附加虚拟阻抗的LCL型并网逆变器电流扰动观测控制方法

Method of Current Disturbance Observation Control for LCL-Type Grid Connected Inverters With Additional Virtual Impedance

针对LCL型并网逆变器输出电流质量容易受电网电压背景谐波及在弱电网条件下电网阻抗的影响,提出一种附加虚拟阻抗的LCL型并网逆变器电流扰动观测控制方法。首先,在常规双闭环控制的基础上引入扰动观测器,将电网电压背景谐波视为系统外部扰动,利用扰动观测器实时估算出扰动量并前馈补偿动态消除扰动对系统的影响;其次通过阻抗分析法来分析弱电网系统中电网阻抗引起稳定性下降的问题,在电流扰动观测控制方法的基础上再加入虚拟阻抗进行优化设计,使得并网阻抗在阻抗交截频率较大范围内变化时的相角裕度仍然大于系统所约束的稳定裕度。仿真对比结果表明,所提方法在保持良好的电流质量的同时提高了系统对电网阻抗的鲁棒性。

Aiming at the fact that the output current quality of actual LCL-type grid connected inverters is easily affected by grid voltage background harmonics and grid impedance under weak current grid conditions,this paper proposes a current disturbance observation and control method for LCL-type grid connected inverters with additional virtual impedance.Firstly,this paper introduces a disturbance observer on the basis of conventional double closed-loop control,treating the background harmonic of the grid voltage as an external disturbance of the system.The disturbance observer is used to estimate the disturbance momentum in real time and dynamically eliminate the influence of disturbance on the system through feedforward compensation.Secondly,impedance analysis method is used to analyze the robustness problem caused by grid impedance in weak current grid systems.Based on the current disturbance observation control method,virtual impedance is added for optimization design,so that the phase margin of the grid connected inverter system is still greater than the stability margin constrained by the system when the impedance intersection frequency changes within a large range.The simulation comparison results show,the proposed method improves the robustness of the system to grid impedance while maintaining good current quality.