Hybrid distribution transformer based on a bipolar direct AC/AC converter

Dynamic states in the power grid – deep voltage sags and swells, voltage fluctuation – can cause faults and defects in sensitive loads and in consequence financial losses. This study presents a voltage conditioner based on a direct PWM AC/AC converter with matrix chopper cooperating with a distribution transformer, called a hybrid distribution transformer (HDT). In comparison with other solutions of hybrid and smart distribution transformers, the proposed HDT is characterised by having a simple construction and small number of power electronic switches, a wide range and continuously variable voltage control character, and good dynamic properties, in combination with a high reliability. The study contains a detailed operational description and the experimental test results of a 1 kVA rated power laboratory model. The experimental tests were conducted in a closed control-loop with a peak detector unit in a feedback path, as well as with various types of voltage perturbation with linear and non-linear loads. In addition, some of the properties of the proposed HDT have been compared with other similar hybrid and smart distribution transformers described in the literature.