电力电子翻译

Silicon Carbide MOSFETs Challenge IGBTs
SiC technology has undergone significant improvements that now allow fabrication of MOSFETs capable of outperforming their Si IGBT cousins, particularly at high power and high temperatures
In light of recent silicon carbide (SiC) technology advances, commercial production of 1200-V 4H-SiC[1] power MOSFETs is now feasible. There have been improvements in 4H-SiC substrate quality and epitaxy, optimized device designs and fabrication processes, plus increased channel mobility with nitridation annealing.[2] SiC is a better power semiconductor than Si, because of a 10-times higher electric-field breakdown capability, higher thermal conductivity and higher temperature operation capability due to a wide electronic bandgap.
SiC excels over Si as a semiconductor material in 600-V and higher-rated breakdown voltage devices. SiC Schottky diodes at 600-V and 1200-V ratings are commercially available today and are already accepted as the best solution for efficiency improvement in boost converter topologies. In addition, these diodes find use in solar inverters, because they have lower switching losses than the Si PIN freewheeling diodes now used in that application.
At 600-V and 1200-V ratings, IGBTs have been the switch of choice for power conversion. Previously, Si MOSFETs were handicapped in those applications by their high on-resistance (R DSON). At high breakdown voltages, R DSON increases approximately with the square of the drain-source breakdown voltage
V DSMAX.[3] The R DSON of a MOSFET consists of the sum of the channel resistance, the inherent JFET resistance and the drift resistance (Fig. 1). The drift resistance (R DRIFT) is the dominant portion of the overall resistance, where d equals
drift-layer thickness, q equals electron charge, ìn equals channel mobility and
N D equals doping factor.
The new generation of SiC MOSFETs cuts drift-layer thickness by nearly a factor of 10 while simultaneously enabling the doping factor to increase by the same order of magnitude. The overall effect results in a reduction of the drift resistance to 1/100th of its Si MOSFET equivalent.
The improved SiC MOSFET discussed here is an engineering sample of a 1200-V, 20-A device with a 100-mV R DSON at a 15-V gate-source voltage. Besides its inherent reduction in on-resistance, SiC also offers a substantially reduced
on-resistance variation over its operating temperature. From 25°C to 150°C, SiC
variations are in the range of 20%, compared with 200% to 300% for Si. The SiC MOSFET die is capable of operation at junction temperatures greater than 200°C, but the engineering sample is limited in temperature to 150°C by its TO-247
plastic package.
Compared with a Si IGBT, a SiC MOSFET has a substantial advantage in
conduction losses, particularly at lower power outputs. By virtue of its unipolar nature, it has no tail currents at turn-off, thereby leading to greatly reduced
turn-off losses. Table 1 shows the switching loss difference when compared with a standard off-the-shelf 1200-V IGBT.
The switching losses of a SiC MOSFET are less than half those of a Si IGBT (1.14 mJ versus 2.6 mJ, respectively). Combining this switching-loss reduction with the lower overall conduction losses, it is clear that the SiC switch is a much more
efficient device for high-power-conversion systems.
Three-Phase Solar Inverter
To demonstrate its application as a solar inverter, a 7-kW, 16.6-kHz three-phase grid-connected system was implemented. This B6 topology, developed by the Fraunhofer Institute ISE, uses a split-link dc capacitor with a connection of the neutral conductor to the center point of both capacitors. The unit connects to a 400-V grid, using 1200-V IGBTs as the standard power-conversion devices. These IGBTs were replaced by 1200-V SiC MOSFETs, and the significant performance difference is clearly visible in Fig. 2. Table 2 shows the maximum efficiency and European-efficiency improvements that were achieved.
As seen by the Fig. 2 curves, the SiC devices offer a performance advantage over their Si IGBT counterparts. Maximum efficiency increased by 1.92%, and the
overall Euro-efficiency rating improved by 2.36%. This equates to a 50%
reduction in overall losses in the system.
Another performance-parameter improvement of note was the system's reduction in heatsink temperature at full-rated power output. At a 25°C ambient, the final steady-state heatsink temperature with the IGBTs was 93°C versus 50°C with the SiC MOSFETs.[3]
There are several different ways of looking at the system benefits obtainable by using a full SiC-based solution in a photovoltaic (PV) power converter:
Cost of inductive components
The volume of an inductive component depends most significantly on the system switching frequency. A good approximation is a reduction close to the reciprocal of the times factor increase in switching frequency, taking into account filling factor and winding technique. The cost of inductive components decreases by about 50% for a two to three times increase in switching frequency (which is
entirely possible with this technology). To keep the third harmonic beneath the lower conducted emission floor of 150 kHz, the practical limit for hard switching is just below 50 kHz in these systems.
∙Reduced cooling requirements
Reductions of up to 50% or more in heatsink temperature are possible with this technology. A comparable reduction in heatsink sizing is possible while still
maintaining the higher-efficiency advantage that this technology enables. This solar inverter example of reduction in heatsink sizing should allow a reduction in production cost of around 5%, while still delivering increased annual benefit
through feed-in tariffs from the grid. A feed-in tariff is an incentive structure to encourage the adoption of renewable energy through government legislation.
