Showing papers on "Isolation transformer published in 2019"

Design Considerations and Development of an Innovative Gate Driver for Medium-Voltage Power Devices With High $dv/dt$

Abstract: Medium-voltage (MV) silicon carbide (SiC) devices have opened up new areas of applications which were previously dominated by silicon-based IGBTs From the perspective of a power converter design, the development of MV SiC devices eliminates the need for series connected architectures, control of multilevel converter topologies which are necessary for MV applications, and the inherent reliability issues associated with it However, when SiC devices are used in these applications, they are exposed to a high peak stress (5–10 kV) and a very high $dv/dt$ (10–100 kV/ $\mu$ s) Using these devices calls for a gate driver with a dc–dc isolation stage that has ultralow coupling capacitance in addition to be able to withstand the high isolation voltage This paper presents a new MV gate driver design to address these issues while maintaining a minimal footprint for the gate driver An MV isolation transformer is designed with a low interwinding capacitance, while maintaining the clearance, creepage, as well as insulation standards A dc isolation test has been performed to validate the integrity of the insulating material The key features include low input common mode current, and a short-circuit protection scheme specifically designed for 10 kV SiC mosfet s The performance of the gate driver is evaluated using double pulse tests and continuous tests Experimental results validate the advantages of the gate driver and its application for MV SiC devices exhibiting very high $dv/dt$ The proposed gate driver concept is aimed at providing an efficient and reliable method to drive MV SiC devices

A Modified DC Power Electronic Transformer Based on Series Connection of Full-Bridge Converters

Abstract: This paper proposes a novel dc power electronic transformer (DCPET) topology for locomotive, ac/dc hybrid grid, dc distribution grid, and other isolated medium-voltage and high-power applications. Compared with conventional PET topology, the proposed DCPET has fewer power semiconductor devices and high-frequency isolation transformers, which can improve the power density and reliability. Fault handling or redundancy design can be achieved to further improve the reliability when some dc–dc modules break down. Also, input voltage sharing control can be omitted to simplify the control system and improve the stability. Meanwhile, soft switching is guaranteed for all the switches, which is beneficial to increase switching frequency and improve power density. In this paper, the principle, evolution, and control of the proposed DCPET are respectively presented and studied in detail. Finally, a prototype of the proposed DCPET is built and the experimental results verify the validity and superiority of the proposed topology.

Soft-Switched Modulation Technique for a Single-Stage Matrix-Type Isolated DC–AC Converter

Abstract: This paper proposes a soft-switched modulation technique with synchronous rectification for an isolated single-stage single-phase matrix-type dc–ac converter. The dc side consists of a full bridge inverter, and the ac side is a 2×2 matrix converter-based cycloconverter. The proposed unipolar modulation strategy provides zero current switching/zero voltage switching (ZVS) for the ac side devices and ZVS-on for the dc side devices. It also allows natural commutation of the current flowing through the secondary side leakage inductor of the isolation transformer and the grid inductor during unity power factor (UPF) condition, thus eliminates the requirement of snubber circuit. An improved soft-switched flyback-based regenerative snubber circuit is also presented for non-UPF operation. Proposed snubber circuit recycles the energy stored in the snubber capacitors in every switching cycle. A guideline to design snubber circuit along with a comparative study is discussed in this paper. Performance of the proposed hybrid modulation technique is evaluated in an SiC mosfet based 1.2-kW dc–ac converter prototype. A detailed analysis of the converter performance has been presented in this paper considering the circuit non-idealities.

A Family of Transformerless Stacked Active Bridge Converters

Abstract: This paper describes a family of transformerless stacked active bridge (TSAB) converters with N-to-1 nominal conversion ratios and continuous voltage regulation capabilities. An N-to-1 TSAB is a hybrid converter derived from the N-to-1 Dickson switched-capacitor (SC) converter, with small ac inductors inserted in the flying-capacitor branches to achieve lossless ("soft") capacitor charging and discharging. In operation, a TSAB converter resembles the isolated Dual Active Bridge (DAB) converter but without the need for an isolation transformer. The TSAB family has several favorable characteristics, which lead to very high efficiency around nominal conversion ratio, including small ac inductors with near-trapezoidal low RMS currents, low voltage stresses, and zero-voltage-switching (ZVS) over wide load range. Moreover, the operation is robust with respect to component tolerances, and continuous voltage regulation can be achieved through simple phase shift control. Experimental results are presented for a 120 W, 48V-to-12V TSAB prototype, demonstrating a flat efficiency characteristic with 98.6% peak efficiency, and 98.0% full-load efficiency.

