Research On The Grid-source Coordinated Control Strategy Based On The Phase-modulated Operation Of Photovoltaic Inverters

With the national’s support for the renewable energy,the photovoltaic industry in China has entered a stage of rapid development.In 2017,the annual output of PV in China exceeded 100 billion kilowatt-hours.However,due to the greater randomness and volatility of its output,the large-scale grid connected photovoltaic power generation will have a great impact on the voltage stability of the power grid.At present,the voltage problem has become an important factor that restricts the large-scale grid connection of photovoltaic power generation.In the thesis,the phase modulation operation control technology of photovoltaic inverter is studied.For the scene of photovoltaic power plant and the distributed photovoltaic,the PV inverter and the current voltage regulation equipment are coordinated,and the corresponding control strategy of the network and source is proposed.The main research work is as follows:Firstly,based on the analysis of reactive power regulation mechanism of PV inverter,the control model of phase modulation operation of inverter is built by DIgSILENT software.The effectiveness of the control method is verified under the condition of active power variation and three-phase short-circuit fault,respectively.The simulation results show that reactive power output of PV inverter can provide voltage support to grid,and suppress the PCC voltage fluctuations due to the change of active power and the drop of the PCC voltage,caused by three phase short circuit fault.Secondly,for the scene of photovoltaic power plant voltage control,this thesis proposes a voltage prevention and emergency control strategy that consists of coordinately arranging the SVG,inverters and capacitor banks in large-scale PV power plants,based on the analysis of voltage distribution characteristics of the photovoltaic power plant and reactive power compensation characteristics of the multiple reactive power sources.The simulation results show that when a disturbance occurs,dynamic reactive power compensation devices are coordinated preferentially to support the PCC voltage.After the disturbance is cleared,the reactive power in the dynamic and fast devices are transferred into the static and slow devices,so that the SVG can maintain a large power margin for coping with the next disturbance.Moreover,the reactive power output of the individual inverter in PV power plants is coordinately allocated using an optimization model,so as to optimize the in-station voltage distribution.Finally,for the scene of distributed photovoltaic voltage control,this thesis proposes a multi-devices coordinated control strategy for distribution network voltage,based on the analysis of the influence of distributed photovoltaic grid connection on distribution network voltage and voltage regulation characteristics of distribution network.The strategy uses sensitivity information to divide the voltage control region of PVs in different positions and the voltage control region of OLTC,and then coordinates the PV and OLTC action to adjust the voltage.The simulation results show that the proposed control strategy can achieve a control region corresponding to a voltage regulator,which ensures the safety and stability of the whole distribution network voltage operation.At the same time,the reactive power margin of the photovoltaic inverter is fully utilized,the number of action times of OLTC is reduced and the service life of OLTC is improved.