Infineon’s new 1700V EconoDUAL™3 IGBT product and its simulation research in medium and high voltage cascade inverters and static var generators

Cascaded H-bridge (CHB) topology has a simple structure and flexible expansion. Since the same power unit is used, modular design and manufacturing are facilitated, which can effectively reduce costs. At present, it has been widely used in medium and high voltage cascade frequency converters (hereinafter referred to as MVD) and static var generators (hereinafter referred to as SVG). The power unit topology of these two devices is shown in Figure 1. In industrial applications, motors are used as driving devices for various mechanical equipment such as fans, pumps, compressors, belt conveyors, elevators, crushers and ball mills, and their power consumption accounts for more than 60% of China's entire industrial power consumption. The combination of MVD and production technology can significantly reduce motor energy consumption. SVG is mainly used to improve the transmission capacity and stable transient voltage of the power grid. It can also realize power factor control and bus voltage control in transmission and distribution grids, wind power and photovoltaic power plants, electric arc furnaces/rolling mills, mining, petrochemicals, coal mines, ports and other industries. Flicker suppression and compensation for unbalanced loads and filtering out load harmonic currents achieve the purpose of improving power quality and saving power. With the establishment of the country's "dual carbon goals", on the one hand, it will continue to promote energy conservation and emission reduction in the industrial sector, and on the other hand, it will vigorously increase the proportion of new energy power generation (wind power and photovoltaics), so the market space for MVD and SVG will also increase. will continue to increase.

As shown in Figure 2, the DC and AC power terminals of the EconoDUAL™3 IGBT module are located on both sides of the module, and the area between the power terminals is used to place the driver board. In this way, the DC busbar, drive board and AC busbar of the busbar capacitor do not interfere with each other in space, which facilitates parallel connection of devices and system design. Infineon's previous generation 1700V IGBT4 includes 4 current levels of 225A, 300A, 450A and 600A. By using a single module or two modules in parallel for each phase, it can basically cover the medium power range of 6kV-10kV MVD and part of the high power range. Medium capacity range of 10kV-35kV SVG. For high-power MVD and large-capacity SVG, there are two solutions for 1700V IGBT. One is to increase the number of parallel connections of EconoDUAL™3 modules, such as using 600A module FF600R17ME4 3 in parallel or 4 in parallel. The other is to use high-current IGBT modules in other packages, such as the 1000A module FF1000R17IE4 or the 1400A module FF1400R17IP4. This can not only increase the capacity of the system, but also reduce the number of parallel modules. The slight disadvantage is that it increases the packaging types of the modules. , the power unit design also needs to be greatly adjusted according to the structure of the module.

In order to further improve the performance of EconoDUAL™ 3 modules, Infineon has developed a new generation of 1700V IGBT7 chips and EC7 diode chips, and launched two new products, 750A FF750R17ME7D and 900A FF900R17ME7, whose current densities are respectively 25% and 50% higher than FF600R17ME4. %. Among them, 900A is the maximum current level of the 1700V EconoDUAL™3 mass-produced product in the industry. In addition, in order to reduce the temperature stress of the diode in negative power factor applications, such as the junction temperature fluctuation of the motor-side converter diode of a doubly-fed wind turbine, the FF750R17ME7D upgrades the diode current to 1200A. Before introducing the chip characteristics and module characteristics of IGBT7, it is necessary to have a preliminary understanding of the application of IGBT4 in MVD and SVG.

