ECM Motors

[Mike01]

Trying to wrap my head around the ECM motor technology with the increased use wanted to reach out to some of the Forum motor guys and get some thought or links to some good reference material related to ECM motors advantages / disadvantages for example it appears from what I have been able to find is that these motors can create increased THD, have trouble with any temporary voltage variations and are not able to catch spinning loads, and inability to to be controlled by an external building management system due to the pre-programmed integral controls. I can see where these may have their place and would be beneficial because of the energy savings / increased efficiency and they seem to be popping up more and more just trying to learn as much about this I was able to locate a lot of mechanical information but not as much electrically figured this would be the best place to start. Thanks!

 

[Jraef]

Phew... the lack of punctuation made that tough to read...

ECMs (Electronically Commutated Motors) are used primarily by HVAC OEMs that must meet stringent Energy Efficiency Ratio (EER) requirements in order to get their equipment certified by someone like Energy Star or when a building is going for LEED ( Leadership in Energy and Environmental Design) certification. Think of an ECM as a motor with it's own built-in VFD right on the motor itself. It not EXACTLY the same, but from our standpoint, that's what is equates to: the power fed to it is usually single phase, then internally the electronics convert it to DC to run the permanent magnet motor very efficiently. The electronics and the fact that it is a PM motor add significantly to the cost, so it only makes economic sense when compared to the alternatives, and/or when getting that EER rating is a necessity. The concept of a VFD built into the motor has been around for a long time, but didn't catch on because the VFD must be kept cool and the motor produces heat, so on the surface, the concept seems to not make sense. But in HVAC machinery where the motor is on a direct drive fan and the cool air is going over the fan and motor all the time, it can work. That's why you only see ECMs in that type of equipment.

ECMs are always capable of running the motor at any speed, but often don't have a separate "analog input" to make it do so from an outside signal. But because they are almost ALWAYS used in HVAC OEM machinery, they typically build-in either a proprietary communication system for whatever piece of equipment it is mounted in, or it has a common Building Management System (BMS) open protocol communication capability, such as BACNet or LonWorks.

Yes, they add harmonics, just like any power electronics does, so you can't really compare them to regular fan motors running across-the-line, the only fair comparison is with VFD controlled motors and they are basically identical in terms of harmonics. Whether or not harmonics is a problem has everything to do with the total installation and whether or not the Engineer decided if it was enough to worry about and if so, what they are going to do to mitigate it. Unfortunately some engineers do not know enough about it and ignore the issue altogether, that's when it can be problematic after the fact.

 

[paulengr]

Harmonics only matters if current TDD (not THD) gets high in which case voltage THD is an issue. This only happens if the harmonic loads are the majority of the load on a transformer and it is the only load. It is very easy to measure current harmonics but it is rarely a big deal. If you are that close chances are the transformer is too small regardless.

The big issue with ECMs is they can be tough to troubleshoot and repair/replace because everything is proprietary and HVAC manufacturers regularly revamp their product lines. I’ve had some success repairing but it’s expensive and not easy. It’s so bad that some customers just give up and convert to more standardized versions.

We are missing a NEMA MG-1 for these. If we had one they would be much more popular as servo motors as well.

 

[__dan]

ECM motors have similarities with AC synchonous and DC motors. They have high starting torque and good torque at low speed like DC motors, and have great variable speed control. The armature or rotor is probably DC magnets, with variable frequency drives for the field coils. They are made for variable speed and will take over the market for some applications.

The small hydronic circulators, Taco Bumblebee, Viridian, the initial products are made for plumber snap in replacements, so no field wiring except for the power cable. Very hard to find one that has 0 - 10V input, but they have built in delta P, delta T control. Ist or 2nd generation products, still very new. There circs can also get good rebate money if your utility has that in the program.

When the market matures, I'm sure these units will be available with 0 - 10 V input or network connection. For now, the early market versions are for plumbers to direct replace the Taco 007, without any field wiring to remote sensors or a BAS. ECM type will take over the market for variable speed applications, it's just a matter of time.

 

[kwired]

Phew... the lack of punctuation made that tough to read...

