Source : Mouser Electronics

Electric motors and their drives consume a significant portion of the electricity that we generate today. In the United States, the Department of Energy (DoE) estimates that electric motor-driven systems consume over half of all electricity produced in the country.[1] The DoE has also estimated that electricity costs make up about 96 percent of the total life-cycle cost of a motor.[2] Therefore, making motors and drives more efficient can provide significant cost-savings over the whole lifetime of the installation.

Eager to meet environmental targets and cut emissions, governments worldwide have introduced legislation that mandates higher efficiency in electric motors. With significant improvements already made in motor efficiency, some entities, such as the EU, have started targeting the efficiency of motor-driven systems. Silicon Carbide offers significant advantages in systems where the drive is packaged into the motor housing due to the reduced losses and cooling requirements.

The Benefits of Silicon Carbide

Fortunately, there is a solution already available: MOSFETs made from silicon carbide (SiC). In addition to providing three times lower thermal resistance and dispersing heat more effectively, SiC MOSFETs have lower conduction and switching losses compared to silicon IGBTs, especially at partial load conditions. Many motor drive systems run at less than full load for the majority of their lifetime, leading to a significant efficiency improvement when using SiC.

In addition to the inverter efficiency improvements, SiC can improve the power factor correction (PFC) circuit in the drive system. Motor drives that incorporate a boost PFC, or a fully bidirectional PFC can benefit from SiC by increasing the switching frequency to reduce the size of the filter magnetics. This size reduction can result in smaller and more cost-effective systems.

A Flexible Platform for Evaluation

Wolfspeed designed its SpeedVal™ Kit Modular Evaluation Platform to assist engineers in the evaluation process for SiC devices. The platform’s unique card-edge connection enables users to change silicon carbide devices to test different combinations of components while maintaining a low-inductance connection to the DC bus meaning testing that took weeks can be completed in minutes. There are four types of boards that can be swapped: power, control, accessories, and gate drivers. This easy customization helps to represent the end application accurately.

The platform is designed for three-phase evaluation, although a half-bridge version is also available. Along with the two additional channels, the three-phase board provides features explicitly targeted to developing motor drives, such as encoder and resolver feedback for closed-loop designs and speed control. A controller area network (CAN) communication interface has also been added an an optional system interface.

Additionally, the kit is designed to evaluate Wolfspeed’s discrete SiC MOSFET portfolio, including products that range from 650V to 1200V, with each MOSFET variation and package option having its own board. It can operate with 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 over 30kW total power. A wide variety of gate driver boards from industry leading suppliers for the SpeedVal platform provide various specifications, allowing designers to choose the correct gate drive for their application and optimize it by tuning the gate parameters and verifying that the MOSFET operates within its safe operation area (SOA). Switching behavior can be tuned to achieve a suitable dv/dt for the motor. This is an essential step in motor drive design, as many motors have been designed for IGBT drives, and matching the speed of the switching edge to the motor ensures system reliability.

The SpeedVal kit’s control board contains a microcontroller to deliver the pulse width modulation (PWM) signal to the gate driver. This allows the engineer to perform hardware evaluation with the actual application software. Alternatively, a function generator can be used to supply control signals to the gate. The control cards have pre-tested firmware and a computer-based GUI to allow the controller board to perform a double-pulse test, run a three-phase motor, and perform other operations. The control card and GUI also provide system-level details of the input and output voltage and current readings.

During the evaluation process, engineers often begin by testing a single phase of the design, with each phase representing a separate electrical circuit. Testing one phase first allows verification of performance metrics like voltage regulation, efficiency, and thermal performance. Once the single-phase performance meets expectations, the remaining phases can be added. After the gate driver optimization and high-power testing process is successfully completed, the designer can proceed confidently to laying out the circuit, knowing that the components and design will meet the required specifications.

SiC Will Only Gain Popularity

As industrial applications and various modes of transportation become electrified, SiC products will gain popularity due to their improved efficiency and thermal performance, which are critical requirements for these applications. Motor drives are just one area where the inherent advantages of SiC can bring rewards. Designers of other high-power applications, such as EV charging and renewable energy generation, are also looking to create more efficient designs and reduce energy costs. The SpeedVal Kit Modular Evaluation Platform is flexible enough to evaluate those and many other high-power, three-phase use cases (Figure 1).

Figure 1: The SpeedVal™ Kit Modular Evaluation Platform motherboards feature a range of control cards and gate drivers with unique card edge connections, enabling designers to save significant development time by rapidly changing silicon carbide devices and evaluating the desired gate driver.(Source: Mouser Electronics)

Conclusion

The SpeedVal Kit Modular Evaluation Platform allows the quick evaluation of the electrical and thermal performance of SiC MOSFETs and gate drive circuits. Furthermore, it allows the chosen devices to be tuned to meet the specific demands of the target application. Wolfspeed’s offerings extend beyond the SpeedVal platform, including the SpeedFit™ Design Simulator software, which helps users select appropriate products and refine system specifications. With flexibility and efficiency being key to SiC evaluation, Wolfspeed provides a range of reference designs with comprehensive documentation, including PCB layout guides to avoid parasitic interference, further aiding designers in their development process.