CN114531078A - Method for inhibiting torque pulsation and bus current pulsation of switched reluctance motor - Google Patents

Abstract

The invention discloses a method for inhibiting torque pulsation and bus current pulsation of a switched reluctance motor. The method needs to obtain flux linkage characteristics and torque characteristics of the switched reluctance motor through off-line measurement. The total torque reference value is output by the speed proportional-integral controller, and each phase reference torque value is calculated by the torque distribution function. And calculating flux linkage and current information at the k +1 moment by combining the optimal switching vector calculated at the previous moment according to the position and current information at the k moment and the position information stored at the k-1 moment for delay compensation. On the basis, the position information at the moment of k +2 and the flux linkage current information under the available switching vector are predicted, then the torque and the inverter input current value under each switching state are obtained by looking up a table and are brought into a cost function, and the operation state with the minimum cost function value is used as a switching signal and is applied to the control power converter, so that the effect of simultaneously restraining the torque ripple and the bus current ripple is achieved. The effectiveness of the method is verified through simulation, the method is simple in control logic, obvious in torque ripple and bus current ripple suppression effect, and the impact of bus current on the supporting capacitor is effectively reduced.

Description

A method for suppressing torque ripple and bus current ripple of switched reluctance motor

technical field

The invention relates to a method for suppressing torque ripple and busbar current ripple of a switched reluctance motor, belonging to the field of motor control.

Background technique

Switched reluctance motors have broad application prospects in aerospace, electric vehicles, wind power and other fields due to their simple structure, wide speed regulation range, and low production cost. However, the unique doubly salient structure leads to large commutation torque ripple, which seriously affects its control performance. Researchers have done a lot of research on torque ripple suppression methods, and proposed a series of control strategies, such as direct torque control, direct instantaneous torque control, torque distribution function, iterative learning, etc. However, most of the methods are only aimed at the suppression of torque ripple, and cannot take into account the bus current ripple, resulting in the support capacitor of the system being subjected to large inrush current and shortening its life.

In digital control operating in discrete mode, finite set model predictive control is a novel control method based on the switching states of power converters. It constructs the cost function in the form of weights to optimize the objective, and realizes multi-objective optimization intuitively and conveniently, which has received more and more attention in power electronic converters. In the switched reluctance motor drive system, the bus current is the sum of the inverter input current and the capacitor current, the inverter input current can be represented by the switching signal and current of each phase, and the torque of each phase is also closely related to the switching signal. Taking the inverter input current ripple and torque ripple as the main objects, by constructing the cost function of the switched reluctance motor torque and the inverter input current value, and using the operating state with the smallest cost function value as the switching signal, it will be possible to achieve Solving the problem of torque ripple directly and indirectly suppressing busbar current ripple plays an important role in improving the compactness and speed regulation performance of the switched reluctance motor drive system.

SUMMARY OF THE INVENTION

For the switched reluctance motor drive system, the present invention proposes a method for suppressing the torque ripple and busbar current ripple of the switched reluctance motor. This method needs to obtain the flux linkage characteristics and torque characteristics of the switched reluctance motor through offline experimental measurements. The total torque reference value is output by the speed proportional integral regulator, and the reference torque value of each phase is calculated by the torque distribution function. According to the position and current information at time k and the stored position information at time k-1, the position information at time k+1 is predicted, and the flux linkage and current information at time k+1 are calculated in combination with the optimal switching vector calculated at the previous time. Carry out delay compensation, on this basis, predict the position information at time k+2 and the flux linkage and current information under the available switching vector, and then look up the table to obtain the torque and inverter input current value under each switching state and bring it with Enter the cost function, and use the operating state with the smallest cost function value as the switching signal, which is applied to control the power converter. The bus current is the sum of the inverter input current and the capacitor current. Taking the inverter input current ripple and torque ripple as the main objects, the weight coefficients are applied separately to select the appropriate switching information so that the two can be suppressed at the same time, that is, to achieve It has the effect of directly suppressing the torque ripple and indirectly suppressing the bus current ripple.

