Applications such as electrolysis, electrowinning, DC arc furnaces and plasma torches require high-current (several kA) power supplies at low-voltage levels (few hundreds of volts). In this study, conventional rectifier topologies (diode- and thyristor-based multi-pulse rectifiers with on-load tap changing transformer and chopper-rectifier) used for high-current, variable-voltage applications are reviewed along with recent advancements in the field. The main applications themselves are also discussed. Issues with conventional topologies are highlighted. Power quality techniques like passive and active filters are discussed for power factor and current harmonics compensation. Advanced medium- to high-frequency transformer-based topologies (with current and voltage source rectifiers) are discussed along with simulation results.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2014.0533

High-current variable-voltage rectifiers: state of the art topologies

Development of single-phase, single-switch AC-AC boost converter

High frequency switching power supplies have become part of electronic equipments to provide regulated DC of desired voltages at a low cost and high efficiency. These power supplies have several advantages over their counterpart the linear power supplies. Main advantages are smaller compact size due to elimination of step down transformer and small filters due to high frequency operation. These power supplies have high efficiency because the regulating devices in them works as switches ensuring low device loss. Their output voltage can be controlled for a wide range of input voltage fluctuation by changing the duty cycle of the switching signals. Four common types of switch mode converters are used in DC to DC conversion. They are BUCK, BOOST, BUCK-BOOST and CI\UK converters. Researchers are trying to modifY these DC regulator to regulate AC voltages. Utility AC voltage fluctuation both momentary and prolonged, affect adversely the domestic, industrial and commercial customers. In this thesis an AC Cl\uk regulator made of. ideal switches and practical IGBT switches have investigated. For generation of switching voltage a commercially available IC chip SG l524B is used, thus circuit is compact and more viable. The same chip is utilized to regulate the output voltage by varying the gate signal voltage of the IGBTs if any changes occur in output voltage. As a result the regulator is maintaining constant voltage across the load during any change in supply voltage as well as for variation of load. Freewheeling path and surge voltage across switches create problem in the proposed regulator. Snubbers are used for suppressing surge voltage across switches. Input current of this regulator is greatly reduced to a acceptable limit but still efficiency of this regulator is very poor and needs further research to increase the efficiency to make the regulator commercially viable. In this thesis input filter capacitor of proper size is used for improving the power factor and which decreases the input current.

AC voltage regulation by C^uk switch mode power supply

Power quality describes the quality of voltage and current. It is an important consideration in industries and commercial applications. Power quality problems commonly faced are transients, sags, swells, surges, outages, harmonics and impulses [1]. Among these voltage sags and extended under voltages have large negative impact on industrial productivity, and could be the most important type of power quality variation for many industrial and commercial customers [1-5].

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Power Quality Improvement Using Switch Mode Regulator

The Buck-Boost dc-dc converter has a series switch with the source and a series diode with the load. The series switch makes the input current discontinuous. Filtering out the high frequency switching component from the discontinuous input current of the buck boost dc-dc converter is difficult. In a recent research the one quadrant buckboost has been modified with additional diode-capacitors to have continuous input current which is easy to filter. There are applications where two quadrant dc-dc converters with boost-buck voltage gain/attenuation are necessary. DC motors and battery chargers are the examples of such applications. In this thesis the modified one quadrant buck-boost dc-dc converter has further been topologically changed to operate the converter in two quadrant mode and yet maintain the continuous input current during whichever side is being used as the input of the converter. The proposed two quadrant buck-boost dc-dc converter with continuous input current has been investigated with R, R-L and R-L-Emf loads by interchanging the positions of source and load of the converter. The simulation results indicate the proposed buckboost converter performs two quadrant operations (i.e.-ve voltage ve current and -ve voltage +ve current with the change of duty cycle of control pulse of the switches of the dc-dc converter). In the proposed two quadrant buck-boost dc-dc converter additional switch, diodes, capacitors and inductors are used as per requirement. Number of switches used in the proposed circuit is two and the gate pulses provided to the switches are compliment of each other.

Development of a two quadrant buck boost DC-DC converter with continuous input current

Typical large silicon rectifier dc power supplies for electrochemical lines have ratings of 20 000 to over 300 000 amperes, at voltages of 50 to 1000 volts. The operating efficiency of such installations is of major economic importance, and experience has shown that the use of high-accuracy current regulation can substantially improve efficiency. Regulation is required to compensate for ac supply fluctuations and electrochemical cell or potline characteristics variations. Underload tap changing transformers provide an economical and highly efficient means of varying the rectifier dc output voltage. Control resolution, however, is relatively limited due to the finite voltage steps between taps, and precautions must generally be taken to avoid unnecessary tap changer operations in order to achieve reasonable operating periods without contact maintenance. Several techniques for achieving high-accuracy current regulation with tap changer controlled silicon rectifier power supplies are described. One approach utilizes partial range saturable reactors to provide vernier control between tap changer steps and a fast response feedback amplifier-driver to give essentially continuous high-accuracy (0.1 to 0.5 percent) current regulation. Another method controls the tap changer by means of an error integrating or reset amplifier technique which ignores minor short-tenn current fluctuations but maintains the average value over several hours of operation to within a fraction of a percent of the preset value.

Roland W. Roberts

Papers

Current Regulators for Large Rectifier Power Supplies Used on Electrochemical Processing Lines