Figure 1. Power unit topology diagram of MVD and SVG,

a-MVD; b-SVG

Figure 2. EconoDUAL™3 IGBT module

The switching frequency of IGBT in MVD and SVG power units is relatively low, generally around 600Hz. By using multi-stage power unit cascades, a higher equivalent switching frequency of the inverter can be achieved, thereby eliminating more harmonics of the output voltage. The lower switching frequency reduces the switching loss of the device, making the device's conduction loss account for a higher proportion. Taking the typical rated operating parameters of MVD and SVG air-cooled power units in Table 1 as an example, the power loss and junction temperature of FF600R17ME4 are analyzed using Plecs simulation software. The results are shown in Figure 3. The power factor of MVD is close to 1, and the sum of conduction loss and switching loss of IGBT is much higher than that of diode, so IGBT has the highest junction temperature, which is 122.3°C. In addition, the conduction loss of IGBT accounts for approximately 73% of its total loss (conduction loss + switching loss). The power factor of SVG is 0, and the conduction loss of the diode is close to that of the IGBT, accounting for 60% and 72% of the respective total losses. The switching loss of the diode is lower than that of the IGBT, so the total loss of the diode is slightly lower than that of the IGBT. Since the junction-to-case thermal resistance of the diode is higher than that of the IGBT, the junction temperature of the diode is the highest, which is 119.9°C. In MVD and SVG, the conduction loss of IGBT accounts for approximately 56.5% and 32.6% of the total loss of IGBT and diode, so using IGBT7 with lower saturation voltage drop can reduce the total loss of the device and improve the output capability of the device. The application value of 1700V IGBT7 in MVD and SVG will be further studied below. For MVD, the main comparison is FF600R17ME4 and FF900R17ME7. For SVG, the three products FF600R17ME4, FF750R17ME7D and FF900R17ME7 will be analyzed.

Table 1. Rated operating conditions of MVD and SVG power units

Figure 3. Power loss and junction temperature of FF600R17ME4

-Working parameters reference table 1

IGBT7芯片技术首先应用于1200V的低功率IGBT，后来逐步扩展到1200V的中功率和大功率IGBT，其主要应用为电机控制类的变频器，比如通用变频器、伺服驱动器和电动汽车主驱逆变器。为了提升1700V IGBT模块的电流密度，英飞凌专门开发了1700V的IGBT7芯片，并首先应用于EconoDUAL™3封装。IGBT7芯片技术采用了微沟槽（micro-pattern trench，简称MPT）结构，以解决芯片高电流密度面临的挑战，MPT结构的简化示意图如图4所示。把栅极沟槽的台面宽度减少到亚微米长度，可以增加载流子约束，实现更低的饱和压降。另外，通过调整栅极沟槽、发射极沟槽和活跃通道的接触方案，则可以同时优化芯片的开关特性、开关损耗和门极电荷。1700V的二极管芯片EC7（emitter controlled，发射极控制）借鉴了1200V EC4和1700V EC5二极管的设计理念，实现了更高电流密度芯片的性能优化。

图4.MPT元胞示意图，中心有一个活跃通道，左上是带有不活跃台面的栅极沟槽，左下是发射极沟槽

图5是FF600R17ME4，FF750R17ME7D和 FF900R17ME7在25度和150度结温的输出特性曲线。由于IGBT采用了微沟槽结构和载流子限制，它的的饱和压降得到了显著的降低，所以相同结温时，FF900R17ME7的曲线位于左侧，FF750R17ME4D位于中间，FF600R17ME4位于右侧。以FF600R17ME4的标称电流600A为基准对比这三种器件在150度结温的饱和压降，FF600R17ME4为2.45V。FF750R17ME7D为 1.81V，比FF600R17ME4低0.64V，大约 26.1%。FF900R17ME7为1.65V。FF900R17ME7为1.65V，比FF600R17ME4低 0.8V，大约32.6%。更公平的比较是基于器件各自的标称电流，此时FF750R17ME7D和 FF900R17ME7D的饱和压降均为为2.05V，比 FF600R17ME4低0.4V,大约16.3%。所以，IGBT7可以明显的降低IGBT的导通损耗。

