Development of asymmetric controllers for frequency converters

Valerijus Zlosnikas

Doctoral dissertation

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The research results of the asymmetric controllers developed for the control of plants with the asymmetric dynamics are presented. The main aim of the work is to create the control algorithms of asymmetric controllers and to investigate them in control systems of plants with the asymmetric dynamics and linear plants. The term of the plant with the asymmetric dynamics is characterized, the problems of control of plants with the asymmetric dynamics and linear plants using popular in the industry PI and PID controllers are formulated. The asymmetric PI (aPI) and PID (aPID) controllers, which implement the control algorithms with the variable parameters are suggested in the work. The values of parameters of aPI and aPID controllers are switched when sign of plant parameter time derivative or control errror changes. The proposed controllers are investigated in the control systems of plants with the time constant, response delay and actuator limitation rate asymmetry. The obtained results show that the developed controllers as compared to the PI and PID controllers allow us to reduce the setpoint change response setling time and overshoot of control systems of plants with the asymmetric dynamics. Additionally, they allow us to decrease the setling time of transient caused by the load disturbance of control systems of plants with the asymmetric dynamics and linear plants as well. The investigation results are obtained using softwares Spice and Simulink, and experimentaly. The new model of plants with the time constant asymmetry based on the standard blocks of Simulink software is proposed. The stability of control systems with the asymmetric controllers is analyzed. The suitable non-linear control systems stability analysis methods are chosen. It has been defined that the Popov criterion and its modifications can be used for stability analysis of control systems based on the asymmetric controllers in the situation when the linear and non-linear parts can be separated. This method can be implemented only in the case when linear plants are controlled using asymmetric controllers. The stability analysis results of such a control systems were verified using software Simulink. The experimental investigation results of control systems based on the asymmetric controllers are presented. The investigation is performed using HIL (Hardware in the loop) technique and industrial ventilation system stand. The proposed asymmetric controllers are implemented in the specialized frequency converters for the automatic control of speed of AC induction motors used in the modern ventilation and water supply systems. The research works were related with the 2 projects financed by the industry and two projects supported by the Lithuanian State Science and Study Foundation and Agency for Science, Innovation and Technology. The results of the dissertation were presented in the 10 scientific conferences and published in the 11 scientific papers.

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145×205 mm
98 p.
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