Application of IGBT technology in flexible direct current transmission

In the past ten years, Insulated Gate Bipolar Transistor (IGBT) has made significant progress in terms of chip design, process, testing and device packaging technology, and the parameters and overall performance of the device have been significantly improved. Currently, The highest level of IGBT reaches 6500V/650A and 3300V/2000 A. The laboratory voltage and current levels are even more reachable. 8000V and 3800A. All kinds of power electronic devices using IGBT.
With the development of China’s power grid, especially wind power and solar power,The rapid development of renewable energy represented by electricity has greatly promoted electricity. The application scale and development process of new Internet technologies. Flexible DC transmission The new generation of power transmission technology represented by the The primary driving force for application acceleration in the force system, high pressure, large capacity, low Loss and safe working area will become the main development direction of IGBT.
To increase the capacity of IGBT, it is necessary to solve the problem due to the increase in voltage and current. The problems caused by IGBT chip manufacturing and packaging, the current domestic leaders. Requires device manufacturers to be positive for high-voltage and high-current IGBT. In the development of research and development, it is expected to be put into commercial use in the next few years with a view to Realize the localization of IGBT.

1 The evolution of IGBT technology
Since IGBT was invented in the 1980s, its surface structure
Structure (metal oxide Semiconductor (MOS)) and bulk structure (pressure-resistant layer and Collecting area) have experienced a series of relatively independent development and improvement. In terms of surface MOS structure, it has mainly experienced from planar grid to trench. The improvement of the trench gate, and the formation of the P-well surrounded by a simple P-well to an N-well. The evolution of the hole blocking layer is shown in Figure 1. In the figure, E and G points.

The trench gate structure borrows from the large-scale integrated circuit (LSI) process.The silicon dry etching technology in China realizes the on-state voltage and turn-off time, Between optimizations. The cell structure uses a more advanced wide cell. Pitch design and hole blocking layer. Typical examples include Hitachi Semi Conductor’s HiGT, Mitsubishi Semiconductor‘s CSTBT chip and ABB, The company’s EP process and other technologies.

In terms of body structure, IGBT has experienced a non-transparent collector area. Pass-through IGBT (PT-IGBT) to transparent collector area is not pass-through. IGBT (NPT-IGBT), and then to the transparent collector area PT-IGBT
Evolution, as shown in Figure 2. In the figure, C is the IGBT collector.

The punch-through technology has a higher carrier injection coefficient, but because it requires. Control the lifetime of minority carriers, causing its transport efficiency to deteriorate; Non-punch-through technology does not need to kill the minority carrier lifetime. Very good transport efficiency, but the carrier injection coefficient is relatively low. therefore. Non-punch-through technology is replaced by a new body structure containing a buffer layer for. This IGBT is now named by different suppliers, such as Infineon Company named it the field suspension IGBT (FS-IGBT), and the ABB company named it soft punch-through (SPT), but its basic principles are the same. At present, scientists are also developing a “reverse blocking type” (reverse blocking type) Function or a new concept with “reverse guided type” (reverse guided type) function IGBT research to further optimize the performance of IGBT.

In recent years, domestic IGBT scientific research and industrialization have experienced rapid progress Development . Especially low power used in induction cookers, household appliances, etc. IGBT has begun mass production. 1200V and above voltage level The research and trial of power IGBT have also made great progress. If used The 1200V IGBT for the inverter welding machine has been trialled. In particular, the original CNR was introduced into the sealing line from ABB, with a sealing The capacity of 1200~6500V IGBT module; the original China South Locomotive Successfully acquired British Dennis Co., Ltd. The Energy Internet Research Institute has successfully developed 1200V, 1700V and
3300V series of IGBT chips and development of smart grid applications. Research on packaging technology used. It is foreseeable that high voltage and high power.

