Research on Control Method of Switched Reluctance Motor

Research on the Control Method of Switched Reluctance Motors in the Journal of Taiyuan University of Technology Hao Runke Gao Liyun (School of Electrical and Power Engineering, Taiyuan University of Technology) (Taiyuan Coal Gasification Company) The theoretical analysis and calculation of the torque of the machine Two control modes: low speed chopping control and high speed single pulse control.
Switched reluctance motor (SR) is a new type of speed-regulating motor, which has attracted wide attention from the domestic and international electrical industry. The SR motor is controlled by its electronic controller and can realize stepless speed regulation. It is a typical electromechanical system with excellent speed regulation performance and operating efficiency, and has many controllable parameters and flexible control. This paper describes the two control methods that SR motors take at low speed and high speed: chopping control and single pulse control.
The structure and basic rotation principle of the motor The stator and rotor core of the SR motor are made up of silicon steel sheets. The inner circumference of the stator core and the outer circumference of the rotor core are evenly distributed with teeth and grooves (the teeth are also called salient poles). , constitutes a double salient pole structure. Figure 1 shows the structure of a 4-phase 8 / 6-pole reluctance motor. Each of the salient cores is provided with a concentrated winding of a DC motor like a main magnetic pole coil. There is no winding on the salient pole of the rotor, and there is no commutator and brush. The windings on the opposite salient poles on the circumference of the stator are connected in series to form a phase winding. When a phase winding is energized, a reluctance torque will be generated in an attempt to make the adjacent rotor salient poles coincide with the phase winding axis of the stator. If the stator windings are energized sequentially, the rotor can be continuously rotated. Changing the energization sequence of the windings also changes the direction of rotation of the rotor.
2 Torque analysis of switched reluctance motor calculation When the center line of the rotor slot coincides with the axis of the salient pole of the stator, the winding inductance is the smallest, and the position of the rotor defining the position is θ = 0 ° when the axis of the salient pole of the rotor coincides with the axis of the stator salient pole The winding inductance is the largest, and θ is the number of convex poles of the rotor). Under the condition of phase winding current setting (i=), the reluctance torque is a function of the rotor position angle. It is known from the literature [1] that the reluctance torque of the SR motor is equal to the partial derivative of the magnetic ensemble W to the rotor position angle θ: the rotor position angle at the moment when the phase winding is turned on is called the opening angle on, and the phase winding is disconnected from the current. The rotor position angle is called the off angle off. Assuming that the SR motor runs at a constant speed, the energization timing of each phase winding is selected when the phase stator salient pole axis coincides with the rotor slot center line, that is, θ = 0 ° each phase winding power failure time selection When the stator salient pole axis coincides with the rotor salient pole axis, that is, θ2. Fig. 2 is the magnetization curve when the magnetic circuit saturation is not considered, the curve 1 is the magnetization curve when θ = 0 °, and the curve 2 is the magnetization curve when θ. The current of each phase winding is constant i=I 1, then the phase winding is energized, the magnetic common energy increment is the difference between the area S and the area S. S can be obtained by closed-circuit integration: the increment of the rotor position angle Δθ= Θ2, so the reluctance torque generated by the energization of a phase winding is: when the q-phase winding of the reluctance motor is cycled through the energization cycle, the position angle of the rotor rotation is exactly 1 pole angle θ2, that is, the rotor 2, the magnetic common The increment ΔW= qS The relationship between the number of motor phases q and the number of salient poles of the stator is: q= N Therefore, the reluctance torque generated by the SR motor winding winding cycle is: Therefore, the reluctance torque expression is: The target motor determines that the opening angle and the closing angle θ are given. The integral part of the above formula is constant. Equation (5) can be written as: where F is the integral and coefficient part of equation (5), and the opening angle and off The break angle is related to U. The phase winding voltage k is the rotational angular velocity. Therefore, the controllable parameters of the switched reluctance motor are: winding voltage s, opening angle θon, and closing angle θoff. By changing one or two parameters, the SR motor speed can be adjusted.
3 SR motor control mode 3.1 Low-speed chopper control When the SR motor runs at low speed, the back EMF is small and the current change rate is large. In order to avoid the current rising too fast, exceeding the maximum current allowed by the power switching components and the motor, we use the chopping method to achieve the purpose of speed regulation.
At the minimum winding inductance, θ = 0 °, energize the windings. When the current increases to a fixed amplitude i, the winding is de-energized. As the winding is subjected to a reverse voltage, the current drops rapidly. After the time T has elapsed, the windings are re-energized. In this way, the power is turned off repeatedly to form a chopping current waveform. When the rotor is turned to the maximum inductance of the winding, that is, θ = /N, regardless of whether the current is in the rising or falling phase, the winding is de-energized, and the current is reduced to zero, and the phase energization process is completed, as shown in Fig. 3. Chopper turn-off time The fixed value is due to the constant change of the winding inductance during the phase energization, so the magnitude of the current drop during time T is not constant.
The inductance current decreases rapidly, and the falling amplitude is large. When the inductance is large, the current decreases slowly, and the falling amplitude is small. From the perspective of the output of the motor, the selection of the time T should be as small as possible, so that the current drop amplitude during the chopping off time is small, and the ratio of the average value of the current to the peak value is increased, which is favorable for the constant current peak. Increase the average torque of the motor. However, it is not possible to take a value that is too small, as a result of the operating frequency of the power switching element in the power circuit, such as 0. 55 to 0. 65 s.
