Study on Sensorless Control Strategy of Multi-Level PWM Rectifier Based on a Novel Virtual Flux Observer

This paper presents a control strategy of multi-level PWM rectifier based on a novel virtual flux observer, which can control without grid voltage sensors as well as restrain harmonic and interference effectively. The conventional method has problems such as the error of amplitude, the shift of phase angle, so 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 experiment.