基于主从控制的微电网电压质量改善策略

针对非线性不平衡混合负载易导致微电网母线电压畸变和不平衡的问题,目前大多采用增加额外的电能质量治理装置来提高母线电压质量。鉴于逆变器具有与电能质量治理装置相同的拓扑结构,本文将微电网母线电压质量治理问题转化为连接在微电网母线上的多逆变器输出侧电压质量治理问题,提出利用并联在微电网母线上的多逆变器系统对母线质量进行治理的策略,即将电能质量治理功能嵌入到从逆变器中,利用从逆变器实现逆变后的剩余可用容量抑制微电网母线电压谐波和不平衡。本文首先以单台逆变器为例,对非线性不平衡混合负载造成逆变器输出电压质量下降的原因进行分析,在此基础上,提出利用从逆变器剩余可用容量来补偿负载中的谐波、负序电流分量,而负载中的基波电流和零序电流分量则有主从逆变器共同分担。该控制策略有效的降低了逆变器输出侧电压的畸变率和不平衡度,避免了增加额外的电能质量治理装置,降低了系统成本。最后通过在PSCAD仿真环境下搭建仿真模型验证了所提控制策略的有效性和可行性。

Strategy for improving voltage quality of microgrid based on master-slave control

To solve the problem of voltage distortion and unbalance caused by non-linear and unbalanced load, additional power quality control devices are usually used to improve the bus voltage quality. In view of the fact that the inverter has the same topology structure as the power quality control device, the problem of bus voltage quality control in microgrid is transformed into that of output voltage quality control in multi-inverter connected to the bus of microgrid, the strategy of bus quality control using multi-inverter system connected in parallel on microgrid bus is proposed, that is, the power quality control function is embedded into the slave inverter, suppression of bus voltage harmonics and unbalance in microgrid by utilizing the remaining available capacity of inverter. In this paper, taking a single inverter as an example, the causes of the output voltage quality degradation caused by the nonlinear unbalanced mixed load are analyzed, the residual available capacity of the slave inverter is used to compensate the harmonic and negative sequence current in the load, while the fundamental current and zero sequence current in the load are shared by the master-slave inverter. The control strategy effectively reduces the distortion rate and unbalance degree of the inverter output voltage, avoids adding additional power quality control devices, and reduces the system cost. Finally, the effectiveness and feasibility of the proposed control strategy are verified by building a simulation model in PSCAD environment.#$NLKeywords: microgrid, nonlinear and unbalanced load, master-slave control, voltage harmonics and unbalance