Three-Phase Photovoltaic Grid Inverter System Low Voltage Ride Through Technology Research

With the rapid development of the global economy and continuous increase in the number of population, energy shortage and environmental pollution have become the problem faced by countries all over the world, the development and utilization of new green energy is imperative, as a quality alternative green energy, photovoltaic power generation will occupy dominant in the new energy field. But with the continuous increase of photovoltaic permeability and photovoltaic power generation, security and stability of power grid has also ushered in new challenges.Based on the analysis of current development of photovoltaic grid inverter and the present situation of photovoltaic grid Low Voltage Ride Through technology in the domestic and foreign, this paper use the photovoltaic grid inverter as the research object, combining that when photovoltaic grid in power grid failure must have a certain low voltage crossing ability, firstly, it analyse when the grid voltage drop temporarily that could make the photovoltaic inverter system to take off the grid, even cause all crew solution column resulting in failure of network voltage drop. So, this paper focuses on when the three phase symmetrical grid voltage sag fault, and then propose the limit of active current component amplitude and change the reactive current reference value according to voltage sag depth. It is sent to the system reactive power to support the grid voltage recovery, so as to realize the Low Voltage Ride Through. To detect the accurate grid voltage phase and amplitude and ensure the symmetrical three-phase output current of inverter when the grid voltage fault conditions, this topic compares their work characteristics through the simple introduction of single synchronous reference frame phase-locked loop based on dq transform Single Synchronous Reference Frame Phase Locked Loop and a single synchronous reference frame phase-locked loop based on symmetrical component method Extended Phase Locked Loop Single Synchronous Reference Frame Phase Locked Loop principle of work, and finally presents an algorithm which has the advantages of simple structure and can quickly remove negative grid voltage, extract positive sequence component of the grid voltage Double Second-Order Generalized Integral Single Synchronous Reference Frame Phase Locked Loop design based on synchronous coordinating phase-locked loop of dual two order of single generalized integrator to realize the Low Voltage Ride Through when the power grid voltage unbalanced falls.The proposed control strategy is verified by simulation in the topic for the symmetric and asymmetric grid voltage fault, the simulation results show that when the grid voltage drops, the proposed strategy could effectively inhibit the increase of grid connected current and harmonic generation, and the system can be fast recovered after the fault. Finally, grid connected operation in the3kW photovoltaic grid connected inverter platform aims at lock performance test of Double Second-Order Generalized Integral Single Synchronous Reference Frame Phase Locked Loop for the unbalanced situation. Through the experimental results, the subject of the proposed control strategy can achieve the technical requirements of the photovoltaic grid connected to Low Voltage Ride Through.