Research On Operation And Control Of Microgrid With Different Types Of Distributed Sources

Microgrid is the significant part of the distribution network in the future smart grid, which has advanced and flexible operation and control pattern, and integrates distributed clean energy in high proportion. Compared with triditional distribution network, distributed sources in the microgrid can change the direction of the power flow, and the new energy such as the wind and solar photovoltaic can also bring profound effects to microgricd operation for their randomness. In the condition of various distributed generations, it is a very important and more wrong-headed subject that we complete the safe and stable operation for the microgrid using advanced and stable control method. In this paper, we begin with the access control for various distributed sources, and do deeply research on the issue of running control strategy, operation mode conversion and power quality management.Firstly, we analysis the basic theory on operation control for the microgrid. We also do some research on structure composition of the microgrid, control methods of interface inverter for distributed sources and the basic control strategy of the microgrid. On this basis, we do other researches on the access and control methods for various distributed sources. In addition, we establish the dynamic mathematical model for the microturbine and the fuel cell generation. Further more, we design the power electronical interface equipment correspondingly, which can be accessed to the microgrid. In order to meet different load demands, we analyze the tracking ability to loads for the microturbine and the fuel cell generation using simulations, and show the control methods of interface inverter for distributed sources according to different operation modes for the grid connected and islanding. At last, we do some researches on control methods for various distributed sources accessing the microgrid such as direct driven permanent magnet wind power generation and solar photovoltaic. The work will lay the foundations for flexible combination of various distributed sources in different natural conditions. The work will also provide some references for widespread use of the microgrid.Doubly fed induction generation (DFIG) is the main type of engine for wind power generation. In order to meet the distributed applying and developing demands, we respectively suggest the corresponding control methods to the operation mode of the grid connected and islanding. At the time of grid connected operation, DFIG can capture the most wind energy. According to the condition of bigger resistance parameter, we adopt sensitivity analysis method to adjust reactive power from DFIG, which can offset voltage fluctuation from active power changing, At the time of islanding operation, DFIG, which combined with the control of pitch angle and energy storage device, acted as voltage frequency and amplitude controllable. Thus, DFIG can cooperate with other droop control inverter-based distributed sources by simulate droop characteristic. The simulation results show that the new control method from this paper could adjust the active power balance in the microgrid and keep system voltage stability. This new method can also keep the microgrid running stable in the condition of grid connected and islanding operation.Based on the foundation that various distributed sources access to the microgrid, we do the research on the microgrid operation strategy and operation mode conversion. According to different microgrid structures, such as master slave structure, peer to peer structure and hierarchical structure, we put forward the corresponding operation strategy respectively. For the hierarchical structure microgrid, we complete the secondary frequency regulation for the islanding operation by choosing the principle frequency regulation source. This can improve the power quality and avoid the influence of energy storage devices and users caused by stable frequency offset. This can also create conditions for the reconnection of microgrid. Conversion from the grid connected operation to the islanding operation need continuous islanding detection. Once found the actual islanding state of microgrid, we adjust the control method of distributed source to maintain the stability of the islanding operation immediately. For the conversion form the islanding operation to the grid connected operation, we consider two cases:For the small scale master-slave structure, we propose an effective auto-switch operation mode for the microgrid, which can determine the operation states by contimuously detecting the voltage phase angle and amplitude in the large grid side and the microgrid side. And the new method can monitor the microgrid operation combining with extracting the positive sequence voltage, phase-locked loop and low-pass filter. Moreover, the method can also realize the smooth transition of grid connected and islanding operation. For the large scale hierarchical structure, the new method can determine the operation states by contimuously detecting the voltage frequency, amplitude and phase angle in the large grid side and the microgrid side. And it can also realize the smooth transition of grid connected and islanding operation by adjusting the interface voltage using voltage sensitivity analysis method.Microgrid is a significant part of the smart grid, an important target of whose is to supply electricity to customers of high quality. The last work of this paper is to study the power quality in the microgrid, and manage the power quality using distributed sources with regulating ability. Firstly, we analyze the influencing factors of harmonic compensation effects in the condition that the harmonic source is not in the access point of the distributed sources. Then a kind of power quality management method for important nodes is proposed, which is based on the inverter interfaced distributed sources controlling. For this method, the most important nodes near the inverter interfaced sources are chosen as the target to manage the power quality in the microgrid. In order to get the final compensation currents, the harmonic and the unbalanced component in the branch current of inverter and the target node voltage are extracted, and optimal compensation coefficients of every components are determined by searching. This new method can sufficiently use the existing equipment in the microgrid to improve the power quality entirely. In addition, the new methods in this paper can also flexiblely choose the target nodes and the level for compensation. It is of practical significance to improve management level in the microgrid and supply optional and top quality electricity to the customers.