∙Annual feed-in benefit
A common PV system with 7 kW in Germany produces approximately 7000 kWh
per year with a feed-in tariff of 0.49 euro/kWh. (In June 2008, the euro
approximately was worth US$1.60.) The annual benefit is approximately 3430 euros. The three-phase inverter given in the previous example showed an increase in Euro efficiency of 2.36%. This equates to an annual gain of 81 euros per year with this particular system. This is the estimation for central Europe. However, if looking at southern Europe, where the irradiation level is about twice that in
Germany, the annual benefit can be even greater, as shown in Table 3.[4]
Three-Phase High-Power-Factor Rectifier
A three-phase six-switch rectifier整流器followed by an isolated隔离的；孤独的；
单独的；偏远的dc-dc converter变换器is typically used in three-phase applications that require high power factor (HPF) and galvanic isolation电隔离between input and output. The rectifier shown in Fig. 3 (a 3-kW zero current switching resonant topology) can achieve the same goal with only two switches. When switches S1 and S2 are turned on, the stored energy in C1 to C3 is quickly moved to the
secondary-side resonant capacitor (C D) through the transformer (T R) and
resonant共振的inductor (L R). The discharging time is designed to be
approximately equal to one-half of the resonant period (T O). For an optimal
design, T O should be relatively shorter than the switching period (T S) to achieve a low total harmonic distortion谐振失真.
The system was run initially最初，首先；开头at full load全负荷with a pair of standard 1200-V, 25-A-rated IGBTs. These devices were then replaced by a pair of standard 1200-V, 40-A IGBTs, and the system was re-run at full load. The efficiency versus output power功率输出curves 曲线were recorded.
The IGBTs were then replaced by a pair of 1200-V, 20-A-rated SiC MOSFETs and the exercise repeated. As seen in Fig. 4, the SiC devices resulted in导致a 2.2% increase in efficiency at a 3-kW output and substantial efficiency improvement 重大的效率改进throughout the entire load curve负荷曲线. Also of note was a 25°C case-temperature reduction with the MOSFETs versus 对，相对the 40-A-rated IGBTs and a 36°C difference when compared with the 25-A-rated devices.[5]
10-kV, 10-A SiC MOSFET in a Boost Converter
SiC technology shows significant improvements in the 1200-V MOSFET arena, as revealed in the two previous examples. The performance improvement becomes even greater when compared to Si power switches rated at 6.5 kV and above.
Recently developed was a 10-kV, 10-A SiC MOSFET. The 10-kV device exhibits a drain-source forward voltage漏源极正向电压drop of only 4.1 V, while conducting当导通full-rated 10-A drain current with a 20-V gate-source voltage. This is equivalent to a specific on-resistance characteristic电阻特性of only 127 mV/cm2. The drain-source leakage current measured 124 nA at a 10-kV blocking voltage. In a direct comparison with a standard 6.5-kV Si IGBT in a clamped inductive switching test fixture, a SiC MOSFET exhibited 1/200th of the total switching energy of the IGBT. This unipolar SiC MOSFET's turn-on delay time was only 94 ns compared with 1.4 ìs for the IGBT and the turn-off time was only 50 ns instead of the IGBT's 540 ns.
To analyze in-circuit performance, a 10-kV SiC MOSFET was combined with a 10-kV SiC Schottky diode and an air-core inductor in a standard boost-circuit topology (Fig. 5). The circuit was designed to boost a 500-Vdc input to a 5-kVdc output at a switching frequency of 20 kHz. The system ran at 91% efficiency throughout the power band up to 600 W. Considering that this same circuit with 考虑同样用标准Si MOSFET 开关的电路standard Si MOSFET switches would only be capable of能够运行在几百赫兹的开关平率下a few hundred Hertz switching frequency, there is 将有更显著的性能提高应用SiC 材料在这个电压水平an even greater performance advantage with SiC material at these voltage
levels. The waveform shown in Fig. 6 exhibits the exceptionally fast turn-off
transient of this system.[6]
With the most recent advancements in SiC materials processing加工and device design, it will soon be possible to produce reliable MOSFET switches for the commercial marketplace. Considering the recent surge in interest in alternative energy systems, SiC technology is now ready to further improve their benefits.
The reduction in power losses 减少能源损耗，that this technology will provide 提供，供给in a PV system's power conversion section这项技术将在光伏系统的功率转换部分提供应用will enable more efficient usage使用of PV panel energy光伏板能量,将使光伏电池的能量更有效地使用in turn providing more power to the grid and allowing a reduction in future fossil-fuel generation在向电网提供更多的权力，允许
在未来减少化石燃料发电.
References
1.4H refers to the SiC crystalline structure used in power semiconductors.
2.Hull, Brett, et al. “Status of 1200 V 4H-SiC Power DMOSFETs,”
International Semiconductor Device Research Symposium, December 2007.
3.Burger, B.; Kranzer, D.; Stalter, O.; and Lehrmann, S. “Silicon Carbide
(SiC) D-MOS for Grid-Feeding Solar-Inverters,” Fraunhofer Institute, EPE 2007, September 2007.
4.Burger, B.; Kranzer, D.; and Stalter, O. “Cost Reducti on of PV Inverters
with SiC DMOSFETs,” Fraunhofer Institute, 5th International Conference on
Integrated Power Electronics Systems, March 2008.
5.Yang, Yungtaek; Dillman, David L.; and Jovanovic, Milan M.
“Performance Evaluation of Silicon Carbide MOSFET in T hree-Phase
High-Power-Factor Rectifier,” Power Electronics Laboratory, Delta
Products, .
6.Das, Mrinal K., et al. “State-of-the-Art 10-kV NMOS Transistors,”
20th Annual International Symposium on Power Semiconductor Devices and ICs, May 2008.
碳化硅MOSFETs挑战IGBTCs
出处:
/discrete-power-semis/silicon-ca rbide-mosfets-challenge-igbts
Michael O'Neill, Applications Engineering Manager, CREE, Durham, N.C.
摘要:SiC技术经历了显著的改善和提高,使现在允许制造MOSFET的性能优于他们的表兄弟Si IGBT,特别是在大功率和高温方面。

