Dynamic load for 3 Phase PMSM

about 1 KW. I need a load for said test. I have a 3 phase VFD converter/controller that can control speed and torque with constant V/F ratio. Is it possible to couple an 3 phase AC induction motor (IM) driven by the VFD controller to the shaft of the PMSM and use it to load the PMSM? Let say I set the IM (load) to 1K RPM and then slowly bring up the PMSM and driver. The PMSM will act as a generator with it's back EMF charging its bridge driver bulk cap. As the PMSM driver exerts more power, will it force the IM to slip more and appear to be a load? As you can see I am not expert in this so I need more enlightenment?

Conservation of energy: that 1KW has got to go somewhere. The VFD controller might be able to absorb the power steady-state, but it might not. You could ask the manufacturer. If it has a small heat sink, it probably won't work.

One nice mechanical load is an induction motor with DC applied to its input. The rotor dissipates the power. We used to do that on reel-reel tape drives, for drag on the feed reel and fast dynamic braking.

ver of about 1 KW. I need a load for said test. I have a 3 phase VFD conver ter/controller that can control speed and torque with constant V/F ratio. I s it possible to couple an 3 phase AC induction motor (IM) driven by the VF D controller to the shaft of the PMSM and use it to load the PMSM? Let say I set the IM (load) to 1K RPM and then slowly bring up the PMSM and driver. The PMSM will act as a generator with it's back EMF charging its bridge dr iver bulk cap. As the PMSM driver exerts more power, will it force the IM t o slip more and appear to be a load? As you can see I am not expert in this so I need more enlightenment?

yeh it will probably go boom..

if not the PMSM driver from over voltage while generating then the VFD driving the induction motor, once the slip gets negative

a car dyno is usually some combination of a big metal cylinder acting as a inertial load, and a magnetic brake as a static load

I guess dc on an induction motor sorta works like a magnetic brake

or just get another identical PM motor and some big resistors

-Lasse

of about 1 KW. I need a load for said test. I have a 3 phase VFD converter/controller that can control speed and torque with constant V/F ratio. Is it possible to couple an 3 phase AC induction motor (IM) driven by the VFD controller to the shaft of the PMSM and use it to load the PMSM? Let say I set the IM (load) to 1K RPM and then slowly bring up the PMSM and driver. The PMSM will act as a generator with it's back EMF charging its bridge driver bulk cap. As the PMSM driver exerts more power, will it force the IM to slip more and appear to be a load? As you can see I am not expert in this so I need more enlightenment?

I guess that the VFDs have to have some capability of absorbing energy, to do deceleration when the induction motor is acting like a generator. Anybody know the details?

Yeah, a car alternator would be a good load. Use a big fixed power resistor load and tweak the field with a bench power supply to control torque.

Yes, most VFDs are set up for a dynamic braking resistor. Some have a small one internally, otherwise an external one can be installed. For the suggested purpose, you need a really big one, so possibly toaster or stove heating elements in series would be good. otherwise, vitreous enamel 100 or 200 W resistor elements can be used.

The problem with the VFD is it will try to control motor RPM rather stiffly, by controlling the frequency. Unless you carefully match the VFD commanded speed to the test motor's commanded speed, the braking action may be rough. Normally for a dyno, you want a fairly soft control, ie. the load applies torque to the test motor, but lets the test motor control the speed. I fear with this scheme, you may end up with the motor drive and the dyno's VFD constantly fighting, and large amounts of transient power hopping back and forth between them.

Possibly placing resistors in series between the load motor and the VFD would give the right effect.

But, an induction motor with adjustable DC injection braking, or a DC brush motor and a big variable resistor makes a great motor dyno.

Jon

They use breaking resistors.