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High Efficiency Wireless Power Transfer

Author : Fady Mishriki, CEO PowerbyProxi

07 May 2010

Increased mobility and operations in dirty or wet environments mean that engineers must develop new approaches to ensure continuous power supply to equipment. The challenges involve power supplies, recharging batteries, optimising sensor placement and dealing with rotating or moving joints.

Proxi-Point provides point to point wireless power transfer through any non-metal material to multiple devices.
Proxi-Point provides point to point wireless power transfer through any non-metal material to multiple devices.

Mechanical slip rings have been the conventional way to provide power to the rotating parts of industrial equipment.

Unfortunately, traditional slip rings can fail, undergo wear and tear and experience intermittent connections for power and data communications that require frequent maintenance or limit mobility. These problems make slip rings less reliable, increase process-related downtime and increase related ongoing maintenance costs.

Industrial assembly lines are another example of where supplying power to difficult, hard-to-reach locations is a problem. In these applications, sensors track each item at different points along the assembly process. These sensors can be powered wirelessly, which simplifies sensor installation and maintenance.

For industrial sensors, cabling costs, cable termination and changing voltage or current requirements might prompt engineers to consider a battery-based power system instead. In battery-based systems, however, recharge and replacement might be the limiting factors. For example, an RF or charged capacitor system can work if power needs are tiny, but batteries won’t work if sensor requirements exceed 50 mA. And the challenge of frequent battery re-charging en masse remains.

The technical impact of these challenges translate into fewer design options for equipment designers and engineers as well as higher installation, maintenance and certification costs for process managers.

What wireless power needs to do
To address these challenges, effective wireless power and data solutions must:

A frictionless slip ring supplies power to rotating, highly mobile industrial equipment.
A frictionless slip ring supplies power to rotating, highly mobile industrial equipment.

* Be reliable. Equipment built for industrial applications must often be designed to operate reliably in wet and dirty environments. For example, robotic arms or rotating joints such as those encountered in construction machinery and wind turbines must be capable of moving continuously through 360 degrees.

* Be efficient. Typically, conventional inductively coupled power transfer (ICPT) systems have achieved efficiency levels of less than 50 percent. This occurs even with minimal distance between coils, a fixed orientation, or precise tuning of the coils. When combined with heat and reliability problems due to systems' inherent inefficiency, these design limitations often offset ICPT benefits.

* Offer flexible design options. New developments in wireless power transfer technology offer the promise of more flexible design alternatives and potential cost savings to industrial equipment manufacturers and users.

New generations of wireless power transfer technology can satisfy all of these requirements. It can be used in a wide variety of applications in many industries.

Specifying a wireless power system requires tradeoffs between these four key parameters:

* Range and orientation: proximity (measured in centimetres) with optimum efficiencies achieved over distances up to 5 cm.

* Power capacity: power ranging from milliwatts to 10 kilowatts.

* System efficiency: power received as a percentage of power transmitted. This can range from 50 to 90 percent.

* System volume: based on the amount of power required, volume ranges from as small as a coin for lower power levels to the size of a phone book for kilowatt power levels.

These parameters are all related. For example, the range of a system directly affects its volume and power level. A system that is not limited by volume but needs to supply a few watts of power will have a much greater range than a volume-limited system that requires hundreds of watts. Similarly, with minimal power requirements, designers can accept lower efficiency but at the cost of greater heat (a by product of inefficiency).

Third-Generation Wireless Power Transfer
Proxi-Wave™ is a third generation, wireless power delivery system. It provides a reliable, efficient way to supply power to devices in hostile environments and hard-to-reach locations.

The technology offers high efficiency levels in relatively loose coupling arrangements across an air gap or through any nonmetallic material.

It uses coils to transmit and receive power. A converter, powered through AC mains, a truck battery or other sources, drives the transmitter coil. The controller regulates the power flow from the receiver coil to the target electrical device or electronics.

