计及虚拟同步与阻抗重构的一体化谐振抑制理论及其在组串型光伏逆变集群中的应用机制研究

The project focuses on the restrain of resonance in clustered photovoltaic string inverters. Clustered photovoltaic string inverters are easy to expansion. Often large amount of inverters are paralleled together and no isolation transformer is adopted. The electric distance among inverters are often very short. Harmonic circuit current among inverters and grid may cause resonance and threaten the stability of the whole system. The characteristics of inertia and damp in virtual synchronous generation have potential ability in restraining the spreading and amplifying of harmonics. Reshape output impedance can change the total impedance network thus avoid resonance. The project focus on the dynamic characteristics and interaction of virtual synchronization and impedance reshaping during active resonance damping process. The project develops a resonance damping control strategy combining virtual synchronization and impedance reshaping together. The virtual inertia and damping can react immediately to restrain the spreading of harmonics. The impedance reshaping ability can be obtained by adding voltage feedforward and other control unit. When system topology and parameters change, trends of harmonic spreading can be restrained by inertia and damping characteristics. At the same time, the real time data collection can help correct impedance network and reshape impedance of key elements. Thus harmonic resonance can be restrained and large-scale inverters can be connected to the grid safely.

本项目聚焦于解决因并联逆变器数量多、拓扑非隔离、并联各机间电气距离短、弱电网阻抗变化等特点导致的组串型逆变器集群谐振问题，研究谐振主动抑制过程中虚拟同步平抑环节与阻抗重构抑制环节的动力学特征与共同作用机制，发展一种计及虚拟同步与阻抗重构的一体化谐振抑制理论并研究其在组串型光伏逆变器集群中的应用。虚拟同步技术中的惯量和阻尼系数在平抑谐波传播放大过程中具有很大潜力；阻抗重构能改变系统网络分布从而抑制谐振发生。本项目通过虚拟同步逆变器的惯量与阻尼特性实现逆变器对谐波放大过程的主动平抑；通过电压电流前馈等控制环节设计实现逆变器特定模态的阻抗重构能力；当系统拓扑和参数变化时，由虚拟同步逆变器的惯量和阻尼特性平抑谐波放大趋势，同时依据实时数据信息采集，在线修正阻抗网络，在谐振关键模态处重构谐振中心元件阻抗特性，最终抑制因阻抗匹配造成的集群谐振，保障MW级组串型逆变器集群规模化安全接入电网。

本项目聚焦于解决因并联逆变器数量多、并联各机间电气距离短、弱电网阻抗变化等特点导致的组串型逆变器集群谐振问题。首先，基于小信号模型和阻抗模型分析组串型逆变器单机振荡模态与谐振特性，引入谐波电流系数和谐波电压系数用于衡量逆变器群集电系统中的谐波传递规律；随后，在理论分析基础上，基于硬件在环仿真手段建立经型式试验数据验证的光伏逆变器单机硬件在环仿真平台，并对单机建模准确度进行评价，建立了基于动态链接库和电流源等值的光伏电站集群模型，提出单机阻抗测量和集群阻抗特性评估方法；最后，虚拟同步技术中的惯量和阻尼系数在平抑谐波传播放大过程中具有很大潜力；阻抗重构能改变系统网络分布从而抑制谐振发生。通过虚拟同步逆变器的惯量与阻尼特性实现逆变器对谐波放大过程的主动平抑，同时结合我国新能源电站面临的实际问题，以青豫直流近区新能源发电的接入方式为背景设置测试场景，对电网短路比1.5时控制策略优化前后的光伏逆变器进行稳定性测试。