图5.IGBT4和IGBT7的导通特性曲线，图表上方的数值为三种器件的V ce 值，条件为：I c =600A，V ge =+15V,T vj =150℃

图6是三种器件二极管的正向特性曲线，结温分别为25度和150度。当电流为600A时，FF600R17ME4的正向压降为1.95V。FF750R17ME7D为1.63V，比FF600R17ME4低0.32V，大约16.4%。FF900R17ME7为1.88V，比FF600R17ME4仅低0.07V，大约3.6%。因为FF750R17ME7D的二极管电流为1200A，所以它比FF900R17ME7的压降更低。当基于器件各自的标称电流时，FF750R17ME7D的正向压降为1.8V，比FF600R17ME4低0.15V，大约7.7%。FF900R17ME7为2.2V，比FF600R17ME4高0.25V，大约12.8%。当电流比较高时，FF600R17ME4二极管的压降是正温度系数，而FF750R17ME7D和FF900R17ME7的压降在全电流范围均为负温度系数。设计EC7二极管为负温度系数的原因是为了优化二极管的反向恢复特性，降低方向恢复损耗，同时降低IGBT的开通损耗。在2-3kHz开关频率的整流或者逆变应用中，由于IGBT的开关损耗和二极管的反向恢复损耗占比较高 [1] ，EC7二极管可以降低器件的总损耗。与FF600R17ME4相比，即便FF750R17ME7D无法明显降低二极管的导通损耗，甚至FF900R17ME7还略微增加，但是FF750R17ME7D和FF900R17ME7的总损耗明显比FF600R17ME4，详见SVG应用部分的分析。

图6.EC4和EC7二极管的正向特性曲线，图表上方的数值为三种器件的V f 值，条件为：I c =600A，T vj =150℃

高电流密度的IGBT模块除了需要用高电流密度的芯片，还需要增强模块设计，比如提升芯片的工作结温、减小模块内部引线电阻发热和降低功率端子温升，以应对系统高功率密度设计面临的挑战。

通过优化EconoDUAL™3模块设计，IGBT7芯片增加了过载结温定义，如图7所示。IGBT7允许的过载结温位于150℃和175℃之间，过载时间小于等于20%过载周期，比如当过载周期T=300秒时，则过载持续时间t1不能超过60秒。60秒也是过载持续时间的最大值，比如如果过载周期T=600秒，则t1仍然不能超过60秒。在通用变频器、中高压MVD和SVG等有一分钟及以内过载工况的应用中，与IGBT4相比，IGBT7额外的25度过载工作结温可以提升器件额定工况对应的工作结温，使过载结温位于150℃和175℃之间，从而增加器件的输出能力和系统的功率密度。

图7.IGBT7和IGBT4芯片允许的工作结温，IGBT过载结温最高175℃，IGBT4最高结温150度

模块的输出电流会在交直流功率端子上产生与电流呈平方关系的欧姆损耗，这些损耗一部分通过模块内部的铜连接线传导到DCB，然后通过模块基板传递到散热器，另一部分损耗传递到与功率端子连接的外部铜排，最终功率端子会达到热平衡。如果EconoDUAL™3模块输出更大的电流，功率端子的温升会成为系统设计的瓶颈。为此，IGBT7 EconoDUAL™3对模块内部连接DCB和功率端子的结构设计进行了优化。IGBT7增加了模块内部功率端子侧的铜片面积，以便于安装更多的铜连接线，因而IGBT7比IGBT4的铜连接线数量多了40%。热测试对比表明，在相同工况（模块输出电流550Arms，IGBT开关频率1000Hz）下，1200V IGBT7 EconoDUAL™3比IGBT4的直流端子低大约20度，参考 [2] ，因1700V IGBT7 EconoDUAL™3的封装与1200V相同，所以1200V的测试结果也适用于1700V IGBT7。

a 直流功率端子

b交流功率端子

图8.EconoDUAL™3交直流功率端子与内部DCB连接图，FF600R17ME4（左），FF900R17ME7（右）

模块内部的绑定线、DCB上表面的覆铜层和芯片与DCB之间的焊接层共同组成了内部引线电阻，其等效值为R _CC’+EE’ ，如图9所示。C是IGBT集电极功率端子，C´是IGBT发射极辅助端子，E是IGBT发射极功率端子，E´是IGBT发射极辅助端子。EconoDUAL™3为半桥拓扑，包含两个等效的IGBT开关和与其并联的续流二极管。每个IGBT开关和续流二极管各包含一个R _{CC’+EE ’} 。如表2所示，由于IGBT7优化了模块内部的连接设计，其常温R _CC’+EE’ 为0.8毫欧，比IGBT4的1.1毫欧降低了27.3%。

