Intercell Transformers Research Articles

Optimization of LCL Filter With Integrated Intercell Transformer for Two-Interleaved High-Power Grid-Tied Converters

Paralleling of voltage source converters (VSCs) with a limited maximum output power is essential when the power rating of a system must be increased. Interleaving (ILV) of the switching signals for parallel-connected VSCs provides a better harmonic spectrum than hard paralleling (HP), i.e., applying identical signals to all VSCs. This can be particularly beneficial for grid-tied converters, since a smaller LCL filter can be realized. To investigate the performance limitations and the impact of ILV operation on the LCL filter hardware, a comprehensive optimization procedure for LCL filters and intercell transformers (ICTs) for two paralleled VSCs is presented in this paper. In addition, a comparative evaluation of HP and ILV operation of VSCs is carried out. The developed optimization procedure and the hardware benefits of ILV operation were verified through testing on a 260-kW full-scale system. Compared with the commercial state-of-the-art weight-optimized LCL filter for HP, the developed LCL filter for ILV utilizing an integrated ICT reduces the total filter weight by 30% while guaranteeing harmonic standard compliance and meeting thermal requirements.

An easy to implement and robust design control method dedicated to multi-cell converters using inter cell transformers

Abstract Parallel multi-cell converters using inter-cell transformers are real multi-input multi-output systems, making their control challenging and possibly requiring increased embedded computing power in the control architecture. The challenge of the current study is to design a control algorithm as simple as possible, in terms of settings and implementation, while meeting standard specification. The state-space representation of multi-cell converters permits to define a full state feedback. Such Multi-Input Multi-Output (MIMO) systems have numerous tuning parameters which enable various ways to tackle the control specifications. Among the specific approaches, both total decoupling and optimal control based on quadratic cost and objective functions are addressed thoroughly and consistently. The studied case is a 3-cell parallel converter for which various settings of the state feedback are considered and analyzed by simulation Linear-quadratic regulator design reveals the best compromise between variables tracking precision and robustness towards system parameters and load variation. Furthermore it is easy to implement utilizing few non-zero setting coefficients. Specifically the feedback gain matrix associated to the integral terms is almost diagonal: this natural decoupling makes it extremely simple to efficiently implement an anti-windup algorithm. This is an important result since until now, the standard solution is mostly based on decoupling strategies. Among other drawbacks, this latter approach proves to be much more sensitive to parameter uncertainties.

DC-DC converter with GaN transistor and coupled with monolithic ICT sintered by PECS/SPS

ABSTRACTThis paper presents an implementation of the voltage regulator module (VRM) DC-DC converter operating at 2 MHz using three interleaved switching cells whose outputs are magnetically coupled by monolithic intercell transformers (ICT). The innovation comes from the manufacturing of the ICTs. Spinel ferrite is sintered around two copper windings by pulsed electric current sintering (PECS), also called spark plasma sintering (SPS). The manufacturing processes are detailed in this paper, and the ICTs magnetic properties are measured. The high-frequency operation of the converter has been possible thanks to the implementation of GaN components. The power density of the converter is 15 kW/dm3.

Flexible Power Control for Wireless Power Transmission System With Unfixed Receiver Position

To improve the stability of receiving power in the wireless power transmission system with unfixed receiving position, a flexible power control strategy without the measurement in secondary side and the wireless communication between primary and secondary sides is proposed. The circuit model of a multiphase resonant inverter (MPRI) with cascaded intercell transformers (ICTs) is developed. The output voltage control strategy of the MPRI is introduced based on the iterative summation method for trigonometric functions. The circuit model of the system is derived to deduce the expressions for the key parameters. Considering the cascaded ICTs and the inductor–capacitor–capacitor ( LCC ) compensation circuit in the primary side, the design method of the compensation parameters is proposed based on the circuit model of the MPRI. After synthesizing the online monitoring, parameter pre-calculation, prediction of several conditions, and online learning, the flexible power control strategy is put forward for the wireless power transmission system with unfixed receiver position. Without the auxiliary positioning methods, the measurement in the secondary side, or the wireless communication between primary and secondary sides, the recognition of the load access and exit, as well as the power stabilization control after access, are realized. Finally, the theoretical analyses and the control strategy are validated by experiments.

