| In order to deal with the energy crisis,reduce environmental pollution and respond to the appeal of national energy conservation and emission reduction,energy saving of electric machine is necessary.According to the survey,the use of frequency control can save about 30%power under full operation for fan,water pump motors.However,compared with foreign advanced level,there are still many technical problems in the development of frequency converter in China.In order to improve the performance of frequency converter,on the one hand,based on the control technology of variable frequency power supply,a hybrid control strategy with PI controller and full order state feedback is proposed.On the other hand,based on the motor control technology,the control method of constant voltage frequency ratio control is selected,which does not depend on the motor parameters,is easy to operate and has strong robustness.However,the problem of light / no-load low-frequency oscillation will occur in the process of variable-frequency starting of asynchronous motor based on V/F control.However,when the variable frequency power supply drive asynchronous motors running nearby the intermediate or low frequency band without load or with light load,the oscillation occurs.It is of great significance to solve the oscillation problem and solve the technical problems so that Chinese variable frequency power supply enters the international market.The specific research contents are as follows:The mathematical models of the rectifier and inverter circuits are established in abc and dq coordinates.Combining the advantages of double closed-loop and state feedback control,the control strategies of rectifier and inverter are determined.The PI +state feedback control scheme is adopted in the rectifier and inverter,which makes full use of the zero point and pole of the closed-loop system,and accelerates the system response while ensuring the performance.Establish the quantitative relationship between the controller parameters and the expected value of the system performance index,and obtain the control parameters through coefficient comparison.In addition,analyzed the significant effect of feedforward decoupling on system performance improvement.The experiment shows that the variable frequency power supply has good dynamic and steady performance.Established the mathematical model of asynchronous motor.Obtained the small signal state equation of asynchronous motor in ideal state and the state equation of asynchronous motor considering dead time.Then the transfer function of input-output relationship at stator side is deduced.Through theoretical analysis,revealed the mechanism of speed,torque and current oscillation in the process of variable frequency starting of asynchronous motor.And discussed the influence of the motor parameters on the system stability.Considering the advantages of power balance based suppression scheme,such as no need to add extra sensors,low cost,independent of motor parameters,strong robustness and so on,proposed a reasonable vibration suppression strategy.Revealed that the effect of active/reactive power on the oscillation of induction motor is the same from the perspective of mechanism.Both active current feedback compensation and reactive current feedback compensation are selected to suppress the oscillation of asynchronous motor.The simulation results show that the speed torque waveform of the motor is significantly improved,and the system oscillation is well suppressed. |
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