Is the vehicle controller in the battery pack?

No. Vehicle controller (VCU) is the brain of electric vehicle, which is equivalent to Windows of computer and Andrio of mobile phone. As the operating platform of all electric vehicles, its performance directly affects the performance of other electrical properties, and it is one of the decisive factors of vehicle performance.

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1

Structural composition

VCU is structurally composed of a metal shell and a set of PCB circuit boards.

Hardware composition

Functionally, the minimum system consists of the main control chip and its peripheral clock circuit, reset circuit, reserved interface circuit and power module.

In addition to the minimum system, it is generally equipped with digital signal processing circuit, analog signal processing circuit, frequency signal processing circuit and communication interface circuit (including CAN communication interface and RS232 communication interface).

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2 How does each electrical appliance cooperate with VCU?

Some signals used to monitor the state of the car body or more importantly, switch signals, analog signals and frequency signals in vehicle-mounted components are directly transmitted to VCU through sensors without passing through CAN bus.

Other electric vehicles with independent systems generally transmit information through CAN bus.

2. 1 Direct transmission signal

The switch signals mentioned here include: key signal, gear signal, charging switch, brake signal, etc.

Analog signals generally include: accelerator pedal signal, brake pedal signal, battery voltage signal, etc.

Frequency signal, such as electromagnetic signal of vehicle speed sensor.

The output switch value, contactor and precharge relay on the power battery power supply circuit are controlled by VCU on some models.

2.2 Electrical unit interacting through CAN

The communication participants on CAN bus have no master-slave status and send information to the bus anytime and anywhere. The order between messages is determined by the priority of the sender. Priority has been stipulated in the communication protocol, and each message has the address code of the sender;

The information coding in communication is clearly defined by the corresponding communication protocol. Who sends out what kind of code and provides what kind of information is mainly based on the agreement between the supply and demand sides. For example, the address code of the electrical unit in the table below comes from the technical agreement between the vehicle manufacturer and the VCU supplier.

CAN fault record is the best helper for maintenance and debugging personnel. The following figure shows the provisions on fault codes in communication protocols, in which common fault types are included. As long as you compare the protocol table, everyone can see the fault record.

Except for systems related to charging and replacing electricity. Due to the strong demand for universality, communication protocols need to be unified, and unified coding has national standards (the relevant national standards are listed below).

2.2. 1 VCU and power battery system

Power battery is the only power source for pure electric vehicles. VCU communicates with battery management system (BMS) through vehicle CAN bus.

The parameters that the power battery pack monitors and reports to VCU in real time include: total current, total voltage, maximum battery voltage, minimum battery voltage, maximum temperature, SOC (state of charge) of the battery pack, and some systems also monitor SOH (state of health) of the battery pack.

The commands sent by VCU to the battery pack include charging, discharging and switching commands.

Charging, after the initial charging connection signal is confirmed, the whole vehicle is in a non-driving state, and VCU hands over control. The whole charging process is completed by the battery management system (BMS) and the charger * * * until the charging is completed or interrupted, and the vehicle control right is returned to VCU.

Discharge, VCU calculates the power demand of the vehicle according to the driver's intention, converts it into current demand, and sends it to BMS. BMS determines the supplied current value according to its own SOC, temperature and system design threshold.

When the thermal management system needs to use resources other than the battery pack, it needs the battery pack to cooperate with VCU to turn on and off management processes, such as compressor system and coolant circulation system. If the thermal management process only involves the electricity inside the battery pack, such as turning on the built-in PTC, heating the heating film, or turning on the fan to cool down, then this information can only be processed inside the battery pack, but not communicated with the VCU.

Switch command, before the start of charging and discharging, VCU controls whether the vehicle high-voltage system is powered on, which is realized by controlling the main circuit contactor of the battery pack. In case of emergency during vehicle operation, VCU will judge whether to close or disconnect the main loop contactor.

2.2.2 VCU and motor and its controller

The instructions sent by VCU to the motor controller include three parts, namely, motor enabling information, motor mode information (regenerative braking, forward driving and reverse driving) and motor torque in corresponding modes;

The motor controller reports various parameters and fault alarm information of the motor and controller to VCU. The main parameters include motor speed, motor torque, motor voltage and current.

VCU and charging system

Charging system includes vehicle charger, off-vehicle charger and generalized power exchange system. The charging and replacing system (here "charging" mainly refers to the off-board charger) needs a unified communication protocol to achieve maximum versatility. The following national standards are the latest version.

Communication Protocol between GBT 27930-20 15 Off-board Conductive Charger of Electric Vehicle and Battery Management System

GB∕T 32895-20 16 communication protocol for quick-change battery box of electric vehicle.

GBT 32896-20 16 communication protocol for electric vehicle powertrain.

The standard uniformly stipulates the billing process, including specific communication codes and communication sentence contents.

From the physical connection between the charging gun and the charging interface on the vehicle, the information exchange in the whole charging process is carried out between the battery management system and the charger, and no longer through VCU.

2.2.4 VCU and braking system

The electric vehicle with compound braking system needs to comprehensively consider the coordination of hydraulic braking system, motor braking system and anti-lock braking system (ABS), and then needs to have its own management system, which is called Brake Management System (BCU). BCU CAN be independent of VCU, communicate only through CAN, or integrate its functions into VCU.

According to the opening of the brake pedal and the speed at which the opening changes, VCU calculates the braking demand torque of the vehicle and transmits it to BCU. BCU makes specific torque distribution according to the specific state of the vehicle.

For medium-speed general braking, directly cut into the motor energy feedback braking, and recover the braking energy as much as possible;

When the vehicle speed is high, the driver suddenly steps on the pedal and needs emergency braking. Then BCU will start the hydraulic braking system first, and then introduce energy feedback braking after the deceleration state is stable, and gradually increase the proportion.

