Abstract
Based on the concept of cyber physical system (CPS), a novel hierarchical control strategy for islanded microgrids is proposed in this paper. The control structure consists of physical and cyber layers. It’s used to improve the control effect on the output voltages and frequency by droop control of distributed energy resources (DERs), share the reactive power among DERs more reasonably and solve the problem of circumfluence in microgrids. The specific designs are as follows: to improve the control effect on voltages and frequency of DERs, an event-trigger mechanism is designed in the physical layer. When the trigger conditions in the mechanism aren’t met, only the droop control (i.e., primary control) is used in the controlled system. Otherwise, a virtual leader-following consensus control method is used in the cyber layer to accomplish the secondary control on DERs; to share the reactive power reasonably, a method of double virtual impedance is designed in the physical layer to adjust the output reactive power of DERs; to suppress circumfluence, a method combined with consensus control without leader and sliding mode control (SMC) is used in the cyber layer. Finally, the effectiveness of the proposed hierarchical control strategy is confirmed by simulation results.
Highlights
With the deterioration of the global environment and the shortage of energy, the distributed generation technologies using clean and renewable energy in power system have been used widely [1,2].Currently, the distributed energy resources (DERs) include photovoltaic, wind turbine, micro turbines, fuel cells, etc
In order to improve the control effect of DERs and suppress the circumfluence, a novel hierarchical control strategy is proposed in this paper
An event-triggered secondary control strategy is proposed to improve the control effect on voltages and frequency obtained by droop control of DERs
Summary
With the deterioration of the global environment and the shortage of energy, the distributed generation technologies using clean and renewable energy in power system have been used widely [1,2]. Studies on improved control methods for inverters have received extensive attention, such as a decentralized controller proposed in [7] to coordinate the reactive power injections of photovoltaic (PV) generators in order to accomplish the voltage regulation in distribution networks. A decentralized nonlinear auto-adaptive controller is proposed in [12] for reducing system losses by the optimal management of the reactive power supplied by the inverters of PV units These two papers do not solve the power allocation problem in DERs. In order to solve this problem, many scholars put forward the corresponding improved control method. The second virtual impedance is used to decouple the control system in dq coordinate system (to make sure the droop control can be applied in a low-voltage microgrid) and share the reactive power of DERs proportionally.
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