In this paper, power electronic transformer (PET)-based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT)-based systems, their pros and cons are summarized. By further reviewing all kinds of PET-based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state of the art, the key challenges and opportunities are identified and discussed. It shows that although PET-based systems are still developing and far from mature, they are already superior to LFT-based systems in terms of system weight, efficiency, and functionalities especially for 15-kV/16.7-Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers, and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.

Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities

Renewable energy sources, such as offshore wind farms, require high voltage gains in order to interface with power transmission networks. These conversions are normally made using bulky, complex, and costly transformers and high-voltage ac-dc converters with unnecessary bidirectional power flow capability. Multiple modules of single-switch single-inductor dc-dc converters can reach high gains without transformers in these applications due to low semiconductor conduction loss in high-power devices. This paper describes a new approach for high-gain high-voltage dc-dc converters using multiple modules of single-switch single-inductor transformerless converters. Results for low-voltage experimental prototypes show gains of up to 29 p.u. and demonstrate the potential of the approach as high-gain dc-dc converters for offshore wind farms. This paper then demonstrates the viability of multiple-module converters compared to a conventional high-voltage dc converter and a theoretical full-bridge converter due to fewer devices and valves, comparable isolation levels, and ease of interleaving for increased reliability.

Multiple-Module High-Gain High-Voltage DC–DC Transformers for Offshore Wind Energy Systems

https://www.cell.com/joule/pdf/S2542-4351(20)30622-X.pdf

Ultrahigh Electricity Generation from Low-Frequency Mechanical Energy by Efficient Energy Management

This work presents an automated design procedure for series parallel resonant converters (LCC) employed in electrostatic precipitator (ESP) power supplies, which reduces the designer effort significantly. The requirements for the power supplies in ESP applications and means to derive an accurate mathematical model of the LCC converter, such as the power loss from commercial insulated-gate bipolar transistors, are described in detail in this paper. The converter parameters, such as resonant tank elements, are selected in order to improve the overall efficiency of the system, when a typical ESP energization operation range is considered. The analysis comprises two different control strategies: the conventional variable frequency control and the dual control. Both control strategies are analyzed by comparing semiconductor losses of five commercial modules. Finally, the circuit operation and design are verified with a 60 kW LCC resonant converter test setup.

Automated Design of a High-Power High-Frequency LCC Resonant Converter for Electrostatic Precipitators

Power transformer is one of the most complex parts of power converters. The complicated behavior of the transformer is usually neglected in the power converter analysis and a simple model is mostly used to analyze the converter. This paper presents a precise analysis of a fifth-order resonant converter which has incorporated the resonant circuit into the transformer. The derived model, which is based on the accurate model of the power transformer, can fully predict the behavior of the fifth-order resonant converter. The proposed fifth-order resonant converter is able to effectively reduce the range of phase-shift angle from no load to full load for a fixed-frequency phase-shift control approach. Therefore, the converter is able to operate under zero voltage switching during entire load range with a fixed-frequency control method. Also, the proposed converter offers a high gain which leads to a lower transformer turns ratio. A 10-kVDC, 1.1-kW prototype has been prepared to evaluate the performance of the proposed converter. The experimental results exhibit the excellent accuracy of the proposed model and the superiority of the performance compared to the lower order resonant converters, especially for high-voltage applications.

Analysis of a Fifth-Order Resonant Converter for High-Voltage DC Power Supplies

A prototype transformer has been designed and built which is novel in its combination of high voltage (50 kV), high frequency (20 kHz) and high power (25 kVA) specifications. The design technique utilized a spreadsheet approach which facilitated an iterative design procedure. The transformer used a ferrite core, nylon insulated secondary bobbins and pressurized sulfur hexafluoride encapsulation. It was designed as part of a high-voltage switched-mode power supply for driving electrostatic precipitators. The transformer was field tested at a large coal-fired power station and was found to have an efficiency of better than 98%.

P.W. Lefley

Papers

A novel prototype design for a transformer for high voltage, high frequency, high power use