POSITION ESTIMATION IN SOLENOID ACTUATORS

This paper describes a novel method of estimating the position of a pl unger inside a solenoid. The solenoid is a single-phase variable reluc tance actuator, with a highly nonlinear magnetic circuit. For the prop osed method, position is estimated indirectly through the solenoid's i ncremental inductance in the high current region, It exploits the adva ntage that motional electromotive force (EMF) is negligible under norm al operating condition. The incremental inductance is obtained from th e rate of current rise of the pulse-width modualed (PWM) waveform, whi ch in turn, is measured by a dedicated current rise measurement circui t Position is estimated from a two dimensional look up table of increm ental inductance and current. The method is simulated and then impleme nted on a typical industrial solenoid valve. Factors which affect the accuracy of the estimation and methods of overcoming them are also des cribed in the paper.