Practical Implementation of Current Derivative Measurement for Sensorless Control of Permanent Magnet Machines

Sensorless technique to estimate position at low speed requires the extraction of the inherent saliencies. The extraction can be done using external signal injection or using the inherent PWM excitation. In the latter method the saliencies are extracted from the sampled current signal. Estimating the current slope from the sampled current is one of the main challenge in position estimation due to high signal to noise ratio and inverter nonlinearities. In this paper a practical architecture is proposed based on oversampling technique, to calculate the current slope without burdening the software throughput of the processor. The proposed architecture provides a robust current slope measurement. Different realization of the current slope measurement is introduced and experimental results are provided showing the improvements in the current slope measurement.