I would like to use an AC chopper to control a water pump (single phase induction motor). I have looked around but I can't see any existing designs/products. I see some phase angle controller boards, but not AC chopping with a PWM wave (as described in the attachments).
I could design one, but it seems to be a relatively popular technique for controlling AC motors, so I was hoping someone had already done so and I could get to building the rest of the project!
Hi MarkT, well that would be technically the best way, but very very expensive*! I think an ac chopper is sufficient for this application, and even if its not, its so cheap there is no great loss if I do need to replace it with a VFD.
*Actually thats not the only reason - this will go in an enclosure where cooling is a potential concern and all the VFDs I've seen require ventilation. The motor I will drive will be low power, so a sufficiently large heatsink on the IGBT should be sufficient for the ac chopper circuit.
To be clear, I am making the assumption that the motor in the pump is an asynchronous motor. I think this is reasonable because synchronous motors are more complex, and there isn't a need for such a motor in a common garden pump.
Was just checking - most induction motors are designed for efficient running under constant load,
trying to slide along the slip curve by undervolting is likely to lead to very poor efficency (the torque
will fall but the current increases). Worse still is the fact that this can lead to melting of the windings
if the motor is not designed with high-slip factor (heating depends on the current only). If the load
has a lot of friction the decreasing torque at lower speeds may eventually cause the motor
to stall, even more likely to melt the windings (many induction motors have a thermal fuse
buried in the windings to help prevent fire breaking out).
So you need to find out more about the characteristics of your motor before deciding if this is
a sensible approach.
V/f drives are much more likely to stay in the low-slip region (again there may be issues if
the motor is matched to the load and not designed for underspeed operation.)
sebjf:
motors]asynchronous motor[/url]. I think this is reasonable because synchronous motors are more complex, and there isn't a need for such a motor in a common garden pump.
Thats a reasonable assumption.
Synchronous motors domestically used to be used for clock mechanisms and other low power applications.
As mark said best to know more about the motor , if its commercial can you post a picture ?