Comparison of High Speed Permanent Magnet Machine Sensorless Drive using Trapezoidal BLDC and Sinusoidal FOC under Insufficient PWM Frequency

Voltage source inverter with pulse width modulation (PWM) usually has the switching frequency limitation at high frequency. It leads to the degradation of high speed machine drive as the rotor frequency f
_e
increases. This paper is to improve the permanent magnet (PM) machine high speed drive under insufficient PMW switching frequency, f
_pwm
, over the rotor frequency f
_e
. In this paper, both trapezoidal brushless DC (BLDC) and sinusoidal field oriented control (FOC) are implemented to compare their performances specifically for high speed PM machine position sensorless drive. Considering the high speed BLDC, conventional EMF zerocrossing point detection causes the commutation error when f
_pwm
/f
_e
≤18. To improve the sensorless drive at high speed, an instantaneous EMF estimation with cross-coupling decoupling is proposed. Considering the sinusoidal FOC at high speed, a discrete-time EMF estimation is used to calculate the rotor position for the vector control with insufficient f
_pwm
/f
_e
. Both drive performance are experimentally evaluated on an interior PM machine among the dynamic response, current harmonics and torque output. It is shown that the FOC drive achieves the lower current harmonics and better dynamic response under load. However, BLDC drive results in the better average torque output and drive efficiency. High speed PM machine drive can be improved by selecting suitable control strategy under different operating conditions.