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The three-level IGBT power module with integrated emitter control diode chip technology

in order to fully explore the design advantages at the system level, the three-level neutral point clamping (NPC) topology circuit, which used to focus on high-power applications, has recently begun to appear in medium and low-power applications. The improved spectrum performance and lower switching loss of low-voltage devices benefit products such as UPS systems or solar inverters that need filters. So far, in order to realize the three-level circuit, we can only use discrete devices or at least combine the three modules together. Now, using chip technology for higher breakdown voltage, by integrating the three-level bridge arm into a separate module, coupled with a drive circuit, this topology can be more attractive in new applications

working principle of three-level NPC topology

in the three-level NPC topology, each bridge arm is connected in series by four IGBTs with anti parallel diodes. In addition, two diodes DH and DL are equipped to connect their intermediate nodes to the neutral point of the DC bus. All power semiconductors used have the same breakdown voltage. According to the characteristics of output voltage and current, the fundamental frequency output of a cycle has four different freewheeling working states

figure 1 Commutation circuit of a bridge arm in three-level NPC

a) short commutation circuit; b) Long commutation circuit

it can be seen from figure 1A that the voltage and current are in the positive direction, T1 and DH constitute the working mode of the buck circuit, while T2 outputs the current in the normal way. When the voltage and current are in the negative direction, T4 and DB form the working mode of boost circuit, and T3 outputs current in the normal mode. In the above two cases, commutation only occurs in two devices, which we call short freewheeling. However, when the output current is negative and the voltage is positive, the current flowing through T3 and DB must be reversed to D2 and D1 as shown in Figure 1b). This commutation involves four devices, so it is called long commutation loop. In other cases, there is another long commutation path. When designing three-level converter, how to control the stray inductance and overvoltage of long converter circuit is another challenge for designers

Figure 2 Easypack 2B package

the latest IGBT module for three-level NPC topology

although the IGBT module with a total of 4 IGBTs and 6 diodes is not suitable for high-power products, it can be suitable for medium and low-power products as long as the power range is certain and the number of control pins allows standard packaging

Figure 3 econopack 4 package

for small power products, the Easypack 2B package shown in Figure 3 has enough DBC area to integrate a complete 150A three-level module bridge arm. Since pins can be arbitrarily arranged in a given grid, these pins can be used as either power terminals or control terminals. Therefore, this package can provide a very ideal connection mode. This package provides auxiliary emitter terminals to ensure high-speed switching of IGBT. For power terminals, up to 8 terminals can be used in parallel to ensure the required rated current and reduce stray inductance and PCB heat

for medium power products, the newly launched econopack 4 package provides an ideal choice, which can integrate all power devices in the three-level. The three power terminals on the right are used to separate the DC bus and bring very low parasitic inductance to the three-level inverter. They are connected in parallel with the two opposite power terminals as the output terminals of each bridge arm. On both sides of the module package are control pins. The PCB drive board of the transmission system inspection of the electronic tensile testing machine can be directly connected through these terminals. The maximum current of the bridge arm in this packaged three-level module is up to 300A

in terms of reducing stray inductance, integrating all devices of a three-level phase bridge arm into one module is a promising solution. However, it is obvious that only 600V devices withstand voltage, which makes it difficult to meet typical applications. The reason is that the voltage sharing of bus voltage is not ideal, and the switching speed of 600 V devices is too fast

in order to make the design easier and ensure that the device has a higher margin in application, these modules use enhanced IGBT and diode chips, with a withstand voltage of 650V. These new chips, like the well-known 600V igbt3 devices, have a precision screw pair drive; 2. The common belt drive has the same conduction characteristics and switching characteristics; And the reliability has not changed (such as SOA, RBSOA, scsoa). These are realized through the development of the latest IGBT and diode terminal structure, and ensure the ultra-thin 70? M chip thickness does not change. Therefore, the Collector Emitter Saturation Voltage VCE of 650V IGBT_ Sat remains at a very low 1.45v level at 25 ° C (1.70v at 150 ° C). The switching loss of the device is low. When the switching frequency is 16KHz, the loss accounts for only one third of the total loss of the inverter. In addition, the IGBT also has a very smooth current tailing characteristic, which will not cause voltage overshoot even under severe conditions. The VF qrr relationship of the diode is also optimized. The forward voltage drop pole is 1.55V at 25 ° C (1.45v at 150 ° C), and the soft shutdown characteristic of the regulator is maintained

