PQ-droop dual-mode adaptive control strategy for photovoltaic inverter based on composite filtering and timing switching
Abstract
In the distributed photovoltaic grid-connected scenario with high penetration rate, the traditional photovoltaic inverter has a single active and reactive power control, droop control, conventional hybrid control, etc, which has large impulse current, excessive voltage harmonic distortion, obvious dynamic overshoot, poor adaptability to operating conditions, and difficulty in balancing the grid-connected steady-state control accuracy and off-grid control accuracy. In order to solve the above technical pain points, this paper proposes a PQ droop dual-mode adaptive smoothing control strategy based on compound filtering and timing switching. Secondly, the LC-LCL composite filter architecture is constructed to meet the needs of power quality optimization under both grid-connected and off-grid conditions, and the rationality of steady-state stability and switching mechanism of the control system is strictly proved by small signal modeling and Lyapunov stability theory. Finally, relying on IEEE519-2014 harmonic standard and national photovoltaic grid specification, a 500 kW simulation model and physical experiment platform are built to complete the comparison verification of multiple algorithms. The test results show that the overshoot of operating mode switching of this strategy is only 2.3%, the total harmonic distortion rate of voltage is as low as 1.25%, which is far lower than the limit of IEEE519 standard 8.0%, and the recovery time of operating mode switching is ⩽25 ms. The grid-connected steady-state power control accuracy is ±0.9%. The overall performance is obviously better than traditional control and mainstream advanced algorithms. This strategy effectively solves the stable switching of photovoltaic inverters under various operating conditions. It integrates rigorous theory, low engineering cost and mass scalability, and can provide new technical solutions and theoretical support for the safe and efficient operation of distributed photovoltaic systems.