An Improved Control Strategy of Triple Line-Voltage Cascaded Voltage Source Converter Based on Proportional–Resonant Controller

In this paper, the operation principle of a multiple converter, which is composed of the traditional two-level six-switch voltage source converter and constructed in line-voltage cascaded mode, is analyzed. The equivalent switching circuit model of the multiple converter is built based on its operation characteristic. By analyzing the feature of the multiple converter control, an improved voltage-current double-loop control strategy based on the proportional-resonant (PR) controller is proposed. The control strategy, which has the merit of the integrated control, can also realize the independent control of the transmission power of each unit of the multiple converter by adding the voltage-sharing compensation control. Meanwhile, a PR controller is adopted in the current loop. By giving a suitable current reference value for the controller, the problem of ac-side line-current asymmetry can be solved, and the effect of unbalanced grid voltages on the system can be avoided as well. The availability of the proposed control strategy is verified by the experimental results.