Design of power battery system for heavy electric commercial Vehicle

2022-05-02 0 By

As the core component of electric commercial vehicle, it is very important to design and match power battery reasonably.The design method of power battery system for heavy commercial vehicle is described in this paper.1 Basic performance parameters of power battery system 1.1 Rated voltage and Operating Voltage Range For rated voltage of power battery system of electric heavy commercial vehicles, refer to voltage Grade of High Voltage System of Electric Vehicles (GB/T31446-2015) and GENERALLY choose DC576V.Generally, the upper limit of the allowed voltage range is 115% to 120% of the rated system voltage, and the lower limit is 75% to 80% of the rated system voltage.The rated voltage and voltage range of the power battery system must be compatible with the driving motor selected by the vehicle, the voltage platform of the motor controller and the upper and lower limits of the working voltage, and the highest working voltage is not greater than the highest voltage allowed by the charger.1.2 Total Energy and Battery System Capacity Starting from the vehicle weight, power system configuration, typical working conditions, according to the continuous driving distance requirements, simulation calculation of the energy Q0 required to carry the power battery, combined with the SOC range available to the power battery (20% ~ 100%), preliminary calculation of the total energy:According to the load power requirements of the driving motor, steering, air compressor, air conditioner compressor, PTC, DC/DC selected by the vehicle, the initial calculation of sustained power Pc0, peak power Pk0, combined with the high voltage distribution unit, the efficiency of the motor controller η, the discharge rate of the battery system (sustained Mc=0.7 ~ 1,Peak power: Pk=Pk0/(Mc·η) kW Because Pc≤Pk, the total energy Q of the initial selection of power battery is: Q=Max(Qt, Pk)kWh battery system capacity = total energy/system rated voltage.1.3 Single battery capacity selection and System Group Matching According to the system capacity, combined with the positive and negative electrode material system, existing mature product specifications, select a reasonable single battery capacity and system parallel scheme;Calculate the number of batteries in series based on the rated battery system voltage n= Rated battery system voltage/Rated battery voltage.Due to the selection of the single battery that has been finalized, the total energy of the group may be different from the total energy of the required battery.Therefore, in the selection of single battery capacity must be through accounting, select the combination of the most close to the expected total energy of the single battery.Due to the requirements of mass and energy density of battery system and the limitation of the installation space of the power battery system on the vehicle, it is equally important to choose the battery box with high mass and volume energy density.1.4 Charging Scheme Heavy commercial vehicles generally adopt DC fast charging mode. Single gun or double gun charging can be selected according to the requirements of electric quantity and charging time of the vehicle.The DC charging protocol is implemented in accordance with the Communication Protocol between Non-on-board Conductive Charger and Battery Management System of Electric Vehicles (GB/T27930).The power battery system used for heavy commercial vehicles is a high-voltage and high-current circuit. If the high-voltage circuit has insulation failure, short circuit, leakage and other circumstances, it will cause serious safety accidents.This paper analyzes the selection and design of high-voltage cable and high-voltage connector, so that the high-voltage connection can not only ensure the driving demand of the vehicle, but also meet the safety of the vehicle operation.2.1 Selection and Design of high-voltage connectors The function of high-voltage connectors is to ensure the safe and reliable connection between cables and electrical components.The selection of high voltage connectors for power battery system has the following requirements.2.1.1 Electrical Performance In order to adapt to the working conditions of high voltage and high current, the connector adopts high-density contact plate and terminal surface silver plating technology to increase the contact area of the connector and reduce the impedance.Voltage resistance should reach DC(2×U+1000)V, U is the rated voltage of the power battery system.2.1.2 Environment and protection Performance The operating temperature is -40℃ ~ 125℃.Meet the requirements of IPXXB, prevent the high pressure part from contacting with personnel;Meet the function of IPX7, ensure the performance of the vehicle under severe conditions such as wading.Flame retardant should reach ULV0 grade.2.1.3 Mechanical properties The connectors shall meet the vibration and impact resistance of the vehicle standard, with secondary locking and anti-misinsertion functions, and meet the requirements of insertion force and insertion times.2.2 high voltage cable conductor of current-carrying capacity according to joule’s law, wire based on heat balance principle, the heat generated by the conductor surface reaches its steady state, the heating power is equal to the heat dissipation power: the electrical connection in the 3 power battery power battery system the electrical connection in the form shown in figure 1, including high voltage electric system, low voltage electrical system, and local bus controller, etc.The design principles of the electrical architecture of the high voltage system are as follows: (1) Each high voltage component should have independent power supply control as far as possible to ensure that the parts that do not work are not charged.(2) Parts with similar working characteristics should share one contactor as far as possible to reduce the number of contactors.③ Parts with similar power levels share fuses as far as possible to reduce the number of fuses.④ Minimize electrical interfaces outside the power battery system.4 Thermal Management Battery thermal management system is a good solution to reduce the thermal problems related to batteries, and is one of the key technologies to ensure the performance, safety and life of batteries.The internal temperature of a battery system has a great impact on the reliability, life and performance of the battery. Therefore, it is very important to keep the temperature of the battery within a certain range.To achieve this requirement, mainly through cooling, heating and insulation to achieve.Liquid cooling scheme is generally used for the cooling of commercial vehicle power battery, and electric heating film scheme is generally used for heating.It is very important to optimize the performance of power battery to adopt reasonable heating and cooling strategy according to charging and driving conditions.5 Power battery system layout Heavy commercial vehicles have a large power demand. In addition to considering the layout space, it is also necessary to arrange power batteries reasonably according to vehicle types and operating conditions.At present, it is more common to arrange the power battery in the rear of the cab on the frame longeron, arranged in the frame left and right lateral longeron, arranged in the inside of the frame longeron.The above arrangement can also be applied in combination to make reasonable use of space and expand electricity.The advantages and disadvantages of various layout forms and recommended application models are shown in Table 1.Through the introduction of the design method of heavy commercial vehicle power battery system and the verification of the practical model application, it can provide reference for the design of pure electric, hybrid and extended range fuel cell commercial vehicle power battery system.Article source: Shaanxi Heavy Duty Vehicle Co., LTD