Just wondering if you are overcomplicating your project?
Have you observed stiction in your project?
All the proportional hydraulic solenoid valves that I work on in earthmoving/construction machines have a steady PWM frequency and just vary the duty cycle.
I am working on controlling proportional valves for cranes and I want to dithering pwm signals. I've been researching for a while and I think dither frequency must be around %10 of main pwm signals amplitude and more than main pwm's frequency. At the end these two signals will be collected and go to the valve. Is it wrong? Or is your method more efficient?