Some new changes are taking place in the world's energy environment, which has brought new challenges to the construction of the power grid, and put forward new requirements to promote the improvement and innovation of the power grid. These challenges include:
Increasing photovoltaic power plants and wind power plants, these electrical energy is unstable
Carbon dioxide emission reduction promotes the development of new energy
Power network security
......
HVDC transmission is the best solution to solve these problems, and its characteristics are as follows:Large conveying capacity: 3 million kilowatts to 7 million kilowatts
Long distance of transportation: up to 3000 kilometers
High voltage level: 200kV~±500kV
The transmission corridor is narrow: the transmission density per unit line is 4 times that of AC, and the cost of the same power line is about 2/3 of AC.
Low power loss
Precise power flow control
Mature technology, more than 60 years
European and American countries have begun to start and strengthen the planning and construction of HVDC transmission grids: Europe plans to build a pan-European Super Smart Grid with HVDC transmission as the backbone around 2050 to comprehensively utilize Europe, North Africa and the Middle East. Renewable energy; the United States plans more than 40 flexible DC transmission projects by 2025 to achieve regional interconnection.
China's demand for HVDC transmission is also huge, mainly to improve the energy consumption structure, thus solving the smog problem in the central and eastern regions caused by thermal power. Several adjustment schemes are as follows:
Utilizing high-voltage direct current transmission to transport northwest solar and southwest water to eastern load centers
Constructing a flexible DC transmission network in North China-Northeast Wide Area to realize flexible grid connection of large-scale wind power
Development of offshore wind power by using direct current transmission technology
China Southern Power Grid Corporation has determined that the development of the West-East Power Transmission Network will focus on DC transmission technology. By 2030, the Guangdong receiving power grid will fall into 12 DC or even more, and Guangxi will fall into 5 DC or even more. .
With the further increase of the number of DCs at the receiving end, multiple DCs are fed in a concentrated manner, and the risk of AC and DC interaction between the receiving and receiving ends of the traditional DC is increased, and the operation difficulty is further increased. In addition, with the remoteness of the hydropower base, the AC grid connected to the DC transmitter is weaker, and the conventional DC faces more technical challenges, making research, design and equipment manufacturing more difficult.
Therefore, the development of flexible DC transmission technology is particularly important. The characteristics of flexible DC transmission are as follows:
Flexible DC is more common in Europe, including networking, power transmission, wind power access, back-to-back, etc.
The cost and loss of flexible DC transmission projects have been reduced, taking into account factors such as land occupation, and comparable with conventional DC transmission.
Flexible DC transmission is of great significance to the safety of the receiving power grid with multiple DC feeds, and is a strategic choice to change the development pattern of large power grids.
Flexible DC transmission converter valves use fully controlled power semiconductor switching devices, including plastic package IGBTs and crimp package IGBTs. The suppliers of crimped IGBTs are shown in Table 1 below:
IEGT is a special name for Toshiba high-power IGBT, IEGT (Injection Enhanced Gate Transistor), that is, a gate injection enhancement transistor. The blocking voltage generated by the conventional IGBT structure causes high conduction loss due to the impedance of the N-base region on the emitter side. Toshiba uses an IE structure to form high concentrations of holes and electron carriers on the emitter side N base layer, thereby reducing the saturation voltage drop Vce(sat).
Toshiba IEGT is available in two packages: PMI module package and PPI crimp package. Rongxin Huike has been using the IEGT in a crimp-type package. Therefore, the IEGT mentioned later refers specifically to the crimp-type package.
The crimp-on package is more suitable for flexible DC transmission converter valves. The main features are as follows:
High reliability comes from double-sided heat dissipation, the internal chip has no wire bonding, and the component is not cracked due to the layered structure formed by wire bonding.
Vacuum inside and inject inert gas to ensure long-term reliability
The traditional round package facilitates the flatness of the crimp
Convenient for series application of multiple devices
Ceramic enclosure package has better explosion-proof performance than PMI
Toshiba introduced the first IEGT product in 1995. So far, the current level is 400A~3000A, and the voltage level is 1700V~4500V.
