Si IGBT Modules for High-Frequency Operation
Several power conversion applications require operation at high switching frequencies (above 20kHz). This includes applications where optimizing the size of passive components such as filter inductances plays an important role. For certain applications, reducing audible noise generated due to the carrier frequency is an important design consideration.
To fulfill the requirements of high switching frequency operation, Mitsubishi Electric has developed the 7th generation TH-Series IGBT modules by optimizing certain characteristics of the latest 7th generation T-Series modules ,. The 7th generation IGBT chip technology is based on the advanced CSTBT™ Si-IGBT technology. An optimization in the switching loss performance of the module enables high switching frequency operation above 20 kHz maximizing the system’s efficiency.
Figure 1. 7th generation trade-off curve for 600 A / 1200 V modules (T-Series: CM600DY-24T and TH-Series: CM600DU-24TH). Image used courtesy of Bodo’s Power Systems
The TH-Series IGBT modules are optimized for high switching frequency operations between ƒc = 20 kHz – 60 kHz due to an optimized chip trade-off characteristic. Figure 1 shows the trade-off curve for Mitsubishi Electric’s 7th generation IGBT chips.
Figure 2. Referential Data: Dynamic Waveform Comparison. Image used courtesy of Bodo’s Power Systems
Mitsubishi Electric’s existing T-Series is positioned in favor of low conduction losses ,. As the TH-Series targets high switching frequency applications, the switching losses will dominate the overall losses in these applications. Therefore, the TH-Series’ trade-off point of the IGBT chip is tuned towards low switching losses. Hence, overall power losses are reduced for high switching-frequency applications.
Figure 3. TH-Series Line-Up. Image used courtesy of Bodo’s Power Systems
In general, shifting the trade-off point for a given IGBT chip technology will have an impact on the ratio of the DC-losses versus the switching losses during operation. Based on the considered operation point, either DC-losses or switching losses may dominate the overall power losses of the IGBT chip. Since the trade-off point of the TH-Series is selected different from the T-Series, the overall loss performance for different switching frequencies will have a threshold point in which the TH-Series will outperform the loss performance of the T-Series as the switching frequency increases and the switching losses become dominant in the system.
The switching loss reduction in the TH-Series has been achieved by reducing the IGBT turn-off losses and the IGBT turn-on losses. Figure 2 shows the dynamic switching waveforms of a T-Series module and the corresponding TH-Series module in the same voltage and current rating of 1200 V / 600 A. The power losses generated during turn-off can be reduced by optimizing the IGBT tail current. Therefore, the TH-Series’ tail current during the turn-off event has been lowered thereby decreasing the turn-off losses. The turn-on losses in the TH-Series are decreased by a lower chip capacitance and internal gate resistance compared to the T-Series. As shown in the switching waveforms in Figure 2, this allows decreasing turn-on loss by higher di/dt during the switching event. In conclusion, the total power loss of the TH-Series will show a superior performance at higher switching frequencies compared to existing IGBT modules such as the T-Series due to its particular optimization for such operating conditions.
7th Generation High-Speed TH-Series IGBT modules:
The TH-Series is available as a 2in1 module (half-bridge module) in a line-up with a rated current of 200 A up to 600 A. The TH-Series line-up is shown in Figure 3. The outline for the 200 A and 400 A module is mechanically compatible with the T-Series std type module and is available in a 48 mm x 94 mm and 62 mm x 108 mm package which is an established standardized module housing in the market. For the current rating of 400 A and 600 A the TH-Series is also available in a 80 mm x110 mm package. The TH-Series’ packaging structure is based on a AlN (Aluminum Nitride) insulator with a copper baseplate.
Application Example- Analysis of Overall System Performance:
The TH-Series has been developed and optimized for applications with high switching frequency operation between 20 kHz - 60 kHz which require high power density and high overall efficiency. Typical applications for the TH-Series include UPS, active filters for power factor correction, welding, medical as well as EV charger applications in which high switching frequencies are necessary to fulfill the application requirements.
Figure 4. Power Loss Comparison for 1200V/600A modules . Image used courtesy of Bodo’s Power Systems
Figure 5. Power Loss vs. Switching Frequency Comparison . Image used courtesy of Bodo’s Power Systems
In order to show the benefits of using the TH-Series IGBT modules, a simulated power loss comparison is presented using the Mitsubishi Electric’s 7th gen. T-Series std-type module and the high speed 7th gen. TH-Series module based on the 1200V/600A rated modules. The simulation results are summarized in Figure 4.
The bar chart shows the power loss components of the modules for an exemplary operation point at a high switching frequency of ƒc= 25 kHz. The electrical characteristics of the TH-Series’ chips enable a superior loss performance for the given operating point due to the optimization in the switching loss characteristics. As a result, the overall losses and also thermal performance of the TH-Series module has a superior performance at 25 kHz compared to the TSeries for this operating point.
Figure 5 indicates the total power loss of the module over an increasing switching frequency ƒc. The higher the switching frequency, the more superior the performance of the TH-Series will become compared to the T-Series as the switching losses become the dominating component in the system. Therefore, the TH-Series is perfectly suited for high switching-frequency applications due to the optimization in the loss performance.
The 7th gen high speed TH-Series IGBT modules have been developed for high switching-frequency applications above 20 kHz up to 60 kHz by optimizing the electrical loss characteristics. As illustrated by power loss and thermal simulation, the superior switching loss performance of the TH-Series IGBT modules enable operations at high switching frequencies and help to achieve the required efficiency in the system. In general, a reduction in the size of passive components such as filter chokes lead to an additional improvement in the power losses of the filter part. As a result, power density can be increased and audible noise is avoided. The TH-Series is now available in 1200 V line-up. Thus, the TH-Series offers an IGBT module solution optimized for excellent performance in high switching frequency applications.
This article originally appeared in Bodo’s Power Systems magazine.