Isolation transformer

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

Electrical power converter with step-gapped transformer

Abstract: An improved electrical power converter is disclosed. The electrical power converter utilizes a step-gapped power transformer having a ferromagnetic core, a primary winding, and one or more secondary windings. The ferromagnetic core is step-gapped such that it has a continuous portion and a gapped portion. A power switch, preferably a MOSFET, alternately couples an input voltage across the primary winding of the transformer, inducing voltage pulses across the secondary windings that are filtered to produce one or more output voltages. The gate terminal of the MOSFET is preferably driven by the voltage induced across a tertiary winding of the transformer.

Reference-Trajectory-Optimized SVM for High-Power Current-Source Converters to Improve Harmonic Performance and Reduce Common-Mode Voltage

Abstract: For medium-voltage high-power drives fed by current-source converters (CSCs), a transformerless configuration has benefits in both cost and volume. Removing the isolation transformer necessitates a common-mode choke to undertake the major portion of the drive's common-mode voltage (CMV) stress, which would otherwise cause premature failure of the motor insulation system. On the other hand, as device switching frequency in high-power CSCs is normally limited to a few hundred hertz, improving harmonic performance via modulation has always been a challenge. Selective harmonic elimination (SHE) is a preferred modulation scheme in such a system owing to its ability to eliminate several unwanted low-order harmonic currents. Alternatively, conventional space vector modulation (SVM) provides continuous modulation index adjustment capability, but its output current contains low-order harmonics with high magnitudes that may arouse harmful resonances in the system. Aiming at reducing CMV and improving harmonic performance at the same time, this paper proposes a new SVM-based modulation strategy for high-power CSCs using synthesized reference trajectory on the hexagon in the αβ plane. Along with the proposed strategy, two methods of reference trajectory optimization (RTO) are investigated. By introducing a coefficient to the duty-cycle function for RTO, the first method can remove an extra low-order harmonic component, or minimize the weighted total harmonic distortion. The second method, with a different approach of RTO, eliminates the unwanted low-order harmonics by combining the proposed SVM with the SHE. The proposed concepts are verified by both simulation and experimental results.

2 MHz high-density integrated power supply for gate driver in high-temperature applications

Abstract: A PCB embedded transformer for harsh environment (i.e., ambient temperature above 200 °C) applications is presented and used in the design of a 2 MHz integrated power-supply prototype for gate driver. The main benefits of using this developed PCB embedding process are the capability to customize the air-gap for the flyback transformer and volume reduction for the converter. The easy modulation of the air-gap distance can be achieved using PCB material in specfic thickness. Moreover, the design of a coplanar-winding transformer structure with very low inter-winding capacitance needs a large winding area and raises the interest for the PCB integration approach. Two-machined ferrite pieces in UI shape were sandwiched into a multi-layer PCB laminate with multiple pressing processes. A converter prototype built with the PCB embedded transformer and other components (GaN transistors, gate driver and passives) mounted above it shows 72% of power efficiency. One thousand thermal cycles between −55 °C and 200 °C were performed on the PCB embedded transformer without observation of any major defects, such as delamination and cracking. The thermal reliability test validates the compatibility between the selected ferrite core and PCB materials as well as the feasibility of this developed transformer embedding method. A three-time volume reduction is achieved when comparing with a benchmark converter prototype using discrete transformer.

Interleaved High-Voltage Transformer Windings

Abstract: Interleaved-turn high-voltage transformer windings are a useful alternative to continuous disc and layer windings for a wide range of transformer output and voltage ratings. Many configurations have been devised to meet different requirements. This paper reports the discovery that the original and most- commonly-used form of interleaved winding has an unexpectedly large internal oscillatory response to chopped-wave or front-of-wave impulse (lightning surge) voltages. It describes the subsequent development of a less-oscillatory winding which allows smaller insulation clearances for equivalent reliability.

Electrical transformer with reduced core noise

Abstract: An electrical transformer includes a housing, a transformer core and winding subassembly located in the housing, and a cooling fan subassembly. The cooling fan subassembly includes a variable speed fan located outside the housing, a temperature sensor located near the housing, and a controller having an output port connected to the variable speed fan and an input port connected to the temperature sensor. The controller reduces the fan speed (and hence the fan noise) when a lower fan speed can maintain the desired temperature as sensed by the temperature sensor. Preferably, the electrical transformer further includes an active mount subassembly and/or (when the housing includes a tank containing transformer fluid) a mechanism for varying the dynamic pressure of such transformer fluid.