Abstract: This paper introduces a design scheme for a hybrid analog-digital control system for a switched reluctance motor. The mathematical model and working principle of the switched reluctance motor are analyzed, and a single-loop speed control scheme based on fixed-angle voltage chopping is proposed. The control loop uses analog methods to achieve PI speed regulation, while the feedback loop uses a single-chip microcomputer system based on the 80C51 microcontroller to convert between position signals and feedback speed. The corresponding hardware structure is also presented. Keywords : Switched Reluctance Motor, Analog Control, Digital Control [align=center]One Kind of Analog and Digital Mixed System Design for Switched Reluctance Motor SHI zheng-guang, HUANG yun-sheng, CHEN xue (School of Information Science & Engineering,Central South University. changsha 410083 China) Shi Zhengguang, Huang Yunsheng, Chen Xue (School of Information Science and Engineering, Central South University, Changsha, Hunan 410083)[/align] Abstract: This article introduces one kind of analog and digital mixed system design proposal for switched reluctance motor. It briefly analyzes the math model and principle of the switched reluctance motor, and proposes single speed closed-loop control plan which is based on the fixed angle voltage wave-cut control mode. The control loop selects the simulation method to realize the PI speed regulation, the feedback loop uses 80C51 as the core monolithic integrated circuit system carries on the position signal and feedback speed transformation processing, at the same time, the article gives the corresponding hardware architecture. Key words: switched reluctance motor; analogous control; digital control 1. Introduction Switched reluctance motors have been increasingly widely used in industry due to their advantages such as simple structure, low manufacturing cost, good controllability, reliable operation, high efficiency and superior comprehensive performance. At present, the United States, Canada, Yugoslavia and other countries have successively carried out research work and made progress in the integrated design of the system, electromagnetic analysis of the motor, application of microcomputer, application of new power electronic devices, and development of new structural forms (such as single-phase motors, sensorless motors, etc.). A number of universities, research institutes and factories in China have invested in the development and manufacturing of switched reluctance motor systems every year. Based on the fixed angle voltage chopper control strategy, this paper uses a speed single closed loop and adopts a hybrid analog-digital approach to design a simple and practical small power switched reluctance motor control system. 2. Basic structure and principle of switched reluctance motor control system 2.1 Linear mathematical model of switched reluctance motor [1] The switched reluctance motor belongs to the double salient pole variable reluctance motor. The salient poles of its stator and rotor are made of ordinary silicon steel sheets. The rotor has neither windings nor permanent magnets, while the stator poles have concentrated windings. In conventional designs, magnetic saturation of the core is generally ignored, and leakage flux is not considered; that is, all flux enters and exits the rotor through the air gap. In this case, the air gap permeability is determined only by the pole arc angle of the overlapping portion of the stator and rotor, meaning the air gap permeability is only a function of the rotor angle. The curve of its inductance versus angle is shown in Figure 1. Analysis shows that in the rising segment of the inductance curve, the current flowing through the windings generates positive electromagnetic torque, while in the falling segment, the current flowing through the windings generates reverse electromagnetic torque. Therefore, the direction of torque can be changed by altering the timing of winding energization, and the speed can be adjusted by controlling the magnitude of the winding current through pulse width. 2.2 System Principle Block Diagram [1][2] The block diagram of the analog-digital hybrid control system is shown in Figure 2: The deviation between the given speed and the feedback speed is output by the speed regulator and used as the input control signal of the PWM circuit to control and adjust the pulse width of a certain frequency. The square wave pulse acts on the power circuit. Through the switching action of the IGBT, the DC power supply voltage applied to the phase winding of the SR motor is chopped into a square wave voltage with the corresponding frequency and duty cycle, thereby changing the effective value of the voltage across the phase winding and realizing the speed control of the SR motor. The logic circuit integrates the angular displacement signal and the control mode to output a multi-channel signal that conforms to the number of phases of the motor and realizes speed control; the position detection signal is output as the feedback speed after passing through the digital frequency multiplication and frequency-voltage conversion circuit. 