Transient analysis of PWM-excited electromagnetic actuators

A coupled field-circuit simulation of transients in a nonlinear electromagnetic device supplied by pulse width modulation is presented. In such case, the current and magnetic flux contain periodic components. Therefore the eddy currents and losses in the conducting parts of the core are generated. An analysis of transients in the actuator and in the semiconductors of the feed system is presented. The mathematical model includes an equation of the transient electromagnetic field, equations of the converter electric circuits and equations of the supply circuits. Semiconductors are represented as nonlinear or time-varying resistors supplemented by capacitors and inductances. The algorithm enables analysis of transients with periodically changing time-step, from milli- to nanoseconds. Analysis of losses in the converter core and in the feed system is included. Numerical implementation of the algorithm is based on the finite-element method. To include nonlinearity the Newton-Raphson process has been adopted.