Common-Mode Current Suppression of Transformerless Nested Five-Level Converter With Zero Common-Mode Vectors

Abstract: Three-phase transformerless multilevel converters are widely used in the high-voltage photovoltaic power generation systems because of their low total harmonic distortion, high power density, and high conversion efficiency. One three-level flying capacitor converter and dual T-type three-level circuits can be combined to derive the compact and cost-effective nested five-level converter. However, due to the lack of an isolation transformer, the common-mode current is generated to degrade the converter performance. First, the common-mode equivalent circuit model of the nested five-level converter is initially derived to further explore its common-mode current generation mechanism. Then, the zero common-mode space vector modulation (ZCM-SVM) is proposed to reduce the common-mode current, which chooses the specific zero common-mode voltage space vectors to synthesize the reference vector. Then, an advanced coordinate transformation is introduced to realize the flexible sector selection and reduce the complexity of the vector action time calculation. The proposed modulation achieves the common-mode current suppression with high dc bus voltage utilization. Finally, the effectiveness of the proposed ZCM-SVM strategy is verified by simulation and experimental results.

Vehicular Integration of Wireless Power Transfer Systems and Hardware Interoperability Case Studies

Abstract: Several wireless charging methods are under development or available as an aftermarket option in the light-duty automotive market. However, there are not a sufficient number of studies detailing the vehicle integration methods, particularly a complete vehicle integration with higher power levels. This paper presents the design, development, implementation, and vehicle integration of wireless power transfer (WPT) based electric vehicle charging systems for various test vehicles. Before having the standards effective, it is expected that WPT technology first will be integrated as an aftermarket retrofitting approach. Inclusion of this technology on production vehicles is contingent upon the release of the international standards. The power stages of the system are introduced with the design specifications and control systems, including the active front-end rectifier with power factor correction, high frequency power inverter, high frequency isolation transformer, coupling coils, vehicle side full-bridge rectifier and filter, and the vehicle battery. The operating principles of the control and communication systems are presented. Aftermarket conversion approaches, including the WPT on-board charger integration, WPT CHAdeMO integration, and WPT direct battery connection scenarios, are described. The experiments are carried out using the integrated vehicles and the results obtained to demonstrate the system performance including the stage-by-stage efficiencies.

Fast Transient Current Control for Dual-Active-Bridge DC-DC Converters with Triple-Phase-Shift

Abstract: A kind of fast transient current control (FTCC) method for dual-active-bridge (DAB) dc-dc converters based on triple-phase-shift (TPS) control strategy is proposed in this paper to suppression the transformer DC bias when the power instruction or the load changes suddenly. The proposed control method brings the benefit of dynamic performance during bidirectional operation, which can achieve new steady state for inductor current, remove dc bias in the isolation transformer effectively within several cycles hence preventing transformer saturation. To analyze both steady and dynamic performance of the DAB converter by using the superposition theorem. According to the results of transient inductance current analysis, a dynamic control approach is proposed to limit the current transient interval in one switching period. Finally, the theoretical analysis is verified by experiments.

A Novel High-Step-Up Coupled-Inductor DC–DC Converter With Reduced Power Device Voltage Stress

Abstract: In this paper, a novel high-step-up coupled-inductor dc–dc converter is presented The proposed converter has an excellent feature, ie, the closer the turn ratio to 1, the higher the gain of the converter, also the lower the voltage stress of the switch Duty cycle and the turn ratio of the coupled inductor together determine the voltage gain of the converter; thus, it can achieve any wanted voltage without the circuit to operate at the extreme duty cycle In addition, the proposed converter can realize higher voltage gain with a small duty cycle And it is suitable for many types of new energy source, especially photovoltaic generation systems, which has a common ground and a continuous input current switch with great benefits for the life of the input power supply The power density of the system improves for the lack of isolation transformer Due to the introduction of the clamp circuit, the voltage spikes across the switch are limited Therefore, we can choose a switch with lower voltage levels that would cut costs and reduce conduction losses As the energy of leakage energy is absorbed by the circuit, the efficiency is further improved The operational principle and the steady-state analysis of the proposed converter are presented in this paper Finally, the experiment with an input 48-V voltage and an output voltage of 380 V is implemented, verifying the validity of this paper