正文:
鉴于最近的碳化硅(SiC)技术的进步和提升,商业生产的1200 v 4 h碳化硅[1]功率MOSFETs现在是可行的。

现在已有改善4 h碳化硅基材的质量和外延,优化设备的设计和制造过程的措施,附加的还增加了沟道载流迁移率利用氮化退火方法。

[2]碳化硅与硅相比是一种更好的功率半导体，由于它的十倍高于Si的电场击穿能力,更高的热导率和更高的温度操作能力都归功于它的宽电子能带。

SiC与Si相比是更适合用在600 v和评级较高击穿电压的设备中的半导体材料。

SiC 肖特基二极管在600 v和1200 v的评级在今天已经得到了广泛的商业用途，它也早已被接受成为解决提高变换器拓扑结构效率的最佳方案。

此外，这些二极管被发现使用在太阳能逆变器中,因为他们比Si引脚续流二极管有更低的开关损耗在现在的应用中。

在600 v和1200 v评级,IGBTs一直作为功率选择开关。

此前,Si MOSFET在这些应用中是不健全的由于它们的高电阻(RDSON导通电阻)。

在高击穿电压下,RDSON增加近似于漏源极击穿电压的平方V DSMAX。

[3] M OSFET的导通电阻是由通道电阻,其固有的JFET的电阻和漂移电阻之和组成(图1),漂移电阻(RDRIFT)占整体电阻的主要部分,其中d等于漂移层厚度,q等于电子电荷数,u等于沟道载流迁移率和ND等于掺杂因子。

