Wide bandgap semiconductors are reshaping the transportation world
The main advantages of GaN power devices , compared to Si and SiC counterparts, are the following: ■ GaN devices can operate in the third quadrant without reverse recovery charge even though they do not have an intrinsic body diode. As a result, there is no need for an anti-parallel diode ■ Low gate charge QG and on- resistance RDS(ON), which translate into lower drive losses and faster switching rates ■ Zero reverse recovery, resulting in lower switching losses and less EMI noise ■ High dv/dt: GaN can switch at very high frequencies and has 4x faster turn-on and 2x faster turn-off than SiC MOSFETs with similar RDS(ON)
Figure 2: Main components of a H/EV. (Source: ROHM Semiconductor)
Figure 1: Potential applications of Si, SiC, and GaN devices. (Source: Infineon )
Rail transportation Electric trains draw power from the grid via a catenary line or a third rail, converting it into a form suitable for the motors and the auxiliary systems. If the train operates on an AC line, a transformer and rectifier must step down and condition the voltage to DC. The DC voltage is then split and delivered through inverters to address the needs of the auxiliary and traction systems. The traction inverter transforms DC into AC for powering the motors and reconditions the electricity produced by regenerative braking. Therefore, this converter is designed to run a bidirectional flow of energy. Instead, the auxiliary
Onboard Charger
Inverter and HV Converter
Type
LV Converter
Hybrid and electric vehicles
on the topology of the inverter. SiC helps reduce losses, size, and weight, allowing solutions with small form factors. The onboard charger (OBC) connects to the grid, converting AC into DC voltage to charge the battery. OBC output power is usually between 3.3 kW and 22 kW and relies on high voltage (600 V and above) power devices. While both SiC and GaN are suitable for this application, GaN’s features, like high switching frequency, low conduction losses, and reduced weight and size, make it the ideal solution for implementing OBCs.
Power
3.3 kV >
12 kW to 400 kW 1 kW to 10 kW
H/EVs use several power electronics systems to transform grid or engine energy into a form suitable for powering motor and auxiliary devices. Most H/EVs also use regenerative braking, in which the wheels rotate the generator to charge the battery. The traction inverter is a crucial component in these vehicles, converting the DC high voltage from the batteries into AC for powering the three-phase motor (see Figure 2). Due to the high power involved, SiC devices are preferred in this application, with a rating of 650 V or 1.2 kV, depending
Input V
120 V to 240 V 200 V to 400 V 200 V to 400 V
Output V
200 V to 400 V 100 V to 650 V 12 V to 48 V
Si efficiency
85% to 93% 83% to 95%
85% to 90%
Applications of WBG devices
SiC efficiency
95% to 96%
96% to 97%
96% to 99%
GaN efficiency
94% to 98%
Not Available
95% to 99%
As highlighted in Figure 1, there are applications where SiC and GaN offer the best performance and others where their characteristics overlap those of silicon. Often, GaN devices are the best choice for high-frequency applications, whereas SiC devices have high potential at high voltages.
Discrete 600 V to 900 V
Discrete/Module 600 V to 1200 V
Discrete 600 V to 900 V
Power device
Table 2: Applications of WBG in H/EVs and comparison of performance with Si.
Another application of WBG in H/ EVs is the low-voltage (LV) DC-DC converter, responsible for stepping down the battery voltage (200 V in HEVs, above 400 V in EVs) to the 12 V/48 V DC voltage required for
powering the auxiliary systems. Featuring a typical power of less than 1 kW, the LV converter can achieve higher frequencies using GaN and SiC devices.
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