Stator Flux Trajectory Tracking Control for High-Performance Drives

Medium voltage ac machines driven by high-power inverters operate at reduced switching frequency in order to restrain the switching losses of the power semiconductor switches. When synchronous optimal pulsewidth modulation is employed, the harmonic distortion of the machine currents is minimized under steady-state conditions. High-performance drives may be subjected to sudden changes of velocity and load. Conventional current-based closed loop control schemes cannot ensure dynamic operation without adversely affecting the preoptimized modulation patterns. To obtain high dynamic control in combination with synchronous optimal pulsewidth modulation, the estimated fundamental component of the stator flux linkage vector is used as a feedback signal. Closed loop control is established by employing a deadbeat algorithm. The harmonic component of the stator flux linkage vector is minimized in real-time, using the optimal stator flux trajectory as a reference. Experimental results obtained from a 30-kW prototype drive operated at only 200 Hz switching frequency demonstrate the effectiveness of the approach