High Voltage 3-Phase Motor Drivers to drive single phase motor


I have the idea of using MOSFET 3 phase driver like this:


but program the PWM to control single phase motor with only 2 pair of MOSFET. Is that only possible ?



Which motor?

120v single phase 1/2 hp

Probably cant PWM a 120V ac motor..... they have start and run capacitors that wont like the PWM. Even if does work, you loose the cooling and fry the motor.

You cannot control the speed of an AC single phase motor in any useful manner.

Tesla invented the polyphase AC system for sound reasons - as single phase provides no rotational vector.

If you need variable speed at 1/2 horsepower, regardless of the load being variable or constant torque in nature - you need a 3 phase motor induction motor and an industrial drive. 230 volt single phase in, 3 phase out AC drives are as common as dirt and not much more money. Everybody makes them.

Those Saken parts may have a place somewhere but without a doubt, it is the strangest motor control topology I’ve ever seen for what has been long considered a standard, plain vanilla application for a six device IGBT bridge. Two modules, three output phase capacitors in addition to a bus capacitor is not a better mousetrap.

Don’t kid yourself, building an AC drive is very difficult. Not to mention dangerous for the unskilled in such matters. You need to be smart about this and buy working hardware. Don’t think for a second that just because “There’s a module for that” you can put the pieces together and have it work.

Designing variable frequency drives is above your pay grade. Mine too.

Shaded-pole or capacitor run induction motors are tuned to a given frequency - though people do some
speed control on shaded-pole motors by switching windings for multi-speed fans, its a very inefficient
way to do things (the motor wastes a lot of heat in the slow settings)

If you've a single winding shaded pole motor there's not much you can do (getting it wrong
may easily cook the windings). With two windings and a phasing capacitor it may be possible to
treat as a 2-phase motor (if the windings are equivalent) and use V/f control (don't know if this
is done really).

3-phase induction motors are the ones you can control flexibly, but you still have to watch out for
cooking them (slow speed means no effective fan cooling unless there's a separate fan motor).

3-phase induction motors are the ones you can control flexibly, but you still have to watch out for
cooking them (slow speed means no effective fan cooling unless there’s a separate fan motor).

Not so, unless you want to become pedantic about it. I routinely encounter large ducted fan systems that utilize standard motors with no external cooling means. Large I define as up to about 200kw.

General purpose motors (totally enclosed or open drip proof, internal fan cooling*) can be used for variable torque loads (fans and centrifugal pumps) since low speed operation requires little to no torque. The most important aspect of VFD operation is that the motors must be built with insulation systems that can withstand the additional voltage stresses created by the VFD. All modern motors are built to NEMA MG1, part 31 which meets these requirements, there is of course an equivalent IEC/EN spec, I just don’t remember it off top of my head. Motors built before perhaps 1990 could be suspect, back before AC drives were common place.

In lower power ranges (<50kw), there is a common range of motors today that can run full torque, zero speed without additional, external cooling. Known as “Vector Duty” or other catchy marketing terms, these motors can handle constant torque applications with 2000:1 speed ranges without concern of overheating. The design takes into account the expected temperature rise at full ambient by employing a combination of higher temperature insulation systems as well as the motor body growing more surface area by way of additional fins.

One example (and no, I have no connection to this company):


  • = internal, shaft mounted fan blade

(edit: added internal fan note)