Passivity-Based Repetitive Control Strategy for LCL-Type Grid-Connected Inverters
Liu Linguo1,2, Luo Jia1,3, Wan Wenjun1,2
1. China Southern Power Grid Technology Co. Ltd Guangzhou 510080 China; 2. Guangdong Engineering Technology Research Center of Energy Storage and Renewable Energy Guangzhou 510080 China; 3. Guangdong Provincial Key Laboratory of New Technology for Smart Grid Guangzhou 510080 China
Abstract：Repetitive controllers (RC) have been widely used in the current control of LCL-type grid- connected inverters due to their ability to achieve zero steady-state error tracking of the fundamental reference signal and harmonic disturbance suppression simultaneously. However, the use of RC can lead to negative real parts in the inverter output admittance near harmonic frequencies, thereby threatening the interconnection stability between the inverter and the grid under weak grid conditions. Although reducing the RC gain can eliminate the negative real part of the admittance, it will reduce the dynamic performance of the system. Therefore, this paper proposes a passivity-based repetitive control strategy that can achieve passive inverter output admittance within the Nyquist frequency range, ensuring system stability under any passive grid impedance conditions. First, an admittance model of the LCL-type grid-connected inverter with grid-side current control is established. Then, the impact of RC on the real part of the admittance is analyzed, revealing that RC introduces negative-real-part admittances around harmonic frequencies. Although reducing the RC gain can eliminate the negative real part of the admittance near specific harmonic frequencies, there is still a negative real part of the admittance near the frequencies of ωs/6 and ωs/2. Moreover, the dynamic response of the RC is degraded. Then, a third-order zero-phase-shift low-pass filter is developed. It exhibits stronger high-frequency attenuation capability than the conventional first-order zero-phase-shift low-pass filter. By setting the zero-magnitude frequencies of the filter at ωs/6 and ωs/2, the negative real part of admittance caused by RC at all harmonic frequencies can be eliminated without reducing the RC gain. Finally, to achieve a passive admittance within the Nyquist frequency range, the inherent negative-real-part admittance of grid-side current-controlled inverters is eliminated using a capacitor voltage feedforward method based on the low-pass filter. The simulation results show that when the grid inductance Lg=0 μH, the inverter can operate stably and the grid current harmonics are effectively suppressed when using RC with either a first-order or third-order zero-phase-shift low-pass filter Q(z). In the case of Lg=200 μH and using the conventional first-order Q(z), the system remains stable when the RC gain krc=1 but becomes unstable when krc=4. From the admittance Bode diagram, it can be observed that increasing krc introduces negative real parts in the inverter output admittance. At this point, the grid admittance intersects with the inverter output admittance in the negative-real-part region. As a result, a phase margin is less than 0, destabilizing the system. In contrast, when using the developed third-order Q(z), the inverter still operates stably even when krc=4. Thus, the developed third-order Q(z) can eliminate the negative real part of the admittance caused by RC without reducing krc, thereby enhancing the system's robustness against grid impedance variations. The simulation results under grid voltage step changes show that during voltage surges or sags, the grid current exhibits no oscillations and returns to the steady state within two fundamental periods. An experimental platform of the LCL-type grid-connected inverter is built. The experimental results align with the simulation results, demonstrating that the proposed RC strategy can effectively suppress grid current harmonics and improve the robustness of the inverter system against grid impedance variations.
刘林国, 罗嘉, 万文军. LCL型并网逆变器基于无源性的重复控制策略[J]. 电工技术学报, 2026, 41(10): 3370-3380.
Liu Linguo, Luo Jia, Wan Wenjun. Passivity-Based Repetitive Control Strategy for LCL-Type Grid-Connected Inverters. Transactions of China Electrotechnical Society, 2026, 41(10): 3370-3380.
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2026, Vol. 41 