ECMs (Electronically Commutated Motors) are used primarily by HVAC OEMs that must meet stringent Energy Efficiency Ratio (EER) requirements in order to get their equipment certified by someone like Energy Star or when a building is going for LEED ( Leadership in Energy and Environmental Design) certification. Think of an ECM as a motor with it's own built-in VFD right on the motor itself. It not EXACTLY the same, but from our standpoint, that's what is equates to: the power fed to it is usually single phase, then internally the electronics convert it to DC to run the permanent magnet motor very efficiently. The electronics and the fact that it is a PM motor add significantly to the cost, so it only makes economic sense when compared to the alternatives, and/or when getting that EER rating is a necessity. The concept of a VFD built into the motor has been around for a long time, but didn't catch on because the VFD must be kept cool and the motor produces heat, so on the surface, the concept seems to not make sense. But in HVAC machinery where the motor is on a direct drive fan and the cool air is going over the fan and motor all the time, it can work. That's why you only see ECMs in that type of equipment.

ECMs are always capable of running the motor at any speed, but often don't have a separate "analog input" to make it do so from an outside signal. But because they are almost ALWAYS used in HVAC OEM machinery, they typically build-in either a proprietary communication system for whatever piece of equipment it is mounted in, or it has a common Building Management System (BMS) open protocol communication capability, such as BACNet or LonWorks.

Yes, they add harmonics, just like any power electronics does, so you can't really compare them to regular fan motors running across-the-line, the only fair comparison is with VFD controlled motors and they are basically identical in terms of harmonics. Whether or not harmonics is a problem has everything to do with the total installation and whether or not the Engineer decided if it was enough to worry about and if so, what they are going to do to mitigate it. Unfortunately some engineers do not know enough about it and ignore the issue altogether, that's when it can be problematic after the fact.

Don't know if it is by nature or if they specially design them so - but when I see them on HVAC air handlers they are a very quiet motor compared to a general purpose three phase motor driven by a VFD.

 

[synchro]

The small hydronic circulators, Taco Bumblebee, Viridian, the initial products are made for plumber snap in replacements, so no field wiring except for the power cable. Very hard to find one that has 0 - 10V input, but they have built in delta P, delta T control. Ist or 2nd generation products, still very new.

I had my boiler replaced a a few months ago and the two new circulators are Grundfos Alpha ECM units.
The autoadapt mode seems to work very well for determining a good operating point for the system.
They're significantly more efficient and quieter than the Bell & Gossett pumps they replaced.

ALPHA2 15-55, North America

ALPHA2 15-55 is a high-efficiency ECM variable speed circulator designed for a variety of heating and hot-water recirculation applications. The pump features AUTOADAPT and constant-pressure control modes.

product-selection.grundfos.com

 

[Mike01]

First I apologize for the lack of punctuation not an English major but will attempt to do better here.

With that I did find some information from ABB [ https://new.abb.com/docs/librariesp..._ecm_30toptips_ebook_v3.pdf?sfvrsn=cf0ec313_2 ]. They bring up some interesting points.

Until recently I have only seen these used as described small, single phase installation typically in a small split system for a communications room cooling setup.

However with that recently I have seen these on three phase pump applications [in the last few weeks actually] and thought this was odd so started to dig into this a little more and where I found the ABB reference [thanks google] and figured this would a good place to follow up and turns out it is.

 

[kwired]

First I apologize for the lack of punctuation not an English major but will attempt to do better here.

With that I did find some information from ABB [ https://new.abb.com/docs/librariesp..._ecm_30toptips_ebook_v3.pdf?sfvrsn=cf0ec313_2 ]. They bring up some interesting points.

Until recently I have only seen these used as described small, single phase installation typically in a small split system for a communications room cooling setup.

However with that recently I have seen these on three phase pump applications [in the last few weeks actually] and thought this was odd so started to dig into this a little more and where I found the ABB reference [thanks google] and figured this would a good place to follow up and turns out it is.

conventional three phase motor design doesn't need to utilize the ECM design, just needs three voltages that are 120 degrees apart and vary frequency/voltage to vary speed.

Or is whatever you mentioned being supplied by three phase, but gets rectified then goes through ECM controller and motor? In that case I'd call the setup somewhat equivalent to having a brushless DC motor.