新一代的SiC MOSFET漂移层厚度削减近10倍,同时使掺杂因子增加到相同的数量级。

整体效果会使得其漂移电阻降低为硅MOSFET的一百分之一。

这里讨论的是改进后的SiC MOSFET的工程样品，一个1200 V，20-A的设备与100 mV 的导通电阻（RDSON）在15-V的栅源电压作用下。

除了其固有的导通电阻的降低，碳化硅也显著降低了导通电阻变化率当超过其工作温度时。

从25℃到150°C，SiC的变化范围
在20％内，而Si却在200％到300％。

SiC MOSFET芯片结温是能够运行在超过200°C，但工程样品的温度被TO-247塑料封装限制在150°C。

与Si IGBT相比，在传导损耗方面SiC MOSFET具有很大的优势，特别是在低功率输出。

凭借其单极的性质，它无尾电流关断，从而大大降低关断损耗。

表1显示了与标准1200-V IGBT比较的开关损耗的差异。

SiC MOSFET的开关损耗不到一半的Si IGBT（1.14毫焦耳和2.6毫焦耳）。

结合开关损耗的减少和整体导通损耗的减少，显然SiC开关是一种效率更高的设备对于高功率转换系统来说。

三相光伏逆变器
为了证明其作为一个光伏逆变器的应用，一个7千瓦，16.6 kHz的三相电网连接系统被实施。

这B6拓扑结构由Fraunhofer Institute ISE开发，利用一个拆分连接直流电容通过一个中性导体连接到两个电容器的中心点。

该装置连接到一个400-V的电网，用1200-V IGBT作为标准的功率转换设备。

这些IGBT 被1200-V的SiC MOSFET取代，显着的性能差异是清晰可见的如图.2所示。

表2显示的最大效率和欧洲效率改进完成实现。

由图.2曲线可以看出，SiC器件比Si IGBT有明显的优势。

最大的效率增加了1.92％，并比欧洲效率等级提高2.36％。

这相当于减少了50％整体系统损失。

另一个值得注意的性能参数的改善是在全额定输出功率条件下系统的散热器温度降低。

在环境温度25°C，稳定状态下，利用IGBT的温度是93°C，利用SiC MOSFETs的温度是50°C。

[3]
通过一个完整的基于碳化硅的解决方案在光伏（PV）电源转换器中的应用可以有多种不同的方法看到系统所获得的益处：
•电感元件的成本
一个电感元件的容量显着取决于系统的开关频率。

容量的一个很好的近似值是在开关频率增加的时候它的减少接近于时间常数的倒数，并要考虑填充因子和绕阻技术。

电感元件的成本降低约50%，并提高开关频率二到三倍（用这项技术是完全可以实现的）。

保持三次谐波在较低的150 kHz的传导发射层之下，这个系统对硬开关的实际限制值仅低于50kHz。

•减少冷却需求
利用这种技术使散热器的温度减少高达50％或者更多可能的。

这种技术能够保证同比减少散热器尺寸的同时又能够维护散热器高效率散热的优势，从而使得调整散热器的大小尺寸成为可能的。

这种光伏逆变器减小散热器尺寸的例子能够允许减少生产成本的5％左右，同时还提供通过电网回购从电网增加每年的效益。

电网回购是通过政府立法的一种激励机制，鼓励采用可再生能源。

•年度回馈效益
一个常见的7千瓦的光伏发电系统在德国每年发电约7000千瓦时，上网电价为0.49欧元/千瓦时（2008年6月，欧元约价值1.60美元），那么年度效益约3430欧元的。

在前面三相逆变器的例子表明欧洲资源利用效率增加2.36％，这相当于利用这个特定的系统每年可增加收益81欧元，而且这只是在欧洲中部的估计。

然而，如果着眼于欧中南部，它的光辐射水平大约是德国光辐射水平的两倍，那么每年的增益可以更大，如表3中所示。

[4]三相高功率因数整流器
一个三相六开关整流器跟随着一个隔离式DC-DC转换器通常使用在需要高功率因数（HPF）和输入、输出之间有电气隔离的三相应用当中。

图3所示的转换器（一个3千瓦零电流开关谐振拓扑）仅用俩个开关同样可以达到这个目的。

当开关S1和S2接通，电容C1至C3中存储的能量通过变压器（T R）和谐振电感器（L R）快速移动到副边谐振电容器C D，它的放电时间被设计成约为谐振周期（T O）大小的一半。

