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News; DC/DC converter for EV industry introduction

Published: Thursday 19 May, 2016

The basic distribution of power electronics in new energy vehicles
Talk about this subject, is mainly wanted to mention the role of power electronics in the future of electrification and high power dc-dc in automobile electrical system to a key role, but also with this kind of inverter and vehicle safety has a directly related to the equipment have substaintial distinction, for the function of the vehicle safety, here temporarily not spread, actually 1 in different product added value, and is involved in core of vehicle safety has direct relationship, will affect the vehicle enterprise whether you want to put components made in-house parts.
Table 1 basic distribution of power electronics in new energy vehicles
So there are three types of DC-DC that we are involved in.
(1) high and low voltage converter (auxiliary power module)
The main function of this module is to replace the traditional 12V generator. As shown in Figure 1, the strong mixing the above system, the engine output power direct drive high voltage relay on the high voltage battery system repair electric, conventional 12V power load, is entirely dependent on the DC / DC transformer supply, so the traditional electricity load supply is implemented here. Such devices, almost all of the new energy vehicles will be applied, the power range from 1KW to 2.2KW, but also a core component of the 48V system in the future, will be carried out on this device.
Fig. 1 application environment of high voltage converter
Three types of DC-DC
2) 12V voltage stabilizer
12V voltage stabilizer, as shown in Figure 2, is mainly used in the part of the Start-Stop system (if it is possible, subsequent to Start-Stop will do a classification, the current European SS system has been widely used in the. In the starting process, if the use of a certain structure to prevent voltage fluctuations on some sensitive devices. Here's the sensitive load, mainly includes the user visible electricity load, such as the interior light and radio, etc.. The power level of the voltage regulator, with sensitive electrical load and decide, usually 200 ~ 400W. Overall, such devices power level is small, cost is relatively harsh, parts manufacturers in Europe earlier cut, this kind of device technology is already very mature.
Figure 2 12V voltage
3) high voltage booster
The high voltage booster, as shown in Figure 3 are shown to be a selective architecture, mainly some car companies, in order to improve the efficiency of the power system, to improve the bus voltage of the inverter input with a boost voltage booster. As a result, this part is integrated in the inverter, as part of the powertrain. This type of device, due to the specific parts under the condition, through the system design optimization of a byproducts, and not every vehicle enterprises, we need to choose, especially with increasing lithium electrochemical system voltage level, the device for common parts enterprises is not very good opportunity.
Figure 3 high voltage booster
History and performance evaluation of high and low voltage converter components
History of high and low voltage converter components
Because of the advantages in the field of magnetic materials and components, coupled with the cultivation of hybrid cars in Japan market more successful, with the simultaneous development of the Japanese automobile, the work in this field is relatively good is Japanese suppliers, such as TDK; its product line from generation to generation evolution as shown in the figure, products are mainly used in Honda's hybrid product line. The competition opponents Denso, Toyota industry products, used in the different Prius / Camry hybrid, in overall sales, is in the leading position, as shown in Figure 5. Other Japanese manufacturers such as Shindengen electric and the Nichicon, relying on the advantages of its components to squeeze into the automobile power electronic components market. The traditional automotive parts suppliers, such as Bosch, continental and Delphi, although cut in this area is not too late, but the characteristics of the components decided is difficult to rely on a single component to earnings, in low yield, the BOM cost will is very high, is not easy to enter. Other more successful in industrial power electronic Emerson and Delta Electronics, especially the latter relies on its industrial & Consumer Power Electronics share in the positive development of the market.
topological structure
DC-DC components mainly have the following technical indicators, as shown in table 2:
1 power rating: different levels of vehicles, often in the configuration there is a very large difference, resulting in the dynamic power requirements of the 14V system changes. In accordance with the concept of modular development, the choice of different power levels, to match the different levels of the vehicle, after the electrical balance, you can cover a lot of models. This is currently a more popular approach.
2 efficiency: the efficiency of this component is an extreme value. It not only determines the heat dissipation of the whole component, but also determines the life of the whole component. When evaluating the efficiency, it is often used to characterize the efficiency curve corresponding to the output current. The maximum efficiency of a single point is actually a very deceptive data.
3 Volume & Weight & power density: parts integration design, the current volume and weight of components have a demanding requirements, from the above graph, in these two indicators, the evolution is more rapid.
4. Cooling way: with most of the power electronic component, in about 2kW level, active air cooling and liquid cooling in two ways. The former is required for system air duct, which has the restriction on the arrangement of coolant lines. Even if the development of the available components, integrated in the vehicle, heat is also a big problem.5 cost: at present, the cost of this component is very strict, so the back of the bridge so the topology of the MOSFET need more, will be abandoned by people.
Figure 6 DC-DC component strategy based on Modular Development
topological structure
In the early stage, the DC-DC of the hybrid electric vehicle is based on the topology of the full bridge structure, as shown in Figure 7:
1 the application of the full bridge early in the large power electrical equipment is very common, so the early hybrid system to learn from.
2 wide input range: the full bridge circuit in a wide range of relatively good characteristics.
Disadvantages:
1 it is obvious that with more MOSFET, the cost is higher.
2 control is more complex, the general need to be independent of the control unit.
If you are interested can look at the evaluation system recommended by Infineon and ST, which itself is based on full bridge system modeled design. According to the limited information and information, the current development of the use of topology, but also learn from the use of industry experience, active clamp forward and 2 Stage DC change topology is worth trying.
A new topology of full bridge topology in Figure 7 and the current Prius Denso
DC-DC walls & bottlenecks
Wall & bottleneck
For this component, the advanced topology is not very high barriers, for the safety requirements of the electric car, the isolation design is a must. The design difficulty is:
1 Thermal Design: the DC-DC requires a good thermal design, need to design a good channel for liquid cooling.
2.EMC design: the need to design the input filter and the output filter to ensure that the EMC can pass, this is particularly critical in the application of the car.
3 efficiency: under different input voltage conditions, to achieve a higher efficiency curve.
4 protection function design: the design of various protection functions to match the entire input voltage curve, as well as the requirements of the 12V protection system.
5 manufacturing requirements: at least to be possible to meet the requirements of semi automation, so for the entire board level design and power circuit connections are more critical. If the amount of electrification can be developed in accordance with the hybrid power, the requirements of the future process becomes an important condition for the selection of suppliers.
In the country to do this component, the biggest challenge is to find a good car with magnetic components, to the Japanese manufacturers to buy is very difficult thing. From the point of view of the component level, there are several points of view:
Fig. 8 development of transformer
1 Transformers: car with a large power transformer 2KW, it seems that there is no domestic qualified suppliers, want to bypass this is not possible. The transformer design, itself is the entire power electronics inside a core thing, out of the characteristics of the product, a large part is derived from the material. According to the instructions of TDK, the transformer of the ferrite material "PC95" (PC95 ferrite core material), the raw material for Fe (iron), Mn, Zn (zinc), Fe ratio of mixed with the original product ("pc44", "PC45").
1) flat panel transformer: I first contact charger, Americans idea is to use flat transformer, the PCB and the process of demanding approach, of course, is a path, but the parameter difference risk directly contact with process technology.
2) integration: Denso description of the document which is the transformer and coil Chock together, according to the information of each show, this is not the idea of it. In my opinion, DC-DC hardware engineers sometimes only local materials, the device level breakthrough has not engineers selected a good plan so simple things.
2.MOSFET: can choose, only a limited number of, according to the performance of the situation, the choice is more limited. So the cost, high.
3 filter inductance: the situation is similar to the transformer, because the process is relatively simple, the main problem lies in the material.
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