Multi-level motor drives to eliminate torque ripple with adaptive dead-time compensation

Abstract

This paper discusses multi-level motor drives to suppress torque ripples of brushless DC motors (BLDC) with an adaptive dead-time compensation. Traditionally, BLDCs are widely driven by two-level inverters, and they are driven by the pulse-width modulation (PWM). Although high switching frequencies can reduce current ripples by the switching, voltage errors caused by dead-times become large; there are trade-off relationships. In our previous study, it was revealed that multi-level inverters could reduce distortions of torques at optimal frequencies. In addition, voltage errors caused by dead-times can be compensated by using a feedforward compensation or a disturbance observer (DOB). Since modeling errors are remained even if designers manage to tune parameters, perfect compensations are difficult in feedforward compensations. In disturbance observers, although offset values of voltage errors can be compensated perfectly, it is impossible to compensate 6k-th order components. In this paper, an adaptive dead-time compensation is applied for multi-level inverters. Here, a value of a voltage error is estimated by using an observer, and it is used to calculate an adaptive feedforward value. The validity of proposed system is confirmed by simulation and experiments.