Being “house proud” became a concept at some point in human history. The original goal may have been to keep your cave floor cleaner than your neighbors’ by sweeping with thorny shrub branch ends. Today, we expect vacuum-cleaner technology to take care of it for us. According to Grand View Research1, the global market for this technology will reach over $10 billion in 2020. According to the same source, it is predicted to have significant growth as well, with a predicted CAGR of 9.1% through 2028.
This trend is being driven by evolving and bettering lives, developing economies, and technological advancements that make cleaning equipment more efficient and more readily available. Consumers are eager for innovative products with lower energy use, while commercially, health and safety concerns are pushing businesses to be “greener and cleaner.” Environmental factors also come into play.
The evolution of vacuum cleaners
Mechanized cleaners have certainly evolved, with the first versions being powered by stationary steam engines with long hoses to reach into buildings. These often blew rather than sucked, but common sense prevailed and vacuum cleaners now are the norm, with or without collection bags. AC-powered cleaners with inconvenient power cords have given way to cordless, battery-operated types, enabled by improving motor and battery technology, with legislation also playing a part. In the EU, for example, since 2017, no corded vacuum cleaner with a rating of greater than 900 W has been permitted.
Cordless vacuum cleaners with lithium-ion batteries are now popular, with useful run times and suction power, but there is always commercial pressure to perform better. While battery technology improves slowly, limited by the physics of chemical processes, there are opportunities with the motor to make performance improvements using known technology.
Early DC motors used in cordless vacuum cleaners were of the “brushed” type and had the advantages of simplicity of drive — just applying a voltage made them run up to their maximum speed. However, brushes wear; produce sparks, noise, and vibration; and the best efficiency attainable is about 80%, wasting battery energy and producing uncomfortable heat. Controlling speed means varying the voltage, which reduces efficiency further.
An alternative is the brushless DC (BLDC) motor, which is longer-lasting, more efficient (at up to about 96%), and much quieter — a major consideration. There’s always a downside, though, and that is that the BLDC motor needs an AC drive, typically in three phases 120˚ apart for three stator windings, with the initiation of each drive phase or “commutation” triggered by the rotor angle. Rotational position is determined typically by three Hall-effect sensors or by more complex, sensorless methods that look at the voltage on the windings to derive position, when they are unenergized in the switching sequence. The current in the windings must also be driven in alternate directions in the commutation sequence, so the most convenient arrangement for the drive is a “bridge” of semiconductor switches, typically MOSFETS (Figure 1).
Figure 1: A brushless DC motor requires a three-phase AC drive. (Source: Qorvo)
Adding this type of electronic drive is more expensive, but this is offset by improvement in performance, not only in power and efficiency but also in controllability: The drive voltage applied during each phase can be pulse-width–modulated (PWM) to keep speed constant under different load conditions and varied to suit the surface type. Costs are also mitigated by increased integration of the electronics required into systems-on-chip (SoCs), which can include all the digital and analog interfaces required, power rail management, PWM generation and control algorithms, and drivers for the power switches. Figure 2 shows the features included in a BLDC motor controller/driver SoC from Qorvo.2
Figure 2: Typical functions needed for an efficient BLDC motor drive (Source: Qorvo)
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Contributors
This is a contributed article submitted by Jose Quinones, senior applications engineer for programmable power management at Qorvo.
You can checkout the complete article on the October 2022 edition of the Power Electronics News eBook.