弱电网下抑制谐波谐振的LCL型并网逆变器鲁棒性CCFAD方法

Robust CCFAD method for suppressing harmonic resonance of LCL grid-connected inverter in weak grid

LCL型并网逆变器采用电容电流反馈有源阻尼在弱电网下进行并网电流控制时,如果系统环路谐振频率高于1/6的采样频率,数字控制延时会导致并网逆变器在较宽范围变化的电网阻抗影响下鲁棒性较差甚至失稳。通过分析指出,电容电流反馈有源阻尼环路可等效为并联在滤波电容两端的虚拟阻抗Zeq(s),表现出的负阻特性是造成系统失稳的主要原因。鉴于此,提出一种采用负一阶惯性环节进行电容电流反馈有源阻尼的鲁棒性方法,在电容电流阻尼环路中引入惯性环节,利用频率稳定性分析对所提方法进行详细论述,并给出相关参数的设计过程。理论分析表明,该方法可保证Zeq(s)在LCL滤波器谐振频率有效范围内始终处于正阻特性范围,不仅提高系统的稳定裕度,并网系统的谐波谐振也得到抑制。此外,该方法具有较好的灵活性,当采用电容电压反馈有源阻尼控制并进行锁相时,可节省一组电流传感器的使用。最后,通过实验验证了所提方法的有效性。

LCL filter grid connected inverter adopts capacitive current feedback active damping for net-work access control under weak current network.When the system resonance frequency is higher than 1/6 of the sampling frequency,the digital control delay will lead to poor robustness and even instability of grid connected inverter under the influence of wide-range varying grid impedance.Through analysis,it is pointed out that the capacitive current feedback active damping method is equivalent to the virtual imped-ance Zeq(s)connected in parallel at both ends of the filter capacitor,and the system instability is mainly caused by the negative resistance characteristic of Zeq(s).A robust method was proposed by using nega-tive first-order inertia link for capacitive current feedback active damping.The inertia link was introduced into the capacitive current damping loop,and the frequency stability analysis method was used to discuss it in detail,and the design process of related parameters was further given.Theoretical analysis shows that this method can ensure that Zeq(s)is always in the range of positive resistance characteristics within the effective range of the resonance frequency of the LCL filter,which not only improves the stability mar-gin of the system,but also suppresses the harmonic resonance of the grid-connected system.In addition,this method has better flexibility.If capacitive voltage feedback active damping control is used and phase-locked,the use of a set of current sensors is saved.Finally,effectiveness of the proposed method is veri-fied through experiments.