Drive Inverters & Mechatronics

The trend towards miniaturization and system integration in power electronics is mainly driven by applications with severe space restrictions such as automotive, robotics, or avionic. Major challenges arise from the fact that the installation space in these applications is usually predefined by mechanical requirements with less consideration for power electronics needs. This often results in complex geometries and contamination in addition to high thermal and mechanical stress. However, the better use of space, the avoidance of expensive cables and failure prone connectors, and the reduction of EMI filter expense make it necessary to choose this path.

A mechatronic system integration requires more than just increasing power density. We are working on innovative integration concepts as well as on new device, interconnection, and cooling technologies that foster a 3D integration, increase ruggedness, and decrease costs of power electronics

We work on highly integrated drive solutions for hybrid and electric vehicles, while offering a complete in-house development and testing of inverter power electronics.

 

We develop customer-specific drive-solutions...

  • Vehicle integration of electrical drive and power management systems 
  • Field-oriented motor control development for various machines (e.g. PMSM, IM, SSM, etc.)
  • Functional safety concept (ISO 26262, up to ASIL-D)
    Highly integrated drive solutions for hybrid or electric vehicles
  • Complete in-house development and testing of inverter power electronics (incl. 3D integration)
  • Vehicle integration of electrical drive and power management systems 
  • Field-oriented motor control development for various machines (e.g. PMSM, IM, SSM, etc.)
  • Functional safety concept (ISO 26262, up to ASIL-D)

Inverted Development

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Design and Prototype Realization of customer specific electric machines

Fraunhofer IISB offers the design and prototype realization of customer specific electric machines fitting to the application. The design process includes a complete 3D-FEM and CAD-based toolchain for the electro-magnetic, thermal and mechanical design and optimization of electric machines.

Download Product Sheet as PDF:

 

> Design & Prototype Realization of custom specific electric machines

> Smart Nodes for Automated Vehicle Power Supply Systems

We can cover a broad range of motor and drive applications:

Applications:

  • Automotive/Commercial vehicles
  • Aircraft
  • Industrial
  • Voltage range: 48 V to 1000 V
  • Power range: up to > 250 kW

Customized motor designs:

  • Highest power-density
  • High-speed traction motors
  • Multiphase motors
  • Concentrated or distributed winding schemes

 

Exemplary motor-topologies:

  • Permanent Magnet Synchronous Motor (PMSM)
  • Induction Motor (IM)
  • Separately Excited Synchronous-Motor (SSM)
  • Brushless DC Motor (BLDC)

Mechatronic and thermal design:

  • (Transient) thermal management of rotor and stator
  • Water-, oil- and air-cooling
  • 3D-CAD design and integration (e.g. housing, interfaces)
  • Customer specific interfaces

Control algorithms for inverter powered drive applications

 

 

  • Induction motors
  • Synchronous motors:
    • Permanent-magnet SM
    • Brushless DC
    • Double fed SM
    • Synchronous reluctance motor
  • Multiphase and multilevel topologies

 

The following solutions are covered by our R&D-work:

  • Conventional drive control methods (e.g. field oriented control) with custom optimizations regarding efficiency, torque precision, and response behavior
  • Adaptive control of drive systems (e.g. iterative learning control)Sensorless control: Algorithms for detecting the rotor or flux angle without sensors (including start-up from standstill)
  • Drive parameter identification
  • Suppression and active damping of harmonics (minimization of harmonic induced losses, acoustic effects and torque ripple)
  • Control and operation concepts for multiphase drives with various phase numbers
  • High sampling frequency control for low inductance motors and high-speed applications
  • Drive control and energy management design for hybrid drive trains
  • Modeling and simulation of drives and the designed control systems
  • Commissioning and test of the developed drive control systems at the in-house dynamometer facilities

System Robustness

Fraunhofer IISB analyses the dynamics of (thermo)mechanical robustness and optimization of mechatronic products characterized by a consistent workflow of experimental and numerical investigations.

The integration of mechatronic systems into highly stressed spaces demands an indication of product life already in the design phase. External vibrations, e.g. roadway bumps or engine oscillations, excite mechanical structures at their natural frequencies, which may lead to uncontrollable dynamic responses and failures at an early stage. The vibration resistance is further lowered by the operational thermal overlay. Common failure patterns in power electronics are fatigue cracks in solder joints, delamination at material boundaries and fretting corrosion of electrical interfaces. Typically, these robustness failures are electrically detected, but mechanically triggered. In the case of safety-critical devices, failures may have farreaching consequences. These critical load spectra are often found in mounting positions that are unsprung or close to an engine and occur in automobiles, aircrafts or wind turbines.

