Stability Improvement Method of Grid-Connected Inverter Based on Proportional Weight Control Loop Parameters Adaptive Adjustment under Weak Grid
Gao Jiayuan1, Huang Shuai1, Jiang Fei1, Tu Chunming2, Xiao Fan2
1. School of Electrical and Information Engineering Changsha University of Science and Technology Changsha 410004 China; 2. National Electric Power Conversion and Control Engineering Technology Research Center Hunan University Changsha 410082 China
Abstract：The interaction between grid-connected inverter (GCI) and grid impedance under a weak grid easily induces system instability, threatening the safe and reliable operation of new energy power generation. At present, the method for optimizing and adjusting the parameters of the control loop is widely used to improve the stability of the GCI under a weak grid because of its simple operation and non-auxiliary control loop. The equivalent current source is defaulted to stable when using the impedance model. However, the actual situation is likely to induce instability in the equivalent current source, which leads to the failure of the impedance analysis method and restricts wide applications. Therefore, the multiple-input multiple-output impedance model of GCI controlled in the dq domain is converted into the impedance form of single-input single-output by equivalent transformation. Then, through impedance transfer and remodeling, the controller parameters in the equivalent current source are transformed into the equivalent output impedance model of GCI, and the impedance loop caused by the phase-locked loop (PLL) is converted to the grid side to characterize the negative impact of the PLL. The impedance modeling method realizes the decoupling between the equivalent current source and the control loop parameters. Under the control loop parameter adjustment, the stability of the equivalent current source can be ensured, and the problem for the stability analysis of GCI is solved. A stability improvement method of control-loop parameter adaptive adjustment based on proportional weight is proposed. The proportional weight coefficient is analyzed and designed, which ensures that the GCI has a sufficient stability margin of more than 30°in the weak grid range. Meanwhile, the stability analysis and simulation verification are carried out with a short circuit ratio of 2 and 20% detection error. The results show that the adaptive control method can promote the GCI to maintain good steady-state and dynamic performance despite grid impedance detection error. It is worth mentioning that the stable operation of the GCI can be maintained when SCR is equal to 1, although the stability margin of the GCI system is insufficient. The following important conclusions can be drawn. (1) The proposed impedance model with decoupling control loop parameters can analyze and judge the stability of GCI without checking the stability of equivalent current sources, regardless of whether the control loop parameters are adjusted. (2) A control loop parameter adaptive adjustment GCI stability improvement method is proposed based on proportional weight, and the proportional weight coefficient is analyzed and designed in detail. The proposed adaptive control method under the setting parameters significantly improves GCI’s adaptability to weak grids. Meanwhile, the stable operation of GCI can still be maintained with detection errors of grid impedance.
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2024, Vol. 39 
