A motor drive control method

Abstract

The present invention provides a synchronous reluctance motor drive control method. The present invention introduces the discrete space voltage vector modulation technology into the model predictive torque control of the synchronous reluctance motor. This technology improves the steady-state performance of the system by synthesizing a large number of virtual voltage vectors. At the same time, a simplified method for voltage vector selection is proposed to avoid calculating all voltage vectors and reduce the computational workload. The present invention can effectively reduce the torque and flux ripple of the motor without calculating all voltage vectors.

Description

Technical Field

[0001] The present invention relates to the field of motor control, and particularly provides a drive control method for a synchronous reluctance motor. Background Art

[0002] Model predictive torque has the advantage of fast dynamic response. However, in model predictive torque control, only one voltage vector is applied to the motor in one control period, resulting in large torque ripple. Discrete space voltage vector modulation divides a sampling period into N time segments, and a basic voltage vector is output in each time segment. The virtual voltage vector is linearly combined by two adjacent basic voltage vectors and the zero vector. By synthesizing a large number of virtual voltage vectors, the control accuracy can be improved, thereby reducing torque ripple. The current best solution is to divide a control period into three times, generating a total of 38 voltage vectors. The discrete space voltage vector modulation technology improves the steady-state performance of the system by synthesizing a large number of virtual voltage vectors, but it requires a large amount of vector calculations. The present invention proposes a method for simplifying voltage vector selection to avoid calculating all voltage vectors and reduce the amount of calculation. Summary of the Invention

[0003] The present invention introduces the discrete space voltage vector modulation technology into the model predictive torque control of a synchronous reluctance motor. This technology improves the steady-state performance of the system by synthesizing a large number of virtual vectors, but it requires a large amount of voltage vector calculations. At the same time, a method for simplifying voltage vector selection is proposed to avoid calculating all voltage vectors, reducing the calculation of 38 voltage vectors to 8, and reducing the amount of calculation.

[0004] The specific steps of the present invention are as follows:

[0005] Step 1: According to the d-q mathematical model of the synchronous reluctance motor, including the voltage equation, magnetic flux equation, and torque equation, discretize its mathematical model to establish the prediction equations for the magnetic flux and torque of the synchronous reluctance motor. The steps are as follows:

[0006] Step a: According to the forward Euler discretization method, discretize the magnetic flux equation to obtain the prediction equations for the d-axis and q-axis magnetic fluxes at the k + 1 moment as:

[0007]

[0008] In the formula, i d (k), i q (k) are the d-axis and q-axis currents at the k moment respectively, u d (k), u q (k) are the d-axis and q-axis voltages at the k moment respectively, ψ d (k), ψ q (k) are the d-axis and q-axis magnetic fluxes at the k moment respectively, R s is the stator resistance, ω e (k) is the motor speed, Ts is the control period;

[0009] Step b: Furthermore, the predicted equation of the flux linkage amplitude at time k+1 is:

[0010]

[0011] In the formula, |ψ s (k+1)| is the flux linkage amplitude at time k+1;

[0012] Step c: Discretize the stator current equation to obtain the predicted equations of the d-axis and q-axis currents:

[0013]

[0014] According to the current and flux linkage at time k+1, the predicted equation of the torque can be obtained:

[0015]

[0016] T e (k+1) is the torque at time k+1;

[0017] Step 2: Sample the d-axis and q-axis currents and voltages at time k, and the steps are as follows:

[0018] Step a: Sample the A-phase, B-phase, and C-phase currents of the motor at time k, and calculate the d-axis and q-axis currents through Park transformation. The calculation formula is:

[0019]

[0020] In the formula, θ is the angle by which the d-axis leads the A-phase axis;

[0021] Step b: According to the inverter switching signals at time k, calculate the A-phase, B-phase, and C-phase voltages, and then obtain the d-axis and q-axis voltages through Park transformation:

[0022]

[0023] In the formula, U dc is the DC bus voltage, [S A (k), S B (k), S C (k)] T are the inverter switching signals at time k.

