Smart Power Modules Help Industry Accelerate Towards Silicon Carbide (SiC)-Based Electric Vehicles
Currently, new fast-switching silicon carbide (SiC) power transistors are widely available mainly as discrete devices or bare chips. performance, enabling system engineers to make significant advances in size, weight control, and efficiency improvements in motor drive controllers and battery chargers, while driving the price of SiC devices to continue to decline. However, there are some important constraints to the adoption of SiC in high-power applications, including the availability of well-optimized power modules and the learning curve for designing highly reliable gate-level drives. Intelligent Power Modules (IPMs) can effectively address both of these challenges by providing a highly integrated, plug-and-play solution that can accelerate time-to-market and save engineering resources.
This article discusses the benefits of choosing the CISSOID three-phase full-bridge 1200V SiC MOSFET Intelligent Power Module (IPM) system in power converter designs for electric vehicle applications, especially as the system is a scalable family of platforms. The system utilizes low internal friction technology to provide an integrated solution, the IPM; the IPM consists of a gate drive circuit and a three-phase full-bridge water-cooled silicon carbide power module, the cooperation of which has been optimized and coordinated. This article not only describes the electrical and thermal characteristics of IPMs, but also discusses how IPMs can take full advantage of the benefits of SiC devices, and the most critical factors, even gate driver designs and SiC power circuit drives can be implemented safely and reliably.
Figure 1 CXT-PLA3SA12450AA three-phase full-bridge 1200V/450A SiC intelligent power module IPM
Achieve higher power density with low internal friction and enhanced thermal stability
CXT-PLA3SA12450AA is a member of CISSOID’s three-phase full-bridge 1200V SiC intelligent power module (IPM) system, which includes multiple products with rated currents ranging from 300A to 600A. This three-phase full-bridge IPM has low conduction losses (Ron is only 3.25mΩ), low switching losses, and turn-on and turn-off energies of 7.8mJ and 8mJ, respectively, at 600V/300A (see Table 1). Compared to state-of-the-art IGBT power modules, switching losses are reduced by at least two-thirds under the same operating conditions. The CXT-PLA3SA12450AA is water-cooled via a lightweight aluminum silicon carbide (AlSiC) pin-fin baseplate with a junction-to-fluid thermal resistance (Rjl) of 0.15°C/W. The CXT-PLA3SA12450AA is rated for junction temperatures up to 175°C, and the gate gate drive circuits can operate in environments up to 125°C. The IPM is capable of withstanding isolation voltages up to 3600V (withstand voltage test at 50Hz, 1 minute).
Table 1 Main features of CXT-PLA3SA12450AA three-phase 1200V/450A SiC MOSFET intelligent power module
3D models and reliable thermal characteristics enable rapid implementation of power converter designs
A big advantage of the CXT-PLA3SA12450AA is the high integration of the gate driver and power section (with AlSiC pin-fin water-cooled backplane). This feature allows the IPM to be quickly combined with other parts of the electric drive assembly, such as DC capacitors and cooling systems, as shown in Figure 2. CISSOID provides accurate 3D reference designs of individual components, from which the customer’s system designer can use as a starting point to implement the target system design in a fraction of the time.
The IPM takes full advantage of the low turn-on and low switching loss characteristics of SiC power devices, and is coordinated at the system level with the gate-level drive to obtain the best optimization of overall performance, while providing the best performance, it also effectively reduces the The cooling system takes up space and improves the efficiency of the power converter.
Figure 2 Integration of CXT-PLA3SA12450AA with DC capacitor and water cooling
The maximum continuous drain current can be calculated at a Rjl (junction-to-fluid thermal resistance) of 0.15°C/W, a flow rate of 10L/min (50% ethylene glycol, 50% water) and an inlet water temperature of 75°C The relationship between allowable value and case temperature (calculated based on on-resistance at maximum junction temperature and maximum operating junction temperature) is shown in Figure 3.
Figure 3 The relationship between the maximum allowable continuous drain current of CXT-PLA3SA12450AA and the case temperature
The maximum continuous drain current (allowed value) helps to understand and compare the rated current of the power module; Figure of Merit (FoM) reveals the relationship between the phase current average and the switching frequency, as shown in Figure 4. The curve is calculated for a bus voltage of 600V, a case temperature of 90°C, a junction temperature of 175°C, and a duty cycle of 50%. FoM curves are more useful for understanding the suitability of a module. Due to the scalability of the CXT-PLA3SA12450AA, Figure 4 also deduces the safe operating range of the 1200V/600A module (shown in dashed lines).
