Patrick J. Piper 2016-08-02 15:14:12
Take one quick look around a commercial building and you’ll quickly realize that electric motors are everywhere—powering refrigerators, freezers, HVAC units and fans, and more. But despite the fact that motors are everywhere, there has been minimal innovation in the electric motors category over the past century. You may recall Nikola Tesla invented the motor back in the late 1800s, but did you know that this 130-year-old technology—the induction (shaded-pole motor)—is still the most widely deployed motor in commercial refrigeration today? In fact, more than 65% of all commercial refrigeration motors deployed today are shaded-pole motors. Unfortunately, shaded-pole motors are only about 20% energy efficient. The second round of innovation in the motor industry came 80 years later—in the 1960s—with the invention of the Electrically Commutated Motor (ECM), a more flexible motor to handle the varying types of applications needing precise control over variable speeds. Since then, ECMs have grown to be utilized in approximately 35% of the electric motor market, predominantly over the last five years as consumer awareness, utility incentives, and regulatory efficiency minimums have accelerated adoption. ECMs are more efficient than shaded-pole motors, but still average only 60% energy efficiency. Because the shaded-pole and the ECM were the primary choices for fan motors over the past century, the vast majority of motors in operation today are based on technology that is at least 50 years old. While improvements have been made over the past half-century, updates to ECMs have been mostly incremental, such as refining better-engineered materials and circuit designs to fix the previous SKU’s design faults. With minimum efficiency regulations increasing two to three times every decade, the engineering preference to make motors more efficient is coming to the fore. Motor manufacturers have been trying to improve the efficiency of their motors for years, however there hasn’t been a new technology to rival ECM motors in efficiency and performance. A recent breakthrough in the rapidly emerging class of high-efficiency permanent magnet synchronous motors (PMSM) now has the potential to disrupt and even displace outdated ECMs and shaded-pole motors in commercial refrigeration and other applications, while providing businesses with powerful new energy savings opportunities at comparable upfront costs. The new technology has the potential to displace incumbent motors with energy savings that would be equivalent to eliminating at least one out of every two motors off of the grid. To understand the advancements in PMSM technology, and how its efficiency gains are achieved, it helps to take a more detailed look back at the history of motor technology. Tesla’s Revolutionary Motor Design While electromagnetic Direct Current (DC) motors were first popularized in the 1880s, when direct current was the primary source of power, their use was fundamentally changed when Nikola Tesla invented the shaded-pole design for use with Alternating Current (AC) power. After demonstrating a polyphase AC motor in 1884, Tesla was granted a broad patent for the use of “rotating magnetic fields” in electrical devices in 1887. Two years later, on December 3, 1889, Tesla was awarded a patent for the original shaded-pole electric motor design. The shaded-pole motor is a robust design that gives trouble-free operation for long periods. With only two parts—a stationary stator and a rotor—the AC motor was a much simpler design than electromagnetic DC motors. Primarily used in fans, appliances, and refrigeration equipment, the advantage of this type of motor is that it reaches a strong torque level once the rotor has begun spinning fast; however, they can be very slow to start and have low torque at start. Shaded-pole motors can be controlled merely by varying voltage, or through a multi-tap winding. This can often be a disadvantage of the design because the motor is susceptible to changes in fan speed throughout the day as voltage varies throughout a building. Furthermore, these motors consume significant amounts of energy, resulting in the motor being about 20% efficient at converting electricity into useful energy used to turn a rotor. The Rise of the ECM When ECMs were introduced in the ’60s, they were hailed as a great leap forward for applications that require variable speed. Over the past five years, the increase of ECM usage has rapidly grown in both adoption and use in commercial applications to now make up approximately 35% of the commercial refrigeration market—refrigeration display cases, vending machines, and walk-in coolers. ECMs have also become popular in many other applications, such as variable air volume (VAV) systems and heating, ventilation, and air conditioning systems. The primary benefit of the ECM solution over shaded-pole motors has been to improve efficiency by using permanent magnets instead of field coils. Typical ECM motors use a three-phase rotor-mounted permanent magnet motor topology, wherein the DC power supply is obtained by rectifying the AC from the power source—typically grid supplied AC. The power electronics section of most ECM motors use three half bridges or six power switches, along with other discrete components, to supply electrical power to the motor’s three phases. ECM motors use rotor-mounted permanent magnets to replace the induction rotor. In fact, the only difference between an induction motor and a three-phase rotor-mounted PM motor are the rotors; both have phased coils that create a rotating magnetic field in the stator. ECM motors use the stored magnetic energy in permanent magnets to achieve a higher efficiency than conventional induction motors, which use a higher loss aluminum conductor squirrel cage rotor. Approximately 40% of the electrical power is not converted to the rotational motion in a conventional low wattage ECM motor, since about 25% of the power is consumed by the electronics alone. The ECM microprocessor-based motor controller that converts the alternating current (from the grid) to direct current can also be regulated to vary the speed of the motor. While this programmability and functionality can be useful in many applications, it is typically not utilized in refrigeration applications where a constant