Voltage Ripple in Three-Phase Unidirectional Resonant Converter for CHB PV Inverter Under Nonunity Power Factor Operation

In recent years, renewables, especially photovoltaic (PV) and wind power, have undergone significant development in all fields of application. This development has been closely linked to advances in multilevel converters, being able to achieve high levels of power and efficiency using low-voltage components. Among the multilevel converters, cascaded H-bridge (CHB) converters are gaining interest due to their many advantages as grid-connected PV inverters. Nevertheless, they also have some drawbacks, such as the possibility of unbalanced power injection to the grid or leakage currents. The three-phase module cascading is an interesting modular solution to overcome most of these drawbacks. Under this assumption, this article proposes and analyzes in detail a unidirectional dc/dc stage based on a three-phase resonant converter topology under nonunity power factor operation. The proposed three-phase association operates in an open loop, removing the low-frequency pulsating power in the oscillator due to the grid and significantly reducing conduction losses in transistors under the unity power factor. For nonunity power factors, the filter capacitor sizing and effects, as well as a dynamic model, are also provided. The proposed analysis is assessed and experimentally verified by a 300-W scale prototype. Extensive results and discussion are also included in this article.