Large Step Ratio Input-Series–Output-Parallel Chain-Link DC–DC Converter

Abstract: High-voltage and high-power dc–dc conversion is key to dc transmission, distribution, and generation, which requires compact and efficient dc transformers with large step ratios. This paper introduces a dc–dc converter with the input-series–output-parallel arrangement of multiple high step ratio subconverter units. Each subconverter unit is an isolated modular dc–dc converter with a stack of half-bridge cells chopping the dc down to low voltage level. The transformer provides galvanic isolation and additional step ratio. The converter achieves a large step ratio due to the combination of the series-parallel configuration, the modular cells, and the isolation transformer. The proposed dc–dc converter is analyzed in a 30 kV–1 kV, 1-MW application to discuss the operation performance, tradeoffs, power efficiency, and selection of components. Finally, the converter is validated through a laboratory downscaled prototype.

A Novel Solar PV Inverter Topology Based on an LLC Resonant Converter

Abstract: In this paper, a new topology for grid-connected solar PV inverter is proposed. The proposed topology employs an LLC resonant converter with high frequency isolation transformer in the DC-DC stage. The DC-DC converter stage is controlled to generate a rectified sine wave voltage and current at the line frequency. An unfolder inverter interfaces between this DC stage and the grid. Both phase-shift and frequency control methods are used to control the LLC resonant converter. The switching frequency is determined depending on the phase-shift angle to extend the zero-voltage switching (ZVS) region. The transformer leakage and magnetization inductances are also properly designed to provide ZVS for wide operation area. The LLC converter operates in the ZVS region except the narrow band around the zero-crossings of the inverter output current. Since the LLC resonant converter has a high frequency transformer, the line frequency transformer requirement is eliminated, and thus more compact and efficient design is obtained. The proposed topology is validated by the simulation and experimental results.

A Leakage-Inductance-Tolerant Commutation Strategy for Isolated AC/AC Converters

Abstract: This paper proposes a generalized commutation strategy suitable for matrix-based isolated ac/ac conversion stages in solid-state transformers for use whenever there is nonnegligible leakage inductance in the isolation transformer. The standard 4-step commutation used in matrix converters can no longer be applied when transformer leakage inductance is present, as overrated switching devices or dissipative snubbers would be necessary, reducing the attractiveness of the topologies that include matrix-based isolated ac/ac stages. A case study of a single-phase ac/ac converter has been investigated in detail to demonstrate the application of the proposed commutation method to a topology that has recently been identified as the potential building block for future multimodular ac/ac converters for grid applications. The proposed leakage-inductance-tolerant commutation strategy is based on the definition of a current decoupling phase in the commutation sequence and only needs suitable timing of the commutation steps, without high bandwidth voltage or current measurements. Matching simulations and experimental results from a 3-kW laboratory scale prototype are presented to support the effectiveness of the proposed strategy.

Analysis of Skin Effect in High Frequency Isolation Transformers

Abstract: In this paper, a high frequency transformer with different conductors and winding arrangements, at presence of eddy currents and skin effect, is studied. By using different winding structures, and conductor types, such as circular, square shaped, and foil wires, the skin effect in the windings is studied and current density within the conductors at a high frequency of 20 MHz and a lower frequency of 20 kHz are investigated using finite element method (FEM) simulation. Moreover, magnetic field distribution in the transformers at 20 MHz is obtained and displayed. Also, magnetizing inductance, leakage inductance and AC winding resistance for all of the transformer types are found and compared, and frequency response for the transformers are obtained and shown. Lastly, based on the results, the skin effect increases the AC winding resistance and decreases the leakage inductance as the frequency increases. Furthermore, different winding arrangements, conductors, and transformer types show a wide range of parasitic and loss behavior, which enable the designers to compromise between various parameters in different applications, especially new fast switches such as SiC and GaN.