2 The application of IGBT in flexible direct current transmission
With the rapid development of IGBT, DC transmission has been greatly promoted
The development of voltage source converter (VSC) and IGBT Basic flexible DC transmission technology. Flexible DC transmission technology is available Grid-connected renewable energy, distributed power generation, isolated power supply, large-scale. Power supply and other aspects of the city’s power grid Especially in wind power and
Power grids, offshore platforms and large-scale urban power grids, flexible and direct The comprehensive advantages of the current transmission system are more obvious. National Energy Administration refers to
During the “Twelfth Five-Year Plan” period, it is necessary to focus on solving large-scale wind power
The bottleneck problem of the source base grid connection. In order to solve the problem of new energy grid connection, Various countries have made many attempts. Experts said that flexible DC transmission
Electricity is one of the best ways to ensure the access to new energy sources. In 2006, domestic research and development of a flexible DC transmission system began; In 2011, China’s independent research and development of Shanghai Nanhui Wind Farm Flexible DC. The power transmission project is put into operation; In 2013, South Australia’s multi-terminal flexible DC transmission. The electricity project is put into operation, and the Zhoushan multi-terminal flexible DC transmission project is about to run. The flexible DC transmission technology relies on its excellent technical characteristics. It has the potential to replace the traditional DC and become the development direction of DC transmission in the future. At present, it is moving towards higher voltage, larger capacity, multi-terminal and networked.
Towards development. As the core equipment of flexible power transmission, high-voltage and high-power
There are currently three topologies for voltage source converter valves: based on IGBT devices. Direct series voltage source converter valve, series-based converter unit. Modular multi-level voltage source converter valve and crimp-based IGBT. Voltage source commutation combining device series and converter unit series Valve.
The application and difference of IGBT in different converter valve topologies. The topological requirements for IGBT characteristics are as follows.

1) Two-level
The two-level voltage source converter adopts series pressure connection type IGBT such As shown in Figure 3, it has the advantages of simple structure, easy engineering implementation and assembly. At the same time, the simplicity of the structure also improves the reliability of the overall system. The high, two-level circuit topology is the most common circuit topology. but the DC side voltage is high, multiple IGBTs need to be connected in series.
IGBT module series voltage equalization puts forward a test, so IGBT module is required. The parameter consistency is good, and the series voltage equalization of the modules is guaranteed. At the same time, in order to reduce
It is difficult to connect the devices in series, and higher requirements are put forward on the withstand voltage level of the devices. In addition, the short-circuit mode of the press-fit package is more conducive to series connection of devices.

2) Modular multilevel converter
Modular multilevel converter (MMC) is through a series of junctions. The sub-units of the same structure are cascaded by SM (half-bridge or full-bridge form), As shown in Figure 4. With the two-level or based on the IGBT series valve
Compared with three-level converters, MMC avoids IGBT series dynamics. The difficulty of equalization control is that it has modular characteristics and is easy to expand. Voltage, capacity, switching frequency and loss are lower. Therefore, in the MMC extension In bashing, IGBT chips with low on-state loss should be used. Shanghai Nanhui The converter stations at both ends of the HVDC Flexible Demonstration Project adopt the 49 level. The modular multi-level topology, this topology has been in the industry Achieved a high degree of recognition. But the number of switching devices increases by one. Times (the full bridge is doubled), the complexity of the control system is greatly increased, and at the same time It is also difficult to control the balance between the capacitor voltages of the sub-modules

3) Cascade two-level
In 2010, ABC Company proposed a new multi-level voltage, Source converter topology-cascaded two-level (CTL), its typical topology, As shown in Figure 5. The core idea is: Use crimping type with IGBT of short-circuit failure mode to improve sub-module reliability and simplify, Sub-module hardware design; Make IGBT valve-level control simpler. level Linked two-level VSC combines modular multi-level technology and IGBT,Series technology, with modular characteristics, easy to expand voltage and capacity, The switching frequency is low, the loss is small, the number of levels is small, and the control and protection system is simple. Especially suitable for higher voltage levels (±320kV) and larger capacity Of flexible DC transmission applications.