 

[__dan]

With that I did find some information from ABB [ https://new.abb.com/docs/librariesp..._ecm_30toptips_ebook_v3.pdf?sfvrsn=cf0ec313_2 ]. They bring up some interesting points.

Nice link, gives some insight into ABB's take on it.

The super application for ECM motors is small single phase loads that need variable speed. The part load efficiency of the load machinery, hydronic circs, minisplit compressors, fans, is a lot better when you take into account the entire equipment as a whole operating at a low maintanance output (and holding setpoint) instead of cycling on off to meet demand, when it needs to run but full output is too much. ECM gives you the option of running the equipment for a longer on runtine at a reduced output to match demand. The demand matching function or feature is what you cannot get from small single phase motors (that also have less torque at starting and weak torque at low speed. Variable speed and good torque delivery at low speed is hard to do with single phase.

The exception to this is the series connected universal AC/DC motor, a DC motor with the field and armature series connected to run on AC. This unit has brushes and is a common corded power tool motor. The DC motor design gives it high torque at starting, good torque at low speed, and good speed control with voltage changes.

The killer app for ECM's is to compete with the series connected brushed AC/.DC motor, where you have to have the speed control, to take advantage of the great part load effeciency. Brushless cordless tool motors, I would guess are in the same family as a Taco Bumblebee.

You can get them in 7.5 hp and above but you're probably looking at a servo drive motor in that size. Super Expensive motor and special drive combo, position encoded motor, probably out of reach costwise for most applications. The three phase motor with drive is the very successful economical choice, when you get into the size range of typical three phase equipment.

 

[winnie]

Jraef did a great job of explaining why an ECM is different from a permanent magnet synchronous motor driven by a VFD.

However I have to wonder if, as the market for such motors expands, if the marketing folk will muddy things by saying that every integrated system that has a motor and power electronics contains an ECM.

A conventional 3 phase induction motor fed by a VFD is a motor using electronic commutation. Clearly not what we currently call an ECM but words get slippery when people want to sell stuff.

Jon

 

[paulengr]

Don't know if it is by nature or if they specially design them so - but when I see them on HVAC air handlers they are a very quiet motor compared to a general purpose three phase motor driven by a VFD.

You will notice newer VFDs will sound much quieter especially with how they are run. The older VFDs run with a “scalar” output. Basically it switches the outputs on or off on a fixed timing schedule. So you are literally hearing the program running which makes it resonate. The past cure was to randomize the switching times a bit. Now VFDs are using space vector mode which naturally sounds more like a white noise hiss. Same sound level but much less noticeable.

 

[kwired]

You will notice newer VFDs will sound much quieter especially with how they are run. The older VFDs run with a “scalar” output. Basically it switches the outputs on or off on a fixed timing schedule. So you are literally hearing the program running which makes it resonate. The past cure was to randomize the switching times a bit. Now VFDs are using space vector mode which naturally sounds more like a white noise hiss. Same sound level but much less noticeable.

ECM's I seen on HVAC blowers make no noticeable sound for the most part, unless maybe you have really good hearing. The driven blower itself makes more noise than the motor so you don't hear any motor sounds.

 

[paulengr]

Nice link, gives some insight into ABB's take on it.

The super application for ECM motors is small single phase loads that need variable speed. The part load efficiency of the load machinery, hydronic circs, minisplit compressors, fans, is a lot better when you take into account the entire equipment as a whole operating at a low maintanance output (and holding setpoint) instead of cycling on off to meet demand, when it needs to run but full output is too much. ECM gives you the option of running the equipment for a longer on runtine at a reduced output to match demand. The demand matching function or feature is what you cannot get from small single phase motors (that also have less torque at starting and weak torque at low speed. Variable speed and good torque delivery at low speed is hard to do with single phase.

The exception to this is the series connected universal AC/DC motor, a DC motor with the field and armature series connected to run on AC. This unit has brushes and is a common corded power tool motor. The DC motor design gives it high torque at starting, good torque at low speed, and good speed control with voltage changes.

The killer app for ECM's is to compete with the series connected brushed AC/.DC motor, where you have to have the speed control, to take advantage of the great part load effeciency. Brushless cordless tool motors, I would guess are in the same family as a Taco Bumblebee.

