As an eco‑friendly means of transportation, new‑energy vehicles boast many advantages over internal‑combustion‑engine vehicles in terms of environmental protection, energy conservation and driving performance. They are complex systems composed of multiple subsystems, mainly including power systems such as batteries, motors and brakes, as well as other accessories (as shown in Figure 1). Almost every subsystem fulfills its respective functions and objectives via its own Electronic Control Unit (ECU). To meet vehicle‑level targets for power performance, fuel economy, safety and comfort, intelligent human‑machine interaction interfaces are required on one hand; on the other hand, all subsystems must cooperate and be optimally matched. This task is undertaken by the Vehicle Control Unit (VCU) within the control system. Bus‑based distributed control networks serve as an ideal solution for coordinated control of numerous subsystems. Featuring low cost, high transmission rate, superior safety and reliability, strong error‑correction capability and favorable real‑time performance, the CAN bus has been widely adopted in real‑time distributed control networks for mid‑ and low‑cost automobiles. As more automotive manufacturers adopt the CAN protocol, CAN has gradually become a general‑purpose standard. Bus‑based networks can drastically reduce signal wiring harnesses between devices and improve system monitoring. Furthermore, new control units can be conveniently added to expand network functions without compromising system reliability.

I. Control System Architecture of the Vehicle Control Unit

The self‑designed and self‑developed new‑energy vehicle VCU consists of modules including a microcontroller, analog input and output, digital signal conditioning, relay driver, high‑speed CAN bus interface and power supply. The VCU manages, coordinates and monitors every link of the new‑energy vehicle powertrain to improve overall vehicle energy efficiency and guarantee safety and reliability. It collects driver operation signals, obtains relevant information from the motor and battery systems via the CAN bus for analysis and computation, and issues motor control and battery management commands over the CAN bus to realize vehicle drive control, energy optimization control and regenerative braking control. The VCU also provides an integrated instrument interface for displaying vehicle status information, complete fault diagnosis and handling functions, as well as vehicle gateway and network management functions. Its structural principle is illustrated in Figure 2.

Brief descriptions of each module are given below:

1. Digital Signal Conditioning Module

The digital signal conditioning module performs level conversion and signal shaping for digital input signals. One end connects to multiple digital sensors and the other end interfaces with the microcontroller;

2. Relay Driver Module

The relay driver module drives multiple relays. It is connected to the microcontroller through opto‑isolators on one side and to multiple relays on the other side;

3. High‑Speed CAN Bus Interface Module

The high‑speed CAN bus interface module provides high‑speed CAN bus access. It connects to the microcontroller via opto‑isolators at one end and to the system high‑speed CAN bus at the other end;

4. Power Supply Module

The power supply module supplies isolated power to the microprocessor and all input‑output modules, monitors storage‑battery voltage, and interfaces with the microcontroller;

5. Analog Input and Output Module

The analog input and output module acquires 0‑5 V analog signals and outputs analog voltage signals ranging from 0‑4.095 V.

6. Pulse Signal Input and Output Module

It acquires and conditions pulse signals within 1 Hz‑20 kHz with an amplitude of 6‑50 V, and outputs PWM signals

ranging from 1 Hz‑10 kHz with an amplitude of 0‑14 V.

7. Fault and Data Storage Module

Ferroelectric memory stores calibrated data, fault codes and vehicle characteristic parameters with a capacity of 32 K.

II. Functional Description of the Vehicle Control Unit

The new‑energy‑vehicle VCU mainly implements the following functions:

1. Vehicle Driving Control

The traction motor of a new‑energy vehicle shall output drive or braking torque according to the driver’s intention. When the driver presses the accelerator or brake pedal, the traction motor outputs corresponding driving power or regenerative braking power. Greater pedal travel corresponds to higher motor output power. Therefore, the VCU reasonably interprets driver operations, receives feedback from all vehicle subsystems to provide decision‑making feedback for the driver, and sends control commands to each subsystem to achieve normal vehicle operation.

2. Vehicle‑Level Network Management

Modern automobiles contain numerous electronic control units and measuring instruments that exchange data. Reliable, efficient and fault‑free data transmission is critical. To address this requirement, Bosch of Germany developed the Controller Area Network (CAN) in the 1980s. Electric vehicles are equipped with more and more complex ECUs compared with conventional fuel‑powered vehicles, making CAN bus application indispensable. As one of many controllers within an electric vehicle, the VCU acts as a node on the CAN bus. In vehicle‑level network management, the VCU serves as the core for information control, responsible for information organization and transmission, network status monitoring, network node management, and network fault diagnosis and handling.

3. Regenerative Braking Control

New‑energy vehicles employ electric motors to output drive torque. Motors support regenerative braking: operating as generators, they convert vehicle braking energy into electric power stored in energy‑storage devices and recharge the traction battery pack when charging conditions are satisfied. During this process, the VCU judges whether regenerative braking is available according to accelerator‑pedal travel, brake‑pedal travel and the State of Charge (SOC) of the traction battery. If applicable, the VCU sends braking commands to the motor controller to recover partial energy.

4. Vehicle‑Level Energy Management and Optimization

In battery‑electric vehicles, batteries supply power not only to traction motors but also to electric accessories. To maximize driving range, the VCU carries out vehicle‑level energy management to improve energy utilization. When battery SOC is low, the VCU issues commands to limit the output power of certain electric accessories so as to extend driving range.

5. Vehicle Status Monitoring and Display

The VCU conducts real‑time detection of vehicle conditions and transmits information from each subsystem to the on‑board information display system. Via sensors and the CAN bus, it collects vehicle and subsystem status information and drives instrument panels to present status data and fault‑diagnosis results. Displayed contents include motor speed, vehicle speed, battery state‑of‑charge and fault information.

6. Fault Diagnosis and Handling

It continuously monitors the vehicle electronic control system and performs fault diagnosis. Fault indicator lamps indicate fault types and partial fault codes. Corresponding safety protection actions are triggered promptly according to fault conditions. For non‑critical faults, the vehicle can travel at low speed to nearby service stations for maintenance.

7. Off‑Board Charging Management

It manages charging connection, monitors the charging process, reports charging status and signals charging completion.

8. On‑Board Diagnostics and End‑of‑Line Testing for Diagnostic Equipment

It handles connection and diagnostic communication with external diagnostic equipment and implements UDS diagnostic services, including data‑stream reading, fault‑code reading and clearing, and control‑port debugging.