PMSM Drive Current and Voltage Limiting as a Constraint Optimal Control Problem

This paper proposes an algorithm for optimal current trajectory control of (interior) permanent magnet synchronous motor (PMSM) drives, considering the motor/inverter current and voltage limitations. In contrast to common voltage feedback flux-weakening strategies, it applies a differential rather than a conventional integral approach to regulate the current vector. Linearized motor equations are used to express torque and voltage amplitude changes relative to the actual operating point as a function of dq-current increments. Optimal dq-current step adjustments are calculated from these approximate voltage/torque increment lines according to machine state feedback. This allows for the constraint optimization problem to be solved in real time. Each iteration, the dq-current setpoint vector is incrementally shifted in an optimal direction, rapidly converging to a solution within the voltage/current limits, which minimizes error on torque request with maximum efficiency. Extensive experimental results on an interior PMSM setup demonstrate the strategy´s dynamic performance and robustness.