Infineon’s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

[Introduction]The installed capacity of household photovoltaics is growing rapidly every year. The power range of single-phase photovoltaic inverters is basically 3~10kW. The schematic block diagram of the system circuit is shown in Figure 1. The DC/AC circuit realizes the energy conversion of green electricity. Infineon can provide one-stop semiconductor solutions including 650V power devices, coreless transformer CT technology driver ICs, main control MCUs and power management chips.

Infineon’s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

Figure 1. Block diagram of a single-phase photovoltaic system

In terms of application requirements, the inverter needs to be small in size, light in weight, easy to install, and easy to maintain. It can integrate energy storage to improve power efficiency and achieve an earlier return on investment. From the perspective of power devices, the mainstream solutions are discrete devices based on the TO-247 package. Once upon a time, the CoolMOS™ solution was widely used due to its advantages in efficiency and high-frequency characteristics. However, with the intensification of cost competition, Infineon cooperated with customers and proposed a new solution, 650V high-speed IGBT solution. From the perspective of circuit topology, the more common topologies are different circuit structures such as H4, H5, H6, H6.5 and HERIC, all of which have no transformer and have parasitic capacitance to the ground. The basic typical value is 10nF/kW. However, the starting points of different topologies are to solve the problem of system-to-ground leakage current caused by common-mode voltage jumps, and to meet the electrical safety guidelines. The efficiency is 98%, and the weighted efficiency is above 97%. Different circuit topologies are essentially the same, but have their own advantages, disadvantages and limitations.

In recent years, 650V single-tube power devices used in household single-phase photovoltaic inverters seem to have few new materials from the technology and products. See the high-power string inverter next door with various customized chips, packaging and SiC technology, and the efficiency and power brought by it. Developers of household inverters can’t help but wonder, apart from the eternal topic of cost reduction, where are we going in terms of frequency and efficiency? Good steel is used on the cutting edge. Under the premise that it is still difficult for the market to accept the price of SiC MOSEET, is there a product that combines the low cost of IGBT and the high performance of SiC? Infineon gave the best answer.

650V Hybrid SiC IGBT Features

650V Hybrid SiC IGBT, as the name suggests, is to make IGBT and SiC diode in the same TO247-3/4 package, as shown in Figure 2, thus taking into account the high cost performance of IGBT and the high speed of sic diode and extremely low reverse recovery current The advantages. The hybrid IGBT single tube is currently available in 40A, 50A and 75A specifications, and the household photovoltaic inverter is mainly based on the H5 chip.

Infineon’s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

Figure 2. Single-Tube TO-247 Package

650V Hybrid SiC IGBT Family

Infineon’s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

Among them, RH5 is a built-in half-current SiC diode, and SS5 is a built-in full-current SiC diode. TRENCHSTOP™ H5 is a chip with fast switching speed and low turn-off loss. It is mainly used in high frequency applications above 30kH to about 100kHz, and has high efficiency. TRENCHSTOP™ S5 is a medium switching speed chip with relatively low saturation voltage drop, and is mainly used in applications around 10kHz to 40kHz. Combined with the characteristics of the built-in SiC diode, the current is optimally matched between the two.

Main technical features:

1. Equipped with Infineon’s excellent 650V H5/S5 IGBT wafers and 650V sixth-generation SiC diodes

2. The SiC diode has a very small Qrr, which effectively reduces the turn-on loss of the IGBT on the tube, and the reverse recovery loss Erec is also significantly reduced.

3. IGBT turn-on loss has little effect with temperature

4. Reduce EMI

The forward conduction and switching parameters of the device are further analyzed according to the latest 650V/50A product specification, as shown in Figure 3. Among them, the SiC diode Vf in RH5 has a positive temperature coefficient, and when If=50A, it has a higher forward voltage drop than EH5 Rapid1, but in practical applications, due to the relatively low junction temperature, the diode current is relatively small, and the two have a negative impact on the power The consumption effect will not be much different.

Infineon’s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

Figure 3. Forward Voltage Drop Vcesat and Vf

As shown in Figure 4, the SiC diode has a great influence on the IGBT turn-on loss, which is 70% lower than EH5 when Ic=25A, and the total switching loss is reduced by 55%. Therefore, in terms of high frequency and efficiency improvement, especially for small-capacity household photovoltaic inverters, the 650V SiC hybrid single tube has good technical advantages, and the system performance analysis will be carried out in the HERIC circuit later.

Infineon’s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

Figure 4. Switching Losses Eon and Eoff

System circuit topology and simulation analysis

The circuit topology of household single-phase photovoltaic inverter is mainly based on HERIC, which is an efficient and reliable inverter topology proposed by Sunways in 2006. switch. It effectively isolates the reactive power exchange between the AC filter inductance L and the parasitic capacitance C at zero level, improves the system efficiency, reduces the high frequency component of the voltage on the parasitic capacitance, and eliminates leakage current.

Taking the HERIC topology as an example, the advantages of the device in system efficiency are expounded. This topology has four high-frequency tubes and two power-frequency tubes. The high frequency tube generally works at 20~30kHz. The power frequency tube is similar to the T-type three-level horizontal tube. When PF=1, the power frequency tube only has conduction loss; its anti-parallel diode has both conduction loss and Reverse recovery losses, detailed commutation are shown in Figures 5 and 6.

