Research On The Second Harmonic Suppression Technology For Photovoltaic Grid-connected Low Voltage Ride Through

With the increase of the penetration rate of photovoltaic power generation,the method of directly removing photovoltaic grid-connected equipment in the event of a failure has become no longer applicable.Therefore,improving the response capacity of photovoltaic grid-connected systems to grid faults has become an urgent need for the development of photovoltaic power generation technology.Under this background,low voltage ride-through technology has attracted widespread attention from researchers at home and abroad(Low Voltage Ride-Through).However,most of the voltage drop faults in power systems are unbalanced voltage drop faults.When the unbalanced voltage drop fault occurs,the output power of the grid-connected photovoltaic inverter will appear second harmonic.In this paper,the following aspects of the second harmonic problem of output power during unbalanced low-voltage ride-through of photovoltaic grid-connected grid-connected inverters are studied.(1)Aiming at the problem of low-voltage ride-through second harmonic suppression,this paper proposes a low-voltage ride-through control strategy that can adjust the harmonic suppression target according to different voltage drop levels.This strategy can automatically switch the second harmonic suppression target according to different voltage drop levels to ensure the suppression effect of the second harmonic under different voltage drop levels.The control strategy was simulated by MATLAB to verify the harmonic suppression effect of the low voltage ride-through strategy under different voltage drop levels.(2)Aiming at the problem of the introduction of higher harmonics caused by the sudden change of negative sequence components when the harmonic suppression target is switched,this paper proposes a photovoltaic low-voltage crossing second harmonic suppression strategy that can flexibly switch the harmonic suppression target.Attenuate the unsuppressed second harmonic to achieve the purpose of flexible switching,and adjust the second harmonic attenuation speed through the RBF neural network controller.Finally,the flexible switching effect is verified by MATLAB simulation.(3)In order to improve the flexibility of reactive power injection during unbalanced low-voltage ride-through and prevent reactive power compensation at the end of voltage recovery,this paper proposes a low-voltage ride-through control strategy for photovoltaic grid-connected inverters that considers the optimal configuration of reactive power.By setting up a reactive power balance model optimized using a parallel genetic algorithm,the reactive power output command value of the grid-connected inverter when the voltage is restored is solved to achieve accurate compensation of reactive power.Finally,the effect of reactive power compensation is verified by MATLAB simulation.