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  • How Three-Phase Integrated GaN Technology Maximizes Motor-Drive Performance

    • SLYY235 June   2024 DRV7308

       

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  • How Three-Phase Integrated GaN Technology Maximizes Motor-Drive Performance
  1.   1
  2.   Overview
  3.   At a glance
  4.   How GaN increases inverter efficiency
  5.   Motor performance improvement with GaN power switches
  6.   Design considerations when using GaN in motor drives
  7.   Impact on system efficiency
  8.   Impact on audible noise
  9.   Conducted and radiated emission considerations
  10.   Impact on solution size
  11.   Protected and reliable system designs
  12.   Conclusion
  13.   Additional resources
  14. IMPORTANT NOTICE
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How Three-Phase Integrated GaN Technology Maximizes Motor-Drive Performance

Given the energy consumption of consumer appliances; building heating, ventilation and air-conditioning (HVAC) systems; and industrial drives, efforts are underway to establish system efficiency ratings through programs such as the seasonal energy efficiency ratio (SEER), minimum energy performance standards (MEPS), Energy Star and Top Runner.

Variable frequency drives (VFDs) offer the best system efficiency in heating and cooling systems, especially if they have an accurate and very wide range of speed control. VFDs use an inverter to control motor speeds, along with high-frequency pulse-width modulation (PWM) switching to obtain truly variable speed control.

Although these inverters are currently realized using insulated-gate bipolar transistors (IGBTs) and metal-oxide semiconductor field-effect transistors (MOSFETs) as the power switches, the switching frequency and power delivery are limited given high overall losses. With advancements in wide band-gap technology, however, gallium nitride (GaN)-based power switches in motor drives can help increase power density, power delivery and efficiency.

Manu Balakrishnan

Systems engineer

Motor drivers

At a glance

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How GaN increases inverter efficiency

The conduction losses attributable to GaN FETs are proportional to the on-state resistance of the GaN, similar to a MOSFET. For an IGBT, however, conduction losses depend on the knee voltage and dynamic on-state resistance, which are typically higher than GaN FETs or MOSFETs.

As for switching losses, GaN FETs offer much lower losses compared to MOSFETs and IGBTs because of these reasons:

  • GaN offers zero reverse recovery. With zero reverse recovery, it is possible to switch a GaN FET at a very high current slew rate (di/dt) and voltage slew rate (dv/dt). In MOSFETs, the body diode suffers from high zero reverse recovery, limiting the switching di/dt and dv/dt and causing additional losses and phase-node voltage ringing. With an IGBT, even the addition of an optimized antiparallel diode can still cause challenges related to reverse recovery.
  • When switching off, IGBTs suffer from minority carrier recombination current, commonly known as tail current, which increases turnoff losses. GaN doesn’t have any tail current.
  • GaN offers lower capacitance compared to IGBTs and MOSFETs, resulting in lower capacitive switching losses.
  • Controlled and faster di/dt and controlled dv/dt help optimize voltage-current overlap losses during switching.

Figure 1 shows a theoretical inverter efficiency comparison between GaN-, IGBT- and MOSFET-based solutions with a 20kHz switching frequency, the phase-node voltage slew rate for the GaN-based inverter limited to 5V/ns, and an ambient temperature of 55°C. You can see that the GaN solution helps reduce power losses by at least half.

 Efficiency comparison of GaN,
                    MOSFET and IGBT solutions. Figure 1 Efficiency comparison of GaN, MOSFET and IGBT solutions.

Figure 2 compares the efficiency of the Texas Instruments (TI) DRV7308 three-phase GaN intelligent power module (IPM) to a 5A peak-current-rated IGBT IPM with a 300VDC supply at a 20kHz switching frequency with a fan motor that has 2m of cable at a 25°C ambient temperature, delivering 0.85A of root-mean-square winding current and 250W of inverter output power. The slew rate of the GaN IPM is configured for 5V/ns.

 Efficiency comparison of the
                    DRV7308 and an IGBT IPM in a 250W application. Figure 2 Efficiency comparison of the DRV7308 and an IGBT IPM in a 250W application.

 

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