| PrefaceAutomotive electric power steering (EPS), which provide steering force by electromotor directly, is one of a new power steering system. The torque generated by motor which is translated by steering mechanical framework, can assist the driver to steer. It is considered as a new high-tech which closely follows the modern vehicle development topic and has been paid close attention as soon as it's appearance. It's one of a main development direction of automotive power steering technology, has broad application prospects.In this paper, the advantages and disadvantages of several types of electromotor were studied, a low-voltage power AC induction motor was used as the power source. In order to study the electrical power control methods, the AC motor test-bed was established. Then, in the motor test-bed, Sine Pulse Width Modulation (SPWM) and Voltage Space Vector Modulation (SVPWM) were implemented. On this basis, these two methods were compared and analyzed. Thirdly, the induction motor variable voltage variable frequency (VVVF) control was studied. The motor mechanical characteristics were measured by the method of VVVF. Finally, simple EPS measurement and control system test-bed was established. At the test-bed, EPS power-assisted control strategy was implemented. Through the EPS test-bed, the effective performance of VVVF control was verified.Main ContentsThe paper is divided into six chapters. The main contents as follows:In chapter one, firstly, the history of the EPS system and the latest Research &Apply was introduced. Secondly, the main existed technical difficulties of EPS were mentioned. The construction and operation of this system, especially four types of EPS, was introduced. Then, the advantages and disadvantages of several types of electromotor were studied, a low-voltage power AC induction motor was used as the power source.In chapter two, research is mainly concerned about the design of AC motor test-bed and it's measurement and control system.The motor is an important power source in EPS. It is controlled by ECU (Electric Control Unit), according to the velocity of the vehicle and the torque of the steering wheel. In order to research on induction motor control method and the mechanical characteristics, the AC motor test-bed was established. AC motor test-bed include EPS motor, torque speed sensor, and magnetic brakes, electronic control units, motor drive circuits and control software.Firstly, finish the overall layout and design the mechanical structure. Then make the design of hardware circuit of measurement and control system, mainly for electric control unit, torque speed sensor interface circuit, motor drive circuit design. A DSP TMS320LF2407A chip, produced by TI, is used as the main chip for control system. The principal part of the motor drive circuit is composed of six MOSFET (metal-oxide semiconductor field-effect transistor), this six MOSFET make up of a Three-phase bridge inverter circuit containing two current sensors, using IR2130 to drive MOSFET Arrays. Furthermore, design the control software, including PC monitoring software and the DSP control software, the communication between PC and DSP using CAN Bus.In chapter three, Sine Pulse Width Modulation (SPWM) and Voltage Space Vector Modulation (SVPWM) were studied.In the electric power steering system, a car battery supply the power to AC motor, so the battery needs to be converted into alternating current to drive motor, which is inverter technology. This paper analyzes the working principle of the inverter using pulse width modulation (PWM) to generate alternating current. Sine Pulse Width Modulation (SPWM) and voltage space vector modulation (SVPWM) are commonly used in PWM control mode in inverter. This paper describes in detail the principle of two kinds of control method and its programming on the DSP implementation. And, in the DC voltage utilization, the distribution of harmonic output voltage, output current waveform, the mechanical output characteristics of these four aspects of these two control methods were compared and analyzed, the effect of SVPWM control is stronger than SPWM. In this paper, the mechanical characteristics of Chapter IV and implementation of power-assisted strategy in Chapter V use in both the SVPWM methods to generate AC sine wave.In chapter four, this paper study the VVVF control and measure the mechanical characteristics of AC assist motor. At present, the commonly used exchange induction machine velocity modulation control methods include the VVVF method, vector control and direct torque control method. In this paper, the VVVF method was selected. In the actual control process, in order to keep the same load capacity of motor, it is necessary to changes in the frequency of power supply at the same time to change the stator voltage. In this paper, based the equivalent circuit of AC motor, the mechanical properties of the motor equations were carried out. The mechanical characteristics under the control of VVVF were analyzed in theoretical. Motor is at a constant power control of above fundamental frequency, at a constant torque control of below fundamental frequency.In this paper, using a specific algorithm, a specific frequency and modulation depth of the SVPWM waveform was generated by the controller, frequency and variable voltage to achieve that purpose. That is, the purpose of variable frequency and variable voltage was reached. In the motor test-bed, combined with the requirements of electric power steering system, the motor mechanical characteristics were measured, with drawn induction motor at 1Hz ~ 100Hz frequency range of the "speed-torque" characteristic curve and block characteristic, which provide support to assist power control in chapter five.In chapter five, simple EPS measurement and control system test-bed was established. At the test-bed, EPS power-assisted control strategy was implemented and verified.In order to verify the EPS power-assisted control strategy as well as the follow-up studies, this paper builds a simple EPS measurement and control system test-bed. EPS test-bed include bench, steering gear, the simulation equipment of road force, steering wheel equipped torque and angle sensor, ECU and PC monitoring and control software. The function of power-assisted control is to assist the driver to reduce the steering force, which is the basic control strategy for EPS.In this paper, EPS power-assisted control strategy applied to AC motor was studied. The power-assisted control strategy in this article was verified in the test-bed environment. It's able to help the initial implementation of the EPS power-assisted control strategy by using SVPWM inverter and VVVF control.In chapter six, the contents and conclusions are summed up. Also some advice on the improvement of the later research is given.
|
PDF Full Text Request