Research On Control Algorithm Of Dodecagon Space Voltage Vector Soft Starter

Three phase asynchronous motor has the many excellent properties such as stable and reliable operation,easy maintenance,simple structure and so on,it takes the lead in the production and life of the mining industry.However,it has the disadvantages of large starting current and small starting torque in asynchronous motor,these defects not only limit the scope of application,but also cause problems of reducing the voltage of the power grid and affecting the normal operation of other equipment.The common solution to this problem is using soft starter,which can adjust the starting voltage and the current of the large and medium asynchronous motor to reduce the harm degree.There are many kinds of control strategies for soft starter,but in the final analysis,the analysis of the internal voltage and current of asynchronous motor is indispensable.By establishing the mathematical model of steady state and dynamic state,qualitative analysis of the voltage and current relations of asynchronous motor plays an important role in the optimal control.This paper takes low voltage soft starter as the object of study,proposes a nonlinear tweleve-sided space voltage vector soft start scheme for AC-frequency conversion.By controlling the turn-on and turn off of the IGBT devices,adjusts the stator voltage and current of asynchronous motor,to make the motor work in the state of alternating conduction of two phase and three phases,until the startup is complete.In this process,the stator’s voltage frequency is increased from the preset frequency point to the power frequency according to the control strategy and then finish the start.In order to achieve the desired starting effect,in this paper,the frequency analysis method is used to give the frequency division strategy: 13,7,4,1,meanwhile,using the piecewise analytical method,givening the dynamic mathematical models of some typical operating states,especially thestator current equation under the state of focus,thus it can reflect the mechanical and electrical characteristics of the asynchronous motor’s soft start.As contrast,in this paper,the dynamic model of the nonlinear hexagon space voltage vector soft-start which controlled by semi-controlled device named thyristor is simple reduction,presents the feasibility analysis of stator voltage operation in two-phase voltage state and the advantages and disadvantages of the motor working on the two phase power supply.In this paper,the control strategy of space voltage vector soft start method is further improved based on the nonlinear hexagon method,the results show that the proposed scheme can further reduce the current during motor starting,improve starting torque,and improve the stability of motor running.This paper elaborates focuses on the following aspects.1)Derivation of equivalent circuit and basic formula of three phase asynchronous motor.This part describes the starting torque of asynchronous motor and characteristics of starting current and speed,introduces several mathematical models of asynchronous motor.The advantage of coordinate transformation method in dynamic analysis of asynchronous motor and the basic principle of space voltage vector are analyzed emphatically.Deductions the state expression in dq0 coordinates,at the same time,establishes the numerical simulation circuit of Simulink,it is necessary for the following research.2)This paper proposes the soft start control strategy of the voltage vector in the twelve nonlinear space and gives the detail implementation.Firstly,introduced the starting strategy of nonlinear hexagon,which realized by predecessors,and analyzes its shortcoming.Then,establishes the dynamic mathematical model of the nonlinear twelve edge starting process by using the analytical method,and deduced the flux variation of each stage.Because there are many frequency points in the starting process,lead to the result of dynamic analysis is large,and some states are repeated at different frequencies,no need for full analysis,so in this paper,only gived the modeling and analysis of four typical states.3)Establishing the dynamic mathematical model of a typical voltage vector in the process of nonlinear hexagonal soft starting,obtaining and analysing the characteristics of current and voltage.Secondly,analysing the asymmetry of themotor under the condition of two-phase power supply,obtaining the characteristics of motor phase lacking operation,furthermore,analysing the feasibility of two phase start-up.