The parameters of electrical energy such as voltage amplitude are very important, particularly from the viewpoint of the final consumer and sensitive loads connected to the grid. The dynamic states in the power grid-deep voltage sags and swells-might cause faults and defects in sensitive loads. This paper deals with a three-phase hybrid transformer (HT) without dc energy storage to compensate voltage sags and swells and to protect sensitive loads against the rapid and extensive changes in supply voltage amplitude. The analyzed HT contains two main units: the first one is the conventional electromagnetic transformer, realizing an electromagnetic coupling, and the second one is the buck-boost matrix-reactance chopper, realizing an electrical coupling in the HT unit. In the presented solution, output voltage is transformed in two ways-electromagnetically and electrically. This paper presents an operational description, the theoretical analysis, and the experimental test results from a 2-kVA laboratory model. On the basis of the authors' research, it can be stated that the HT makes it possible to compensate deep voltage sags (deeper than 50% of nominal source voltage) and overvoltages (up to 140% of nominal source voltage) while maintaining good dynamic properties. The main advantages of the proposed solution, in comparison to other conventional solutions, are the ability to control the output voltage in the range of 0.66-3.5 US, good dynamics (transient state during source voltage uS amplitude change is shorter than 10 ms), and galvanic separation between source and load (such as in the case of the conventional electromagnetic transformer).

This paper deals with an ac-ac voltage regulator/compensator based on a hybrid transformer with a matrix converter realizing electrical coupling in the hybrid transformer unit. The parameters of electrical energy, such as voltage amplitude, are very important, particularly from the viewpoint of the final consumer and sensitive loads connected to the grid. Furthermore, a hybrid transformer using a matrix converter can be used for power-flow control and for transient stability improvement in ac transmission systems. Active power flow and voltage magnitude in transmission lines can vary by using a conventional mechanical or thyristor-controlled regulator. However, the control parameters can be executed only in steps depending on the taps available in the electromagnetic transformer. An approach for obtaining continuous control of the voltage magnitude and phase shift using a conventional transformer with two windings and a pulsewidth-modulated matrix converter is presented in this paper. The operating principles and steady-state properties are discussed. Detailed computer simulation results are presented in this paper. Furthermore, experimental test results obtained from a three-phase 3 kVA laboratory model are also presented.

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.