Study of Multi-level Rectifier in High Power System Based on a Novel Virtual Flux Observer

In the control of PWM rectifier, it can restrain harmonic and interference effectively by constructing a virtual line-flux-linkage to serve as the oriented vector. However, there are some problems in the conventional method, such as the error of amplitude, the shift of phase angle and the nondeterminacy of initial oriented angle. In the thesis, two one-stage low-pass filters are adopted instead of the pure integrator in the virtual line-flux-linkage observer, which can steady the phase and amplitude. Furthermore, a novel method of voltage estimate at the three-level rectifier terminals is advanced based on the simplified SVPWM algorithm. The good dynamic and static performance under the proposed control strategy is verified by simulation and experiment.