An article analyzing the composition and principle of vehicle controller

The vehicle controller is the control center for the normal operation of electric vehicles, the core component of the vehicle control system, and the main control component for the normal operation, regenerative braking energy recovery, fault diagnosis and processing, and vehicle status monitoring of pure electric vehicles. The vehicle controller consists of two major components: hardware and software . Its core software and programs are generally developed by manufacturers, while automotive parts suppliers can provide vehicle controller hardware and underlying drivers. At present, foreign research on pure electric vehicle vehicle controllers is mainly focused on pure electric vehicles driven by wheel hub motors . Pure electric vehicles with only one motor are usually not equipped with a vehicle controller, but use a motor controller to control the vehicle. Many large foreign companies can provide mature vehicle controller solutions, such as Continental, Bosch , Delphi, etc.

1. Composition and Principle of Vehicle Controller

The vehicle control system of pure electric vehicles is mainly divided into two schemes: centralized control and distributed control. The basic idea of ​​the centralized control system is that the vehicle controller completes the acquisition of input signals alone, analyzes and processes the data according to the control strategy, and then directly issues control instructions to each actuator to drive the normal driving of the pure electric vehicle. The advantages of the centralized control system are centralized processing, fast response and low cost; the disadvantages are complex circuits and difficult heat dissipation. The basic idea of ​​the distributed control system is that the vehicle controller collects some driver signals and communicates with the motor controller and battery management system through the CAN bus at the same time . The motor controller and the battery management system transmit the collected vehicle signals to the vehicle controller through the CAN bus. The vehicle controller analyzes and processes the data based on the vehicle information and combined with the control strategy. After receiving the control instructions, the motor controller and the battery management system control the motor operation and battery discharge according to the current status information of the motor and battery. The advantages of the distributed control system are modularity and low complexity; the disadvantage is relatively high cost. The schematic diagram of a typical distributed vehicle control system is shown in the figure below. The top layer of the vehicle control system is the vehicle controller. The vehicle controller receives information from the motor controller and the battery management system through the CAN bus, and sends control instructions to the motor controller, the battery management system and the vehicle information display system. The motor controller and battery management system are responsible for the monitoring and management of the drive motor and power battery pack respectively , and the on-board information display system is used to display the vehicle's current status information, etc.

Schematic diagram of a typical distributed vehicle control system The figure below is a schematic diagram of the composition of a pure electric vehicle controller developed by a company . The hardware circuit of the vehicle controller includes microcontroller, switch quantity conditioning, analog quantity conditioning, relay drive, high-speed CAN bus interface , power supply and other modules.

Schematic diagram of the vehicle controller for a pure electric vehicle developed by a company

(1) Microcontroller module The microcontroller module is the core of the vehicle controller. Considering the functions of the vehicle controller of a pure electric vehicle and the external environment in which it operates, the microcontroller module should have the characteristics of high-speed data processing performance, rich hardware interfaces, low cost and high reliability.

(2) Switch quantity conditioning module The switch quantity conditioning module is used for level conversion and shaping of switch input quantities. One end of the module is connected to multiple switch quantity sensors , and the other end is connected to the microcontroller.

(3) Analog quantity conditioning module The analog quantity conditioning module is used to collect the analog signals of the accelerator pedal and the brake pedal and transmit them to the microcontroller.

(4) Relay driver module The relay driver module is used to drive multiple relays. One end of the module is connected to the microcontroller through a photoelectric isolator, and the other end is connected to multiple relays.

(5) High-speed CAN bus interface module The high-speed CAN bus interface module is used to provide a high-speed CAN bus interface. One end of the module is connected to the microcontroller through an optoelectronic isolator, and the other end is connected to the system high-speed CAN bus.

(6) Power module The power module provides isolated power for the microprocessor and each input and output module, monitors the battery voltage, and is connected to the microcontroller. The vehicle controller manages, coordinates and monitors each link of the electric vehicle power chain to improve the energy utilization efficiency of the vehicle and ensure safety and reliability. The vehicle controller collects the driver's driving signals, obtains relevant information about the drive motor and power battery system through the CAN bus, analyzes and calculates, and gives motor control and battery management instructions through the CAN bus to achieve vehicle drive control, energy optimization control and brake energy recovery control. The vehicle controller also has a comprehensive instrument interface function that can display vehicle status information; has complete fault diagnosis and processing functions; and has vehicle gateway and network management functions.

2 Basic functions of vehicle controller

The vehicle controller collects driving information such as accelerator pedal signal, brake pedal signal and gear switch signal, and receives data from the motor controller and battery management system on the CAN bus. It analyzes and judges this information in combination with the vehicle control strategy, extracts the driver's driving intention and vehicle operation status information, and finally issues instructions through the CAN bus to control the operation of each component controller to ensure the normal driving of the vehicle. The vehicle controller should have the following basic functions.

(1) Function of vehicle driving control The drive motor of an electric vehicle must output driving or braking torque according to the driver's intention. When the driver steps on the accelerator pedal or the brake pedal, the drive motor must output a certain driving power or regenerative braking power. The larger the pedal opening, the greater the output power of the drive motor. Therefore, the vehicle controller must reasonably interpret the driver's operation; receive feedback information from each subsystem of the vehicle, provide decision feedback to the driver; and send control instructions to each subsystem of the vehicle to achieve normal driving of the vehicle.

(2) Network management of the whole vehicle The vehicle controller is one of the many controllers in an electric vehicle and a node in the CAN bus. In the network management of the whole vehicle, the vehicle controller is the center of information control and is responsible for the organization and transmission of information, monitoring of network status, management of network nodes, and diagnosis and processing of network faults.

(3) Recovery of braking energy An important feature that distinguishes pure electric vehicles from internal combustion engine vehicles is the ability to recover braking energy. This is achieved by operating the motor of the pure electric vehicle in a regenerative braking state. The vehicle controller analyzes the driver's braking intention, the power battery pack status, the drive motor status and other information, and combines the braking energy recovery control strategy to send motor mode instructions and torque instructions to the motor controller under the conditions of meeting the braking energy recovery requirements, so that the drive motor operates in the power generation mode. The energy recovered by electric braking is stored in the power battery pack without affecting the braking performance, thereby achieving braking energy recovery.

(4) Vehicle energy management and optimization In pure electric vehicles, the power battery not only supplies power to the drive motor, but also to the electric accessories. Therefore, in order to obtain the maximum driving range, the vehicle controller will be responsible for the energy management of the vehicle to improve energy utilization. When the battery SOC value is relatively low, the vehicle controller will issue instructions to certain electric accessories to limit the output power of the electric accessories to increase the driving range.

(5) Monitoring and display of vehicle status The vehicle controller obtains real-time data of vehicle operation by directly collecting signals and receiving data on the CAN bus, including speed, motor working mode, torque, speed, remaining battery power, total voltage, single cell voltage, battery temperature and fault information, and then sends this real-time information to the vehicle information display system through the CAN bus for display. In addition, the vehicle controller regularly detects the communication of each module on the CAN bus. If it is found that a node on the bus cannot communicate normally, the fault information is displayed on the vehicle information display system, and reasonable measures are taken to deal with the corresponding emergency situation to prevent the occurrence of extreme conditions, so that the driver can directly and accurately obtain the current operating status information of the vehicle.