System
Component
Design Element

Deriving global loads to efficiently evaluate local vibration resistance

Possible subjects are approached based on the geometric complexity and may comprise different functional elements:

  • Electrical devices: resistors, capacitors, transistors, inductors, transformers
  • Electrical interfaces: connectors, busbars
  • Circuit boards: multilayer, flex rigid

 

3D Robustness Simulation

By applying the Finite Element Method, the physical response of the system is calculated and its design efficiency approved. In general, numerical investigations are made for all structural bodies and optionally interfered with thermal loads. Modal analyses are approached to identify natural frequencies and visualize the corresponding shapes. Harmonic and spectral analyses detect characteristic frequency responses and acceleration amplitudes. In the case of circuit boards, disadvantageously placed components are determined and recommendations to the electrical layout given.

Both, deformation and stress states. are calculated and referred to the material limits (e.g. tensile strength). The effects of global loads on local design elements are determined efficiently by subjecting the problem of different geometry scales with a special multi-level simulation approach. As solder joints are prone to micro cracks and delamination caused by mechanical vibration, the solder contour is modeled realistically by minimizing its surface tensions. Knowing the vibration induced stress state, an analytical reliability model is applied and cycles to failure are quantified.

 

The following simulation services are offered:

  • Thermomechanical robustness simulation of customer systems based on material parameters and CAD files
  • Analyzing the physical response of sinusoidal and random vibration signals
  • Identification of natural frequencies and measuring frequency responses at any location
  • Trace mapping of electrical layouts
  • Parameter studies in terms of design, loads and materials
  • Optimizing structural design by minimizing thermomechanical response

Research & Development of next-generation Electric Machines

Download fact Sheets as PDF:

 

> Power Electronic System Robustness

> Electrical Drive Control Systems

  • Electric drive systems
  • Inverter development
    (integrated or standalone)
  • Control boards and gate drivers
  • Mechatronic integration of
    power electronics
  • Advanced thermal management

Regarding inverter power-electronics, our R&D work focuses on:

 

  • Wide-Band-Gap semiconductor based power-stages (SiC, GaN)
  • Highest inverter efficiency, incl. part-load and drive-cycle operation
  • High switching frequencies for high-speed drives (> 30 kHz)
  • 3D mechatronic integration and thermal management
  • Motor control software (FOC)

Smart Nodes for automated vehicle power supply systems

Building Set for Smart Power Distribution Nodes for On-Board Power Supply Systems of Highly Automated Vehicles

HiBord DC/DC with DLC storage

© Fraunhofer IISB
© Fraunhofer IISB
Hardware modules of the smart power distribution node building set
© Fraunhofer IISB
Block diagram of the HiBord DC/DC with DLC storage

Highly automated vehicles as of SAE level 3 lack the driver as a fallback during power failures.

In the research project HiBord, funded by the German Ministry of Education and Research, new on-board power supply system topologies where investigated which can handle faults in the power supply system without full redundancy.

  • Energy flow control
  • Fault isolation
  • Network reconfiguration
  • Local reflexes and global decisions

 

Advantages:

  • Logic module with μC and FPGA for advanced monitoring algorithms and quick fault reactions
  • Scalability by using standardized interfaces
  • Modules equipped with sensors for current, voltage, temperature
  • Different communication options (CAN, Automotive Ethernet, …)
  • Scalable housing and cooling solution due to standardized module dimensions and connectors

 

Modules:

Many modules already available

  • Uni-directional and bi-directional switch modules (12V or 48V)
  • 48V/12V DC/DC converter module
  • Double layer capacitor module
  • Active and passive DLC pre-charging modules
  • Logic module with powerful FPGA and µC

… and more, depending on project requirements

 

Application Example

A combination of an on-board DC/DC converter and a DLC was realized with the building set and is a key component of the HiBord power supply system.

The system combines  a DC/DC converter with a transient power storage and thus can replace a 12V battery in fail-operational scenarios.

In-house Testing Possibilities

A variety of motor test benches up to 300 kW and 800 V DC-power supply are available at Fraunhofer IISBs' own test-center for electric vehilces and can be used for the characterization of electric motors and complete drive systems.

  • Engine test bench
  • Air-conditionable all-wheel roller dynamometer
  • Battery tests
  • System reliability
  • Electromagnetic compatibility (EMC)

Project Examples

100 kW SiC-Inverter for automotive application

Siliconcarbide (SiC) MOSFETs offer huge potentials for power electronic systems due to their significantly reduced conduction and switching losses and their capability for highest junction temperatures. Based on this novel semiconductor technology, a modular and compact 3-phase 800 V drive-inverter for automotive application with a maximum output power of 100 kW was designed and realized. Using four parallel MOSFETs per switch, the system provides a maximum phase current of 150 Arms.

The inverter demonstrates the advantages of SiC-semiconductors on system level:

  • Highest power density
  • Highest (part-load) efficiency
  • Highest switching frequency
  • Reduced cooling effort

Due to possible switching frequencies of up to 100 kHz, the SiC-inverter is suitable for machines and applications with highest electric frequencies like high-speed traction-motors, compressors and electric turbochargers.
Download Product Sheet "100 kW SiC-Inverter for automotive application"

© Anja Grabinger / Fraunhofer IISB

Air-cooled 40 kW SiC-Inverter

Wide Band Gap (WBG) semiconduc-tors 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"

 

© Anja Grabinger / Fraunhofer IISB

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.

