Speed Ripple Suppression of Reduced DC-link Capacitance IPMSM Drives for Air-Conditioning Applications

The speed ripple is an important concern in the air conditioning compressor drive system, and it is more obvious in reduced DC-link capacitance motor drive for the large DC-link voltage fluctuation. In this paper, a compensation method is proposed to reduce the speed fluctuation caused by the load torque fluctuation and the DC-link voltage fluctuation, which is realized by the sliding mode observer and PI-type iterative learning controller. The sliding mode observer for the load torque is designed to obtain the load torque. The iterative learning controller is applied to calculate the expected current for the q-axis current tracking compensation. Both fluctuations are periodic, which could be reflected in the q-axis current. Hence the iterative learning controller can effectively compensate the two types of the speed ripple. Compared to the traditional iterative controller, the proposed controller is improved by projecting time domain to angle domain, which is fit for different speed with same parameters. Experimental results are provided to verify the effectiveness of the proposed method.