Bidirectional Transformerless PV Inverter Based On High-frequency-leg Techniques

In photovoltaic (PV) power generation systems, PV inverter is the connectionbetween PV array and the user. The inverter is the core of the power system. Itsproperty directly influences the whole performance and efficiency of the PV powergeneration systems. In order to guarantee the safety and the quality of the outputpower, all inverters need to adopt isolation transformer to restrain the output currentharmonics in traditional photovoltaic inverter topology structure. However, the largesize, heavy weight and the low energy efficiency of the traditional transformers havehad a great effect on the performance of the entire photovoltaic system.A novel bidirectional transformerless PV inverter based on the High FrequencyLeg (HFL) technique is proposed with Discontinuous Current Mode/ContinuousCurrent Mode (DCM/CCM) operations having greatly enhanced reliability. With thehigh-frequency-leg, the smooth ac current is achieved as the higher equivalentswitching frequency can reduce the inductor current ripple decreasing the passivecomponents’ volume. There’s no dead time issue which can push the duty cycle to thetheoretical limit and fully transfer the energy to grid through total Pulse WidthModulation (PWM). And the capacity of the PV (Photovoltaic) inverter can beexpanded easily by increasing the number of high-frequency legs. Additionally theproposed topology can work under the rectifier mode having the bidirectional powercapability, which is attractive for PV (Photovoltaic) application. In the end theexperimental results of8kW laboratory prototype has verified the feasibility andeffectiveness of the proposed transformerless PV (Photovoltaic) inverter understandalone mode.