基于动态磁网络法大型感应电机阻抗参数及起动特性计算

Calculation of Impedance Parameters and Starting Characteristics of Large Induction Motor Based on Dynamic Magnetic Network

为提高大型感应电机动态阻抗参数及起动特性计算的准确性及计算效率,构建了考虑电机转子转速变化引起气隙磁导变化的非线性动态磁网络模型。以一台6.5 MW大型感应电机为例,分析起动电流变化对电机内各处饱和程度的影响机理,在此基础上,根据磁力线路径及电机内饱和程度确定动态磁网络模型中的非线性磁导的计算方法。将动态磁网络模型与转子趋肤效应模型相结合,提出计及漏磁并考虑转子转速变化及饱和偏移现象的电机动态阻抗参数的计算方法。推导并建立基于转子多回路法的大型感应电机的动态数学模型,根据电机瞬态过程中的电磁耦合关系,确定动态数学模型与磁网络模型的动态耦合求解方法,提出大型电机瞬态过程中考虑电流、转速、饱和及趋肤程度变化的动态阻抗参数及起动特性的计算方法。通过与有限元计算结果及实验结果对比,验证了所提出计算方法的正确性。

Large induction motors are widely used in traction and drive applications.The accurate calculation of impedance parameters is crucial for predicting motor performance,determining the driving load,and optimizing motor design.The large induction motor has a long starting time and large current,experiencing apparent time-varying core saturation and skin effect.Current approaches,such as the magnetic network method,often neglect the nonlinearity in the magnetic permeance of the motor during the starting process,leading to inaccuracies in considering the saturation deviation caused by variable starting currents.Accordingly,the dynamic magnetic network method is proposed to analyze the electromagnetic performance of large induction motors in the transient process.Considering the influence of the saturation effect and skin effect on the motor impedance,the calculation method for motor starting characteristics is proposed,thereby improving the accuracy and efficiency of calculating dynamic impedance parameters and starting characteristics.The proposed nonlinear dynamic magnetic network model considers the air gap’s magnetic permeance variation caused by the rotor’s speed changes.The effect of the starting current characteristic on the saturation degree inside the motor is discussed.According to the magnetic field line and the saturation degree,the calculation method for nonlinear permeability in the dynamic magnetic network model is determined.Based on the dynamic magnetic network model and the rotor skin effect model,the dynamic impedance parameters are calculated by considering leakage flux,rotor speed variation,and saturation phenomena.The dynamic mathematical model of large induction motors is derived from the rotor multi-circuit method.According to the electromagnetic coupling relationship in the transient process,a dynamic coupling solution is determined to obtain dynamic impedance parameters and starting characteristics,considering variations in current,speed,saturation,and skin depth.Calculation accuracy at a lower computational cost is improved.Calculation results show that when the motor starts to reach the stable running state,the resistance increase coefficient gradually decreases from 5.517 to 1.025,and the reactance decrease coefficient increases from 0.36 to 1.Using dynamic parameters for calculating the starting characteristics of large motors improves accuracy.Compared with the traditional calculation method,the relative errors of starting torque,starting current,and maximum torque are reduced by 2.54%,0.68%,and 5.39%,respectively.Compared with the finite element method(FEM),the solution time is reduced by about 90%.The following conclusions can be drawn.The proposed method ensures accurate calculation by coupling dynamic impedance parameters and starting characteristics for large induction motors,considering the nonlinearities in the magnetic permeance during the starting process and the saturation deviation caused by the time-varying starting current.Compared to the traditional calculation method and FEM,it improves accuracy and computational efficiency,facilitating calculations for related motor types.