A Novel Voltage Balancing Control in Multilevel Inverters for Pure Active Power Applications

Multilevel inverters are increasingly finding new applications in renewable energy. However, they have some technical challenges that diversely affect their performance. One of the most important concerns in these inverters is the DC-link capacitor voltage balancing. This paper presents an open-loop Carrier-based Pulse Width Modulation (CBPWM) voltage balance control algorithm. The proposed algorithm presents an excellent inherent voltage balancing even during load changes. For evaluating the proposed control strategy, a 7-level single-phase Modified Diode Clamped Inverter is developed and the method is successfully implemented. The results illustrate that the proposed method can successfully keep the capacitor voltage balanced during load changes. Analytical expressions together with experimental results completely describe the approach. The main novelty of the technique is the introduction of a voltage balancing algorithm for multilevel inverters that eliminates the need for a feedback loop and numerous and costly sensors. This method is suitable for applications which only deal with active power such as solar inverters which inject pure active power into the grid.