Modernization of power systems leads to more power electronic interfaced units in the generation, demand, and transmission. Examples are remotely installed renewable energy sources, loads with constant power, or high voltage direct current (HVDC) corridors. These changes significantly affect the frequency stability margins of the system and thus special control techniques should be applied in the converters of the new installed units so as to shoulder the frequency regulation in case of commonly occurred active power imbalances. The response of such units has to be cooperative in order to avoid problems such as insufficient reactions or overshoots. In this chapter, a coordinative tuning approach of the active power gradient control scheme applied to the controllers of modular multilevel converter (MMC)-based HVDC links and proton exchange membrane electrolyzers with the provision of fast frequency support in a multiarea hybrid HVDC-HVAC power system with responsive demand units is proposed. This tuning uses an optimization approach based on mean variance mapping optimization and is able to minimize the frequency excursions in all interconnected areas participating in the frequency regulation even without communication between the system nodes. This technique has shown great results in terms of quality and convergence rate within a short number of fitness evaluations achieving a set of frequency responses within acceptable limits set by operators even in case of the loss of the largest generating unit in the weakest system area. It has also revealed the applicability of such a method in more complex systems and the necessity for sophisticated tuning methods according to the application needs and the system characteristics.

Power electronic dominated power systems formed nowadays are characterized by fast and frequent dynamics, limited short circuit support, low inertia conditions and lack of inertial support. Under these conditions, coping with active power imbalances in a power system may becomes a significant challenge for transmission system operators (TSOs) that may experience extensive frequency deviations and steep rates of change of frequency (RoCofs). To deal with the frequency stability issues encountered, power electronic interfaced (PEI) units can rapidly respond to provide fast frequency support (FFS) taking advantage of their controllability levels and their rapid response to setpoint changes. FFS may depend on the active power gradient (APG) control strategy that determines the required amount of active power, and the rate the power injection takes place. However, when multiple elements try to regulate simultaneously the frequency adverse control actions such as insufficient or over frequency regulation may be encountered. To solve this issue, this paper proposes a formulation for the optimal and coordinative tuning of the APG controllers of PEI elements installed in a multi-area, multi-energy hybrid HVDC/HVAC power system with modular multilevel converter (MMC) HVDC links and proton exchange membrane (PEM) electrolyzers. This formulation focuses on creating an artificially coupled frequency response for an electromagnetically decoupled multi-area system taking advantage of the available active power reserves and the inertia levels of each area. In that way, an active power imbalance can be optimally shared among the interconnected areas leading to effectively improved frequency response for the affected and supporting areas. The proposed formulation is solved using the mean variance mapping optimization (MVMO) algorithm after a series of RMS simulations is performed in DIgSILENT PowerFactory 2021.