Configurations, Power Topologies and Applications of Hybrid Distribution Transformers

Abstract

Distribution systems are under constant stress due to their highly variable operating conditions, which jeopardize distribution transformers and lines, degrading the end-user service. Due to transformer regulation, variable loads can generate voltage profiles out of the acceptable bands recommended by grid codes, affecting the quality of service. At the same time, nonlinear loads, such as diode bridge rectifiers without power factor correction systems, generate nonlinear currents that affect the distribution transformer operation, reducing its lifetime. Variable loads can be commonly found at domiciliary levels due to the random operation of home appliances, but recently also due to electric vehicle charging stations, where the distribution transformer can cyclically vary between no-load, rated and overrated load. Thus, the distribution transformer can not safely operate under highly-dynamic and stressful conditions, requiring the support of alternative systems. Among the existing solutions, hybrid transformers, which are composed of a conventional transformer and a power converter, are an interesting alternative to cope with several power quality problems. This article is a review of the available literature about hybrid distribution transformers.

Multi-Mode Control of a Hybrid Transformer for the Coordinated Regulation of Voltage and Reverse Power in Active Distribution Network

“…The proposed HT architecture is ca pable of maintaining a stable supply voltage in the transmission networks. A detailed re view of the recently updated HT design can be found in [7,12,13].…”

Operation Assessment of a Hybrid Distribution Transformer Compensating for Voltage and Power Factor Using Predictive Control

“…Depending on the configuration used, the HDT can perform specific compensation tasks, so the topology to be used is directly linked to the variables that need to be controlled [14].…”

“…Addressing the limitations of solid-state transformers (SSTs) and seeking to maintain controllability in voltage and current variables, Hybrid Distribution Transformers (HDTs) have emerged as a viable alternative. Combining a conventional low-frequency transformer with a power converter, HDTs enable the partial control of voltage and current, resulting in lower power loss and reduced construction costs compared to SSTs [13,14]. Furthermore, HDTs offer a fail-safe mechanism through a switch that isolates the converter in case of failure, allowing operation solely via the LFT, thus ensuring compatibility with existing protection systems [11].…”

“…In the literature, there are multiple HDT configurations proposed, leading to various converter topologies being applied [14]. In general, there are two types of configurations, those that operate on one side of the transformer and those that operate on both sides of the LFT.…”

Voltage Control in LV Distribution Grid Using AC Voltage Compensator with Bipolar AC/AC Matrix Choppers

“…Various HT topologies with different regulatory capabilities have been proposed in the scientific literature. A few review articles have been published to explain the concept of how they work [5][6][7][8][9][10]. The most frequently considered HT systems are topologies with a back-to-back converter [11][12][13][14][15][16][17], matrix converter [18][19][20][21] or various types of AC/AC choppers [22][23][24].…”