Electric power conversion

There are also devices and methods to convert between power systems designed for single and three-phase operation.

The standard power voltage and frequency vary from country to country and sometimes within a country. In North America and northern South America, it is usually 120 volts, 60 hertz (Hz), but in Europe, Asia, Africa, and many other parts of the world, it is usually 230 volts, 50 Hz.[2] Aircraft often use 400 Hz power internally, so 50 Hz or 60 Hz to 400 Hz frequency conversion is needed for use in the ground power unit used to power the airplane while it is on the ground. Conversely, internal 400 Hz internal power may be converted to 50 Hz or 60 Hz for convenience power outlets available to passengers during flight.

Certain specialized circuits can also be considered power converters, such as the flyback transformer subsystem powering a CRT, generating high voltage at approximately 15 kHz.

Consumer electronics usually include an AC adapter (a type of power supply) to convert mains-voltage AC current to low-voltage DC suitable for consumption by microchips. Consumer voltage converters (also known as "travel converters") are used when traveling between countries that use ~120 V versus ~240 V AC mains power. (There are also consumer "adapters" which merely form an electrical connection between two differently shaped AC power plugs and sockets, but these change neither voltage nor frequency.)

Transformers are used in power converters to incorporate:

• Electrical isolation
• Voltage step-down or step up

The secondary circuit is floating, when you touch the secondary circuit, you merely drag its potential to your body's potential or the earth's potential. There will be no current flowing through your body. That's why you can use your cellphone safely when it is being charged, even if your cellphone has a metal shell and is connected to the secondary circuit.

Operating at high frequency and supplying low power, power converters have much smaller transformers as compared with those of fundamental frequency, high power applications. Usually, in power systems, transformers transmit power simultaneously, no charge! The current in the primary winding of a transformer plays two roles:

• It sets up the mutual flux in accordance with Ampere's law.
• It balances the demagnetizing effect of the load current in the secondary winding.

Flyback converter's transformer works differently, like an inductor. In each cycle, the flyback converter's transformer first gets charged and then releases its energy to the load. Accordingly, the flyback converter's transformer air gap has two functions. It not only determines inductance but also stores energy. For the flyback converter, the transformer gap can have the function of energy transmission through cycles of charging and discharging.

${\displaystyle W_{e}={\frac {1}{2}}BH={\frac {1}{2}}{\frac {B^{2}}{\mu }}}$

The core's relative permeability ${\displaystyle \mu _{r}}$ can be > 1,000, even > 10,000. While the air gap features much lower permeability, accordingly has higher energy density.

• Power supply
• Cascade converter
• Motor-generator
• Resonant converter
• Rotary converter

• Abraham I. Pressman (1997). Switching Power Supply Design. McGraw-Hill. ISBN 0-07-052236-7.
• Ned Mohan, Tore M. Undeland, William P. Robbins (2002). Power Electronics: Converters, Applications, and Design. Wiley. ISBN 0-471-22693-9.
• Fang Lin Luo, Hong Ye, Muhammad H. Rashid (2005). Digital Power Electronics and Applications. Elsevier. ISBN 0-12-088757-6.
• Fang Lin Luo, Hong Ye (2004). Advanced DC/DC Converters. CRC Press. ISBN 0-8493-1956-0.
• Mingliang Liu (2006). Demystifying Switched-Capacitor Circuits. Elsevier. ISBN 0-7506-7907-7.

• A general description of DC-DC converters
• U.S. based 50 Hz, 60 Hz, and 400 Hz frequency converter manufacturer
• GlobTek, Inc. Glossary of electric power supply and power conversion terms