Government regulators and consumers alike are pushing for more energy efficient appliances. International Rectifier (El Segundo, CA) says that motors consume about 50% of the world's electricity, with washing machines, air conditioners, and refrigerator/freezers consuming on the order of 1.1 terawatts (1,000 billion watts) annually, worldwide. IR says that the use of variable speed motors can save up to 60% of this consumption.
But wringing the most efficiency out of these motors hinges on their efficient control. To do this, IR's PlugNDrive™ integrated power module technology relies on a compact package made possible by a single circuit substrate supporting both the power components and high-voltage integrated circuits within an overmolded plastic housing, says Alberto Guerra, director of the Appliance Business Unit. The first of this line, the IRAMS10UP60A, is rated at 10A for 400 to 750W motors.
The aluminum IMS (integrated metal substrate) is bonded to the ground return to serve as a shield against conductive noise and EMI, notes Guerra. Between this substrate and the circuitry is an insulating oxide layer on top of the aluminum and a dielectric layer below the copper circuits. "We achieve lower thermal resistance due to a dielectric layer that is 50 microns thick, as compared to previous designs where the layer was on the order of 150 to 200 microns thick. Yet, we still meet the 2,000V isolation requirement," he explains. Short internal component leads also contribute to electronic noise reduction. And a switching frequency of 20 kHz, up from some previous devices using half that value, improves dynamic performance and is above the human audible spectrum, making for a quieter appliance, Guerra says.
Other hardware features include a built-in temperature signal that allows engineers to monitor temperature and shut down the power elements at a preset level.
Control algorithms allow for vector control. Three-phase signals are reconstituted into a single-phase current in the vector-control algorithm to govern current directly. Previously, outputs of speed and torque were used for control.
The integrated module can also help engineers shorten design cycles, says IR. A reference design kit (IRADK10) is available for $349 on IR's website. It is a complete three-phase drive system that requires only a motor and line voltage. With a Windows-based interface, engineers can investigate the effects of varying speed, acceleration, input voltage, switching frequency, etc. And they can create function cycles, for example, to simulate washing machine operation. Guerra adds, "Engineers can understand features and their applicability to find a final solution in a shorter time." International Rectifier Inc., www.irf.com Enter 588