Abstract：Nowadays, more and more power-electronics-interfaced distributed generations （DGs） and new loads are connected to the distribution network, which endows the electricity grids superior flexibility and controllability. However, with the penetration of DGs and intensive utilization of nonlinear loads, the resulting grid distortion will seriously threaten the grid current quality of DGs and deteriorates the voltage of critical loads in the distribution network. Recently, few researches geared toward the quantitative analysis of the fundamental limitation in the dual harmonics suppression, nor the adaptability improvement of DGs in the presents of both the local nonlinear loads and distorted grid. To address these issues, this paper proposes a hybrid harmonic suppression scheme, which leads to substantially lower total harmonic distortion for both the local load voltage and the grid current at the same time. First, the constraint involved in the simultaneous elimination of distortion for both the inverter local voltage and the grid current is quantitatively analyzed. The conventional method to restrain local voltage harmonic uh s was to abate the inverter output harmonic impedance Zh o via a negative feedforward. However, the suppression of grid current harmonic ih g might be compromised since ih g is also nonlinear with Zh o from the numerical expression. Therefore, the restriction of the two distortions entirely and simultaneously appears infeasible for the intrinsic contradiction by using one control variable Zh o. Then, a hybrid harmonic suppression based on multiple harmonic sequence component observer （MHSCO） is proposed, which mainly consists of a local voltage harmonic control loop and a grid current-controlled voltage compensator. MHSCO is introduced rather than conventional DFT for the accurate and exhaustive extraction of individual harmonics simultaneously, so that individual harmonic components in grid current and local voltage are extracted respectively and with superior time-varying response characteristics. A local voltage harmonic control loop is designed to scale down Zh o, while a grid current-controlled compensator is elaborated to reduce the harmonic admittance 1/Zh g via an additional voltage. The system small-signal model is deduced and the adaptability of proposed strategy to the perturbation of grid impedance Lg is studied. The eigenvalue locus indicates Lg should be maintained neither too large nor too small to ensure system stability. Hardware in the loop simulation is performed subsequently. The local voltage harmonic control loop and grid current-controlled compensator of the proposed strategy are activated successively in the first simulation scenario. When the local voltage harmonic control loop is first operated, uh s decrease from 8.9% and to 2.29%, while ih g increase from 15.35% to 26.13% because of constraint of the two harmonics. When the grid current-controlled compensator is added at the same time, uh s and ih g are suppressed to 2.42% and 2.24% respectively. In the subsequent simulation scenario, Lg is decreased from 2.3 mH to 1.8 mH to investigated the robust against the variation of grid impedance. The THDs of us and ig are maintained low at 2.69% and 2.83% in this scenario, respectively. In the case of load fluctuations, the effectiveness of proposed strategy and conventional strategy is compared and evaluated. When the proportion of linear load at PCC increases, the THD of us drops by 20.7% with the proposed method, which is greater than that of the conventional method 13.3%, while the THD of ig increases by 42.4% with the proposed method, lower than the that of the conventional method 85.8% . When nonlinear load doubles, the THD of us and ig of the conventional method rise by 36.7% and 17.8%, which are significantly higher than those of the proposed method 5.2% and 6.6%. The following conclusions can be drawn from the simulation analysis: (1) The concurrent suppression of voltage harmonics and grid current harmonics can be achieved with the proposed strategy, thus ensuring the power quality of the inverter and the local critical loads. (2) The THD of local voltage and grid current maintained low with a small grid impedance. In this sense, the proposed control strategy is robust to the perturbation of grid impedance to a certain extent. (3) Compared with conventional control methods, proposed method exhibits lower volatility of THD under load variation, which indicate superior adaptability against load fluctuation.
杨权, 梁永昌, 魏建荣, 刘艺林, 袁志聪. 多谐波源下分布式电源并网逆变器的谐波抑制策略[J]. 电工技术学报, 2023, 38(11): 2908-2920.
Yang Quan, Liang Yongchang, Wei Jianrong, Liu Yilin, Yuan Zhicong. Research on Harmonic Suppression Strategy of Grid Connected Inverter under Multi-Harmonic Sources. Transactions of China Electrotechnical Society, 2023, 38(11): 2908-2920.
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2023, Vol. 38 
