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Research On Decentralized Hierarchical Self-optimizing Control Strategy For DGs In Islanded Microgrids

Posted on:2017-01-27Degree:MasterType:Thesis
Country:ChinaCandidate:R ZhaoFull Text:PDF
GTID:2272330482483009Subject:Electrical engineering
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A microgrid is a system that can combine the generation, load, energy storage device and control device to form a single controllable unit, and can provide electricity and heat simultaneously. A microgrid can operate in both grid-connected and islanded mode. Compared to the traditional grid, the microgrid reveals obvious advantages, one of which is that it gives a new idea to acceptance of new energy, and improving the efficiency and reliability of power system. However, the microgrid has some characteristics such as low inertia, strong randomness and intermittence of internal source, and variability of load power etc. Therefore, the microgrid depends on fast communication excessively when it operates in islanded mode, which results in the difficulty in design, debugging and maintenance of the control system. Among the traditional control modes of the microgrid, the centralized control mode and distributed control mode are unable to get rid of the constraints of the communication. The decentralized control mode can be realized without communication. However, due to limited local information, it can not usually realize the function of system frequency and voltage modulation and economic operation. In this context, focused on the active and reactive power control principle of the distributed generators (DGs), this paper does some research around the issues mentioned above and completes some works as follows:1. The decentralized hierarchical self-optimized active power control strategy for DGsIn the islanded microgrid, a droop control scheme is widely used to make the load power properly shared among DGs. In terms of the active power control, the DGs in the microgrid can be generally classified into two basic types:1) Voltage controlled voltage source inverter power-frequency droop type (P-F type DGs); 2) Current controlled voltage source inverter frequency-power droop type (F-P type DGs). Focused on the two types of DGs above, this paper proposes corresponding decentralized hierarchical self-optimized active power control strategies without the microgrid centralized controller (MGCC) and communication. The proposed control strategies can realize the traditional three-level hierarchical control of the power grid, i.e., the decentralized primary control (DPC), the decentralized secondary control (DSC) and the decentralized tertiary control (DTC) by a method based on partial feedback. Among, the DPC keeps the traditional linear droop control method to maintain the good linear dynamic of microgrid; the DSC makes the microgrid frequency can be restored to permitted range; the DTC makes each DG’s output power decided by the equal increment principle.2. The decentralized hierarchical self-optimized reactive power control strategy for DGsIn terms of the reactive power control, the DGs in the microgrid can be generally classified into two basic types:1) Voltage controlled voltage source inverter reactive power-voltage droop type (Q-V type DGs); 2) Current controlled voltage source inverter voltage-reactive power droop control (V-Q type DGs). Focused on the two types of DGs above, this paper proposes corresponding decentralized hierarchical self-optimized reactive power control strategies without MGCC and communication. The proposed control strategies can overcome the issues that the output reactive power may not be sharing accurately due to effects of mismatched feeder impedance of DGs, and the voltage at the point of common coupling (PCC) may drop due to the reactive loads fluctuation and the drawback of traditional droop control.The proposed decentralized hierarchical self-optimized control strategies in this paper can get rid of the constraints of the communication and make DGs have complete plug&play of characteristics, which not only improve the flexibility of DGs access to the microgrid, but also make the microgrid have good self-organizing. They have a good application prospect in the smart grid.
Keywords/Search Tags:Islanded microgrid, distributed generator, hierarchical decentralized self-optimized control strategy, power-frequency droop type DGs, frequency-power droop type DGs, reactive power-voltage droop type DGs, voltage-reactive power droop type DGs
PDF Full Text Request
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