The double salient pole motor is a new type of AC speed regulating motor emerged in the 1990s. It is another new research direction in the field of speed regulation and transmission of AC motor in recent years following the switched reluctance motor. Its unique structure and excellent electrical Performance has been more and more attention and research [1 ~ 5]. Doubly salient pole motor is similar in structure to stepping motor and switched reluctance motor with closed-loop control, only on the stator (or rotor) There are permanent magnets (or electric excitation coils), similar in speed control performance to DC motor speed control systems [3, 4]. The main advantages of double salient pole motors are their simple structure, flexible control, fast dynamic response and good speed control performance. Large torque/current ratio, power factor close to 1, high efficiency.
However, due to the double salient pole structure of this kind of motor and the switching form of the power supply, its inevitable torque ripple characteristics are caused.
The torque generated on the rotor of the double salient pole motor is formed by a series of pulsed torque superposition. Due to the influence of the double salient pole structure, the resultant torque is not a constant torque, and the torque ripple is large. The torque pulsation of the double salient pole motor mainly comes from two situations. One is the steady-state torque ripple, which is caused by the high-frequency PWM work of the switch tube. The impact on the motor performance is relatively small. The other is the current commutation. Torque ripple, this torque ripple has a greater impact on motor performance. Because the torque ripple is an important factor influencing the speed governing performance of a double salient pole motor, the torque ripple characteristics of the electric excitation double salient pole motor are simulated and analyzed, and how to control the two-shot control and improve the control parameters and excitation current waveform are studied. The method reduces the torque ripple and lays the foundation for the optimal design of a double salient pole motor system.
1Torque simulation analysis It is assumed that the inductance of the double salient pole motor is an ideal situation of piecewise linearization. The inductance of the motor does not change with the armature current, and it is considered that in the case of electric excitation, the excitation magnetic flux is infinite, so that the phase and phase are between The mutual inductance is approximately zero. The output torque of the double salient pole motor is taken as phase A. The output torque of the motor phase is as follows: T is the reluctance torque. When the A phase winding passes through the current, the armature changes with the position of the rotor. The torque component T generated by the change in the winding inductance is the excitation torque, which is the torque generated by the mutual inductance between the armature winding and the field winding depending on the rotor position when the A-phase winding passes through the current. When the phase-to-phase mutual inductance is not considered, the output torque of each phase can be calculated separately, and then they are superimposed linearly to obtain the total output torque.
1. 1 Output torque pulsation analysis in current control Under the condition that the current is not controlled, the current waveform is asymmetric, and the positive amplitude is smaller than the negative amplitude, as shown in Figure 1 (a). This is because when the forward current reaches the peak value, the inductance L reaches the maximum value, and the inductance hinders the current change greatly, so that the current changes slowly, the waveform is bald, and when the reverse current peaks, the inductance L reaches a minimum value, and the inductance hinders the current The effect of the change is small, so that the current changes rapidly, the waveform is more pointed, so that the forward and reverse current is asymmetric. After the current control is added, the current is controlled near a certain value, making the current waveform more symmetrical, as shown in Figure 1(b). In addition, due to the influence of inductance, in both cases, when the forward current is commutated to the negative current, the current changes slowly, and when the negative current commutes to the forward current, the current changes rapidly.
The symmetry makes the torque waveform asymmetrical in the positive and negative two and a half cycles, and the commutation torque ripple is relatively large. If the current control is performed, the positive and negative half-cycle currents are relatively symmetrical. Although torque ripple still exists, compared to when the control is not controlled ( a) Inductance, phase voltage, current and excitation current waveform under current control (b) Inductance, phase voltage, current and excitation current waveform under current control (c) Torque waveform under current control (d) Current In the case of control, each torque waveform is turbulent, and so on: the simulation of the torque ripple of the double salient pole motor becomes smaller. According to formula (2), since the torque of the doubly salient motor is the reluctance torque added to the excitation torque, the excitation torque is always positive, and the reluctance torque is positive and negative, and only when the excitation torque When the reluctance torque is much larger than the reluctance torque, the output torque will not generate a large pulsation due to the reluctance torque. When the current is not controlled, the reluctance torque and the excitation torque are almost the same, and the reluctance torque may even be larger than the excitation torque at a certain moment, which makes the output torque ripple larger. In the case of current control, the pulsation of the phase current itself is small, and in this case, it is possible to make the reluctance torque smaller than the excitation torque and make the motor torque ripple smaller.
1. 2 Influence of Control Parameters on Torque Ripple during Single-shot Operation Double salient pole motors generally have two working modes: single-shot operation mode and double-shot operation mode. The single-shot operation mode has only one phase winding turned on at any one time, and the double-shot operation mode has two-phase windings conducting at the same time. Obviously, the output torque of the two-shot operation mode is greater than the single-shot operation mode, and the torque/current ratio of the double-shot operation mode is greater than the single-shot operation mode.
The moment pulsation is significantly reduced, but the torque ripple caused by the current commutation will still have a large impact on the performance of the motor. It is therefore necessary to study the reduction of commutating torque ripple by changing the motor control parameters.
