Controlled power supply

Details Controlled power supply Controlled power supply

1993-10-08

1994-12-20

Stephan, Steven L.

Electric power conversion systems

Current conversion

Using semiconductor-type converter

H02M 706

Patent

active

053750535

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to electric-discharge heating systems and, more particularly, the invention relates to controlled power supplies.
The invention can be used in electric arc furnaces, in welding equipment, as well as in other similar devices, in which use is made of a short-circuit operating mode.
Known in the art are two ways of building up the electric circuit of electric arc furnaces. According to one way, the supply source is based on an uncontrolled or controlled reactor connected in series with a primary winding of a control transformer. The secondary winding of this transformer is connected to a diode rectifier which, in turn, is connected to the furnace electrodes.
The systems based on a diode rectifier with a non-controlled reactor has a low power factor and causes significant voltage fluctuation in the supply network.
The electrode position regulators are designed for maintaining an electric arc of the same length, and a large number of transformer steps are used for controlling the power during the process.
In order to eliminate the negative effect on the other consumers in networks of low and medium power range, dynamic compensators of reactive power are used. This increases the weight and overall dimensions of the power supply as a whole.
Known in the art is an ac-to-dc inverter with an uncontrolled rectifier connected in a bridge circuit comprising a matching transformer whose secondary winding has a tap connected directly to one input of the rectifier bridge, while the end and beginning of the secondary winding are connected to the remaining inputs of the rectifier bridge through a capacitor and a choke respectively. This inverter was proposed for supply of an electric arc and makes it possible to enhance the power factor and reduce the supply network voltage fluctuation. However, the use of this inverter with the known devices to control the position of the electrode for arc sources, in which there is no controlled elements (for example, for electric arc furnaces with a diode rectifier or for furnaces operating with alternating current) needs a switch and a transformer with a large number of control steps. This reduces the operational reliability of the power supply, deteriorates its weight and size and, while continuous control of output power, which is very important for efficient run of the process, is not provided.
Furthermore, higher current harmonics appearing during the rectification do not allow this inverter to be used in the low-power networks. This inverter can hardly be used in high-power furnaces and those with a low arc voltage.
The use of a circuit with a controlled reactor makes it possible to reduce the number of control steps of the transformer, because the inductive reactance of the reactor can be controlled. However, this is attained by complicating the reactor design and using a complex system to control the reactor. The remagnetization of the reactor rods in this system need relatively long time so that the compensation of fast current variation of the electric arc furnace is insufficient, and the voltage fluctuation in the network cannot be adequately reduced. In addition, such a power supply has a low power factor and a high level of the higher harmonics of the consumed current.
Therefore, the above-mentioned technical solutions have not found wide practical application.
Known in the art is a controlled power supply for an electric arc furnace based on a thyristor rectifier.
The power supply comprises a controlled ac-to-dc inverter and a device for controlling the furnace arc. The inverter has a step-by-step controlled transformer whose secondary winding is connected to a thyristor bridge which supplies dc current to the furnace electrodes through a high-power smoothing choke.
The device for controlling the arc current has a circuit to control the arc current with current regulator whose input is fed with a difference between a preset reference value and the measured actual value of the dc arc current. The output signal of the current

REFERENCES:
patent: 2261699 (1941-11-01), Rampacher
patent: 4187449 (1980-02-01), Knoble
patent: 4316125 (1982-02-01), Noguchi
patent: 4730243 (1988-03-01), Glennon
patent: 4807106 (1989-02-01), Baker et al.
patent: 4876634 (1989-10-01), Paice
patent: 5200887 (1993-04-01), Ioroi et al.

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