3-Phase, 1.25kW, 200Vac GaN Inverter Reference Design for Integrated Drives

September 17, 2019 by Paul Shepard

The TIDA-00915 reference design from Texas Instruments is a three-phase inverter with a continuous power rating of 1.25kW at 50°C ambient and 550W at 85°C ambient for driving 200Vac servo motors. It features 600V LMG3411R150 gallium nitride power modules with an integrated FET and gate driver mounted on a 1.95-mm Insulated Metal Substrate (IMS) board for efficient heat dissipation.

This reference design can support the development of integrated motor drive solutions, servo drives, CNC machines, robotics, and similar industrial motion control systems.

Isolation and control circuits are mounted on separate FR-4 boards - the dimensions of the design are 80mm × 46mm × 37mm, including heatsink, control, isolation, and power stage. This small form factor, coupled with the ability to be natural convection fanless cooled, allows for easy integration of the drive with the motor, reducing the required cabinet space by up to 50% and cable lengths by up to 90 meters in 6-axis motor applications including robotics, CNC machines, and so forth.

Summary of Features

  • 600V, 6A LMG3411R150 GaN enables a power density of 150W/in3 in 50°C ambient conditions up to 1.25kW and in 85°C ambient conditions up to 550W
  • Ultra-small form factor and natural convection fanless cooling allows easy integration of the drive with the motor-saving floor space and cabling costs
  • Very fast switching transition (<5ns) with minimal switch node voltage ringing reduces EMI
  • High-efficiency power stage (peak efficiency >99% at 32kHz pwm) reduces heat-sink size
  • Protection against gate undervoltage, device overcurrent, and overtemperature

TIDA-00915 Three-phase, 1.25-kW, 200-VAC small form factor GaN inverter reference design for integrated drives block diagram. (click on image to enlarge)

System Description

The challenges posed by Industry 4.0 demand miniaturization of manufacturing equipment to save floor space and reduce the time required to install and commission equipment. Motors and drives are at the heart of manufacturing and occupy significant space in a manufacturing environment.

Due to the demands of increased automation at higher efficiency and smaller footprint, there is an increasing need for motor-integrated drives. There is a two-fold benefit to integrating a drive with the motor:

  1. It saves floor space since the drive and motor are housed as one unit
  2. It eliminates the need for long cables connecting the motor and drive

Cabling can be an involved an expensive and complicated process, especially in multi-axis systems in advanced manufacturing. Additionally, troubleshooting cable faults are cumbersome and leads to increased downtime and loss in productivity. Integrating drive with the motor helps eliminate the cabling problem and also saves floor space, providing an immense benefit.

The major challenge in integrating the drive with the motor is the thermal design - the drive components are exposed to higher ambient temperatures with limited cooling. The drive should be able to deliver the rated power at higher ambient temperatures with limited cooling. This puts a stringent limit on the losses in the drive inverter; and hence, requires a high-efficiency drive.

Conventional IGBT-based inverter drives cannot be easily integrated with the motor due to the high losses in the IGBTs because of the reverse recovery in the diode and slower slew rates. These switching losses necessitate a larger heatsink or forced air or liquid cooling, both of which eliminate the possibility of integration with the motor. The solution to this problem, as illustrated in this reference design, is to use GaN FETs, which can operate in more challenging conditions than an IGBT with significantly lower switching losses.

GaN FETs can switch much faster than silicon IGBTs, which allows the potential to achieve lower switching losses. However, at high slew rates, certain package types can limit GaN FET switching performance. Integrating the GaN FET and driver in the same package reduces parasitic inductances and optimizes switching performance. The faster switching is achieved with little or no turn-on or turn-off ringing, which reduces the electromagnetic interferences.

The low-power dissipation benefits servo and integrated drives. In servo drives, the low-power dissipation results in a small form factor. In integrated drives, the drive electronics is enclosed inside the motor hub, and the inverter uses the motor frame as the heat sink. Here, the inverter has to operate at high ambient temperatures with natural convection fanless cooling. The low-power dissipation allows the embedded drive inverter to deliver more power for the same operating temperature.

The TIDA-00915 reference design is a 1.25kW, three-phase inverter for driving 200Vac motors. It features a 600V LMG3411R150 GaN power module with an integrated FET, gate driver and protection circuitry. The TIDA-00915 design provides the required isolation between the microcontroller and power stage. This reference design also generates an active low signal to indicate a GaN fault. The TIDA-00915 supports an interface to a C2000™ F280049C control card through an interface board.