Isolation Transformer for 3-Port 3-Phase Dual-Active Bridge Converters in Medium Voltage Level

Abstract: In this paper, an isolation transformer with integrated filter inductances for three-phase three-port dual-active bridge (DAB) converters in the wye-wye-delta (Yyd) configuration is introduced and designed. A large number of ports and phases in the application necessarily requires a proportionally increased number of components, accessories, and connections. These additional parts induce significant losses and electromagnetic interference during high-frequency operations. Hence, fully manipulating the parasitic components, especially the leakage inductances of the transformer as the circuit element in the interconnected multi-port configuration, is a key to reduce the system’s overall size and to improve its reliability. The proposed geometry and design method enables the full integration of a large number of otherwise bulky inductors to be included in the isolation transformers so that the latter function not only a step-up/down transformers but also as filter networks required for three-port DAB operations. The transformer is suitable for high-power and high step-up/down ratio dc-dc converters, which prefers a parallel combination of converters that share current, on the low-voltage side. The operating principles and steady-state analysis are presented with respect to power flow, and a three-winding shell-type isolation/filter transformer has been designed for a three-port three-phase Yyd DAB converter for solid state transformer applications. The finite element method simulations are used to validate the feasibility of the proposed approach. A prototype was fabricated and tested in an experimental setting.

Novel three-level T-type isolated bidirectional DC–DC converter

Abstract: This study presents a novel three-level T-type isolated bidirectional DC-DC converter (3LTT-IBDC) for bidirectional DC power transfer. Owing to of the T-type structure of the proposed converter it has less number of switches and thus, lower cost and higher efficiency, as well as easy control are the advantages of the proposed converter compared to three-level counterparts. Additionally, 3LTT-IBDC is more reliable than three-level converters since unequal voltage blocking does not occur in T-type structure. Moreover, the symmetrical operation of the isolation transformer due to three-level symmetrical voltage waveform, lower voltage stress of switches and thus, higher efficiency are other advantages of 3LTT-IBDC compared to two-level counterparts. Here, the DC voltage gain and power transfer characteristic of the proposed converter for steady-state operation and the expressions of the leakage inductance are derived. The proposed converter is simulated using PSIM. A 2-kW prototype is built to verify the theoretical analysis of the converter. Theoretical and experimental results show a good agreement and validate the competency of the presented converter design. The efficiency of the proposed converter and switching transitions of the switches are analysed. The full load and maximum efficiency of the converter are measured as 96.27% and 96.81%, respectively.

Analysis of Skin Effect in High Frequency Isolation Transformers

Abstract: In this paper, a high frequency transformer with different conductors and winding arrangements, at presence of eddy currents and skin effect, is studied. By using different winding structures, and conductor types, such as circular, square shaped, and foil wires, the skin effect in the windings is studied and current density within the conductors at a high frequency of 20 MHz and a lower frequency of 20 kHz are investigated using finite element method (FEM) simulation. Moreover, magnetic field distribution in the transformers at 20 MHz is obtained and displayed. Also, magnetizing inductance, leakage inductance and AC winding resistance for all of the transformer types are found and compared, and frequency response for the transformers are obtained and shown. Lastly, based on the results, the skin effect increases the AC winding resistance and decreases the leakage inductance as the frequency increases. Furthermore, different winding arrangements, conductors, and transformer types show a wide range of parasitic and loss behavior, which enable the designers to compromise between various parameters in different applications, especially new fast switches such as SiC and GaN.

Development of an IGBT-Diode based Fault Current Limiter for Fault Ride-Through Enhancement in Microgrid Application

Abstract: This paper deals with a developed insulated gate bipolar transistor (IGBT) and diode based fault current limiter (FCL) for simple microgrid application. The developed FCL utilizes a three-phase circuit arrangement that has fault current limiting ability with an uncomplicated control strategy that simply samples the voltage at the point of common coupling (PCC) for the FCL control using Clarke’s Transformation, low pass filtering and pulse generating circuit. The IGBT-Diode based FCL regulates the magnitude of the fault current and enhances the PCC voltage under transient faults to ensure continuous supply of active and reactive power to the local load of the microgrid irrespective of the transient condition of the main grid. The power electronic switching arrangement employed interfaces the grid using an isolating transformer whose primary is connected in series with the feeder line and the secondary is shorted by an optimally sized AC reactor. The IGBT-Diode switching operations for the pre-fault, fault and post-fault conditions are triggered by the control proposed which detects fault occurrence in less than a period. The analytical investigation of the IGBT-Diode switched FCL is presented in details and the results of simulation lay credence to effectiveness of the developed FCL in improving Fault Ride-Through (FRT).

