Research on Design Scheme of Motor Drive Circuit for Electronically Controlled Power Steering System Luo Shi, Shang Gaogao (School of Automobile and Traffic Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China) Advantages and disadvantages of DC motors, proposed a design scheme for the drive circuit of the electric power steering system: N-channel MOS transistors are used for the lower and upper tubes, the upper tube is always on or normally closed, and the lower tube is controlled by the PWM logic level. This program is applied to the electric power steering system developed by the author. The test shows that it is feasible, reliable, and can meet the requirements. In recent years, with the development of electronic technology and control theory, electric power steering (EPS) has been rapidly developed. It not only improves the force control characteristics of the car steering, but also effectively reduces the driver's steering load. The entire EPS system is composed of a speed reduction mechanism, a motor, and a controller. The motor outputs torque according to the command of the controller and is transmitted to the steering gear via the speed reduction mechanism to achieve the functions of assisting power. The control circuit is the hardware foundation of the control software, which directly affects the performance and reliability of the controller. Therefore, the research on the controller hardware circuit design scheme has a positive practical significance. 1. Analysis of design solutions 1.1 EPS system drive motor work requirements During the driving process, the driver constantly turns the steering wheel according to the actual road conditions to adjust the direction of travel. Therefore, the drive motor of the electric power steering system must be capable of bidirectional operation. Automobiles use batteries as their power source, taking into account the followability and responsiveness of the electric power steering system. This determines the choice of a brushed DC servo motor (or brushless DC servo motor) as its power source, and the motor drive. The requirement of the control circuit is to be able to adjust the speed of the motor and the output torque K5 quickly and with high precision. 1.2 Analysis of the design scheme of the drive circuit The pulse width modulation (PWM) control of the H-bridge circuit l6*7 is commonly used in the control of the power steering system. The four high-power MOS transistors in the H-bridge circuit can use N-channel and P-channel MOS transistors, respectively. However, P-channel MOS transistors are generally not used for the down tube drive motor. There are two possible solutions: One is to use the circuit shown above, and the upper and lower tubes use two fund projects respectively: six talents peak funded projects in Jiangsu Province (E-2002-12) P-channel and two N-channel high-power tubes. In the figure, when Vdd is powered on, the Ugs is between 1015V, which is the control pole power supply; the other upper and lower tubes are all N-channel MOS transistors (see ). The voltage changes with the change of the gate voltage, that is, the floating gate drive. In contrast, the use of two N-channel and two P-channel high-power MOS tube drive motor program, the control circuit is simple, low cost; but due to the processing process, P-channel MOS tube performance than N The difference of the channel; The program drive current is small, more used in the drive circuit with smaller power l8,9. Electric power steering system, requires a larger drive current, the working state changes frequently, requires that the control circuit has better Performance and high service life. On the one hand, N-channel MOS transistors have higher mobility, better frequency response, and larger transconductance. On the other hand, N-channel MOS transistors increase the on-state current and reduce the conduction. Resistance, reduced cost, and reduced area l9*10. Considering power requirements, reliability requirements, and the advantages of N-channel MOS transistors, four identical N-channel MOS transistors are used in the design. H-bridge circuit, with better performance and higher reliability. In an H-bridge circuit of four N-channel MOS transistors, to control each MOS transistor, a sufficient voltage higher than the gate voltage must be provided at the gate of each tube. Normally, the tube must be completely reliably conducted. Its voltage is generally more than 10V, that is Ugs> 10V. For the H-bridge lower tube, it can be directly applied with a voltage of more than 10V. For the two tubes above, To make Ugs > 10V, it is necessary to make Ug> Vdd+10V, that is, the driver circuit must be able to provide a voltage higher than the power supply voltage. This requires a boost circuit in the driver circuit to provide a driver with a floating gate driver chip higher than 1.3. Circuit international major chip manufacturers have introduced their own floating gate drive PWM drive chip. The IR2103 chip of IR company is used in this article. The driving circuit principle is as shown in the figure. The input of the high-side driver is PWM wave. This PWM wave is used as the signal source to control the high-end PWM, and it is used as the excitation source of the bootstrap circuit inside the IR2103 to generate the high-end driver. High voltage required. The low-side driver is directly controlled by a logic level, so that the low-side MOS transistor is normally open or normally closed during operation. This circuit has a simple structure and fewer devices. The internal boost circuit