Switched reluctance motor low-speed rotor position estimation method

Abstract

The invention provides a switched reluctance motor low-speed rotor position estimation method, and belongs to the technical field of switched reluctance motor control. The method comprises the following steps: firstly, discretizing a winding voltage equation of the switched reluctance motor, obtaining predicted current of each phase through programming calculation and formula recombination of a controller, and acting the predicted current on hysteresis control of a conduction region; secondly, in combination with a partition PWM hysteresis variable-duty-ratio pulse injection method, setting three high-frequency pulses with different duty ratios to be injected into a conduction region, a follow current region and a non-conduction region respectively, and increasing the number of sampling current slope difference values when a switch tube in the conduction region is switched off; and finally, performing logic combination and comparison on the three-phase current slope difference curve generated by calculation to obtain a real-time rotor position. According to the method, the rotor position estimation precision is improved, the rotating speed range is widened, the amplitude of response current in a non-conducting region is limited, negative torque is avoided, and low-speed stable operation of the motor is facilitated.

Description

Technical Field

[0001] The invention relates to a method for estimating the low-speed rotor position of a switched reluctance motor, and belongs to the technical field of switched reluctance motor control. Background Art

[0002] The switched reluctance motor adopts a double salient pole structure, with a concentrated winding on the stator and no winding and permanent magnet on the rotor. It has the characteristics of simple structure, strong fault tolerance, high operating efficiency, etc., and is suitable for high-speed operation and harsh working environment. In high-performance and high-reliability applications such as new energy vehicles and aerospace, the stable operation of the switched reluctance motor depends on the accurate detection of the rotor position, which is crucial for achieving effective speed control. Usually, in order to obtain rotor position information, a position sensor is installed inside the motor. However, the installation of the position sensor not only increases the cost and volume of the motor, but may also be affected by factors such as high temperature, dust, humidity and electromagnetic interference, thereby interfering with the logic judgment of the controller and reducing the accuracy of the control system. The position sensorless technology uses voltage and current for indirect rotor position detection, which reduces the system cost, improves the accuracy of the control system, and enhances the stability of the motor operation.

[0003] The present invention proposes a method for estimating the low-speed rotor position of a switched reluctance motor, which not only improves the rotor position estimation accuracy but also ensures the low-speed stable operation of the motor. Summary of the invention

[0004] The main purpose of the present invention is:

[0005] A method for estimating the low-speed rotor position of a switched reluctance motor. This method can not only alleviate the delay in obtaining the current slope difference caused by the time lag of the traditional current hysteresis loop comparison, but also increase the number of current slope difference calculations within one motor operation cycle, thereby improving the accuracy of the rotor position estimation. At the same time, it broadens the motor speed regulation range, suppresses the generation of negative torque, and ensures the low-speed stable operation of the motor.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] The present invention is a method for estimating the low-speed rotor position of a switched reluctance motor, characterized in that it comprises the following steps:

[0008] Step 1: Discretize the winding voltage equation and set the sampling time T s Small enough, the winding voltage U and the motor speed ω remain unchanged within the two sampling intervals, and the current value i at the current moment is sampled. t , then the current value i at the next moment t+1 According to the current U, ω, i tThe predicted current value is calculated based on the known quantities such as L, phase winding R, etc. The calculated predicted current value is used as the input of the hysteresis controller and compared with the given chopping limit for logical judgment.

[0009] Step 2: Set the low and high chopping limit switching angle thresholds θ 1 , so that the conduction interval current characteristics present a low-high double chopping form, low chopping limit i 1 The current rises rapidly to perform current hysteresis comparison control, high chopping limit i 2 Increase the motor torque.

[0010] Step 3: Divide a motor operation cycle into different intervals to inject high-frequency pulses with different duty cycles, and use a delayed τ-second pulse injection method in the freewheeling area and a double-threshold pulse injection method in the non-conduction area.

[0011] Step 4: In the conduction region, set the high-frequency injection pulse duty cycle D 1 , so that the current exhibits PWM hysteresis control characteristics when the switch tube is turned off, increases the number of current slope differences collected, and improves the accuracy of rotor position estimation using the current slope difference method.

[0012] Step 5: In the freewheeling region, set the high-frequency injection pulse duty cycle D 2 , and delay the high-frequency pulse injection time by τ seconds, which can shorten the freewheeling time while ensuring that the required current slope difference can be sampled in the freewheeling area, avoiding the current freewheeling from entering the negative torque area.

[0013] Step 6: Use the lower limit threshold of the dual-threshold hysteresis pulse injection as the distinguishing mark between the freewheeling area and the non-conducting area. When the freewheeling current is lower than the lower limit threshold, start to inject the pulse with a duty cycle of D 3 The high-frequency pulse injection and the response current of the dual threshold control will not produce negative torque and can reduce switching losses.

