current flows out of the stator three-phase windings, the drive system operates in Mode 4; when the upper bridge arm is turned on (s1 = 1) and the lower bridge arm is turned off (s2 = 0) while the current flows out of the stator three-phase windings, the drive system operates in Mode 5; when both the upper and lower bridge arms are turned off (s1 = s2 = 0), the upper bridge arm conducts through the anti-parallel diode while the current flows out of the stator three-phase windings, the drive system operates in Mode 6; the B and C phase bridge arms of the switching tube are similar, the upper and lower bridge arms of the B phase bridge arm correspond to the switching tubes s3 and s4, and the upper and lower bridge arms of the C phase bridge arm correspond to the switching tubes s5 and s6;

[0076] Establish a model for the discrete part through the working mode, and use a triple to represent the model of the discrete part. The triple is X = (E, M, T), where E represents events, M represents the working mode, and T represents event transitions.

[0077] Step (3), Define each event and event transition as corresponding simple propositions. Complex events are represented by compound propositions formed by logical operations on simple propositions; the truth or falsehood of a proposition is represented by the value of a logical variable. A logical variable taking 1 represents the proposition is true, and a logical variable taking 0 represents the proposition is false; specifically, in the present invention, s i (i ∈ (1, 6)) represents the state of the switching tube, s i = 1 represents the switching tube is turned on, s i = 0 represents the switching tube is turned off. At the same time, introduce an auxiliary logical variable δ = [δ a , δ b , δ c . Take the current flowing into the winding as positive and the current flowing out of the winding as negative. This proposition can be represented by logical variables as:

[0078] Step (4), According to Figure 4 The equivalent circuit diagrams of the inverter drive circuit and the motor, deduce the phase voltages U an 、U bn 、U cnLogical expression; First, analyze the three-phase winding terminal voltages U ag 、U bg 、U cg for all their value cases and list them side by side in a truth table (Table 2, taking phase A as an example). Obtain the logical expression of the three-phase winding terminal voltages by the truth table method, as shown in formula (6). Then, based on the circuit voltage balance equation and combined with the three-phase winding terminal voltages, derive the logical expression of the three-phase winding phase voltages, as shown in formula (7):

[0079]

[0080]

[0081] Wherein: is the negated variable of the switch tube state, is the three-phase auxiliary logic variable δ a 、δ b 、δ c 's negated variable;

[0082] Table 2

[0083]

[0084]

[0085] In the table, 1 represents on and 0 represents off.

[0086] Step (5), introduce auxiliary continuous variables z1, z2, z3 to represent the coupling relationship between logical variables and continuous variables, in the form of z i =δ i f(x) (i = 1, 2, 3), specifically as shown in formula (8); and δ i is the introduced auxiliary logical variable, Convert the product relationship between the linear function f(x) and the logical variable δ i into a mixed-integer linear inequality by the conjunctive normal form method, as a constraint condition of the optimal control problem. In the process of using the conjunctive normal form method to derive the mixed-integer linear inequality, first convert the Boolean expression z i =δ i f(x) into the form of conjunctive normal form through the distributive law, implication rate, and De Morgan's law, and then convert it into a mixed-integer linear inequality, such as L is the maximum value of f(x);

[0087]

[0088] Combining formulas (5)-(7) and discretizing using Euler discretization, a hybrid logical dynamic model of the motor drive system that includes both continuous-time variables (i a 、i b 、i c ) and discrete event variables (switching tube states) is obtained:

[0089]

[0090] Where: I is the identity matrix, and T s is the sampling time.

[0091] Step (6), establish the following cost function to transform the model predictive control problem into an optimal control problem, where the constraint conditions are the mixed-integer linear inequalities derived in step (5) and the established hybrid logical dynamic model:

[0092]

[0093] Where: Q1, Q2, Q3, Q4 are the introduced weight coefficients, u(k) is the discrete input at time k (discrete input including switching tube states), u * is the reference trajectory of the discrete input, δ(k + 1) is the auxiliary logical variable at time k + 1, and δ * is the reference trajectory of the auxiliary logical variable, z(k + 1) is the auxiliary continuous variable at time k + 1, and z * is the reference trajectory of the auxiliary continuous variable, i non (k + 1) is the predicted current at time k + 1, and i * is the reference current, and T is the prediction horizon.

[0094] The described embodiments are the preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Without departing from the essential content of the present invention, any obvious improvements, substitutions, or variations that those skilled in the art can make all belong to the protection scope of the present invention.

