| In real life,we usually use the diesel generator or gas turbine to provide power to the remote islands,such as isolated islands or drilling platforms.However,the transmission efficiency is not high,which leads to the safety of the power supply system can not achieve the desired results.Therefore,it is safer and more reliable to supply power to the passive network through the large power grid.HVDC transmission system based on modular multilevel(MMC-HVDC)is a new type of flexible DC power transmission mode,voltage source converter with shutdown device can realize self commutated converter,this structure has advantages of flexible operation and high density in the case of transmission,can solve the above the problem,so the use of voltage source converter is very suitable for supplying power to passive networkThis paper first describes the background and significance of the research and research status at home and abroad,and the traditional two levelconverter and clamped multilevel converter is modular multilevel converter(MMC)technical performance is more ideal,and the functional properties of all the many advantages of the MMC is more suitable for the high voltage of HVDC system in practical engineering in china.Then the paper studies the MMC-HVDC system structure,operation mechanism,characteristics and control methods,introduces the modulation mode for MMC,focusing on the NLM(the nearest level),and NLM is selected as the suitable modulation strategy.Then established the mathematical model of MMC-HVDC system in maintaining stable AC voltage when,on the model of the control strategy of the MMC-HVDC system and design the corresponding controller from the converter control strategy and the two aspects of valve level control strategy,the steady state operation of passive network access control strategy at that is,the access network side passive MMC with constant AC voltage control and constant frequency control system,side MMC by DC voltage control and constant reactive power control.Then a detailed study of the principle,structure and different types of fuzzy control,and compared the difference between fuzzy control and fuzzy adaptive control,fuzzy adaptive control can compensate for the defects of general fuzzy control rules is not perfect or rough.In this paper,the fuzzy adaptive PI controller is designed by combining fuzzy control with PI control,and the fuzzy adaptive PI controller is applied to the outer loop controller of MMC-HVDC inverter which is connected to the passive network Built in PSCAD access network MMC-HVDC system model of passive adaptive fuzzy PI control based on the steady state and fault conditions are simulated,the results prove the effectiveness of the proposed control strategy,the MMC-HVDC can access network passive response and good anti-interference performance and dynamic verification for the improvement of the overall performance of the system,a fuzzy adaptive PI controller has very practical feasibility. |
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