Hierarchical frequency control strategy of doubly-fed induction diesel generator under emergency condition

Natural disasters lead to the uncertain topological structure of the urban distribution network. It is difficult for the communication system to recover quickly, which brings great difficulties to restoring the power supply. Therefore, the deployment of an emergency power supply is one of the critical measures to ensure the stable operation of isolated network systems and reduce power loss. Compared with the traditional synchronous diesel generator (SDG) as an emergency power supply, a doubly-fed induction diesel generator (DFIDG) has the advantages of flexible and controllable, rapid response and high operation efficiency. This paper presents a layered frequency control strategy for a doubly-fed induction diesel generator in an emergency scenario. Firstly, the models of doubly-fed induction diesel generator and its control system, prime mover and its speed regulation system are established. Secondly, the hierarchical frequency control strategy is proposed, including primary integrated frequency control (including droop control and virtual inertia control) and secondary frequency regulation control based on translation method. The virtual inertia control can make the doubly-fed machine quickly release the rotor kinetic energy when the frequency changes rapidly, so as to improve the frequency supportability. According to the overall shortage of the system and the maximum output power of the doubly-fed induction diesel generator, the strategy calculates the secondary frequency regulation power adjustment as the DFIDG power setting value, and then can realize automatic secondary frequency regulation without a communication system. Finally, simulation results verify the effectiveness of the proposed strategy.