Scientific journal
European Journal of Natural History
ISSN 2073-4972

RATIONALIZATION OF SECONDARY POWER SUPPLY

Magazinnik L.T.
Single phase secondary power supply (SPS), thanks to small weight/torque ratio (kg/kW) and quick response time, has found widespread use in a range of capability from tens W (home video) to several kW (electrical constant-voltage regulator, electric arc welding sets and so on).

One of the essential disadvantages of SPS is low power factor (PF). By using a power factor corrector of modified algorithm of operating it, which allows PF up to 0, 95 and more [1], this issue can be considered solved. The following rationalization of SPS in terms of, for example weight/torque ratio decrease and wastage decrease has the following restrictions:

  • because of asymmetry of output strain of a chopper power isolation transformer is fulfilled with an airspace in the core and is used only at a private loop, that makes ineffective two- cycle bridge scheme of a chopper in comparison to single- cycle, and eventually leads to transformer overall factors increase.
  • increase of output strain frequency of a chopper allows to decrease size of a transformer and smoothing inductor. However, wastage in power transistor is increased. The last is especially essential for powerful SPS.

Including capacitors successively in a chain of power transistor primary coil allows excluding constant constituent in output strain of a chopper and in some cases decreases commutation wastage in power transistors.

Using semi-bridge transistor choppers with capacitors in a power chain for SPS provides two-cycle mode of transformers while there´s no constant constituent in a stress curve. This allows using a core without airspace and with high extent of rectangularity of a loop. As a result transformer´s size and wastage in it may be decreased (with the same frequency) in 2-4 times in comparison to schemes without capacitors. The advantage of this solution is also simplicity of a chopper power part (two-cycle mode is achieved only by two power transistors). Correspondingly, operating system is simplified.

A bridge scheme, as well as semi-bridge, allows two-cycle mode of a power transformer and its whole usage. There are twice more power transistors and output channels of chopper operating system in this scheme, but there´s only one commutating capacitor.

The two considered SPS schemes with capacitors in power chain are identical by its external characteristics, however bridge scheme (except for low power SPS) is more preferable than semi-bridge.

Including capacitors into chain of primary coil of chopper power transformer gives an opportunity to use the core of the transformer without airspace and with little excitation current and with the use of the whole loop that allows essentially decreasing its size. Natural external characteristic of capacitor choppers has lineal part with rigidity determined by total resistance of SPS and a section with load constant power. The lineal part may be, for example, used for welding in carbon dioxide, and section with constant power is ideal for welding in the air. Moreover, capacitor´s real doubling of rectified voltage amplitude simplifies starting and arc stabilization. At a section with constant power current through chopper transistors is broken, that means transistor commutation is without current, wastage is minimal, and that allows increasing frequency and decreasing SPS sizes. Technologically necessary quantity of steps of power may be achieved by two-three capacitors of different volume with a step switch without any close ADS. Not operating chopper- a chopper without PWM or any other way of strain regulation allows solving a problem of galvanic separation of chopper power transistors with the help of a tiny isolation transformer at self-excited oscillator output. There´s no need in expensive power units with composite transistors and optoelectronic isolation [2]. Defense from through currents in "non-operating" choppers may be achieved by small-size triple wound choke [3] and current limitation by the diode-thyristor block action upon the operating system.

The work is presented for an International Science Conference "Contemporary issues of science and education", Moscow, February 16-18, 2010. Came to the editorial office on 1.12.2009.