Bumpless Transfer Control for Transmission System Secondary Voltage Regulation With a LQRI Controller

The operation of the hierarchy-based voltage regulation architecture of the Italian transmission system is being affected by the efforts to fight climate change. Energy production is becoming more distributed and converter-based, as a result of the increased use of renewable energy sources and the progressive shutdown of less-sustainable power plants (like coal-fired ones), which affects the controllability of the system. Therefore, the actual secondary voltage control, dedicated to maintaining the voltage of specific transmission system nodes at a given reference value, is becoming less effective. A coordinated Linear Quadratic Regulator with Integral action (LQRI) secondary voltage controller can be used to face such issue. However, issues must be solved to provide an implementation suitable for the Italian transmission system. Need of adaptivity, due to power system's operating points frequent modification, and a variable number of actuators, due to the reactive power resources' connection/disconnection, pose a significant challenge. The resulting frequent update in controller parameters’ leads to unwanted step variations in the control signals at each update, if not properly addressed. To solve such an issue, in this paper a bumpless control realization for an LQRI is proposed, demonstrating its effectiveness with a linear system model, and validating the results with a more detailed non-linear system model based on recursive power flow calculation.