Gysler Castelino

A Single-Stage Dual-Active-Bridge-Based Soft Switched AC–DC Converter With Open-Loop Power Factor Correction and Other Advanced Features

A dual-active-bridge-based single-stage ac/dc converter may find a wide range of emerging applications such as interfacing plug-in hybrid vehicles with the ac grid, interconnection of dc grid, etc. This type of converter can be used due to unique features such as 1) high-frequency isolation resulting in a) high power density and b) safety and voltage matching; 2) bidirectional power flow; 3) soft switching leading to higher efficiency. In this paper, a modulation strategy has been proposed that results in 1) open-loop power factor correction; 2) zero current switching in the ac-side converter for all load conditions; 3) linear power relationship for easy control implementation; and 4) Zero voltage switching in the load side converter. The converter with the proposed control has been analyzed. Simulation and experimental results on a 1-KW prototype confirm the advantages.

A novel integrated three-phase, switched multi-winding power electronic transformer converter for wind power generation system

In this paper, a novel wind power generation system is proposed which uses an intermediate high frequency (few kHz) ac link for power conversion. The high frequency ac link is achieved by using a reduced switch-count three-phase power electronic transformer (PET). There are two primary windings and one secondary winding in each phase of the PET. The primary windings are coupled in exact phase opposition. A 3×3 matrix converter is used to convert the high frequency secondary voltage to the desired low frequency voltage to be applied at the generator terminals. Two modulation modes as a part of the PWM of the matrix converter are described. In the first mode of operation, the common-mode voltage is eliminated at the generator terminals however, the output voltage transfer ratio of the matrix converter is limited to 0.75. The other modulation mode has higher output voltage transfer ratio equal to 0.866 with finite high-frequency common-mode voltage at the generator terminals. A method for smooth transition between the two modes of operation is described.

Research in matrix-converter based three-phase power-electronic transformers

This paper presents a review of the current research in the area of ac/ac power conversion with power electronic transformer. The topologies considered have the following features: 1) generation of adjustable frequency and magnitude PWM ac voltage waveform from a balanced three-phase ac voltage source with a high frequency ac link, 2) bidirectional power flow capability, and 3) single stage power conversion without any storage elements. All of these topologies provide power factor correction. Based on the operation and control, these topologies have been classified into three groups. The operation, advantages and drawbacks of each of these topologies have been presented along with a comparison of their performance in the presence of leakage inductance, complexity to control and reliability.

A bi-directional, isolated, single-stage, DAB-based AC-DC converter with open-loop power factor correction and other advanced features

In this paper, a control method for an AC-DC converter is proposed that simultaneously has the following features: a) galvanic isolation b) bi-directional power flow, c) Zero Current Switching (ZCS) for the primary side switches and Zero Voltage Switching (ZVS) turn-on for the secondary side, d) linear power relationship for easy control implementation, e) unity power factor with open-loop control and f) single-stage power conversion. It is thoroughly analyzed by first assuming it to be a DC-DC converter in a push-pull topology and then extending the results to analyze an AC-DC converter. The conclusions of the analysis are confirmed by simulations.

A novel three-phase bi-directional, isolated, single-stage, DAB-based AC-DC converter with open-loop power factor correction

In this paper, a modulation method for a single-stage three-phase AC-DC converter with only two active switches on the AC-side is proposed. The Dual Active Bridge (DAB) based modulation provides the advantages of Zero Current Switching (ZCS) for the primary side switches, linear power relationship for easy control implementation and unity power factor with open-loop control. Some other features of this topology are galvanic isolation and bi-directional power flow capability. This converter is analysed and the conclusions of the analysis and simulation concur.

Power electronic transformer with reduced number of switches: Analysis of input clamp circuit and a modulation strategy to eliminate input snubber requirement

This paper presents an analysis of the protective snubber circuits in a high frequency transformer (HFT) linked three phase ac/ac power conversion system with reduced number of switches. This topology provides single stage power conversion with bidirectional power flow capability and input power factor correction. This topology is important because of reduced number of switches in the voltage source side (usually the high voltage side). The presence of non-ideal leakage inductance in transformer windings necessitates the use of a snubber circuit for the safe commutation of leakage energy. A new modulation technique is proposed in order to reduce the protection requirements in the source side. This topology with the proposed control technique has been analyzed and simulated. The simulation results confirm the analysis and predicted advantages.

Power electronic transformer with reduced number of switches: Analysis of clamp circuit for leakage energy commutation

High frequency linked ac/ac converters are important in harnessing energy from renewable energy sources and connecting them to the high voltage ac grid. Theoretically, these converters provide single stage power conversion and obviates the need for any storage elements. Any switching transition in the load side converter causes overvoltages due to the presence of non-ideal leakage inductances in the windings of the high frequency transformer. A clamp circuit is needed for commutation of this leakage energy and to protect the power electronic devices. This paper provides a detailed analysis of the power loss incurred in the clamp circuit along with a method to design the clamp components. The entire circuit has been simulated along with non-ideal leakage inductance and the presented simulation results confirm the analytical predictions.

A Dual-Active-Bridge-Based Single-Phase AC to DC Power Electronic Transformer With Advanced Features

Power electronic transformers (PETs) offer the advantage of size and weight reduction compared to line-frequency transformers by operating at much higher frequencies than line frequency. In this paper, a push–pull-based ac/dc PET has been proposed and analyzed. The PET offers bidirectional power flow between single-phase ac and dc, using the dual-active bridge principle. Such a system may find applications in interfacing plug-in hybrid and electric vehicles to the grid. The proposed PET offers advantages of open-loop unity power factor operation, soft switching of secondary-side converter power switches for all operating points, high power density owing to use of a high-frequency transformer, and high utilization factor (UF), compared to previous work. Analysis has been done for power transfer, UF, and soft switching. Simulation and experimental results have been provided to demonstrate the operation of the PET.

Power electronic transformer with reduced switch count and dual matrix converters to eliminate load common-mode voltage and input snubber requirement

This paper presents a pulse width modulation (PWM) technique for a reduced switch count high frequency power electronic transformer (PET) with direct ac-ac power conversion using dual matrix converters. High frequency switching common-mode voltages produced by power electronic converters across a machine can cause bearing currents, leading to premature bearing failure. The proposed PWM method for the PET with dual matrix converters aims at eliminating common-mode voltages across the open-end winding load. Also, the proposed PWM method facilitates zero current switching (ZCS) of PET primary side switches, thus eliminating snubber requirements for these switches. In addition, using dual matrix converters instead of a single matrix converter (proposed in a previous paper) results in increased maximum output voltage to input voltage ratio.

Modulation and commutation of Matrix Converter based Power Electronic Transformer using a single FPGA

Power Electronic Transformers (PETs) have been proposed for future power distribution systems as well as for use in adjustable speed drives where space and weight are at a premium. This paper investigates the commutation of Matrix Converter (MC) based PETs where finite leakage inductance is present at the input of the matrix converter and it is no longer purely a voltage port. A PET with reduced number of switches on the primary side is selected for the presented research. This paper compares modulation based on carrier comparison and space vector along with commutations using four-step and dead-time. All these combinations of modulation and commutation are implemented efficiently in a single FPGA chip and some of the experimental results are presented.