3. Design of Power Converter [2] In the commonly used power converter main circuit of SRM, the commonly used types are motor dual winding type, capacitor split phase type, H-bridge type, and asymmetrical half-bridge type. This paper adopts the design scheme shown in Figure 3, which has achieved good results in the experiment. Designed for 8/6 pole switched reluctance motors, in the above circuit, we apply three-phase AC rectification to both ends of the motor windings. Taking phase A as an example, each phase has only one controllable device T1 and one freewheeling diode DL1, which can be carried out in single-phase or dual-phase mode. This paper uses single-phase to verify. When the controllable device T1 is turned on, the rectified current passes through winding A and drives it to generate motor torque; when it is turned off, the winding freewheels through diode DL1, where R2 and C3 play the role of protecting the controllable device. In order to avoid current surge during startup, a high-power resistor R1 is connected in series in C1 circuit. After the system enters the stable operating state, it is disconnected. [align=center] Figure 3 SRD power conversion circuit schematic diagram[/align] 4. Design of the digital-analog hybrid system of switched reluctance motor 4.1 Rotor angular displacement detection [1][2] There are many types of angular displacement sensors suitable for switched reluctance motor speed control systems. The most commonly used one is photoelectric. Its advantages are simple structure and high position accuracy, but it is more susceptible to dust and requires a well-sealed dust cover. This paper adopts a four-phase 8/6-pole structure, using a half-detection scheme for position detection. The step angle is 15 degrees, and the rotor pole pitch angle is 60 degrees. The number of teeth and slots on the turntable is the same as the number of salient poles and grooves on the rotor, both being 6 and evenly distributed, each occupying an angle of 30 degrees. The turntable is mounted on the rotor shaft and rotates synchronously. Two photoelectric pulse generators, S1 and S2, with an included angle of 75 degrees, are fixed at 75/2 degrees to the left and right of the stator centerline, respectively. When the raised teeth on the turntable rotate to the position of the slotted photoelectric pulse generators S1 and S2, the light from the light-emitting tubes is blocked, resulting in an output state of 0. When the light is not blocked, the output state is 1. Within one rotor angular cycle of 60 degrees, S1 and S2 generate two square wave signals with a phase difference of 15 degrees and a duty cycle of 50%. These signals combine to form four different states, representing different reference positions of the four-phase windings of the motor. [align=center] Figure 4. Photoelectric pulse generator circuit[/align] The position pulse signal output by the photoelectric pulse generator shown in Figure 5 has a certain rising and falling edge. For this reason, after the output voltage of the phototransistor, we use a comparator with a hysteresis loop to shape it to eliminate the "glitch" of the output position signal and its rising and falling edges. 4.2 Determination of θ[sub]off[/sub] and θ[sub]on[/sub] and starting mode[2] Analyzing the inductance curve in Figure 1 above, it can be seen that changing θ[sub]on[/sub] changes the current in the rising segment of the inductor, thereby changing the motor torque. Changing θ[sub]off[/sub] generally does not affect the current peak value, but affects the width of the current waveform and its relative position with the inductance curve. This paper adopts the fixed angle chopping control mode. θ[sub]off[/sub] and θ[sub]on[/sub] should be taken as the middle value that takes into account both high and low speed operation. The applicable speed regulation range is generally not too large, such as a ratio of 1:20. When the motor starts, the rotor is required to start with the maximum torque at any position. Therefore, the winding current needs to be allowed to switch on and off naturally. In this paper, the four-phase 8/6 pole motor takes θ[sub]on[/sub] = 0[sup]. [/sup] , θ[sub]off[/sub] = 30[sup]. [/sup] , but as the speed gradually increases, θ[sub]off[/sub] < 30[sup]. [/sup] , otherwise the braking torque will be formed due to the freewheeling current, affecting the operation. 4.3 Digital frequency multiplication and frequency-voltage conversion circuit [3][4][5] As a feedback detection link, this paper adopts a control structure with the 80C51 microcontroller as the core. The frequency multiplication and frequency-voltage conversion of the position signal are completed by two timer/counter chips 8253. The signal output is DAC0832 chip and I/V conversion circuit. Simultaneously, using a microcontroller system to handle the forward and reverse rotation of the motor, as well as stopping and starting, is relatively simple. Its P3.5 and P3.6 ports output forward and reverse control signals. The digital frequency multiplier circuit uses the 8253 chip. When the two position signals are XORed, the mechanical angle is 15 degrees, which is used as the original position pulse in Figure 6 and fed into the system structure. In the 8253, counter 0 counts once for each 15-degree square wave Q, i.e., requests an interrupt. The CPU responds by reading the count value N of the fixed pulse from counter 1 and clearing it. Then, this value is divided by 50, and the resulting value is sent to counter 2 as its time constant value N/50. Counter 2 is also counted by a fixed clock pulse. When it returns to zero, it outputs a frequency-multiplied pulse F. If we let the period corresponding to the 15-degree interrupt pulse be T, and the period of the fixed pulse be t, then the period of the frequency-multiplied pulse is Nt/50, and since Nt=T, then TF=T/50. It can