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highpowerZONE Products for the week of April 28, 2008
Fairchild Semiconductor Says…
FCAS30DN60BB: First SPM Products for Driving Highly Efficient Two-Phase Switched Reluctance Motors
SRM-SPM Modules Provide 40% Space Savings for Two-Phase SRM Motor Designs
Fairchild Semiconductor introduced another industry innovation in SPM technology with the industry’s first SRM-SPM power modules for driving two-phase switched reluctance motors (SRM) in small motor applications such as vacuum cleaners. Switched reluctance motors are an attractive alternative to AC drives due to their high efficiency. The small motor industry is migrating from single-phase to two-phase SRM motors due to their ability to startup under difficult load conditions and the lower components that these motors require. Each SRM-SPM module,FCAS20DN60BB and FCAS30DN60BB, integrates two HVICs, one LVIC, four NPT IGBTs, four fast recovery diodes (FRDs), two bootstrap diodes, a thermistor and various protection functions in a single package. By integrating 14 fully tested power components in a compact 45mm x 28mm SIP package, these products offer 40 percent space savings. This space conservation allows vacuum cleaner designers to incorporate the controller into the SRM assembly, and also improves design productivity and manufacturability. System reliability is further enhanced by incorporating protection features such as under-voltage lock-out and short circuit protection into this thermally efficient package.
“Fairchild continues to provide cutting-edge, efficient solutions that innovate today’s electronics. These SPM power modules for two-phase switched reluctance motors are an example of how Fairchild provides solutions that deliver excellent performance, while minimizing design and manufacturing time,” said Taehoon Kim, vice president of Fairchild’s Functional Power Solutions.
EN-Genius Says…
Switched Reluctance Motors (SRMs) were first discussed in the late 19th Century but were not really practical until high-voltage switching devices became available in the last two decades. They have become very popular for variable-speed drives with the advantage of being extremely simple in design, which gives them a lower cost to manufacture and also makes them more reliable. But they have quirks: a large torque ripple and the non-linear nature of torque generation. The inductance equations are complex and the inductance vs. rotor position characteristic has to be dealt with. The best text on the subject, in my opinion, is now a little dated but offers a straightforward approach to the necessarily quite complex math of understanding SRMs. It is Switched Reluctance Motor Drives, by Krishnan Ramu, 2001, CRC Press, ISBN (10) 0849308380.
The Smart Power Module developed here by Fairchild looks to be fairly opportunistic and is fine tuned for a fairly power-limited two-phase drive home vacuuming system. That is OK; when the market recognizes that Fairchild can solve one application problem it means that they can probably move on to solving “my” SRM control challenge as well.
Fairchild has taken the lessons it has learned from its other motor drive modules to produce a 550 V inverter with an absolute maximum 30 A IGBT collector current with a maximum collector dissipation of 39 W. The recommended operating conditions are for a typical supply voltage of 300 V with 15 V for both the control and high-side bias with a PWM frequency of 3 kHz. The IGBTs and FRDs are highly efficient with low EMI. Bootstrap diodes are included.
This asymmetric converter has the gate drive circuit for the high-side IGBTs with high-voltage isolated high-speed level shifting , and control supply circuit undervoltage protection. For the low-side IGBTs there is also has the gate drive circuit plus short-circuit protection and the control supply undervoltage protection. The input interface from the microprocessor control is 5 V CMOS/LSTTL. Temperature sensing is provided on-chip for feedback to the MCU.
That Fairchild has managed this design without a negative rail is remarkable. This is new business for the company but their module history for other drives will help them in getting in the door for other SRM applications. The SIP modules have all the connecting pins on one side of the package, of course, making mounting very simple. Fairchild should do very well from these and the other SRM modules that are undoubtedly on the way.
The FCAS30DN60BB and the lower current rated 20 A FCAS20DN60BB are both in production in Pb-free SIP packaging and are priced at $17.94 and $16.38, respectively, in 100-piece lots.
Data Sheet FCAS30DN60BB
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