The technical scheme of the present invention is as follows:

The method for suppressing torque ripple and bus current ripple of a switched reluctance motor includes the following steps:

Step 1: Obtain the flux linkage characteristics and torque characteristics of the switched reluctance motor by experimental measurement; obtain the flux linkage characteristics of the switched reluctance motor ψ(i, θ) by the rotor fixed clamping method, where ψ is the flux linkage, i is the current, θ is the position; according to the flux linkage characteristic ψ(i, θ), the current data table i(ψ, θ) is constructed by means of interpolation. On the basis of the magnetic linkage characteristics, the torque data table T(i, θ) is constructed according to the partial derivative of the position according to the magnetic common energy; the calculation formula of the magnetic common energy W' is:

The formula for calculating torque T is:

Step 2: Given a reference torque T _ref , in a closed-loop system, T _ref can be obtained from the output of the speed loop proportional-integral regulator;

Step 3: The torque distribution function calculates the reference torque T _ref to obtain the torque reference value T _ph,ref of each phase;

Step 4: Collect the rotor position θ(k) and phase current i _ph (k) of the motor at time k, and further check the flux linkage characteristic data table ψ(i, θ) to obtain the flux linkage ψ _ph (k) at time k, and store Rotor position information at time θ(k-1);

Step 5: Predict the rotor position θ(k+1) and phase flux linkage ψ _ph (k+1) at time k+1, and further predict the current i at time k+1 by checking the current characteristic data table i(ψ, θ). The specific calculation formula of _ph (k+1); θ(k+1) is:

θ(k+1)=θ(k)+(θ(k)-θ(k-1))

The formula for calculating ψ _ph (k+1) is:

ψ _ph (k+1)=ψ _ph (k)+[V ^* -R _ph i(k)]T _s

In the formula, T _s is the sampling frequency, R _ph is the winding resistance, and V ^* is the optimal voltage vector calculated at the moment of k-1.

Step 6: Predict the rotor position θ(k+2) at time k+2 and determine the operating state of the motor, predict the phase flux linkage ψ _ph (k+2) at time k+2, and further find out by looking up the table i(ψ, θ) The current i _ph (k+2) at time k+2 is obtained, and the calculation formula of rotor position θ(k+2) at time k+2 is:

θ(k+2)=2θ(k+1)-θ(k)

The formula for predicting the phase flux linkage ψ _ph (k+2) at time k+2 is:

ψ _ph (k+2)=ψ _ph (k+1)+(V _ph (k+1)-R _ph i _ph (k+1))T _s

In the formula, V _ph (k+1) is the predicted phase voltage value at time k+1, and its value is related to the switching vector, T _s is the sampling frequency, and R _ph is the winding resistance;

Step 7: Combine the predicted phase current and rotor position information at time k+2, predict the torque T _ph (k+2) of each phase at time k+2 by looking up the table T(i, θ), and calculate the torque prediction of each phase The sum of squares T _p (k+2) of the difference between the value and its reference value T _ph,ref , and the inverter input current value i _SRM (k+2):

where N _ph represents the number of phases of the switched reluctance motor, and T _p (k+2) represents the sum of the squares of the difference between the predicted torque value of each phase and its reference value at time k+2;

Among them, i _SRM (k+2) represents the predicted inverter input current value at time k+2, and s _ph is the switching vector;

Step 8: According to Step 7, predict the sum of the squares of the difference between the predicted torque of each phase and its reference value at time k+2 and the input current value of the inverter, and calculate the cost function J

J=ω _T T _p (k+2)+ω _i i _SRM (k+2) ²

In the formula, ω _T and ω _i are the sum of the squares of the difference between the predicted torque value of each phase and its reference value and the weight coefficient of the inverter input current value, respectively;

Step 9: Control the switches in the power converter with the operating state with the smallest cost function value as the optimal state as the switching signal.

beneficial effect

The invention discloses a method for suppressing torque ripple and busbar current ripple of a switched reluctance motor. This method needs to obtain the flux linkage characteristics and torque characteristics of the switched reluctance motor through offline experimental measurements. The total torque reference value is divided by the speed loop proportional controller, and the reference torque value of each phase is calculated by the torque distribution function. According to the position and current information at time k and the position information at time k-1, combined with the optimal switching vector calculated at the previous time, the flux linkage and current information at time k+1 are calculated to perform delay compensation. The position information at time k+2 and the flux linkage and current information under the available switching vector, then look up the table to obtain the torque and inverter input current value in each switching state and bring it into the cost function, and take the operating state with the smallest cost function value. As a switch signal, it is applied to control the power converter, thereby directly suppressing the torque ripple, and indirectly suppressing the bus current ripple by reducing the inverter input current ripple.

Simulation verifies the effectiveness of the method. The method has simple control logic, obvious effect of suppressing torque ripple and bus current ripple, and achieves smooth control of the motor while effectively reducing the impact of bus current on support capacitors.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

Figure 1 is the flux linkage characteristic curve of the switched reluctance motor;

Figure 2 is the current data table curve of the switched reluctance motor;

Fig. 3 is the torque characteristic curve of the switched reluctance motor;

Fig. 4 is the principle block diagram of the control method proposed by the present invention;

Fig. 5 is a flow chart of a method for predicting torque control by an efficiency optimization model of a switched reluctance motor;

Figure 6 is a control effect diagram of traditional current chopper control when running at 1000rpm;

Fig. 7 is the control effect diagram of the traditional model predictive torque control method when running at 1000rpm;

8 is a control effect diagram of the model predictive torque control method proposed by the present invention when running at 1000 rpm;

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific examples. The motor used in the example is a 1kW three-phase 12/8-pole switched reluctance motor.

