Disturbance rejection in a current regulator for proportional electro-hydraulic valves

Solenoid current regulation is well-known and standard in any proportional electro-hydraulic valve. The goal is to provide a wide-band transfer function from the reference to the measured current, thus making the solenoid a fast and ideal force actuator within the limits of the power supplier. The latter is a Pulse Width Modulation (PWM) amplifier fixing the voltage bound and the Nyquist frequency of the regulator. Typical analogue regulators include three main terms: a feedforward channel, a proportional feedback channel and the electromotive force compensation. The latter may be accomplished by an integrative feedback. Here the problem is faced through a model-based design (Embedded Model Control), on the basis of a wide-band embedded model of the solenoids which includes the effect of eddy currents. To this end the model must be identified. The embedded model includes a disturbance dynamics capable of estimating and correcting the electromotive contribution together with parametric uncertainty, variability and state dependence. The embedded model fed by the measured current and the supplied voltage becomes a state predictor of the controllable and disturbance dynamics. The control law combines reference generator, state feedback and disturbance rejection to dispatch the PWM with the appropriate duty cycle. Modeling, identification and control design are outlined together with regulator performance.