Today more than ever, energy efficiency dominates many product developments. From auto and truck engines to air conditioning, refrigeration, household appliances (large or small), and beyond, component space is at a premium. Fewer parts are a plus, and cool running, long-life power is a must.
Fuel efficiency in autos is probably the most prominent energy example, with demand from consumers as well as federal mandates giving it top priority. New cars average 24.5mpg, but that's a far cry from the 54.5 average mandated for 2025. It's also well below the 35.5 required by a much closer deadline of 2016.
Whatever the end product, there is no magic bullet; efficiency must be gleaned from many sources. In automotive and other industries, years of product development point toward a series of observations. For one thing, low-cost power electronics have made sensorless control of brushless DC (BLDC) motors with integrated controllers a viable option for numerous applications. This leads to several interrelated trends and challenges for both design engineers and manufacturers:
- Increased interest in sensorless BLDCs to deliver component power
- Frequent reliance on off-the-shelf generic control algorithms provided by numerous semiconductor manufacturers
- Lack of advanced-level control engineering expertise to address canned algorithm limitations and, more importantly, provide rapid, cost-effective custom designs
- Emergence of outside specialists and new model-based development techniques for sensorless BLDC motor controls.
Pluses and pitfalls of sensorless controls for BLDCs
The search for efficient energy and cool, long-running power finds a powerful ally in sensorless control technology. For example, a control recently designed for an engine pump motor could result in a 5 percent fuel savings. At $3.50 to $4 per gallon, that adds up to a tidy sum for any car, pickup, or SUV owner, and it would amount to a rather large sum for the operator of a fleet of long-haul semi-trailer trucks.
Sensorless controls are also highly reliable, in large part because sensors aren't needed for feedback. This adds complexity to the controller, however, as sensorless BLDC motors depend on a closed-loop algorithm for operation. Therein lies the rub.
Many semiconductor manufacturers offer canned control algorithms. The tendency for some design engineers is to view them as a means to jump-start development and get to market quicker while reducing costs. Fact is, they usually have the opposite effect. Promoted as plug-and-play (assuming all hardware components are available), they may be acceptable in some applications, but they typically fall far short of expectations for several reasons.