Isolation transformer

About: Isolation transformer is a research topic. Over the lifetime, 8145 publications have been published within this topic receiving 72396 citations.

Solid-State Transformer for Grid Interface of High-Power Multipulse Rectifiers

Abstract: This paper proposes a medium-frequency (MF) solid-state transformer (SST) based grid interface for high-power multipulse rectifiers. In the proposed approach, the low-frequency ac (grid) voltage is transformed to MF voltage via front-end converters. The three single-phase MF outputs from these converters are fed to the primary side of a three-phase, five-limb multiwinding isolation transformer (or alternately three one-phase transformers). The secondary side windings from the transformer are configured in a certain “zig-zag” arrangement, which are connected to the inputs of three-phase diode rectifier modules as in a typical multipulse system. The proposed topology can better than double the power density by reducing volume (or weight) of the required front-end isolation transformer while maintaining the same input current quality as a conventional low-frequency transformer based approach. Usage of an open-loop square wave pulse width modulation for the front-end converters makes this approach simple to implement. This paper explains the proposed concept taking an adjustable speed drive application's perspective using modeling, simulation, and experimental results from a scaled down laboratory prototype.

Losses and temperature rise within power transformers subjected to distorted currents

Abstract: The currently high energy efficiency demands and control requirements impose an extensive usage of power electronic devices and circuits in both domestic and industrial applications. These intrinsic nonlinear loads generate prominent level distortion of the electric current waveforms, which lead to additional losses and thermal stress within the power supply distribution system. Thus, due to the supplementary harmonic losses, the power transformer, experience an increase of its hot-spot temperature that may cause the machine insulation failure and ultimately the transformer lifetime expectancy reduction. In order to overcome these undesirable consequences, the reduction of the apparent power rating of the transformer (derating) is commonly adopted. This paper quantitatively investigates the nonsinusoidal steady state of the transformer by evaluating the losses distribution within the machine, its hot-spot temperature rise and the corresponding transformer loss of life. The computation procedure is exemplified on a 250 kVA liquid filled three-phase power distribution transformer that supplies both linear and nonlinear industrial loads.

Comparative study of power factor correction converters for single phase half-bridge inverters

Abstract: A half-bridge inverter is very suitable for single-phase on-line UPS applications because it offers very desirable features. These include fewer active switches, a common neutral connection-not requiring an isolation transformer, and sinusoidal input currents if a power factor correction (PFC) converter is used at the front end. This paper presents a comparative study of PFC converters for single-phase half-bridge UPS inverters. A traditional half-bridge converter and two recently introduced AC-DC/DC-DC boost converters are comparatively investigated for active switch count, voltage stresses on the switches and capability of voltage balance control of the DC bus capacitors. Analytical and experimental results are included in this paper to illustrate performance differences among the converters in terms of input current harmonic distortion and energy efficiency.

Improved three stage power source for electric arc welding

Abstract: A three stage power source for an electric arc welding process comprising an input stage having an AC input and a first DC output signal; a second stage in the form of an unregulated DC to DC converter having an input connected to the first DC output signal, a network of switches switched at a high frequency with a given duty cycle to convert the input into a first internal AC signal, an isolation transformer with a primary winding driven by the first internal high frequency AC signal and a secondary winding for creating a second internal high frequency AC signal and a rectifier to convert the second internal AC signal into a second DC output signal of the second stage, with a magnitude related to the duty cycle of the switches; and, a third stage to convert the second DC output signal to a welding output for welding wherein the input stage has a regulated DC to DC converter with a boost power switch having an active soft switching circuit.