CN111726042B - Braking torque control method of switched reluctance motor based on four-phase current and voltage - Google Patents

Abstract

The invention provides a braking torque control method of a switched reluctance motor based on four-phase current and voltage, which belongs to the technical field of motor control. The system mainly includes torque estimator, current detector, torque selector and torque regulator. First, the four-phase current and voltage output by the switched reluctance motor are input to the torque estimator, and the estimated four-phase torque is calculated and input to the torque selector. At the same time, the current detector detects the four-phase current of the motor and outputs a four-phase torque control signal; then the torque selector selects the four-phase estimated torque according to the torque control signal and outputs the total estimated torque; finally, the torque regulator further adjusts the reference torque and the total estimated torque to output the reference current of the switched reluctance motor to form a closed-loop control of braking torque. The invention can accurately and timely estimate the actual torque, satisfy the driver's demand for accurate and responsive braking torque, and improve the comprehensive braking performance of the electric vehicle driven by the switched reluctance motor under braking or coasting conditions.

Description

Braking torque control method of switched reluctance motor based on four-phase current and voltage

technical field

The invention relates to the field of control of switched reluctance motor drive systems, in particular to a braking torque control system and method for switched reluctance motors based on four-phase current and voltage.

Background technique

Electric vehicles driven by switched reluctance motors require that the braking system can promptly and effectively feed back the driver’s required braking force under sliding or braking conditions. The driver will step on the brake pedal according to the actual braking conditions to request the electric vehicle to brake and decelerate. The braking force comes from the mechanical braking force of the mechanical braking system and the motor braking force of the regenerative braking system. Control response speed to ensure electric vehicle braking safety performance and stability.

Since the switched reluctance motor is a nonlinear dynamic model, and there is no precise mathematical expression to calculate the output torque of the motor, when the switched reluctance motor is applied in the braking or coasting conditions of electric vehicles, the motor torque must be controlled indirectly by braking torque. At present, there is no research on the closed-loop control of the braking torque of the switched reluctance motor through the four-phase current and voltage. Even if there is research on the torque, it is the control of the motor torque through the one-phase current and voltage. Moreover, the total estimated torque obtained by four-phase current and voltage is much more accurate than the total estimated torque estimated by one-phase current and voltage. After one electrical cycle, the total estimated torque is only a quarter of an electrical cycle behind the actual torque, so that the braking torque control system of the switched reluctance motor responds quickly, and the estimated torque can track the reference braking torque required by the driver in a timely and effective manner.

Contents of the invention

The content of the present invention is to improve the braking torque response speed and braking torque stability performance of an electric vehicle driven by a switched reluctance motor under braking or coasting conditions. Therefore, under the working condition of the electric vehicle under the action of motor torque, a switching reluctance motor braking torque control system and method based on four-phase current and voltage are proposed.

The purpose of the present invention can be achieved through the following technical solutions:

The braking torque control system of switched reluctance motor based on four-phase current and voltage includes torque estimator, current detector, torque selector and torque regulator.

The four-phase current and voltage enter the torque estimator to estimate the estimated torque of the four phases. There is no precise mathematical expression to calculate the four-phase estimated torque of the torque estimator. Therefore, it needs to be calculated through the principle of electromechanical energy conversion, that is, through the calculation of the magnetic energy. Its calculation formula is:

ψ＝∫(u-Ri)dt+ψ ₀

Among them, m is the number of motor phases, N _r is the number of motor rotor poles, W′(i, θ) is the magnetic co-energy of the motor, u is the phase winding voltage, i is the phase winding current, R is the phase winding resistance, Ψ is the flux linkage, and Ψ ₀ is the initial flux linkage.

The four-phase current enters the current detector to detect whether the phase current is greater than zero, and outputs a selection control signal for the estimated torque.

The relationship between the detection phase current output selection control signal is as follows:

(1) If the current detector detects that the phase current is greater than zero, the current detector outputs a signal with a low level of 0;

(2) If the current detector detects that the phase current is equal to zero, the current detector outputs a signal with a high level of 1;

(3) If the current detector detects that the phase current is less than zero, the current detector outputs a signal with a high level of 1.

The torque selector performs logical judgment on the four-phase estimated torque estimated from the torque estimator according to the selection control signal output by the current detector, that is, selects the four-phase estimated torque based on the four-phase selection control signal, and finally outputs the total estimated torque.

