Research On Four Quadrants Control System Of AC Induction Motor Based On Dual-PWM Converter

With the extensive application of the AC motor drive and its speed control, theperformance of the motor control system has been highly regarded. On one hand, people wantthe control system to have high dynamic performance and strong robustness. On the otherhand, people want the control system to have little energy cost to meet the requirements ofenergy saving and environmental protection. Nowadays, the vector control has become mainstrategy of the AC motor control because of its advantage of small current ripple, goodstarting performance, wide speed range, etc. In order to achieve fast control of the speed, thespeed signal is needed and added into speed control loop. However, the general approach isusing the speed sensor to detect the rotational speed. This method is simple and intuitive, buthigh-precision speed sensor is expensive and some occasion is inconvenient to install thespeed sensor. Thus, speed sensorless vector control method solved the above problems. Thismethod uses the existing detection information, such as voltage and current, to estimate themotor speed by software algorithm. It works during the low speed range or high speed range.As the general inverter, its AC current includes large harmonic component and energy can notbe reserved to the power grid. To overcome above disadvantage, it needs to improve thetopology of General inverter. Using the PWM rectifier to replace the diode rectifier andcomposed of dual PWM inverter enables two-way flow of electrical energy and meet therequirement of the motor four-quadrant operation. Electricity generated by RegenerativeBraking or power generator operation of the motor can be transported back to the griddirectly.This paper analyzes the working principle of double PWM converters. It consists of twoparts, including PWM rectifiers and PWM inverters. Because of the intermediate DC link, wecan regard these two parts as two independent subsystems. This paper also analyzedaccording to the two parts separately.Firstly,as the PWM inverter section of the motor side, byanalyzing the mathematical model of induction motor in the dq rotating coordinate system,the rotor flux oriented vector control strategies was adopted.Estimation module was designedbased on the voltage and current mixed flux observer and motor speed. The speed sensorlessvector control system was achieved. Secondly, the mathematical model of PWM rectifier wasbuilt. The vector control strategy oriented by the grid voltage vector was established and thevoltage and current double closed-loop controller was designed. The targets of sinusoidal ACcurrent and stable DC bus voltage were achieved.Finally, regarding DSP and FPGA as the core of control, we designed a dual PWMcontrol system prototype to have related experiment. The main circuit of the system hardwareand its software modules are introduced. During the experiment, we introduce the grid-sidePWM rectifier subsystems, motor-side speed sensorless vector control subsystem, and thewhole system of joint experiment respectively. The experimental results show good overallsystem performance. Results consistent with theoretical simulation analysis and verify thecorrectness of the theory and show certain practical value.