| With the continuous improvement of industrial production level,electric motors are widely used in various fields of industrial production and become the main equipment of large power grid with energy consumption.The motor has a large inrush current at startup,which will cause the voltage amplitude of the grid to drop,and the power factor is very low during the operation of the motor,and will be even lower at light load or no load.In this paper,we study the motor motion model and reactive power compensation mechanism,and investigate the cascade SVG control strategy with the background of the operation of high-power crushing motor in the scrap steel processing line of Masteel Chengxing Company.First,based on the amplitude-phase motion model,the nature of motor instability and its influence on grid stability are analyzed.According to the amplitude and phase motion model of the asynchronous motor,the stable operation criterion of the motor under the condition of internal and external disturbances is deduced.Combined with the dynamic idea,the nature of the motor instability under different disturbance conditions and the influence on the stability of the power grid are more clearly recognized.Based on this,a reasonable and effective solution is proposed,that is,the use of cascaded SVG to compensate the motor on-site reactive power.Finally,it is proved from the perspective of impedance that the system impedance can be increased and the system stability can be improved when SVG is put into the system.Second,based on the model prediction algorithm,the reactive current tracking,DC side voltage fluctuation and modulation strategy of cascaded SVG are studied.(1)The problem of timely tracking control in model predictive control is analyzed when the system changes or is disturbed.In order to obtain better model predictive control parameters,an ant colony algorithm(ACO)is designed to improve model prediction(MPC).A cascaded SVG control strategy based on ACO-MPC control is presented.(2)Using model prediction to track reactive current tracking,in order to avoid the delay caused by sampling,duty cycle update,etc.,a multi-step prediction method is adopted,and the dependence of the model prediction algorithm on the model is considered.The Romberg anti-jamming observer is used to improve the system robustness.(3)When controlling the DC side voltage,a zero-sequence voltage injection method based on model prediction is proposed,and the boundary conditions of the zero-sequence voltage are set,which can effectively avoid overmodulation while realizing the voltage equalization between phases and phases.Third,take the power quality problem caused by motor operation in the reconstruction project of Maanshan Iron and Steel Chengxing Company’s scrap steel crushing production line as the research background,calculate the reactive power compensation capacity and the parameters of the main components of SVG,and compare and analyze the power quality of the production line before and after the SVG is put into operation.The results show that the cascaded SVG has good dynamic compensation performance in the starting process of high-power motors and under different load conditions,and can accurately compensate the reactive power required for motor operation in a very short response time.After compensation,the system power factor The highest can reach 0.98,which improves the power quality of the power supply system of the production line and reduces the energy consumption of the enterprise. |
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