Research On Operation Control Method Of Photovoltaic Generation As Virtual Synchronous Generator

Influenced by the large-scale integration of renewable energy,the permeability of distributed power generaotr,including photovoltaic generator,has increased dramatically in recent years.The stable operation of power system has been rigorously challenged.Virtual synchronous generator(VSG)control is kind of power grid friendly technology,which can make inverter of distributed generator perform the same operating characteristics as synchronous generator,and improving the capacity of the grid for renewable energy acceptance.In this paper,the operation control method is explored for photovoltaic generator working as a virtual synchronous generator,based on the technology of photovoltaic power generation and virtual synchronous generator.Firstly,the topology structure of virtual synchronous generator system is set up,constituted by photovoltaic generator and energy storage device.Mathematical model of photovoltaic array and super capacitor is established for further explortion.And operating characteristic of synchronous generator is introduced into the control of inverter,while the control principle of virtual synchronous generator is analyzed.Secondly,three VSG realization schemes are summarized.By using small signal model,the dynamic and static performances of three methods are compared in island mode and grid-connected model.Problems and solutions of the three methods are analyzed.And the start-up characteristics are studied as a priority.Original control schemes are improved by synthesizing the advantages of different control strategies.Thirdly,based on the improved method,a coordinated control strategy is designed for grid-connected VSG system with photovoltaic and energy storage.Energy flow between DC/AC sides is coordinated through energy management.Unbalanced power,appearing in the transient process,is compensated by the charging and discharging of super capacitor.As consequence,impact on gird,caused by the sudden change of photovoltaic output is reduced,and the stationary of DC bus voltage is achieved.In addition,in order to avoid equipment damage,the state of charge of energy storage device is transferred to VSG control in the strategy,for adjusting the active power output of the system.Finally,an energy management control strategy is designed for the photovoltaic-energy storage system working in independent microgrid.The concept of adaptive droop characteristic is introduced.By changing the slope and shifting curve of droop characteristic,photovoltaic-energy storage system can independently switch operation mode.And the output of active power and frequency,as well as the input of photovoltaic power,would be adjusted according to the operating conditions.Thus,an autonomous wireless control of photovoltaic-storage system and the active support for microgrid are realized,while influences on system stability,caused by mode switching,are avoided at the same time.