I am attempting to control the current through a generator rotor by adjusting PWM input to a DC to DC solid state relay (SSR), specifically a TWTADE SSR-40DD.
The power supply for the output side of the SSR is 20VDC. The input side of the SSR is an ESP32 microcontroller. I have verified that the output voltage (with the rotor disconnected) on the SSR is what is expected according to PWM input.
With the rotor connected to the output side of the SSR, when I set the SSR input to 100% duty cycle, the output through the rotor goes to 2A which is expected and great. However at anything less than 100% duty cycle, the current passed through the rotor drops precipitously. I would like to be able to smoothly control the time-averaged rotor current from 0A to 2A, but instead the current goes from 5mA gradually to about 30mA then jumps to 2A at about 100% duty cycle.
The rotor tests at 10 Ohms and 2.2 H inductance. I have varied the PWM input pulse frequency over a wide range (60 Hz to 6000Hz) and the results on the output are only slightly different.
When I was using an L298N motor controller instead of the SSR, I was able to modulate the current through the rotor quite well. This is also PWM output. However the L298N does not have as safe a power output margin as the SSR, so that is why I tried to replace it with the SSR.
Why can't the SSR modulate a time-averaged current through the rotor with PWM input?