| Because of a series of reasons like people’s demand for electrical power isincreasingly growing, the energy crisis is becoming sharper, the environment isgradually damaged and ultrahigh pressure distance power grid’s performance atrespect of safety, reliability as well as flexibility etc, people is promoted to doresearch on new energy power technology and microgrid control technology.Amongvarious kinds of renewable energy sources, Photovoltaic(PV) Power Generation andWind Power Generation become hot spots in the research for its advantages of richresources, safety and pollutionless characteristics. The distributed generation researchfocus lies in how to control the DC power generated by photovoltaic array and themechanical energy produced by wind turbine to translate into AC power with the samevoltage amplitude,frequency and phase as grid as much as possible.Microgrid is asystem consisting of distributed power, energy storage unit and load,which can workin grid-connected mode or in island mode.Microgrid is the supplementary form oflarge power system, which is an inevitable trend of electric power systemdevelopment.The physical properties and its simulation model of the pv array has beenanalyzed in the paper. Besides, voltage and current double loop PI control methodbased on power feedforward control has been put forward according to photovoltaicgrid-connected inverter. The transfer function of the control method has beenanalyzed and the related bode plot and root locus plot has been obtained. Simulationmodel of single-phase photovoltaic grid-connected inverter has been set up, whichanalysed the impact of power feedforward link on system stability and sensitivity ofdynamic response.According to wind power generation, bidirectional converter control strategy ofVSCF (variable speed constant frequency) DFIG (doubly-fed induction wind powergeneration) system has been studied on the basis of wind turbine and DFIG. Highpower wind power generation simulation model has been constructed. The paperemphatically introduces relationship between rotor speed and rotor current frequencyon the condition of variational wind speed and reference rotor speed.Aiming at the three common control strategies: PQ control method, V/f controlmethod, droop control methods (including P-f droop control and Q-V droop control). The mechanism of various control method has been discussed and control blockdiagram of voltage and current double loop that adopted in V/f control has beenresearched. The paper odeduced transfer function of current inner loop and voltageouter loop respectively. the impact of current disturbance quantity on current innerloop has been analyzed based on the obtained bode plot.Moreover, control blockdiagram of V/f control method in rotary two-phase coordinates has been deduced. DGcontrol model adopted with3control strategies has been set up and temporaryevent,like load fluctuation and source output power variation has been set. Thesimulation results verifies the effective, rapidity and accurate of the theoreticalanalysis.Finally, on the basis of source control theory and simulation, simulate researchhas been done under3different microgrid operating conditions: grid-connectedoperation mode, island operation mode,grid-connected operation mode switching toisland operation mode. Directing at large harmonic current and reactive powershortage, the paper analysed improvement of harmonic treatment and reactive powerbalance by inputing APF and capacitor. |
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