Research On Power Comodulation Control Of Bidirectional AC/DC Converters In AC/DC Hybrid Microgrid

Aiming at the bidirectional AC/DC converters in ac-DC hybrid microgrid,this paper studies a bidirectional droop control strategy based on model prediction algorithm to suppress the power fluctuation of the system and improve the power coordination control ability of the system as the main control objective.Based on the power mutual aid of micro-power supply,battery and bidirectional AC/DC converter,specific coordinated control strategies under different working conditions are analyzed and simulated.The specific contents of the paper are as follows:This paper first describes the research background and significance,introduces the basic structure,mathematical model and research status of hybrid microgrid and bidirectional AC/DC converter,and summarizes the application status of droop control strategy and model prediction algorithm in bidirectional AC/DC converter.Then the mathematical models of photovoltaic,wind turbine and battery are established,the basic control mode is studied,and the operation characteristics are simulated and verified.Secondly,the power fluctuation of the hybrid microgrid is suppressed,the dynamic response speed of the system is improved,and the power coordination control is realized.For bidirectional AC/DC converters,a control strategy combining model prediction algorithm and bidirectional droop is adopted in this paper.The core of the control strategy is to replace the current inner loop in the traditional bidirectional droop controller with model prediction algorithm.Through the current reference value obtained by bidirectional droop and power loop control,the output state of the converter at the next moment is obtained by the predictive algorithm,and the optimal path selection is realized by the cost function.The control can shorten the time to return to steady state after voltage and current fluctuation and speed up the dynamic response of the controller.It effectively reduces the harmonic distortion rate of current,achieves accurate power transmission between subnets,and makes full use of distributed energy.In this paper,the control strategy is analyzed theoretically,the mathematical models and controllers of the bidirectional sag outer loop,power loop and model prediction inner loop controller are established,and the cost function is established.Then,in the same working condition,the traditional current inner loop using PI controller and the controller using model prediction inner loop are simulated and compared,the results show that the control strategy has better dynamic performance than the traditional current inner loop.Then,in order to realize the power coordination control of ac-DC hybrid microgrid,based on the active power reference value obtained by bidirectional sag control,this paper analyzes the power coordination control strategy under different conditions of parallel off-grid.When connected to the grid,the frequency of the microgrid is always consistent with that of the large grid.Considering the dc bus voltage and its rating value,the hybrid microgrid is divided into three operating conditions.In off-grid condition,according to the reference value obtained by bidirectional sag control,it can be divided into three operating conditions,namely rectification and inverter.The mutual-aid and coordinated control of each micropower source in the hybrid microgrid is analyzed under each working condition,and the specific coordinated control strategy is studied.Finally,the overall simulation model of AC-DC hybrid microgrid is established.In two operating modes,the bidirectional droop control strategy based on model prediction algorithm and the coordinated control strategy of each working condition are adopted and verified in MATLAB software.Simulation shows that the output power of both micro power source and load changes,the control strategy can fast accurate control of power between subnets two-way flow,effectively reduce the system steady-state error and current harmonic distortion rate,improve the voltage and frequency fluctuations used time back to the steady state,realize the stability of the mixed micro network running.