Sunday, March 15, 2015

Smog Alert

The worldwide push to increase electric motor efficiency that I spoke of in my last blog has some major implications for OEMs that incorporate motors in their products. For OEM's using induction motors, achieving the required IE3 efficiency requirements may mean adding electronics where none had been employed before. All the major semiconductor manufacturers have jumped into this space with components and processors to implement V/F or Field Oriented control inverters. Drive manufacturers, too have off the shelf drives to offer.

Texas Instruments
ST Microelectronics

However, the OEM that is incorporating inverters in their product for the first time must address a problem they may not have had before; electromagnetic interference or EMI. All conventional inverter technologies control the motor by chopping the voltage to the motor stator into a 4Khz to 20Khz pulse width modulated square wave (PWM). One side effect of PWM is that the voltage to and on the stator now has high frequency harmonics that extend well in the radio spectrum. We can think of this as a radio frequency smog raising the noise level of the radio spectrum and making it more difficult for radio based communication to occur.

                          Motor Voltage Spectrum: Conventional Drive

If not constrained, this energy can appear on the motor leads, the power leads into the inverter and even on nearby conductive or magnetic structures that resonate at the harmonic frequencies. Industrial drive manufacturers and system integrators have dealt with this problem for years and have developed a portfolio of tools, techniques and products to solve EMI problems, typically on a case by case basis. However, for the OEM new to inverter development, these solutions may be too costly or too application specific. While the basics of EMI mitigation are the same for the industrial drive and a dishwasher, the business constraints of cost, size and repeat-ability are worlds apart.

At Digital Power Engineering, we had EMI in mind when we developed our Resonant Field Exciter technology (patent pending). Our EMI mitigation approach is to eliminate the problem, or at least make it a lot easier, by not producing the high frequency harmonics in the first place. By using a wound field synchronous motor with a Resonant Field Exciter providing the rotor field energy, the stator voltage need not be pulse width modulated, resulting in a much cleaner EMI excitation spectrum.

                              Motor Voltage Spectrum: WSM with RFE

For applications that turn at a constant, grid frequency related speed, using RFE technology means there is no inverter at all and the EMI footprint is little different than the original induction motor. For applications that are either driven from a DC source or need to be variable speed, the electronics between the source and the motor stator only steer, or commutate, the source power into the motor leads in sync with the motor rotation with no PWM. There is still power switching occurring, but it is at the rotor pole speed, which is typically less than 400Hz and usually 50 or 60Hz.

As a result, EMI mitigation, if required at all, is not only much simpler, smaller and less costly, but more effective over a broader range of installations and environments.

For more information on DPE's Resonant Field Exciter technology drop me an email at or visit our website at

Saturday, February 14, 2015

Staying the Course to a More Efficient Future

A few days ago, I posted a link on Linkedin to a recent IEEE article on U.S. electricity demand ( ).  Domestic electricity per capita has been flat since 2007. Much of this is attributed to energy efficiency efforts, including legislation that raised the bar on acceptable, minimum efficiency levels, including minimum efficiency of the largest consumer of electricity in America; electric motors.

The International Electrotechnical Commission (IEC), an international, non-government, consensus based standards  organization founded in 1906, has established four levels of motor efficiency to date.

Level IE1 was pretty much the worldwide de-facto standard for motors operating under 690V around 1990. In 1992, the U.S led the way by adopting IE2, effective in 1997. Followed, albeit slowly, by the rest of the world. By 2013 most of the world had adopted IE2.

Almost everyone in the U.S. is aware that legislation in 2007 raised electric lighting efficiency standards, ushering in the era of CFC and LED lighting, but few know that the same legislation raised the bar again on electric motor efficiency, to the IE3 level, effective in 2010. This time the world was quicker to follow. By 2017 the IE3 minimum efficiency standard will be the law of the land for new motors manufactured almost worldwide.

At the moment, there is no legislation in process anywhere in the world to implement IE4. At least not yet. But there it sits as the "holy grail" of motor efficiency. Many OEM's that use IE2 motors in their products aren't waiting for legislation. In the pump, compressor or HVAC worlds IE4 provides a significant competitive advantage over the IE2 motors they now have to design out. As long as they have to pull out a white sheet of paper, they might as well go IE4 if they can.

But IE4 technology can be expensive. Induction motor technology alone can't get there without adding electronic drives, and not every induction motor can be driven by an electronic drive. Permanent magnet technologies also need drives and have the hidden variable cost and long supply chain of rare earth magnets. Switch reluctance technology is so different from conventional motor and drive manufacturing that a new manufacturing infrastructure must be built to provide them in volume, and they can be noisy.

At the Motor and Drive 2015 conference in Orlando in January, we at Digital Power Engineering introduced another solution. A technology that takes a motor configuration that's been around for 120 years and is the electric motor of choice above 400 HP, and makes it practical at low HP as a motor that exceeds IE4 efficiency, has no magnets, requires no drive for single speed operation and is compatible with contemporary motor manufacturing. If you or anyone you know uses a motor above 200 watts in their product, they may already know about the need to shift to IE3. Have them drop me an email at and let's start the conversation about an accessible IE4 solution that can provide them a significant competitive advantage.

Monday, January 19, 2015

Eagles, Shields and Sparks: The New World of Electronic Hardware Prototyping

Now that the new year has started, I'd like to share a couple product development trends we've been using at DPE over the last year or two.

At some point in the development of any product, a prototype is built. In electronic products over the last 40 years, I've seen this process morph from classic bread boarding on perforated fiberglass boards, through wire wrap, to PC based CAD and inexpensive, small quantity PCB's ordered over the internet.

Likewise, forty years ago, electronic systems used hardware to compute and make decisions. Today, we use software to do that.

Physical products that still have to interface with the real world are becoming platforms. These are dedicated devices with the hardware necessary to sense and/or manipulate the real world and enough processing power to carry out the tasks. However, what the platform actually does may change over time through reprogramming.

At the same time, the cost of producing an electronic hardware prototype has fallen dramatically. Microcomputer modules such as Arduino, Nucleo and Spark run $20 or less, have the computer power of a $1000 computer board of the mid 1990's, can be as small as a postage stamp and have built in capabilities like Wi-Fi that were unheard of then. In the past, many products required substantial development of a display or other human-machine interface (HMI). Today, most of us are literally carrying around our own personal HMI; our smartphones and tablets. With a microcomputer module as the brain, a smartphone or tablet as the HMI and the hardware necessary to interface with the real world built onto a "shield" (or equivalent), the prototype platform can be ready for software development in as little as two or three weeks.

The result of this evolution is to dramatically shift the entry fee of new products, services and whole industries from capital to labor. The advantage accrues to those teams who have the necessary skills. Think of the process as employing corporate "sweat equity". The more the team skills match those required, the less "sweat equity" is expended and the faster the improvement, product or service hits the market.

If "Shield" prototyping isn't a strong-point for your organization, Digital Power Engineering can help. Depending on the circuit complexity, "shield" prototype turn around can be as little as two or three weeks.

Drop us an email at to start the conversation.