Influence of cold isostatic pressing on the magnetic properties of Ni-Zn-Cu ferrite

In power electronics, there is the need to develop solutions to increase the power density of converters. Interleaved multicellular transformers allow interleaving many switching cells and, as a result, a possible increase in the power density. This converter is often composed of a magnetic core having the function of an intercell transformer (ICT) and, depending on the complexity of the designed architecture, its shape could be extremely complex. The switching frequencies (1-10 MHz) for the new wide band gap semiconductors (SiC, GaN) allow to interleave switching cell at higher frequencies than silicon-based semiconductors (<1 MHz). Intercell transformers must follow this increase in frequency times-fold the number of switching cells. Current applications for ICT transformers use Mn-Zn based materials, but their limit in frequency drive raises the need of higher frequency magnetic materials, such Ni-Zn ferrites. These materials can operate in medium and high power converters up to 10 MHz. We propose to use Ni0,30Zn0,57Cu0,15Fe2O4 ferrite and to compress it by cold isostatic pressing (CIP) into a a green ceramic block and to machine it to obtain the desired ICT of complex shape prior sintering. We compare the magnetic permeability spectra and hysteresis loops the CIP and uniaxially pressed ferrites. The effect of temperature and sintering time as well as high-pressure on properties will be presented in detail. The magnetic properties of the sintered cores are strongly dependent on the microstructure obtained.

Design and fault-operation analysis of a modular cyclic cascade inter-cell transformer (ICT) for parallel multicell converters

Nowadays, parallel multicell converters including inter cell transformers (ICTs) are usually used in many different conversion systems and with various topologies. In this paper, an analysis of a modular cyclic cascade ICT is presented for nominal and fault operation. The first part of the article presents a pre-design methodology for cyclic cascade ICTs in nominal operation. Afterwards, an analysis of magnetic behaviour during failure operation as imbalance current or case of k disconnected phases will be presented. The aim of this article is to design a cyclic-cascade ICT that is more robust in failure operation. Air gaps (AGs) have been inserted in order to limit this saturation. A concept of compact cyclic-cascade ICT with just a single winding by phase is presented. We will show its principle of realization and 2D fine element simulation in order to validate this concept.

Simple control technique for interleaved inverters with magnetically coupled legs

Recent works of different authors have shown that the use of intercell transformers in interleaved inverters bring many improvements to this kind of parallelism. However, even though a balanced current distribution is necessary and not guaranteed by the converter itself; just a few of those studies are focused on the modelling and control of the inverter. Moreover, the fact that the paralleled modules are coupled and that the control signals are not updated simultaneously have not been considered yet. In this way, the current paper takes those facts into account and proposes a simple procedure for modelling and control a single-phase interleaved inverter. A mathematical analysis, some simulation and experimental results are shown in order to prove the simplicity and effectiveness of the proposed procedure.

Optimal PWM method for flux reduction in InterCell Transformers coupling double three-phase systems

Optimal PWM method for flux reduction in InterCell Transformers coupling double three-phase systems

Parallel Three-Phase Inverters: Optimal PWM Method for Flux Reduction in Intercell Transformers

Parallel multilevel converters are now widely used in the industry, particularly in high-current applications such as voltage regulator modules. The reduction of the output current ripple and the increase of its frequency are possible due to the use of interleaving techniques and, as a consequence, the filters associated with the converter may be reduced. The current ripple reduction in each commutation cell of a parallel converter is possible by the use of intercell transformers (ICT). The design of such a special magnetic component depends very strongly on the magnetic flux flowing through their cores. In three-phase systems coupled by ICTs, the injection of zero-sequence signals in the output voltage reference changes this flux. The aim of this paper is to explain the influence of the most popular pulse width modulation (PWM) methods regarding the ICT flux for applications to three-phase loads. An optimal PWM method that minimizes the size of the ICT design is developed. Experimental results verify the analysis presented in this paper and validate the flux reduction provided by the developed optimal zero-sequence signals.

