Coordinated control strategy of hybrid topology for low voltage ride-through of photovoltaic inverters

To enhance the low-voltage ride-through performance of photovoltaic grid-connected systems during voltage faults, an optimized scheme based on a hybrid topology of a Boost step-up circuit and a neutral-point-clamped three-level inverter is proposed. Combined with a composite control strategy and dynamic phase-locked loop technology, a high-robustness photovoltaic grid-connected inverter simulation model is constructed to achieve efficient and stable operation during grid faults. This scheme suppresses DC bus voltage fluctuations by dynamically adjusting the duty cycle of the Boost circuit and reduces harmonic content by utilizing the multi-level output of the neutral-point-clamped three-level inverter. A positive and negative sequence separation control strategy is adopted to achieve symmetric output of the grid-connected current, while a dynamic adaptive phase-locked loop is used to track the grid phase in real time, reducing the impact of voltage distortion and frequency fluctuations on synchronization accuracy. Simulation results show that the system can recover within 15 ms, inject reactive current quickly when the voltage drops to 0.2 p.u., and continue operating for more than 0.15 seconds, demonstrating the superiority of the proposed scheme in dynamic response speed, harmonic suppression capability, and fault ride-through stability.