Design of four-wheel independent drive control system based on CAN bus communication technology

“With the event of electrical autos, CAN bus communication know-how is an increasing number of broadly used. It may be used for four-wheel unbiased drive management of pure electrical autos, in addition to lively security methods comparable to brake anti-lock braking system (ABS) and Electronic stability gadget (ESP). implementation facilitates.

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Authors: Wu Zhihong; Xin Ying; Zhu Yuan; Radar

With the event of electrical autos, CAN bus communication know-how is an increasing number of broadly used. It may be used for four-wheel unbiased drive management of pure electrical autos, in addition to lively security methods comparable to brake anti-lock braking system (ABS) and digital stability gadget (ESP). implementation facilitates.

When designing the CAN bus communication system, the issue of analysis and evaluation of CAN knowledge is all the time confronted. If the issue can't be solved, the design can't be accomplished. Based mostly on Kvaser Leaf Skilled HS, a USB_CAN software, this paper develops an information evaluation system on a PC with the assistance of Visible Fundamental atmosphere, and implements CAN communication between the evaluation system and the four-wheel unbiased drive electrical car motor management board. By diagnosing and analyzing the CAN bus knowledge, the design of the CAN bus system will be higher accomplished.

4-wheel unbiased drive electrical car management technique

The distributed four-wheel digital differential system used within the electrical car bodily mannequin consists of a central controller, 4 electrical wheel controllers and a CAN bus community. Its format on the electrical car bodily mannequin is proven in Determine 1. .

Determine 1 Format of the distributed four-wheel digital differential system on the physique

On this distributed system, the digital differential algorithm based mostly on four-wheel unbiased management is split into two components: the car differential algorithm and the velocity management algorithm. The velocity management algorithm is predicated on the velocity of every electrical wheel. The central controller and 4 electrical wheel controllers are linked to type a real-time management community by way of CAN bus.

Within the system management course of, the central controller obtains the car steering angle sign from the steering sensor and the car velocity setting sign from the deal with by way of A/D sampling. The correct velocity, and this result's used because the velocity management set worth of the corresponding wheel on the present second, and despatched to the corresponding electrical wheel controller by way of the CAN bus. The 4 wheel controllers take the velocity setting worth acquired from the CAN bus because the management goal, and use the electrical velocity management algorithm to manage their respective electrical wheels, in order that the precise velocity of every electrical wheel meets the necessities of the car differential algorithm in actual time. In flip, clean steering of the electrical car is achieved.

4-wheel unbiased drive electrical car CAN management community

Via the CAN bus, the central controller of the four-wheel drive electrical car transmits the wheel velocity and different set values ​​to the controller of every wheel, and on the similar time, every motor controller feeds again the precise velocity and different info to the central controller by way of the CAN bus. The topology of the CAN community is proven in Determine 2.

Determine 2 CAN management community topology

There are 5 CAN nodes in the entire community: 4 electrical wheel motor controllers a, b, c, d, and one electrical car central controller e.

When designing the appliance layer protocol, it's essential to rearrange an inexpensive bus arbitration precedence order for the bus message in response to the precise utility, in order to enhance the real-time efficiency of CAN communication. On this utility, the downlink knowledge, that's, the management command despatched by the central controller to every electrical wheel motor controller, has the next precedence than the uplink knowledge, that's, the suggestions info of every electrical wheel motor controller. As well as, the instructions from the central controller to the 4 wheel controllers have to be synchronized with a view to present dependable preconditions for subsequent management.

Contemplating the above elements, this paper designs the CAN knowledge message ID system proven in Desk 1.

The motor controllers a, b, c and d respectively management the left entrance wheel, the proper entrance wheel, the left rear wheel and the proper rear wheel of the electrical car. Determine 3 reveals the construction of the CAN message knowledge discipline despatched by the central controller.

Determine 3 Central controller CAN message knowledge discipline construction

The CAN knowledge with IDs 0x010 and 0x020 despatched by the central controller represents the set worth of the velocity and torque, and the corresponding precise worth is an analog worth, which is represented by a 16-bit fixed-point quantity with restricted precision. Within the 16-bit knowledge, the higher 9 bits signify an integer, and the decrease 7 bits signify a decimal, that's, a fixed-point quantity within the 9Q7 format. For the CAN knowledge with ID 0x00F despatched by the central controller, the command despatched to every motor controller can be 16-bit knowledge, the decrease 8 bits signify the braking command, and the higher 8 bits signify the management mode choice command.