fixed speed is preferred to maintain optimum refrigeration performance. As a result, the electronics are adding an additional expense and parts that both consume additional power and can potentially fail, reducing reliability. A Motor for the 21st Century: Permanent Magnet Synchronous Motors Recent breakthroughs in motor design have finally moved the bar in motor performance. The new class of PMSM motors that is now available allows for such a significant reduction in energy that it is likely ECMs will be viewed the same way shaded-pole motors are in terms of efficiency when compared to this new technology. Whereas an ECM requires continual conversion between AC and DC power throughout its use to operate, the beauty and simplicity behind this new class of motors lies in its ability to operate at the AC line frequency of grid-supplied power, essentially eliminating the need for power conversion after the motor starts (the need to rectify to DC and back to AC). Once the motor reaches its targeted speed, innovative circuitry efficiently shifts the motor to AC power supplied directly from the grid. This recent advancement in PMSM controller technology eliminates the power conversions found in other EC designs, and has been found to save in excess of 30% (watts) to 50% (amps) over ECMs and about 80% more electricity than shaded-pole motors. The stability and performance of airflow in the refrigeration applications is further improved by operating at the AC line frequency, because changes to voltage do not affect fan speed (which is the case with many ECMs). This new technology achieves its efficiency improvement from using a permanent magnet synchronous motor topology and a simple, low-cost, electronic controller to achieve a higher efficiency than that of an ECM—and without the associated cost premium typically found with next-generation products. This new PMSM design protects from any surges in the line current because the coils, not the electronics, absorb any excess voltage. Furthermore, by reducing the duty cycle on the motor from less electronics, the design gains reliability that can extend the life of the motor. The reduction of electronic circuitry and streamlined design also helps keep the costs of a PMSM comparable to the price of existing ECMs today. This should produce a much shorter path to adoption than other motor technologies before it. There are several additional benefits that a PMSM refrigeration fan provides, including: • Higher peak and average efficiency over a broader range of operating conditions. Once synchronous motor speed is achieved, the motor’s drive circuit essentially drops off and electronic commutation is no longer required to sustain operation. Losses in the drive electronics are removed from the system to obtain efficiencies higher than state-of-the-art ECMs that require continuous power conversions. This not only increases efficiency, but also reduces the acoustic signature (noise), which can be of significant value in the application, but also improves reliability. • The elimination of induced EMI and harmonics on the power line due to the bypassing of electronics when the motor has reached its steady state operating point. This provides a higher power factor (>0.90 versus ~0.60), and further reduces power requirements that are both beneficial to utilities and can provide more generous rebates for retrofit opportunities, while helping to avoid utility surcharges for poor power factor. • Displacing incumbent motors with this new type of motor would be similar to taking at least one out of every two ECM motors off of the grid and as many as four out of five shaded-pole motors off the grid. Independent Research Validates The Benefits of PMSMs The most recent study of PMSMs was conducted by Alternative Energy Systems Consulting (AESC), and prepared for a southern California utility, to determine energy savings and demand reduction ( http://bit.ly/29TAnwN ). Following a field trial with 173 (9–12 W) fan motor retrofits at a San Diego supermarket, each fan motor demonstrated a savings of 73.6 kWh per year, relative to the baseline of ECMs, and reduced demand by 8.5 W. According to the report, “The 173 fan retrofits showed clear and consistent improvements in power factor and consumption without negatively impacting case operation. “With an idealized 100% market penetration of the nine- to 12-watt model, extrapolation to the California retail food segment suggests the statewide savings potential of this technology is 189 gigawatt-hours of site energy, 17.2 megawatt demand reduction, and 66,540 metric tons of annual carbon dioxide emissions. The effectiveness, market potential, and ease of replacement suggest that this technology should be considered for further study or immediate rebate program inclusion.” The Department of Energy (DOE) has also recognized the significant potential for energy savings and named it a High-Impact Technology. The DOE is working with QM Power, the only manufacturer of PMSMs offering this new technology, to install and demonstrate over 10,000 higher-efficiency fan assemblies in over 50 grocery sites throughout the US. The results of the first DOE demonstration were documented by Oak Ridge National Laboratory and revealed that a broader upgrade of PMSMs to applications beyond commercial refrigeration could reduce source energy consumption by as much as 300 billion kWh or more, with proportional environmental benefits ( http://bit.ly/29U37br ). In Conclusion Many of us don’t think about motors until they stop working, at which point historical purchasing decisions have been largely made based on upfront costs. However, considering that motors consume 50 to 70% of all electricity used in the industry and 98% of the total cost of an electric motor can be in the energy it consumes, it makes sense to rethink your approach to motors as one of your greatest cost-saving opportunities. Just as businesses have set out to retrofit their properties with LED lighting to cut energy costs, the advent of PMSM provides powerful new savings opportunities, by retrofitting electric motors. With minimum efficiency regulations rising regularly, it’s practical to take a look at the motors powering your organization. BE Patrick J. Piper is the President and CEO of QM Power.
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