Proportional Valve Driver
A typical proportional valve driver consist of a H-bridge that is PWM driven. The base frequency is approx 2-5kHZ. You could use a DC motor or stepper motor driver with a chopper, to control the current.
Moreover a valve driver has also a dithering frequency, that is superimposed on DC signal. This is a nice feature that provides anti-sticking. The friction of the spool is high, then at low currents the spool got sticked, then at higher current it suddenly frees, making jerking movements. That's why a dithering is used for.