Claims

1. A method for suppressing torque ripple of a permanent magnet motor based on the theory of hybrid systems, characterized in that: The motor adopts PI-PWM control during non-commutation; During commutation, the motor adopts model predictive control: a hybrid logical dynamic model is established, and based on the current i of the continuously conducting phase non to predict the current i non (k + 1) at the next moment. Then, based on the reference current i * and the current i non (k + 1), a cost function is established, and a set of control sequences that minimize the cost function are solved. The control sequences are the states of the switching tubes. Applying the states of the switching tubes to the motor drive system can achieve torque ripple suppression of the square-wave drive permanent magnet motor; The hybrid logic dynamic model is: where: i a 、i b 、i c are the phase currents of the three-phase stator winding, R is the resistance of the three-phase stator winding, L is the inductance of the three-phase stator winding, z1, z2, z3 are auxiliary continuous variables, I is the identity matrix, T s is the sampling time, e a 、e b 、e c are the back electromotive forces; The cost function is: Where: Q1, Q2, Q3, Q4 are introduced weight coefficients, u(k) is the discrete input at time k, and u * is the reference trajectory of the discrete input, δ(k + 1) is the auxiliary logic variable at time k + 1, and δ * is the reference trajectory of the auxiliary logic variable, z(k + 1) is the auxiliary continuous variable at time k + 1, and z * is the reference trajectory of the auxiliary continuous variable, and i non (k + 1) is the predicted current at time k + 1, and i * is the reference current, and T is the prediction time domain; The constraint conditions of the cost function are mixed integer linear inequalities and hybrid logic dynamic models; The mixed integer linear inequality is: Where: δ i is the introduced auxiliary logic variable, f(x) is a linear function, L is the maximum value of f(x), s1 - s6 are the states of the switching tubes, is the negation variable of the switching tube state, is the three-phase auxiliary logic variable δ a , δ b , δ c 's negation variables, and i = 1, 2, 3.

2. The torque ripple suppression method of the permanent magnet motor according to claim 1, wherein Auxiliary logic variable δ = [δ a , δ b , δ c ; Taking the current flowing into the winding as positive and the current flowing out of the winding as negative, it can be expressed in logical variables as:

3. The method for suppressing torque ripple of a permanent magnet motor according to claim 1, characterized in that The states of the switching tubes include on and off, and the change between on and off corresponds to a control transition; when the current flows into the three-phase stator winding, it is positive, and when it flows out of the three-phase stator winding, it is negative, corresponding to a condition transition. The working mode of the inverter drive circuit is determined by the control transition and the condition transition.

4. The method for suppressing torque ripple of a permanent magnet motor according to claim 3, wherein Switching tube state of phase A bridge arm: The switching tube of the upper bridge arm is off, and the switching tube of the lower bridge arm is on. At the same time, the current flows into the three-phase stator winding, and the drive system works in mode one; The switching tube of the upper bridge arm is on, and the switching tube of the lower bridge arm is off. At the same time, the current flows into the three-phase stator winding, and the drive system works in mode two; The switching tubes of both the upper and lower bridge arms are off. The lower bridge arm conducts through the anti-parallel diode and the current flows into the three-phase stator winding at the same time, and the drive system works in mode three; The switching tube of the upper bridge arm is off, and the switching tube of the lower bridge is on. At the same time, the current flows out of the three-phase stator winding, and the drive system works in mode four; The switching tube of the upper bridge arm is on, and the switching tube of the lower bridge arm is off. At the same time, the current flows out of the three-phase stator winding, and the drive system works in mode five; The switching tubes of both the upper and lower bridge arms are off. The upper bridge arm conducts through the anti-parallel diode and the current flows out of the three-phase stator winding at the same time, and the drive system works in mode six.

5. The method for suppressing torque ripple of a permanent magnet motor according to claim 4, wherein Analyze the terminal voltages U ag 、U bg 、U cg of the three-phase windings according to the event transition and working mode, list all the value cases in a truth table, and obtain the terminal voltages of the three-phase windings by the truth table method: Among them: s1 - s6 are the states of the switching tubes, is the complementary variable of the switching tube state, V dc is the DC bus voltage, are the complementary variables of the three - phase auxiliary logic variables δ a 、δ b 、δ c .

6. The method for suppressing torque ripple of a permanent magnet motor according to claim 1, characterized in that The switching of the control method is carried out according to the commutation moment. Specifically: When the rising edge or falling edge of the Hall signal is detected, at this time the flag signal V = 1, and the current is at the commutation moment, and it is switched to model predictive control; When it is detected that the current of the turned-off phase drops to 0, at this time the flag signal V = 0, the commutation has ended and it enters the non-commutation moment with two-phase conduction, and it is switched to PI-PWM control.

7. The method for suppressing torque ripple of a permanent magnet motor according to claim 6, wherein During commutation, the relationship between the commutation torque and the continuous conduction current of the square-wave drive permanent magnet motor is: T e = e non i non ω Where: i non is the continuously-conducting phase current, e non is the continuously-conducting back electromotive force, and ω is the motor speed.

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