TRENCHSTOP 5 boosts efficiency in Home Appliance, Solar and Welding Applications Davide Chiola - Senior Mgr IGBT Application Engineering Mark Thomas Product Marketing Mgr Discrete IGBT Infineon Technologies Austria AG, Siemensstr. 2, 9500 Villach, Austria Abstract Modern trends in power electronics require higher efficiency power semiconductors at competitive cost. The new 650V TRENCHSTOP 5 IGBT technology cuts the switching losses of previous generations by half, still maintaining low conduction losses. It sets a new benchmark in power density, allowing significant benefit for the end application. This paper presents the fast switching version of this technology platform and highlights the benefits in the target applications by extensive application tests. 1. Introduction Energy efficiency requirements set by Regulatory Agencies in different regions are steering the adoption of very efficient power semiconductors and enabling smart system solutions in order to meet the efficiency standard. In Photovoltaic applications for example, any fraction of % efficiency gained in the Solar inverter will translate in lower energy bill or shorter time to get to a grid parity. At the same time the inverter cost must cope with declining PV panel costs. In consumer applications like Motor Drives for Home Appliance, the solution cost must be kept within the limits set by a very competitive marketplace. In modern split Air conditioning above 1kW for example, a Power Factor Correction circuit is required to reduce the energy wasted by the system. In this case high efficiency of the PFC conversion along with very low solution cost must be guaranteed to win these high volumes, cost-driven consumer markets. Also in the industrial segment new regulations are coming up: PFC is being introduced in portable welders in the Chinese market to improve the grid quality. In these applications high switching frequency of the AC/DC stage allows to reduce the size of the output filters and hence the weight of the machine. Reducing switching losses for the IGBT allows to lower the operating temperature of the device, translating in longer lifetime for these system operating in harsh environments. The above general trends call for new switch technologies offering an overall reduction of power losses (W / mm 2 ), still keeping the same or lower chip cost / mm 2. At the same time different flavors of the technology are required to address specific requirements of each application.
2. TRENCHSTOP TM 5 and High Speed 5 IGBT To address these needs a new technology platform called TRENCHSTOP TM 5 has been developed: a special cell design and ultrathin wfr technology allow to achieve simultaneously low conduction and switching losses. The architecture of the new technology is shown in figure 1: Figure 1: TRENCHSTOP 5 technology platform and its derivatives The fast switching version High Speed 5 is currently being released and will be discussed in this paper. It addresses fast switching applications like PFC or boost stages as well as inverter stages in Solar and UPS, DCDC converters in Welding. A comparison with previous IGBT generations is provided in Figure 2:
Figure 2: High Speed 5 vs previous Infineon IGBT generations. Additional technology variants are currently in development and will be released in 2013 and 2014: an R version for resonant topologies to be found in Inductive Cooking and a low Vcesat L version to be used mainly as polarity switch in Solar inverters. The high Speed 5 is offered in 2 versions to offer additional flexibility to the end-user: High Speed 5 H: plug&play replacement of previous generation High Speed 3. It results in a drastic performance improvement and doesn t require any special precaution in design-in. High Speed 5 F: it provides additional loss reduction, however needs a split Rg,on and Rg,off driving stage. It is a best fit for design with low stray inductance in the commutation loop and in combination with SiC Schottly diode, for example as boost Diode in active PFC. The different switching behavior of H and F version is illustrated in Figure 3, capturing the turn-off event during application test on an internally developed 2 kw H4 Bridge topology: Figure 3: Current and Voltage waveforms during turn-off: H5 and F5 vs previous generation H3. The H5 provides a faster voltage rise than H3, resulting in lower turn-off losses. The current waveform is however very similar to the H3. The apparent oscillation of the tail current are amplified by the time scale used (20ns / div). The F5 on the other hand provides shorter tf
and faster current fall di/dt. This translates in additional loss reduction, but also in additional voltage overshoot Ls di/dt beyond the DC link voltage. In this case 900A/us provides almost 100V of voltage overshoot, meaning approx 110 nh of stray inductance. In order to keep the voltage spike within a more reasonable ~50V, stray inductance of the PCB tracks should be limited to 30~50 nh. A multilayer PCB is preferred, as well as Surface Mounted SMD discrete packages or modules with low lead inductance. The voltage spike increases as load current is increased, therefore it can be mitigated by slightly over-rating the device or paralleling multiple devices. The Voltage spike can be finally reduced by increasing Rg,off, hence a split Rg,on-Rg,off driver stage is preferred for the F version, keeping the Rg,on as low as possible to meet the required EMI specs and increasing Rg,off the meet de-rating specification of normally 80% Vbrces. The High Speed 5 provides drastically improved performance compared to High Speed 3 across the whole range of electrical parameters: lower conduction losses, higher blocking voltage, lower switching and capacitive losses, lower gate charge (Figure 4, left). This results in a drastically improved Vcesat-Eoff trade-off compared to previous 600V IGBT generations (Figure 4, right): Figure 4: Electrical parameter comparison (left) andtrade-off Vcesat / Eoff (right) of the HighSpeed5 in comparison to previous technologies HighSpeed3 and TrenchStop TM 3. Application test. 3.1 Power Factor Correction (PFC) We verified the improvement of the new technology by extensive characterization and application test. In Figure 5 we show an efficiency test in a 1 kw CCM mode PFC test board, where the High Speed 5 (H5) is compared to previous generation High Speed 3 (H3) and competitor s IGBTs commonly found in these applications. Switching frequency is 60 khz in
