Resolve design based on the CAN bus electric vehicle power management communication

As oil prices rise and environmental protection requirements, the electric has become an important direction for future vehicle development. For battery-powered electric power system or the engine and battery hybrid system, the design of the power management system is an important factor in the relationship between vehicle performance, be considered when designing a comprehensive vehicle overall design and external use of the environment, in order to save power, but also need to design a control strategy to ensure the best use of power. Therefore, it is necessary to the all-electric vehicle power management systems in depth.
1, the importance of electric vehicles, energy management
Electric vehicles, power management, the main purpose is to give full play to the fuel burning efficiency, make the engine work in the vicinity of the optimum operating point, and by the energy reserves and output of the motor and battery, timely adjustment of vehicle operating conditions and the outside world road conditions matches. After ten years of development, the electric vehicle power system design, the most practical value and pattern of existing commercial operation, only hybrid vehicles. The hybrid system assembly from the original discrete structure of the engine and the motor to the engine motor and gearbox integrated structure of the development of integrated hybrid powertrain system. So, here only consider the hybrid system power management.
Hybrid system power management function, you need to achieve the following two objectives:
(1) to ensure the best conditions of the engine, to avoid the inefficiency of the engine. Usually the engine will adjust in the best situation near the stable operation by adjusting the battery and the motor output to adapt to a variety of outside traffic changes. For example, when the vehicle is low, the taxi, idle conditions the drive motor from the battery pack when the vehicle at the start, acceleration, climbing condition when the engine - motor group and batteries common to the motor to provide power.
Due to the engine to avoid idling and low speed in order to improve the efficiency of the engine, not only to reduce emissions, and saving power.
(2) make full use of the inertial energy of the vehicle. By the inertia force of the wheel drive motor when the vehicle deceleration, braking or driving downhill.
When the motor becomes a generator, reverse battery charging, and fuel savings.
Statistics show that accounted for more than 80% of road conditions, an ordinary car using only 40% of the potential power in the urban areas but also fell to 25%, and power to optimize the management of electric vehicles, such as the Toyota Prius car.
its power has exceeded its class level, 75% fuel savings.
2, the communication needs of the power management system with CAN bus technology
Electric vehicles, power management, the need to monitor the working conditions of the engine, electric motor, battery, vehicle speed, driving the resistance data, as well as the driver's operation, and after intelligent processing based on the above data to automatically control energy-saving device or circuit,
so it is necessary first to solve the energy consumption and energy conversion components running state sensor connection.
Data communications, automotive interior measurement and implementation of the components between the CAN bus, the bus technology was first introduced by the German company BOSCH, mainly used to solve the data exchange between the many modern automotive control and test equipment. Sharing and vehicle CAN bus electric vehicle power management systems, not only the communication rate is high, accurate, high reliability, and easy to be compatible with the vehicle control network, the sensor signal, the calculation of information and running status of each control unit
or away from the car fault diagnosis provides a basic platform, so this topic, using the CAN bus as the basic communication technology for power management.
3, energy management and control systems based on CAN bus topology
Electric vehicle chassis part of energy consumption and energy saving systems to connect together to form a CAN bus-based energy management and control of network topology in Figure 1, consists of brake energy conversion device, the powertrain, battery management, motor controller, the driving resistance test
several key monitoring nodes and one by the onboard computer system consisting of the host master node.
Figure 1 CAN bus-based energy management and control the network topology
Dynamic energy conversion device and driver control monitoring system, battery motor controller to work together. When the driver depress the brake pedal, the brake motor is close to be braking the rotation device, such as drive shafts, vehicle inertial energy consumption, and converted to electricity, while manipulation of the monitoring system to monitor the brake pedal action, the battery
charging circuit to adjust to achieve the storage of electrical energy to pass over the brake motor.
The powertrain system is mainly used to achieve the optimal operation of the engine condition. In the normal exercise of the case, the energy of the engine is divided into two, all the way passed to the vehicle drive propulsion system, the normal exercise-drive vehicles, other road is to drive the motor to the battery supply.
At this point, the motor and battery consisting of an auxiliary power system is equivalent to an energy-conditioning, battery motor controller and the driving resistance testing device, according to the changes of the outside traffic, engine output energy adjustment and distribution.
Upper master node through the CAN bus, car computer system constitutes the entire energy management and control network connections through a dedicated software system, data acquisition, data analysis and output of the control strategy, to achieve the outside world traveling between the resistance and engine energy adjustment
optimized to match the energy of the vehicle interior conversion utilized to achieve the regulatory role of the motor, battery systems, energy conservation, energy storage, and replenish their energy.
4, based on CAN bus monitoring node structure and communication flow
CAN bus node structure is generally divided into two categories: one connected to the CAN adapter and PC, between PC and CAN bus communication; the other by the microcontroller, CAN controller and CAN drive, as a class node for data transmission with the CAN bus CAN bus node structure in the energy management and control system designed in this paper, host master node, each of the key monitoring / control system using CAN bus node structure. Structures and systems connected, each node shown in Figure 2.
Configured with two 120Ω resistor at both ends of the bus, whose role is to match bus impedance, can increase the stability and anti-jamming capability of the bus transfer, and reduce the error rate in data transmission.
For each monitor nodes, can usually be the 51 series microcontroller as the primary treatment center for monitoring signal of the node device to do with SJA1000 CAN controller, the PCA82C250 is a common CAN transceivers and the physical bus interface. mainly to provide differential transmit capability to the bus and differential ability to accept the CAN controller.
These three components constitute a lower circuit patterns of the monitoring node is shown in Figure 3.
The three-tier structure of the CAN bus model: the physical layer, data link layer and application layer. Which the function of the physical layer and data link layer from the SJA1000 completed. SJA1000 hardware reset after power-on, must be the software initialization before they can carry out data communication, its main role is to achieve the rate of the bus, acceptance mask, the output pin drive mode, the bus mode and clock frequency definition. The communication process in the entire energy management and control system, the controller sent the required format and cycle data (speed, battery voltage, current, and resistance to the vehicle and engine speed, etc.) to the bus, but also to receive information from other controllers. Other controllers on the bus according to need what they need packets. For receiving data, the system uses interrupts to achieve, once an interrupt occurs, will receive the data is automatically loaded into the corresponding packet register. Can be applied to the shielded filter mask and filter registers the received message identifier and the identifier of a pre-set in the receive buffer initialization selected bit by bit, only the message identifier matching to enter the receive buffer, and those who do not meet the requirements of the packets will be blocked in the receive buffer, so as to reduce the burden on the CPU processing of packets.
The host computer interrupt receiving data flow shown in Figure 4.
5 Conclusion
As a reliable car computer network bus, the CAN bus in the car has been applied, making the car computer control unit through the CAN bus to share all the information and resources to simplify wiring and reduce the number of sensors to avoid the control function to repeat and improve the system reliability and maintainability, reduce costs, to better match and coordinate the purpose of each control system.