[0024]

[0025] Step 3: Identify the d-axis and q-axis inductances using the recursive least squares method with a forgetting factor:

[0026] Step a: The form of the least squares method is Writing Equation (4) in the form of the recursive least squares method gives:

[0027]

[0028] Step b: Identify the d- and q-axis inductances according to the iterative formula of the recursive least squares method:

[0029]

[0030] where λ is the forgetting factor, P(k) is the covariance matrix, K(k) is the intermediate matrix, is the parameter matrix to be identified;

[0031] Step 4: Discrete space voltage vector modulation divides a sampling period into N time periods, and a basic voltage vector is output in each time period. The virtual voltage vector is linearly combined by two adjacent basic voltage vectors and the zero vector. By synthesizing a large number of virtual vectors, the control accuracy can be improved, thereby reducing torque ripple. The current best solution is to divide a control period into three times, generating a total of 38 voltage vectors. If the stator flux linkage amplitude and torque under the action of all 38 voltage vectors are predicted and the optimal vector is selected, the computational load is very large. Therefore, it is necessary to reduce the number of voltage vectors to be calculated. In this step, the inductance value obtained by identification in Step 3 is used. The simplified voltage vector selection steps are as follows:

[0032] Step a: Redivide the sectors;

[0033] Step b: Determine the sector where the optimal voltage vector is located according to the deadbeat principle. The steps are as follows:

[0034] (1) Differentiate the electromagnetic torque equation, discretize the electromagnetic torque expression. According to the basic principle of deadbeat control, in order to make the torque in the next cycle equal to the reference value, let T e (k + 1) = T e *, and at the same time substitute the stator current differential equation and the flux linkage differential equation to get:

[0035]

[0036] (2) Denote T e * - T e (k) as ΔT e (k), and rewrite (10) in the form of u q (k)T s = Au d (k)T s + B, where

[0037] (3) Make the stator flux linkage amplitude in the next cycle equal to its given The reference values are equal. In this step, the resistance term is ignored, and the relationship between the stator flux linkage amplitude and the voltage can be expressed as:

[0038]

[0039] (4) Substitute u q (k)T s = Au d (k)T s + B into Equation (11) to obtain:

[0040] (|ψ s | * ) 2 =(ψ d (k)+ u d (k)T s + ω e ψ q (k)) 2 +(ψ q (k)+ Au d (k)T s + B - ω e ψ d (k)) 2 (12)

[0041] By solving Equation (12), the d- and q-axis components u d (k), u q (k) of the optimal voltage vector can be obtained:

[0042]

[0043]

[0044] Transform to the α-β coordinate system through the coordinate transformation formula. The coordinate transformation formula is:

[0045]

[0046] Determine the sector where the optimal voltage vector is located through Equation (16):

[0047]

[0048] Step c: Perform Park transformation on the zero vectors and virtual vectors in the sector of the optimal voltage vector to transform them to the d-q coordinate system. Predict the torque and flux linkage under the action of these voltage vectors according to the prediction equations (1) to (4). A total of 7 voltage vectors need to be calculated in this step. Select the optimal voltage vector from these 7 voltage vectors according to the cost function and apply it to the synchronous reluctance motor. The cost function is as follows:

[0049]

[0050] Complete the control.

[0051] The advantage of the present invention lies in that the discrete space voltage vector modulation is introduced into the synchronous reluctance motor model predictive torque control, which can reduce the torque ripple of the motor, improve the steady-state performance, and at the same time, a simplified method for voltage vector selection is proposed to reduce the calculation amount and avoid calculating all vectors.

[0052] The control strategy of the present invention has certain reference value for the control strategies of permanent magnet synchronous motors and induction motors. Description of the Drawings

[0053] Figure 1 It is the control structure diagram of the synchronous reluctance motor;

[0054] Figure 2 It is the virtual vector and sector distribution of the discrete space voltage vector modulation; Detailed Implementation Manner

[0055] The present invention will be further described below in conjunction with the drawings:

[0056] A control method for a synchronous reluctance motor, the structure of which is as Figure 1 shown. The discrete space voltage vector modulation is introduced into the synchronous reluctance motor model predictive torque control to achieve the purpose of reducing torque ripple. The discrete space voltage vector modulation improves the steady-state performance of the motor by synthesizing a large number of virtual vectors, but increases the calculation amount. The present invention proposes a voltage vector simplification method to reduce the calculation amount.

