This is the problem, i'm designing a water pump's universal drive (3 HP Max) controlled by Arduino, so my first vision is to convert 220VAC/50Hz to DC, Then reduce the voltage by DC-DC chopper circuit, and finally use DC-AC inverter to control the frequency, and the switching is controlled by Arduino, but the problem is the output of inverter will be square wave (Not sin), which contains a lot of Harmonics.

So the question is this, how much the harmonics will affect the system??

And is it possible to design a low-pass filter(100Hz Cut-off frequency for example)for this high voltage system to reduce the harmonics?

  • \$\begingroup\$ google "magic sinewaves". \$\endgroup\$ – Harper Jul 7 '17 at 16:55
  • 2
    \$\begingroup\$ What you have described is a variable frequency drive or VFD. There are thousands of these on the market already. Why are you designing your own with so little knowledge? Have a look at some published designs first and then see if you reckon that you can understand the electronics and how you would write the software (which is highly complex). \$\endgroup\$ – Transistor Jul 7 '17 at 17:27
  • \$\begingroup\$ Why do you want variable speed for a water pump anyway? \$\endgroup\$ – Transistor Jul 7 '17 at 17:28

Electronic variable frequency drives (VFDs) have been supplied for three phase motors for about 55 years. I can name about a dozen large manufacturers that sell VFDs over a wide part of the world. There must be a dozen more that I am not as familiar with. The early designs did not have very good waveforms, but there was not a lot of difficulty with the motors. The most significant problem was with high torque at low speeds. That is something that a centrifugal pump does not require. Newer designs have better waveforms except that they use fast-switching IGBTs that generate high voltage switching transients causing motor insulation stress failures. There are several remedies for that including improved insulation in VFD rated motors.

There is much less history of using VFDs for single-phase motors. There may be only one manufacturer making VFDs for single-phase motors. Capacitor-start motors do not work with VFDs at all. Permanent-split-capacitor (PSC) and shaded pole motors will work with a single-phase VFD for centrifugal pumps and fans. It may be difficult to find information about waveform quality requirements. Centrifugal pump motors are likely be quite tolerant of extra heating due to harmonics. Since the power required to drive the pump drops drastically as the speed is reduced, the average load on a variable-speed pump is significantly less than what the motor is designed for. Therefore the extra heating can be tolerated well. Using the VFD to operate the motor at full-speed all the time would probably be the highest risk operating condition.

The VFD design must include a ramp-up circuit to avoid high starting current. A ramp-down circuit is required to prevent regeneration. Other protection circuits will also be needed.


Study industrial AC drives. They output square waves as well. But keep in mind that you are driving a highly inductive load, so plan accordingly.

  • \$\begingroup\$ So the square wave will not affect the motor's performance? \$\endgroup\$ – Mohammad Asmar Jul 7 '17 at 16:51
  • \$\begingroup\$ You should use an "inverter rated" motor. \$\endgroup\$ – Glenn W9IQ Jul 7 '17 at 16:51
  • \$\begingroup\$ I'm sorry i wasn't clear enough, the project is to make an universal drive with maximum load 3 HP for example, the drive will be connected to any water pump below the rated value of the drive. \$\endgroup\$ – Mohammad Asmar Jul 7 '17 at 17:03
  • \$\begingroup\$ I could not recommend that. \$\endgroup\$ – Glenn W9IQ Jul 7 '17 at 17:05

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