FPGA-based voltage measurements in AC drives

In the modern sensorless and self-commissioning drives scenario, the availability of precise phase voltage measurement represents an undoubted advantage. But the task is not trivial, and few viable solutions are available. The present paper proposes an up-to-date digital method for the measurement of the instantaneous phase voltages of a three-phase PWM inverter. The phase-to-phase PWM inverter voltages are oversampled with respect to the switching period by fast A/D converters, which feed the FPGA-based digital integrator. The digital output is ready for further uses in any advanced control and estimation algorithm. Measurement repeatability, reduced size, tuning-free circuit are among the inherent side-advantages of the FPGA-based solution with respect to the existing analog ones. The paper includes design hints and a full batch of experimental tests and validations.