[0014] In the further step 1, the predictive current chopping control can be used to advance one sampling period to alleviate the time lag problem of the traditional hysteresis control. The control is simple and easy to program. s It needs to be set according to the hardware conditions of the experimental platform. The double chopping limit in step 2 is not only conducive to the rapid rise of current for low-speed stable operation, but also can broaden the speed range and facilitate the combination with high-speed position-free detection technology. 2 The setting needs to be made according to the actual motor speed regulation experimental platform. Setting it too high will weaken the current chopping control characteristics, affect the calculation accuracy of the current slope difference and be detrimental to the stable operation of the motor at low speed.

[0015] Compared with the conventional pulse injection current slope difference comparison rotor position estimation method, the present invention has the following effective effects:

[0016] The present invention proposes a low-speed rotor position estimation method for a switched reluctance motor. On the basis of a traditional current slope difference comparison method, a dual-chopping hysteresis control method of predicted current is combined to suppress torque pulsation, alleviate the time lag of traditional current chopping control, broaden the motor speed regulation range, and improve the stability of motor operation; the partitioned PWM hysteresis variable duty cycle pulse injection method adopted increases the number of samplings of the current slope difference within one cycle, thereby improving the accuracy of rotor position estimation; the delayed τ second pulse injection shortens the freewheeling time, and the dual threshold hysteresis pulse injection rule in the non-conduction zone can limit the response current amplitude, suppress the generation of negative torque, and further ensure the stable operation of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the pulse injection method principle and the pulse injection response current peak envelope;

[0018] Figure 2 This is a schematic diagram of the principle of the current slope difference comparison method;

[0019] Figure 3 is a schematic diagram of the topology of an asymmetric half-bridge power converter for a switched reluctance motor;

[0020] Figure 4 This is a schematic diagram of the principle of the proposed switched reluctance motor low-speed rotor position estimation method. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0022] Figure 1 This is a schematic diagram of the pulse injection method. Pulse injection uses the principle that each phase is controlled independently during operation, injects high-frequency PWM pulses into the non-conducting phase winding, and the high-frequency switching of the power converter generates a small response current in the non-conducting phase. Since the amplitude of the response current generated by the non-conducting phase is very small and the frequency is very high, it will hardly affect the movement of the motor. Usually, the effect of current on inductance and the voltage drop of the winding, as well as the motion back electromotive force, can be ignored, and only the change in current causes the change in transformer electromotive force. The obtained pulse injection time and pulse injection response current can be used to indirectly obtain inductance information or use the inverse relationship between current increment and inductance for position estimation, but the duration and frequency of the injected pulse must be strictly calculated.

[0023] Figure 2 This is a schematic diagram of the principle of the current slope difference comparison method. When the motor is running in the chopper control mode and pulse injection, the switch tube is in a high-frequency on and off switching state, causing the phase current to rise and fall briefly.

[0024] When the k-th phase switch is turned on, switches T1 and T2 are turned on at the same time, so that the two ends of the winding are positively voltageed, and the motor is in an excitation state. The circuit equation is:

[0025]

[0026] When the k-th phase switch is turned off, switches T1 and T2 are disconnected, and the winding is subjected to a negative voltage through the freewheeling circuit. At this time, the motor is in a negative voltage freewheeling state, and its circuit equation is:

[0027]

[0028] represents the rising slope of the current, Indicates the falling slope of the current. In the chopping control mode and high-frequency pulse injection state, the switching tube action time is very short. Assuming that the phase current and motion electromotive force remain unchanged in the switching interval within a very short time interval, subtracting the two equations will obtain the slope difference of the k-th phase current, and its equation is expressed as:

[0029]

[0030] It can be seen from the equation that the current slope difference is inversely proportional to the phase inductance, so the current slope difference can also be divided into angle partitions. The current slope difference method partitions the three-phase 12 / 8-pole switched reluctance motor as follows: Figure 2 As shown, based on the comparison of the current slope difference curves of the three phases ABC, six special points of 0°, 7.5°, 15°, 22.5°, 30°, and 37.5° are logically judged to estimate the rotor position.

[0031] Figure 3 The schematic diagram of the topological structure of the asymmetric half-bridge power converter of the switched reluctance motor is shown in FIG. The pulse injection method principle and the current slope difference comparison method are both proposed based on the asymmetric half-bridge power converter topological structure, and the partitioned variable duty cycle pulse injection method of the present invention is also proposed based on this.

[0032] Figure 4 This is a schematic diagram of the principle of the proposed switched reluctance motor low-speed rotor position estimation method.

