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Smart power modules accelerate towards SiC-based electric vehicles

Currently, new fast-switching silicon carbide (SiC) power transistors are widely supplied in the form of discrete devices or bare chips. A series of characteristics of SiC devices, such as high blocking voltage, low on-resistance, high switching speed, and high temperature resistance Performance enables system engineers to make significant progress in the size, weight control and efficiency improvement of motor drive controllers and battery chargers, while driving the continued decline in the price of SiC devices.

Currently, new fast-switching silicon carbide (SiC) power transistors are widely supplied in the form of discrete devices or bare chips. A series of characteristics of SiC devices, such as high blocking voltage, low on-resistance, high switching speed, and high temperature resistance Performance enables system engineers to make significant progress in the size, weight control and efficiency improvement of motor drive controllers and battery chargers, while driving the continued decline in the price of SiC devices.

However, the use of SiC in high-power applications still has some important constraints, including the availability of well-optimized power modules, and the learning curve for designing highly reliable gate-level drivers. Intelligent Power Modules (IPM) can speed up product launches and save engineering resources by providing highly integrated, plug-and-play solutions, thereby effectively addressing the above two challenges.

This article discusses the benefits of choosing a CISSOID three-phase full-bridge 1200V SiC MOSFET intelligent power module (IPM) system in the design of power converters for electric vehicle applications, especially when the system is a scalable platform series. The system utilizes low internal consumption technology to provide an integrated solution, namely IPM; IPM is composed of a gate drive circuit and a three-phase full-bridge water-cooled silicon carbide power module, the cooperation of the two has been optimized and coordinated. And how IPM can make full use of the advantages of SiC devices, and the most critical factor in it, even if the gate driver design and SiC power circuit drive are implemented safely and reliably.

Achieve higher power density with low internal friction and enhanced thermal stability

CXT-PLA3SA12450AA is a member of the CISSOID three-phase full bridge 1200V SiC intelligent power module (IPM) system, which includes multiple products with a rated current of 300A to 600A. This three-phase full-bridge IPM has low conduction loss (Ron is only 3.25mΩ), low switching loss, and the turn-on and turn-off energies are 7.8mJ and 8mJ at 600V/300A (see Table 1). Compared with the most advanced IGBT power module, the switching loss under the same working condition is reduced by at least two-thirds. CXT-PLA3SA12450AA is water-cooled by a lightweight aluminum silicon carbide (AlSiC) pin-fin base plate, and its junction-to-fluid thermal resistance (Rjl) is 0.15°C/W. The rated junction temperature of CXT-PLA3SA12450AA is as high as 175°C, and the gate drive circuit can operate in an environment up to 125°C. The IPM can withstand isolation voltages up to 3600V (50Hz, 1 minute withstand voltage test).

Smart power modules accelerate towards SiC-based electric vehicles
Table 1: Main features of CXT-PLA3SA12450AA three-phase 1200V/450A SiC MOSFET smart power module

Three-dimensional models and reliable heat dissipation characteristics make it possible to quickly implement power converter designs

One of the major advantages of CXT-PLA3SA12450AA is that the gate-level drive and power section (containing AlSiC pin-fin water-cooled base plate) are highly integrated. 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 design of each component, and the customer’s system designer can use this as a starting point to realize the target system design in a very short time.

IPM makes full use of the low conduction and low switching loss characteristics of SiC power devices, and performs system-level coordination with gate-level drivers to obtain the best optimization of overall performance. While providing the best performance, it also effectively reduces The heat dissipation system takes up space and improves the efficiency of the power converter.

Under the conditions of Rjl (junction-to-fluid thermal resistance) of 0.15°C/W, flow rate of 10L/min (50% ethylene glycol, 50% water), and inlet water temperature of 75°C, the maximum continuous drain current can be calculated The relationship between the allowable value and the case temperature (calculated based on the on-resistance at the highest junction temperature and the maximum operating junction temperature).

The maximum continuous drain current (allowable value) helps to understand and compare the rated current of the power module, and the Figure of Merit (FoM) reveals the relationship between the average phase current and the switching frequency.

In addition, the gate driver also includes the DC side voltage monitoring function, and uses a more compact transformer module; finally, the safety specification of CXT-PLA3SA12450AA meets the creepage distance required by pollution degree 2.

Robust SiC gate driver makes it possible to achieve fast switching and low loss

CXT-PLA3SA12450AA’s three-phase full-bridge gate driver design makes full use of CISSOID’s accumulated experience in single-phase SiC gate drivers. For example, CISSOID is designed for 62mm 1200V/300A and fast switching XM3 1200V/450A SiC power modules. CMT-TIT8243 and CMT-TIT0697 [3]Single-phase gate driver.

Like CMT-TIT8243 and CMT-TIT0697, the maximum working environment temperature of CXT-PLA3SA12450AA is 125°C. All components have been carefully selected and dimensionally confirmed to ensure operation at this rated temperature.The IPM also relies on CISSOID’s high-temperature gate driver chipset[4,5]And the design of the power transformer with low parasitic capacitance (typical value is 10pF), so that the common mode current under high dv/dt and high temperature environment is reduced to the lowest point.

The CXT-PLA3SA12450AA gate driver still has margin to support the scalability of the power module. The total gate charge of this module is 910nC. When the switching frequency is 25KHz, the average gate current is 22.75mA. This is far lower than the 95mA maximum current capability of the on-board isolated DC-DC power supply. Therefore, without modifying the gate driver board, the current capability and gate charging of the power module can be improved. Using multiple parallel gate resistors, the actual maximum dv/dt value can reach 10-20 KV/µs. The gate drive circuit is designed to withstand dv/dt up to 50KV/µs, thus providing sufficient margin in terms of dv/dt reliability.

The protection function of the gate driver improves the functional safety of the system

The protection function of the gate driver is essential to ensure the safe operation of the power module, especially when driving fast-switching SiC power components. The CXT-PLA3SA12450AA gate drive circuit can provide the following protection functions:

Undervoltage lockout (UVLO): The CXT-PLA3SA12450AA gate driver will monitor the primary and secondary voltages at the same time, and report a fault when the voltage is lower than the programmed voltage.

Anti-overlap: Avoid turning on the upper arm and the lower arm at the same time to prevent the half bridge from short-circuiting.

Prevention of secondary short circuit: The cycle-by-cycle current limit function of the isolated DC-DC power supply can prevent any short circuit in the gate driver (such as gate-source short circuit).

Glitch filter: suppress the glitches of the input PWM signal, these glitches are likely to be caused by common-mode currents.

Active Miller Clamp (AMC): A negative gate resistance bypass is established after the turn-off to protect the power MOSFET from parasitic turn-on.

Desaturation detection: When turned on, check whether the drain-source voltage of the power channel is higher than the threshold after the blanking time.

Soft shutdown: In the event of a fault, the power channel can be closed slowly to minimize the overshoot caused by high di/dt.

in conclusion

CISSOID’s SiC intelligent power module system provides system designers with an optimized solution that can greatly accelerate their design work. The integration of drive and water cooling modules provides reliable electrical and thermal characteristics from the start, thus shortening the long learning curve that is often required to effectively use new technologies. CISSOID’s new and scalable IPM system will provide strong technical support for explorers of SiC technology in electric vehicle applications.

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