Most mains-operated equipment in use today is connected to the supply via plugs and sockets. These are generally acceptable in benign environments, but can be unsafe or have limited life in the presence of moisture. In explosive atmospheres and in undersea applications, special connectors must be used. This paper describes a technique, the contactless energy transfer system (CETS), by which electrical energy may be transmitted, without electrical connection or physical contact, through nonmagnetic media of low conductivity. The CETS, which has been used to transfer up to 5 kW across a 10-mm gap, employs high-frequency magnetic coupling and enables plug-in power connections to be made in wet or hazardous environmental conditions without the risk of electric shock, short circuiting, or sparking. Energy may be transmitted without the necessity for accurately manufactured “plug-and-socket” mechanisms and may be transmitted from source to load, even when there is relative motion. Load-source voltage matching may be made inherent to the system. Recently, contactless (or contact-free) energy transfer (CET) systems have become more widely developed and investigated. This innovative technology brings about new possibilities of supplying mobile devices with electrical energy by allowing elimination of cables, connectors, and/or slip rings. This increases reliability and maintenance-free operation of such systems in critical applications such as aerospace, biomedicine, multisensors, and robotics. A large number of technologies for CET have been established, but these can be summed up in three commonly accepted terminologies: * CET
* Contactless (or contact-free) power transfer (CPT)
* Wireless power transfer (WPT).
In the most popular applications, the core of CET systems is the inductive or capacitive coupling between power source and load, and high-switching frequency power electronic converter for energy flow control. The capacitive coupling is used in the low-power range whereas the inductive coupling allows transferring power from a few milli watts throughout several kilowatts up to hundreds of kilowatts. Today industry is moving toward a wireless world. Like consumers with their cell phones, laptops and PDA’s, industrial companies want wireless technologies that improve versatility, reduce costs and maintain connectivity. One of the latest developments to draw interest among engineering personnel is contactless energy transfer for powering and controlling motors.
CONCEPT OF CETS
A transformer may be used to supply electrical energy to a load and, at the same time, provide galvanic Isolation. If the primary and secondary windings of the transformer are wound on separate magnetic structures, as shown In Fig.2.1, then energy coupling is possible without physical Connection between the source and load units. A transformer having the form shown in the figure may be represented by the well-known transformer circuit model Shown, with source and load, in Fig. 2.2. The large air gap in the magnetic path gives the transformer a low magnetizing Inductance Lm and high leakage inductances Li1 and Li2 . The Magnetizing current will be high, resulting in high primary Winding loss, and the output voltage will be load sensitive, So that voltage regulation is poor. The transformer will be Inefficient and, although the high reluctance of the air gap will Result in low flux density, flux leakage will be high. There is also a high probability of noncompliance with electromagnetic Compatibility (EMC) and safety regulations.
There is (or may be) relative motion between transmitter and receiver, contact-based techniques (rolling/sliding carbon/metal contacts, trailing leads) Have clear disadvantages. Even when there is no relative Motion and the environment is relatively benign (for example, the charging of electric vehicles, the absence of physical galvanic...
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