Geometry optimization and characterization of three-phase medium frequency transformer for 10kVA isolated DC-DC converter

Three-phase Dual Active Bridge converter is advisable for the High-power DC-DC conversion system. In the ac link, galvanically isolated transformer operated at a medium frequency range provides stepping up or down of the secondary bridge voltage. This paper provides a magnetic design optimization of the medium frequency transformer for maximizing its efficiency when excited by a non-sinusoidal waveform. In this paper, a mathematical design of a 10kVA non-sinusoidal transformer had been developed and validated using two-dimensional (2D) transient finite element analysis (FEA). The set of selected design variables is defined in order to enhance the power density and efficiency of the targeted transformer and an optimization is carried out. Finally, a 10kVA transformer is prototyped and the results of core losses for nonsinusoidal excitation is confirmed experimentally

An analytical modeling and estimating losses of power semiconductors in a three-phase dual active bridge converter for MVDC grids

Due to the increasing installation of renewable and decentralized power sources, Medium-voltage dc (MVDC) grids has been considered for an alternative application to medium-voltage ac (MVAC) application. Three-phase dual active bridge DC-DC (3DAB) converter is proposed as an attractive topology for MVDC grids due to its high power capability, smaller filtering parts, and galvanic isolation. In this paper, a first harmonic approximation (FHA) modeling of 3DAB converter is derived. Using the FHA modeling, a symmetrical modeling of switching devices is introduced and a 4MVA system for 40kV MVDC system has been validated in terms of conduction and switching losses. Experimental implementation of a 10kVA prototype and the results are presented

Design considerations for a high-power dual active bridge DC-DC converter with galvanically isolated transformer

Multi-megawatt scale isolated DC-DC converters are likely to become increasingly popular as means to interconnect the MVDC grids of different voltage levels. Threephase dual active bridge DC-DC (3DAB) converters operating with the zero-voltage switching (ZVS) is a promising candidate for the target multi-megawatt application. This paper presents a systematic approach of the design considerations for a 3DAB converter. Firstly, the use of snubber capacitors in medium voltage and medium frequency operating conditions is proposed. Snubber capacitor influence on turn-off current levels and ZVS operating range are introduced and analyzed. In addition, details of thermal management design are introduced. It is established through power loss analysis that the proposed design method reduces the semiconductor losses substantially at full load conditions. Finally, the proposed method has been validated from a 10kW simulation model using PLECS software package

Design optimization of a high-power transformer for three-phase dual active bridge DC-DC converter for MVDC grids

High-power DC-DC converter will be one of the essential technologies for the future DC grids. Especially, a three-phase dual-active bridge DC-DC (3DAB) Converter is highly suitable for high-power DC systems. Key component within this converter is the high power transformer operated at a medium frequency (MF) range. The design and optimization of this key component is presented in this paper. The transformer provides galvanic isolation from low voltage level to medium level or high voltage level and provides stepping up or down of the output (secondary) voltage. At first, a design of three-phase medium frequency transformer is developed. The designed transformer is then validated using two-dimensional (2D) transient finite element analysis (FEA) and performance under the non-sinusoidal excitation is determined. After that, the optimization is carried out, for the set of selected design variables, in order to enhance the power density and efficiency of the targeted transformer. Finally, the performance of the full system, 3DAB converter, is determined using the parameters of optimized transformer. Also, two different rated input voltages for 4MW/1kHz three-phase transformer are considered and analysed in this paper

Design optimization of integrated rotational inductor for high-speed AC drive applications

