A vehicle controller comprises two main components: hardware and software. Its core software and programs are typically developed by the manufacturer, while automotive component suppliers provide the controller hardware and underlying drivers. Currently, international research on vehicle controllers for pure electric vehicles primarily focuses on those driven by in-wheel motors. Pure electric vehicles with only one motor typically do not have a dedicated vehicle controller; instead, they utilize a motor controller for overall vehicle control. Many large international companies offer mature vehicle controller solutions, such as Continental, Bosch, and Delphi.
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 a centralized control system is that the vehicle controller independently acquires input signals, analyzes and processes the data according to the control strategy, and then directly issues control commands to each actuator to drive the electric vehicle. The advantages of a centralized control system are centralized processing, fast response, and low cost; the disadvantages are complex circuitry and difficulty in heat dissipation.
The basic idea of a distributed control system is that the vehicle controller collects driver signals and communicates with the motor controller and battery management system via a CAN bus. The motor controller and battery management system then transmit their respective collected vehicle signals to the vehicle controller via the CAN bus. The vehicle controller analyzes and processes the data based on the vehicle information and the control strategy. Upon receiving control commands, the motor controller and battery management system control the motor operation and battery discharge based on the current state of the motor and battery. The advantages of a distributed control system are modularity and low complexity; the disadvantage is its relatively high cost.
A typical distributed vehicle control system diagram is shown below. The top layer of the vehicle control system is the vehicle controller. The vehicle controller receives information from the motor controller and battery management system via the CAN bus and sends control commands to the motor controller, battery management system, and on-board information display system. The motor controller and battery management system are responsible for monitoring and managing the drive motor and power battery pack, respectively. The on-board information display system is used to display the vehicle's current status information, etc.
Typical Distributed Vehicle Control System Diagram
The diagram below shows the schematic of a pure electric vehicle controller developed by a certain company. The hardware circuit of the vehicle controller includes modules such as a microcontroller, digital signal conditioning, analog signal conditioning, relay driver, high-speed CAN bus interface, and power supply.
Schematic diagram of the vehicle controller for a pure electric vehicle developed by a certain company
(1) Microcontroller Module The microcontroller module is the core of the vehicle controller. Taking into account the functions of the pure electric vehicle controller and its external operating environment, 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 quantity. One end is connected to multiple switch quantity sensors, and the other end is connected to a microcontroller.
(3) Analog signal conditioning module The analog signal conditioning module is used to collect analog signals from the accelerator pedal and brake pedal and send them to the microcontroller.
(4) Relay drive module The relay drive module is used to drive multiple relays. One end of it is connected to the microcontroller through an opto-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 it is connected to the microcontroller through an opto-isolator, and the other end is connected to the system's high-speed CAN bus.
(6) Power Module The power module provides isolated power to 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 all aspects of the electric vehicle's powertrain to improve overall energy efficiency and ensure safety and reliability. It collects driver signals, obtains relevant information about the drive motor and battery system via the CAN bus, analyzes and processes this information, and issues motor control and battery management commands through the CAN bus to achieve vehicle drive control, energy optimization control, and regenerative braking control. The vehicle controller also features a comprehensive instrument panel interface for displaying vehicle status information; robust fault diagnosis and handling capabilities; and vehicle gateway and network management functions.
2. Basic functions of the vehicle controller
The vehicle controller collects driving information such as accelerator pedal signals, brake pedal signals, and gear shift switch signals. It also receives data from the motor controller and battery management system on the CAN bus. Combining this data with the vehicle control strategy, the controller analyzes and judges this information to extract the driver's driving intentions and vehicle operating status information. Finally, it sends commands via the CAN bus to control the operation of various component controllers, ensuring normal vehicle operation. The vehicle controller should possess the following basic functions.
(1) Functions 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 presses the accelerator pedal or brake pedal, the drive motor must output a certain driving power or regenerative braking power. The greater the pedal opening, the greater the output power of the drive motor. Therefore, the vehicle controller must interpret the driver's operation reasonably; receive feedback information from various subsystems of the vehicle to provide decision feedback for the driver; and send control commands to various subsystems of the vehicle to achieve normal vehicle operation.
(2) Networked Management of the Vehicle The vehicle controller is one of many controllers in an electric vehicle and is a node in the CAN bus. In the network management of the vehicle, the vehicle controller is the center of information control, responsible for the organization and transmission of information, monitoring of network status, management of network nodes, and diagnosis and handling of network faults.
