Sensorless-FOC for PMSM With Single DC-Link Shunt

Abstract

The three-phase current sensing with only one dc link shunt resistor can be used for cost sensitive applications. However, special efforts need to reconstruct three-phase current from a dc link current. Moreover, phase current cannot be correctly measured from the single shunt when the active vector duration is less than the minimum measurement time. In order to get dc link current in unmeasurable vector area, a special algorithm for PWM compensation is required. This application report describes how to reconstruct three phase currents with a single current sensor in the inverter dc link. This solution is verified through InstaSPIN™-FOC with MotorControl SDK software platform.

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1 Introduction

A Brushless Permanent Magnet Synchronous Motor (PMSM) has been widely applied to industrial and automotive applications due to lots of advantage over other motors. For control side, Field Oriented Control (FOC) and Pulse Width Modulation (PWM) have become a general control method in variable-speed ac motor drivers applications with PMSM. For most of applications power rating is lower than a couple of kW, three shunt resistors located in low side of power switches are generally used to measure three-phase motor currents for FOC. However, a single-shunt feedback located in dc link return side is also widely used for cost sensitive applications like digital appliance. This application report shows how to reconstruct three-phase currents with a single dc link current by using InstaSPIN-FOC solution with MotorControl SDK.