弱电网下LCL型并网逆变器的高鲁棒性加权平均电流控制策略

High Robustness Weighted Average Current Control for LCL-type Grid-connected Inverter in a Weak Grid

加权平均电流(weighted average current,WAC)控制方法由于其环路降阶特性,在并网逆变器系统中得到了广泛的应用。然而,传统WAC控制方法并未充分考虑数字控制延时对并网逆变器系统造成的影响。该文分析表明,数字控制延时引入的相位滞后导致传统WAC控制方法不再具备环路降阶特性,而使得环路增益中出现一个随电网阻抗变化的反向谐振峰,使并网系统存在失稳的风险。针对此问题,该文提出一种基于超前补偿器的高鲁棒性WAC控制策略,该策略利用前馈通道中引入的超前补偿器来补偿反向谐振峰频率范围内的相位滞后,以此来实现环路降阶特性及弱电网适应性。对比分析和实验研究表明,所提控制策略能够保留传统WAC控制的降阶优点,同时对弱电网亦有很强的适应能力。

Weighted average current(WAC)control method is widely used in grid-connected inverters because of its order reduction characteristics.However,the impact of digital control delay on grid-inverter system has not been fully considered in the traditional WAC control methods.The analysis in this paper shows that the phase lag introduced by control delay makes the traditional WAC control method no longer have the characteristics of loop order-reduction,and leads to a reverse resonance peak in loop gain varying with the grid impedance,which puts the grid-inverter system at risk of instability.In order to solve this problem,the high-robustness WAC control strategy based on lead compensator was proposed in this paper,which used the lead compensator introduced in feed-forward channel to compensate the phase lag in the frequency range of the reverse resonant peak,so as to acquire the characteristic of loop order-reduction and the adaptability to weak grid.The comparative analysis and experimental results show that the proposed control strategy can retain the reduced-order advantages of the traditional weighted average current control,and has strong adaptability to weak grid meanwhile.