Design of Digital Current Regulator for PMSM with Low Carrier Ratio

High-frequency permanent-magnet synchronous motors are used in industry; the maximum synchronous frequency is higher than 1 kHz in High-frequency area such as turbocharger and Hybrid Electric Vehicle. However, the sampling and switching frequencies of the digital inverter that consists of the digital controller and pulsewidth-modulation voltage source inverters are limited due to the cost and efficiency reasons. As a result, the current regulation loop has some problems when the high-frequency PMSM runs around its maximum speed and the ratio of the sampling frequency over the synchronous frequency is small. In this paper, the three aspects of current loop decoupling, one-step time delay and parameter sensitivity are analyzed to propose a control strategy under low carrier ratio, which aims at solving the problems. On the basis of the theoretical analysis, a simple improved method is presented, where the one-step time delay is taken into consideration in output of regulator, aiming to enhance current dynamic performance. Besides, a digital current regulator with active damping terms is developed to stabilize the current regulation loop. The developed solutions are verified by simulations and experiments.