An Improved Hybrid Modulation Method for the Single-Phase H6 Inverter With Reactive Power Compensation

Transformerless photovoltaic (PV) inverters are more widely adopted due to high efficiency, low cost, and light weight, etc. Many novel topologies and their corresponding modulation methods have been proposed, verified, and put into use, solely focusing on active power injection without leakage current issues. However, some new grid codes require PV inverters to have the ability of injecting reactive power into the utility for grid support. In order to map the challenge, an improved hybrid modulation method is proposed and evaluated for one nonisolated H6 topology as an example. With only simple modification for switching patterns and phase shift for current reference, the variable reactive power generation ability with zero crossing distortion is achieved, while the common mode voltage is also eliminated. The operation modes with the improved hybrid modulation approach are presented in detail and some design considerations are also provided. Extensive results from a 4-kVA prototype along with the SMPLIS simulation verify the proposed hybrid modulation method.