1. Wireless Power Transfer System Development for Biomedical Applications
Vitali Tikhomolov, P. Eng., Mechanical Engineer, Elix Wireless Charging Systems, Vancouver, BC
Project supervised by: Dr. Boon Chong Ng, VP R&D, Elix Wireless Charging Systems, and Dr. Anthony Chan, Affiliate Professor, University of British Columbia; Project Duration: 16 May – 16 Sept 2014
Overview
We have designed and built a prototype of a wireless power transfer
system suitable for biomedical applications. The system is based on
Elix’s proprietary technology of magneto-dynamic coupling for wireless
power transfer. This technology has previously been used to construct
prototypes with 60W-1200W power transfer capacity. As the
technology is easily scalable, in this project we have investigated its
potential for use in medical devices with power requirements of about
10W.
Applications Investigation
On one hand there is a strong demand for wireless power transfer
technologies to power/charge electrical medical devices; on the other hand,
there are currently no wireless power transfer solutions that meet
requirements of many medical device applications (for example size and
power transfer efficiency).
Ventricular assist devices (VADs) are especially interesting as a potential
application due to the following:
1) No wireless power transfer solution is currently on the market for use
with VADs.
2) Infections near the percutaneous power leads is a widely acknowledged
problem affecting 15% of VAD recipients [1].
3) Implantable VAD technology is currently emerging and is starting to gain
widespread adoption.
Reference: [1] Study of LVAD: Extended Mechanical Circulatory Support With a Continuous-Flow Rotary Left Ventricular
Assist Device by F. Pagani, et al., Journal of the American College of Cardiology, Vol. 54, No. 4, 2009
Design Work Completed
The prototype design was completed using SolidWorks CAD software.
Preliminary prototype tests were conducted with only the essential
components constructed. The tests resulted in further design refinement.
Thereafter, all the remaining parts (with some changes) were ordered and the
prototype assembled.
Prototype Testing
Prototype tests were conducted to characterize its performance. Multiple
configuration details were adjusted and tested.
Future Work
Parasitic loss analysis identified ways to further improve the prototype. These
improvements can be incorporated in a future prototype. Main points for
improvement:
1) Rotors need to be balanced. Unbalanced rotors was a well-known weakness
throughout the project. Unfortunately, commercially available balancing
machines are not able to balance rotors containing strong permanent magnets.
As a result, a semi-custom balancing rig needs to be built for this purpose.
Balanced rotors will improve the following 3 performance parameters: noise
level, vibration, and bearing friction losses.
2) New bearing design must be implemented to reduce frictional losses and noise.
Ferromagnetic and active magnetic bearings are to be considered.
We estimate that these improvements will bring power transfer efficiency to 86% in
the future prototype.
Intellectual Property
Elix Wireless Charging Systems owns all intellectual property rights for inventions
conceived during the project’s duration.
Two US provisional patents were filed with myself being a co-inventor:
Method and Apparatus for Foreign Object Removal in a Wireless Charging System
(App# 62/021084)
Method and Apparatus for a Magnetically Coupled Wireless Power Transfer System
(App# 62/038102)
Both of these inventions are broadly applicable to wireless power transfer systems
employing magneto-dynamic coupling. The prototype presented in this report may
further be improved to make use of these inventions.
Specifications For Unit Tested
Transmitter
Type Rotating Magnet Producing Time Varying Magnetic Field
Input Voltage, VDC 12
Power Source Max. Current Rating, A 2
Size, mm 85L x 53W x 40H
Volume, cc 153
Mass, grams 104.0
BLDC Driver Model DFRobot Veyron 1x5A
Rotational Speed at no Load 346 Hz (20,760 RPM)
Rotor Bearings Type Hybrid ball bearings, 6mm OD x 3mm ID x 2.5 mm wide. APEC #7
Winding Configuration 3-phase, 6-windings, 15 coils/winding. 2xAWG28 coils
Receiver
Type Coupled Rotating Magnet Inducing 3-phase AC
Nominal Output Voltage, VDC 12
Max. Output Current, Amps 1.0
Size, mm 25.0 Dia x 39.5 Wide
Volume, cc 19.4
Mass, grams 48.0
Rotor Bearings Type Hybrid ball bearings, 6mm OD x 3mm ID x 2.5 mm wide. APEC #7
Winding Configuration 3-phase, 6-windings, 36 coils/winding. 1xAWG28 coils
Output Rectification Full bridge with shottky diodes. 2 x 180uF capacitors
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
10 20 30 40
RECEIVERLOAD(WATTS)
AIR GAP BETWEEN TRANSMITTER AND RECEIVER
(MM)
Max Load Supplied at Each Air Gap
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10 15 20 25 30 35 40
OVERALLPOWERTRANSFEREFFICIENCY
AIR GAP BETWEEN TRANSMITTER AND RECEIVER (MM)
Max Load Supplied at Each Air Gap
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
5.0 6.0 7.0 8.0 9.0 10.0
OVERALLPOWERTRANSFEREFFICIENCY
LOAD POWER (WATTS)
Various Load Supplied at 25mm Air Gap
6.3%
6.3%
9.6%
9.6%
7.6%
1.0%
59.7%
WIRELESS POWER TRANSFER SYSTEM EFFICIENCY
ANALYSIS
Load Power
Power consumed
by Rx rectifier
Power consumed
due to resistive
losses in Rx
windings
Power consumed
due to resistive
losses in Tx
windings
Power consumed
by the Drive
Power consumed
by Rx Rotor Friction
and Vibration
Power consumed
by Tx Rotor Friction
and Vibration
Magneto-Dynamic Coupling in a Nutshell
Elix’s technology is based on the ability of one magnet to transfer torque to
another magnet without physical contact. If one magnet is spun as a
synchronous machine, the second magnet close to it will spin at the same
frequency in the opposite direction. Torque transferred to the second magnet
may then be converted to electrical energy.
Rendering of the prototype design with cup shown for size reference Photo of a completed prototype