One of the methods to reduce the commutation torque ripple is to make the excitation torque much larger than the reluctance torque, so that the excitation torque plays a major role in the motor output torque. Try to reduce torque ripple by changing two control parameters, armature current and field voltage.
1. 2. 1 Changing the armature current Decreasing the phase current can significantly reduce the commutation torque ripple. The torque pulsation rate is defined here as the difference between the positive semi-weekly average torque and the negative semi-weekly average torque over the average torque within one week. Figure 2 shows that when the armature average current amplitude I is 7 A, the torque ripple is 43. 5 and when I is 5 A, the torque ripple drops to 11. 8. This is because of the reduced phase current I squared. Decreasing according to the square relationship, so that the reduction is much greater than the reduction of T, so that T is far less than T ae, so using this method can effectively reduce the commutation torque ripple.
1. 2. 2 Change the excitation voltage It can be seen from Fig. 3 that increasing the excitation voltage U f can significantly reduce the torque ripple. At U 14 V, the torque ripple is 31. 6 and the U torque ripple drops to 24. 0. According to formula (2), the exciting torque T is proportional to I and the reluctance torque T does not change with I, so when the excitation voltage U increases, I f is increased accordingly, so that the output exciting torque T Correspondingly, the armature current remains unchanged and remains unchanged. Therefore, the ratio of T to the motor output torque increases. Therefore, the purpose of reducing the commutation torque ripple is achieved.
1. 3 Double-tapping operation method Torque analysis There is a large commutation torque ripple in the single-shot operation mode. In addition, since the inductance value is about 1/3 period constant in the inductance characteristics, it is determined that this working mode has about The output torque of 1/3 cycle is zero. To further improve the torque characteristics of the double salient pole motor, two-shot operation can be used.
Compared with Figures 3 to 5, the Journal of Nanjing University of Aeronautics and Astronautics shows that the output torque of double-tapping mode is about twice larger than that of single-shot mode, and there is no range where the output torque is zero. This is due to the double-tapping mode of operation at any moment. When there are two identical jobs, the output torque is a two-phase torque superposition. In addition, due to the symmetry of the two-phase operation, when the output torque of the two phases is superimposed, the currents of the two phases are reversed, and the reluctance torque generated is also reversed. When the two phases are superimposed, the effect of the reluctance torque can be cancelled. Reduced commutation torque ripple.
1. 4 Torque Ripple Analysis of Changing the Exciting Current Waveform Although the double-tapping operation method effectively reduces the commutation torque ripple caused by the current commutation, the working principle of the double salient pole motor determines that the current must exist due to the commutation. The zero-crossing point makes the torque of each phase inevitably have a zero-crossing point. The inductance characteristic determines that there may be two identical commutation moments in the output torque, the torque crosses zero at the same time, and the torque in the other phase is non-zero. The inductance is at a maximum, obstructing the change of the phase current, so that the rate of change of the current commutation is not large enough to form a commutation gap, such as during t in FIG. 5 . To eliminate this gap, consider increasing the excitation phase of the third phase during t, etc.: The simulation of the torque ripple of the double salient motor investigates the current (see Figure 7) to increase its output torque to compensate for the phase change. Induced gaps reduce commutation torque ripple. From FIGS. 6 and 8 , it can be seen that changing the waveform of the excitation current increases the output torque of the other phase during the other two-phase commutation, so that the commutation notch of the output torque of the motor is reduced.
It can be seen that changing the excitation current waveform can effectively reduce the commutation torque ripple.
Excitation Current Waveform Output Torque Waveform 2 Conclusion Torque ripple is an important index that affects the steady state performance of a double salient pole motor. Therefore, it is of great significance to reduce the torque ripple caused by the current commutation and current commutation in a double salient pole motor. . In this paper, the torque pulsation characteristics of the double salient pole motor are improved by changing the control parameters of the double salient pole motor, adopting two-shot working mode and changing the excitation current waveform, and the following conclusions are drawn: (1) To reduce the double salient pole motor The commutation torque ripple is such that the excitation torque plays a major role in the output torque. The methods that can be used in single-shot operation are: reduce the phase current of the motor and increase the excitation voltage, but the former is at the expense of reducing the output torque, while the latter can increase the output torque, so it is best to This combination of methods reduces both commutating torque ripple and the required output torque.
(2) In the double-shooting mode, the output torque is increased, and the torque/current ratio is large. In addition, since the two phases work in the same way, the opposite reluctance torque is generated when the two-phase currents are in opposite directions, and they are offset in the output torque. Therefore, the commutation torque ripple is effectively reduced compared to single-shot operation.
(3) Changing the waveform of the excitation current of the double salient pole motor can increase the torque of the other phase when a certain two-phase current is commutated, and can make up for the gap caused by the commutation when superposed. Therefore, changing the waveform of the excitation current can improve the commutation gap and effectively reduce the commutation torque ripple of the motor.
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