Research Of Three-Phase Photovolatic Grid-Connected Inverter Based On Fuzzy Control Technology

The one-time energy that human used is mainly fossil energy in the 20th century energy structure, but with the gradual consumption of fossil energy, the status of energy crisis and environment pollution has been showed in front of human. Now it is the most important thing to develop and utilize new energy. Through the research we know solar energy is one of the cleanest and the most promising regeneration energy resource. PV(photovoltaic) power generation has become the main trendency of utilizing the solar energy, and the PV grid-connected inverter, which is the key part of PV power system, has become the reseach fcous. In this paper, 10kw three-phase PV grid-connected inverter has been designed by making DSP(digital signal processor) as main control chip.Firstly, we analyzed the characteristics of PV cells and established its corresponding functional model. Meanwhile we researched the tracking method of maximum power of PV arrays'output, and in theory analyzed how to achieve MPPT(maximum power point tracking) by changing the conduction duty of the switch in DC-DC circuit. The result of simulation reflects the superiority of use fuzzy control method to achieve MPPT.Secondly,we studied the topolgy structure of PV grid-connected inverters of differrent power sizes, and also designed the 10kw three-phase PV grid-connected inverter's hardware topology. The topology structure has two stages with isolation transformer. Through the topology structure we designed the main circuit of inverter, including Boost circuit, main circuit and its protection circuit, filter circuit and sampling circuit and so on. Meanwhile we design the device parameters in the main circuit.Finally, this paper put the hysteresis current control method to apply to PV grid-connected inverter technology. The result of application indicates that hysteresis current control technology can make the control system more accurate,stable and dynamic. The hysteresis current control include constant and variable width control loop. For many defects in constant width control loop, for example, wide rang of frequency change of switch , poor spectrum of the inverter output signal, noise and so on, we use fuzzy control technology to design a real-time loop change hysteresis to make the change rang of switching frequency less, and to make the PV inverter grid-connected. The results of simulation experiment indicate that the output current of inverter is synchronize with system voltage, and the current has higher accuracy and less harmonic compared with constant hysteresis, which reflects the effectiveness of variable hysteresis loop width control method of real-time based on fuzzy technology.