A Simple Autonomous Phase-Shifting PWM Approach for Series-Connected Multi-Converter Harmonic Mitigation

In order to reduce the high-frequency switching harmonics of cascaded H-bridge (CHB) converters, phase-shifting pulsewidth modulation (PWM) using a centralized controller has been extensively studied. In this letter, an improved decentralized PWM strategy is proposed as an alternative approach for decentralized modulation. First, the output current of CHB converter is measured by each power cell as an effective synchronization indicator to identify the digital carrier angle of each power cell at the exact time of output current fundamental component zero crossing. Then, a PI controller dynamically adjusts the carrier relative angles of all power cells until they are properly interleaved. Together with the an inverse power factor droop for power sharing control, a CHB converter system can operate at autonomous islanded mode in a fully decentralized manner. Experiments from a single phase islanded CHB converter have been conducted to validate the correctness of the proposed approach.