Research On A Highly Efficient Micro PV Grid-connected Inverter With Low Input Voltage

With the rapid development of global economy, energy crisis and environment problem are increasingly prominent. Therefore, the development of new energy is imminent. Solar energy which is clean, abundant and with no pollution recently draw more and more attention. Gradually, micro photovoltaic inverter is popular because of its advantages of high reliability, high efficiency and easy extensibility. Against this background, a high efficient micro PV grid-connected inverter with low input voltage is proposed in this paper aiming at solving the problem that single PV panel output voltage is relatively low. Two-stage structure is adopted in this topology:proceeding stage is a non-isolated high step-up DC/DC converter with soft-switching technology while backward stage is a full bridge inverter where single inductor filter, SPLL, repetitive control and voltage-loop control are adopted to achieve a high quality of grid-connected current. Low input voltage, high efficiency and low switch voltage stress are salient features of this topology.Specifically, the main contents of this paper are as follows:(1).The background and significance of this study is briefly introduced and several typical topologies are investigated in detail. Based on existing research results, a high efficient micro PV grid-connected inverter topology is proposed.(2).Several typical DC/DC boost converter topology with high gain are analyzed and compared in order to design the proceeding stage of micro inverter. Then, the proceeding stage is an improved high step-up DC-DC converter based on active clamp coupled inductor with voltage multiplier cells. The working principle of this circuit are presented in detail, including gain curve, soft-switching conditions and switch voltage stress. Finally, simulation results verify the correctness of the topology.(3).The control of grid-integration current is mainly depend on the control of inverter in backward stage. In terms of hardware, the type selection and parameter determination of filter is investigate; In terms of software, phase locked loop is guaranteed by detecting positive zero crossing point of grid voltage, and the voltage stability is ensured by this voltage loop. What’s more, current loop with repetitive control is utilized to realize the grid-integration current with low THD. Both the voltage loop and the current loop with repeated control are modeled and analyzed in this paper and the detailed design process of compensation loop is simultaneously given out.(4).Base on the analysis aforementioned, a 300W prototype whose nominal input voltage is 48V is developed. The related voltage and current waveform of output and soft switching are given out. The result shows that the prototype realize grid-connection successfully and its maximum efficiency can be 94%. Therefore, the practicability and effectiveness of this topology is confirmed.