LAUSR

A low switching frequency of power converter is mandatory in high-power motor drives to suppress the switching loss and thermal stress. In this case, the asynchronous modulation may incorporate abundant harmonics. The well-known approach to solve the problem is to adopt the synchronous modulation. Among existing techniques, synchronous space vector modulation (SSVM) owns the simpler implementation. However, it is a big challenge to establish a closed-loop scheme based on SSVM. Therefore, this manuscript proposes the flux trajectory tracking based implementation of SSVM for induction motors. A state observer is first built up in a hybrid reference frame to acquire the stator flux with a long sampling period. Then, the stator flux is enforced to move on a predefined trajectory with an adjustable rotation speed. As a result, synchronizations and symmetries of voltage pulses, smooth transitions between different pulse patterns and fast dynamic response can be achieved without complex compensations and extraction of fundamental signals. Both simulations and experiments verify the effectiveness of proposed method. Particularly, the current harmonics are effectively suppressed compared with traditional method with asynchronous modulation.