Rugged 650V Trench IGBTs for Inverter Applications

绝缘栅极双极性晶体管(IGBT)是具有高输入阻抗和大双极性电流能力的少数载流子功率器件。由于这些特性，IGBT非常适合电力电子中的许多应用，尤其是电机驱动器、不间断电源(UPS)、可再生能源、电焊机、感应加热炉具和其他需要高电流和高电压能力的逆变器应用。短路耐受能力也是IGBT用于逆变器应用的一项重要功能。在逆变器驱动UPS或电机应用中，IGBT如果在故障电机、输出短路或输入总线电压直通情形中导通，可能会损坏。在这些条件下，经过IGBT的电流快速增加直至饱和。在故障检测和保护功能激活前，IGBT将承受电压力。从拓扑上看，三级中点箝位拓扑越来越普遍，甚至可应用到中低功率逆变器，因为更好的输出电压性能可减小滤波器尺寸并降低成本，同时在不过分牺牲开关损耗的情况下增加开关频率。在这种情况下，650V击穿电压为满足应用要求提供了极大的帮助。由于无法在三级NPC拓扑中完美平衡直流母线电压，较高的阻断电压对此拓扑极其重要。开发650V IGBT时，将开关和传导损耗保持在与600V IGBT相同水平至关重要。通常较高的击穿电压会造成Vce(sat)增加，并导致逆变器应用中的性能降低。同时，Vce(sat)和开关性能存在权衡取舍。这意味着补偿因较高电压设计导致的Vce(sat)增加可能会减慢开关性能，增加系统中的开关损耗。因此，在选择曲线中找到最佳设计点对开发650V IGBT至关重要。新的场截止沟道IGBT正是为满足这些要求而开发的。它具有650V击穿电压、极低的Vce(sat)和短路耐受能力。新IGBT的性能已通过系统级评估验证。

Field Stop Trench Technology

场截止沟道技术利用沟道栅结构和高度掺杂n+缓冲层获得沟道穿通特性。借助这些功能，此新的IGBT技术实现了比上一代技术更高的单元密度。因此，在给定硅面积下它具有低得多的通态压降。新场截止沟道IGBT的电流密度是之前场截止平面技术的两倍以上。图1显示FGH75T65UPD、新的75A/650V场截止沟道IGBT和FGH75N60UF、75A/600V上一代场截止平面IGBT的权衡特性。FGH75T65UPD在25℃、75A时实现1.65V的Vce(sat)，而FGH75N60UF在相同条件下提供1.9V。考虑到击穿电压增加到650V和活动面积减小，此特性有显著改进，因为较高的阻断电压和较小的尺寸导致Vce(sat)增加。此低Vce(sat)是新场截止沟道IGBT的主要优势。场截止沟道技术还减少了每转换周期的关断能耗，如图1所示。此增强的权衡特性使逆变器设计能够满足较高系统效率的市场需求。尽管硅面积减小，新场截止沟道IGBT在因热失控出现故障之前提供5us短路耐受时间，这是上一代IGBT无法提供的。新场截止沟道IGBT也有较低的关断状态漏电流，最大结温为175℃。

Figure 1: Trade-off characteristics

Comparative evaluation results

The new field stop trench IGBT is evaluated by a competitive device that also utilizes similar field stop technology. In a switching test at Tj=25℃, Ic=80A, Vce=400V, Vge=15V and Rg=5Ohm, the FGH75T65UPD shows a turn-off loss of 183uJ. The switching loss of a competitive IGBT rated at 75A/600V is 231uJ. The reverse recovery characteristics of the diodes in the same package are evaluated. The test conditions are If=40A, Tj=125℃, Vr=400V, di/dt=500A/us. The Qrr of the new field stop trench IGBT is 1.17uC, which is much smaller than the 3.98uC of the competitive IGBT. This small Qrr value reduces the turn-on loss of the IGBT in the bridge arm in the case of a bridge topology. The switching performance is verified by a commercial 5.5kW rated PV grid-tied inverter with a front-end boost stage and a bipolar control full-bridge inverter stage. The switching frequency of both stages is 19kHz. The boost stage remains unchanged from the original design, and the FGH75T65UPD and competitor IGBTs are applied to the full-bridge inverter stage. Figure 2 shows the efficiency test results of the FGH75T65UPD and competitor IGBTs. The EURO and CEC weighted efficiencies of the FGH75T65UPD are 94.37% and 95.08%, while those of the competitor IGBTs are 93.67% and 94.37%, respectively. The new field stop trench IGBT has superior switching performance, resulting in higher efficiency.

Figure 2 PV inverter efficiency

Figure 3 shows another trade-off between the new field stop trench IGBT, FGH50T65UPD and its competitors rated at 50A. The FGH50T65UPD shows a trade-off at 10A and 20A, which are practical operating current levels in most applications. Based on these characteristics, the power losses in the system are estimated. The target system is a 3kW rated mixed frequency full bridge inverter. The two low side IGBTs are switched at line frequency and the two high side IGBTs are switched at 17kHz. The estimated power losses are summarized in Figure 4. To verify the power loss estimates, the system efficiency is evaluated using two IGBTs; the FGH50T65UPD and a competitor 3 IGBT (which has similar power losses to the FGH50T65UPD). Figure 5 shows the measured efficiency of the 3kW inverter system. The competitor 3 IGBT is close to the FGH50T65UPD at full load. This matches the estimates. Furthermore, the efficiency gap widens as the load decreases. This is also consistent with Figure 3, which shows that the FGH50T65UPD outperforms the competition at lower current levels.

Figure 3 PV inverter efficiency

Figure 4 Power loss estimation

Figure 5: Efficiency of mixed frequency full-bridge inverter

in conclusion

The new 650V field-stop trench IGBT has been introduced and its performance has been evaluated. The new IGBT provides better DC and AC characteristics, longer short-circuit withstand time, and lower leakage current than the previous generation IGBT. With all these improvements, the new field-stop trench IGBT can realize a highly efficient and reliable inverter system.