You can get them in 7.5 hp and above but you're probably looking at a servo drive motor in that size. Super Expensive motor and special drive combo, position encoded motor, probably out of reach costwise for most applications. The three phase motor with drive is the very successful economical choice, when you get into the size range of typical three phase equipment.

That’s exactly what it is. Brushless DC.

Brushed DC was THE variable speed workhorse for about a century. Then AC VFD blew away a lot of it because of the high maintenance costs and some efficiency issues. Two things have changed. On the small end we can use rare earth magnets and build super efficient brushless DC. But we can’t scale this up because of the magnet cost. That’s where we see brushless DC exciters that convert AC or DC from a second exciter field into AC on the exciter armature coils then back to DC via diodes to feed the rotor.

The two other technologies “waiting in the wings” are salient pole and reluctance motors. Both have the property that they are entirely magnetic...no currents on the rotor and no magnets at all. Both are inherently synchronous motors, ideal for VFD. Reluctance motors in particular actually use a standard AC stator. Efficiency is very high with both of them, and salient pole especially scales up well. Salient pole generators have been used in large turbines and other places for years. Reluctance seems to be limited on the low and high end for now.

Not mentioned is wound rotor. These are used in wind mills now. Put a slip ring system in a rotor but it’s 3 phase AC, not DC (synchronous). In fact synchronous motors often start as wound rotors. The normal use for wound rotor is to put resistance on the rotor to adjust torque. But if you drive it with a VFD you get a doubly fed motor...twice the torque in the same volume. Which is the big advantage for wind mills where reducing mass a couple hundred feet in the air on top of a narrow tower is a huge cost advantage.

There is no doubt that over time induction motors will be displaced by better designs first in niche markets then eventually elsewhere. 30 years ago if you wanted to put in a VFD over 10 HP instead of a shunt wound DC drive I’d say you were an idiot. Today that has flipped almost 180 degrees.

 

[kwired]

That’s exactly what it is. Brushless DC.

Brushed DC was THE variable speed workhorse for about a century. Then AC VFD blew away a lot of it because of the high maintenance costs and some efficiency issues. Two things have changed. On the small end we can use rare earth magnets and build super efficient brushless DC. But we can’t scale this up because of the magnet cost. That’s where we see brushless DC exciters that convert AC or DC from a second exciter field into AC on the exciter armature coils then back to DC via diodes to feed the rotor.

The two other technologies “waiting in the wings” are salient pole and reluctance motors. Both have the property that they are entirely magnetic...no currents on the rotor and no magnets at all. Both are inherently synchronous motors, ideal for VFD. Reluctance motors in particular actually use a standard AC stator. Efficiency is very high with both of them, and salient pole especially scales up well. Salient pole generators have been used in large turbines and other places for years. Reluctance seems to be limited on the low and high end for now.

Not mentioned is wound rotor. These are used in wind mills now. Put a slip ring system in a rotor but it’s 3 phase AC, not DC (synchronous). In fact synchronous motors often start as wound rotors. The normal use for wound rotor is to put resistance on the rotor to adjust torque. But if you drive it with a VFD you get a doubly fed motor...twice the torque in the same volume. Which is the big advantage for wind mills where reducing mass a couple hundred feet in the air on top of a narrow tower is a huge cost advantage.

There is no doubt that over time induction motors will be displaced by better designs first in niche markets then eventually elsewhere. 30 years ago if you wanted to put in a VFD over 10 HP instead of a shunt wound DC drive I’d say you were an idiot. Today that has flipped almost 180 degrees.

Maybe just a little more than 30 years ago. I know of a 250 HP AC drive that was in operation at least 32-33 years ago, maybe a little longer, that is just when I was introduced to it.

 

[paulengr]

Maybe just a little more than 30 years ago. I know of a 250 HP AC drive that was in operation at least 32-33 years ago, maybe a little longer, that is just when I was introduced to it.

VFDs existed prior to that. Cycloconverters for instance go back much earlier. But forced commutation schemes and GTO drives were awful. It worked but it wasn’t very reliable. Liebherr used GTO drives on their haul trucks (diesel over electric) and typically the GTOs would explode about every 18 months. Compare this to DC drives that are nearly as trouble free as AC VFDs are today.