When driving on ice and snow roads, BCU will introduce ABS and set it as the highest priority to ensure the normal and safe driving of vehicles.

2.2.5 VCU and intelligent instruments

Electric vehicle dashboard, combined with the original layout of traditional vehicles, the national standard GB/T 19836-2005 puts forward requirements for display content, as shown in the following table.

The principles of high-end and low-end intelligent instruments are quite different. We only take one form as an example.

The instrument system is connected with VCU through CAN bus, and obtains data from VCU for display. After the data is transmitted to the instrument controller, the signal processing circuit restores the information to the display content of each instrument.

The previous generation of pointer instruments need to use stepping motor as the medium to convert the obtained data into the power to drive the pointer to rotate. A slightly advanced liquid crystal display can be displayed on the display screen in real time directly through information processing without driving a stepping motor. The following is the hardware design block diagram of intelligent instrument for perceptual knowledge only.

3 Detailed description of typical working conditions

As the core of the vehicle, VCU controls and monitors every movement of the vehicle. The process of vehicle control is to compare several related parameters according to different operation modes. What kind of operation mode the car will perform when the parameters belong to which range.

Vehicle working modes are generally divided into neutral mode, normal driving mode, braking mode, fail-safe mode, starting mode and charging mode.

The following is a rough description of the working process of the vehicle according to its different working modes.

3. 1 startup mode

The most important feature of this mode is that after entering the starting mode, if the vehicle is on a horizontal road, it will start driving at a smaller speed; If the vehicle is on a slope, the vehicle will at least remain stationary. This is a special design of the startup mode. In this mode, the motor automatically outputs a basic torque without stepping on the accelerator pedal to prevent slipping.

3.2 Normal driving mode

Refers to the normal operation of the vehicle, including acceleration, deceleration and reversing. In this process, VCU continuously monitors the current, voltage, temperature and other parameters of various electrical systems, as well as the vehicle's own speed, slip rate and other driving parameters. Identify the driver's intention, and calculate the driving torque of the motor and the output power of the battery according to the opening of the accelerator pedal and the change rate of the opening.

3.3 Braking mode

Depress the brake pedal to start the braking mode. VCU analyzes the opening of the brake pedal, the change rate of the opening and the vehicle speed, and calculates the braking torque according to the vehicle parameters. Command the brake controller to make the most reasonable braking torque distribution scheme (the main body providing braking torque includes hydraulic braking system and motor recovery braking), and whether to start the ABS leading braking process first. Safe and effective realization of the driver's braking intention.

3.4 Fault Protection Mode

During the operation of electric vehicles, faults in the system are defined as several levels.

The lowest fault level generally only reminds the driver. For example, the battery temperature reaches 50℃; ;

The vehicle with the highest fault level will be forced to stop in a relatively short time, for example, a system insulation fault is detected.

The middle fault will not force the stop, but it will limit the driving state of the vehicle. For example, if the battery SOC is lower than 30%, drive at the speed limit. At this time, the power battery system has been unable to output rated power and can only work with less power.

3.5 neutral mode

There is no mechanical connection between the motor and the transmission system of the vehicle, and the motor is suspended and will not output any torque.

3.6 charging mode

After the physical connection between the charging gun and the vehicle-mounted charging socket is confirmed, the auxiliary power supply is powered on, and handshake messages are sent to each other to complete insulation detection.

Handshake completed, parameters confirmed. The charger sends the message of the maximum output capacity of the charger, and the BMS confirms whether it can be charged at the maximum capacity. If it cannot, it sends the maximum accepted capacity of the battery pack.

Enter the formal charging stage. In this process, the charger and BMS send status information to each other in real time, and BMS sends demand parameters regularly.

At the end of charging, the judgment conditions are different according to the different settings of BMS. Generally speaking, in the last constant voltage stage of charging, the current decays to a set value or a set rate, which means that the battery pack is full and the charging process can be ended.

In this process, if any party fails, such as over-temperature and over-current, the charger will give an alarm. Depending on the fault level, some will terminate directly, and some will wait for human processing.

5 development process

In the automobile industry, V-mode development has been recognized as an efficient mode, and the development process of VCU generally follows this process. The following is a general V-mode development flow chart.

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The concept of V-mode development is to make software design achieve the goal of high efficiency and high quality through cooperation. The horizontal direction of the model emphasizes the timeliness and applicability of verification. The general experience is that at the bottom of the "V", the basic work is to use white box testing. The higher the level, the more complex the system is, and the black box is often over-tested.

Development process of vehicle controller.

Firstly, according to the requirements of refining, a mathematical model is established and simulated.

Then download the model data to the rapid prototype and replace the logical interface in the original model with the hardware interface;

Next, professional software is used to generate C code, which is integrated with the underlying program and downloaded to the hardware of the vehicle controller through the interface program to prepare for debugging. In this process, each functional module will be debugged separately;

The next step is hardware-in-the-loop simulation test, which simulates the vehicle running environment and tests the function of VCU.

Finally, VCU loads the vehicle, evaluates the real vehicle, and completes the calibration of communication protocol. After the evaluation, the first version of the product was obtained.

Six major manufacturers

The vehicle controller of pure electric vehicle, the major automotive electronic components giants are the main bodies of foreign manufacturers, such as Delphi, Continental, Bosch Group and so on.

In China, some automobile companies tend to develop their own vehicle controllers, such as BYD, Changan, SAIC, Yutong and Jinlong, all of which are self-operated. In addition, the main suppliers of VCU are some motor manufacturers, such as Ocean Electric, Founder Electric and Huichuan Technology.

Vehicle controller performance, main control chip and system integration are the main bottlenecks for domestic manufacturers to improve performance.

Composition and design flow of thermal management system for power battery