"Today, more and more automakers are developed in electric vehicles (EV), but the electric car is too short but is always a problem. Despite the air kinetic design, lighter materials, more efficient power consumption It is not enough to achieve, but this is still enough. Automotive electrical electronic designers also need to use advanced broadband semiconductor (WBG) materials to meet energy efficiency and power density requirements.
These materials are mainly composed of gallium nitride (GaN) and silicon carbide (SiC), and is an improvement in existing semiconductor technologies such as silicon (Si) metal oxide semiconductor field effect transistor (MOSFET) and an insulated gate bipolar transistor (IGBT). . Thus, the semiconductor loss made from these materials is lower, faster switching frequency, higher operating temperature, and is more robust in harsh environments. As the automotive industry turns higher, the charging time is shorter, the total loss is lower, and the WBG material that can be operated at high voltages can be particularly useful.
This article will make a brief overview of WBG technology and its role in automotive EV electronic fields. In addition, the GaN and SiC appropriate solutions launched by Rohm Semiconductor, StMicRoeCtronics, Transphrm, and Infineon Technologies are also introduced, and their applications are guided.
WBG semiconductor advantage
Let's take a look at that the band gap is to excite the energy of the electron from the material to the energy required to the tape, and the band gap of the WBG material is significantly wider than silicon (Figure 1). The band gap of the Si is 1.1 EV, and the band gap of the SiC is 3.3 EV, and Ga is 3.4 EV.
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Figure 1: The band gap between the Si semiconductor conduction band and the valence band is narrower than SiC and GaN, so the latter two will receive a "wideband semiconductor" name. (Source: STMicroelectronics)
Compared to conventional silicon semiconductors, WBG semiconductor devices operate at higher voltages, frequencies and temperatures. More importantly, the switches and conduction losses are lower. The conduction and switching characteristics of the WBG material is about ten times the Si material. These capabilities have contributed to the combination of WBG technology and power electronics technology, especially for EV industry, because SiC and Gan components are smaller, faster, and higher energy efficiency.
However, although the WBG device has an advantage, the designers have to clarify their complexity and high cost of manufacturing and high-volume production. Although the initial cost of WBG components may be more high, their overall declines and usually reduce the total system cost. For example, using SiC devices in EV may additionally increase hundreds of dollars in the pre-cost, but due to the decrease in battery cost and space requirements, the total cost is finally reduced by the simplification of cooling measures (such as using small radiator or convection cooling).
SIC is applied to the main reactor
The traction inverter for controlling the traction motor in EV is an EV key system benefit from an example of WBG components. The core function of the inverter is to convert the DC voltage to a three-phase AC waveform to drive the EV motor, and then convert the AC voltage of the regenerative brake back to the DC voltage to charge the battery. Since the inverter converts the energy stored in the battery pack to an AC to drive the motor, the lower the energy conversion loss, the higher the system energy efficiency. Compared to silicon, the electrical conductivity of the SiC device is larger, the switching frequency is faster, and the power consumption is lower because there is less energy loss in heat. In the end, the SIC inverter energy efficiency is higher, which is reflected in the mileage of EV.
The large current power module typically uses the IGBT type, combined with the Si IGBT with the Si Fast Recovery Diode (FRD) is a common configuration of the automotive inverter module. However, the operating temperature of the SiC device is higher than the existing SI IGBT device, and the switch speed is faster. These features undoubtedly become the best choice for traction inverters because the traction inverter needs to transmit a large amount of energy inflow and out of the battery.
The reasons are as follows: Since IGBT is a switching element, switching speed (on time, shutdown time) is one of the key parameters that affect energy efficiency (loss). For IGBT, the low resistance of high-shift voltage can be achieved to sacrifice the switch performance; there is "dissipation time" during device shutdown, which increases the switching loss. Therefore, the energy efficiency of IGBT is relatively low. If the inverter module replaces the IGBT with MOSFET, a higher energy efficiency can be achieved because the MOSFET has a shorter shutdown time and the operating frequency is higher. However, there is also a problem with Si MOSFET, and its "on" resistance is greater than Si IGBT.
SiC MOSFET fully utilizes the favorable characteristics of SiC, and the chip size is only half of IGBT, and four ideal features with power switch:
high voltage
Low-conducting resistance
Switch speed
Low switch loss (especially shutdown loss)
In addition, the band gap is wider means that the SiC device typically operates from 150 ° C to 175 ° C, and if the package is appropriate, it can reach 200 ° C or higher.
