Abstract：With the large consumption of traditional fossil energy and its adverse impact on the environment, distributed power generation technology has been widely concerned and applied. The stability problem brought by PQ power control to grid-connected inverter (GCI) system under a weak grid has been widely studied. Firstly, the small signal mathematical model of grid connected inverter under PQ power control is derived, and the small signal control block diagram of grid connected inverter considering the influence of grid impedance is constructed. In the small signal control block diagram, there are two positive feedback loops and two negative feedback loops at the same time. At the same time, from the composition of positive feedback and negative feedback loops, it can be seen that the parameters of the reactive power loop controller not only exist in the self control loop, but also exist in the active power loop in the form of positive and negative feedback loops, which means that the parameters of the reactive power loop controller will affect the stability of the active power loop and the reactive power loop at the same time. However, the parameters of the active power loop controller only appear in the active power loop, which only affects the stability of its own loop. Therefore, when considering the influence of grid impedance, the small signal control block diagram of PQ power control grid connected inverter shows an asymmetric control phenomenon, revealing the mathematical essence of PQ power control as an asymmetric control. Secondly, in order to verify the influence of active/reactive loop parameters on the stability of grid connected inverter, the impedance model of PQ power controlled grid connected inverter under weak current grid is built. It can be seen from the simulation and experimental results that, within the same parameter variation range, the influence of the parameter variation of the reactive power loop controller on the stability of the grid connected system is obviously stronger than the parameter variation of the active power loop controller, which further verifies the asymmetry of the small signal control block diagram of the active/reactive power loop under the weak current network. On this basis, with the help of the positive and negative feedback loop effect formed in the small signal control block diagram, the law of the stability of grid connected inverter changing with the parameters of the reactive power loop controller is analyzed. When the parameters of the reactive power loop controller are adjusted, the asymmetric positive and negative feedback loop effects will cancel each other, leading to a change process of system stability from instability to stability and then to instability. This is not a gradual weakening of the stability of the grid connected system as the parameters of the reactive power loop controller increase. The following conclusions can be drawn from the simulation analysis: ① It is revealed that PQ power control in weak current network is the essence of asymmetric control, that is, the reactive power loop controller will form an asymmetric positive and negative feedback loop in the active and reactive power control loops. ② The change of reactive power loop controller parameters has a stronger influence on the stability of GCI than the change of active power loop controller parameters, that is, the stability of GCI is more sensitive to the change of reactive power loop parameters. ③ When the parameters of the reactive power loop controller are adjusted, the asymmetric positive and negative feedback loop effects will cancel each other, leading to a change process of system stability from instability to stability and then to instability, that is, the “inflection point” phenomenon. It is not that the stability of the grid connected system gradually weakens with the increase of the parameters of the reactive power loop controller. It is worth noting that how to find the critical point of mutual cancellation of positive and negative feedback loop effects by constructing analytical expressions or quantitative indicators will be the work that needs further exploration in the future.
涂春鸣, 邹凯星, 高家元, 肖凡, 葛平娟. 基于不对称正负反馈效应的PQ功率控制并网逆变器稳定性分析[J]. 电工技术学报, 2023, 38(2): 496-509.
Tu Chunming, Zou Kaixing, Gao Jiayuan, Xiao Fan, Ge Pingjuan. Stability Analysis of Grid-Connected Inverter under PQ Power Control Based on Asymmetric Positive-Negative-Feedback Effects. Transactions of China Electrotechnical Society, 2023, 38(2): 496-509.
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2023, Vol. 38 
