Stability Analysis and Control of Hybrid Microgrids

The principal methodology of this thesis is to use voltage against active power to regulate voltage and track power under constant frequency. The frequency is fixed with the phase-locked loop. In this method, the frequency is fixed at a certain value, and only the power and voltage are regulated by specific algorithms and parameters, which greatly reduces the mutual perturbation of parameters and simplifies the calculation. The frequency-power interaction in the traditional technical barrier is greatly avoided, also simplifying the calculation and retaining reasonable control effect. This method makes active power equally produced by power generation. When all loads are switched on and off, the sources will supply power synchronously, distributing power to satisfy all linked loads. MATLAB/Simulink simulation and hardware experiment results prove the feasibility and stability of the proposed control method. The reactive power balance is satisfied by proportional tracking and residual compensation. Reactive power tracking prioritizes the grid-supporting generations to reach a specific proportion, the rest compensated by grid-forming generations. The reactive power tracking of this method is also adapted according to the different system structures. This thesis also contains the optimized Kalman filter, the two-level hierarchical small signal model construction, the various stability analysis, and the coefficient influence study. In terms of accuracy, this thesis makes a detailed comparison with the traditional method in terms of response time, overshoot, transient oscillation, steady-state error, THD, spectrum diagram, bode diagram, and other aspects. The system can quickly respond to setpoint when switching the system topology, during the initial startup, and the switch is turned on and off. This thesis solves different types of problems occurring in the hybrid microgrid control systems, such as systematic modeling, parameter optimization, resonant peak attenuation, active power precise control, reactive power compensation, and hybrid grid stability identification. The significance of this study is to promote technological progress in the field of renewable energy, especially for the analysis and use of different microgrid models in the case of future system expansion. It fills the gap that there is no comprehensive and concise control method in previous research and makes the future design more convenient. Compared with the traditional methods, the advantages of this method mainly lie in a small amount of calculation and fast operation under the condition of the same control effect. Also, there are still some problems to be solved, such as reactive power matching, supplier priority selection, transmission line loss, circuit protection, and parameter initial selection