SiC/GaN Converters

As novel power devices emerge from research to industry, the characterization of these novel devices and their application in power electronic converters is essential in order to assess the future potential. By taking into account comprehensive characterization results for the system development, record values of 200 kW/l power density, efficiencies above 99 % and switching frequencies up to 1 MHz are not uncommon anymore.

Be our partner for innovative solutions with wide bandgap power semiconductors and participate in the future of power electronics!

SiC Mechatronic Systems

From material to system and thus, completing the whole process chain of available SiC services, we work on the integration and optimization of SiC mechatronic systems for various fields of application.

Characterization

• Dynamic switching behavior of devices
• Burst ruggedness of gate control circuits
• EMC characterization and optimization up to mid-size cars
• System verification on lab bench up to 1000 V and 500 A
   

Characterization

• Analytic evaluation of converter topologies
• Optimum operating points for power semiconductors and passive devices
• Determination of critical operating conditions by electro-thermal co-simulation and deduction of customized solutions
   

Prototype Systems

• Bidirectional DC / DC and AC / DC converters for automotive and energy management
  
• Inductive charging systems for electric cars
• Ultra-high power densities exceeding 100 kW/l and switching frequencies up to 1 MHz
• Multiport concepts with lowest profile
• Customized gate drivers for optimum device performance
• Fully digital control boards powered by microcontroller or FPGA with scalable CAN interface

HoskA - 9-phase automotive SiC-Inverter

Within the project HoskA, a SiC-based 9-phase automotive inverter based on B6-powercores was developed. The powercores include the DCB-based powermodules with SiC-MOSFETs and SEMIKRON SKiN technology, the gate driver, the DC-link capacitor as well as current and temperature sensors (Fig.1) .

Using three B6 powercores in parallel, a symmetrical 9-phase 150 kW electric drive with a phase displacement of 40 degree of the PMSM was realized. The modularization concept allows also the realization of 50 kW (3-phase) and 100 kW (6-phase) drive systems using one or two identical powercores.

Air-cooled 40 kW SiC-Inverter

Wide Band Gap (WBG) semiconductors offer huge potentials for power electronic systems due to their significantly reduced conduction and switching losses.

Based on SiC-MOSFET technology, a modular and compact three-phase 800 V drive-inverter with a constant output power of 40 kW and a continuous phase current of 70 Arms was designed and realized.

Due to the raised efficiency with significantly reduced heat-losses, an air-cooled design with additively manufactured heatsink was realized.

The heatsink structure is directly integrated into the inverter housing and combines an optimized heat dissipation with the used fans, low weight and good manufacturability.

Download Product Sheet "Air cooled 40 kW SiC-Inverter"

Bidirectional 6kW Charger Using GaN Devices

Insulated and Bidirectional On-board Charger With Normally-Off GaN Gate Injection Transistors

New power semiconductors such as 600 V normally-off GaN gate injection transistors (GaN GITs) offer new opportunities for power topologies especially in bidirectional power-flow applications. There are very interesting implementations in bidirectional on-board chargers (OBC) for electric vehicles. Here, a bidirectional energy flow can either be used for vehicle-to-grid scenarios or for providing a high-power on-board AC socket. Because of a very low output capacitance and the ability of reverse current operation, GaN GITs offer advantages in hard switching topologies (low switching losses) as well as in soft switching topologies, where no additional leakage inductance is necessary.

Within a bilateral project with Panasonic, the Fraunhofer IISB has developed a bidirectional insulated OBC specially designed for the customer. The result was a novel 6 kW OBC with normally-off GaN gate injection transistors from Panasonic presented within only 2 dm³. The OBC is fully digitally controlled by using a special current regulator technique to reduce the higher grid harmonics. The utilized insulated power stage works like a DC transformer, determining primary-side DC operation voltage without applying any voltage regulator. The two-phase OBC consists of six equal full-bridge power modules next to the gate driver circuitry and DC link capacitors following a modularized approach.

A very high power density of approx. 3 kW/dm³ was reached with the developed prototype - which means an outstanding value for a complex bidirectional galvanically insulated OBC.

Challenges and solutions

To obtain the full performance of modern wide-band-gap power semiconductors such as GaN GITs, a low inductive realization of the switching power paths is necessary. Hence full-bridge power modules were developed with four 600 V (34 mΩ) Panasonic normally-off GaN GITs soldered and bonded on a FR4 together with gate drive units and DC-link capacitors.

To obtain a high efficiency OBC, a modern totem-pole circuit topology for converting the AC mains voltage to an internal DC-link voltage was chosen. For the galvanically insulated power stage, a low-loss soft-switching so-called CLLC converter was used. For extending the very efficient operation area, a switchable variable transformer ratio was implemented.

Hence, the AC/DC as well as the insulated DC/DC power stage achieve approx. 98% efficiency.

The performance of modern power electronic systems is not only dominated by power semiconductors but by control circuits as well. In this project, the 6 kW output power was divided into two identical 3 kW units each controlled by a 32 bit micro controller. Each microcontroller controls 12 power switches at a high switching frequency at approx. 130 kHz. Due to restrictions of the higher harmonic 50/60Hz grid frequency, the control of sinusoidal AC mains current is important. For this, a special version of the so-called low bandwidth current mode control technique, which is based on a non-linear feed forward control method, could be successfully implemented.

Due to the chosen double 3 kW power units, the OBC can be also used on two phases of the common three-phase 400 V AC mains system. In this case, the battery current has a pure DC portion with a superimposed AC sinusoidal content.

Bidirectional full SiC 200 kW DC/DC Converter

for Electric, Hybrid and Fuel Cell Vehicles

In electric and hybrid vehicles many compromises have to be accepted to avoid different HV - levels and a lot of extra money and effort is spent to keep input and output voltage ranges as wide as possible to match different applications.

Fraunhofer IISB offers non-isolating HV-DC/DC Converters that match all different occuring voltage levels, saving space and costs and offering more degrees of freedom for the vehicle designers.

The Fraunhofer engineers have managed to design an extreme lightweight, small and powerful DC/DC converter based on SiC-MOSFETs, extremely flat and small gate drivers, full ceramic capacitors and custom-made low-weight ferrite inductors.

The unique design has been awarded by the Semikron foundation with the innovation award 2015.  

Low-Loss GaN Converter - Prototype

The objective of the study was to explore the potential of GaN components for increasing the achievable efficiency in electronic power systems beyond the current possibilities. The results speak for themselves: For instance, an overall efficiency of up to 99.3 % could be determined for the compact converter with hard-switching topology developed at the Fraunhofer IISB. Furthermore, a switching frequency of 1 MHz was achieved – depending on the operating point – with the same design. In load tests, a stable operation could be demonstrated up to an input power of 2.5 kW. With a construction volume of only 0.09 liters, this corresponds to a power density of almost 28 kW / l. The excellent results are also not the least due to using an especially compact and low-inductance layout with an integrated gate driver. All electrical measurements of the extremely high efficiencies were calorimetrically validated.

In the framework of the investigations, designs and structures were realized for so-called hard-switching converters, and their electrical and thermal values were characterized. Pilot production components made of the promising semiconductor material gallium nitride (GaN), which were developed and produced by the industrial partner in Japan, were used for this. Specifically, these were close-to-production GaN transistors and GaN diodes whose mass production is imminent.