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Beginners / Re: Powering DC Motor from Solar panel
« Last post by Siwastaja on Today at 08:28:02 am »I don't think any sensible amount of electrolytic capacitors would help at all. In 30-second timescale, supercapacitors and batteries are the only sensible energy storage options, and if they are banned, then the 30-second "charge" time is a red herring. This leaves you running the motor in realtime by whatever amount of light is produced at that very moment.
You definitely could do maximum power point control directly to the motor, then only modest amount of capacitance in parallel with the PV panel is needed, basically to satisfy the ripple current need of the buck input. When I say buck, I just mean a half-bridge driving the motor; the motor itself is the inductor, and the motor RPM (back-EMF voltage) is equivalent to output "capacitor".
It doesn't need to be an actual maximum power point tracking algorithm, even just constant input voltage control would be an improvement over direct connection of the motor.
You see, if you directly connect the motor, then maximum motor current will be just the short circuit current of the panel, slightly more than I_mpp. On the other hand, if you run the panel at I_mpp at V_mpp, and buck down for the motor (again, motor winding itself does the job of the inductor), then motor current can be many times higher than I_mpp. Since power is conserved in a switching converter (which motor controller is), e.g. 10V * 1A input can provide 1V * 10A output for the motor - minus losses of course, so maybe 1V * 9A in reality.
Does this make a lot of difference, I don't know. Maybe in a boat, even with unoptimal low-speed torque, the motor pretty much accelerates near maximum speed in split second anyway, because there is little inertia, and the work done by the rotor kinda quadratic to RPM, so there is not much mechanical load at low speed anyway. In a car things would be pretty different; higher motor current during the first few seconds would give you better acceleration.
You definitely could do maximum power point control directly to the motor, then only modest amount of capacitance in parallel with the PV panel is needed, basically to satisfy the ripple current need of the buck input. When I say buck, I just mean a half-bridge driving the motor; the motor itself is the inductor, and the motor RPM (back-EMF voltage) is equivalent to output "capacitor".
It doesn't need to be an actual maximum power point tracking algorithm, even just constant input voltage control would be an improvement over direct connection of the motor.
You see, if you directly connect the motor, then maximum motor current will be just the short circuit current of the panel, slightly more than I_mpp. On the other hand, if you run the panel at I_mpp at V_mpp, and buck down for the motor (again, motor winding itself does the job of the inductor), then motor current can be many times higher than I_mpp. Since power is conserved in a switching converter (which motor controller is), e.g. 10V * 1A input can provide 1V * 10A output for the motor - minus losses of course, so maybe 1V * 9A in reality.
Does this make a lot of difference, I don't know. Maybe in a boat, even with unoptimal low-speed torque, the motor pretty much accelerates near maximum speed in split second anyway, because there is little inertia, and the work done by the rotor kinda quadratic to RPM, so there is not much mechanical load at low speed anyway. In a car things would be pretty different; higher motor current during the first few seconds would give you better acceleration.
I'll have another look, it took me several attempts to trace that one
