Research On Inverter Control Strategy With Characteristics Of Synchronous Generator

With the increasing of penetration of distribute generation(DG), inverters, key devices of power transmission between the DG and the grid, play a more and more important role in the performance of the DG system. Power quality is related to the inverter greatly. The increase of the penetration also reduces the rotating inertial of the system and threats the stability of the grid. Research of the inverter control strategy is vital.An inverter control strategy that mimics characteristics of synchronous machines is proposed in this paper. Inverter with proposed control strategy is equal to a controllable voltage source with controllable equivalent impedance. The amplitude and the frequency of the voltage source and the equivalent impedance can be set precisely by certain control parameters. The rotation equation of synchronous generator is embedded into the frequency regulation part and system frequency can be maintained when load changes. Axial voltage controllers are designed and the 1st axial voltage controller controls the voltage amplitude and 2nd controls frequency.The synchronous generator characteristics such as the coordinated control between frequency and active power, between amplitude and reactive power in the inverter control system are analyzed. The inverter can work like a synchronous generator in different working status. Several further control strategies are proposed for different working status. When working in grid connected mode, the 2 axial voltage controllers control the active and reactive power respectively and the inverter can produce precise active and reactive power. When working in island mode, the 1st axial voltage controls the voltage amplitude and the 2nd controls the frequency. Compensation control loops are added so that voltage amplitude and frequency of the out circuit are maintained standard. When working in parallel, inverter power can be shared by control parameter designs. The inverter can output active and reactive power in reaction to the grid status change and helps to restrain the change of the grid status.Both simulation and experiments based on proposed inverter control strategy are carried out. The results verified the theoretical analysis. The control strategy is effective.