New power electronic device IGCT and its application

It can be turned on and off on the root fiber. Due to the ideal design of IGCT, the turn-on loss of IGCT is negligible, and its low conduction loss makes it able to operate at high frequencies that were not met by high-power semiconductor devices in the past.

Overview An ideal power device should have the following ideal static and dynamic characteristics: in the off state, it can withstand a higher voltage; in the on state, it can withstand a large current and have a very low voltage drop; At the time, the on / off speed is fast, can withstand high di / dt and dv / dt, and should also have full control function.

Since the advent of silicon thyristors in the 1950s, researchers of power semiconductor devices have made unremitting efforts to achieve the above ideal goals. In the late 1960s, the turn-off thyristor GT0 realized the gate turn-off function and extended the chopping operating frequency to above 1kHz.

In the mid-1970s, high-power transistors and power MOS-FETs were introduced, and power devices realized the field control function, opening the door to high-frequency applications. In the 1980s, insulated gate-gated bipolar transistors (IGBTs) were introduced, which integrated the functions of both power MOSFETs and bipolar power transistors. Its rapid development has stimulated people's research on a new power device, a MOSFET gated thyristor, which combines the functions of both power MOSFET and thyristor. Therefore, the current research focus of power devices mainly focuses on the performance improvement of existing power devices, MOS gated thyristors, and the use of new semiconductor materials to manufacture new power devices.

High-power devices and their development High-power thyristors (SCRs) have been the only semiconductor devices that can withstand high voltages and high currents for quite some time in the past. Therefore, in view of the shortcomings of SCR, people naturally lead the direction of efforts to how to make the thyristor have the ability to turn off, and therefore developed the gate turn off thyristor.

Using GT0 thyristors as inverter devices has achieved satisfactory results, but its shutdown control is more likely to fail, so it is still more complicated and the operating frequency is not high enough. At almost the same time, power transistors (GTR) developed rapidly, making GTO thyristors comparable. Therefore, in a large number of small and medium-capacity inverters, GT0 thyristors are basically not used. But because of its large working current, it still occupies a major position in the large-capacity inverter.

Thing. The main part is the same as the transistor, and also has the collector (C) and the emitter (E), but the driving part is the same as the field effect transistor, which is an insulated gate structure.

The working characteristics of IGBT are: the control part is the same as the field effect transistor, the control signal is the voltage signal Ua, the input impedance is high, the gate current I., and the driving power is very small. The main circuit part is the same as GTR, and the working current is the collector current input. In addition, its operating frequency can reach 20kHz. The carrier frequency of the inverter with IGBT as the inverter device is generally above 10kHz, so the current waveform of the motor is relatively smooth, and there is basically no electromagnetic noise.

Although the research of silicon bipolar and field-controlled power devices has matured, their performance is still improving and improving. The integrated gate commutated thyristor (IGCT) that has emerged in recent years is expected to quickly replace GTO. Integrated gates Pole commutated thyristor (IGCT) integrated gate commutated thyristor IGCT a new type of semiconductor switching device that came out in the year. The device is formed by integrating the gate drive circuit and the gate commutation thyristor GCT into a whole. The gate commutated thyristor GCT is a new type of power semiconductor device based on the GT0 structure. It not only has the same high blocking capacity and low on-state voltage drop as GT0, but also has the same switching performance as IGBT, that is, it is GTO and The result of IGBTs complementing each other's strengths and weaknesses is an ideal MW level, medium voltage switching device, which is very suitable for 6kV and 10kV medium voltage switching circuits. The IGCT chip has a capacity of 0.5M3MVA for two-level inverters and 1M6MVA for three-level inverters without stringing together. If the reverse diode is separated, it is not integrated with IGCT. The capacity of the two-level inverter can be Expanded to 4.5MVA, three-level expanded to 9MVA, now there are inverter series products composed of such devices. At present, IGCT has been commercialized. The highest performance parameter of IGCT products manufactured by ABB is 4.5kV / 4kA, and the highest development level is / 4kA. In 1998, Mitsubishi Corporation of Japan developed a 6kV / 4kA GCT thyristor with a diameter of 88. See IGCT outline drawing.

