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

Solar energy generation is one of the most important renewable energy technologies. Inverter plays a key role in the whole system. Usually, in order to obtain a high output voltage, a boost circuit would be added to the front-end of the inverter to compose a two-level inverter. That structure reduces the efficiency and strictly prohibit the shoot-through state of the inverter bridge. Based on Z-source inverter and its specific application in grid-connected photovoltaic system, in-depth study on grid-connected control method and anti-islanding protection etc. this paper analyzes deeply the grid-connected control.First of all, this paper summarizes the development of PV grid-connected power generation technology at home and abroad; Then analyzes and compare the Z-source inverter with traditional inverter. It can be conclude that the unique z-net composed of capacitance and inductance not only can adapt to various input sources, but also brings a wider range of the input voltage of the inverter for Z-net’s buck-boost characteristic. Moreover, the system reliability is greatly improved because z-source inverter allows the shoot-through state and the efficiency is improved by Z-net instead of boost circuit which is used to get a high inverter output. Then, according to the conditions of Z-source inverter parallel with the grid to determine the control objectives, establish the grid-connected inverter model to design the controller. Due to the coupling of d-axis and q-axis in the model, three phases alternating currents are transformed into dc variables used as feed forward values in synchronous reference coordinate to realize the current vector control in inner loop. No static error was achieved by pi controller. Then the reference vector is oriented by grid voltage, namely component on q-axis is zero. SVPWM wave with shoot-through zero vectors is applied to control Z-source boost and grid-connected inverter while the grid is stable and balanced. The active power and reactive power decoupling control is achieved by using the strategy of vector control oriented by grid voltage and close-loop control of d-axis and q-axis current as control strategy of the grid-connected inverter. Further, the grid-connected current was synchronous with the grid voltage. In the end, simulation in the MATLAB environment validates controlling shoot-through vector’s duty ratio of z-net can boost z-net’s output and achieve the set value; The active power and reactive power decoupling control is achieved by using vector control oriented by grid voltage with shoot-through vector and the grid-connected system can run of unit power factor.lOkW experimental prototype is designed and after analyzing experiment waveforms and data, the results indicate that the control scheme of three-phase grid-connected photovoltaic system based on Z-source inverter to control reached the goal expected. Further, the system take active frequency drift methods for anti-islanding to ensure safety and the detection time of simulation is less than the specified maximum time.