Hybrid stepless distribution transformer with four-quadrant AC/DC/AC converter at low voltage side - simulation tests

Abstract

The article presents the work of the stepless hybrid distribution transformer (HT), as an alternative to the so far applied Automatic Voltage Regulator (AVR) solutions, used to control the voltage in the power system in terms of the fundamental harmonic. The HT is a combination of a conventional distribution transformer and an AC/DC/AC converter connected in series with the transformers secondary winding. In the work the basic control algorithm of the AC/DC/AC converter operated as a series connected additive voltage source in the HT system, has been described. The article contains the preliminary results of computer simulation studies of the model elaborated in PSIM. Streszczenie. W artykule opisano działanie bezstopniowego hybrydowego transformatora dystrybucyjnego (HT), jako alternatywę dla dotychczas stosowanych rozwiązań AVR (Automatic Voltage Regulator), służących do kontroli poziomu napięcia w systemie elektroenergetycznym w zakresie podstawowej harmonicznej. Układ HT to połączenie konwencjonalnego transformatora dystrybucyjnego oraz przekształtnika AC/DC/AC włączonego w szereg z uzwojeniem wtórnym transformatora. W pracy przedstawiono podstawowy algorytm sterowania przekształtnikiem AC/DC/AC jako szeregowe źródło napięcia dodawczego w układzie badanego HT. Artykuł zawiera wstępne wyniki badań symulacyjnych modelu opracowanego w programie PSIM. (Hybrydowy bezstopniowy transformator dystrybucyjny z czterokwadrantowym przekształtnikiem AC/DC/AC po stronie niskiego napięcia-badania symulacyjne).

Controlling Hybrid Transformers by Lyapunov Method for Application in Smart Distribution Network

“…To obtain the last condition , from which the switching law can also be obtained, the derivative Eq. ( 12) is written as follows: 13 In Eq. ( 13), we substitute two equations ( 10) and ( 11): 14 After simpli cation, we have:…”

“…Due to heavy computational load and variable switching frequency, practical implementation is not provided. In [13],…”

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“…Therefore, the hybrid transformer is a hopeful solution to enhance the power quality of the grid. The power electronic converter is capable of compensating active and reactive power, regulating the voltage, balancing the currents of the load, and filtering harmonics [25].…”

Configurations, Power Topologies and Applications of Hybrid Distribution Transformers

“…In a similar manner, it is possible to utilize it in configuration of Figure 2g since both ends of the power converter are connected to auxiliary windings, which are designed to comply with the converter rating requirements [59]. In cases when the shunt converter is connected to four-wire grids, the neutral wire can be obtained from the middle point of the split DC-Link capacitor, as Figure 9d shows [48,96]. In this case the rectifier-end is connected to an auxiliary winding, while the inverter-side is connected in series to the secondary-side of the LFT, and the neutral connection is provided by the split capacitor.…”

“…Tap changers commutation systems allow us to add an offset into the voltage regulation in steps, without an increase in the power converter rating. The operating region of this alternative is shown in Figure 14b [96,101]. When utilizing HDT configurations that are able to inject unrestricted active and reactive power, the operating vector can be represented, as shown in Figure 14c.…”