Isolation transformer

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

Replacing the Grid Interface Transformer in Wind Energy Conversion System With Solid-State Transformer

Abstract: In wind energy conversion systems, the fundamental frequency step-up transformer acts as a key interface between the wind turbine and the grid. Recently, there have been efforts to replace this transformer by an advanced power-electronics-based solid-state transformer (SST). This paper proposes a configuration that combines the doubly fed induction generator-based wind turbine and SST operation. The main objective of the proposed configuration is to interface the turbine with the grid while providing enhanced operation and performance. In this paper, SST controls the active power to/from the rotor side converter, thus, eliminating the grid side converter. The proposed system meets the recent grid code requirements of wind turbine operation under fault conditions. Additionally, it has the ability to supply reactive power to the grid when the wind generation is not up to its rated value. A detailed simulation study is conducted to validate the performance of the proposed configuration.

Partial discharge investigation of a power transformer using wireless wideband radio-frequency measurements

Abstract: The remote detection of a transformer internal partial discharge (PD) has been demonstrated using mobile wideband radio-frequency receiving equipment. The PD is externally detectable due to coupling within the transformer tank, causing impulsive signals to be radiated from external connections. A wideband direction-finding technique using a four-antenna array has shown the source of the radiation to be the tertiary winding connections; the radiated impulse has characteristics typical of this method of emission. No other external site of radiation from the transformer was detected. Due to the lack of coupling to the primary and secondary windings, it is believed that the PD is present between the tertiary windings and the core.

Switching control strategy for full ZVS soft-switching operation of a Dual Active Bridge AC/DC converter

Abstract: A switching control strategy to enable Zero-Voltage-Switching (ZVS) over the entire input-voltage interval and the full power range of a single-stage Dual Active Bridge (DAB) AC/DC converter is proposed. The converter topology consists of a DAB DC/DC converter, receiving a rectified AC line voltage via a synchronous rectifier. The DAB comprises primary and secondary side full bridges, linked by a high-frequency isolation transformer and inductor. Using conventional control strategies, the soft-switching boundary conditions are exceeded at the higher voltage conversion ratios of the AC input interval. Recently we presented a novel pulse-width-modulation strategy to fully eliminate these boundaries, using a half bridge — full bridge DAB configuration. In this papers the analysis is extended towards a full bridge — full bridge DAB setup, providing more flexibility to minimize the component RMS currents and allowing increased performance (in terms of efficiency and volume). Experimental results are given to validate the theoretical analysis and practical feasibility of the proposed strategy.

A Dual Active Bridge Converter With an Extended High-Efficiency Range by DC Blocking Capacitor Voltage Control

Abstract: A Dual active bridge (DAB) converter can achieve a wide high-efficiency range when its input and output voltages are equal, assuming a 1:1 turns ratio for its isolation transformer. If its input or output voltage is doubled, efficiency of the DAB will drop significantly, because of the introduction of the hard switching and high circulating power. Thus, a new modulation scheme has been proposed, whose main idea is to introduce a voltage offset across the dc blocking capacitor connected in series with the transformer. Operational principle of the proposed modulation has been introduced, before analyzing its soft-switching area and circulating power mathematically. The final modulation scheme is not difficult to implement, but can help the DAB achieve soft switching, low circulating power, and thereby high efficiency, even with its input or output voltage doubled. These features have been verified by experimental results obtained with a 1.2-kW prototype.

The Thyristor Electronic Transformer: a Power Converter Using a High-Frequency Link

Abstract: The electronic transformer is a device which behaves in the same manner as a conventional power transformer in that it steps voltage levels up or down while providing isolation and can accommodate load current of any power factor. It contains thyristor power switches which convert the low-frequency (dc to 400-Hz) voltage wave to a high-frequency (in the order of 10 000 Hz) wave. A comparatively small magnetic transformer then provides the voltage level transformation and isolation functions. Similar thyristor power switches then reconstruct the original low-frequency wave at the desired output voltage level. This device can incorporate additional features not found in a conventional transformer, such as current limiting and current interruption. The theory of operation is presented and confirmed by experimental data.