Dimensionnement de transformateurs intercellulaires pour un convertisseur flyback multicellulaire de forte puissance

The simplicity of the flyback converter is attractive but this topology is not used in high power converters because of the efficiency limitation due to the coupled inductor. This drawback can be eliminated in high power multicell flyback converters by using interleaving techniques and Intercell Transformers (ICT). The first part describes the ICT flyback converter and the experimental results obtained on a 2kW-100V-70kHz demonstrator. In second part, we present the ICT design methodology, including heat transfer features. Finally, the ICT design for a 12kW converter is proposed. Experimental thermal results are given to valid the design process.

Nouvelles architectures de convertisseurs électroniques de puissance utilisant des transformateurs intercellulaires

This paper deals with new architectures for power electronics converters. These architectures are based on interleaved elementary power conversion cells interconnected and coupled using intercell transformers. The advantages of such architectures are demonstrated through three kinds of applications.

Design and Comparison of Inductors and Intercell Transformers for Filtering of PWM Inverter Output

This paper presents an original design option dedicated to output-filtered pulsewidth modulation inverters used in uninterruptible power systems, embedded networks, or motor drives operating on long cables. It is based on the coupling of interleaved inverter cells by means of intercell transformers (ICTs) and is characterized by very good dynamic behavior on load transients, which is an important issue in such applications. ICT solutions are compared with the classical interleaved solutions using separate inductors. A specific design method is developed to achieve this comparison based on toroidal core shapes. The results obtained with a 600 V, 7.5 kW inverter show the usefulness of ICT-based designs, especially when nanocrystalline magnetic material is used; high specific power and very good dynamic performances are obtained.

Design of Intercell Transformers for High-Power Multicell Interleaved Flyback Converter

This paper presents the developments and the results of an analytic method elaborated to design isolated intercell transformers. These particular magnetic components are intended for multicell interleaved flyback converters recently proposed and well-suited to low-voltage, high-power applications. A specific 2-D model to evaluate the winding losses is included in the design process. The results, obtained for standard core shapes, allow defining the ranges of the main parameters, number of cells, and switching frequency, required for future realizations.

A Theoretical Approach to InterCell Transformers, Application to Interleaved Converters

The theoretical advantage of InterCell transformers over separate inductors is demonstrated in an interleaved power converter. Different practical ways to build InterCell transformers are described. A theoretical approach dedicated to interleaved converters and InterCell Transformers analysis is presented. This analysis tool is used to understand and overcome the main drawback of InterCell transformers. It is shown how the phase shifts between two adjacent phases must be modified to reduce the maximum flux density that influences core sizing and core losses.

Multicell Interleaved Flyback Using Intercell Transformers

An original converter composed of interleaved flyback is presented. The cells are interconnected through intercell transformers replacing the standard multi-winding inductors used as insulation and storage magnetic device in the flyback. The combination of the interleaving effects and of the intercell transformer characteristics allows eliminating the mains limitations of the standard flyback due to the low performances of multiwindings inductors. In a first part, the different ways to interleave galvanic insulated converters as forward or flyback are briefly recalled. The second part presents the intercell transformers and shows that they can be used to interconnect interleaved converters cells. In the third and last part, this particular magnetic interconnection is applied to interleaved flyback cells and leads to create an ldquointercell transformer flybackrdquo. Its specific properties and advantages are described. Experimental results, obtained on a 2-kW test bench are finally presented.

Optimization of the Supply Voltage System in Interleaved Converters Using Intercell Transformers

Interleaved power converters are now used in many different conversion systems involving various topologies (series or parallel) and related to different fields or loads. This paper deals with interleaved parallel commutation cells using coupling transformers with a possibly high number of cells. The first part of the paper is a reminder of the basics of magnetic couplers addressing monolithic as well as distributed implementations. The limits associated with the conventional supply of such couplers (supply voltages forming a direct polyphase system) are described. In the second part of the paper, an optimized voltage supply improving the performances of the system is introduced. Experimental results obtained on a seven-cells test bench validate the approach