Study On Low Voltage Ride Through Control Strategy Of Photovoltaic Grid-connected System

Because the traditional fossil energy is consumed,it will cause serious pollution to the environment,and the energy reserves have dropped sharply.The problem of energy shortage has already constrained the development of the global economy.Therefore,countries have begun to develop and utilize new energy sources.As a kind of new energy,solar energy plays a more important role in solving the energy crisis.With the increase of installed capacity,it is required that solar energy must have Low Voltage Ride Through(LVRT)capability.This paper first studied the maximum power point tracking(MPPT)control of photovoltaic power generation system.The energy storage device was added on the DC side.The bidirectional circuit was connected with the DC bus voltage to stabilize the bus voltage during the system operation.In order to filter out the inversion process,In the generated harmonics,an LCL filter was designed,and the resonance of the LCL filter was effectively suppressed by the series resistance of the capacitor branch.In order to shorten the detection time when the grid voltage is asymmetrically faulty,the detection accuracy is improved and the synchronization is improved.Based on the rotating coordinate system,a rapid detection module was added to detect the drop amplitude accurately,and the detection time was controlled within 5ms.According to the second-order generalized integrator,the principle of positive and negative sequence separation of the grid voltage can be realized,and the second-order generalized integral was proposed.Phase-locked loops can accurately phase-lock under asymmetrical faults and detect the magnitude of network voltage droop;inverters adopt PQ control strategy when the energy storage device is put in,and when the energy storage device exits operation due to reaching the energy storage limit,it turns to Double closed-loop control improves the low-voltage ride-through capability of photovoltaic grid-connected systems.The simulation model of photovoltaic system was built in Matlab/simulink.The simulation of the low-voltage ride-through capability when the single-phase voltage dropped to 60% and 50% of rated voltage was verified.The results show that the proposed control strategy improves the photovoltaic grid-connected system.LVRT capabilities.