Position estimation in solenoid actuators

This paper describes a novel method of estimating the position of a plunger inside a solenoid. The solenoid is a single-phase variable reluctance actuator, with a highly nonlinear magnetic circuit. For the proposed method, position is estimated indirectly through the solenoid's incremental inductance in the high current region. It exploits the advantage that motional electromotive force (EMF) is negligible under normal operating condition. The incremental inductance is obtained from the rate of current rise of the pulse-width modulated (PWM) waveform, which in turn, is measured by a dedicated current rise measurement circuit. Position is estimated from a two-dimensional look-up table of incremental inductance and current. The method is simulated and then implemented on a typical industrial solenoid valve. Factors which affect the accuracy of the estimation and methods of overcoming them are also described in the paper.