[0033] Step 1: Discretize the winding voltage equation and set the sampling time T s Small enough, the winding voltage U and the motor speed ω remain unchanged within the two sampling intervals, and the current value i at the current moment is sampled. t , then the current value i at the next moment t+1 According to the current U, ω, i t The predicted current value is calculated based on the known quantities such as L, phase winding R, etc. The calculated predicted current value is used as the input of the hysteresis controller and compared with the given chopping limit for logical judgment.

[0034] Step 2: Set the low and high chopping limit switching angle thresholds θ 1 , so that the conduction interval current characteristics present a low-high double chopping form, low chopping limit i 1 The current rises rapidly to perform current hysteresis comparison control, high chopping limit i 2 Increase the motor torque.

[0035] Step 3: Divide a motor operation cycle into different intervals to inject high-frequency pulses with different duty cycles, and use a delayed τ-second pulse injection method in the freewheeling area and a double-threshold pulse injection method in the non-conduction area.

[0036] Step 4: In the conduction region, set the high-frequency injection pulse duty cycle D 1 , so that the current exhibits PWM hysteresis control characteristics when the switch tube is turned off, increases the number of current slope differences collected, and improves the accuracy of rotor position estimation using the current slope difference method.

[0037] Step 5: In the freewheeling region, set the high-frequency injection pulse duty cycle D 2 , and delay the high-frequency pulse injection time by τ seconds, which can shorten the freewheeling time while ensuring that the required current slope difference can be sampled in the freewheeling area, avoiding the current freewheeling from entering the negative torque area.

[0038] Step 6: Use the lower limit threshold of the dual-threshold hysteresis pulse injection as the distinguishing mark between the freewheeling area and the non-conducting area. When the freewheeling current is lower than the lower limit threshold, start to inject the pulse with a duty cycle of D 3 The high-frequency pulse injection and the response current of the dual threshold control will not produce negative torque and can reduce switching losses.

[0039] In the further step 1, the predictive current chopping control can be used to advance one sampling period to alleviate the time lag problem of the traditional hysteresis control. The control is simple and easy to program. s It needs to be set according to the hardware conditions of the experimental platform. The double chopping limit in step 2 is not only conducive to the rapid rise of current for low-speed stable operation, but also can broaden the speed range and facilitate the combination with high-speed position-free detection technology. 2 The setting needs to be made according to the actual motor speed regulation experimental platform. Setting it too high will weaken the current chopping control characteristics, affect the calculation accuracy of the current slope difference and be detrimental to the stable operation of the motor at low speed.

Claims

1. The present invention is a method for estimating the low-speed rotor position of a switched reluctance motor, characterized in that: The steps include: Step 1: Discretize the winding voltage equation and set the sampling time T s Small enough, the winding voltage U and the motor speed ω remain unchanged within the two sampling intervals, and the current value i at the current moment is sampled. t , then the current value i at the next moment t+1 According to the current U, ω, i t The predicted current value is calculated based on the known quantities such as L, phase winding R, etc. The calculated predicted current value is used as the input of the hysteresis controller and compared with the given chopping limit for logical judgment. Step 2, setting the low and high chopping limit switching angle thresholds θ1, so that the current characteristics of the conduction interval present a low and high dual chopping form, the low chopping limit i1 makes the current rise rapidly to perform current hysteresis loop comparison control, and the high chopping limit i2 increases the motor torque. Step 3: Divide a motor operation cycle into different intervals to inject high-frequency pulses with different duty cycles, and use a delayed τ-second pulse injection method in the freewheeling area and a double-threshold pulse injection method in the non-conduction area. Step 4: In the conduction region, set the high-frequency injection pulse duty cycle D1 so that the current exhibits PWM hysteresis control characteristics when the switch tube is turned off, increase the number of current slope differences collected, and improve the accuracy of rotor position estimation using the current slope difference method. Step 5, in the freewheeling zone, set the high-frequency injection pulse duty cycle D2, and delay the high-frequency pulse injection time by τ seconds, while ensuring that the freewheeling zone can sample the required current slope difference and shorten the freewheeling time, avoiding the current freewheeling from entering the negative torque zone. Step 6, using the lower limit threshold of the dual-threshold hysteresis pulse injection as the distinguishing mark between the freewheeling area and the non-conduction area, when the freewheeling current is lower than the set lower limit threshold, start to inject high-frequency pulses with a duty cycle of D3, the response current of the dual-threshold control will not generate negative torque and can reduce switching losses.

2. A method for estimating the low-speed rotor position of a switched reluctance motor according to claim 1, characterized in that: The use of predictive current chopping control in step 1 can solve the hysteresis problem of the traditional hysteresis comparison method.

3. A method for estimating the low-speed rotor position of a switched reluctance motor according to claim 1, characterized in that: The dual chopping limit control in step 2 is not only beneficial to the low-speed stable operation of the motor, but also can widen the speed range and facilitate the combination with high-speed position sensorless technology.

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