Institute of High Voltage & High Current, School of Electrical Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia.
Institute of High Voltage & High Current, School of Electrical Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia.
ISA Trans. 2019 Nov;94:352-369. doi: 10.1016/j.isatra.2019.04.025. Epub 2019 May 4.
This paper proposes an improved hierarchical control strategy consists of a primary and a secondary layer for a three-phase 4-wire microgrid under unbalanced and nonlinear load conditions. The primary layer is comprised of a multi-loop control strategy to provide balanced output voltages, a harmonic compensator to reduce the total harmonic distortion (THD), and a droop-based scheme to achieve an accurate power sharing. At the secondary control layer, a reactive power compensator and a frequency restoration loop are designed to improve the accuracy of reactive power sharing and to restore the frequency deviation, respectively. Simulation studies and practical performance are carried out using the DIgSILENT Power Factory software and laboratory testing, to verify the effectiveness of the control strategy in both islanded and grid-connected mode. Zero reactive power sharing error and zero frequency steady-state error have given this control strategy an edge over the conventional control scheme. Furthermore, the proposed scheme presented outstanding voltage control performance, such as fast transient response and low voltage THD. The superiority of the proposed control strategy over the conventional filter-based control scheme is confirmed by the 2 line cycles decrease in the transient response. Additionally, the voltage THDs in islanded mode are reduced from above 5.1% to lower than 2.7% with the proposed control strategy under nonlinear load conditions. The current THD is also reduced from above 21% to lower than 2.4% in the connection point of the microgrid with the offered control scheme in the grid-connected mode.
本文提出了一种改进的分层控制策略，由一个主层和一个次层组成，用于三相四线微电网在不平衡和非线性负载条件下的控制。主层由多环控制策略、谐波补偿器、下垂控制策略组成，以提供平衡的输出电压、降低总谐波失真（THD）和实现精确的功率分配。在次层控制中，设计了无功功率补偿器和频率恢复环，以提高无功功率分配的准确性和恢复频率偏差。使用 DIgSILENT Power Factory 软件和实验室测试进行了仿真研究和实际性能测试，以验证控制策略在孤岛和并网模式下的有效性。零无功功率分配误差和零频率稳态误差使该控制策略优于传统控制方案。此外，所提出的方案还具有出色的电压控制性能，如快速瞬态响应和低电压 THD。与传统的基于滤波器的控制方案相比，所提出的方案的瞬态响应时间减少了 2 个线周期，证实了其优越性。此外，在非线性负载条件下，孤岛模式下的电压 THD 从高于 5.1%降低到低于 2.7%，而在并网模式下，微电网连接点的电流 THD 从高于 21%降低到低于 2.4%。