Figure 4. Phase current (Arms) versus switching frequency of CXT-PLA3SA12450AA
(Test conditions: VDC = 600V, Tc = 90°C, Tj <175°C, D = 50%), and extrapolation for a future 1200V/600A module (CXT-PLA3SA12600AA, under development)
In addition, the gate driver includes a DC link voltage monitoring function, using a more compact transformer module; finally, the safety specification of the CXT-PLA3SA12450AA meets the creepage distance required for pollution degree 2.
Robust SiC gate drivers enable fast switching and low losses
The three-phase full-bridge gate driver design of the CXT-PLA3SA12450AA leverages CISSOID’s experience with single-phase SiC gate drivers, for example, CISSOID is designed for 62mm 1200V/300A and fast switching XM3 1200V/450A SiC power modules, respectively CMT-TIT8243 [1，2]and CMT-TIT0697 [3]Single-phase gate driver (see Figure 5).
Like the CMT-TIT8243, CMT-TIT0697, the CXT-PLA3SA12450AA has a maximum operating ambient temperature of 125°C, and all components have been carefully selected and sized to guarantee operation at this temperature rating.The IPM also leverages CISSOID’s high temperature gate driver chipset[4，5]The power transformer design with low parasitic capacitance (10pF typical) minimizes common mode current in high dv/dt and high temperature environments.
Figure 5 CMT-TIT0697 gate driver board for fast switching XM3 1200V/450A SiC MOSFET power module
The CXT-PLA3SA12450AA gate driver still has headroom to support power module scalability. The module has a total gate charge of 910nC. When the switching frequency is 25KHz, the average gate current is 22.75mA. This is well below the maximum current capability of the onboard isolated DC-DC power supply of 95mA. Therefore, the current capability and gate charging of the power module can be improved without modifying the gate driver board. Using multiple gate resistors in parallel, the actual maximum dv/dt value can reach 10~20 KV/µs. The gate drive circuit is designed to resist dv/dt up to 50KV/µs, thus providing sufficient margin in dv/dt reliability.
The protection function of the gate driver increases the functional safety of the system
The protection features of gate drivers are critical to ensure safe operation of power modules, especially when driving fast-switching SiC power components. The CXT-PLA3SA12450AA gate driver circuit can provide the following protection functions:
Undervoltage Lockout (UVLO): The CXT-PLA3SA12450AA gate driver monitors both the primary and secondary voltages and reports a fault if it falls below the programmed voltage.
Anti-overlap: Avoid turning on the upper and lower arms at the same time to prevent short-circuiting of the half-bridge.
Protection against secondary short circuits: The cycle-by-cycle current limiting function of the isolated DC-DC power supply prevents any short circuits (eg gate-source shorts) in the gate driver.
Glitch filter: Suppresses glitches on the input PWM signal, which are likely to be caused by common mode currents.
Active Miller Clamp (AMC): Creates a negative gate resistor bypass after turn-off to protect the power MOSFET from parasitic turn-on.
Desaturation Detection: On turn-on, checks whether the drain-to-source voltage of the power channel is above the threshold after the blanking time.
Soft Shutdown: In the event of a fault, the power channel can be turned off slowly to minimize overshoot due to high di/dt.
in conclusion
CISSOID’s SiC smart power module architecture provides system designers with an optimized solution that can greatly accelerate their design efforts. The integration of the drive and water cooling modules provides reliable electrical and thermal characteristics from the start, reducing the lengthy learning curve often required to effectively use new technologies. CISSOID’s new and scalable IPM system will provide strong technical support for the explorers of SiC technology in electric vehicle applications.
references
[1] CMT-TIT8243: 1200V High Temperature (125°C) Half-Bridge SiC MOSFET Gate Driver Datasheet. http://www.cissoid.com/files/files/products/titan/CMT-TIT8243.pdf.
[2] P. Delatte. A High Temperature Gate Driver for Half Bridge SiC MOSFET 62mm Power Modules. Bodo’s Power Systems, p54, September 2019.
[3] CMT-TIT0697: 1200V High Temperature (125°C) Half-Bridge SiC MOSFET Gate Driver Datasheet. http://www.cissoid.com/files/files/products/titan/CMT-TIT0697.pdf.
[4] High Temperature Gate Driver Primary Side IC Datasheet: DC-DC Controller & Isolated Signal Transceivers. http://www.cissoid.com/files/files/products/titan/CMT-HADES2P-High-temperature-Isolated-Gate-driver- Primary-side.pdf.
[5] High Temperature Gate Driver -Secondary Side IC Datasheet: Driver & Protection Functions. http://www.cissoid.com/files/files/products/titan/CMT-HADES2S-High-temperature-Gate-Driver-Secondary-side.pdf .
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