DC motor (pump) control problem

[Houssem85]

I'm working on a project where I control the regulation of the water level in tanks from the PC via a microcontroller STM32.

My problem is this: when I am sending a low duty cycle (less than 40%) at the pump, it does not rotate! This then causes a response delay of the system so that the controller sends 100% .. The control signal of the pump thus resembles a PWM signal! 0% or 100%!

Is this problem is the circuit of the power amplifier https://www.electro-tech-online.com/attachments/power-amplifier-jpg.83626/ (I use NPN transistors instead of IGBT, ie running attack and not voltage)? Or should I define a dead zone for the pump in the program?

Is the circuit of the power amplifier has a role in this problem?

Do you have any ideas for improvement? solutions?

 

[barry]

I don't think the problem is the amplifier (assuming that with a 40% duty cycle in you get 40% out). Your motor probably needs a minimum starting current, which is not supplied at 40%. You might need to set a minimum pulse width. It would be interesting to know if it's only when you are trying to start the motor, or if the problem occurs when you are already rotating and you are slowing it down to 40%. You might also play with your controller gains. Are you using PID? PI?

 

[crutschow]

You may need to start with near 100% duty-cycle and the reduce it to the desired value once the pump has started. There likely is also a minimum duty-cycle that the pump needs to run.

 

[chuckey]

Your amplifiers have a total gain of 2.5, is this enough? I would put a diode in series with R6 (cathode to output), so output amp runs at max gain to switch between +Vcc and -.8V. I would return R8 to to output (saves more drive current for T2 base. You op-amps can swing +ve and -ve, the -ve might destroy the output transistors
If you want to control the level in the tank, you need an on/off switch, so the pump runs "flat out" until the desired level is required. If there is too much overshoot, i.e. the tank level is too high, you need a PID controller to take into account the inertia of the pump.
Frank

 

[Houssem85]

I changed this circuit and I posted a new thead. Help me please !