高渗透率分布式发电中并网逆变器并联系统鲁棒运行关键技术研究

In distributed power generation system with high penetration, the parallel operation of grid-connected inverters is seriously challenged by the non-ideal factors including the non-linear elements of the inverter itself (such as the phase-locked-loop, the pulse width modulation and so forth), the asynchronous carriers of the inverters, the complicated grid characteristics at the point of common coupling (PCC) and so on. This project proposes to study the key technologies for the robust operation of parallel grid-connected inverters. Taking the non-linear units into account, the multi-frequency output impedance model of the parallel inverters is firstly built. Based on this model and considering the circulating currents related to the carrier phase, the harmonic coupling in the non-ideal units and so on, the mechanism of the wide-frequency-band harmonic resonance in the system is revealed. Further on, to suppress the harmonics which is induced by the interactions not only among the parallel inverters but also between the inverters and the complicated utility, the high robustness phase-locked-loop and current control strategies for passivating the inverter output impedance, the configuration method of the carrier phase for suppressing the circulating currents and a series active damper implemented at the system level are proposed. In addition, with respect to the stability problem of power control which arises when the multiple inverters participate in regulating the PCC voltage amplitude and frequency, the method for analyzing and regulating the power control loop of the parallel inverters is explored. The breakthroughs in the above core technologies facilitate to connect more inverters into the grid and makes sense for increasing the penetration of the distributed energy.

针对高渗透率分布式发电中并网逆变器并联系统运行受逆变器自身的锁相及脉宽调制等非线性因素、各逆变器控制载波不同步以及公共耦合点处复杂电网特性等非理想因素严重影响的问题，提出研究并联并网逆变器鲁棒运行关键技术。在计及逆变器非线性因素构建并联系统的多频输出阻抗模型的基础上，明晰多逆变器并联系统的宽频率范围谐波谐振机理，包括控制载波相位差异激励的谐波环流以及非线性环节引起的谐波耦合等机理；进而，提出以输出阻抗无源化为目标的逆变器强鲁棒锁相与电流控制策略、抑制逆变器间谐波环流的载波相位配置方法以及从集群系统层面进行串联有源阻尼的实现方案，解决多逆变器间及其同复杂电网的谐波交互作用问题；针对多逆变器参与耦合点电压频率和幅值调节存在的由功率控制引起的稳定性问题，提出适用于并联系统的功率控制环路特性分析及优化设计的方法。上述关键技术的突破有助于促进逆变器规模化入网，对提高分布式能源渗透率具有重要意义

在高渗透率分布式发电系统中，并网逆变器并联运行受逆变器自身的锁相及PWM等非线性因素、各逆变器控制载波不同步以及公共耦合点处复杂电网特性等非理想因素严重影响。为解决这一系列问题，本项目分别从系统建模、稳定性分析及鲁棒控制器改进上展开了深入研究，旨在实现复杂并联系统的高质量稳健运行。.首先，本项目充分考虑锁相环同步及PWM非线性的影响，提出了考虑频率耦合的多机小信号模型，并基于阻抗稳定性判据，明晰了锁相环及PWM环节对多机集群系统低、高频稳定性的影响机制，为多机系统实现精确的小信号稳定性设计及鲁棒性改进提供了重要的理论依据。进一步，通过非线性手段实现系统的稳定性分析，兼顾了系统受到大小扰动影响的情况。如：对于PWM引起的饱和问题，通过描述函数法进行了非线性分析；计及锁相环及PWM饱和非线性因素，提出了基于Lyapunov直接法推导的整体稳定的矩阵不等式条件。.为实现多逆变器间及其同复杂电网交互作用所引起的复杂谐波谐振抑制，提出锁相环改进策略以及基于输出阻抗无源化的电流控制方案，极大地提高了集群系统的鲁棒稳定性。对于多机系统中载波不同步引起的高频振荡问题进行了深入研究，提出了无互联线通信的虚拟振荡器载波同步技术，极大地简化了集群控制复杂度，并且新同步技术下系统的稳定性问题也得到了很好的解决。另外，采用了基于状态扰动观测器的电流控制策略，有效地抑制了系统中存在的不确定扰动，提高了进网电流质量。进一步通过改变同步输入，实现了单传感器控制，减少了控制成本。.通过搭建实验测试平台验证了提出的理论及技术的正确性和有效性，一系列研究成果对支撑分布式能源大规模接入电网时的稳健运行、高质量输出具有重要作用。