High-speed trains run fast, not by the front
In fact, the statement that we often say "take high-speed rail" is not rigorous, the full name of high-speed rail is high-speed railway, which refers to the rail line that can meet the requirements of high-speed trains.
The definition of high-speed is well understood, at present, the international usually think that more than 200km/h trains are considered high-speed trains, in China G trains are generally 250km/h~350km/h, D trains are generally about 200km/h, in fact, G and D cars are EMU trains.
What does EMU mean? An EMU is a fixed train consisting of several powered and unpowered cars.
This allows the train to distribute its weight more evenly and accelerate faster. The first German Siemens developed the first EMU train in 1903, which was driven by electric motors and ran at a speed of 210km/h in that year. It doesn't look like it could go that fast, but it's pretty impressive to think that it did so over a hundred years ago.
But today, more than 100 years later, China has built the world's longest high-speed rail line in operation, currently more than 36,000 kilometers, more than the rest of the world combined.
But today, more than 100 years later, China has built the world's longest high-speed rail line in operation, currently more than 36,000 kilometers, more than the rest of the world combined.
Now you should understand why the high-speed rail train is not running with the front?
Now let's take a closer look, who drives these powered wheels?
The high-speed rail is electrified and of course the motor drives the wheels. Which controls the speed of the motor?
This is the traction converter, the converter is divided into two parts, as shown in the figure below, the AC line on the left is the overhead wire above the roof of the car, also called the contact line, the voltage is 25kV high voltage alternating current. The pantograph on the roof of the car introduces high voltage into the transformer, as shown below.
After voltage reduction, the transformer is connected to the rectifier side (AC to DC) of the traction converter, and then the inverter side (DC to AC) is connected to the drive motor through the three-phase cable.
Some readers may not understand why the voltage has to change from AC to DC and then back to AC, this is not a fool, although the AC motor is driven by AC, but the speed of the motor is related to the AC frequency, and the fixed frequency of AC can not actively control the motor torque and speed. Therefore, the converter (also called frequency converter) is required to output AC power with specific frequency and specific voltage and current according to the real-time speed and torque requirements of the motor, so that the variable frequency drive motor can accurately control torque and speed smoothly. The principle of the converter output frequency conversion voltage and current is to change the direct current into the corresponding frequency and voltage current by controlling the duty cycle of the inverter bridge switch device.
What are the benefits of this, let's say the most intuitive feeling, you think back more than a decade ago when you took the green car, the start of the moment will not be a clanging rush, the experience is very bad, sometimes sleeping in the sleeper can be shaken out of bed. Today's high-speed trains accelerate so smoothly that you don't even know it's moving when you don't look out the window. This is the gap between the DC motor of the past and the AC variable frequency motor of today. In addition, most of the traction converters are four-quadrant rectification, which means that the energy of the train when braking at the station can be generated back to the grid, more energy saving.
Let's get back to traction converters.
What does this thing look like?
It is a large iron box hanging at the bottom of the car, and the installation position is shown in the following figure.
As shown in the figure above, the appearance of the traction converter is a large iron box, and the core unit inside the box, that is, the rectifier and inverter function part, is generally called the converter power component (blue block diagram). The core semiconductor device of the converter is the IGBT module in the red box in the figure above.
Talk about tractor-grade IGBT,
let's take a look at Infineon's tractor-grade IGBT.
These models in the figure below can be said to be the elders of the traction system, they belong to the IHV series, although their appearance is a little old fashion, more than 20 years have not changed, but their internal chip technology has been updated. The latest 3300V E4 chip products have begun mass production, in the size of 140mm*190mm, the internal integration of more than 2000A IGBT chip, and has a longer durability, strength to lead the IGBT industry.
As an innovative company, Infineon has not only old fashion, but also new fashion, which is the XHP series, a new high-power module package that can be flexibly assembled.
The future rail transit traction system, whether it is subway or high-speed rail, whether it is Si IGBT device or SiC MOSFET, can be modular design with the same package, which can greatly reduce the design workload and the type of procurement.
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