Ole Cornelius Thomsen

Optimal Design and Tradeoff Analysis of Planar Transformer in High-Power DC–DC Converters

The trend toward high power density, high operating frequency, and low profile in power converters has exposed a number of limitations in the use of conventional wire-wound magnetic component structures. A planar magnetic is a low-profile transformer or inductor utilizing planar windings, instead of the traditional windings made of Cu wires. In this paper, the most important factors for planar transformer (PT) design including winding loss, core loss, leakage inductance, and stray capacitance have individually been investigated. The tradeoffs among these factors have to be analyzed in order to achieve optimal parameters. Combined with an application, four typical winding arrangements have been compared to illustrate their advantages and disadvantages. An improved interleaving structure with optimal behaviors is proposed, which constructs the top layer paralleling with the bottom layer and then in series with the other turns of the primary, so that a lower magnetomotive force ratio m can be obtained, as well as minimized ac resistance, leakage inductance, and even stray capacitance. A 1.2-kW full-bridge dc-dc converter prototype employing the improved PT structure has been constructed, over 96% efficiency is achieved, and a 2.7% improvement, compared with the noninterleaving structure, is obtained.

Analysis and Design of a Bidirectional Isolated DC–DC Converter for Fuel Cells and Supercapacitors Hybrid System

Electrical power systems in future uninterruptible power supplies or electrical vehicles may employ hybrid energy sources, such as fuel cells and supercapacitors. It will be necessary to efficiently draw the energy from these two sources as well as recharge the energy storage elements by the dc bus. In this paper, a bidirectional isolated dc-dc converter controlled by phase-shift angle and duty cycle for the fuel-cell hybrid energy system is analyzed and designed. The proposed topology minimizes the number of switches and their associated gate driver components by using two high-frequency transformers that combine a half-bridge circuit and a full-bridge circuit together on the primary side. The voltage doubler circuit is employed on the secondary side. The current-fed input can limit the input current ripple that is favorable for fuel cells. The parasitic capacitance of the switches is used for zero voltage switching (ZVS). Moreover, a phase-shift and duty-cycle modulation method is utilized to control the bidirectional power flow flexibly and it also makes the converter operate under a quasi-optimal condition over a wide input voltage range. This paper describes the operation principle of the proposed converter, the ZVS conditions, and the quasi-optimal design in depth. The design guidelines and considerations regarding the transformers and other key components are given. Finally, a 1-kW 30~50-V-input 400-V-output laboratory prototype operating at 100-kHz switching frequency is built and tested to verify the effectiveness of the presented converter.

Discontinuous PWM Modulation Strategy With Circuit-Level Decoupling Concept of Three-Level Neutral-Point-Clamped (NPC) Inverter

A new pulse width modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is developed and presented in this paper. The proposed PWM scheme not only takes advantage of the special properties available in NPC inverters, but also reduces the switching loss of the inverter along with an inherent neutral point (NP) voltage control. Based on a circuit-level decoupling concept, the NPC inverter can be decoupled into two three-level Buck converters in every defined operating section, and thereby the controller design can be simplified. The salient features of the proposed scheme, as compared with the existing carrier-based DPWM strategies, are: 1) its reduced computational processing time, 2) its capability to balance the dc-link voltage without any additional control, and 3) its reduced complexity, e.g., only one carrier wave needed for pulse width modulating. Same as a space-vector modulation, the maximum modulation index, 1.1547, can be attainable by the proposed scheme. Moreover, compared to conventional continuous sinusoidal PWM, using this technique proposed here, the switching losses of the devices can be reduced by one third. In order to explain the operation of this topology properly, the decoupling principle including the driving signal synthesis and the NP potential variation are analyzed in detail in this paper. Finally, the viability and performance of the proposed modulation scheme are shown through simulation and experimental results in a laboratory prototype.

The analysis and comparison of leakage inductance in different winding arrangements for planar transformer

The coupling of the windings can be easily increased by using multiply stacked planar windings connection. Interleaving is a well-known technique used to reduce leakage inductance and minimize high-frequency winding losses. The paper aims to analyze leakage inductance based on magneto motive force (MMF) and energy distribution in planar transformer and correct the formula of leakage inductance proposed by previous publications. The investigation of different winding arrangements shows significant advantages of interleaving structure. In this work, a novel half turn structure is proposed to reduce leakage inductance further. Some important issues are presented to acquire desired leakage inductance. The design and modeling of 1 kW planar transformer is presented. In order to verify the analytical method for leakage inductance in this paper, finite element analysis (FEA) and measurement with impedance analyzer are presented. Good matching between calculation, FEA 2D simulation and measurement results is achieved.

