A Constrained Coordination and Frequency Control Framework for Dynamic Virtual Power Plants

This study presents a constrained coordination and frequency control framework for plants containing a collection of heterogeneous generators, including synchronous generators (SG) and grid-forming (GFM) photovoltaics (PV) and wind turbines (WT). While we focus on distributed dynamic virtual power plants (DDVPP) with units at different buses of a transmission system, the results also apply to control of conventional renewable plants with units interconnected through a collector network. Our framework explicitly considers unit-level constraints and enables the plant to 1) provide frequency control, 2) supply load demand considering weather and load volatility, and 3) maintain frequency stability without violating physical constraints, e.g., dc voltage, blade pitch angle, and rotor speed limits. The proposed framework spans plant-level and unit-level control and coordination. The plant-level control computes unit-level dispatch signals and frequency control coefficients by solving an optimization problem considering individual unit constraints and plant-level requirements. Then, at the unit-level, a curtailment and tuning problem is solved to translate the plant-level dispatch and frequency control gains into operating points and control gains for the SG and GFM controls of each unit. Moreover, we provide conditions for frequency stability of the DDVPP that are independent of the network configuration and explicitly account for weather conditions and operating points. While the underlying autonomous GFM grid support ensures system stability, the plant-level control coordinates units' operating points and control gains to satisfy plant-level requirements and maintain operation within unit limits. Detailed electromagnetic transient (EMT) simulations are used to validate the performance of the proposed framework in different scenarios.