Inter-area and intra-area oscillation damping for UPFC in a multi-machine power system based on tuned fractional PI controllers

The low-frequency oscillations such as inter-area and intra-area modes of oscillations are difficult to avoid their occurrence and control in a weakly connected power system. It is essential to damp these multi-modal oscillations because these oscillations may lead to many instability issues. In this study, the application of one of the flexible AC transmission systems (FACTS) compensating device, a unified power flow controller (UPFC) is focused on its small-signal stability issues referring to inter-area and intra-area modes of operation in a multi-machine power system. Factional order Proportional Integral (FOPI) controller is applied for the control strategy against the conventional PI controller due to its flexibility and higher controllability for its extra degree of freedom to control. FOPI controller performance isn't free from parameter dependency. An adaptive differential evolution (ADE) algorithm is suggested to optimally tune the FOPI parameters for enhancing the performance. Apart from that, the dynamic characteristics of UPFC are extensively presented through modeling in the d-q axis rotating synchronous frame of reference. To justify the feasibility and effectiveness of the proposed approach, comparative results are presented under a wide variety of disturbances in a standard multi-machine power system. It is found from the non-linear simulations that UPFC based power system is well capable to damp out these oscillations effectively to enhance the stability of small-signal disturbance substantially. The result analysis with PI and FOPI control procedures employing ADE justifies the enhanced control performance of the UPFC.

Automated summary

This study focuses on the application of a unified power flow controller (UPFC) in a weakly connected power system to damp low-frequency oscillations. The performance of the FOPI controller is improved by optimizing its parameters using an adaptive differential evolution (ADE) algorithm. Extensive modeling and nonlinear simulations demonstrate the effectiveness of the UPFC-based power system in suppressing oscillations and enhancing stability.