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.

Project partners: Volkswagen Aktiengesellschaft, Semikron, TDK, Liebherr, Federal Ministry of Education and Research, VDI|VDE|IT

Download Product Sheet HoskA - 9-phase automotive SiC-Inverter"

EMiLE

Electric motor integrated power electronics with Smart Stator Teeth

In the EMiLE project, ten partners from the German industry and research-institutes are working on innovative drivetrain  solutions for tomorrow's e-mobility.

The project focusses on compact and efficient electric vehicle traction-drives with a high degree of integration of electric machine, power electronics, and gearing, which are perspectively suitable for large scale production.

High power density, high efficiency and cost minimization are benefits of the realized Smart Stator Tooth – structure within the drive unit. Each stator segment of the PMSM electric machine has its own local control and power electronics. The modular system approach can be adapted to different vehicle and drive classes.

Drivetrain with Smart Stator Teeth

Each Smart Stator Tooth (SST) consists of a motor segment and an electronics assembly. Twelve SST form one PMSM stator and the corresponding inverter.

Each tooth electronic is built up of an IGBT full bridge power-module, phase current sensor, current control loop, gate driver unit, and a fault detection block. The stator windings are directly connected to the AC terminals of the power module, thus minimizing space and reducing the number of parts. The pre-assembled SST is fully testable before mounting the complete system.

Novel Control and Safety Functions

The advanced SST control functionalities have two objectives: First, a failure in one phase power module does not lead to a full system failure. Second, after detecting faulty parts, the remaining SST can be used to actively compensate the influence of the failure.

The SST concept redefines and improves both availability and failure mitigation: The aim is to achieve a safe system state, concerning vehicle stability and passenger safety, without additional hardware effort. At the same time, the availability is increased, which means that partial faults do not stop the whole system. In summary,  the drive system is fail-operational.

 

Project Partners:  VDI|VDE|IT, Aix Control, Bosch, Infineon, iSEA RWTH Aachen, Lenze, Siemens, TDK-EPC, VW, ZF

Download Product Sheet "EMiLE - Electric motor integrated power electronics"

60 kW SiC-Inverter for High-Speed Drives

High-speed electric motors – like traction drives, compressors and electric turbo-chargers – require higher inverter output-frequencies and therefore higher switching-frequencies to avoid additional losses and torque-ripple within the machine. With state-of-the-art inverter systems (e.g. using Si-IGBTs and Si-diodes) the switching frequency in the considered power-range is typically limited to values of 10 to 20 kHz due to higher switching losses.

In order to meet these demands, a 60 kW inverter system for high-speed electric machines was developed and realized. The use of siliconcarbide 1200 V MOSFETs, ceramic-capacitors and a low inductive system design allow switching frequencies up to 100 kHz at reasonable efficiencies.

The novel semiconductors with their reduced losses enabled a power-density of the overall power-stage of >150 kW/l which is far beyond state-of-the-art. This offers also the possibility to integrate the inverter directly into electric machines.

The  power stage is realized in B6 topology and consists of three half-bridge DCB-powermodules equipped with 25 mOhm SiC-MOSFETs. Antiferroelectric ceramic capacitors with a high current-ripple capability are placed directly above the switches to achieve best switching performance. Integrated drivers provide the required gate-voltages for the semiconductors (+20 V to -5 V) as well as safety and monitoring functions.

The inverter system is realized in a highly integrated mechatronic package. In order  to achieve the best cooling performance and overall power-density, the DCB-modules are directly attached to a pin-fin cooling structure.

Download Product Sheet " 60 kW SiC-Inverter for High-Speed Drives"

COSIVU – Integrated 1200 V SiC-Inverter for Commercial Vehicles

The aim of the Fraunhofer IISB is the development of a 1200 V inverter in cooperation with its partners. The inverter is integrated in an electric drive-unit for commercial vehicles of Volvo. The inverter will use SiC bipolar transistors manufactured by TranSiC.

The advances over the current state of the art can be summarized as follows:

  • Decentralized drive-train system with one compact system package and wireless communication between drive units and central computer 
  • Development of next generation of highly integrated inverter modules based on novel SiC technology (1200 V, 500 A)
  • Fail safe concepts for increased functional safety
  • Closed hardware-in-the-loop technology to always guarantee optimal working  conditions
  • Innovative functional and health monitoring
  • Improvement of durability and total driving range by factor 2
  • The electric power train developed in the COSIVU project was evaluated on a test rig and test vehicles

Project Partners: Volvo Technology, Hella, TranSiC, Sensitec, Nanotest, Elaphe, Swerea, TU Chemnitz and Fraunhofer ENAS

Download Product Sheet "COSIVU"