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In recent years, railway gets accelerated development, and has grateful achievement, especially in high speed train. In order to reach the level of developed countries’ rail traffic, we still need do more research in technology.
As electric traction gets incomparable advantages than traditional internal-combustion engine traction and steam engine traction—high power loss, high speed, high energy utilization rate, few environment pollution. Nowadays, the traction system of diesel locomotive、electric motor car、high speed train all use electric drive.
There are two ways of traction drive: (1) A.C.- D.C. drive, in this kind of drive, the function of traction converter is transforming the A.C. to D.C. by 4-quadrant rectifier, controlling every D.C. machine through adjusting voltage of D.C., it belongs to voltage-source speed governing. (2) A.C.-D.C.-A.C. drive, traction converter output A.C.to D.C. with four-quardant rectifier, D.C. output to A.C. which voltage and frequency can be adjusted, it belongs to frequency control. The characters of D.C motor are: electricity exchange problem, big volume, big weight, short service time, complex structure, high price, and also, the examine and repair is also complex. In a word, there is small to improve with speed with D.C. The characters of A.C motor are: small voltage, small weight, long service time, simple structure, relatively lower cost. So high speed train transmission usually use A.C.-D.C- A.C to adjust the speed.
The traction converter mainly uses IGBT as electrical components. IGBT is an electrical component close and open with high frequency, it consumes electric energy and changes electric energy to heat. Normally, the electricity to IGBT is very large and the frequency of open and close is very high, so the wastage of the device is very large. If the heat can’t be dissipated timely, the inter temp of IGBT may up to 125℃, IGBT may break with this high temp. there is data shows that the temp of the electrical component rise every 2℃, the reliability goes down 10%; life time is 1/6 of temp rise 25℃ when the temp rise is 50℃. Therefore, to ensure the IGBT’s performance, we need to dissipate the heat quickly and timely.
IGBT water cooling theory: water cooling is a closed liquid recycle system, water-glycol goes to the base plate through cooling pipe, circulatory water takes the heat away produced by power module, and then water pump suctions the mixture liquid to the air-water heat exchanger, put the heat to the environment.
Cooling system structure:
High speed traction invertor IGBT water cooling system strusture
Heat sink 2 fan 3. Electronic component 4. Cooling plate (medium and micro channel included)
The medium in the cooling plate is as shown:
Whether the heat produced by IGBT can be dissipated timely and effectively, depends on the contact surface between IGBT and cooling plate, and the lower the temp is, the better of the performance will be.
we can know from the Newton cooling formula:
Q stands for the heat of IGBT
h stands for surface coefficient of heat transfer
s stands for the contact surface between IGBT and cooling plate
tw stands for the wall temp between the IGBT and cooling plate
stands for the liquid temp
The reduce of can cause the decline of, but if the power loss of IGBT remains, there is little room change the
The increase of can cause the decline of, but in fact the limitation of weight and space, also the requirement of high speed train, there is small room to enlarge, which makes the limitation of the decline of
The decline of cooling liquid can cause the decline of,but the declice of cooling liquid is limited by climate, out temp, the exchange of heat transfer and fan,which makes the effect unsteadiness.
The improvement of heat transfer coefficient of can reduce , and there is no limitation, so it can reduce efficiently.
In conclusion, when gets to the highest, is the lowest, so the wall temp of IGBT is the lowest, the performance of IGBT will be more safe and reliable.
Therefore, the key point is how to get the biggest surface heat transfer coefficient.
In order to get surface heat transfer coefficient , we need to measure the area between the heating area and cooling plate ,measure the unit: m²;test the temp of heating area; the input temp of cooling liquid, output temp ,calculate by，then get the temp of cooling liquid ，unit ;to warm the heat area we use D.C.to power on, use ammeter and voltmeter to test I and U,，calculate power loss through P=UI，Q=P ，Q，unit is：W。finally, use formula：
(2)We can calculate surface heat transfer coefficient h 。
In order to get the biggest heat transfer coefficient, we adapt micro channel as liquid channel, the inner structure of micro channel is as shown:
Experimental system is as shown:
The system includes one thermostatic water tank, one electric water pump, one water purification installation and water supply system, one glycol supply system, two DC power systems (two voltmeters, two ammeter, two slide resistance, two lights and several wire), two heat sources, one cooling plate(with medium and micro channels), two data collecting board, one computer.