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 e.m.f. is negligible under normal operating conditions. The incremental inductance is obtained from the rate of current rise of the 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.