Research On Grid-connected Photovoltaic System Based On Z-Source Inverter

With the fast development of the society and economy, the demand for energy is increasingly urgent for every country. With fossil energy being used up in the future, it can not maintain the social development any more, so it is especially significant to take the place of fossil energy with new energy. Solar energy is caused wide public concern, because of its characteristic of no pollution, obtaining easily, inexhaustible supply. Presently, it have two technologies of solar electrical energy generation, photovoltaic power generation and solar-thermal power generation. Due to the higher energy utilization, photovoltaic power generation is a key research subject for a large mount of experts and professors. This paper replaces the DC/DC conversion circuit and the inverter in the traditional photovoltaic grid-connected system with the Z source inverter. This paper mainly has a research on the Z source inverter and its application on the photovoltaic grid-connected system.Firstly, this paper introduces the operating principle and several kinds of common modulation strategy of the Z source inverter. Based on the analysis of relation between the shoot-through vector and the current ripple of the Z source inductor, this paper proposes an improved modulation strategy. Compared with the traditional modulation strategies, the improved one can reduce the current ripple on the Z source inductors and the capacitor voltage ripple on the Z source capacitors effectively. With the two advantages, the quality of the output waveform of the inverter can be improved.Secondly, this paper introduces some common topologies of Z source inverters and its characteristic. On account of the traditonal topologies, this paper applies the switched coupled inductor cells to the Z source inverters to replace inductors in the Z source network. Thus, the voltage gain ability of Z source inverters can be enhanced obviously. This paper provides a new method for stepping up the voltage gain, this method has a number of application value especially for some occasions that the input voltage is low, but the output must be high, such as photovoltaic, wind power generation and so on.Thirdly, this paper employs state-space average method to model Z source inverters, and introduces two common control strategies in the photovoltaic grid-connected system based on Z source inverters, constant capacitor voltage control strategies and singe stage control strategies based on voltage space-vectors. Taking the constant capacitor voltage controlstrategies for examples, this paper utilizes MATLAB as a tool to built up the simulation platform of photovoltaic gird-connected system.Finally, this paper designs 4kW photovoltaic grid-connected system experimental platform based on Z source inverters. In the process of the design, this paper also introduces how to confirm the parameters of the inductors, capacitors and switches in the main circuit. In addition, this paper designs some relevant hardware circuits, such as voltage current detection circuits, zero crossing detection circuits, drive circuits of insulated gate bipolar translator(IGBT). Besides, software is designed, like main program, AD interrupt program, frequency capture and network voltage synchronization interrupt program, EPWM interrupt program and fault interrupt program. At last, by the photovoltaic gird-connected experiment, the relative waveform is obtained. The result illustrates the experimental platform have the function of stepping up voltage and grid connection.