Research On Single-Phase Inverters Parallel Techniques Under Island Condition

As the representatives of the new energy generations,photovoltaic and wind power generations have been connected to the grid increasingly in the past few years.The penetration of new energy generations is gradually increasing,which will bring great impact to the power network and affect the security and quality of power supply because of their inherent intermittency and uncertainty.The microgrid technology,which integrates distributed generation,loads and energy storage as a local power system,is an important method to solve this problem.Single phase inverter is an important form for distributed generations access in a micro-grid system.With the increase of micro-grid scale and distributed generations capacity,the parallel connection of different capacity inverters under island condition is greatly significance.In the micro-grid system,a large amount of nonlinear loads will be connected.The diode rectifier circuit is usually used as the front stage to supply power for the power electronic equipment,which is the main form of nonlinear load.This paper researched the single-phase inverter parallel techniques under island condition and compared current mainstream parallel methods.Droop control without interconnections was chosen as fundamental of the further study.The traditional P-Q droop was based on instantaneous power detection and required constant power value.In the single-phase inverter system,virtual synchronous rotating coordinate system based on SOGI was established to solve the power fluctuation problem.In the rotating coordinate system,control quantity in AC systems can be described as a DC quantity.Rectifier load will bring a large number of low time harmonic currents to the circuit.Harmonic suppression methods were compared and the PI and repetitive compound control was chosen as focus of this paper.PI and repetitive compound control in virtual rotating coordinate system was studied.The parallel harmonic current sharing technology of single-phase inverter based on PI and repetitive compound control was proposed.Virtual impedance technology was used to improve the precision of current sharing,which reduced the effect of output impedance and line impedance.The proportional power distribution of inverters with different capacities was realized by setting the droop curves.The system operation point adjusting was achieved by setting the droop curves.The validity and correctness were verified by real-time simulation experiment platform.