Micro-grid Adaptive Control System

There are some shortcomings in the traditional centralized, remote power supply for bulk power system, such as the power quality, safety, reliability, economy, etc. And with the exhaustion of coal, oil and other fossil energy sources, the renewable energy has been developing fast. It has the characteristics of dispersion, and the best way to utilize it is develop and build a local small grid, which includes kinds of microsources and the local load, namely, microgrid. The microgrid can operate interconnected to the main distribution grid, or in an islanded mode. In the grid-connected mode, it could realize bi-directional flow of power with the utility grid. During disturbances, the microgrid can separate from the distribution system to isolate the local load from the distribution grid. After disturbances, it has the ability of smoothly and automatically reconnecting to the distribution power system. On the other hand, since the renewable energy is intermittent, which is limited by nature, the microgrid always includes many microsources for reliable power support of the load by the coordination between each microsource. As the operation state switching and internal of microsources, the microgrid should adopt a reasonable control strategy for the reliable power supply to local custom and the maximum utilization of renewable energy.According to the characteristic of microsources and microgrid, this paper set up the microgrid structure with multi-microsources based on the direct-drive wind power system for capturing the maximum wind energy, which using the fast compensation capability of battery and the hydro complementing intermittent of the wind power. Develop a typical microgrid system for the area with sufficient wind and water energy. The fast and accurate switching between states of microgrid is particularly important for the reliable power supply to sensitive load, and a appropriate coordination control strategy should be adopted by each microsource and switch. Base on power and load management, according to the target of reliable power supply to local custom and the maximum utilization of renewable energy, this paper proposes the adaptive control strategy based on state transition of the microgrid. The main contents are shown as following.(1) Build the models of a direct-drive wind power system, hydro generator and its excitation and speed control systems, battery energy storage system and its DC-AC power electronic interface. Direct-drive wind power system uses the maximum power tracking control, battery control include charging control, PQ control, V/f control ,hydraulic power generation uses PQ control,Droop control of two strategies, which charging according to the different operating conditions of microgrid.(2) For the establishment of wind power, hydropower and energy storage in hybrid microgrid, according to the requirement of power and load management, this paper lists of all the microsources combinations, and achieve the corresponding state transition diagram.(3) Study the 9 types of running states and 39 types of state transitions of wind power, hydro and energy storage in the hybrid microgrid for the reliable power supply to local custom. Propose the adaptive control strategy, and establish the adaptive control system which includes input variable detection, coordination management of converter and switch and control action output.(4) Analyze three typical state transitions of the main source support state transforming to emergency state, main source support state transforming to main source output state, emergency state transforming to wind power output state by PSCAD/EMTDC simulation software. Verify the accuracy of the adaptive control strategy and carry out the fast and accurate conversion between states.