Rongxin Huike successfully applied IEGT in flexible DC transmission converter valve
Flexible DC transmission converter valves use MMC VSC (Modular Multi-Level Voltage Source Converter) scheme, a total of 6 bridge arms, each bridge arm consists of multiple identical power modules connected in series, the advantages of this scheme Including: less harmonics, low frequency noise, low switching losses, etc. The power module circuit topology includes: a half bridge, a full bridge, a clamp double bridge, and the like.
Rongxin Huike has been developing power units based on Toshiba IEGT since 2008 and has successfully applied to many fields such as large-capacity inverters, large-capacity STATCOMs, and large-capacity flexible converter valves.
The main project performance is shown in Table 2 below:
Flexible DC transmission converter valves have very high reliability requirements. Therefore, Rongxin Huike has always insisted on using IEGT. Compared with plastic module IGBT (PMI), the reliability of IEGT is reflected in:
After the PMI fails, it presents an open state; after the IEGT fails, it presents a short circuit condition.
The PMI shell is made of plastic material, which is resistant to internal high temperature and high heat capacity and is easy to crack. The IEGT shell is made of ceramic and is not easy to crack.
The PMI has a short life due to the presence of solder layers and connecting wires that are prone to aging inside the device; there are no solder layers or wires in the IEGT.
The diode inside the PMI has a weak surge capability and cannot withstand the fault current generated by the DC side short circuit. IEGT externally equipped with a crimp diode can solve this problem.
Rongxin Huike uses a half-bridge power module in the South Australia multi-end flexible straight city station converter valve. The system schematic (Figure 1) is as follows:
Fig.1 Schematic diagram of multi-terminal flexible straight plastic city station converter valve half-bridge power module system
The schematic diagram of the half-bridge power module based on IEGT (Fig. 2) is as follows. T1 and T2 are Toshiba 85mm IEGT, there is no diode inside, and D1 and D2 are Infineon's 85mm diode.
Figure 2 Schematic diagram of half-bridge power module based on IEGT
IEGT power module design featuresThe design features of this half-bridge module are described in several aspects below.
Structure and thermal design
The IEGT used in this half-bridge module has no diode inside and is equipped with an Infineon diode with the same contact surface size. Two IEGTs, two diodes, and one thyristor, together with six heat sinks, are pressed into a string. On the left is the DC busbar and capacitor, and on the right is the power and control board. Both sides of the heat sink are capable of dissipating heat, and the temperature of the surface of the heat sink is uniform. The figure below is a schematic diagram of the structure layout (Figure 3):
Figure 3 Schematic diagram of the structure
Using a thyristor as a bypass switch
The thyristor is connected in parallel with the DC-side capacitor. When the power module fails, the thyristor is triggered. After the thyristor breakdown fails, the stable short-circuit failure mode can be maintained, that is, the conduction current can still be stabilized after the failure, so that a diode and a thyristor are formed. A stable current path, the bypass is successful. It is worth noting that the possibility of DC-side thyristor bypass is only possible with crimp IGBTs and crimp diodes. This program is the patented technology of Rongxin Huike.
Commutation analysis
For fully controlled devices, such as MOSFETs, IGBTs, IGCTs, when turned off, the current is switched to the corresponding freewheeling diode. In this process, voltage overshoot occurs across the IGBT. From a circuit analysis perspective, this The rush is caused by stray inductance in the commutation path. The voltage overshoot is proportional to the stray inductance and proportional to the rate of change of the current drop. The greater the voltage overshoot, the greater the turn-off loss and the higher the risk of electric field breakdown. Therefore, the stray inductance should be carefully evaluated in the design and should not be too large.
When the IGBT is turned on, the load current is switched from the freewheeling diode to the IGBT. Due to the reverse recovery current of the diode, the current overshoot of the IGBT is present, and the overshoot size is related to the rate of change of the on current.