challenges in designing IGBT Driver with three-level topology

in the application of medium and small power three-level NPC topology, in order to give full play to the system performance, some specific requirements are put forward for IGBT Driver

higher switching frequency since the switching frequency ranges from 16KHz to 30kHz, the driver must provide a consistent and small transmission delay time for each IGBT in order to reduce the dead time. Because 650V devices have a fast switching speed, the dead time mainly depends on the drive. There are several representations: Shore hardness (also known as shore hardness), Rockwell hardness, Brinell hardness (also known as Brinell hardness), Rockwell hardness; See the following formula for the conversion relationship: change of transmission delay time of actuator. If the dead time is too long relative to the switching period, the output of the inverter will be nonlinear, which will bring more challenges to the control algorithm

topology circuit structure although the withstand voltage of these devices is only 600V or 650V, the isolation requirements of the driver are the same as 1200V. As the number of driving circuits is doubled, the design suitable for the driver must be adopted, and its power supply is required to have a small number of components and a small PCB space. The protection characteristics of the drive circuit, such as short circuit detection and undervoltage locking, must match the three-level NPC topology. First, turn off an internal IGBT (T2, T3 in Figure 1), which will make the bus voltage fully applied to the device. Because it exceeds the device scsoa or RBSOA area, the device will immediately fail

these requirements can be easily met by using the new integrated IGBT driving technology of the eicedriver series:

* the integrated micro transformer technology provides basic insulation functions with an insulation voltage of 1420 Vpeak

* the integrated active Miller clamping function can be realized by using a single power supply, whether visual, tactile or olfactory. This driver will not have the risk of parasitic conduction even at high switching speeds [8]

* compared with the traditional optoelectronic coupling driver technology, this micro transformer technology can greatly reduce the transmission delay time and mutual deviation

* the integrated vcesat protection function can also be used for the outer switch, but it needs to be shielded for the inner IGBT

experimental test results

this part will introduce the switching waveform of Easypack 2B three-level module. In this circuit, the IGBT gate of IGBT drives the drive chip of 1ed020i12-f. The current transformer is used to measure the current at the positive end of the DC bus dc+ or dc-

figure 4 Switching waveform of short commutation (the peak voltage is 550 V, and the voltage is still within the allowable range.)

Figure 4 of short commutation circuit shows the switching waveform under the condition of short commutation at nominal current, 400V DC bus voltage and 25 ° C junction temperature

Fig. 5 switching waveform of long commutation (the peak voltage is 580v. This voltage is only 30V higher than the peak voltage of short commutation, and still does not exceed the breakdown voltage of 650 v.)

long commutation circuit figure 5 shows the switching waveform of long commutation under the same conditions

the first test results show that the long commutation can almost achieve the same switching performance as the short commutation because a complete three-level bridge arm is integrated in one module. However, in order to obtain sufficient margin under higher current conditions, it is still necessary to further reduce the stray inductance of the circuit. The parasitic inductance can be effectively reduced by paralleling multiple capacitors and using multilayer circuit boards to reduce the current loop between the module and the capacitor. In addition, it must be considered that the current transformer will not be used on the DC bus in practical applications. The current transformer used here will generate 15nh stray inductance, resulting in 45V overvoltage


by integrating a complete three-level bridge arm in a module, the device withstand voltage is increased from 600V to 650V, and then equipped with a highly integrated drive solution. This three-level NPC topology brings very attractive solutions for medium and small power inverters such as high-efficiency ups and PV that need to work at high switching frequencies and are equipped with filters

by Zhang Xi, UWE Jansen and Holger ruething (end) of Infineon Technology Co., Ltd

Copyright © 2011 JIN SHI