Application of orthogonal dq components and positiveegative sequence components in simutation of induction motor with an asymmetrical start-up system

摘要

Description of an induction machine with asymmetrical starting system in a rotor short-circuited in a cycle; symmetric step, two asymmetric steps, is presented. Physical equations were transformed by introducing for stator an orthogonal axis system co-rotating with the rotor. Two types of motor models with asymmetric resistor starter were presented, for transient and steady-state simulation. In the latter case, additional dependences were introduced, which enable to determine positive and negative sequence components of rotor current, stator currents induced by counter-rotating rotor fields as well as torque components with oscillating torque amplitude. Short-circuiting of neutral points of the winding and the starter was significant assumption in formulation of equations of the rotor with asymmetrical resistor starter. This way a zero sequence component was introduced to phase currents. Taking into account idealising assumptions as infinite magnetic permeability of magnetic core and mono-harmonic field distribution, the zero sequence component doesn't influence the electromagnetic torque. The physical rotor currents are obtained by deducting the zero sequence component from computed currents. As an example, results of start simulation (static characteristic) of 1000 kW motor are shown. Real rotor phase currents are compared to currents which result from adopting so called equivalent resistance of asymmetric steps.