非理想电网下三相LCL滤波并网逆变器对称电流控制

非理想电网包括电网存在不平衡、谐波畸变、频率变化等情况,在非理想电网下,三相电网中除正序分量外还含有一定量的负序、零序以及谐波分量。一方面,电网负序分量会使得d轴上含有2倍工频的脉动,从而导致锁相环锁相失准,虽然通过增加适当的滤波器可以滤除脉动量、提高锁相精度,但难以同时保证较好的频率适应性;另一方面,电网的负序及谐波分量易导致进网电流不对称且谐波含量增大,污染电网。针对上述问题提出了采用变采样周期锁相环(VSP-PLL)和电网负序电压前馈的方案,并结合逆变侧电流反馈控制以实现对称电流控制,最后,在一台5 k W三相LCL滤波并网逆变器样机上进行了实验验证。实验结果证明了方案的有效性。

Symmetrical Current Control for Three-phase Grid-connected Inverters under Non-ideal Grid Conditions

Non-ideal grid conditions include voltage unbalance, distortion and frequency variation. In addition to positive-sequence components, three-phase grid contains negative-sequence, zero-sequence and harmonic components under non-ideal grid conditions. On the one hand, an oscillating signal of two times the line frequency on the d-axis was generated by negative sequence, which caused a phase error finally. The error can be eliminated by adopting some special filters, but the adaptation to the grid frequency variation cannot be achieved simultaneously. On the other hand, the negative sequence and voltage harmonics usually caused asymmetrical and poor grid current quality. In this paper, a control strategy integrated with variable sampling period phase-locked loop(VSP-PLL), negative-sequence grid voltage feedforward and inverter-side current control was proposed specifically to solve the aforementioned problems. At last, experimental results form a three-phase LCL-filtered grid-connected inverter of 5 kW demonstrates the effectiveness of the proposed strategy.