Decentralized Hierarchical Coordinated Control For Microgrid With Heterogeneous Distributed Generators

Microgrid,which can effectively integrate distributed power,deepen the application of power electronics technology,and solve the problem of renewable energy consumption,is becoming the current development trend.The microgrid contains a variety of heterogeneous distributed generators,including:1)Heterogeneous structure of DG connected to Common bus.such as diesel generators and energy storage systems;2)Heterogeneous control method of converters interfaced DGs,which can be classified into two types:droop-based voltage-controlled converter and the PLL-based current-controlled converter interfaced DGs.In order to realize the autonomous operation of the island microgrid with heterogeneous generators,the control needs to realize multiple objectives,such as real-time balance of the active power and reactive power of the system,improving the frequency and voltage quality,and ensuring the stability of the system.The traditional decentralized control has a clear control structure to realize multiple operational targets,but often uses centralized communication,which restricts the flexible operation and capacity expansion of the micro grid.The peer control has good dynamics based on the droop control,but cannot achieve voltage regulation.Therefore,the two control can be combined to implement hierarchical control functions in a decentralized mathod.Thus,this paper mainly carried out the following research around the problems mentioned above:1.The coordination and equalization active power control strategy for diesel generators and energy storage systems in MicrogridSince diesel generators cannot acquire accurate local speed signals generally,which will affect active power allocation,and storage of charge of different energy storage systems are inconsistent,a hierarchical coordinated control strategy is proposed,including:the primary droop control,the secondary control for voltage recovery,and the auxiliary equalization control.The control can realize coordinated operation of diesel generators and energy storage units,and maintain the microgrid's frequency in the permitted range,without microgrid central controller.The control can also correct speed measurement error of diesel generators,and can also realize state of charge(SOC)balance for energy storage systems.Multiple heterogeneous generators can have complete "plug&stabilize","plug&optimize" characteristics,which can improve the reliability and flexibility of power supply effectively.2.The decentralized and hierarchical reactive power sharing control strategy for microgrid with heterogeneous distributed generatorsA decentralized and hierarchical reactive power sharing control strategy is proposed for islanded microgrid with both droop-based voltage-controlled converter and the PLL-based current-controlled converter interfaced DGs.By adjusting floating voltage,reactive power sharing error caused by the mismatched feeder impedance can be reduced.The control has a hierarchical structure,in which the secondary control and the auxiliary correction control are successively slower than the primary droop control,which can maintain good linear dynamic characteristics of the system.The proposed strategies can get rid of the constraint of communication system,and achieve the plug-and-play effect of distributed generators,which can effectively enhance the flexibility and reliability of the system.