A simple, novel method for variable-hysteresis-band current control of a three phase inverter with constant switching frequency

A novel method for implementing a variable hysteresis band current controller is described which achieves constant switching frequency without requiring a precise knowledge of the motor parameters. The controller works by using feedback and feedback variables to create a variable hysteresis band envelope, and then compensating for the interaction between phase back-EMFs that occurs when the neutral of a three-phase motor is left floating. The controller has good dynamic and steady-state response, and its performance is substantially immune to variations in the inverter DC supply voltage and motor parameters. It can be readily implemented in hardware, and only requires a few additional components compared to a conventional hysteresis current controller. Analytical, hardware implementation, simulation, FFT (fast Fourier transform) analysis, and experimental results are presented