be seen that the output pulse achieves a 50-fold frequency multiplication through this stage. In digital frequency-to-voltage conversion circuits, the strategy used is based on the common speed measurement method for motors: the M/T speed measurement method. In practical applications, the M speed measurement method is more suitable for high-speed segments, while the T speed measurement method is more suitable for low-speed segments. The combination of the two, namely the M/T method, is widely used in digital speed measurement. Its speed measurement formula is as follows: (5) Where f[sub]0[/sub] represents the frequency of the clock pulse, m[sub]1[/sub] represents the number of position pulses after frequency multiplication, m[sub]2[/sub] represents the number of high-frequency clock pulses in the same time period, and P represents the number of pulses for the motor to rotate one revolution after frequency multiplication. In the hardware circuit above, counters 0 and 1 on the 8253 count m1 and m2 respectively. The D flip-flop is mainly used to synchronize the counting of m2 with the speed measurement pulse count. Since the 8253 uses falling-edge counting, an inverter M is used. The signals to start and stop speed measurement are output from port P3.4 of the 80C51 microcontroller, and port P3.1 is used for the reset pulse output. The 8253 is a down counter; during programming, the initial value of the 16-bit counter is set to 0000H, and it is also set to 0000H after the reading. Within one speed measurement cycle, the maximum allowed number of speed measurement pulses and clock pulses should be less than FFFFH. After data processing, the output is converted by a DAC0832. It should be noted that to obtain the actual analog voltage, an I/V converter is used at the complementary current output terminal. 4.4 Forward and Reverse Power-On Logic Circuit [1] The forward and reverse logic power-on circuit actually converts the position signal into a four-phase power-on signal. Here, a 74LS14 inverting buffer is used in conjunction with two 74LS09 AND gates. The two port signals of the microcontroller control the opening and switching of its forward and reverse logic. Special attention should be paid to the synchronization of the signals to ensure that the converted signals have similar time delay times and to ensure that the subsequent signals are reliably triggered. [align=center] Figure 6 Forward and Reverse Logic Control Circuit [/align] 4.5 Design of Speed ​​Regulator [2] According to the system principle, the signal converted from frequency/voltage is processed by the analog speed regulator, and the output control signal is sent to the PWM generator to finally control the logic sequence of the power conversion device. The speed regulator is based on OP07 and adopts the PI algorithm, as shown in Figure 8. R6 adjusts the speed setpoint and compares it with Vout. R8 and C4 form a PI calculation circuit with adjustable parameters. VD1 is the output limiting clamping diode of the regulator. The parallel switch J of the PI circuit is set to prevent drift output from causing malfunctions in the transmission system. Under zero input conditions, drift often occurs, causing the system to "creep." That is, in the stopped state, switch J is closed, meaning the PI regulator is not engaged, and the output is zero; conversely, in the operating state, switch J is open, and the PI regulator is engaged in the system. [align=center] Figure 7 Speed ​​Regulator[/align] 5 Conclusion This paper designs this analog-digital hybrid control system for a 2.2KW small switched reluctance motor with a maximum speed of 1500r/min. This method is very effective for situations where anti-interference and dynamic response requirements are not very high. Since the design of the control system is based on a simplified small-signal linearized dynamic model of the SR motor, it naturally differs significantly from the actual operating SRD. Further optimization is still needed in terms of parameters, structure, and function. After the system starts at maximum torque and enters a steady state, the speed increases smoothly at approximately 7.5 degrees Celsius and 22.5 degrees Celsius. Decreasing the speed results in a significant decrease, and pulsation appears at a certain point. Increasing the speed significantly causes the motor to accelerate noticeably, exceeding 17.5 degrees Celsius. Due to the narrow leading-edge pulse, motor pulsation becomes very pronounced. Therefore, during adjustment, the adjustment level must be kept within a certain range. This system has been tested and found to be stable and simple in design, suitable for applications with low power requirements. References: [1] Hu Chongyue. AC speed regulation technology [M]. Machinery Industry Press. 1998. 198-203 [2] Wang Honghua. Speed ​​regulation control technology of switch type reluctance motor [M]. Machinery Industry Press. 1995. 101-102 [3] Luo Guie. Fundamentals of analog electronics [M]. Central South University Press. 2005. 203-205 [4] Li Tiecai and Du Kunmei, eds. Motor control technology [M]. Harbin Institute of Technology Press. 2000. 155-159 [5] Li Rending. Microcomputer control of motor [M]. Machinery Industry Press. 1999. 101-103 Author's profile: Shi Zhengguang (1983-), male, from Xianyang, Shaanxi, is a master's student at the School of Information Science and Engineering, Central South University, Hunan Province. Research direction: control theory and control engineering My contact information: 13874886479