As RF antennas must to be tuned to maximise signal strength, the Proxi-Wave system must be tuned to maintain high-efficiency power transfer, even under variable-load and zero-load environments. Patented, dynamic harmonisation control (DHC) tuning technology provides significant advantages over other solutions. In response to environmental and load changes, DHC varies frequency dynamically. DHC achieves greater power transfer efficiency, enabling smaller receiver sizes and generating negligible electromagnetic interference, even as it allows greater transmission range.

In most circumstances (slip-ring applications, for example) Proxi-Wave technology achieves a 90 percent efficiency level. The technology is particularly suited for variable-load environments, in which power requirements change on a continual basis, depending on the requirements of the machinery it is supplying.

Four platforms
There are four solution platforms, which are designed to meet the requirements of a wide range of applications and customers.

Proxi solutions demonstration module.
Proxi solutions demonstration module.

Proxi-Point™ is a wireless, one-to-one or one-to-many power transfer solution. This solution delivers power at distances of up to 2 metres in a wide range of applications, which include heavy equipment, aviation, and security access control. It enables autonomous charging and the ability to charge multiple devices simultaneously.

Proxi-Ring™ is a friction-free, contact-free slip ring, which supplies power to rotating, highly mobile industrial equipment. This solution is a totally electrical device with no moving parts or friction-based components. It enables complete freedom of movement (360° continuous rotation), unlimited RPM and no need for lubrication and cooling.

Proxi-Loom™ is a track loop system, in which multiple sensors with receivers mounted on them can draw power and signal without a physical connection to the loom. ProxiLoom enables easy replacement of faulty sensors or devices as well as moving or delivering power to the sensors without rewiring.

Proxi-Fi™ is a miniaturisation of the PowerbyProxi wireless receiver onto silicon. This solution provides power for a wide range of electronic devices and equipment such as power management chips. Designers can use Proxi-Fi to power thin or small form factors and to overcome the size constraints of physical connectors. These solutions enable designers to migrate to rechargeable batteries and to deliver wireless power for mobility and convenience. The benefits include a broader range of rechargeable, battery solution designs and applications and significant installation and ongoing maintenance cost savings.

A sensor network example
Consider a manufacturing facility with a sensor network that captures data during the manufacturing process. Sensors are placed on items that are in constant motion. Power requirements vary from 5 to 10 watts, and the maximum range is 20 centimetres.

The factory environment is dirty, and management overhead and form-factor considerations make batteries inappropriate. Traditional slip rings are also impractical. Instead, process planners choose ICPT (inductively coupled power transfer) in a loom configuration to power the factory-wide network of sensors on moving items. This process can include photoelectric, temperature, humidity or pressure sensors as well as strain gauges and accelerometers. Although Ethernet and RS-485 standards are supported, the sensors usually communicate by CANbus.

The planners chose to use the Proxi-Loom system. Given the 5-to-10-watt power requirement, they estimate that a PowerbyProxi receiver the size of 4 AA batteries could achieve a transmission range of 20 cm between the Proxi-Loom track and transmitter plugged into the electrical mains.

The Proxi-Loom concept: power to multiple sensors or devices along a single cable instead of current wiring loom implementations.
The Proxi-Loom concept: power to multiple sensors or devices along a single cable instead of current wiring loom implementations.

To ensure system compatibility with wireless sensor nodes, the engineers also compare PowerbyProxi technology with wireless sensors that use the 802.11b wireless protocol and operate at 2.4 GHz. They also plan for a SensiFi, G2Microsystems and Decawave platform, (all of which generally operate in the 2.4 GHz band and communicate using an 802.11-based protocol). Intel Atom and ARM processors will function alongside PowerbyProxi technology.

And finally, the planners added Proxi-Com, a new wireless communications product. Proxi-Com encapsulates a wireless link for common industrial standards such as PLC, RS485, RS422, CAN Bus and Ethernet. When used with a PowerbyProxi ICPT product, Proxi-Com provides a complete wireless power transfer solution.

Author: Fady Mishriki, CEO PowerbyProxi

For more information, visit www.powerbyproxi.com


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