For the SiC Schottky Barrier Diode (SBD), SiC Semiconductor-Metal Number is formed in SiC Semiconductors. However, with silicon FRD, the advantage of SiC SBD does not change significantly in the case where the current and operating temperature range is wider. In addition, the dielectric strike of the SiC component is also ten times that of silicon devices. Therefore, the SiC product of the rated voltage 1200 V is being put into large-scale production, and the cost is declining. In addition, the product of the rated voltage 1700 V is being developed.
The SiC diode has no positive and reverse recovery loss, just a small amount of capacitor charging loss. Studies have shown that SiC SBD's switching loss is reduced by 90% compared to Si fast recovery diodes, and the latter's junction temperature affects recovery current and recovery time. Therefore, the quality factor (FOM) (QC X Vf) of the SiC diode is relatively low compared to the Si diode. FOM low means that the power consumption is low, so electrical performance is better.
There are some shortcomings in silicon carbide materials. One of them is that the thermal coefficient is positive, the higher the temperature, the higher the forward voltage (VF). The larger the current through the diode, the greater the forward voltage. This conduction loss causes thermal shot when the diode is subjected to a large current.
However, combined with SiC MOSFET and SBD enables system designers to improve energy efficiency, reduce the size and cost of the heat sink, and improve the switching frequency to reduce the size of the magnetic component, thereby reducing the final design cost, reduced size and weight. Compared to Si-based devices, the EV inverter using SiC devices can be 5 times, 5 times slight, 50% power consumption is reduced.
For example, the BSM300D12P2E001 semi-bridge SiC power module developed by ROHM Semiconductor, the SiC MOSFET is encapsulated, minimizes switching loss caused by the previous IGBT tail current and FRD recovery loss (Figure 2).
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Figure 2: The total SiC power module loss of the integrated SiC MOSFET and SBD is lower than the IGBT module, even if the high speed switch is operated. (Source: Rohm Semiconductor)
Compared to IGBT, the SiHM Semiconductor's SiC-based MOCTOR has significantly reduced 73%. The company's MOSFET series was as high as 1700 V, and the conduction resistance range was 45 mΩ to 1150 mΩ, which was encapsulated by TO-247N, TO-3PFM, TO-268-L and TO-220.
In addition, the SiC Schottky barrier diode launched by RoHM passed the AEC-Q101 automotive standard identification. The device recovery time is short, the switching speed is fast, the temperature is small, the forward voltage is low, the pressure is 650 V, and the current range is 6 to 20 A.
The role of SiC device played in EV applications
As the first main inverter integrated all SiC power module, Tesla has adopted this technology in Tesla 3 cars. The S-type and X-type, such as Tesla models, all of which are packaged in TO-247 packaged IGBT. Tesra works with StMicroelectronics to assemble SiC power modules on the radiator of the inverter. 1 Like the SCT10N120 of StMicroelectronics, this MOSFET rated voltage is 650 V, which is heat dissipated with a copper substrate.
The EV charging device is ready for installation in the factory, called "Car Charger" (OBC). The AC power supply can be charged using an AC power source through the socket of the home or personal / public charging station, EV or plug-in hybrid EV (PHEV). OBC uses the AC / DC converter to convert 50/60 Hz AC voltages (100 to 240 V) to DC voltages, charge the high pressure traction battery (usually about 400 V DC). In addition, the DC level can be adjusted according to the battery requirements, providing current isolation and AC / DC power factor correction (PFC) (Fig. 3).
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Figure 3: For example, in a typical EV OBC application, the SiC diode can be used as a boost diode for the PFC stage, or in parallel with the N-channel IGBT constituting the TC PFC. (Source: Infineon Technologies)
Ga is popular with high energy efficiency
OBC's design requires to maximize energy efficiency and reliability to ensure fast charging, while meeting EV manufacturers on space and weight limit requirements. OBC design using GaN technology can simplify EV cooling systems, shorten the charging time, reduce power consumption. In terms of car market share, commercial GAN power devices are slightly less abolished by SiC devices, but now quickly rush to the beach with its excellent performance. Like the SIC device, the switch loss of the GaN device is lower, the switching speed is faster, the power density is higher, and the system size and weight can be reduced.
For example, Transphrm's TP65H035WSQA has passed the AEC-Q101 automotive standard identification. This GaN FET is at the test of the temperature up to 175 ° C (Figure 4). The device adopts a standard TO-247 package, and there is 35 mΩ. Like the Group II TPH3205WSBQA of 49 MΩ in the previous generation, the device is suitable for an AC / DC OBC, DC / DC converter, and DC / AC inverter system that plug-in hybrid electric vehicle and battery EV. / DC Totem column bridge PFC design.