The logical relationship of the torque selector is (assuming that the stator energization sequence of the switched reluctance motor is A→D→B→C):

(1) The control signal of phase A is a signal of high level 1, and the control signal of phase D is a signal of low level 0, then the selector judges and selects the estimated torque of phase A as the total estimated torque;

(2) The control signal of phase D is a signal of high level 1, and the control signal of phase B is a signal of low level 0, then the selector judges and selects the estimated torque of phase D as the total estimated torque;

(3) The control signal of phase B is a signal of high level 1, and the control signal of phase C is a signal of low level 0, then the selector judges and selects the estimated torque of phase B as the total estimated torque;

(4) The control signal of phase C is a signal of high level 1, and the control signal of phase A is a signal of low level 0, then the selector judges and selects the estimated torque of phase C as the total estimated torque.

The torque regulator calculates the total estimated torque output by the torque selector and the reference torque required by the switched reluctance motor drive system, and finally outputs the reference current of the motor drive system to form a closed-loop control of the braking torque of the switched reluctance motor drive system. The torque regulator includes two links, the torque feedforward link and the compensation link. The feedforward link outputs the feedforward current i _ref according to the reference torque, as follows:

Among them, T _e is the electromagnetic torque, k _L is the inductance slope.

The compensation current _ic of the compensation link is calculated by inputting the error of the reference torque and the total estimated torque into the PI regulator, and the final reference current is obtained by adding the feedforward current and the compensation current. The torque feedforward link will increase the dynamic response speed of the braking torque of the switched reluctance motor drive system, and the torque saturation link will improve the steady-state torque accuracy of the system.

The beneficial effects of the present invention are:

At present, there are few studies on improving the comprehensive braking performance of electric vehicles by controlling the braking torque of electric vehicles driven by switched reluctance motors in braking or coasting conditions. In order to better improve the use of switched reluctance motors in electric vehicle braking or coasting conditions, meet the driver's braking torque requirements, improve the braking response speed and braking torque accuracy of the switched reluctance motor drive system, and increase the dynamic stability of the braking torque. The present invention is dedicated to solving this problem, and proposes a switched reluctance motor braking torque control system and method based on four-phase current and voltage. According to the driver's demand for braking torque, the motor outputs actual torque to achieve the purpose of braking and decelerating the electric vehicle. The total estimated torque can accurately and timely estimate the actual torque output by the motor, making the motor torque control system more accurate and stable. Through the simulation of the established switched reluctance motor drive system model, it is verified that the flux linkage integrator can estimate the flux linkage well, and the total estimated torque calculated by the torque estimator can effectively track the actual torque of the motor, so the motor can output the actual braking torque according to the driver's demand for reference torque. Finally, the torque regulator outputs the reference current to form a closed-loop control of the braking torque of the switched reluctance motor, which satisfies the accuracy and stability of the braking torque control of the switched reluctance motor based on four-phase current and voltage, and improves the dynamic response speed of the switched reluctance motor.

Description of drawings

Fig. 1 is a diagram of a braking torque control system of a switched reluctance motor based on four-phase current and voltage according to the present invention. Among them, U _ph and I _ph are the four-phase voltage and current, T _ABCD-est is the four-phase estimated torque, S _ABCD is the four-phase torque control signal, T _est is the total estimated torque, and T _ref is the reference torque.

Fig. 2 is the torque estimator of A phase. Among them, i _A (t), U _A (t) are A-phase current and A-phase voltage, Reset is a reset signal, Trigger is a trigger signal T _{A_est} is an estimated torque of A-phase.

Fig. 3 is a comparison diagram of the estimated flux linkage obtained by the flux integrator and the actual flux linkage.

Figure 4 is a schematic diagram of the torque selector. T _{A_est} , T _{B_est} , T _{C_est} , T _{D_est} are estimated torques of phases A, B, C and D respectively, and S _A , S _B , S _C and _SD are torque control signals of phases A, B, C and D respectively.

Figure 5 shows the total estimated torque output by the torque selector, the actual torque output by the motor and the required reference torque.

Figure 6 is a block diagram of the torque regulator, which outputs a reference current to form a closed-loop control of the motor braking torque.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific examples.

The present invention relates to a switching reluctance motor braking torque control system and method based on four-phase current and voltage. The control structure block diagram is shown in FIG. 1 . The braking torque control system mainly includes a torque estimator, a current detector, a torque selector and a torque regulator.

The four-phase current and voltage output by the switched reluctance motor body enter the torque estimator, and the calculated torque estimator outputs the four-phase estimated torque T _ABCD-est to the torque selector. At the same time, the current detector detects the four-phase current and outputs the four-phase estimated torque control signal S _ABCD . The torque selector outputs the total estimated torque T _est to the torque regulator under the action of the four-phase estimated torque and the four-phase torque control signal.

