Wireless Power Transmission

Transmission of electrical energy from source to load without having any physical wired connection, i.e. wireless power transmission will play significant role in future electronics and electrical applications. This paper discusses about wireless power transmission, principles, advantages and its scope in future.

Brainstorming on WPT

There is an unsolved problem over a century, Wireless Power Transmission (WPT). It all started in last decades of 19th century, as we know, Nicolas Tesla was the first to propose and work on Wireless Power transmission. He demonstrated Wireless bulbs at World Columbian Exposition in early 1890s. In early 1961s William C Brown proposed possibilities of microwave power transmission. In 2007 a team from MIT (Massachusetts Institute of Technology) has achieved to light a 60W bulb at a distance of 2 meters with ~40% efficiency. Recent years so many experiments and advancements are being happening on WPT. Different wireless mobile chargers are results of these experiments.

Figure 1: Simple Transmitter and Receiver circuits

Practicality of WPT

Induction Method

Induction charging usually called as wireless charging. This technology is used to manufacture wireless charges for toothbrushes, mobiles, shavers and portable devices. Wireless charging uses same principle as transformer where there is no direct connection between primary and secondary coils. Mutual induction makes the energy transfer between primary and secondary circuits. Similarly induction coil on the charger acts as primary coil and makes alternating electromagnetic field when power is supplied to it. Secondary coil on the portable device (which needs to be charged) receives power from this electromagnetic field when it is placed on the charger and converts it to electrical current and charges the battery. This amazing principle is applied to charge devices with very small range.

It is advantageous as there are no hazardous conductors are exposed, so no risk of electrical shock and it is convenient and safe. Same principle with resonant inductive coupling can be used for power transmission. Resonant inductive coupling increases the transmission range. Here, primary and secondary coils resonate at same frequency. Electricity given to the primary coil produces oscillating current generates oscillating magnetic field and is picked up by secondary coil which is converted into electricity for the load.

Another type of coupling capacitive coupling or is electrostatic induction. Principle is capacitive coupling between two or more electrodes or plates with high frequency, high potential AC current.

All above principles are limited to small distances. These technologies can’t be implemented for larger distances.

Microwave Power Transmission

Through this method power can be transmitted over greater distances. William C Brown demonstrated wireless power transmission through microwaves using Rectenna in 1964. Rectenna is an antenna with rectifier device. Microwave power transmission gives us feasibility of directional power transmission. Typically, this system contains microwave transmitter which generates microwaves using an antenna. Receiver contains a Rectenna which converts microwaves back to electricity. One of the major obstacles with this method is it needs very large scale antennas.

Laser Beam Power Transmission

This method uses photovoltaic cells, which converts light into electricity by photovoltaic effect. First power is converted to laser beam and transmitted from the source. Photovoltaic cells are used at receiver. These cells are used to convert laser beam back to electricity by exposing them to laser beam. Laser beams cross section is very less and it is advantageous for transmitting over larger distances, but laser beams are dangerous to humans and animals. Other disadvantage is it is highly directional receiving photovoltaic cells should be exposed to the transmitted laser beam otherwise complete loss of power could happen. Atmospheric absorption, environmental scattering effects, weather difficulties could affect the efficiency of this system.

Trends and Future of WPT

There are number of technologies for transmitting electric energy from one point to other for shorter distances. Inductive coupling is most commonly used technology for very short distances in mobile charging as discussed.

Recently one of the major mobile manufacturers has filed a patent for scheduled charging of its appliances. Reportedly it is RF based wireless power. It makes an impact on wireless charging mobile devices. It would irk its competitors to do R&D on futuristic wireless charging facilities. Energy square developed a conductive wireless charging. A strip with two conductive points is used to charge mobile. Mobile is placed on top a pad which is connected to power source to charge.

Future mobiles could be charged with mobile service provider, delivering required power from mobile base station. Mobile inbuilt software and hardware takes care of energy threshold level to charge from base station. Higher efficiency is possible with proper handshake between mobile and service provider’s base station. No need to carry a charger or a power bank. Mobiles adopt such change, and soon charging devices become history.

Trends are towards wireless charging points at signals for Electrical Vehicles. In order to minimize carbon footprints, EVs are being replaced with petroleum product vehicles. Charging EVs while driving for longer distances is obstacle to replace existing vehicles. Special roads are to be constructed across utilities and maintained with inductive coupling to provide continuous charging for EVs. Each EV is identifiable from source perspective. Alternative charging possibilities are being researched to construct roads for continuous charging for EVs.

Wireless power plays major role in life saving departments in future. Remote power is a demanding requirement for hurricane prone areas. Quick recovery is possible with wireless power and also it is possible to stop major equipment damage from such disasters. Remote power receivers dug into earth when hazard level meets threshold. Later raises and receives energy and distributes it to required load.

We are not far from wireless power transmission and distribution with high efficiency. Utilities have to take step on it as it has advantages over wired connections.

Advantages of Wireless Power

Wireless power is future and will replace existing wired communication of electricity. Some of the advantages are listed below:

 Power can be transmitted to remote areas where wiring is not feasible.
 Wireless power is not hazardous as wired power where conductors are exposed.
 Transmission and distribution losses of existing system can further more decreased when high efficiency wireless power transmission is implemented.
 Electric vehicles can be charged from anywhere.
 Advantageous to customers is they can be free from power cords, plug in cables and plug in adaptors.
 Expenses on transmission and distribution assets can be reduced, and maintenance costs on transmission and distribution assets can be mitigated.
 Devices can be free from chargers as devices can be charged from anywhere.
 Secure from power theft with handshake from source to load.
 Market enhancement with possibility of welcoming more power vendors to larger distances and customer choice of selecting the power vendors when more power vendors enter into the market
 Market based prices can be applied on power when more vendors are participated in the market.

Efficiency is one of key factors to consider in WPT. Still the problem which Tesla tried to answer is not answered yet. Transmission and distribution of electrical energy with utmost efficiency is not practically implemented. High capital cost and interference are also considerable points to make commercial implementation of wireless power over long distances. More researches required having wireless power system with safe, secure, high efficiency and optimal capital cost as it has so many advantages. As technologies are growing, it is possible to see complete wireless power in future and that day is not too far.