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Figure 4: TPH3205WSBQA 650 V, 49 MΩ GaN FET is passed through automotive-level standard identification and the AEC-Q101 pressure test of automotive-grade semiconductor devices. (Source: Transphrm)
Although the maximum rated DV / DT value of Si MOSFET is typically 50 V / NS, the switching DV / DT of the TP65H035WS GaN FET is 100 V / NS or higher to minimize switching loss. In this case, even the layout will also seriously affect system performance. When the layout is recommended, the gate drive loop is recommended to minimize the length of the line length between the switch nodes, and the power bus is grounded by the shortest return trace. The cross-sectional area of the power ground plane is large, thereby achieving uniform grounding potential of the entire circuit. The layout must be separated from the power supply and IC (small signal), both only in the source of the FET, to avoid any possible ground loops.
Infineon's AIDW20S65C5XKSA1 is one of the fifth generation of CoolSic, the company, which is also developed for the OBC application of hybrid and electric vehicles. It is the company's IGBT and COOLMOS product line supplements, which can meet 650 V The requirements for automobile applications.
Thanks to the new passivation layer concept, this product has become one of the most durable automotive devices on the market, with moisture resistance and corrosion resistance. This device is based on 110 μm thin wafer technology, so the FOM performance in the similar products is highlighted, which is reflected in lower power consumption, thereby achieving more excellent electrical performance.
Compared to traditional Si FRD, Infineon's Coolsic Automotive Schottky diode can increase the OBC energy efficiency under all load conditions.
Use SiC and GaN devices
In addition to the above-mentioned care layout, another potential problem with the SiC components is that the driver requirements are very different from the IGBT device. Although most of the transistors typically use symmetric power rails (such as ± 5 V), the SiC device requires a smaller negative voltage to ensure complete shutdown, so asymmetric power rails (such as -1 V to -20 v) .
Further, although SiC has excellent heat dissipation characteristics, the thermal conductivity is also extracted with silicon, but the SiC component is often used as a package of Si device design, such as chip bonding and lead bonding. Although this packaging method is good with SiC, it is only suitable for low frequency circuits (tens of kilozo). Once applied to high frequency circuits, parasitic capacitors and inductors will increase accordingly, thus hindering SiC devices to give full potential.
Similarly, it is necessary to make full use of the advantage of the GaN device, the package must have extremely low parasitic inductance and excellent thermal performance. A new package method such as an embedded chip package (similar to multi-layer printed circuit board), which achieves the desired performance at low cost, and also eliminates the lead bonding to avoid the reliability of devices itself.
Gate driver This key component is mainly used as a controller and power.Interface between pieces. For electronic designers adopting new devices, the gate drive design is always a problem, so it is especially important to understand the driving method of SiC and GaN power devices. The specific requirements are:
High energy supply, high energy efficiency is achieved by low-conducting loss
High drive strength, low switching loss
Quick short circuit protection
Propagation delays and changes in high energy efficiency and rapid system control
DV / DT antisense
Some early GaN devices require special drives to prevent gate overvoltage. At present, a new generation of E-HEMT with large VG tolerance is introduced, and only the gate voltage can be driven by many standard MOSFET drivers. GaN FET is a lateral device, so the best drive voltage required is relatively low. All in all, the gate drive requirements of the GaN device are similar to Si MOSFET and IGBT. Specific requirements include:
The gate charge is low - the driving loss is low, the rise and fall time is short.
Low gate voltage
Negative voltage to improve the robustness of gate drive
Use the gate resistance to control the slew rate
Its advantage is that many SiC and GAN solution vendors add other electronic components in the package, so they can directly replace the current design.
Summarize
In order to meet the energy efficiency and power density requirements of EV systems such as inverters and in-vehicle chargers, automotive power electronic designers can now use more advanced WBG semiconductors such as SiC and GaN. Compared to traditional silicon devices, the WBG semiconductor has a lower loss, faster switching frequencies, higher operating temperatures, and more robust in harsh environments.
GaN and SiC work at higher temperatures, and the service life is expected to be no different from Si devices; or working at equivalent temperatures, longer service life. This provides design engineers with different design, depending on the application requirements.
In addition, using the WBG material allows the designer to select the designed target from a variety of strategies: using the same switching frequency, improve the output power; use the same switching frequency, reduce the heat dissipation requirements and total cost of the system; or increase the switching frequency , But maintain the same switching power consumption.
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