An improved modulation strategy for quasi-Z-source rectifier with minimum switching frequency and high efficiency

Quasi-Z-Source rectifier can achieve the traditional PWM rectifier's function, as well as implement buck and boost conversion of the input voltage. Due to the unique impedance source network, the shoot through (ST) state increases the reliability of rectifier impressively. As to three-phase Quasi-Z-source rectifier, many modulation strategies are proposed to achieve low output voltage and high efficiency. This paper proposes an improved modulation strategy that can minimize the voltage stress of switches and reduce the equivalent switching frequency of rectifier stage to about 1/3f (f is the frequency corresponding to the switching time period Ts). Minimum voltage conversion ratio is also obtained. During each sextant, only one phase leg operates at a high switching frequency to achieve ST interval control and output voltage regulation, while other two phase legs maintain the fixed switching states. Finally, the proposed modulation strategy is verified by simulation and experiment.