Modified Current Control Schemes for High-Performance Permanent-Magnet AC Drives With Low Sampling to Operating Frequency Ratio

These days, high-frequency permanent-magnet synchronous motors (PMSMs) are used in industry; their maximum synchronous frequency is higher than 1 kHz. 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,
F

_ratio
= (
f

_samp
/
fr
), is small. In this paper, the problems of the current regulation loop caused by small
F

_ratio
in the high-frequency PMSM drive are carefully investigated. Two problems are discussed in this paper: the stability problem and the sampling error. In addition, solutions for the problems are developed; a complex proportional and integral controller with predicted active damping terms is developed to stabilize the current regulation loop, and a model-based error estimator is offered to compensate the sampling error. The developed solutions are verified by simulations and experiments.