【目的】LCL型逆变器现有电容电压全反馈方案存在对高次谐波抑制能力不足等问题。为解决高频段全反馈策略实际谐波抑制效果与系统稳定性之间的矛盾,本文提出一种自适应电容电压全反馈方法。【方法】首先,分析了数字延时环节对全反馈策略实际谐波抑制效果的影响,提出利用一阶惯性环节来模拟数字延时环节的相频特性,补偿全反馈函数因忽略控制延时而造成的相位偏差。其次,提出虚拟阻抗矫正方法,在二阶反馈环节中引入阻抗系数,矫正等效虚拟电阻,以保证并网系统的稳定性,并推导了引起系统失稳的阻抗系数下限值。接着,分析了阻抗系数取值对电容电压全反馈策略实际谐波抑制效果的影响,引入阻抗系数自适应调整方法,详细阐述了各模块功能,给出了具体的参数取值方法,使阻抗系数能够根据系统谐波含量动态调整。最后,搭建了一台10 kVA并网逆变器样机以验证本文所提自适应电容电压全反馈策略的有效性。【结果】试验结果表明,本文所提自适应电容电压全反馈方法能根据并网电流谐波含量自适应调整阻抗系数的大小,保证系统稳定性的同时,对高次谐波有较强的抑制效果。【结论】所提方法有效地解决了系统稳定裕度与高次谐波抑制效果间的矛盾,显著提升了电容电压全反馈策略对并网电流高次谐波的抑制能力,在当下电网阻抗变化范围大、谐波分布随机性强的弱电网环境中有较强的适用性。

Abstract: [Objective] The existing capacitor voltage full-feedback scheme for LCL-type inverters presents issues such as inadequate suppression capability for high-order harmonics. To address the contradiction between the actual harmonic suppression effect of the strategy in high frequency band and the stability of the system, an adaptive capacitor voltage full feedback method is proposed in this paper. [Methods] Firstly, the impact of digital time delay on the actual harmonic suppression performance of the capacitor voltage full-feedback scheme was analyzed, and a first-order inertia link was utilized to simulate the phase-frequency characteristics of the digital delay, compensating for phase deviations caused by neglecting digital delay in the full-feedback function. Secondly, virtual impedance correction method was proposed. By introducing an impedance coefficient into the second-order feedback loop, the equivalent virtual resistance was adjusted to ensure the stability of the grid-connected system and the lower limit of impedance coefficients that triggers system instability was theoretically derived. Subsequently, the influence of the impedance coefficient value on the actual harmonic suppression effect of the capacitor voltage full feedback strategy was analyzed. An adaptive impedance coefficient adjustment method was proposed, which was designed to dynamically regulate the impedance coefficient in response to real-time system harmonic content. The function of each module was elaborated in detail, with the specific parameter determination method for critical components provided. Finally, a 10 kVA grid-connected inverter prototype was developed to experimentally validate the efficacy of the proposed adaptive capacitor voltage full feedback scheme. [Results] Experimental results demonstrated that adaptive capacitor voltage full feedback schemes can adjust the impedance coefficient according to the harmonic content of the grid-connected current. This adaptive regulation ensures system stability while maintaining strong suppression efficacy against higher-order harmonics. [Conclusion] The proposed method effectively solves the contradiction between system stability margin and high harmonic suppression effect, significantly enhance the suppression capability of the capacitor voltage full-feedback strategy to high-order harmonics of the grid-connected current, which demonstrates strong applicability in the present weak grid environment with wide range of grid impedance variation and high randomness of harmonic distribution.