| In recent years,the demand of traditional energy is growing because of the rapid development of the global population and the increasing of economy,however the energy shortage and environment pollution caused by the energy loss are increasingly serious.In this case,The emergence of distributed power supply not only reduces the environmental pollution,but also slows down the loss of non renewable energy sources.But then,when the distributed power is connected,it may have a huge impact on the power grid because of the sudden short-circuit fault in distributed generation or grid.In this paper,based on the establish of the distributed power grid simulation model,the influence and government of harmonics in the grid connection point and transient power quality disturbances are studied and simulated,the main work is as follows.According to the composition and characteristics of the photovoltaic power generation system,The mathematical model of the PV array and grid connected inverter are established.The MPPT control strategy based on boost converter and a double loop control strategy based on the voltage and current control are proposed.The model of PV power generation system is built on the platform of MATLAB.The simulation results are as follows,the proposed control strategy is feasible,the grid side’s voltage and current curves are all standard sine wave with same frequency,and the output power of the photovoltaic array can also quickly trace to the maximum power and steadily run with maximum power.The structure and characteristics of grid connected wind power generationsystem are analyzed.The mathematical model of wind turbine,permanent magnet synchronous generator and converter are established.The control strategy that the machine side adopts zero d axis current control,the grid side adopts the voltage oriented vector control is proposed.The modulation wave signal is generated by the voltage space vector pulse width modulation. The simulation model of wind power generation is built on the platform of MATLAB.The simulation analysis of all kinds of fault is carried out.The simulation results are as follows,the voltage and current of the grid are the standard sine wave,the DC side’s voltage is constant under normal wind speed.Wind turbine is almost not affected by the network side’s fault,but the grid side and DC side are greatly affected under grid voltage sag fault simulation.In simulation analysis of short circuit grounding fault,single-phase short circuit grounding fault has little effect on the system,three-phase short-circuit grounding fault has great influence on the system.The problems of steady state and transient power quality caused by the grid connected distributed generation are studied.With the establishment of grid connected PV and wind power generation system simulation model as a fundamental.Firstly,thep qi ?i detection method is proposed to detect harmonics,the active power filter is used to reduce the harmonic wave,and the simulation model is established and the simulation of the harmonic control is carried out on the platform of MATLAB.The simulation results show that after the active power filter is adopted,the waveform change from original distorted wave into a sine wave,the harmonic distortion rate of the PV power generation system is reduced from 43.38% to 17.67%,and the harmonic distortion rate of the wind power generation system is reduced from 30.32% to 11.80%.Secondly,the two kinds of system simulation of transient power quality analysis is carried out.The simulation results show that the single-phase grounding fault can cause the voltage sag and the pulse transient,and the three-phase short circuit fault can cause the voltage sag,voltage interruption and transient oscillation.The faultdistance to network is closer,the degree of voltage sag is greater.Compared with the PV power generation system,the wind power system is more sensitive to the distance of fault point,but the sensitivity of the pulse transient and transient oscillation is not high. |
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