Coordinated Frequency Control Based on Hierarchical MPC Considering Tie-Line Power Flow

The frequency response characteristics of inverter-based resources (IBRs) and synchronous generators (SGs) vary significantly during system contingencies, often resulting in prolonged electromechanical transients due to resource interactions. However, limited attention has been given to coordinated control strategies among varying generators providing multiple frequency services, particularly fast frequency response (FFR) and virtual inertia. Furthermore, the strict limit of transmission line power capability during transients and the need for quick recovery of power flow on tie-lines are often overlooked, increasing the risk of system separation. In this paper, a coordinated frequency control methodology is proposed by employing hierarchical model predictive control (HMPC). The proposed HMPC consists of an upper-layer controller to manage multi-area power flows and lower-layer controllers to recover the zonal centre-of-inertia (COI) frequency by setting active power references for various resources. These include FFR-based photovoltaic (PV) and wind farms, virtual synchronous generator (VSG)-based batteries and primary frequency response (PFR)-controlled SGs. Finally, the proposed HMPC approach achieves a higher frequency nadir and faster tie-line power flow recovery, as demonstrated through co-simulation studies using PSCAD and MATLAB.