Shielding of Leakage Flux Induced Losses in High Power, Medium Frequency Transformers

Abstract: Metal Amorphous Nanocrystalline core materials have shown great promise as the magnetic material for the isolation transformer used in high power, high frequency power converters. However, many current designs require special winding configurations that result in high parasitic capacitance. Similarly, when these designs are used in active bridge circuits where a certain minimum series inductance is required, auxiliary inductors are required. These dramatically reduce the power density and can have impacts on the efficiency. Designs that integrate the series inductance through inherently geometric approaches have resulted in catastrophic increases in losses that are not predicted by typical core magnetizing loss models and have not been viable as a result. This paper demonstrates a method of using a mix of materials to manage and direct the leakage flux through paths that are more efficient. Similarly, this approach enables deliberate tuning and design of the series inductance. This introduces a method to independently design the series inductance with the magnetizing inductance of the transformer. This will prove to enable high efficiency transformer designs with very high power density, empowering wide bandgap semiconductor-based converters to reach their full potential.

Isolation Techniques for Medium-Voltage Adjustable Speed Drives: Drive Topologies for Maintaining Line-Side Performance

Abstract: Compression and pumping applications represent a majority of all rotating machinery in modern industrial plants. In the past two decades, electric motors have been replacing turbines as the prime mover of choice for large rotating equipment at an increased rate. The use of electrically driven equipment is widespread even for critical applications. As semiconductor technology evolves, adjustable speed drives (ASDs) gain favor as the best option for both motor starting and speed control. Volume, pressure, and flow are adjusted by varying the speed of electric motors, even in motors that are larger than 50,000 hp. Multiple medium-voltage (MV) ASD topologies exist today that offer excellent motor performance. One of the key topics of discussion among specifiers and end users concerns the effects of ASDs on the utility line. Several methods for improving line-side performance use incoming isolation transformers, but some do not. It is often not clear when drive isolation transformers (DITs) should be used and which converter topology should be employed. This article is a guide to drive isolation techniques and major types of converters for various topologies of MV ASDs. It briefly explores the theory, advantages, and disadvantages of each configuration and application with considerations for selecting the optimal drive isolation technique.

Power electronic transformer with true bipolar DC output ability and application control

Abstract: The invention relates to a power electronic transformer with true bipolar DC output ability. By controlling a switch tube of a full-bridge/three-level combined converter (4), the balance of anode andcathode DC output voltage is realized, and the normal operation of non-fault pole DC output under a single pole fault condition is realized; by controlling a full-bridge converter (2) and the full-bridge/three-level combined converter (4), the original secondary side voltage of an isolation transformer (3) is adjusted, so that bidirectional transmission adjustment of input and output side power isrealized; a soft switch of a switch device in the converter can be realized, so that the operation efficiency of the converter is enhanced; the designed converter can be combined with a cascaded H bridge converter or a modularized multi-level converter to form the power electronic transformer with medium/high-voltage AC input and true bipolar DC output; and a DC converter with true bipolar DC output ability can be formed through series-parallel connection of modules.

Single-Phase Five-Leg AC-DC-AC Multilevel Converter to Enhance Power Quality

Abstract: This paper proposes a single-phase ac-dc-ac multilevel converter composed of a three-leg module series-connected to an H-bridge at load side of the system to achieve a higher and multilevel voltage at the output converter. The proposed system is appropriate for applications with same input and output frequencies to enhance power quality, such as uninterrupted power supply and unified power quality conditioner, and for electric power conversion systems in which the output voltage required is twice the input voltage, without isolation transformer. Circuit model equations, power flux analysis, dc-link voltage specifications and a PWM strategy based on vector approaches are discussed. The proposed system control ensures fixed load voltage with constant amplitude and frequency, maximizes the grid power factor and regulates the dc-link voltages. Compared with conventional, proposed topology has lower dc-link voltage rating, lower harmonic contents and lower power losses. Simulation and experimental results demonstrate the operation of control system and validate the theoretical studies.

Three-Phase Unidirectional Transformerless Hybrid Rectifier with Boost Converter

Abstract: In this paper, a three-phase hybrid rectifier is proposed, employing a boost converter without the addition of isolation transformer and output voltage control. This topology is usually considered to be not viable due to the current interactions. In order to mitigate those interactions, the boost inductor is replaced by a magnetically coupled inductor. The coupled inductor forces the balance between the two interconnected windings, placed at the positive and negative poles, and thus eliminating the current interactions. The results show that the proposed three-phase rectifier does not undergo a current interaction and functions as a hybrid rectifier. Furthermore, it was noted that the proposed rectifier at 20 kW presents an elevated power factor and a low total harmonic distortion.

