Dynamic modelling and control of distribution energy systems: comparison with transmission power systems

This paper explores the fundamental differences between distribution and transmission systems, regarding dynamic behaviour under a high penetration of distributed generators (DGs). The paper shows that because of large resistance to reactance ratio in distribution networks the frequency and voltage dynamics are strongly interdependent. Therefore only coupled models should be used for control design of DGs. Large resistance to reactance ratio and low inertia and fast dynamic response of DGs also result in strong interactions between DGs. These interactions can cause stability problems if DGs are connected electrically in close areas and/or the control of DGs is poorly tuned. Block Gerschgorin theorem is used to determine bounds on interactions between each DG with the rest of the system so that no interactions occur. Next, a more systematic fully decentralised, and, therefore simple control design is proposed. The logic of the decentralised control is to cancel out strong interactions between DGs and to improve the dynamic response of DGs. The theoretical findings are illustrated on two practical distribution systems.