| Virtual synchronous generator(VSG)technology for integration of distributed energy resources attracts increasing attentions for its ability in enabling inverters to simulate the inertia and damping characteristics of synchronous generators and thus improving the stability of the system.At present,the researches of VSG mainly focus on the control of the inverter,and DC side is usually replaced by an ideal voltage source without consideration of the output characteristics of primary energy,and the maximum utilization of renewable energy sources may not be always guaranteed.In this paper,the power management for islanding microgrids consisting of photovoltaic generators combined with battery energy storages(BES)in DC side(PV/BES-VSG)is focused,and the main contributions of this paper are as follows:1.In terms of the basic principle of VSG method,a small signal model for the single grid-connected VSG is derived,through which the influence of main control parameters,such as virtual inertia,damping coefficient,active power-frequency droop coefficient and equivalent output impedance on the system dynamic performance is analyzed,which provides a theoretical basis for optimizing the control parameters.The small signal model for paralleled VSGs is also derived,through which the principle of parameters matching is obtained.Simulation results in Matlab/simulink show that,if the parameters satisfy the matching principle,the oscillation of the output power can be suppressed effectively during the load changes.2.Based on the operation characteristics of microsources in DC side,the power coordination control method between PV and BES is presented for a single PV/BES-VSG.By the proposed control method,the controllers of PV,BES can automatically shift the operation mode to maximize the output power of PV only according to the DC voltage level,while keeping battery SOC within a reasonable range,which are verified by simulation results with the model under Matlab/simulink.3.Islanded microgrid,which has multiple PV/battery-VSG units,requires power coordination control to maintain the power balance from three aspects:power management between different PV/battery-VSG units;power management between PV,BES and inverter in each PV/battery-VSG unit;power management between PV and BES in each PV/battery hybrid unit.To maximize the use of PV and ensure reasonable distribution of the load,a decentralized VSG-based adaptive coordinated control strategy is proposed.By the control strategy,the system can realize the power coordination control without central controller and communications among the PV/battery-VSG units.The simulation results show that the proposed decentralized coordinated control strategy can provide voltage and frequency support for the microgrid,and BES supply power only when PV output powers reach the limit.At the same time,the reasonable fairness of power distribution between inverters is ensured. |
PDF Full Text Request