Permanent Magnet Machine Position Sensorless Drive at Low Speed with Phase Voltage Measurement

This paper improves the position sensorless drive by directly measuring machine three-phase voltages. On the basis, the machine phase voltage is obtained based on the digital integration of phase pulse width modulation (PWM) voltage. The capture modulator in existing drive microcontrollers (MCU's) is used for the PWM voltage measurement. Comparing to existing phase voltage measurement, no separated A/D converter and communication hardware are required because PWM pulses are directly measured using MCUs. However since the capture based on TTL logics receives only digital signals, a preprocess circuit is developed to convert AC PWM line voltages to equivalent digital signals. According to experimental results, a 150MHz sampling rate for phase voltage measurement is achieved based on the proposed capture-based voltage measurement. Although the physical limitation of back electromotive force (EMF) estimation still results, the stability of proposed sensorless drive greatly improves at low speed. The proposed sensorless drive is suited for non-salient permanent magnet (PM) machine where the saliency-tracking position estimation is not possible.