Correction on current measurement errors for accurate flux estimation of AC drives at low stator frequency

This paper presents an online-correction method for current measurement errors for a pure-integration-based flux estimation down to a stator frequency of 1 Hz. A measurement-disturbance-observer (MDO)-based approach is taken as one possible solution for eliminating the dc offset and the additional negative-sequence component due to unbalanced current measurement gains in the synchronous coordinate. From the motor parameter sensitivity analysis, an MDO gain selection method is proposed to remove the estimation error resulting from a parameter mismatch. At the same time, the positive-sequence component estimation is performed by creating an error signal between a motor model reference and an estimated q-axis rotor flux established by a permanent magnet in the synchronous coordinate. The compensator utilizes a PI controller that controls the error signal to zero. Experimental results confirm that the proposed scheme has great potential for applications to acquire the accurate motor flux at a low stator frequency. Index Terms--DC offset, measurement disturbance observer (MDO), negative-sequence component due to unbalanced current measurement gains, online-correction method of current measurement errors, positive-sequence component estimation, pure-integration-based flux estimation.