The electrical characteristics of GaNHEMTs have led engineers to choose them for designing more compact motors that can withstand high voltage and high frequency. In summary, these devices offer the following advantages:
The higher breakdown voltage allows for the use of higher input voltages (greater than 1000V).
The higher current density allows GaN devices to be designed to be more compact without reducing power.
Fast switching capability, supporting high-frequency (200kHz and above) motor operation.
High-frequency operation limits output current fluctuations and reduces filter component size.
Reduce switching power consumption, limit power loss, and improve efficiency.
High temperature resistance, allowing for the use of smaller heat sinks
High integration allows for the integration of GaNHEMT (unlike silicon materials) on the chip.
With less BOM material and simplified design, GaNHEMT can handle various currents in motor drive solutions without the need for the reverse diode required by IGBT.
These advantages allow engineers to design highly compact electric motors that have the same output power as conventional motors, but are only half the size and consume far less power. The only drawback is that GaNHEMT design requires a higher level of expertise in circuit development and testing.
Figure 1: Integrated solutions maximize the benefits of GaNHEMT devices.
Until recently, a key advantage of MOSFET and IGBT devices over GaNHEMT was their widespread commercial availability. However, engineers can now easily utilize GaNHEMT technology. Even better, silicon suppliers can now provide integrated solutions based on GaNHEMT, greatly simplifying the design of inverters for high-voltage, high-frequency AC motors.
Previously, GaNHEMTs were packaged as discrete devices with separate drivers because the transistors and driver components were based on different process technologies and were often supplied by different manufacturers. This approach had the disadvantage of introducing parasitic resistance and inductance in the connecting wires, increasing switching losses. Integrating the GaNHEMT and driver components within the same package eliminates the common-source inductance, which is especially important in fast-switching circuits, as unwanted inductance can cause humming, potentially leading to malfunctions in current protection circuits. A second key advantage of the integrated package is the ability to incorporate a thermal sensor within the driver component, ensuring the GaNHEMT shuts down before it is damaged by overheating.
Texas Instruments (TI) has introduced the LMG3410R070 (Figure 2), a power stage device based on GaNHEMT, featuring high-speed drive and protection mechanisms. This product is the industry's first 600V GaN integrated power stage device, housed in an 8mm x 8mm QFN multi-chip module (MCM) for easy design. With an extremely low on-resistance of only 70mΩ, this gate driver incorporates a buck/boost converter, enabling the generation of a negative voltage to turn off the GaNHEMT.
Figure 2: TI's LMG3410R070 power stage device integrates a GaNHEMT and a driver (Source: Texas Instruments)
A key advantage of the LMG3410R070 GaN power stage device is its control over the slew rate during hard switching. This control is crucial for suppressing PCB parasitic resistance and EMI. This TI product uses programmable current to drive the GaN gate, allowing the slew rate to be set between 30 and 100 V/ns.
Two LMG3410R070GaN power stage devices can be combined to form a half-bridge structure, enabling fast hard switching operations, reducing switching losses, and eliminating parasitic inductance and reverse charge, all of which are required by designers to drive high-power motors at different stages (Figure 3).
Figure 3: The schematic diagram of this application circuit shows a half-bridge structure composed of two TIGaN power stage devices, which can be used to drive one phase of a three-phase motor (Source: Texas Instruments).
Build a high-performance motor driver
A complete AC motor drive solution (Figure 4) consists of three parts: a rectifier (AC/DC converter), a DC circuit, and an inverter (DC/AC converter).
Figure 4: The schematic diagram of this motor drive solution illustrates the placement of the capacitors in the DC circuit section. (Source: KEMET)
Rectifiers typically use diode or transistor topologies to convert standard 50 or 60 Hz AC power into DC power. The DC power output from the rectifier is filtered and stored in the DC circuit section, and then input to the inverter. The inverter converts the DC power into three sinusoidal PWM signals to drive a three-phase AC motor.
The DC circuit section serves the following functions:
Filtering the voltage and current output of the rectifier
Eliminate glitches in the rectifier output voltage; otherwise, they may damage the inverter's transistors.
Improve circuit efficiency
Eliminate induced currents that may damage transistors
Ensure that power can be smoothly transmitted to the load.
The DC section typically uses a single capacitor and is designed between the rectifier and inverter stages of the motor drive circuit. Although the DC section is easy to implement, its importance to the overall performance and efficiency of the motor makes the selection of components crucial.
Designing the DC section is challenging, involving high-speed voltage conversion (dV/dt) and high voltage peaks. Therefore, it is crucial for designers to select components that can withstand this pressure. KEMET's KC-LINK capacitors, which use ceramic (calcium zirconate, CaO3Zr) material and nickel electrodes, are an excellent choice. They are specifically designed for high-voltage, high-frequency circuits.
Key features of KC-LINK devices include very low equivalent series resistance (ESR) and equivalent series inductance (ESL), which helps improve system efficiency, especially in high-voltage applications. In addition, the capacitors can operate at high frequencies and high temperatures, which is essential for next-generation motors. The capacitors must be able to withstand frequencies of up to 10 MHz and temperatures ranging from -55 to 150°C. Another feature of the device is that the capacitors do not drift with voltage changes, which is certified to the AEC-Q200 standard.
Summarize
The commercial availability of WBG semiconductor devices, such as GaNHEMTs for motor inverters and high-performance capacitors for DC sections, is continuously meeting designers' reliability requirements for high-power motor drives. These key components enable designers to improve existing products, making motors more compact, lightweight, and cheaper, while expanding the application range of motors to a wider range of new application areas. In addition, the next generation of high-power motors will significantly reduce energy demand and contribute to a greener planet.
Key points
High-frequency, high-voltage motors will increase power and improve efficiency.
In motor applications, the rapid switching of high-frequency drive inverters would result in unacceptable losses if traditional MOSFETs and IGBTs were used.
WBG semiconductor transistors, such as GaN, can overcome these problems.
Integrated GaNHEMT and driver solutions can now be applied to motor systems.
High-performance capacitors capable of withstanding high voltage conditions can also be used in the DC section of high-voltage, high-frequency motor drive circuits.
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