According to the paper, Intelligent Power Module Simplifies, Speeds Development of Motor Drives for Three-Phase Appliance Motors, by Mor Hezi, marketing manager; Mario Battello, senior application engineer; and Alberto Guerra, director of Application and Technical Marketing for International
Rectifier (IR) (El Segundo, CA, U.S.), appliance engineers need a design approach that simplifies the development of three-phase, variable-speed motor drives for efficient washers, refrigerators, air-conditioners, and other home appliances. The paper continues, "Variable-speed motor drives use electronic circuits to vary the motor speed instead of the less reliable mechanical speed changing employed in older-generation appliances. Plus, varying speed under electronic control saves energy by reducing speed when higher speeds are not necessary. For example, instead of a refrigerator cycling on and off to regulate its internal temperature, it can vary the speed to maintain a constant temperature. Power consumption is less at a lower speed than at a higher speed. An integrated power module (IPM) provided this capability."
According to David Tam, vice president of IR's iMotion integrated design
platform division, the company has been supplying such devices to certain
applications in the appliance industry. "The applications we supply into are mainly the newer types of inverterized appliances," Mr. Tam tells APPLIANCE. He says that inverters are used in appliances that require more precise motor control due to energy saving features. "The three main applications are washers/dryers, refrigerators, and air-conditioners, a more recent application being a vacuum cleaner," Mr.
According to the technical paper, the traditional approach of using discrete components and insulated gate bipolar transistors (IGBTs) can meet the power requirements of variable-speed motor drives, but they require substantial printed circuit board space. Also, the paper says, the traditional discrete approach requires more components, adding to design complexity and increasing the development time. Plus, more components increase the inventory required to support the hardware. Newer approaches are needed to give appliance system designers a solution that simplifies the effort, while cutting the overall development time and risks, the authors of the paper say.
"After looking at the market, we decided to embark on efforts to design a complete type of reference system," says Mr. Tam. "We call it a design platform." Mr. Tam says that IR started on a platform for industrial applications 3 years ago. "We only started the appliance platform a few months ago," he adds. "Today we have a very generic platform. Later, we will be launching specific platforms for washing machines, air-conditioners, etc. A complete design of the inverter platform for an air-conditioner - besides the motor - would include a user interface, the electronic control for the compressor motor, and also an interface for the temperature sensor, room air sensor, and so on." IR would take those interfaces and put together a design platform to include a digital controller and analog IC together with power devices to be delivered to a customer, including software. "They can use the platform as the basis for customization of their complete design," says Mr. Tam. "The design will take care of additional issues such as power factor and power quality issues."
According to the authors of the intelligent power module paper, an advanced integrated power module for motor applications, such as IR's IRAMS10UP60 PlugNDrive(TM), combines the latest refinements in low-loss, high-voltage IGBT and ICs with advances in packing technology, delivering a compact motor drive solution for its intended application.
Mr. Tam thinks that the design platform is the most effective way of providing motor control solutions to appliance OEMs. He says the design platform gives customers a starting point for their motor control designs, as well as providing a one-stop shop for motor control needs due to the integration of IGBTs and driver ICs.
DVD+R/W Motor Driver
Royal Philips Electronics (Eindhoven, The Netherlands) recently announced the SA56202 motor driver IC for DVD+R/W applications. According to Sharadh Bindiganavale, strategic marketing manager for the motor driver, the key to the drive is that it integrates virtually all the driver functions on a single IC. "It is actually a 7-channel driver in a monolithic single IC," says Mr. Bindiganavale. "Essentially, all the motor functions that a recordable DVD player requires are handled through this single IC," Mr. Bindiganavale says.
"Up until a year ago, Philips Semiconductors had a reference design platform that involved several of the semiconductor contents, with the exception of the motor driver IC," says Mr. Bindiganavale. "Last year, we identified an opportunity for an innovative motor driver IC and decided to fill that void by developing the SA56202 and completing the Nexperia reference platform."
Mr. Bindiganavale says that Philip's Nexperia reference design can be viewed as a type of design kit. "A third party can utilize the Nexperia reference design to quickly develop a DVD+R/W platform," he explains.
According to Mr. Bindiganavale, one of the most important features of the driver IC is its active braking scheme. Unlike the braking schemes of traditional ICs for DVD+R/W applications, Mr. Bindiganavale says that Philips' active braking manages heat more effectively and increases the overall efficiency. "The competition usually relies on a combination of the traditional forms of braking - short braking, reverse braking, and air braking - to stop their disc," he explains. "One of the characteristics of a motor is that when you drive a motor and it is running in a certain direction, it has a reverse back EMF voltage that is generated as a result of that motion. That inherently opposes the power that you are supplying to the motor to drive it in a particular direction. The faster you turn a disc in a certain direction, the larger the opposing force is. So when you have this disc running at maximum speed, you will have this maximum force available in the opposite direction." In short braking, the terminals that are supplying power to the motor are shorted to ground. "What used to be a driving force is now grounded instantaneously and the motor sees a tremendous reverse back EMF voltage. This opposing force generates a lot of wasted heat. In reverse braking, you actually force the motor to run in the opposite direction (reverse commutate) to what was originally intended. This backward force adds to the reverse EMF to offer a bigger braking force, but causes an even greater heat problem," says Mr. Bindiganavale. Air braking is letting the air friction slow the disc down and bring it to a halt. But air braking is very unpredictable - stopping time cannot be predetermined.
According to Mr. Bindiganavale, active braking is applying a controlled force in the opposite direction, which compensates for the back EMF and keeps that difference very constant for the entire duration of the braking. This resulting braking force profile is linearly controlled and the speed is linearly reduced from maximum to zero. "If you can do that in a controlled manner, then what happens is three things," says Mr. Bindiganavale. "One is that you limit the amount of wasted heat that you have; two, if you do it right, you can actually pump that energy back into the power supply; and three, you get the fastest braking times." This is beneficial not just from a thermal management standpoint, but from an energy-efficiency standpoint. "The smaller the package, the more strenuous it is to dissipate the heat," Mr. Bindiganavale says. "If we were to employ the short braking as in the conventional method, it would be very difficult, if not impossible to employ the HTSSOP56 package - the smallest in the industry for a 7-channel DVD+R/W motor driver IC."
Mr. Bindiganavale says the device from Philips can go from 11,320 rpm to a dead halt at zero in less than 3 sec.