The torque estimator consists of a multiplier, a flux integrator, a current detector, a magnetic co-energy integrator and a sample-and-hold device, as shown in Figure 2. The torque estimator that obtains the A-phase current and voltage outputs the flux linkage to the magnetic co-energy integrator under the action of the multiplier and the flux-linkage integrator. At the same time, the magnetic co-energy integrator also obtains the reset signal output by the A-phase current detector to output the magnetic co-energy. The sample-and-hold device outputs the magnetic co-energy variation of one electronic cycle under the action of the magnetic co-energy and the trigger signal output by the current detector, and finally outputs the estimated torque of the A phase under the action of the multiplier. Its calculation formula is:

ψ＝∫(u-Ri)dt+ψ ₀

Among them, m is the number of phases of the motor, N _r is the number of poles of the motor rotor, W′(i, θ) is the magnetic energy of the motor, u is the phase winding voltage, i is the phase winding current, R is the phase winding resistance, Ψ is the flux linkage, Ψ ₀ is the initial flux linkage

In order to evaluate the accuracy of the torque estimator, the estimated flux linkage obtained by the multiplier in the estimator is compared with the actual flux linkage, as shown in Figure 3. It can be clearly seen that the estimated flux linkage obtained by the flux linkage integrator basically coincides with the actual flux linkage. Even at the peak position at the time of 0.0075s, it is basically coincident after zooming in. The gap is very small, which shows the accuracy of the flux linkage integrator and also reflects the effectiveness of the torque estimator.

The four-phase current of the switched reluctance motor enters the current detector and detects whether the four-phase current is greater than zero, and outputs a selection control signal of the four-phase estimated torque to the torque selector.

The relationship between the detection phase current output selection control signal is as follows:

(1) If the current detector detects that the phase current is greater than zero, the current detector outputs a signal with a low level of 0;

(2) If the current detector detects that the phase current is equal to zero, the current detector outputs a signal with a high level of 1;

(3) If the current detector detects that the phase current is less than zero, the current detector outputs a signal with a high level of 1.

The torque selector performs logical judgment on the four-phase estimated torque estimated from the torque estimator according to the selection control signal output by the current detector, that is, selects the four-phase estimated torque based on the four-phase selection control signal, and finally outputs the total estimated torque. As shown in Figure 4, it is assumed that the energization sequence of the stator of the 8/6-pole switched reluctance motor is A→D→B→C.

The logical relationship of the torque selector is:

(1) The control signal of phase A is a signal of high level 1, and the control signal of phase D is a signal of low level 0, then the selector judges and selects the estimated torque of phase A as the total estimated torque;

(2) The control signal of phase D is a signal of high level 1, and the control signal of phase B is a signal of low level 0, then the selector judges and selects the estimated torque of phase D as the total estimated torque;

(3) The control signal of phase B is a signal of high level 1, and the control signal of phase C is a signal of low level 0, then the selector judges and selects the estimated torque of phase B as the total estimated torque;

(4) The control signal of phase C is a signal of high level 1, and the control signal of phase A is a signal of low level 0, then the selector judges and selects the estimated torque of phase C as the total estimated torque.

After a cycle, the total estimated torque is output according to the four-phase estimated torque and the four-phase torque control signal, and the output total estimated torque is accurate and timely. Compared with the estimated total estimated torque of one-phase current and voltage, the estimated total torque of four-phase current and voltage is only a quarter of a cycle behind the actual torque.

In order to effectively evaluate the accuracy and effectiveness of the switching reluctance motor braking torque control system and method based on four-phase current and voltage, the actual torque output by the motor, the total estimated torque output by the torque estimator, torque selector and current detector, and the reference torque demanded by the driver were obtained for comparative analysis, as shown in Figure 5. The braking torque closed-loop control strategy can well estimate the actual torque according to the demand of the reference torque, and output the reference torque required by the driver with the motor. At the same time, the estimated torque can also track the actual torque accurately and efficiently. The actual torque of the motor drops rapidly at 0.0025s, and the estimated torque also drops rapidly at about 0.005s. After 0.01s, the estimated torque can be estimated in a timely and effective manner according to the change of the actual torque, which shows that the estimated torque can be efficiently tracked to the actual torque. Theoretically, the estimated torque is only a quarter of an electronic cycle behind the actual torque.

The torque regulator calculates the total estimated torque output by the torque selector and the reference torque required by the switched reluctance motor drive system, and finally outputs the reference current of the motor drive system to form a torque closed-loop control of the switched reluctance motor drive system, as shown in Figure 6. The torque regulator includes two links, the torque feedforward link and the compensation link. The feedforward link outputs the feedforward current i _ref according to the reference torque, as follows:

Among them, T _e is the electromagnetic torque, k _L is the inductance slope.

