I hear that a GaN - based inverter can get more torque than MOSFET inverter. What is the logical reason why GaN inverter can get more torque?
In simple words, this is what happens:
1: The dead time introduces discontinuities in the applied voltage waveforms to the motor. The inverter is a VSI (Voltage Source Inverter), but during the dead time, it is not the inverter to decide the voltage, but it is the motor load, depending on the current direction (positive to the load or negative back to the inverter).
2: The discontinuities in the voltage are two per phase and reflect in the motor phase current. Each motor phase current has 6 discontinuities.
3:The discontinuities in the currents are responsible of the 5th and the 7th harmonic in the current.
4: The 5th and the 7th harmonic in the current convolute in the motor to form a 6th harmonic in the torque. Note: you do not want to have any harmonic in the torque; the torque must be DC. Any harmonic generates vibrations and, hence, wasted energy.
5: By reducing the dead time the 6th harmonic in the torque disappears and its energy goes back to the DC part of the torque, which is responsible of the motion.
Please review chapter 6 in EPC’s latest text book, “GaN Power Devices and Applications” (https://epc-co.com/epc/products/publications/gan-power-devices-and-applications) to learn more.