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.
Paul & Warren, Glad you mentioned the drawbacks of off-the-shelf generic control algorithms. I have never been asked to design a generic motor drive which runs at a generic speed and torque for a generic customer. It's always been a new, unique design for a new invention with very unique capabilites. I've seen very substandard operation of motors using a generic control algorithm for which the engineers just stare and 'wonder' why it doesn't run correctly. An off-the-shelf generic control algorithms can get a toy airplane running for a hobbyist but, for a robust new product, it's wise to seek and hire someone with knowledge and experiance in control, power electronics and a capability to think outside of a generic box.
This is a good article and it certainly points out the errors made in dispensing with those experienced engineers when times were slow and money was tight. So what is left is a less than optimal collection of consultants who were unable to get jobs when the economy started to recover.
Those brilliant new engineers using simulation and modeling may yet arrive at the best answers, but it is always wise to understand that the results of simulation are never more accurate than the model used for that simulation. That is where experience is vital, in being able to look at the results and answer that big question: "Is this answer reasonable?" The ability to decide correctly comes from having a lot of insight and understanding, which generally come from experience.
Excellent article. Definitely energy efficiency has been raised up as a substantial design goal for new products in motor control, and can be an absolute key feature depending on the application. It will be interesting to see how the trend plays out over the long haul with engineering minds focusing on the problem/opportunity.
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