(3) Recovery of braking energy A key feature that distinguishes pure electric vehicles from internal combustion engine vehicles is their ability to recover braking energy. This is achieved by having the electric motor of the pure electric vehicle operate in a regenerative braking state. The vehicle controller analyzes messages such as the driver's braking intention, the status of the power battery pack and the status of the drive motor, and combines them with the braking energy recovery control strategy. Under the condition of meeting the braking energy recovery requirements, the controller sends motor mode commands and torque commands to the motor controller, so that the drive motor operates in the power generation mode. Without affecting the braking performance, the energy recovered by electric braking is stored in the power battery pack, thereby realizing the recovery of braking energy.
(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 entire vehicle to improve energy utilization. When the battery's SOC value is relatively low, the vehicle controller will issue instructions to certain electric accessories to limit their output power in order to increase the driving range.
(5) Monitoring and Display of Vehicle Status: The vehicle controller obtains real-time vehicle operating data by directly acquiring signals and receiving data from the CAN bus, including speed, motor operating mode, torque, rotational speed, remaining battery charge, total voltage, individual cell voltage, battery temperature, and fault information. This real-time information is then sent to the on-board information display system via the CAN bus for display. Furthermore, the vehicle controller periodically checks the communication of each module on the CAN bus. If a node on the bus fails to communicate normally, the fault information is displayed on the on-board information display system, and appropriate measures are taken to handle corresponding emergencies, preventing extreme situations and enabling the driver to directly and accurately obtain the vehicle's current operating status information.
(6) Fault Diagnosis and Handling: Continuously monitor the vehicle's electronic control system to perform fault diagnosis. The fault indicator light displays the fault type and some fault codes. Based on the fault content, take appropriate safety protection measures in a timely manner. For less serious faults, drive at low speed to the nearest repair shop for inspection.
(7) External charging management enables charging connection, monitors the charging process, reports charging status, and ends charging.
(8) The online diagnostic and offline testing of the diagnostic equipment is responsible for connecting and communicating with external diagnostic equipment, realizing UDS diagnostic services, including reading data streams, reading and clearing fault codes, and debugging control ports.
The diagram below shows an example of a pure electric vehicle controller. It collects control signals during driving and charging to determine the driver's intentions, manages and schedules the vehicle's electronic control equipment via the CAN bus, and employs different control strategies for different vehicle models to achieve vehicle drive control, energy optimization control, regenerative braking control, and network management. The vehicle controller utilizes technologies such as microcomputers, intelligent power drives, and CAN bus, and features good dynamic response, high sampling accuracy, strong anti-interference capabilities, and high reliability.
Example of a pure electric vehicle controller
3. Vehicle Controller Design Requirements
Sensors that directly send signals to the vehicle controller include the accelerator pedal sensor, brake pedal sensor, and gear position switch. The accelerator pedal sensor and brake pedal sensor output analog signals, while the gear position switch outputs a switching signal. The vehicle controller indirectly controls the operation of the drive motor and the charging and discharging of the power battery by sending commands to the motor controller and battery management system, and controls the power supply to and from the on-board modules by controlling the main relay.
Based on the structure of the vehicle control network and the analysis of the input and output signals of the vehicle controller, the vehicle controller should meet the following technical requirements.
① When designing the hardware circuit, the driving environment of electric vehicles should be fully considered, electromagnetic compatibility should be emphasized, and anti-interference capabilities should be improved. The vehicle controller should have a certain degree of self-protection capability in both hardware and software to prevent extreme situations from occurring.
② The vehicle controller needs to have a sufficient number of I/O interfaces to quickly and accurately acquire various input information. It should have at least two A/D conversion channels for acquiring accelerator pedal signals and brake pedal signals, multiple digital input channels for acquiring vehicle gear signals, and multiple power drive signal output channels for driving vehicle relays.
③ The vehicle controller should have multiple communication interfaces. The CAN communication interface is used to communicate with the motor controller, battery management system and vehicle information display system. The RS232 communication interface is used to communicate with the host computer. An RS-485/422 communication interface is also reserved, which can be compatible with devices that do not support CAN communication, such as some models of vehicle touch screens.
④ Under different road conditions, cars will encounter different impacts and vibrations. The vehicle controller should have good impact resistance to ensure the reliability and safety of the car.
