MIMO Control Architectures for Secondary Voltage Regulation in Electrically Coupled Transmission Grids: Design and Dynamic Performance

The progressive shift towards renewable energy sources in electric power production requires a revolution in transmission system control. In the latter, progressive reduction of high-power conventional power plants in favor of small distributed ones based on renewable energies (which present different dynamic performance), as well as the integration of new elements (regulating HVDC links, STATCOMs, etc.), makes the present transmission system structure and behavior significantly different compared to those taken as bases for the design of voltage control systems. Moreover, limitations due to technology obsolescence of the existing architecture and the greatly increased capabilities of modern Phase Measurement Units (PMU) contribute to requiring a revision of the voltage control architecture, which should also provide robustness to parameter variation and be adaptive in nature. To this end, in this work the applicability of different multiple input multiple output control methods to the transmission system secondary voltage regulation is investigated. Specifically, the Decoupling control method and the Linear Quadratic Regulator with Integral action control method are applied to the secondary voltage regulation of the Italian transmission system. Three different control system architectures, resulting from the application of these methods to the peculiarities of Italian transmission system voltage control architecture, are proposed in the paper. Their dynamic performance is tested on the model of a portion of the Italian transmission network in different scenarios, and compared with current Italian voltage control. The results suggest one of the proposed architectures as a promising solution to address the power system's evolution.