The schematic diagram of the structure of the analog device meal gate commutation thyristor GCT, as shown in (B), the left side of the figure is the GCT, and the right side is the anti-parallel diode. Similar to GTO, IGCT is also a four-layer, three-terminal device. See (A). The interior of GCT consists of thousands of GCTs. The anode and gate are shared, while the cathode is connected in parallel. The important difference from GTO is that there is a buffer layer inside the GCT anode, and the short-circuit anode of GTO is replaced by a transparent (penetrable) anode. The turn-on mechanism is the same as GTO, but the turn-off mechanism is completely different from GTO. During the turn-off process of GCT, GCT can instantly turn from on to blocking state, become a PNP transistor and then turn off, so it has no additional du / dt limit; and GTO must go through a non-conducting and The non-shutdown intermediate unstable state is converted, that is, the nGTO region, so GTO needs a large absorption circuit to suppress the rate of change of the reapplied voltage du / dt. The equivalent circuit of the GCT in the blocking state can be considered as a basis Open-circuit, low-gain PNP transistor in series with gate power supply.

The mechanism of GCT without intermediate zone and bufferless shutdown is that it can stop its cathode injection instantaneously during strong shutdown, and does not participate in the subsequent process. Change the device to turn off in the bipolar transistor mode, provided that a very high negative voltage is applied outside the P-based N emitter junction, so that the anode current is quickly transferred (or commutated) from the cathode to the gate (the gate commutation thyristor is Named), as soon as the inactive NPN tube stops injecting, the PNP tube is easily turned off due to the absence of base current. GCT became a PNP tube before it withstands the full blocking voltage, but GTO withstands the full blocking voltage in the SCR transition state, so GCT can operate like an IGBT without buffering, no secondary breakdown, and the tail current Big but short time.

(1) Buffer layer In traditional GTO, diode and IGBT devices, a buffer layer is used to form a through-type (PT) structure. Compared with a non-through-type (MT) structure, it can reduce the thickness of the device under the same blocking voltage Approximately 30%. Similarly, using a buffer layer in the GCT, that is, using thinner silicon wafers can achieve the same blocking voltage, thus improving the efficiency of the device, reducing the on-state voltage drop and switching losses, and can get better VT-Eoff. At the same time, the use of a buffer layer also enables the combination of a monolithic GCT and diode.

In order to achieve low turn-off loss, the transparent anode needs to limit the gain of the anode transistor, so the thickness of the anode must be thin and the concentration must be low. The transparent anode is a very thin PN junction, and its emission efficiency is related to the current. Because electrons penetrate the anode as if the anode were short-circuited, it is called a transparent anode. The traditional GTO uses an anode short-circuit structure to achieve the same purpose. The use of a transparent anode instead of an anode short circuit can reduce the trigger current of the GCT by an order of magnitude compared to the conventional GTO without a buffer layer. Compared with IGBT, the structure of GCT is fundamentally simplified because it does not contain MOS structure.

The reverse conduction technology GCT is mostly made of reverse conduction type, which can be monolithically integrated with the optimized freewheeling diode FWD on the same chip. Since the diode and the GCT share the same blocking junction, the P base of the GCT is connected to the anode of the diode, thus forming a resistive channel between the gate of the GCT and the anode of the diode. Because there is a PNP structure in the reverse conduction GCT and diode isolation region, there is always a PN junction reverse biased, thus blocking the current flow between the GCT and the diode anode.

The IGCT drive technology has a low trigger power, which can make the trigger and status monitoring circuit and the IGCT die as a whole, input the trigger signal through two optical fibers, and output the working status signal. In (A), the GCT is very close to the gate driver (15cm pitch). The gate driver can be easily installed in different devices, so the structure can be considered as a general form. In order to make the structure of IGCT more compact and sturdy, the gate drive circuit surrounds the GCT, and forms a natural whole with the GCT and the cooling device, called the wrap-around IGCT, as shown in (B), which includes the GCT gate drive circuit. All necessary components. Both of these forms can further reduce the inductance of the gate circuit and reduce the number of components, heat dissipation, electrical stress and internal thermal stress of the gate drive circuit, thereby significantly reducing the cost and failure of the gate drive circuit rate. Therefore, IGCT has the best performance under the premise of achieving the lowest cost and power consumption. In addition, the consistency of IGCT switching process is good, which can easily realize series and parallel connection, and further expand the power range.

