Abstract
The high current ripple and torque ripple are the main drawbacks of the switched reluctance motor (SRM) since the nonlinearity and double saliency, which limits its applications. In order to eliminate the current variation and torque ripple, an optimized pulse width modulation (PWM) control is presented in this paper. The voltage ratio duty is able to be predicted precisely according to the information of the motor running parameter. Based on torque sharing functions (TSFs), the current profile is pre-computed and four regions are defined according to the reference current profiles. The three modes, excitation, demagnetization and freewheeling, are flexibly chosen according to the characteristic of the current profile. It is indicated that it is better than that of conventional PWM modulation in terms of current ripple and the current tracing performance is improved without increasing the switching frequency or changing the hysteresis band. The current ripple is defined as the peak-to-peak value dividing the average value and it is reduced by 40%. A comparison in terms of the torque ripple and copper loss is also carried out: the torque ripple is significantly reduced via the proposed scheme under both magnetic linear and saturation conditions. The torque ripple and copper loss are reduced by about 70% and 12%, respectively. The validity and effectiveness of the proposed control strategy is verified by simulation and experimental results.
Highlights
The results show torque ripple reduction is achieved by optimizing the current profile in this paper
The reference phase torque is assigned by the torque sharing functions (TSFs), the torque reference of the phase is simplified as Tphase = Ttotal · f TSF, where Tphase is the torque reference of the phase, the Tphase stands for TA∗, TB∗, TC∗, Ttotal is the total torque of three phases. f TSF is the distribution coefficient
The proposed and conventional current control methods are compared in terms of their current tracing ability and torque ripples
Summary
Due to the scarcity of rare earth permanent magnets, permanent magnet synchronous motors (PMSMs), in which permanent magnets are widely used, are becoming increasingly more expensive. As is shown via a fixed switching frequency in paper [41], the duty ratio and voltage exerted for the actual current to reach the reference current were predicted using the flux linage based or a back-EMF based controller. To solve the aforementioned problem, a novel precise current control is proposed to reduce torque ripples based on TSFs in this paper. A better current tracking ability is achieved, which makes it possible for IGBT to operate at a low switching frequency, and torque ripples are remarkably reduced. (1) In the previous method, the switch states, including the excitation and freewheeling modes, are fixed and not suitable for the condition in which the rate of current change is large.
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