图9.EconoDUAL™3 IGBT功率端子和等效的内部引线电阻示意图

表2.1700V EconoDUAL™3 IGBT4和IGBT7的内部引线电阻

常温状态下，R _CC’+EE’ 的损耗计算参考公式(1)。

R _CC'+EE' ：模块内部的等效引线电阻

i(t)=sin⁡(ωt) ：正弦输出电流

τ'(t)：IGBT或diode的脉冲函数，导通时为1，关断时0。

IGBT模块的温度也会影响R _CC’+EE’ 的数值，参考计算公式(2).

α:铜材料的温度系数，为3.85·10 ^-3 /K。

T _{R CC^'+EE'} ：假定引线电阻的温度与IGBT模块的壳温 Tcase 相同。

根据公式(1)、公式(2)和IGBT模块的三个壳温，图10给出了FF600R17ME4和FF900R17ME7 R _CC’+EE’ 的

损耗对比。在小电流范围内，两种器件的引线电阻损耗差别不大，当输出电流较大时，FF900R17的损耗明显更低。以75度壳温为例，当模块输出电流分别为300A和500A时，FF900R17ME7比FF600R17ME4的损耗分别低16W和45W，因而IGBT7更有损耗优势。接下来的MVD和SVG仿真均考虑了RCC’+EE’对损耗、结温和输出能力的影响。

图10.FF600R17ME4和FF900R17ME7内部引线电阻损耗对比

如上文分析，在MVD应用中，FF600R17ME4的IGBT导通损耗约占总损耗的56.5%（不包括引线电阻损耗），FF750R17ME7D和FF900R17ME7的IGBT饱和压降均比FF600R17ME4有明显降低。所以，在相同工况下，FF900R17ME7的输出能力最高，FF600R17ME4最低，FF750R17ME7D介于二者之间。因此，本部分的仿真分析主要对比FF900R17ME7和FF600R17ME4。仿真参数见表1，使用风冷和水冷两种散热器，热阻分别为0.15K/W和0.05K/W。对于MVD的过载工况，虽然110%额定电流1分钟过载在风机、水泵类负载中比较普遍，从更严苛的角度考虑，本文的过载工况为120%额定电流1分钟。

图11为风冷MVD的输出电流和IGBT最高结温的仿真结果，包括了额定工况和过载工况。结温为150度时，两种器件的额定输出电流分别为350A和442A。FF900R17ME7比FF600R17ME4高92A，大约26.3%。考虑FF900R17ME7具有1分钟的过载结温，额定输出仍为442A时，过载结温大约为175度。刚好充分利用了25度过载结温。为了使FF600R17ME4的过载结温不超过150度，其额定输出电流需要降低到320A。所以，过载工况时FF900R17ME7的输出比FF600R17ME4高122A，大约38.1%。

Similar to the air-cooled condition, Figure 12 summarizes the simulation results of water-cooled MVD. When the junction temperature is 150 degrees, the rated output current of FF600R17ME4 is 570A and that of FF900R17ME7 is 721A, which is 151A higher than FF600R17ME4, about 26.5%. Under overload conditions, the output currents of the two devices are 480A and 672A respectively. FF900R17ME7 is 192A higher than FF600R17ME4, which is about 40%. The simulation results of the above two cooling forms show that the additional 25 overload junction temperature of IGBT7 can further improve the output capability of FF900R17ME7 relative to FF600R17ME4.

In addition to improving the output capability of the device, IGBT7 can also reduce the total loss of the device and improve the efficiency of the system. As shown in Figure 13, the total loss of an IGBT and anti-parallel freewheeling diode in FF900R17ME7 is 297W, which is 105W lower than the 402W of FF600R17ME4, about 35.4%. Except for the increase in the switching loss of the diode, the losses in other parts have been reduced to varying degrees, reflecting the value of the IGBT7 chip and EconoDUAL™3 package optimization introduced above. Among them, the IGBT conduction loss is reduced by 51W, the IGBT switching loss is reduced by 16W, the diode switching loss is reduced by 11W, and the lead resistance loss is reduced by 20W.

