基于逆变器剩余容量及自适应虚拟谐波阻抗控制的孤岛微电网谐波功率分配策略

Harmonic Power Allocation Strategy in Islanded Microgrid Based on Remaining Capacity and Adaptive Virtual Harmonic Impedance Control of Inverter

孤岛微电网中,非线性负载产生的谐波电流导致发电单元的逆变器也需要承担部分谐波视在功率。为避免逆变器因承担过量谐波功率过载,目前研究者们大都致力于实现谐波功率在逆变器间的均分。然而,谐波均分策略忽略了不同逆变器改善电压质量能力的差异性,致使微电网电压质量无法得到有效改善。针对此,提出了一种以改善微电网电压质量为目标的谐波功率分配策略,根据逆变器剩余容量及其承担的谐波功率,自适应地调节其虚拟谐波阻抗值在第四象限内变化,从而在不过载的前提下使各逆变器到微电网母线的谐波阻抗达到最小值,为谐波电流提供低谐波阻抗通路,达到尽可能改善微电网电压质量的目的。为了实现该目标,基于根轨迹确定了逆变器虚拟谐波阻抗的稳定调节范围,并进一步设计了一种变参数积分控制器,令所提自适应虚拟谐波阻抗控制能够兼顾调节速度及收敛性能。仿真和硬件在环实验验证了所提控制方法的有效性。

In an islanded microgrid, the harmonic current generated by the nonlinear loads causes the inverters of the generation units to assume a part of the harmonic apparent power. Researchers are mainly committed to realizing the harmonic power sharing between the multiple inverters to avoid the overload of the inverters. However, this sharing strategy ignores the difference of the inverters in the voltage quality improvement abilities so that the voltage quality of the microgrid cannot be effectively improved. To this point, a harmonic power allocation strategy which gives priority to improving the voltage quality of the microgrid is proposed. The virtual harmonic impedance of the inverter is adaptively adjusted in the fourth quadrant according to its remaining capacity and harmonic power. In this way, the harmonic impedance from the inverter to the microgrid bus reaches the minimum on the premise that no inverters is overloaded, thus providing a low impedance path for the harmonic current and improving the voltage quality as much as possible. To achieve this, the stability region of the inverter’s virtual harmonic impedance is determined by the root locus analysis, and a variable parameter integral controller is further proposed to make the adaptive virtual harmonic impedance control coordinate both the regulation speed and the convergence performance. The effectiveness of the proposed method is verified by the simulation and the hardware-in-the-loop experiment.