[0057] The specific implementation method is as follows:

[0058] Step 1: Sample the A, B, and C phase currents of the motor at time k, and calculate the d and q axis currents through Park transformation. The calculation formula is:

[0059]

[0060] Step 2: According to the inverter switching signals at time k, calculate the A, B, and C phase voltages, and then obtain the d and q axis voltages through Park transformation. The calculation formula is:

[0061]

[0062]

[0063]

[0064] Step 3: Use the recursive least squares method with a forgetting factor to identify the d and q axis inductances:

[0065]

[0066] Step 4: Redistribute the voltage vector sectors. The sector distribution and the vectors in each sector are as shown in the appendix. Figure 1 as shown.

[0067] Step 5: Use the deadbeat technique to determine the optimal voltage vector and determine the sector it is in:

[0068]

[0069]

[0070]

[0071] Step 6: Perform Park transformation on the zero vectors and virtual vectors in the optimal voltage vector sector, transform them to the d-q coordinate system, and predict the torque and flux linkage under the action of these voltage vectors according to the prediction equation. A total of 8 voltage vectors need to be calculated in this step. Calculate the given torque and the given flux linkage amplitude through PI control and the MTPA strategy. Select the optimal voltage vector from these 7 voltage vectors according to the value function and apply it to the synchronous reluctance motor. The value function is as follows:

[0072]

[0073] Complete the control.

[0074] The beneficial effect of the present invention is that introducing discrete space voltage vector modulation into the model predictive torque control of synchronous reluctance motors can reduce the torque ripple of the motor, improve the steady-state performance, and at the same time propose a simplified method for voltage vector selection to reduce the calculation amount. The present invention has certain reference value for other motor control strategies.

Claims

1. A control method for a synchronous reluctance motor drive. The present invention introduces the discrete space voltage vector modulation technique into model predictive torque control. This technique can generate 38 voltage vectors, and improve the steady-state performance of the motor drive system by synthesizing virtual voltage vectors. The present invention proposes a simplified method for voltage vector selection. The steps of the voltage vector selection simplification method are as follows: Step 1: Redivide the voltage vector sectors; Step 2: Determine the sector where the optimal voltage vector is located according to the deadbeat principle. The steps are as follows: Step a: Differentiate the electromagnetic torque equation, discretize the electromagnetic torque expression. According to the basic principle of deadbeat control, in order to make the torque in the next cycle equal to the reference value, let T e (k + 1)=T e *, and at the same time substitute the stator current differential equation and the flux linkage differential equation to obtain: where u d and u q are the d - axis and q - axis voltages, i d and i q are the d - axis and q - axis currents, L d and L q are the d - axis and q - axis inductances, ψ d and ψ q are the d - axis and q - axis flux linkages, R s is the stator resistance, ω e is the rotational speed, T e is the electromagnetic torque, T e * is the reference value of the electromagnetic torque, p is the number of pole pairs, T e (k) is the electromagnetic torque at time k, T s is the sampling period; Step b: Take T e *-T e (k) and denote it as ΔT e (k). Rewrite (1) as u q (k)T s = Au d (k)T s + B, where Step c: Make the stator flux amplitude in the next period equal to the given stator flux amplitude reference value. In this step, the resistance term is ignored. The relationship between the stator flux amplitude and voltage can be expressed as: where, |ψ s | is the amplitude of the stator flux linkage, |ψ s (k + 1)| is the amplitude of the flux linkage at time k + 1, |ψ s | * is the given value of the amplitude of the stator flux linkage; Step d: Substitute u q (k)T s = Au d (k)T s + B into Equation (2) to obtain: (|ψ s | * ) 2 =(ψ d (k)+u d (k)T s +ω e ψ q (k)) 2 +(ψ q (k)+Au d (k)T s +B-ω e ψ d (k)) 2 (3) Step e: The d-axis and q-axis components u d (k) and u q (k) of the optimal voltage vector can be solved by solving Equation (3), and then transformed to the α-β coordinate system through the coordinate transformation formula to obtain u α (k) and u β (k). The sector where the optimal voltage vector is located is determined by Equation (4): Step 3: Perform Park transformation on the zero vectors and virtual vectors in the optimal voltage vector sector and transform them to the d-q coordinate system. Predict the torque and flux under the action of the voltage vector according to the prediction equation. A total of 8 voltage vectors need to be calculated in this step. Select the optimal voltage vector from these 8 voltage vectors according to the cost function and apply it to the synchronous reluctance motor. The cost function is as follows: Complete the control.

Images