Saliency-Based Position Sensorless Drive for Permanent Magnet Machine with Low Cost Shunt Resistor Current Sensing using Modified PWM Voltage Injection

Saliency-based position sensorless drive with the pulse width modulation (PWM) switching frequency injection can achieve the high position estimation bandwidth. However, in order to obtain the rotor position, multiple currents should be sampled every PWM cycle to calculate the saliency reflected current difference. Considering the low-cost inverter using shunt resistors for phase current sensing, it is not possible to obtain this saliency current difference because machine current can only be measured once the low-side switch is ON. To implement the PWM injection sensorless drive on shunt-based sensing inverters, this paper proposes two modified PWM voltage controls for the measurement of saliency reflected current difference. The first modified PWM is based on the asymmetric PWM for both the field-oriented control (FOC) and position estimation. This proposed PWM requires only a single interrupt service routine (ISR); however, the current total harmonic distortion (THD) is higher. By contrast, the second modified PWM consists of both discontinuous PWM (DPWM) for FOC and asymmetric PWM for the position estimation. Although two ISR's are required for this proposed PWM pattern, the current THD is reduced through the separated PWM control. All the proposed PWM patterns are experimentally verified on an interior PM machine where the inverter with shunt resistors is used for current sensing.