Determine 4 reveals the construction of the CAN message knowledge discipline of the 4 motor controllers feeding again the present state info to the central controller.

Determine 4 Construction of motor management suggestions standing info

There are two methods to set off CAN bus messages: occasion set off and time set off. The previous is appropriate for sending swap state portions that change discretely in time, comparable to braking instructions and management mode choice instructions; the latter is appropriate for sending analog portions that change constantly in time, comparable to velocity setpoints and torque setpoints. For the reason that management system has each the above two varieties of bus info, the mix of occasion triggering and time triggering is used to transmit.

Introduction to Kvaser Leaf Skilled HS

Kvaser Leaf Skilled is a single-channel USB interface for CAN and LIN. The gadget offers the opportunity of merely connecting a number of interfaces to a PC, and may simply join a number of Kvaser Leaf gadgets to the identical USB Hub with out extra Connection. As well as, it additionally has good EMC (Electro Magnetic Compatibility) efficiency and plug-and-play options. On the similar time, since a number of gadgets will be linked to at least one USB Hub, every gadget will be powered by the Hub with very low energy consumption.

The library features supplied by Kvaser are very wealthy, and customers can name the corresponding library features in response to their very own must flexibly course of CAN bus knowledge.

Design of PC CAN Knowledge Evaluation System

In line with the CAN communication knowledge between the central controller of the electrical wheel unbiased driving car and the 4 motor controllers, the info evaluation system dynamically shows the instructions despatched by the central controller and the present operation info of every motor. On the similar time, it may possibly additionally Display the change curve of every motor velocity, and has the operate of information saving, which is handy for offline evaluation.

The system is designed and developed based mostly on Visible Fundamental language, and the CWGraph management in Measurement Studio software program is used to show the velocity curve. With the Kvaser Leaf Skilled HS, CAN communication between the PC and the management board is feasible. The preservation of the motor operating knowledge is accomplished by connecting to the Microsoft Entry database by way of VB programming. On this means, the system will be composed of a primary window and 5 sub-windows displaying the motor velocity curve, as proven in Determine 5.

Determine 5 Type construction diagram

Right here, the primary window is the startup window, and the sub-forms A, B, C, D, and E should not displayed when the primary window is began. The startup and shutting of the sub-forms will be managed by way of the corresponding buttons on the primary window. Which means that the person wheel velocity curves are displayed and switched off.

When the system is operating, the primary window is began first. By clicking the corresponding buttons on the primary window, CAN communication will be simply established with every management board, and the communication between the primary management board and the motor management board will be acquired. CAN messages are displayed within the corresponding show space after being processed by the interior knowledge processing operate of the interface.

After the CAN communication is regular, the 5 show areas will dynamically replace and show the corresponding info in response to the messages on the CAN bus.

When it's essential to save lots of knowledge, click on the Data_Record button, and a window for choosing a database will pop up. After deciding on a database that has been established, the state knowledge of the motor will be saved within the chosen database, and the info saving will be terminated at any time. It must be famous that the saved motor operating state knowledge is the info acquired by the interface after clicking the Data_Record button and deciding on the database, and the earlier knowledge is just not saved. That's to say, if you wish to save the info of all the motor operating course of, you could click on the Data_Record button and choose the database earlier than the motor begins operating.

When exiting the interface, you need to first disconnect the CAN bus, click on the Disconnect button to disconnect. Then click on the Give up button to exit the interface usually.

The design of this technique adopts the tactic of utilizing ADO (ActiveX Knowledge Object) object mannequin in VB, connecting Microsoft Entry database, and saving knowledge. So long as a collection of tables are established in a database, the info will be conveniently saved within the corresponding tables. For instance, on this design, an unbiased desk is established for every of the 4 motors to retailer the state info of their operation, together with info comparable to velocity, torque, battery voltage, and management mode. Utilizing the info processing operate of the Entry database will be very handy for offline knowledge evaluation and processing.

With a view to facilitate the usage of the system by totally different customers, earlier than the info is saved, the system offers a dialog field for the consumer to pick out an current database, which is handy for the consumer to customise the info saving path.

Epilogue

By way of software program of this design, in VB atmosphere, MeasurementStudio offers highly effective controls; when it comes to {hardware}, there are instruments comparable to Kvaser Leaf Skilled HS and Peak_CAN, which make the belief of this technique simpler, and the impact is best than standard design strategies higher. After on-line debugging, it's proved that the system can successfully analyze and course of the info of CAN bus.