Study on Modular Multi-Level DC-DC Converter with Cell Voltage Balancing and Fast Output Response Using Sub Commutation Circuits

Abstract: DC power supplies for a battery testing are becoming significantly important for developments of electrical vehicles (EVs), mobile devices, and renewable energy generations. In the recent decade, modular multi-level converters (MMC) have been actively studied and started to use on some practical applications such as high- or medium-voltage DC-AC or AC-DC power converters. However, the widely used MMC topology has a significant issue to extend to a DC-DC converter, because it cannot achieve capacitor voltage balancing of each cell unlike the case of the DC-AC and AC-DC conversions. Therefore, most of the MMC-based DC-DC converters are realized by combining the DC-AC converter, isolation transformer or inductor, and AC-DC converter. In this study, the DC-DC operation in the MMC and its problem are analyzed and clarified. This paper proposes a circuit topology and control method of the MMC-based DC-DC converter with cell voltage balancing and fast dynamic response while the DC-AC and AC-DC converters are not used. Simulation results verify the validity of the capacitor voltage balancing control. Finally, an experimental result in a prototype converter with 6-cells using SiC-MOSFETs shows the performances of the voltage balancing control and fast dynamic response.

50kW Nano-Crystalline Core Based Three Port Transformer for Triple Active Bridge Converter

Abstract: This paper discusses a 50kW high frequency three port transformer made of Nano-Crystalline core, for three port phase shifted DC-DC converter integrating Renewable Energy Sources(RES) & Energy Storages(ES). Phase shifted DC-DC converters need an isolating transformer with series inductances or leakage inductances for power transfer among different ports. However, using leakage inductances for a tape wound or Nano-Crystalline transformer as energy transferring element, causes high leakage fluxes to induce significant eddy currents & related losses in transformer cores. At high switching frequency, this eddy current losses can go too high, reducing efficiency. In order to avoid the eddy current losses in cores, an external inductor based approach along with the concentric winding transformer is presented in this paper for Three Port Phase Shifted Triple Active Bridge(TAB) converter. The three port converter can use either a three inductor or two inductor approach, which is discussed in this paper. The TAB converter uses 1.2kV & 1.7kV SiC Mosfets as switching devices along with Nano-Crystalline core based transformer & ferrite based series inductors. In this paper, analysis & design for concentric winding transformer and experimental results are presented.

Energy storage charging system

Abstract: Disclosed is an energy storage charging system. The system includes a bidirectional DC/DC conversion apparatus capable of high-frequency isolation conversion and a direct-current bus bar, an AC/DC conversion apparatus capable of high-frequency isolation conversion and a direct-current bus bar, and an electric vehicle charging system. A first connection point of the bidirectional DC/DC apparatus is connected to an energy storage apparatus, a second connection point thereof is connected to the direct-current bus bar, and the bidirectional DC/DC apparatus carries out high-frequency isolation conversion on electric energy of the energy storage apparatus and then carries out bidirectional communication with the direct-current bus bar; and a first connection point of the AC/DC apparatus is connected to a power grid, and a second connection point thereof is connected to the same direct-current bus bar. The energy storage apparatus of the present invention is isolated from the direct-current bus bar by means of a high-frequency isolation transformer of the bidirectional conversion apparatus capable of high-frequency isolation, and electric energy passing through the transformer is adjusted, so that a charging voltage and a charging current of the direct-current bus bar for the energy storage apparatus are adjusted, and a discharging voltage and a discharging current of the energy storage apparatus for the direct-current bus bar are adjusted, thereby achieving the aim of charging an electric vehicle.

Core Loss Studies using FEM of a Three Phase Isolation Transformer under Harmonic Conditions

Abstract: This paper aims to investigate the effect of voltage harmonics on transformer core losses. A three-dimensional finite element method (FEM) is employed to model a three-phase isolation transformer supplied by a contaminated power source. The effect of harmonics is accurately modelled in FEM. The proposed model in FEM is verified by experiment where the results obtained using FEM show good agreement with experimental results. Different case studies with different harmonic conditions are investigated. The results show an increase in the core loss value up to 67.3% when the input voltage is formed based on the highest percentage of harmonic orders stated in the IEC 61000-3-6. As the core loss is always present, the energy loss continuously accumulates. Thus, voltage harmonics contribute to increase in the core loss in transformers.

