Hi everyone! The solution is not so simple. Why? because proportional valves have a very ugly tendency to heat terribly. Therfore chopping the supply voltage with a given duty cycle will not give a reproducible current. Furthermore, you have to do something with the magnetic hysteresis of the valve which may produce up to 50% error on flow. The easiest solution is to buy a driver on the market. They all have at least two buttons where you can set the gain and offset values. It costs around $50 to $200 depending where you buy it. Otherwise, you may spend 3-6 months before you have the working solution. (By the way, Bosch has also a driver)