Discrete Implementation Aspects for Online Current - and Voltage-Sensor Offset Calibration Based on Inverter Voltage Distortion

Electrical drive systems without dedicated speed transducer require precise information about the terminal phase voltage to achieve acceptable low-speed performance. Recently, voltage-sensing techniques have gained in importance as they improve stability at low-speeds compared to the conventional estimation from the reference values. But, the additional sensors increase the sensitivity to sensor-offset drift, which can cause self-sensing control algorithms to fail at very low speeds. A novel online offset calibration method was introduced, which compensates for this drawback and offers full decoupling from the control algorithm. Using a pair of phase current and voltage sensors, the dead-time-related inverter voltage-distortion curve is measured continuously. Its point-symmetrical nature is utilized for sensor-offset detection. This way, both sensor offsets can be calibrated continuously during operation and for each phase individually. This paper addresses implementation aspects to achieve deterministic calibration dynamics. A step by step description of the calibration algorithm is given. The method is evaluated through measurements performed on a test bench for an electric-vehicle traction drive.