为获得最优的设计，实现较低的总谐波失真，谐振周期（To）应该比开关周期（T S）短。

该系统最初利用一对标准的1200-V，25-A-额定IGBT在满负荷情况下运行。

然后用一对标准1200-V，40-A的IGBT替换25A的，并使该系统重新在满负荷运行，记录效率和功率输出的对比曲线。

然后换成一对1200-V，20-A级的碳化硅MOSFET重复以上的实验。

如图4所示，SiC 器件使得一个3千瓦的输出的效率增加了2.2％，并且在负荷曲线方面也有重大的效率改善。

另外值得注意的是MOSFETs外壳温度与40-A额定IGBT相比降低25°C，与25-A额定设备比较有36°C的差异。

[5]
升压转换器中的10千伏，10A SiC MOSFET
在前面的两个例子中，SiC技术在1200-V MOSFET 领域显示出显著的性能提高和改善。

当与6.5kv及以上Si功率开关相比较时，Sic具有的性能更加卓越。

最近开发的10千伏，10A的SiC MOSFET。

当通入额定为10-A漏极电流、20-V栅极-
源极电压时，10千伏设备具有漏极- 源极正向压降仅为4.1 V。

这相当于一个特定的只有127 mV/cm2的电阻特性。

在10千伏阻断电压下测得的漏极- 源极漏电流为124 nA。

在直接比较标准的6.5 kV的硅IGBT在钳位感性开关测试夹具，的碳化硅MOSFET展出两百分之总开关能量的IGBT。

相比于IGBT这种单极的SiC MOSFET导通延迟时间只有94ns，IGBT为1.4 ìs，其关断时间仅为50纳秒，而IGBT为540 ns。

为了分析电路的性能，一个10千伏SiC MOSFET组合一个10千伏SiC肖特基二极管再加上一个标准升压电路拓扑结构空芯电感器组成电路（图5）。

该电路的目的是在开关频率为20 kHz情况下使500伏的直流输入得到一个5-KV的直流输出。

在贯穿600 W波段的功率带该系统可在91%的效率下运行。

考虑同样的用准Si MOSFET 开关的电路仅够运行在几百赫兹的开关频率下，应用SiC材料在这个电压水平将有更显著的性能提高。

图6中所示的波形，表现出这个系统异常快速的关断瞬态。

[6]
最近在SiC材料的加工和设备的设计方面的进步，很快就有可能产生可靠的MOSFET 开关满足商业市场。

考虑到最近对替代能源系统兴趣的激增，SiC技术已做好准备，提高替代能源系统的效益。

减少能源损耗，这项技术将在光伏系统的功率转换部分提供应用，能够保证光伏板能量更有效地使用，向电网提供更多的电力，减少未来化石燃料的使用。

参考文章：
1.4 h碳化硅晶体结构是用于功率半导体
2. Hull, Brett, et al.“1200 V 4H SiC功率立式DMOSFET的地位”，国际半导体器件研究研讨会，十二月2007
3. Burger, B.; Kranzer, D.; Stalter, O.; and Lehrmann, S. “碳化硅（SiC）网格喂养太阳能逆变器D-MOS”，弗劳恩霍夫研究所、EPE 2007期,2007年9月
4.Burger,B。

,Kranzer,D。

,Stalter,o .“成本降低,光伏逆变器与碳化硅DMOSFETs”,弗劳恩霍夫研究所,5日国际会议集成电力电子系统,2008年3月。

5. Yang, Yungtaek; Dillman, David L.; and Jovanovic, Milan M.“碳化硅MOSFET在三相高功率因数整流器的性能评价,“电力电子实验室,三角洲产品,。

6.Das,Mrinal K。

,et al.“最先进的10 kv NMOS晶体管、“第20届国际研讨会电力半导体元件和集成电路,2008年5月。