Soft-Switching Smart Transformer Design and Application for Photovoltaic Integrated Smart City Power Distribution

Abstract

Smart city power distributions have become promising technologies to meet the demand for energy in developed countries. However, increase in smart grids causes several power quality problems on the smart grid, in particular, current and voltage harmonic distortions, sudden voltage sag and swells, fault current, and isolation deterioration. Smart transformers are potential solutions to improve the power quality on the electric grid. They present energy efficiency, ensure grid reliability and power flow control, voltage regulation, bidirectional power flow, fault current limiting, harmonic blocking, and galvanic isolation. Therefore, this paper offers an optimal selection of a three-stage (AC-DC-DC-AC) smart transformer model and power control strategy for solar PV power plant integrated smart grids. The topology of the rectifier, isolated bidirectional converter, and inverter has soft-switching features. This enables low conduction loss, low electromagnetic interference (EMI), high efficiency, achievable zero-voltage switching for converters, and zero-current switching for electrical auxiliary systems. Operation strategies of the proposed ST, PWM control, voltage, and current control between converters, including a medium-voltage (MV) high-frequency transformer to realize a 10 kVA, 450 Vdc to 220 Vdc, or 220 Vac ST, are presented. Significantly, the ST prototype achieves 96.7% conversion efficiency thanks to its control strategy, even under unstable power generation conditions from the solar PV plant. Experimental results obtained on the 344 Vac 10.4 A load current validates the dv/dt rate 6.8 kV/us. The dynamic and experimental results of the proposed bidirectional smart transformer demonstrate the success in preventing power quality problems for photovoltaic integrated smart city power distribution.

Improved Dynamic Performance of Average-Value Modelled Active Front-End Rectifiers

“…To address these challenges, many approaches have been investigated to guarantee the proper control and operation of power systems equipped with power converters. Among these solutions, smart transformers, also called power electronic transformers, have been widely applied to interface medium-and low-voltage systems through fully controllable power electronic devices [3]. Similarly, power electronic transformations have played a key role in the onboard systems for transportation applications, aircraft, and shipboard [4,5].…”

Direct Power Control for Three-Level Multifunctional Voltage Source Inverter of PV Systems Using a Simplified Super-Twisting Algorithm

“…It is also known that this serious production contributes to increasing carbon dioxide emissions and global warming, as well as pollution of the Earth. It represents a depletion of natural resource stocks, which primarily constitutes a threat to future generation capabilities [2]. These obstacles made several governments of countries exploit all kinds of distributed energy resources based on renewable energy technologies or green energy technologies, due to their natural renewal.…”