MALLIKA ASHWIN MAYA CORPORATION — Department of Energy SBIR Phase II: C52-08a

Description

Large scale deployment of BESS will enable storage during off peak-load time; help better integration of Renewable energy by mitigating intermittencies and assists in other grid support function. Due to inherent flexibility, Dual active Bridge Converter (DABC) is used as an interface between BESS and grid. DABC Provide the Galvanic isolation, Level shifting and soft switching to minimize the power conversion losses. In DABC- either PWM controlled or frequency controlled resonant types- besides the turn’s ratio of the HF transformer, its leakage and magnetizing inductances play active and critical roles.to realize the soft switching of the power devices. The proposed LOI has three areas of Thrusts as follows: • Integrating precise leakage and magnetizing inductances in the HF transformer for DABC • Methods of printing the cores using high saturation flux and high temperature Nano-crystalline materialon PCBs leading to uniform HF transformers with precise parameters in high performance mass produced DABCs for BESS to AC grid integration • Testing of the magnetics on a DABC with Li-ion BESS.Thrust-1: Integrating precise leakage and magnetizingPlanar Primary WindingPlanar Secondary Winding(a)Nano Crystalline Cores of Different Geometries Series Inductor Series Inductor Parallel Magnetizing Inductor Equivalent Electrical Circuitinductances in the HF transformer for DABC: The leakage inductance on bothFig.1 Multi-core magnetic components for DABC: Trimetric view with mounted PCB windings and the equivalent electrical circuit of the magneticsprimary and secondary windings due to the non-coupled portion of the magnetic flux which can be utilized to form the series inductors on the two sides of the transformer. Proposed Approach: The approach proposed by BU’s power electronics group reduces the reluctance of the leakage flux path in a controlled manner in the two PCB windings of the HF Transformer by introducing additional U-I magnetic cores of different geometries on the windings, an example is depicted in Fig. 1. The advantages are: • Reduced EMI of the magnetic components due to better confinement of this flux in the auxiliary cores. • Elimination of external AC inductors and their losses in DABC, • Integration of precise leakage and magnetizing inductors by adjusting the geometry and permeability of the cores in HF DABC Transformers. Thrust-2: AM of the multi-core transformer on PCBs using nano-crystalline material. Presently Nano crystalline material is produced using spin casting or Rapid solidification Process. Ribbon is wound in ‘C’, ‘E’ or toroidal shape to realize the desired core shapes. With conventional core manufacturing techniques, one cannot realize the full benefits of high curie temp, high flux density of NanoHead office: 10, Hastings court, Bridgewater, NJ-08807 Land Line: 908 393 2571, Mobile : 908 448 6580 statikola@maminc.net ; www.maminc.netcrystalline magnetic material leading to sub-optimal use of the material properties. Using the conventional core production methods do not lend itself to effective heat dissipation-compromising the performance more. AM using gas atomized powder can help us alleviate these limitations of the conventional core and component fabrication. AM has been studied for soft magnets for Electrical machines by NREL/ORNL. It is highly likely to integrate the entire converter and magnetics using the AM techniques. Success of these techniques will streamline the supply chain, reduce the cost and optimize the use of Nanocrystalline properties of the core for reduced losses, increased power density and operation above 150?C. Exploiting the incredible cooling rates of AM (106-107 °C/sec) available at BU’s Powder bed metal selective laser melting printer (EOS m290), HF nanocrystalline magnetic material conforming to the geometry shown in Fig. 1 can be printed using AM.1 Through engineered spatial cooling gradients, the formation of lower electrical conductivity dendrites can be controlled, for lowering the electrical conductivity in the direction in which eddy currents form inside the magnetic core thus reducing eddy current losses relative to conventional ribbon form of this material at HF operation (=100 kHz). Also, critical to this effort, BU’s AM research group has developed a printing process to print metals onto silicon and dielectrics, which will be adapted to print directly onto fiber glass reinforced FR4 PCBs for DABC and to bond dielectric airgaps.2–4 This can be achieved by using a low-melting point alloy that reactively bonds to the FR4 and most metals.