Research On Photovoltaic Interface Converter In DC Distributed Power System

Solar energy, as one of the most rich and widely distributed cleaning resources, has been paid more attention to the development of new resources. And the photovoltaic power has been one of the most popular ways to use solar energy. Also as the most important part of photovoltaic power generation system, the PV inverter when connected to the grid as single generation will be hard to control and have higher costs. So some scholars proposed a conception of distributed power supply system (micro-grid, or nanogrid), which means make these single generations form a micro-grid when connect to the grid.In recent years, with the studies of distributed power supply system have advanced, the DC distributed power supply system has draw more attention to research institute all over the world. The DC distributed system can bring many advantages: less energy connection, higher efficiency and easier to control. On the other hand, it can also be helpful to the development of using new resources.This paper, based on the DC distributed power supply system, has mainly researched on the PV interface converter. The topology has been chosed as two-switch Buck-boost converter, which has a wide range of input voltage and high efficiency. With advantages of buck/boost, same input and output polarityand isolated, it is widely used in many applications. However, in the CCM the reverse-recovery-related losses of its own diodes become a bottleneck to improve the efficiency. Based on some literature, this paper proposed a new circuit structure which shifts the inductor current to another path (using coupling inductor) to solve this problem. The relevant theoretical formula, method of parameter design and loss analysis has given.In order to coordinate the DC micro-grid and the converter work well, the PV interface needs a special output Characteristics, which, according to the DC bus voltage, requires the converter can operate in different mode that is the MPPT mode and output voltage regulation mode. This paper proposes a control strategy to achieve the above modes, and gives the small-signal model of converter to design the control loop.According to the proposed requirements, finally, this paper gives a design prototype of 3kW, including its main power circuit and control circuit. The simulation and experiment result shows the Correctness of the PV interface in topology and its control theory.