Hierarchical Frequency Control of Hybrid Power Plants Using Frequency Response Observer

With frequency stability being challenged in modern power systems, transmission system operators have been designing new mitigation measures, such as fast frequency response (FFR), to maintain operation security of power systems. To accommodate technical requirements of new frequency control services (FCSs), the corresponding control should be implemented at asset controllers to enable fast responses. However, control counteraction can arise between plant controllers and asset controllers during the provision of FCSs. In this paper, a novel hierarchical frequency control approach is proposed to allow hybrid power plants (HPPs) to provide three types of FCSs, namely FFR, frequency containment response (FCR) and frequency restoration response (FRR). To solve control counteraction issue, an innovative frequency response observer (FROB) is proposed. The FROB at plant controllers and the hybrid power plant controller (HPPC) accurately estimates frequency response initiated by asset controllers, and the obtained estimation is used for control compensation at plant controllers and the HPPC to avoid control counteraction. Design guidelines and robustness analysis of the FROB are then discussed. Case studies are implemented in a power system dynamic model in MATLAB/Simulink, and the results show that the proposed frequency control approach enables coordinated operation of multiple technology power plants, with robust performance achieved when there are system uncertainties in HPPs.