3 IGBT future development
With large-scale new energy power generation and grid-connection technology, large-scale storage
The development of energy technology, ultra-long-distance and ultra-large-scale power transmission technology
The voltage, power capacity and reliability of DC transmission equipment have been improved.
High demands. In order to adapt to the development of the DC grid in the future, its
The demand for higher voltage and larger capacity is proposed. IGBT in the future
Will be at the highest existing voltage (6500V) and current (2000A) base. On the basis of higher voltage (8000V) and current (30000 A to 4000A) direction development. At the same time, in the form of packaging, we have to adapt to
The need for high voltage and high current, and innovation.
In order to meet the needs of the future power grid, scientific researchers will The structure, process, and packaging of the company are continuously explored, and the following are expected to be presented. Development trends in several areas.
1) Exploration of new structure. Set N-type reasonably in the P collector area Short circuit point, combined with local lifetime control or P-well doping optimization, forms.The internal integration of fast recovery anti-parallel diodes, thus manufacturing the reverse guide. IGBT (RC-IGBT) or dual-mode IGBT (BiGT), make it in. Achieve greater current capacity and power capacity within a given package size,the amount.
2) Exploration of semi-super junction IGBT. Half super junction is super junction structure, A kind of change, through the P injection, N injection (the doping concentration of the two can be higher, Conventional N-two orders of magnitude) and N-Reasonable allocation of zones, the universe The radiation-induced failure rate can be reduced by 1 to 2 orders of magnitude. with At the same time, the structure can also resist dynamic avalanche, improve the on-state pressure drop and turn-off Loss, and its required process technology is not difficult. In addition, the semi-super
When the junction is used in the reverse-guided IGBT structure, it can also effectively reduce the output
Rebound of characteristic curve (Snapback) phenomenon.

3) Higher working temperature. The highest work of the current part of the device
The temperature has increased to 175°C. Increase the working temperature to 200℃
The possibility is being explored.
4) A more suitable packaging form. Welding type commonly seen at present
IGBT module, this type of package adopts single-sided heat dissipation, and the power of the device
The efficiency is limited, it is not easy to be connected in series and parallel, and is resistant to salt spray and vibration.
Poor impact and thermal fatigue performance. New type flat full crimping high-power IGBT
The device not only completely solves the problem that the welding process is prone to voids and welding materials
The problem of thermal fatigue of the material and low single-sided heat dissipation efficiency has also eliminated
Due to the thermal resistance of various parts, the volume and weight are reduced, greatly
Improve the work efficiency and reliability of IGBT, which is very suitable for future
The high-power and high-voltage power of the converter valve device in the flexible DC transmission system
High-reliability requirements, new flat-panel full crimping high-power IGBT device Parts will widely replace welded IGBT in flexible DC transmission systems Module.
In addition, the application of new materials will continue to mature, arsenic-doped buffer layer IGBT and silicon carbide IGBT will become important for future IGBT. Development direction to make products more adaptable to high frequency, high voltage and high power. Rate of application. Wide-gap Semiconductor devices represented by silicon carbide. Pieces are in the ascendant. Compared with traditional silicon devices, silicon carbide devices have. The following advantages.
1) The silicon carbide device has a high withstand voltage level, and there are currently 15kV

Progress in IGBT technology and its application in flexible DC transmission, According to the report of SiC IGBT, the highest withstand voltage can reach 24kV, this will Greatly reduce the number of devices in series in the DC transmission converter valve, it can Solution 6. 5kV silicon IGBT series devices that exist in this application
Many problems with low efficiency and low frequency.
2) The silicon carbide device has excellent switching performance.
There are only one tenth of similar silicon devices of the same voltage level,
The switching frequency of the device can be greatly improved.
3) The on-resistance of silicon carbide devices is only a few tenths of that of silicon devices
One, can greatly reduce the conduction loss.
4) Silicon carbide devices have high thermal conductivity and high temperature resistance. At present
The highest reported device junction temperature can reach 300 ℃, which can be greatly reduced
The power loss of auxiliary circuits and equipment reduces the need for cooling.
4  Conclusion
IGBT is currently the most advantageous in the field of power electronics, One of the power devices, more than 20 years from its inception to the present, IGBT in Constantly constant static and dynamic parameters such as voltage, current, switching loss, etc. Improvement, the continuous maturity of process and reliability technology, for its
The application of current transmission has created conditions for the improvement of the transmission capacity of the system, The stable operation of the power grid and the integration of new energy into the grid provide the possibility. Otherwise In addition, with the rapid development of the power system itself and the advancement of device technology. Step forward, scientists proposed “DC grid, DC microgrid and DC power consumption”
Waiting for new concepts, and the improvement and technical realization of these new concepts require more
Plus the support of high-performance IGBT technology