In order to make an efficient and power dense overall system, a close physical and functional integration of passive components is required instead of having a separate sub¬system for passives. Such power dense system is vital in aerospace and marine applications. This paper presents the design optimization of integrated rotational inductors for high speed AC drive applications. Design degrees of freedom like slot-pole combinations along with different winding configurations such as, single layer (SL), double layer (DL), concentrated winding (CW) and distributed winding (DW) are considered. In this paper, the rotational inductors are optimized for these degrees of freedom and compared with a benchmark EE core inductor in terms of total losses, weight and AC copper resistance at both fundamental frequency (1 kHz) and switching frequency (10, 15 and 20 kHz). The comparative analysis between EE core and rotational inductors has shown a significant reduction in total losses and AC copper resistance at fundamental frequency and all switching frequencies. In comparison with EE core inductor, 12 slots 2 poles rotational inductor with SL DW gives lowest total losses at fundamental frequency whereas 6 slots 2 poles rotational inductor with SL DW offers the lowest AC copper resistance at both fundamental and all switching frequencies

Design optimization of integrated rotor-less inductors for high-speed AC drive applications

Discrete sub-system due to passive elements in motor drive require functional and structural integration to make efficient and power dense overall system. Such power dense system is the prerequisite in aerospace and marine applications. This paper presents the design optimization of integrated rotor-less inductors for high speed AC drive applications. Different slot-pole combinations are considered in this process. The single layer (SL) and double layer (DL) windings are chosen with concentrated winding (CW) and distributed winding (DW) configurations. The rotor-less inductors are optimized and compared in this paper with EE core inductor in terms of total losses, weight and AC copper resistance at both fundamental frequency and switching frequencies (10, 15 and 20 kHz). The comparative analysis between EE core and rotor-less inductors has shown a significant reduction in total losses and AC copper resistance at both fundamental frequency and all switching frequencies

Integrated output filter inductor for permanent magnet motor drives

This paper presents a novel approach to integrate the output filter inductor in permanent magnet synchronous motor (PMSM) drive system. The integrated output filter inductor is based on utilizing the motor magnetics as a filter inductance instead of introducing a separate filter inductor. Thus, eliminating added filter inductor losses and associated weight and volume. The vector controlled model, taking modulation and switching effect in to account, has been developed using MATLAB/Simulink tool for the proposed integrated output filter inductor. The currents obtained from MATLAB/Simulink model are then injected into the Finite Element model to validate the concept. The performance of the proposed and conventional system is analyzed in terms of mean electromagnetic torque, torque ripple, motor losses, inductor losses, weight and volum

Novel integrative options for passive filter inductor in high speed AC drives

This paper presents novel integration options for passive inductor which include: motor-shaped rotational and motor-shaped rotor-less inductor for high speed motor drive system. The novel options have been designed and their performance is compared with the conventional EE core inductor using finite element analysis. It is observed that there is a significant reduction in total losses at fundamental frequency along with substantial reduction in the AC copper loss at 10, 15 and 20 kHz switching frequencies, when the proposed integrated options are utilized. For the motor-shaped rotational inductor, the total losses at fundamental frequency and AC copper loss at different switching frequencies are reduced by 26.1% and 73.8% (at different switching frequencies) respectively. There is a reduction in overall volume by 3.6%, but this comes with 11.7% increase in weight. For the motor-shaped rotor-less inductor, the total losses at fundamental frequency and AC copper loss at different switching frequencies are reduced by 10.4% and 73.8% (at different switching frequencies) respectively. There is a reduction in overall volume by 3.6% but this comes with 6.1% increase in weight. The proposed designs can share the cooling system of the motor thus, eliminating the requirement of separate cooling system

A high-power DC-DC converter based dual active bridge for MVDC grids on offshore wind farms

This paper presents the steady-state analysis of a high power step-up DC-DC converter based three-phase dual active bridge (3DAB) for use as a medium voltage (MV) DC-DC collector of offshore wind farms. An optimization procedure for a high-power medium frequency transformer is explained and moreover, a design of an optimal control phase shift angle is explained and verified through simulation. The comparisons with two scenarios are presented: 4MW converters for power conversion from low dc voltage (LVDC) of the wind turbine output terminal to 40kV MVDC grid of offshore wind farms. The proposed 3DAB DC-DC converter is investigated for the given scenarios in terms of losses of the semi-conductors and the magnetic part as well as the quantity of semi-conductors