Application Of Impedancesource Converter Theory In Key DC-DC Device For DC PV Power Station

As the demand for energy keeps growing,solar energy,which is clean,eco-friendly and widely distributed,has become the focus of much research on renewable energy.The main method to massively develop and utilize solar energy is by building photovoltaic(PV)systems.Power generated by PV plants should get through a power collection system before being connected to the grid,so voltage raising and power collecting technologies has become the key technologies in PV generation.In this paper,a novel structure of DC power collection grid for PV station with consideration of impedance network concepts has been proposed to cope with technical challenges in large-scale DC PV station.An impedance-source multi-module series-connected DC-DC step-up converter serves as key device for the proposed collection grid,which has an integrated function of multi-MPPT control and high-gain DC voltage stepup conversion.The low-voltage DC bus and distributed MPPT devices can be omitted to make the system simple and reliable.The system structure is beneficial to realize internal fault isolation and unitary dynamic control at station level.The introduction of impedance network makes it possible to adjust the voltage gain flexibly as well as resisting shoot-through of bridge arms,which can improve the operational adaptability against input power mismatch and reliability of the DC power collection grid for PV station.Firstly,the DC-DC step up converter for PV station is introduced.Detailed theoretical analysis of the converter has been given in this paper,including circuit topology,operating principle,control strategy,small signal model and dynamic characteristics.On this basis,a structure of DC power collection grid for PV station based on this converter is proposed.The general structure and components of the system are presented,and the operational reliability of the system when power mismatch occurs is analyzed in quantity.Based on the theoretical analysis,simulations on the power collection grid under balanced an mismatched power inputs are established to verify the system operational reliability.In addition,station-level control and protection strategy is studied with consideration of scheduling instructions and fault isolation conditions.Simulations for corresponding steady-state and transient control strategy are established.From the simulation results,it can be concluded that the novel DC power collection grid for PV station proposed in this paper can meet the operational requirements in different conditions,and the control strategy is effective.The simulation results validate the theoretical results in this paper,and show that the proposed system has potential application value in the future construction of largescale DC PV stations.