Step 1: Obtain the flux linkage characteristics and torque characteristics of the switched reluctance motor by experimental measurement; obtain the flux linkage characteristics of the switched reluctance motor ψ(i, θ) by the rotor fixed clamping method, where ψ is the flux linkage, i is the current, θ is the position; the current look-up table i(ψ, θ) is constructed by means of interpolation. On the basis of the flux linkage characteristics, the torque data table T(i, θ) is constructed according to the partial derivative of the position according to the magnetic co-energy. The characteristics of flux linkage, current and torque are shown in Figure 1-3. The calculation formula of magnetic common energy W' is shown in formula (1), and the calculation formula of torque T is shown in formula (2);

Step 2: The reference torque T _ref is given. In the closed-loop system shown in Figure 4, T _ref is obtained from the output of the speed loop proportional-integral (PI) controller;

Step 3: The torque distribution function calculates the torque value of each phase; the torque distribution function is shown in formula (3);

In the formula, θ _on , θ _ov , θ _off , and θ _p represent the turn-on angle, commutation angle, turn-off angle and rotor period angle, respectively, and T _ph,ref represents the torque reference value of each phase;

Step 4: Collect the rotor position θ(k) and phase current i _ph (k) of the motor at time k, and further check the flux linkage characteristic data table ψ(i, θ) to obtain the flux linkage ψ _ph (k) at time k, At the same time, the rotor position information at the moment of θ(k-1) is stored;

Step 5: Predict the rotor position θ(k+1) and phase flux linkage ψ _ph (k+1) at time k+1 according to equations (4) and (5), and further check the current data table i(ψ, θ) predicts the current i _ph (k+1) at time k+1.

θ(k+1)=θ(k)+(θ(k)-θ(k-1)) (4)

ψ _ph (k+1)=ψ _ph (k)+[V ^* -R _ph i(k)]T _s (5)

In the formula, T _s is the sampling frequency, R _ph is the winding resistance, and V ^* is the optimal voltage vector calculated at the moment of k-1;

Step 6: Predict the rotor position θ(k+2) at time k+2 by formula (6) and determine the running state of the motor, predict the phase flux linkage ψ _ph (k+2) at time k+2, and further check the table i( ψ, θ) to obtain the current i _ph (k+2) at time k+2. The relationship between the defined switching vector s _ph and the phase voltage is shown in formula (7), where s _ph =1 means that both switches of the asymmetric half-bridge power converter are turned on, and s _ph =0 only one switch is turned on, It means that s _ph = -1 means that both switches are closed; the combination principle of switch states is: in the one-way conduction area, only the switch state of the current conduction phase is calculated, and the remaining phases are -1; in the commutation area, only the current conduction phase is predicted The two-phase switching state of the commutation, the prediction table of the switching state is shown in Table 1. According to the predicted phase voltage at time k+1, the phase flux linkage ψ _ph (k+2) at time k+2 is predicted by formula (8), and the current i _ph ( k+2);

θ(k+2)=2θ(k+1)-θ(k) (6)

where θ(k+2) is the predicted rotor position at time k+2;

where V _bus represents the bus voltage, and V _T , V _D , V _ph , and s _ph represent the voltage drop of the switch tube, the voltage drop of the freewheeling diode, the phase voltage and the state variable, respectively;

ψ _ph (k+2)=ψ _ph (k+1)+(V _ph (k+1)-R _ph i _ph (k+1))T _s (8)

In the formula, V _ph (k+1) is the predicted phase voltage value at time k+1, T _s is the sampling frequency, and R _ph is the winding resistance;

Step 7: Combine the phase current and rotor position information at time k+2, predict the torque prediction value of each phase at time k+2 by looking up the table T(i, θ), and then use formula (9) and formula (10) respectively. Obtain the square sum T _p of the difference between the predicted torque value of each phase and its reference value and the inverter input current value i _SRM ;

In the formula, N _ph represents the number of switched reluctance motor phases, T _p (k+2), i _SRM (k+2) represent the sum of the squares of the difference between the predicted torque value and the reference value of each phase at the time k+2, and the inverter Enter the current value, s _ph is the switching vector;