The compensation current _ic of the compensation link is calculated by inputting the error of the reference torque and the total estimated torque into the PI regulator, and the final reference current is obtained by adding the feedforward current and the compensation current. The torque feedforward link will increase the dynamic response speed of the braking torque of the switched reluctance motor drive system, and the torque saturation link will improve the steady-state torque accuracy of the system.

The reference current and the four-phase current output by the above torque control through the torque regulator constitute a current closed-loop control, and the brake torque closed-loop control system is formed by the switched reluctance motor braking torque control system and method based on the four-phase current and voltage to form a double closed-loop braking torque control system.

Matters not covered in the present invention are known technologies.

The above-mentioned embodiments are only to illustrate the technical concept and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and not to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (5)

1. A switched reluctance motor braking torque control method based on four-phase current and four-phase voltage, is characterized in that: obtain total estimated torque by four-phase current and four-phase voltage, the total estimated torque of an electrical cycle only lags behind actual torque 1/4 electrical cycle, drive system comprises torque estimator, current detector, torque selector and torque regulator; The four-phase estimated torque is obtained after the four-phase current and the four-phase voltage of the switched reluctance motor are estimated by the torque estimator; Detecting the four-phase current by the current detector, and outputting the estimated torque control signal of the four phases, specifically including: if the phase current is greater than zero, the current detector outputs a low-level signal, and if the phase current is less than or equal to zero, then outputs a high-level signal; The torque selector selects the estimated torque of the four phases according to the four-phase high and low level signals, and selects the estimated torque of one of the four phases as the total estimated torque of the switched reluctance motor drive system; A reference current is obtained by the torque regulator according to the total estimated torque and the reference braking torque of the drive system, thereby realizing closed-loop control of the torque of the motor. 2. the switched reluctance motor braking torque control method based on four-phase current and four-phase voltage according to claim 1, is characterized in that: calculate the estimated torque of four phases by magnetic total energy, first calculate the flux linkage of each phase by the current of four phases and the four-phase voltage, then integrate each phase flux linkage, finally obtain the estimated torque of four phases, its calculation formula is: ψ＝∫(u-Ri)dt+ψ ₀ Among them, m is the number of motor phases, N _r is the number of poles of the motor rotor, W′ _m (i, θ) is the magnetic co-energy of the motor, u is the phase winding voltage, i is the phase winding current, R is the phase winding resistance, Ψ is the flux linkage, and Ψ ₀ is the initial flux linkage. 3. the switching reluctance motor braking torque control method based on four-phase current and four-phase voltage according to claim 1, is characterized in that: whether current detector detects phase current is greater than zero, outputs the control signal of estimated torque; The relationship between the detection phase current output control signal is as follows: (1) If the current detector detects that the phase current is greater than zero, the current detector outputs a signal with a low level of 0; (2) If the current detector detects that the phase current is equal to zero, the current detector outputs a signal with a high level of 1; (3) If the current detector detects that the phase current is less than zero, the current detector outputs a signal with a high level of 1. 4. the switched reluctance motor braking torque control method based on four-phase current and four-phase voltage according to claim 1, is characterized in that: the torque selector selects the estimated torque of four phases according to the control signal that current detector outputs, and finally outputs the total estimated torque; In the case that the stator energization sequence of the switched reluctance motor is A-D-B-C, the logic relationship of the torque selector is: (1) The control signal of phase A is a signal of high level 1, and the control signal of phase D is a signal of low level 0, then the selector selects the estimated torque of phase A as the total estimated torque; (2) The control signal of phase D is a signal of high level 1, and the control signal of phase B is a signal of low level 0, then the selector selects the estimated torque of phase D as the total estimated torque; (3) The control signal of phase B is a signal of high level 1, and the control signal of phase C is a signal of low level 0, then the selector selects the estimated torque of phase B as the total estimated torque; (4) The control signal of phase C is a signal of high level 1, and the control signal of phase A is a signal of low level 0, then the selector selects the estimated torque of phase C as the total estimated torque. 5. the switched reluctance motor braking torque control method based on four-phase current and four-phase voltage according to claim 1, is characterized in that: the torque regulator calculates the total estimated torque and the reference torque, and finally outputs the reference current of the motor drive system to form the closed-loop control of the switched reluctance motor drive system torque; wherein the torque regulator comprises two parts, a torque feedforward part and a compensation part; the feedforward part outputs the feedforward current _if according to the reference torque, as follows: Among them, if _is the output feed-forward current, k _L is the inductance slope, and T _ref is the reference torque; In the compensation part, the error between the reference torque and the total estimated torque output by the torque selector is input to the PI regulator, and the PI regulator outputs the compensation current _ic , and then the reference current is obtained by adding the feedforward current and the compensation current.