Evaluation of an FPGA current derivative measurement system for the fundamental PWM excitation sensorless method for IPMSM

The Fundamental PWM Excitation (FPE) is a recent sensorless motor control method in the electrical drive system which uses the current derivative measurement to estimate the rotor position. However, parasitic effects arising from the IGBT switches cause high frequency oscillation in current, so the current derivative estimation cannot be made until these high frequency oscillations die down. In this case, the voltage vector needs to be extended to the minimal pulse width in order to have accurate current derivative estimation. The voltage vector extension however leads to current distortion and reduces the performance of machine, which are compensated by inserting opposite voltage vectors. This paper will describe the FPE method briefly and then focus on the evaluation of current derivative based position estimation in the FPE method which uses a high-bandwidth current sensor and a Least Square curve fitting algorithm in an FPGA. Position estimation accuracy is checked experimentally via a mechanical position sensor.