What are the key technologies of rail transit fuel cell/18650 lithium rechargeable battery hybrid power?

　　From April 24 to 26, the 9th China International Energy Storage Conference, hosted by the Energy Storage Application Branch of the China Chemical and Physical Power Industry Association, was held at the InterContinental Hotel in Hangzhou, Zhejiang Province. At the "Hydrogen Energy and Fuel Cell" special session on the morning of April 26, Dai Chaohua, associate professor and doctoral supervisor of Southwest Jiaotong University/National Rail Transit Electrification and Automation Engineering Technology Research Center, shared the theme report "Key Technologies of Rail Transit Fuel Cell/18650 lithium rechargeable battery Hybrid Power" at the meeting. The following is the transcript of the speech:

　　Dai Chaohua: Hello everyone! Our laboratory mainly focuses on new energy for rail transit, mainly in two aspects: one is that we consider energy storage for new energy such as solar energy and wind power as needed, and connect them to the electrified railway traction power supply system. The other aspect is on-board, rail transit on-board new energy, mainly focusing on the application of fuel cells, photovoltaics, lithium batteries, etc. on vehicles. In terms of fuel cells, we mainly consider high-power low-temperature proton exchange membrane fuel cells. Of course, we are also paying attention to high-temperature proton exchange membranes and low-temperature solid oxides, mainly considering the use of waste heat to improve the energy utilization rate of the entire system. Today, I will report to you mainly on the application of hybrid power systems composed of low-temperature proton exchange membrane fuel cells and lithium titanate batteries on rail transit vehicles in recent years.

　　This report will be made from three aspects. First, the research background. Hydrogen energy was included in Premier Li Keqiang's government work report for the first time, indicating that hydrogen energy will have a good development from the national level. In addition, the situation of industrial hydrogen production in our country, with an annual hydrogen production of 25 million tons, and the "three abandonments" of wind, light and water, about 100 billion kWh of abandoned electricity each year. If used for electrolysis to produce hydrogen, it can produce about 2 million tons, so our country has abundant hydrogen sources. In addition, in terms of rail transit, China has the most complex and largest railway network in the world, and the annual electricity consumption of electrified railways is more than 60 billion kWh. In addition, 30% of them use internal combustion locomotives. It can be seen that the energy-saving and emission-reduction pressure of rail transit is very large.

　　Fuel cells are efficient and environmentally friendly, and have a very good application potential in rail transit. Our team, especially our team leader Professor Chen Weirong, has been promoting the application of fuel cells in the following scenarios. The first is the intercity EMU, which is currently being developed. The other is the city EMU, which is a car with a speed of 120 kilometers per hour. Then there is the tram. We already have this fuel cell car. In addition, the station shunting and engineering operation car use fuel cells as their power, which is also a good choice. So our laboratory mainly focuses on the application of high-power fuel cells in rail transit. Professor Chen, the head of our team, has a point of view that fuel cells are more suitable for rail transit, so we have always been very confident that fuel cell rail transit will have a bright future. Of course, we also take into account other public transportation, special applications, etc.

　　Second, key technologies. The first key technology is the matching and simulation of the rail transit fuel cell hybrid system. System matching is to design the topology and parameters of fuel cells and energy storage based on lines, vehicles and operating indicators, so as to meet the constraints of real-time balance of power, volume weight, power performance, etc., so as to minimize the cost of the whole life cycle and maximize the system efficiency. After the matching is completed, the feasibility is verified through simulation, involving traction calculation, energy management, fault handling, etc.

　　The second key technology is the control of the fuel cell system. As you know, Toyota's buses and passenger cars have different hybrid system topologies and controls because of their different operating conditions. The operating conditions of rail transit are completely different from those of cars. There will be current fluctuations of thousands of amperes in a few seconds. Even if there is energy storage to track load changes, the bus voltage will still fluctuate violently, which has a great impact on fuel cells. Therefore, rail transit fuel cell system control is very important. We have been studying this for about ten years. Fuel cell system control mainly focuses on four control goals, which are to meet the power requirements of the load, improve efficiency, extend life, and maximize its response speed under permitted conditions. The factors that affect these four goals include temperature, pressure, humidity, and the dynamic spatial and temporal distribution of gas and vapor-liquid. Combined with the operating conditions of rail transit, how to carry out the control of the fuel system so that the above multi-physical fields and multi-temporal and spatial scales are evenly distributed to meet the realization of the four goals is our concern.

　　To study the control problem, system modeling is required. For the control on the cathode side, we focus on the optimal oxygen ratio, that is, OER, from the constant value optimal OER control to the curve optimal OER, and then to the regional optimal OER, mainly to reduce the power consumption of the air compressor itself, improve the efficiency of the system, and avoid the phenomenon of "oxygen starvation" or "oxygen saturation". In addition, some controls on the hydrogen supply side also follow the changes in load and couple with the cathode pressure to propose some corresponding control methods. In addition, in terms of thermal management, we also have multiple aspects of control, mainly for the coupling control between the circulation pump and the cooling fan, combined with the changes in load and the pressure changes of the positive and negative poles to carry out a comprehensive control to meet the temperature value and temperature balance, and strive to achieve the goal at the lowest cost.

　　In terms of rail transit, the topology of the entire system is slightly more complicated. For this reason, we have carried out various energy management strategy studies, combined with the working conditions of rail transit vehicles, and done some energy management work. The specific strategies will not be mentioned. Another aspect is fault diagnosis and health management. Now rail transit also has so-called intelligent and even autonomous control. How to perform online fault diagnosis, life prediction, etc. for rail transit vehicles when they are running fast. This is also one of our concerns.

　　In this regard, we have developed fuel cell systems and energy management controllers for rail transit. Unlike automobiles, controllers are based on single-chip microcomputers to reduce costs, while rail transit pays more attention to reliability, so we develop based on PLC. In addition, in terms of power batteries and energy storage, rail transit has very high requirements for safety. As you all know, the 7.23 accident had a huge impact. Safety is paramount to rail transit, so we will not consider using ternary or even lithium iron phosphate batteries for rail transit. At present, we only choose lithium titanate batteries, mainly based on its safety. We work with some battery manufacturers to develop energy storage systems specifically for rail transit. We mainly focus on high rates, because rail transit has a current change of thousands of amperes in a few seconds, so high rates are required. This train may run from south to north, and the climate changes greatly throughout the year, and it also requires good temperature applicability. The battery cell is in cooperation with Sichuan Guochuangcheng. Our school mainly does four major managements, namely thermal management, balance management, safety management and life management.

　　Let me report our research results below. We mainly focus on the work of fuel cells and power batteries in rail transit. Our projects, from national to ministerial to provincial, are all related to fuel cells and rail transit. This is the first fuel cell electric shunting locomotive in China developed by our team in 2013. It uses the shunting locomotive actually used in the subway. This is a fuel cell hybrid tram made in April 2016. The above is what the prototype looked like when it was developed. Now this car is in Tangshan, as shown in the picture below, painted red, and is intended to be used as a means of transportation for Tangshan's industrial tourism route. Now this car is ready to start another two years of operation. We have been doing this kind of experimental testing work. This is the layout of our car's energy storage and fuel cell system at that time. This is the video of the car when it came out.

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