Termination for wire pair carrying DC and differential signals using isolation transformer with split primary and secondary windings

Abstract: A PHY is coupled across split primary windings of an isolation transformer for differential data transmission and reception between PHYs and for DC isolation. Positive and negative low impedance terminals of a DC power supply are coupled to first and second secondary windings of the transformer as split center taps of the transformer. Respective ends of the wires in the wire pair are coupled to the other ends of the secondary windings. Therefore, the power supply conducts DC current through the secondary windings, while the differential data signals also flow through the secondary windings, generating corresponding differential data signals at the inputs to the PHY. The transformer also attenuates common mode noise. Therefore, the circuit makes multi-use of the isolation transformer, allowing fewer components to be used for the DC coupling, wire termination, and common mode noise cancellation.

A modified 12-Pulse Three-Phase Bidirectional Dual Active Bridge DC/DC Converter for E-Vehicles Applications

Abstract: This paper presents an isolated bidirectional DC-DC converter for the use in electrical vehicles on-board power supply systems. For this purpose, a modified 12-pulse three-phase DAB is evaluated. A second low voltage bridge is added to the original circuit, so that the topology now works with six transformers, being two transformers per phase connected in series on the high voltage side and in parallel on the low voltage side. Furthermore, the primary side and one of the secondaries present a wye connection, whereas the other secondary side is delta connected. The steady-state operation principle of the proposed topology has been studied and design parameters of the isolation transformer are analytically determined. Although the higher number of components, it is expected to achieve a design with higher efficiency, compactness and lower filter requirements.

Control Strategy of Three-Phase Inverter with Isolation Transformer

Abstract: In order to improve the control performance of a train auxiliary inverter and satisfy the requirements of power quality, harmonics, and unbalanced factor, this paper proposed a design method of a double closed-loop control system based on a complex state variable structure. The method simplifies the design process and takes full account of the effects of coupling and discretization. In the current closed-loop process, this paper analyzed the limitations of the proportional integral (PI) controller and simplified to P controller. In the voltage closed-loop, the paper employed the PI controller plus the resonant controller, designed the parameters of the PI controller. and analyzed the optimal discretization method of the resonant controller under dq axis coupling. Finally, experiments and simulations were conducted to show that the proposed method can achieve the above improvements.

Isolated bidirectional converter device

Abstract: The utility model discloses an isolated bidirectional converter device. The isolated bidirectional converter device comprises a first unit conversion circuit and a second unit conversion circuit. Thefirst unit conversion circuit and the second unit conversion circuit are both bidirectional conversion circuits. Wherein the second unit conversion circuit at least comprises an isolation transformer,and further comprises a first digital controller, a second digital controller and an isolation circuit, the first digital controller is in circuit connection with and controls the first unit conversion circuit, and the second digital controller is in circuit connection with and controls the second unit conversion circuit. Due to the fact that the two digital controllers are adopted, the two digital controllers can switch off the unit conversion circuits controlled by the two digital controllers in time under the abnormal condition, and the situation that power flow flows backwards is prevented. The isolated bidirectional converter device can realize isolated bidirectional conversion between alternating current voltage and direct current voltage and isolated bidirectional conversion between direct current voltage and direct current voltage, and has the characteristics of high power density, high efficiency, flexible external communication mode and the like.

Analysis, Design, and Performance of Isolated Three-Port UPS Converter for High-Power Applications

Abstract: In this paper, an uninterrupted power supply (UPS) and an isolated three-port bidirectional converter (TPBC) are developed by connecting a three-phase voltage source converter(VSC), a battery energy- storage system (BESS) and a grid-connected boost converter-fed three-phase DC/AC converter through a single three-winding isolation transformer(Tr). This design presents features that are suitable for multiple voltage electrical systems. The three-port power exchange is multi-directional which can be delivered either separately or simultaneously. In consideration of the safety requirements, electrical isolation is achieved between any of the two ports. Besides the power-flow concept, different operating principle stages, power flow equations, small signal model, network simulation model, and control strategy are discussed. Furthermore, the steady-state analysis are evaluated to determine the power flow equations. The control strategy proposed is based on single-phase shift control, with the small signal model for optimized controller design, which can predict the accurate frequency response and obtain a fast dynamic response. Meanwhile, this can be used in many applications of electronic power converters. The simulation results have been provided under various operating conditions, which confirms the effectiveness of the proposed control strategy. The result showed that the power management feature of the system was successful and waveforms are obtained. Finally, theoretical considerations and simulation results for different operating stages are verified by MATLAB / SIMULINK