Research On Optimal Operation Method Of Hybrid AC/DC Microgrid With Generations

The hybrid AC/DC microgrid is a new structure of microgrid that emerged in recent years. It is capable of integrating different types of distributed generations(DGs) effectively, raising the proportion of DGs in power system and promoting operation efficiency of DGs. By adopting the complementary of AC power supply and DC power supply mode, the hybrid AC/DC microgrid saves the use of power electron conversion devices, thus the energy loss caused by multistage conversion is reduced and the power supply efficiency is improved significantly. With the diversification of DG, energy storage device and load, the prospect of AC / DC is destined to be bright. The hybrid AC/DC microgrid is able to reduce the cost of the equipment in the power supply system, in the meanwhile, it can improve the operation status of power supply system. The hybrid AC/DC microgrid is conducive to create a flexible, stable, reliable, high quality, green, low carbon emission power supply system, its importance in the construction of smart grid is indispensable.Research on optimal operation of AC/DC hybrid microgrid is in the ascendant,due to the different features between AC / DC hybrid microgrid and AC,DC microgrid, it has an important theoretical and practical significance to investigate the characteristics and interaction mechanism of distributed generations in AC/DC hybrid microgrid, grasp the laws governing the operation of the AD/DC hybrid microgrid, propose proper method for hybrid AC / DC microgrid optimal operation method. This paper focuses on optimal operation method of the hybrid AC / DC microgrid. Conceding the randomness of the output power of wind turbine and photovoltaic cell and the volatility of load, the stochastic model is built respectively. The models of microturbine, fuel cell, energy storage device and AD/DC convertor are given as well. Then the mathematical model of hybrid AC/DC microgrid is established. Based on the research of the operational characteristics of AC / DC hybrid microgrid, the cost objective function of microgrid is presented, which includes fuel cost, environmental cost, operation and maintenance cost, the cost of the power interaction between microgrid and the grid,and the conversion cost of AD/DC power. At the same time, the constraints of microgrid operation are given. Then the optimal operation model of microgrid is proposed, which transforms the problem into solving the minimum value of a nonlinear function with mixed constraints and random variables. In order to deal with the uncertainties in the optimization model, the random variables are treated by the three point estimation method and the Cornish-Fisher series expansion, and the mesh adaptive direct search algorithm is applied to solve the problem. The simulation of a hybrid AC/DC microgrid is processed, which verifies the accuracy and efficiency of the proposed method. The probability density function and distribution function of the operation cost of microgrid under different standard deviations of load are analyzed. The influence of the degree of load fluctuation on microgrid operation is clarified, provides a meaningful guidance for the microgrid operation.