WIRE LESS POWER
INTRODUCTION:
INTRODUCTION:
Electricity is today a necessity of modern life. It is difficult to imagine passing a day without electricity. The conventional use of electricity is made possible through the use of wires.Witricity which is basically a for wireless electricity. WiTricity,a "wireless electricity", is a trademark of WiTricity corporation, referring to their devices and processes which use a form of wireless energy transfer including resonant energy transfer etc. The ability to provide electrical energy to remote objects without wires using oscillating magnetic fields. This principle of wireless electricity works on the principle of using coupled resonant objects for the transference of electricity to objects without the use of any wires. A vitricity system consists of a witricity transmitter and another device called the receiver.
PRINCIPLE OF OPERATION:
WiTricity is based on strong coupling between electromagnetic resonant objects to transfer energy wirelessly between them. This differs from other methods like simple induction, microwaves, or air ionization. The system consists of transmitters and receivers that contain magnetic loop antennas critically tuned to the same frequency. Due to operating in the electromagnetic near field, the receiving devices must be no more than about a quarter wavelength from the transmitter (which is a few meters at the frequency used by the example system).The WiTricity devices are coupled almost entirely with magnetic fields (the electric fields are largely confined within capacitors inside the devices), which is argued to make them safer than resonant energy transfer using electric fields (most famously in Tesla coils, whose high electric fields allow them to be used as lightning generators), since most materials couple weakly to magnetic fields .The WiTricity devices are also claimed to be unusual in that they support efficient energy transfer for "mid-range" distances several times larger than the diameter of the resonant objects.
Unlike the far field wireless power transmission systems based on traveling electro-magnetic waves, WiTricity employs near field resonant inductive coupling through magnetic fields similar to those found in transformers except that the primary coil and secondary winding are physically separated, and tuned to resonate to increase their magnetic coupling. These tuned magnetic fields generated by the primary coil can be arranged to interact vigorously with matched secondary windings in distant equipment but far more weakly with any surrounding objects or materials such as radio signals or biological tissue.
In particular, WiTricity is based on using 'strongly-coupled' resonances to achieve a high power-transmission efficiency.The researchers suggest that the exposure levels will be below the threshold for FCC safety regulations, and the radiated-power levels will also comply with the FCC radio interference regulations.
Researchers attribute the delay in developing wireless-power technology to limitations of well-known physical laws and a simple lack of need. Only recently have modern consumers obtained a high number of portable electronic devices which currently require batteries and plug-in chargers.
WIRELESS POWER EFFICIENCY:
The energy consumption of battery chargers has two main contributors:
1) charging efficiency
2) standby power consumption.
STANDBY POWER CONSUMPTION:
Unfortunately, many people leave the chargers and cradles connected to mains power when the charger is not used. The standby power consumption (also called “no-load power consumption”) is significant. A simple calculation shows that power consumed in standby mode is about the same as the energy consumed when loading the battery. The wireless battery chargers continuously plugged into the mains,so main design goals was, therefore, minimize standby power. Go low!
CHARGING EFFICIENCY:
The other contributor is charging efficiency. Our wireless chargers have the same ingredients as a wired charger (an AC-DC adaptor plus charging electronics) and one additional ingredient: the copper wire between adaptor and the mobile phone is replaced with a wireless link. That link is not efficient as a copper wire,but careful design made it possible to achieve at least 70% transfer efficiency. And that percentage can go up a bit if a manufacturer is willing to spend more on high-quality components.
TOTAL ENERGY CONSUMPTION:
A wireless power transmitter can be more efficient, or less efficient than the wired chargers it replaces. It depends on the number of wired chargers that are replaced. It also depends on the type of chargers, and on the habits of the owner.We estimate that in typical situations a wireless power charger breaks even with wired chargers if you replace two wired chargers. Details of that calculation are here.
An estimate of power consumption by wireless chargers.
POWER CONSUMPTION OF WIRED CHARGERS:
The power consumption of a classic mobile phone charger. These chargers are simple so-called “external power adapters”. Efficiency at max load: 72% on average for 5 Watt adaptors.Power consumption at no load: 0.12W on average for 5 Watt adapters with a few exceptionally good adapters going down to 0.01 W.
Suppose that, the adapter for 1 hour per day, and that it remains plugged in for the rest of the day. That is not a good practice, but it is quite common to leave power adapters and cord continuously connected to the mains.
You see that the total energy consumption is:
charging: 1 hour * 2 W / 72% = 2.8 Wh (this assumes that 5 W charger will supply, on average, 2 W during a complete charging cycle) charging: 1 hour * 2 W / 72% = 2.8 Wh (this assumes that 5 W charger will supply, on average, 2 W during a complete charging cycle)
standby (no load): 23 hours * 0.12 W = 2.8 Wh
You see that standby power contributes significantly to the total energy consumption of a mobile phone charger.
WIRELESS CHARGERS CONSUMPTION:
Our wireless chargers also contain an AC-DC power adapter. Let’s assume that is has the same efficiency (72%). Let’s also assumes that it has the same standby power (0.12 W).The transfer efficiency of the wireless power link is typically 70%. And assume that the wireless charger replaces 2 wired chargers. The total energy consumption is:
charging: 1 hours * 4 W / 72% / 70% = 7.9 Wh (we are now charging 2 devices simultaneously)
standby (no load): 23 hours * 0.12 W = 2.8 Wh
Total power consumption of two wired chargers: 2 * ( 2.8 + 2.8 ) = 11.2 Wh
Total power consumption of one wireless charger with two receivers: 7.9 + 2.8 = 10.7 Wh
You see that the total energy consumption is comparable. Although wireless transfer is obviously not as efficient as transport over a copper wire, wireless power transmitters saves standby power energy when the wireless Inductive Power Transmission.
APPLICATIONS:
1)Generating power by placing satellites with giant solar arrays inGeosynchronous Earth Orbit and transmitting the power asmicrowaves to the earth known as Solar Power Satellites (SPS) isthe largest application of WPT.
2) Another application of WPT is moving targets such as fuel free airplanes, fuel free electricvehicles, moving robots and fuel free rockets.
3) The other applications of WPT are Ubiquitous Power Source (or) WirelessPower Source, Wireless sensors and RF Power Adaptive
ADVANTAGES:
1)Wireless Power Transmission system would completely eliminates the existing high-tension power transmission line cables, towers and sub stations .
2) It has more freedom of choice of both receiver andtransmitters. Even mobile transmitters and receivers can be chosen for the WPT system.
3) The cost of transmission and distribution become less and the cost of electrical energy for the consumer alsowould be reduced.
4) The power could be transmitted to the places where the wired transmission is not possible.
5) Power is available at the rectenna as long as the WPTis operating. The power failure due to short circuit and fault on cables would never exist in the transmission and power theft would be not possible at all.
DISADVANTAGES:
1)The Capital Cost for practical implementation of WPT seems to be very high.
2)The other disadvantage of the concept is interferenceof microwave with present communication systems.
CONCLUSION:
The technological developments in Wireless Power Transmission(WPT), the advantages, disadvantages and applications of WPT are also discussed.This concept offers greater possibilities for transmitting power with negligible losses and ease of transmission.So ,Youdon’t need cables, pipes, or copper wires to receive power. It can be sent like a cell phone call – where and when you want it.We can expect with certitude that in next few year’s wonders will be wrought by its applications if all the conditions are favourable.
BY
J.SARAN KUMAR( 3rd EEE)
Categories:
TECHNICAL ARTICLES(session-1)