Fast forward to the 1990s and two things emerged. First IGBTs were introduced which finally provided us with the power handling of BJTs and the low leakage of MOSFETs, allowing low voltage drives to scale to nearly any size. Second big technology was the advent of DSP processors fast enough to actually run the field oriented control algorithms invented in the 1960s.

 

[kwired]

VFDs existed prior to that. Cycloconverters for instance go back much earlier. But forced commutation schemes and GTO drives were awful. It worked but it wasn’t very reliable. Liebherr used GTO drives on their haul trucks (diesel over electric) and typically the GTOs would explode about every 18 months. Compare this to DC drives that are nearly as trouble free as AC VFDs are today.

Fast forward to the 1990s and two things emerged. First IGBTs were introduced which finally provided us with the power handling of BJTs and the low leakage of MOSFETs, allowing low voltage drives to scale to nearly any size. Second big technology was the advent of DSP processors fast enough to actually run the field oriented control algorithms invented in the 1960s.

I don't know much about that first 250 HP drive, I kind of doubt it was IGBT drive. We replaced it in mid 90's with Allen Bradley 1336 drive. It was much smaller.

 

[paulengr]

I don't know much about that first 250 HP drive, I kind of doubt it was IGBT drive. We replaced it in mid 90's with Allen Bradley 1336 drive. It was much smaller.

The Westinghouse Accutrol came out in the late 80s. Late models were IGBT. The drive manual was 11 pages including title page and a couple pages of safety warnings. It did most of the things that a modern diode front end drive does.

Older forced commutation drives require lots of reactors or drive transformers like a 12+ pulse drive. You can turn on an SCR but it naturally commutates at current zero. So to force commutation take a second SCR and short out the first one. They are diodes so you need to do some phase shifting gymnastics to make it work. Based on this description I think it’s clear why reliability was not good. Efficiency clearly wasn’t pushing 90%+ either.

Cycloconverters are much simpler. If you say delete every other cycle you get 30 Hz. Deleting more pieces of cycles plus some filtering makes a simple VFD that can easily be built for almost any voltage or current. It can’t exceed 30 Hz but this is just a factor in motor and gearbox selection. Still used for very large VFDs and it provides an inching/jog/slow roll function in soft starts.

I’ve spent a lot of time around some very large and old facilities. What is obvious to me is that what was old can be new again. The inherent issue with DC is the atrocious power factor and the commutator. With modern electronics and without a brushed commutator suddenly efficiency and torque rivals AC. Fundamentally a DC coil is 3 times stronger than the same coil on AC and electronic commutation gets rid of the inherent electro-mechanical limitations. It’s just too bad it doesn’t scale up very well. I will know how far we’ve come when water plants start putting ECM motors in neighborhood lift stations.

 

[kwired]

The Westinghouse Accutrol came out in the late 80s. Late models were IGBT. The drive manual was 11 pages including title page and a couple pages of safety warnings. It did most of the things that a modern diode front end drive does.

Older forced commutation drives require lots of reactors or drive transformers like a 12+ pulse drive. You can turn on an SCR but it naturally commutates at current zero. So to force commutation take a second SCR and short out the first one. They are diodes so you need to do some phase shifting gymnastics to make it work. Based on this description I think it’s clear why reliability was not good. Efficiency clearly wasn’t pushing 90%+ either.

Cycloconverters are much simpler. If you say delete every other cycle you get 30 Hz. Deleting more pieces of cycles plus some filtering makes a simple VFD that can easily be built for almost any voltage or current. It can’t exceed 30 Hz but this is just a factor in motor and gearbox selection. Still used for very large VFDs and it provides an inching/jog/slow roll function in soft starts.

I’ve spent a lot of time around some very large and old facilities. What is obvious to me is that what was old can be new again. The inherent issue with DC is the atrocious power factor and the commutator. With modern electronics and without a brushed commutator suddenly efficiency and torque rivals AC. Fundamentally a DC coil is 3 times stronger than the same coil on AC and electronic commutation gets rid of the inherent electro-mechanical limitations. It’s just too bad it doesn’t scale up very well. I will know how far we’ve come when water plants start putting ECM motors in neighborhood lift stations.

I want to say the original drive on this was a Siemens-Allis. First time I set foot in the plant was 1988, it was already in place then. Don't think that part of plant was anymore than 5 or 6 years old at the time