Aiming at the problem that mechanical position sensor increases the complexity of control system and reduces the reliability of system, a new Position-free sensor controller for switched reluctance motor is proposed. Based on the inductance model of switched reluctance motor, the sensorless mathematical model is deduced and the sensorless control system is constructed. The actual position of the rotor is estimated by measuring the voltage and current of the exciting phase. The current chopper control method is used to control the low-speed operation of the SRM, and the angle position control method is used to control the high-speed operation of the SRM. The position sensorless system is simulated and the sensorless control of switched reluctance motor is realized. The experimental results show that this method can accurately estimate the rotor position of SRM in a wide speed range. Switched reluctance motor (SRM) has the characteristics of simple structure, high efficiency, thermostatic element wide speed range and large starting torque at low speed. The stator and rotor are salient pole structure. The stator has centralized windings, and the rotor has no windings.
The windings of each phase of the stator turn on in turn to generate electromagnetic torque. The position signal controls the opening and closing of the exciting phase windings. The position detection link is an important part of the speed control system of the switched reluctance motor. Switched Reluctance Motor (SRM) usually uses photoelectric encoding disc as position sensor to detect rotor position signal, but the use of position sensor increases the complexity of the system, increases the cost of the motor, reduces the power volume ratio of the motor, and reduces the reliability of the motor operation. Because of the high power density of the motor, and reduces the size of the installation and other factors. Considering that the research of sensorless technology has become a hotspot of switched reluctance motor. Nowadays, there are many research methods in switched reluctance motor, such as phase current analysis and analysis, torque current position characteristic analysis, neural network rotor position estimation, state observer based position sensorless technology, phase flux waveform based position sensorless technology, additional capacitance detection method and reverse series coil method. 。 In this paper, the inductance model of switched reluctance motor (SRM) and the saturation of magnetic circuit are considered. A new Position-free detection method is proposed, which shortens the operation period of position estimation of SRM. Experiments show that the Position-free detection algorithm is simple, real-time and reliable. Figure 1 shows the phase inductance model L(i,theta) of the switched reluctance motor. The phase difference between two-phase inductors is equal to the step angle of 2 pi/mNr (where m is the phase number of the motor and Nr is the pole number of the rotor). In single-phase excitation, the mutual inductance has little effect on the on-phase inductance, which can be neglected. The inductance of the exciting phase can be described by its self-inductance model expression. La(i) inductance is the largest, the inductance of stator and rotor salient pole is in the complete overlap position, the inductance of Lu is the smallest, the inductance of stator and rotor salient pole is in the non-overlap position, and the inductance of Lm(i) is in the middle position. The size of La (i) and Lm (i) is related to phase winding and phase current, and is affected by magnetic saturation. K is the estimator, k = 5. An and BN are polynomial parameters, which are obtained by curve fitting method, so that the La (i) and Lm (i) curves obtained by formula (6) and formula (7) are consistent with those obtained by experiment or finite element analysis. Lu is related to phase winding. The values of inductance La (i), Lu (i) and Lm (i) in formula a, 6 and C are all measured values. The values of inductance La (i), Lu (i) and Lm (i) in formula a, 6 and C can be obtained by formula (7) and formula (8), respectively.
_is the estimated value of previous speed. Thus the values of parameters a, B and C can be calculated. This method considers the role of rotor poles in rotor position estimation and is suitable for switched reluctance motors with any rotor poles. The system simulation calculation is electromagnetic torque, T1 is load torque, J is inertia, F is friction coefficient. Current chopping control (CCC) is used at low speed, i.e.
keeping constant theta on and theta off (theta on is the turn-on angle and theta off angle), and limiting the current to a given upper and lower limit through multiple turn-on and turn-off of the main switching device. In high speed, angle position control (APC) is used to control the motor torque by adjusting the conduction angle of theta C = theta on-theta off to achieve speed regulation. The lower limit of velocity is n=60 r/min, and the critical velocity is nb=1000 r/min. Figure 2 (a) shows the current waveform when n = 500 R / min, θ on = 7.5 ° and θ of = 22.5 °. It can be seen from the figure that in the constant torque working area, SRM has good current chopping characteristics. Figure 2 (b) is the current waveform at n=1500 r/min. It can be seen from the figure that the current under APC control is smaller than that under CCC control in the constant power region because of the high speed of SRM and the short turn-on time of each phase main switch. Fig. 3 is the block diagram of sensorless control system for switched reluctance motor, in which the power of switched reluctance motor is 1.5 kW, 3-phase and 6/4 poles, and the asymmetric half-bridge circuit is used as the main circuit of SRM power converter. Fig. 4 is the block diagram of SRM main circuit. The circuit has three working states: S1 and S4 are turned on, A phase winding plus positive voltage is added to establish current and flux linkage; S1 is disconnected, A phase current continues to flow in the loop composed of S4 and D4, and flux decreases slowly; S1 and S4 are disconnected, phase current flows through D1 and D4, flux linkage drops rapidly, winding energy feedback power supply. It can be seen from the figure that the windings of the motor are connected in series with each phase switch, and the phase and phase are independent of each other, thus avoiding the problem of direct and short circuit between the upper and lower arms of the phase circuit. The controller uses DSP to realize the functions of position estimation, current chopper control and angle position control of switched reluctance motor. The input of the rotor position estimation module is SRM excitation phase current I and phase voltage U detected in real time. Phase current I passes through frequency doubling subdivision module and phase voltage through position estimation module, and the output is rotor position estimation value theta, and_is speed estimation. The switched reluctance motor speed is controlled by a PID regulator, which compares the opening and closing of theta control phase with the given value of speed_ref. Fig. 5 is the flow chart of the main program of the system, which mainly completes the initialization of peripheral equipment, determines the initial position of the rotor, triggers the opening of the phase, detects the excitation phase current and phase voltage, estimates the position of the rotor, commutates the phase and chooses the control strategy. Fig. 6 (a) is the current waveform when current chopper control n=500 r/min turn-on angle, turn-off angle fixed theta on=7.5 degree and theta off=22.5 degree. Fig. 6 (b) is the current waveform when angle position control n=1 500 r/min. From its current waveform, it can be seen that the switched reluctance motor with this position estimation method has good steady-state performance in both low-speed operation and high-speed operation. In order to further verify the accuracy of position estimation, Hall element is installed in the experiment to measure the rotor position and obtain the rotor position measurement value. The estimated value is calculated by the position estimation module through the real-time detection of the excitation phase current. Figures 7 (a) and 7 (b) are curves of position measurements and estimates when n = 500 r/min and N = 1 500 r/min, respectively. The solid lines in the figure represent the rotor position measurements, the dotted lines represent the rotor position estimates, the dots in the figure represent the sampling points of the rotor position measurements, and the circles in the figure represent the sampling points of the rotor position estimates. Table 1 and Table 2 list the position measurement and position estimation at sampling points when the speed of SRM is n=500 r/min and n=1500 r/min respectively. By comparing the actual measured value with the estimated value, it can be seen that the estimated result of the rotor position of SRM is consistent with the actual situation and the error is very small. Switched Reluctance Motor (SRM) speed regulation system has attracted the attention of many experts and scholars at home and abroad because of its excellent dynamic and static speed regulation performance. This scheme provides a new Position-free sensing technology for SRM. The sensorless sensor based on inductance model can detect the rotor position of switched reluctance motor well, reduce the system cost, simplify the mathematical model of position estimation, increase the reliability of the system, reduce the system running time and improve the real-time performance of the system. Experiments show that the system runs stably.