of this kind of circuit uses the input PWM control signal as the oscillating source of the booster pump. In practical use, when the PWM wave has a high duty ratio, its internal circuit cannot work normally, making the output control voltage drop. That is, the Ugs voltage drops, the tube cannot be completely turned on, and the internal resistance increases, causing the temperature rise of the MOS tube to be too high. At the same time, the driving current is also lowered, which affects the PWM wave working range and deteriorates the working performance of the power steering gear, resulting in insufficient assistance. The main reason for this phenomenon is that the PWM wave acts both as a control signal and as an oscillatory source for the booster pump. 1.4 Multivibrator Drive Circuit To increase the operating range of the circuit, a multivibrator is added as the oscillating source of the booster pump, as shown. When the duty cycle of the PWM wave is large, the oscillator charges the boost circuit. This overcomes the problem that the PWM wave not only serves as the control signal but also serves as the oscillating source of the booster pump when the high duty cycle is used, and basically meets the requirements after adopting this scheme. The circuit actually adds a charge pump circuit on the original basis. When the duty cycle is relatively large, the charge pump circuit is mainly working, which greatly expands the PWM operating range. From an application point of view, the solution is still flawed. First of all, there are many components in the circuit, which is not conducive to plate making, and the circuit board is bulky. Secondly, the circuit has a high cost and is not conducive to large-scale production. 1.5 directly using the charge pump to control the high-end drive circuit Through the above analysis, we can see that to achieve a wider range of PWM control, a charge pump is indispensable, and if there is a charge pump circuit, the high-end has a full turn-on The necessary conditions, then whether it can directly use the charge pump circuit to drive the high end of the H-bridge, for this reason, made changes in the circuit, remove the floating gate driver chip, directly by the PWM wave control high-end MOS switch, such as Show. The charge pump consists of an oscillator, two diodes and a capacitor. The oscillator generates a square wave of 12V. The square wave is superimposed on point A through the capacitor C1. When the square wave is low, D1 is on, D2 is off, and the voltage at point A is Vdd. When the wave is positive for half a week, voltage at point A is equal to Vdd+12V, D2 is turned on, D1 is turned off, and capacitor C2 is charged through D2 until the voltage across C2 reaches Vdd+12V, taking into account that the voltage drop across the diode is 0.7V, and the actual capacitance is two. The terminal voltage reaches about Vdd+10.6V, and the size of the capacitor C2 determines the driving ability of the charge pump. The larger the C2 is, the larger the output current is, but in the initial state, the charging time is longer. In actual use, this circuit will overheat the high-side MOS tube. After analysis, it is found that the upper tube of this kind of circuit has a slow opening speed and a low operating frequency. When the high frequency tube occurs, the upper tube does not completely conduct, and the output power decreases. Increased consumption and other phenomena. The PWM operation frequency of the booster motor is above 15 kHz. This circuit is obviously not practical. 2 EPS drive circuit design The final solution of the drive circuit, PWM wave control whether it is directly applied to the high-end or direct application of low-end, can produce a continuous adjustable control voltage, so you can consider the following scheme: When the motor is working, the upper tube is in Normally open or normally closed state, and the PWM logic level controls the down tube, the control circuit is as shown. In this scheme, the high-end MOS tube switches only when the motor is commutating, and the commutation frequency of the motor is extremely low. The low end is controlled directly by the logic circuit, and the signal level of the logic circuit switches faster, so it can meet the requirements; In addition, this circuit has an advantage that since the upper tube is opened slowly and the lower tube is opened more quickly, the commutation does not occur at the same time when the upper and lower tubes are turned on at the same time in actual control, and the commutation is reduced. Current shocks increase the life of the MOS tube. In actual design, both sides of the H-bridge can use the same oscillator as the charge pump excitation source. 3 Test results The circuit designed by the above scheme has been applied to the actually developed electric power steering controller, and has passed bench tests and road tests of several thousand kilometers after loading. Assume that the EPS driving circuit adopts an N-channel MOS transistor for the upper and lower tubes, and the upper tube is in the normally open or normally closed state. The high-end MOS tube is only used for motor replacement. The switch is switched to the time, the lower tube is controlled by the PWM logic level, and both sides of the H-bridge use the same oscillator as the charge pump excitation source. The circuit of this scheme has low cost, few devices, and simple and reliable circuit. 3D Printing Ceramics,RBSic 3D Printing,3D Printing Service,Ceramic Components Using 3D Printing Ningbo FLK Technology Co., Ltd. , https://www.flk-global.com