In short, after adopting the buffer layer, transparent anode, reverse conduction technology and gate drive technology, IGCT stands out from the GTO, and replaces GTO in all medium and high voltage fields and applications with a power of 0.5M100MVA. IGCT frequency converters are all use. IGBT has fast switching performance, but its conduction loss is large in high-voltage frequency conversion, and analog device bookmark7 requires many IGBTs to be connected in series in series. For low-voltage IGBTs, the number of high-voltage IGBTs connected in series is relatively small, but the conduction losses are higher. The increase in the total number of components reduces the reliability of the inverter, increases the size of the cabinet, and increases the cost. Therefore, based on the mature technology of IGBT and GTO, the high-voltage, high-current variable-frequency speed governor has a concise solution-IGC. This optimized technology includes the redesign of GTO, which makes it an important design breakthrough. The new IGCT introduces fast, balanced commutation and inherently low loss. The main design features include a reliable anode design to achieve fast current leakage, low-loss thin silicon wafers that enable fast switching and integrated gate drivers that use high-power semiconductors.

Because IGCT has fast switching function like IGBT and low conduction loss like GTO, it is more reliable in various application fields of high voltage and large current. All components in the IGCT device are packed in a compact unit, reducing costs. IGCT uses a voltage source inverter, which has a simpler structure and higher efficiency than other types of inverter topologies. For a 4.16 kV inverter, 24 high-voltage IGBTs are required in the inverter. If low-voltage IGBTs are used, 60 are required, and if the same type of inverter uses IGCT, only 12 are required.

The optimized technology requires fewer components, and the number of IGCTs used in inverters of the same voltage level is only one-fifth of the low-voltage IGBT. Moreover, since the loss of IGCT is small and the cooling device required is small, the inherent reliability is higher. Fewer components also means smaller volume. Therefore, the inverter using IGCT is simpler and more reliable than the inverter using IGBT.

Buffer circuit, but IGCT itself can not control di / dt (this is the main disadvantage of IGCT), so in order to limit the rate of rise of short-circuit current, appropriate reactance is often in series in the actual circuit, as shown. The complete inverter consists of 11 components: 6 IGCT (with integrated reverse diode), 1 reactance, 1 clamp diode, 1 clamp capacitor and 1 resistor, a set of gate drive power. A 3MVA inverter is only 780mmx590mmx333mm in size, compact in structure, few components, high reliability and low cost.

The advantages of small effective silicon area, low loss, and fast switching ensure that IGCT can be used reliably and efficiently in 300kVA10MVA converters without the need for series or parallel connection. When connected in series, the inverter power can be expanded to 100MVA. Although high-power IGBT modules have some excellent characteristics, such as active control of di / dt and dv / dt, active clamping, and short-circuit current protection And active protection. However, due to shortcomings such as high conduction loss, low silicon effective area utilization rate, open circuit after damage, and no long-term reliable operation data, the practical application of high-power IGBT modules in high-power low-frequency converters is limited. Therefore, before the advent of high-power MCT, IGCT is expected to become one of the preferred power devices for high-power high-voltage inverters. The turn-off characteristics of the HB1 MCT device are on page 37) From the knowledge, the turn-on time of the MCT is only 200 ~ 300nS. From the knowledge, the turn-off time of the MCT is about S, and the main reason for the longer turn-off time is the choice The reason for the long life of the minority children in the P-type long base region.

Conclusion By comparing the structure, principles and internal laws of various foreign MCT devices, we have absorbed advanced foreign experience, combined with the existing process of Xi'an Microelectronics Research Institute, and successfully developed the 10A / 500VMCT chip. The method is feasible under the existing conditions in China. Turn-on characteristics of HD MCT devices

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