Heat Dissipation Challenge in Automotive High-Power Integrated Magnetics
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MAGNETIC COMPONENTS CONTENT Heat Dissipation Challenge in Automotive High-Power Integrated Magnetics In 2016, Premo Group launched 3DPower™, the first product to integrate two magnetics components that share the same core and feature two orthogonal magnetic fields at all points within the core. As a result, the increased power density in the component makes heat dissipation a tough challenge for our designers. By Hector Perdomo Díaz, R&D Engineer, PREMO Group and Juan Manuel Codes Troyano, R&D Engineer, PREMO Group, in collaboration with MSMP Power GmbH This article focuses on discussing the advances achieved by PREMO regarding heat dissipation techniques in 3DPower™. The biggest impact of magnetic integration is volume reduction when compared to a discrete solution for the same component. A consequence of increasing the power density is a temperature rise of the part. Introduction 3DPower™ Pot-Core uses a custom potcore shape where 2 inductive components are integrated. One of them is placed in the pot-core itself and the other one outside the pot-core as if it were a toroid. This product allows us to solve the engineering challenge of integrating magnetics: in this case it consists of a choke and a transformer. Unlike other magnetics integration technologies, both components share the whole core volume in the 3DPower™. For this purpose, the magnetic field of one component is orthogonal to the other, resulting in 2 independent and fully uncoupled magnetic elements. As it can be seen in Figure 1, there is one winding inside the ferrite core (70a); while the other orthogonal winding is outside (70b/c/d). Designers of magnetics for mass production know that ferrite cores break easily, particularly when the winding is machinemade. Hence, it was necessary to cover the core with a coil. The readers can imagine how hot a core can be when it contains a winding with a few tens of amps, and it is covered by a plastic coil that has also wires around it; plus, this adds up to the core selfheating due to core losses. Most of the times overheating failures are caused not only by the overall temperature increase, but also by hot spots. Hot spots can create temperature gradients in the ferrite core that could lead into breaks or a poor performance. Therefore, the main goal in a product is to avoid hot spots by creating good thermal link between all the components and then ensure a proper cooling system to remove heat. Premo can provide fully customized solutions of the 3DPower™. However, due to its geometry, the main applications are Phase-Shifted Full-Bridge and Resonant LLC DCDC converters. The output power range spans from 1 kW to 11 kW, but higher powers can be reached on demand. One of our latest developments can be seen in Figure Bodo´s Power Systems® Figure 2: Step-down transformer + series inductor + parallel inductor for a 3.5kW LLC converter Thermal Link A proper design and a wise selection of materials are key for thermal performance. The picture below shows an 11kW transformer where windings were made using stereolithography 3D printing technology and cooled with water in the bottom core. The wire is much hotter than the core, particularly on the bottom. The solution consists of using thermal conductive plastics on the coils to create a thermal link between the wire and the core, for example with thermal pad or thermal liquid gap filling material. In the 3DPower™, thermal liquid gap filler was dispensed to guarantee a reliable thermal link between coils, windings and core. Core Adhesive Core sets are supplied in halves. The easiest and cheapest way to join two cores is to use tape, which is common for cheap and small transformers. Although the magnetic path is not affected, the thermal resistance is high Figure 1: Pot-core solution (left); detailed cross-section (right) 2, where three magnetics components are combined in one single core (1 transformer and 2 inductors). This is just one example of how easy is to integrate magnetics by using our technology.

MAGNETIC COMPONENTS CONTENT Resins In EV/HEV vehicles, all high-power magnetics must be cooled down by means of a forced cooling technique. Since semiconductor power modules are attached to a cooling plate, this is used also to mount the magnetic components on it. Most of our clients use only thermal pads, but there is a growing trend in the industry towards the use of resins to pot the whole on-board charger or the power converter. The size of the power Coil Plastics electronics units is reduced thanks to the better thermal dissipation and electrical isolation As explained, the pot core...

MAGNETIC COMPONENTS CONTENT divergences among samples. The time response of the system was slower for the PA6 sample (25% slower). High Power Test Setup To test the electrical and thermal performance of the 3DPower™ magnetics under all load conditions a high-power test setup from MSPM Power GmbH was used. A TTG1000SIC square wave generator is the main part of the test equipment and it generates the square wave signal of up to 1000V. The square wave frequency can be set within a range of 10 kHz to 450 kHz and it is also possible to set the duty cycle from 0 to 100%. An external full-wave...