Step 8: According to step 7, predict the sum of the squares of the difference between the predicted torque value of each phase and the reference value at the time k+2 and the input current value of the inverter, and solve the value of the cost function by formula (11);

J=ω _T T _p (k+2)+ω _i i _SRM (k+2) ² (11)

In the formula, ω _T and ω _i are the sum of the squares of the difference between the predicted torque value of each phase and its reference value and the weight coefficient of the inverter input current value, respectively;

Step 9: Control the switch in the power converter with the operating state with the smallest cost function value as the optimal state as the switch signal;

Fig. 5 is the flow chart of the control method proposed by the present invention, Fig. 6, Fig. 7 and Fig. 8 are respectively the control effects of the current chopping control, the traditional model predictive control method and the control method proposed by the present invention when the motor is running at 1000rpm In the simulation, the power supply resistance is set to 0.16Ω, the calculation formulas for defining the average torque T _avg and the torque ripple T _ripple are shown in Equations (12) and (13), and the calculation formula for the busbar current ripple i _{SRM_ripple} is shown in Equation (14) ) shown;

In the formula, θ ₁ and θ ₂ represent the starting value and ending value of a rotor angular cycle, respectively, and T(θ) is the sum of the torques of each phase;

In the formula, i _{SRM_max} , i _{SRM_min} , i _{SRM_avg} represent the maximum value, minimum value and average value of the bus current respectively.

The control performance of the three methods is shown in Table 1.

Table 1 Comparison of the effects of different control methods

From the results in Table 1, it can be seen that the method for suppressing the torque ripple and bus current ripple of the switched reluctance motor proposed by the present invention has obvious effects on suppressing the bus current ripple while reducing the torque ripple. Little hazard.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Variations, modifications, substitutions, and alterations to the above-described embodiments are possible within the scope of the present invention without departing from the scope of the present invention.

Claims (4)

1. a method for suppressing torque ripple and bus current ripple of a switched reluctance motor, characterized in that: Include the following steps: Step 1: The rotor fixed clamping method is used for experimental measurement to obtain the flux linkage characteristics and torque characteristics of the switched reluctance motor; Step 2: Given a reference torque T _ref , in a closed-loop system, T _ref can be obtained from the output of the speed loop proportional-integral regulator; Step 3: The torque distribution function calculates the reference torque T _ref to obtain the torque reference value T _ph,ref of each phase; Step 4: Collect the rotor position θ(k) and phase current i _ph (k) of the motor at time k, and further check the flux linkage data table i(ψ, θ) to obtain the flux linkage ψ _ph (k) at time k, and store k The rotor position information θ(k-1) at time -1; Step 5: Predict the rotor position θ(k+1) and phase flux linkage ψ _ph (k+1) at time k+1, and further predict the current i _ph at time k+1 by checking the current data table i(ψ, θ) (k+1); Step 6: Predict the rotor position θ(k+2) at time k+2 and determine the operating state of the motor, predict the phase flux linkage ψ _ph (k+2) at time k+2, and further find out by looking up the table i(ψ, θ) Get the current i _ph (k+2) at time k+2; Step 7: Combine the predicted phase current and rotor position information at time k+2, predict the torque prediction value T _ph (k+2) of each phase and the inverter at time k+2 by looking up the table T(i, θ) Input current value i _SRM (k+2); Step 8: According to Step 7, predict the sum of the squares of the difference between the predicted torque value of each phase at time k+2 and its reference value and the input current value of the inverter, and calculate the cost function; Step 9: Control the switches in the power converter with the operating state with the smallest cost function value as the optimal state as the switching signal. 2. a kind of switch reluctance motor torque ripple and bus current ripple suppression method according to claim 1, is characterized in that: step 7 is according to formula

Calculate the inverter input current value; where i _SRM (k+2) represents the predicted inverter input current value at time k+2, and s _ph is the switching vector; According to the formula

Calculate the sum of the squares of the difference between the predicted torque value of each phase and its reference value; in the formula, N _ph represents the number of switched reluctance motor phases. 3. a kind of switch reluctance motor torque ripple and bus current ripple suppression method according to claim 1, is characterized in that: step 8 is according to formula J=ω _T T _p (k+2)+ω _i i _SRM (k+2) ² Calculate the cost function; in the formula, ω _T and ω _i are the sum of the squares of the difference between the torque prediction value of each phase and its reference value and the weight coefficient of the inverter input current value, respectively. 4. A method for suppressing torque ripple and bus current ripple of a switched reluctance motor, characterized in that: the method inputs a reference torque, and utilizes any one of the methods described in claims 1 to 3 to realize the rotation of the switched reluctance motor. Torque ripple and bus current ripple suppression.

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