Author:
Ally Winning, European Editor, PSD
Date
07/18/2024
PDF
Wolfspeed's three-phase SpeedVal Modular Evaluation Kit for electrical motor drive design
SiC MOSFETs are superior to IGBTs in many ways. They are more efficient, they are tougher, they have much better thermal resistance, and they enable smaller designs. However, care needs to be taken when incorporating SiC MOSFETs in a design as the gate drive and circuit parasitics of the board become more critical compared to designs with silicon IGBTs.
To assist customers make the change from silicon to SiC, Wolfspeed has broken the challenge into 3 separate phases - learn, evaluate and develop - and developed solutions for each.
The first stage is learning. It is software-based using the company’s free, online Speedfit Design Simulator. The software allows users to learn about the technology and important specifications, while cutting down the choice of products. Users can then experiment to see how the devices operate in a variety of power topologies.
Adam Anders, Power Platforms Manager at Wolfspeed explained, “Discrete solutions and modules can be compared in the Speedfit Design Simulator. Then more details can be defined about other parameters in the system, such as dead time and switching frequency. Some applications require additional information, for example a motor drive applications would require power factor, inductance and details of the inverter topology. Mission profiles can also be chosen for metrics like overload transients, so that the tool will simulate the steady state and then show that transient overload condition. Finally you can define the thermal constraints”.
After the user is satisfied with the results of the first stage, the next phase is evaluation. For this process, Wolfspeed offers platforms that allow the user to begin working with the parts without any design effort. The company has a range of platforms for different devices and applications, and it has also formed industry partnerships with leaders in the gate drive, control, and sensing areas to allow the evaluation of the design using industry-leading components.
Wolfspeed already has a single-phase motor-drive platform, but as a lot of higher-power drives that would benefit from SiC components use three-phase inputs, and the three phases need to be evaluated together to judge the operation and efficiency of the complete design, the company has now launched a new three-phase version. The fully featured evaluation system allows users to swap four different types of daughter cards – power, control, accessories and gate driver. These boards can be quickly swapped out to allow the evaluation of different MOSFETs, sensors, gate drivers and controllers and see how they work together. The user can then tailor the gate resistance and capacitance, tune DV/DT, as well as tinker with other parameters to get the desired results. Once the parts have been chosen for one phase, the other two phases can be populated and the board run at full power for testing.
Anders expanded on the board’s capabilities by saying, “DV/DT is a critical factor in motor drive designs for compatibility with existing motors. With the MOSFET and the gate driver boards in place, the user can start adjusting the gate resistance and gate capacitance to tune switching behaviour. Then all three phases can be populated for the full power testing of voltages, currents, efficiency and thermal behaviour. That process will verify that the design is going to meet requirements operating under real conditions with the gate drive tuning. Short circuit testing can also be undertaken at this point in the process.”
SpeedVal is intended to evaluate Wolfspeed’s 650V to 1200V SiC MOSFET portfolio. It can provide a DC bus voltage of up to 900V, handle input and output currents of 40A and is capable of testing motor drive and other applications to up to 30KW total power. As it is intended to primarily evaluate motor drives, it includes encoder and resolver feedback for closed-loop designs and speed control, and a CAN interface for system control. However, the design is not entirely focussed on motor control, and the ability to swap out a wide range of cards means that the evaluation board can easily be used to evaluate SiC MOSFETs for many other three-phase applications.
Once the parts of the system have been chosen and tuned, the develop phase helps users design the actual product. In this phase, Wolfspeed offers a range of reference designs to accelerate and de-risk development. Designs are available for applications including server power supplies, motor drives, EV charging, renewable systems, and automotive traction. The reference designs come with detailed design tips and considerations, test results, and design files to make things easier.