L - Inductance curve In the phase energization process, the phase current waveform can be approximated as a flat-top square wave current. When the current amplitude i is changed, the amplitude of the flat-top square wave current also changes accordingly, which in turn can change the average torque of the motor.
Since the 4-phase 8 / 6-pole SR motor rotor has 6 salient poles, the phase inductance curve is based on the rotor angular displacement θ = 2/4 = 60 °. The phase interval of each phase is from θ = 0 ° to θ = 30 °, that is, the energization interval accounts for half of the period of the inductance waveform. When the motor is running in a steady state, the 4-phase winding wheel is circulated and evenly switched, and the operation of each phase winding is the same. Since the inductance waveforms of adjacent phases are different by 15°, the phase interval of each phase winding is also different by 15°, and the current waveform of each phase winding is also different. 2. High-speed single-pulse control When the high-speed operation is performed, the phase current period is very short, and the current is established. The freewheeling section occupies a considerable proportion, and the back EMF is sufficient to suppress the rise of current. Therefore, at high speed, a single-pulse control method is adopted, that is, the winding is energized when the winding is at the minimum or small inductance, and as the rotor rotates, the inductance gradually increases in the middle of the rising portion of the inductor to turn off the phase winding, thereby in a period of inductance. Inside, a current waveform that gradually increases and then gradually decreases to zero is formed, as shown in FIG.
In the high speed single pulse control, the turn-off angle θ remains unchanged, and the turn-on angle θ can be adjusted over a wide range. When θ is appropriately advanced, the height and width of the current waveform increase. Since the main portion of the waveform is in the rising portion of the winding inductance curve, the resulting electromagnetic torque increases, and the motor speed increases as the angle decreases at a constant load torque. However, the adjustment of the advance opening angle θ is limited. When the conduction angle θ reaches 30°, the total width of the current waveform is about 60°. If the angle θon is further advanced, the freewheeling current will not drop to zero, and the next phase conduction has come, thus forming a continuous phase current, resulting in the motor not working properly. Therefore, the forward angle θ forward adjustment is limited by the θ condition, that is, θ 30 °. For safe operation, the limit value of θ can be appropriately pushed back, leaving room for 2 ° ~ 3 °.
In Fig. 4, the front of the turn-off angle θ is the energizing current generated when the winding is energized, and the waveform after the angle θ is the freewheeling current after the winding is turned off. When the opening angle θ is advanced, the area occupied by the energizing current is widened, and the area occupied by the freewheeling current is also widened. In the adjustment range of the conduction angle (θ), the energizing current and the freewheeling current occupy the same width.
It can be seen that the θ point can be regarded as the midpoint of the winding current waveform. Therefore, the center of the winding current waveform is always in the middle of the rising section of the inductance curve, which enables the motor to generate torque efficiently.
4 basic control circuit motor control basic principle circuit.
AH4 is used as an analog input channel. The potentiometer is used to change the analog input, which is converted to a digital quantity by the on-chip 10-bit A/D converter to indicate the external given speed.
The position detection circuit signals P and Q. HSI are input from the input terminals HSI. 0 and HSI. 1 not only to detect the state change of an input signal, but also to simultaneously record the time at which the state change occurs. Therefore, input mode 3 in the mode register can detect the upper and lower four transition signals of P and Q. The current level state of P and Q can be read in the status register and which signal has a transition. Using this information: a. Measure the average rotational speed of the motor during the past 15° operation b. Determine the reference reference point for controlling the main switch opening angle θ and the closing angle θ of each phase. The P (or Q) signal is angularly subdivided by the detected number of clock pulses recorded during the past 15° corner.
8155 is mainly used for the detection of P and Q level combination logic. Since the control of the motor starts from a standstill state, P, Q jump and combined signals are not detected with the high speed input HSI. The detection of P and Q by 8155 can determine the law of control of the main switch. When the motor rotates, it is detected by HSI.
It is used to control the opening and closing of the 4-phase winding main switch. Because the HSO command register is used to specify the channel that triggers the event at the set time and the output level state corresponding to that channel, the HSO time register is used to store the trigger time of the set event. With these features of high-speed output, it is very convenient to achieve high-speed single-pulse control of SR motors. HSO. 0― HSO. 3 Output combined with phase chopping signal and phase chopping signal for low speed chopping control. A and BD are connected to the A, phase and B, D phase current comparators and the output of the one-shot circuit. In the chopper control, HSO. 4=1. When the current exceeds the chopping value i, the gate 1 or gate 2 output is at the 0 level, so that the main switch that is being turned on is turned off, when the motor enters high speed operation, HSO. 4=0, the gate 1 and gate 2 outputs are all 1 level, and the circuit is switched from chopper control to high speed single pulse control.
The operation of the prototype laboratory shows that the 8089 single-chip microcomputer is used as the control core. The chopper control is adopted when the motor runs at low speed, and the single-pulse control is used during high-speed operation, which can effectively control the speed of the switched reluctance motor.

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