A robust hybrid multilevel rectifier with adjustable output voltage and variable load

In order to obtain synergic benefits by using two different semiconductors such as thyristors and IGBTs, hybrid multilevel converters have been studied recently in the literature. In a grid connected application, unity power factor (PF) control and load voltage control should be achieved. The proposed hybrid multilevel rectifier consists of a main neutral point clamped (NPC) and cell cascaded H-bridges (CHB). Each CHB has a floating capacitor. Therefore, in order to reduce costs, the system regulates the floating capacitor voltages without using independent DC power sources. Additionally, a control strategy concerning the voltage unbalance problem on the main NPC is also considered. Under load resistance changes, the hybrid multilevel rectifier accomplishes unity PF and load voltage control as well as the regulation of CHB capacitor voltages. Experimental results combining all mentioned technologies show verification of the robust hybrid multilevel rectifier in a grid connected application.