Power consumption and junction temperature
When IEGT is working, it must open current, turn on current and turn off current. The internal semiconductor chip will heat up, and the heat needs to be conducted through the water-cooled heat sink in time, otherwise the chip will be overheated and damaged. Firstly, it is necessary to accurately estimate the heat generation (power consumption) according to the working conditions, and then calculate the temperature of the chip. Through proper and reasonable heat dissipation design, the chip temperature is guaranteed to not exceed the recommended maximum value of the device manufacturer, and the low failure rate is maintained. In the flexible system, there are different operating conditions such as rectification and inverter. The total power consumption of the power module and the power consumption of the single device are also different. In particular, the power consumption of the upper and lower arms is different. The upper and lower arm devices are in an asymmetrical operating state.
Prospects for flexible DC transmissionChina's flexible DC transmission has just started, its development speed is fast, and its prospects are good. It is expected to replace AC transmission and traditional DC transmission and become the mainstream transmission technology. The flexible DC transmission converter valve uses a fully controlled power switch IGBT. Compared to plastic package IGBTs and square crimp IGBTs, circular crimp IGBTs have significant advantages.
Toshiba's technical strength, device quality and engineering performance in circular crimp IGBTs are second to none, and as the largest customer of Toshiba IEGT, Rongxin Huike has been widely used in flexible DC transmission, high-power inverters, large-capacity STATCOM and other fields. IEGT devices have been used for more than 10 years, IEGT uses more than 25,000 pieces, and has more than 50 engineering projects, with customers all over the world.
Toshiba is the chief expert in the design and manufacture of IEGT on a global scale. Rongxin Huike is the chief application specialist of circular crimp IGBTs (including IEGT), and will join hands to create a better tomorrow.
Yuhai piezo materials include : hard piezo material, soft piezo material and lead free piezo material
Soft piezo material exhibits: larger piezoelectric constants, higher permittivity, larger dielectric constants, higher dielectric losses, larger electromechanical coupling factors, low mechanical quality factors, a lower coercive field, poor linearity, and is easier to depolarize. The ideal application of soft piezo materials is sensing needs. Yuhai soft pizeo materials are PZT-5, PZT-5H, PSnN-5 and PLiS-51.
Hard piezo material exhibits: smaller piezoelectric constants, lower permittivity, smaller dielectric constants, lower dielectric losses, smaller electromechanical coupling factors, high mechanical quality factors, a higher coercive field, better linearity, and is harder to depolarize. The ideal application of hard piezo materials is high power transducer needs. Yuhai hard pizeo materials are PZT-4, PZT-8, PCrN-4 and PBaS-4.
Yuhai company developped lead free piezo material BaTiO3 and apply for the Chinese Patent in 2011, to meet the needs of environmental protection in today's society.
Piezoelectric ceramic material
Properties and Classification
General description of material properties
Material Code
Properties
Application
Soft PZT ceramic
PZT-51
Characteristics:
larger piezoelectric constants, higher permittivity, larger dielectric
constants, higher dielectric losses, larger electromechanical coupling
factors, low mechanical quality factors, a lower coercive field, poor
linearity, and is easier to depolarize.
low-power ultrasonic transducers
PZT-52
low-frequency sound transducers
PZT-53
applications with high g coefficient, for example,
PZT-5H
microphones,vibration pickups with preamplifier
PLiS-51
low-frequency vibration measurements
PMgN-51
Hydrophones, transducers in medical diagnostics
PSnN-5
Actuators
Hard PZT ceramic
PZT-41
Characteristics: smaller
piezoelectric constants, lower permittivity, smaller dielectric
constants, lower dielectric losses, smaller electromechanical coupling
factors, high mechanical quality factors, a higher coercive field,
better linearity, and is harder to depolarize.
PZT-42
High-power acoustic applications
PZT-43
Hydroacoustics, sonar technology
PZT-82
piezomotor
PCrN-4
PBaS-4
Lead free piezo ceramic
BaTiO3
Characteristics: Low density, low curie temperature, lead free.
Ultrasonic transducers suitable for low-temperature underwater, for example ultrasonic transducer in fishfinder
Piezoelectric Material,Piezo Ceramic Element,Piezo Electric Cylinder ,Piezo Sphere
Zibo Yuhai Electronic Ceramic Co., Ltd. , https://www.yhpiezo.com