Figure 11. Output current of air-cooled MVD and maximum junction temperature of IGBT

-Rated and 120% overload for 1 minute

Figure 12. Output current of water-cooled MVD and maximum junction temperature of IGBT

-Rated and 120% overload for 1 minute

Figure.13 Losses of FF600R17ME4 and FF900R17ME7 in air-cooled MVD (one IGBT and one anti-parallel diode), output current 300A

According to the SVG operating parameters in Table 1, a comparative analysis of the three devices was conducted using the same simulation method as MVD, heat sink thermal resistance and overload conditions.

Figure 14 shows the simulation results of air-cooled SVG. When the junction temperature is 150 degrees, the rated output currents of FF600R17ME4, FF750R17ME7D and FF900R17ME7 are 367A, 427A and 417A respectively. FF750R17ME7D is 60A higher than FF600R17ME4, about 16.3%. FF900R17ME7 is 50A higher, about 13.6%. The output current of FF600R17ME4 at 120% overload for 1 minute is 325A. When the overload is 120% for 1 minute and the IGBT7 overload junction temperature does not exceed 175 degrees, the output current of FF750R17ME7D is still 427A and that of FF900R17ME7 is still 417A. They are 102A and 92A higher than FF600R17ME4 respectively, about 31.4% and 28.3%.

Figure 15 shows the simulation results of water-cooled SVG. When the junction temperature is 150 degrees, the rated output currents of FF600R17ME4, FF750R17ME7D and FF900R17ME7 are 612A, 715A and 673A respectively. FF750R17ME7D is 103A higher than FF600R17ME4, about 16.8%. FF900R17ME7 is 61A higher, about 10%. The output current of FF600R17ME4 at 120% overload for 1 minute is 512A. When the overload is 120% for 1 minute and the overload junction temperature of IGBT7 does not exceed 175 degrees, the output current of FF750R17ME7D is 675A and that of FF900R17ME7 is 645A. It is 163A and 133A higher than FF600R17ME4 respectively, about 31.8% and 26%.

As shown in Figure 16, the total loss of an IGBT and anti-parallel freewheeling diode in FF750R17ME7 is 608W, and that of FF900R17ME7 is 607W. They are about 173W, 22.1% lower than the 781W of FF600R17ME4. All loss parts of FF750R17ME7D are lower than FF600R17ME4. The conduction loss of the FF900R17ME7 diode is 5W higher than that of FF600R17ME4, and the remaining losses are lower than that of FF600R17ME4. The comparison results once again verify the value of the IGBT7 chip and EconoDUAL™3 package optimization introduced above.

Figure 14. Output current of air-cooled SVG and maximum diode junction temperature

-Rated and 120% overload for 1 minute

Figure 15. Output current of water-cooled SVG and maximum diode junction temperature

-Rated and 120% overload for 1 minute

Figure 16. Losses of FF600R17ME4, FF750R17ME7D and FF900R17ME7 in water-cooled SVG (one IGBT and one anti-parallel diode), output current 500A

This article introduces the characteristics of Infineon's new generation 1700V IGBT7 and diode EC7 chips. By comparing with the previous generation product FF600R17ME4, the optimized design of the EconoDUAL™3 module and the value it brings to the system are analyzed in detail. Simulation results based on typical MVD application conditions show that, regardless of air-cooling or water-cooling conditions, FF900R17ME7 has lower losses than FF600R17ME4, has stronger output capabilities, and can achieve higher current density. Similarly, in SVG applications, the loss of FF750R17ME7D is similar to that of FF900R17ME7, and the output capability is slightly higher than that of FF900R17ME7. The loss of these two new products is much lower than that of FF600R17ME4, so they can achieve higher output capabilities. The simulation results in this article are based on ideal working conditions. The loss and output capability of the IGBT module in the actual system should be based on the actual system estimate.