As the world continues to shift towards clean and renewable energy sources, wind energy has emerged as a promising alternative to traditional fossil fuels

To reduce the influence of voltage harmonics on the grid current, a control strategy based on adaptive quasi-proportional phase compensated resonance (QPR_PC) is proposed. Firstly, the LCL grid-connected photovoltaic inverter system model is established, and the stability performance of the three-level inverter system under double closed-loop control is analyzed using the output impedance model of the inverter. Then, a QPR regulator for the zero steady-state error tracking of AC signals is studied. To solve the problem that the system has poor robustness against frequency changes when the traditional QPR regulator is used in the static coordinate system, this paper improves the traditional QPR regulator to optimize the response characteristics of the closed-loop system. Based on the QPR regulator, a phase margin compensation structure is introduced to form QPR_PC control. Then adaptive frequency design is added to ensure good control even when the power grid frequency drifts, which is the control strategy proposed in this paper. Verification shows that the proposed method improves the phase margin of output impedance at a specific frequency, restrains the interference of the 3rd, 5th, and 7th harmonics of grid voltage, and improves the dynamic performance of the system and the quality of grid-connected current. Finally, the simulation results show that the total harmonic distortion rate of grid-connected current is reduced by 1.03% after adopting this strategy, which verifies the effectiveness and correctness of the proposed method.

A thirteen-level inverter based on switching capacitor is proposed in order to improve the boost capacity and output power quality of inverter in renewable energy power generation system. The proposed topology is composed of one DC input power supply, three capacitors and 14 switching devices, and achieves thirteen-level output with six times voltage boost. It has smaller volume, lower cost and output harmonic content. Moreover, it can realize inverter without H bridge and reduce the voltage stress of switching tube. In addition, the proposed inverter can achieve self-balancing capacitor voltage without any auxiliary method, simplifying the complexity of control. The superiority of the proposed topology is verified by comparing with other traditional multilevel inverters. The simulation and experimental verification on the simulation and prototype platform show that the inverter has good performance in both steady and dynamic conditions.