Optimal Design of a Push-Pull-Forward Half-Bridge (PPFHB) Bidirectional DC–DC Converter With Variable Input Voltage

This paper presents a low-cost bidirectional isolated dc-dc converter, derived from dual-active-bridge converter for the power sources with variable output voltage like super capacitors. The proposed converter consists of push-pull-forward circuit half-bridge circuit (PPFHB) and a high-frequency transformer; this structure minimizes the number of the switching transistors and their associate gate driver components. With phase-shift control strategy, all the switches are operated under zero-voltage switching (ZVS) condition. Furthermore, in order to optimize the converter performance and increase efficiency, optimal design methods and criteria are investigated, including coupled inductors design, bidirectional power flow analysis, harmonics analysis, and ZVS range extension. Based on all the optimal parameters, higher efficiency can be achieved. Finally, prototypes are built in laboratory controlled by digital signal processor for comparison purpose. Detailed test results verify the theoretical analysis and demonstrate the validity of optimization design method.

Planar-Integrated Magnetics (PIM) Module in Hybrid Bidirectional DC–DC Converter for Fuel Cell Application

In most power electronics converters, the overall volume is mainly determined by the number of parts and the size of passive components. Integrated magnetics and planar magnetics techniques, therefore, have been an excellent option in order to reduce the counts and the size of magnetic components, hereby increasing the power density of converters. In this paper, a new planar-integrated magnetics (PIM) module for a phase-shift plus duty-cycle-controlled hybrid bidirectional dc-dc converter is proposed, which assembles one boost inductor and two transformers into an E-I-E core geometry, reducing the number of parts, the total volume of converter, as well as the total core loss of the magnetic components. AC losses in the windings and leakage inductance of the transformers are kept low by interleaving the primary and secondary turns of the transformers. To verify the validity of the design approach and theoretical analysis, a laboratory prototype employing the PIM module is implemented for a fuel cell application with 20-40-V input voltage and 400-V output voltage. Detailed results from the experimental comparisons demonstrate that the PIM module is fully functional and electromagnetically equivalent to the discrete magnetics and a significant reduction of size can be achieved by using the PIM module.

Analysis and Design of Fully Integrated Planar Magnetics for Primary–Parallel Isolated Boost Converter

A high efficient planar integrated magnetics (PIM) design approach for primary parallel isolated boost converters is presented. All magnetic components in the converter including two input inductors and two transformers with primary-parallel and secondary-series windings are integrated into an E-I-E core geometry. Due to a low reluctance path provided by the shared I-core, the two transformers as well as the two input inductors can be integrated independently, reducing the total ferrite volume and core loss. AC losses in the windings and the leakage inductance of the transformer are kept low by interleaving the primary and secondary turns of the transformers. To verify the validity of the design approach, a 1-kW prototype converter with two primary power stages is implemented for a fuel cell fed battery charger application with 20–40 V input and 170–230 V output. An efficiency of 96% can be achieved during nominal operating conditions. Also experimental comparisons between the PIM module and two separate cases have been done in order to illustrate the advantages of the proposed method.

Four Quadrants Integrated Transformers for Dual-Input Isolated DC–DC Converters

A common limitation of power coupling effect in some known multiple-input dc-dc converters has been addressed in many literatures. In order to overcome this limitation, a new concept for decoupling the primary windings in the integrated multiple-winding transformers based on 3-D space orthogonal flux is proposed in this letter. And thus, a new geometry core and relative winding arrangements are proposed in accordance with the orthogonal flux decoupling technology. Due to the four secondary windings are arranged in a quadratic pattern at the base core plate with the two perpendicular primary windings, a name of “four quadrants integrated transformers” (FQIT) is, therefore, given to the proposed construction. Since the two primary windings are uncoupled, the FQIT allows the two input power stages to transfer the energy into the output load simultaneously or at any time-multiplexing scheme, which can optimize the utilization of input sources, simplify the system structure, and reduce the overall cost, so they are attractive for the hybrid renewable power system. Section IV initiates a discussion for the advantages of the FQIT. In order to verify the feasibility of the FQIT in multiple-input converter, a dual-input isolated boost dc-dc converter with the FQIT is designed and tested. The results have excellently demonstrated that the two input power stages can be operated independently and the correctness of all the analysis in the letter.

Analysis and Design of Bi-directional DC-DC Converter in Extended Run Time DC UPS System Based on Fuel Cell and Supercapacitor

In this paper, an extended run time DC UPS system structure with fuel cell and supercapacitor is investigated. A wide input range bi-directional dc-dc converter is described along with the phase-shift modulation scheme and phase-shift with duty cycle control, in different modes. The delivered power and peak current are analyzed and calculated. The key parameters of the bi-directional dc-dc converter, the relationships between the input voltage, phase-shift angle, ratio of the transformer and leakage inductance are analyzed and optimized. Build the system mathematic model and a novel input voltage combined with load current feedback using PI controller with anti-windup scheme to realize closed-loop control of the whole system, and verify the feasibility of the control scheme proposed by simulation. A 1kW prototype controlled by TMS320F2808 DSP is implemented and tested. Experimental results show the validity of design.

Conduction losses and common mode EMI analysis on bridgeless power factor correction

In this paper, a review of Bridgeless Boost power factor correction (PFC) converters is presented at first. Performance comparison on conduction losses and common mode electromagnetic interference (EMI) are analyzed between conventional Boost PFC converter and members of Bridgeless PFC family. Experiment results are given to validate the efficiency analysis and EMI model building.