| Asynchronous motor is a multi-variable, high order, strongly coupled nonlinear system, it’s not as easy as the DC motor to control torque. With the new power electronic devices and microprocessor’s launch and the continued development of the control theory of the AC motor, AC variable frequency technology has long-term development.In this paper, three different control algorithms based on AC drive technology of induction motor, three sets of control system were designed, and the results were analyzed and compared. They are:open-loop speed variable voltage variable frequency (V/F) speed control system based on SVPWM technology, speed closed-loop slip frequency speed control system and vector control system.Algorithm Ⅰ:On account of the problem that traditional sinusoidal pulse width modulation (SPWM) can not take advantage of the inverter DC voltage, using a space vector pulse width modulation (SVPWM) technology, which makes the DC voltage utilization increased by 15%, and the total Harmonic distortion becomes smaller, and the switching frequency is also reduced. According to open-loop variable voltage variable frequency (V/F) speed control principle, incorporated in the electric vehicle during acceleration-and-deceleration user satisfaction survey, an acceleration-and-deceleration curve is set, so that the motor will not be subjected to large current impact damage during acceleration and deceleration.Algorithm Ⅱ:For the problem that there is just a limited speed range and precision is affected by the load of the open-loop speed VVVF speed control system, using a closed loop speed control slip frequency method to control the speed of the electric vehicle. Combined with space vector pulse width modulation technology, increasing a speed loop on the basis of open-loop speed control, and then comparing with a given speed, outputting a value corresponding to the slip frequency, through a proportional-integral (PI) control to adjust the output speed, ultimately controlling the motor speed.Algorithm Ⅲ:The main idea of vector control is that making sure that the asynchronous motor is equivalent to a DC motor to control. Through vector coordinate transformation, making sure that non-linear, strong coupling of flux and torque of the AC motor model is decoupled,then the stator current vector is decomposed into two components:an excitation current component and a torque current component, through the control of the two vectors respectively, the asynchronous motor can be like a DC motor as the magnetic field and the torque are controlled independently.In this paper, the above three algorithms were analyzed in the simulation analysis through Simuink, and the algorithms were verified in the actual hardware circuit with a TMS3202812 chip to control the core, through the open-loop and closed-loop control system with current and speed detection circuit, a DSP program was given for the real-time control software. Experimental results show that the open-loop speed variable voltage variable frequency speed control can track a given curve by a certain steady-state error, but does not have the capability of anti-load disturbance, so it can’t meet the requirements of the general frequency control system. On the contrary, speed closed-loop slip frequency speed control system can not only eliminate steady-state error, but also has good anti-disturbance performance, we can see that the system has high speed accuracy and stability, so it can achieve a more accurate signal interference frequency control, but for situations that require high dynamic performance it is a little inferior. However, the vector control system not only has strong non-steady-state error, interference and anti-load capacity, but also has good dynamic performance, it is suitable for the occasion which has the requirements that a number of high dynamic performance, steady-state performance and robustness of, it is also a control system which should be widely adopted in the future. |
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