this case. Figure 5: Efficiency and case temperature (at max power) comparison in a 1kW PFC test board The High Speed 5 shows an efficiency improvement of 0.5% to the High Speed 3 and 1% to the best competitor. The PFC circuit is normally the AC/DC conversion stage of motor drives to be found in modern Air conditioning split systems above 1 kw. Assuming that the Airc conditioning is running on average at 50% load and an efficiency of 95% for the inverter stage, this would translate in 5 W average power saving for each Air conditioning unit sold with a High Speed 5 IGBT on it. Considering that only the top 4 Aircon suppliers in China produce approximately 25 Million inverterized Aircon units / years, this would result in a power saving of 100 MW in China only, equivalent to 430 Million of kwh saving in one year, assuming a utilization rate of 50%. The device can work at relatively high switching frequency of 60 khz, where normally 20 khz are used by conventional IGBTs. This translates in the possibility to reduce the size of the PFC choke still keeping the same ripple current, and hence reduce system cost. Even more interesting are the thermal results: thanks to the reduce power dissipation, the Hi gh Speed 5 in TO220 package can reduce the case temperature compared to previous IGBT s housed in the much bigger TO247 package (up to 30 C compared to the best competitors at 800W). This allows to save board spacing due to the smaller footprint, reduce the cooling r equirement and finally reduce the solution cost, very important in this demanding consumer
market. 3.2 Solar inverter Before looking into the real application of solar inverter, let s firstly get a direct feeling of the power loss improvement of H5 against previous generation HighSpeed3. Based on a very simple condition of a 20A square wave with 50% duty cycle, junction temperature 100 C, the total power loss per IGBT vs switching frequency is shown in Figure 6 below: Figure 6: Power dissipation as a function of switching frequency At 20KHz, which is commonly used in state-of-the-art inverter design, the total power loss per IGBT dropped from 32.80 W by HighSpeed 3 to 25.04 W by using the H5, that means approximately 24% reduction. Moreover, if we replace the anti-parallel diode with Infineon 2nd Gen SiC Schottky diode, another 11% power loss reduction could be achieved. This allows to either increase the system output power by keeping the same device temperature, or increase the switching frequency, as explained below. In the application field, with specific thermal design of the power system, the allowable total maximum loss is defined according to heatsink size, ventilation as well as the configuration of power devices, magnetic components etc. At the same time the junction temperature of all the power devices must fulfill the de-rating requirement of e.g. 80% of the Tjmax. That means also that the maximum allowable power loss per device is defined as well. Take a practical value e.g. 40W for standard TO247, and the same load condition mentioned above (20A square wave, 50% duty cycle) for a 40A device. The maximum operation frequency of HighSpeed3, with respect to max junction temperature 100 C, is around 28 KHz. As a comparison, the new IGBT H5 it could be driven up to 50 KHz. At this frequency
the cost and reliability benefit brought by the frequency increase, like smaller and light-weight magnetic components, as well as possibility of reduction or even elimination of electrolytic capacitors in some cases, would definitely overcome the additional design complexity (thermal, layout optimization etc). This is extremely important for applications like Solar and UPS, where the cost of the passive components dominate the bill of material. To validate the above considerations, an application test was carried out on a Solar inverter at Fraunhofer Institute ISE. The HERIC topology consists of 6 duo-pak IGBTs and 2 discrete diodes. By replacing the High Speed 3 IGBT with High Speed 5 - H5 at 16 khz, the peak efficiency is increased by 0.2 % to reach 98.3%. In a separate test, the H5 allows to triple the switching frequency (from 16 to 48 khz) by keeping the same or higher efficiency as previous generation High Speed 3 over the entire load range, confirming the simulated results. Figure 7: Efficiency measurement on Solar inverter with HERIC topology. Courtesy of Fraunhofer ISE. 4. Conclusions In summary, we presented in this paper the newly developed High Speed 5 IGBT, fast version of the TRENCHSTOP TM 5 technology platform. Thanks to advanced thin wafers technology, it provides drastically improved performance compared to previous generation and competitor s IGBT. After highlighting the major electrical parameters and switching behavior, the benefit of the new technology are verified in real application test circuits, resulting in drastically improved efficiency and thermal behavior. This translates in higher system reliability, and possibility to meet higher efficiency targets not increasing the BOM cost.