In the medium and high voltage high power drive system, in order to reduce the switching losses at a tolerable level, the switching frequency must be reduced to hundreds of Hertz. The synchronous optimal pulsewidth modulation method can meet the requirements of low current harmonic distortion at low switching frequency. Based on the off-line optimal pulse method, a closed-loop flux trajectory tracking control method which shifts the optimal pulse on-line to compensate the error is proposed in this paper. This method combines the selected harmonic elimination PWM (SHEPWM), which is used to reconstruct the reference flux and realizes the stator flux trajectory tracking with the full order observer. The real-time pulse pattern change strategy is adopted to eliminate the system dynamic modulation error and realize the high-performance control at low switching frequency. The simulation results on the neutral point clamped three-level inverter asynchronous motor control system prove the effectiveness of the stator flux trajectory tracking control strategy, which meets the requirements of low current harmonic distortion, low sensitivity of parameter and fast dynamic response at 280 Hz.

synchronous optimal pulsewidth modulation,low switching frequency,stator flux trajectory tracking control,high performance closed-loop control