Study On Robust Droop Control And Its Stability Problem In Microgrid

With the increasingly prominent and other energy and environmental issues, distributed generation technology continues to evolve. The traditional power system of electricity production, transmission and distribution gradually changes, and microgrid and its interface technology more widely applied. Thus, the permeability of variable distributed micro-source increasingly boosts, and power electric devices are widely applied in electronic network. However, compared with traditional power grid, microgrid has many differences, including diversity of micro-source type and its operation mechanism, control strategy or operation model and so on, which have result in a series of new problems and restricts the development and application of micro-grid energy technologies.In this paper, according to the problem of that how to improve the power sharing of micro-grid among micro-sources, the droop proposed robust control strategy based on local signal is proposed. Then, to verify the validity of the method, simulation and experiment are all carried out. In addition, on account of the new proposed control strategy-robust droop control method, the analysis of static ability of the micro-grid based on bifurcation theory, including microgrid stability region and its impact factor, is carried out. What is more, the transient stability of microgrid based on the principle of the transient energy function is also studied. And specific studies are as follows:(1) For the problem of microgrid power sharing, the traditional droop control and other improved control strategy including strengths and limitations are analyzed, and a robust droop control strategy based on local signal is proposed. Then, a power sharing degree model of the robust droop control with influence factors is established. Finally, to verify the correctness and effectiveness of the proposed strategy, simulation is carried out in PSCAD/EMTDC.(2) According to analytical method of static stability based on bifurcation theory, the differential-algebraic equations (DAE) of robust droop control is structured to obtain equilibrium solution and bifurcation point in Macont. At the same time, the influence of various factor on static stability region of microgrid is analyzed in detail.(3) Meanwhile, for microgrid system controlled by robust droop strategy, the transient energy function model based on transient stability analysis using energy function is established in a inertial system. Then, through simulation and analysis in PSCAD/EMTDC, the results reveals the relationship between energy function and transient stability of microgrid. Following, the mechanism and influence factor of transient instability of a microgrid controlled by robust droop control are draw.(4) The design of robust droop control microgrid hardware-in-the-loop (HIL) based on RT-LAB is illustrated. After testing this HIL device, it can be seen from the experimental results that the robust droop control strategy can enhance the capacity of the power sharing among micro-sources. At the same time, voltage drop rate can be reduced, too. Hence, the robustness of voltage of microgrid is improved, which verifies the effectiveness of proposed control strategy.