Sensorless position estimation by using the high frequency zero-sequence generated by the inverter

A method for sensorless position estimation in PM synchronous motors is proposed. The high frequency zero sequence voltage generated by the PWM is used as carrier source. It is applied to the motor by closing the neutral point to the DC-link through a filter. The anisotropy information, and consequently the position of the rotor, is evaluated from the resulting non-zero sequence current. When compared with the usual methods that inject the carrier in non-zero sequence, the proposed method provides a resulting anisotropy dependent signal four times higher for equal applied voltage. This advantage is useful in motors with weak saliencies as is the case of long-primary linear motors. An analysis of the method and experimental results, using a long-primary linear motor, are presented.