Zero and low speed sensorless control for CSC-fed IPM drive system

In this paper, a sensorless control method for low and zero speed operation is proposed for a high-power medium-voltage pulse-width-modulated Current-Source-Converter (CSC)-fed Interior Permanent Magnet Motor (IPM) drive system. The proposed method is based on injection of a high-frequency (HF) pulsating sinusoidal signal in the estimated synchronous reference frame of the drive´s Field Oriented Control (FOC) scheme. The conventional FOC control scheme, low switching frequency, dc-link inductor and the inverter output three-phase filter capacitor of the medium-voltage high-power current-source drive present some challenges in the generation of the high-frequency injection signal. To overcome these challenges, the FOC scheme is modified by introducing a modulation index control with suitable dc-link current compensation to enhance the dynamic response of the injected signal and prevent any clamp in the injected signal. In addition, a Multisampling Space Vector Modulation (MS-SVM) method is proposed to prevent the distortion in the high-frequency signal due to a low switching frequency to injected signal ratio. It is found that by using the proposed FOC scheme and multisampling modulation scheme, and proper design of the high-frequency signal, an accurate rotor flux angle can be estimated for sensorless zero/low speed operation. Experimental results are provided to verify the proposed control method.