Infineon’s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

(a)Uo>0,Io>0

Infineon’s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

(b)Uo>0,Io<0

Figure 5. First and second quadrant commutation circuits

When the output Uo>0, Io>0, the device works in the first quadrant, the high-frequency tube is T1 and T4, the power frequency tube is T5, and D6 bears the reverse voltage. The load current flows as shown in the left of Figure 5(a), and the main losses are T1, T4 turn-on and conduction losses and D6 reverse recovery losses. When the high frequency tubes T1 and T4 are turned off, the power frequency tube T5 is turned on, D6 is conducting freewheeling in the forward direction, and the load current flows as shown in the right side of Figure 5(a). T5, D6 forward conduction loss.

When the output Uo>0, I<0, the device is in the second quadrant, the inverter generates reactive power, the diodes D1 and D4 freewheel, and the load current flows as shown in the left of Figure 5(b). D4 forward conduction loss and D6 reverse recovery loss. When the high-frequency tubes T2 and T3 are turned on, the power-frequency tube T6 is turned on, D5 is conducting freewheeling in the forward direction, and the load current flows as shown in the right side of Figure 5(b). The commutation circuits of the other two quadrants are shown in Fig. 6, which will not be repeated here.

Infineon&#8217;s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

(a)Uo<0,Io>0

Infineon&#8217;s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

(b)Uo<0,Io<0

Figure 6. Third and fourth quadrant commutation circuits

Through the commutation analysis, it can be seen that the characteristics of the reverse recovery diode D6 in the power frequency tube will affect the turn-on loss of the T1 and T4 high-frequency tubes, which is actually a switching commutation between the two. Therefore, by using the low switching loss characteristics of SiC, the 650V hybrid tube can effectively reduce the loss of the high-frequency tube, significantly reduce the operating junction temperature of the device, and improve the system efficiency.

Taking the 8kW household photovoltaic inverter as an example, the basic circuit simulation working conditions are Vdc=360V, V0=230V, fs=20kHz, Io=35A, PF=1, Th=100℃. From the commutation analysis, the main circuit high-frequency tube adopts H5 chip, and the power frequency AC switch adopts H5 and mixed RH5, SS5 scheme for comparative analysis.

Infineon&#8217;s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

Figure 7. EH5 losses at different switching frequencies fs

Scheme 1 all use IKW50N65EH5 to simulate the loss and efficiency of the system under the conditions of different switching frequencies fs. Simply increasing the switching frequency of the device to 30kHz and 40kHz in the original scheme will only increase the system loss and reduce the efficiency, as shown in Figure 7. At this time, when the operating junction temperature of the device is observed, when the switching frequency fs is raised to 40kHz, both T1 and D6 have exceeded the maximum operating junction temperature, as shown in Figure 8. Therefore, according to the characteristics of the HERIC commutation circuit, reducing the loss during the commutation process is the main consideration in the design of the power frequency tube device.

Infineon&#8217;s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

Figure 8. Junction Temperature Distribution

Scheme 2 uses a 650V hybrid SiC device to replace the position of the power frequency AC tube, and chooses IKZA50N65RH5 and IKZA50N65SS5 to compare the system performance differences, as shown in Figure 8. Compared with the previous EH5 solution 1, the RH5 can improve the system efficiency by 0.24% and reduce the total loss by about 19.6W under the same fs=20kHz condition; SS5 can improve the system efficiency by 0.34% and reduce the total loss by about 27.2W. It can be increased by 0.1%. At this time, the corresponding temperature of T1 tube is 140.3oC, the corresponding junction temperature of T5 is 106.2oC, and the corresponding junction temperature of D5 is 108oC.

Infineon&#8217;s 650V hybrid SiC IGBT single-tube boosts frequency and efficiency of household photovoltaic inverters

Figure 9. Loss and Efficiency with Different Line Frequency Tubes

If the EH5 and SS5 solutions increase the switching frequency to 40kHZ, it is 2 times higher than the traditional EH5 solution, but the inverter efficiency is still 0.16% higher, and the total loss is reduced by about 13 watts. At this time, the junction temperature of the high frequency tube T1 in the device is 142.4oC, the junction temperature of the power frequency tube T5 is 110.4oC, and the junction temperature of the SiC diode D6 is 113.2oC. In addition, the reverse recovery loss of the SiC diode is less affected by the junction temperature and remains basically unchanged. In practice, the turn-on loss of the T1 tube may be small, which helps to further reduce the loss of the high-frequency tube. Therefore, the 650V hybrid full-current SiC device can effectively increase the switching frequency of the HERIC topology circuit and increase the system efficiency in a wide range.

in conclusion

The 650V hybrid SiC product inherits the classic TO247 package. Customers can directly replace the old product without changing the PCB and circuit, so as to achieve the purpose of improving the system efficiency and increasing the switching frequency in the shortest time. At the same time, because the device brings the advantage of reducing system losses, it can reduce heat dissipation design requirements and costs; increasing the switching frequency can effectively reduce the size and size of the grid-connected inductance, and reduce the pollution of current harmonics to the grid. In the single-phase HERIC circuit, replacing with a single device can bring such advantages, why bother to toss various patented topologies and various soft switches?

Source: Infineon Industrial Semiconductor, original: Zhao Zhenbo Sun Dunhu

The Links:   CLAA170EA07QL RM500DZ-24

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