三相LCL-LC型仅网侧反馈的改进时滞抑制

Improved time delay suppression in three-phase LCL-LC rid-connected inverters with only grid-side feedback

LCL-LC电压源型逆变器仅网侧电流反馈的有源阻尼相比于电容电流反馈下的有源阻尼减少了检测元件的使用,能有效抑制LCL-LC逆变器产生的谐振峰。但由于数字电路里存在控制延时影响,因此电网阻抗的变化会引起谐振频率fr偏移,当fr处于采样频率fs的16附近时系统将会失稳。为了解决LCL-LC有源阻尼逆变器仅网侧反馈时控制延时对逆变器的影响,研究了在数字域下电网阻抗的变化对系统稳定性的影响,并提出了一种新的延时补偿方法,即在控制回路的前向通路中加入改进型延时补偿,将有源阻尼的等效正电阻从原有的fs 6扩展到0.4965fs,补偿后的有缘阻尼在fr发生偏移时由于等效正电阻的扩宽使得系统在fs 6附近不会失稳,从而极大地提升了系统的稳定性。仿真和实验验证了理论的正确性。

The active damping(AD)of LCL-LC voltage source inverter with only grid-side current feedback reduces the use of detection components in comparison with the AD with capacitor current feedback,which can effectively suppress resonance peaks generated by LCL-LC inverters.However,due to the control delay effects of digital circuits,variations of grid impedance will cause the shift of resonance frequency(fr).When fr is near 16 of the sampling frequency(fs),the system becomes unstable.To eliminate the impact of control delay on the inverters when LCL-LC AD inverters only have grid-side feedback,the influence of changes of grid impedance on system stability in the digital domain is studied,and a novel delay compensation method,that is,an improved delay compensation is added to the feedforward path of the control loop,is proposed.In this method,the equivalent positive resistance of AD is extended from the fs 6(the original)to 0.4965fs.Because of the compensation of widening the equivalent positive resistance,the system remains stable around fs 6 even when fr shifts,which enhances system stability greatly.Simulation and experimental results validate the theoretical correctness of the method.