Steady-state Characteristic Analysis And Comprehensive Optimization Research Of Chopper Cascade Speed Control System

The energy-saving speed control of high-voltage and high-power motor has important national economic significance.Chopper cascade speed control is an efficient way of high voltage and high power motor speed regulation,which is widely used in industry.The cascade speed control equipment is connected from the rotor side of the motor,which transforms the high-voltage speed control of the stator side into the low-voltage speed control of the rotor side,and only needs to control the slip power which is far less than the rated power of the motor.It has the advantages of low control voltage,small control power,simple structure,low self loss,low operation environment requirements,etc.Therefore,the chopper cascade speed control system has a unique advantage in the high-voltage high-power motor speed control.At present,the research on the chopper cascade speed control system mainly focuses on theoretical research,parameter calculation and simulation modeling,which is rarely combined with engineering application.Due to the lack of research on the steady-state performance and comprehensive optimization of the system,device characteristics and unit structure,the reliability of the chopper cascade speed control system has not been guaranteed for a long time.In this dissertation,the chopper cascade speed control system is studied and analyzed aiming at the above problems for the first time,and the correctness of the research results is confirmed by engineering practice.The following research work is mainly carried out:1.According to the basic equation and equivalent circuit of asynchronous motor,based on the nameplate data of asynchronous motor,the calculation formula for calculating the equivalent circuit parameters of asynchronous motor is established.Through sample calculation,the value range of equivalent parameters of different power motor is provided,which provides theoretical basis and engineering data reference for the equivalent parameters of wound motor.The accurate model of equivalent circuit and parameter identification of equivalent circuit is established,and the nonlinear equation solving problem is transformed into optimization problem.The parameter identification method of asynchronous motor based on nameplate data and PSO optimization algorithm is obtained,which improves the calculation accuracy of equivalent parameters of motor under speed regulation.2.The working states of the main circuit components and power units in three steady states of the chopper cascade speed control system are analyzed,and the control logic is designed to realize the stable conversion between the speed regulation steady states,which provides the design principles for the steady-state conversion control of the chopper cascade speed control system.According to the equivalent circuit of the main circuit,the mathematical model of the main circuit in the speed regulation steady-state is established,and the function relationship between the main electrical parameters of the main circuit in the chopper cascade speed control system is obtained,as well as the ripple formula of the main electrical parameters,which provides the theoretical basis for the steady-state analysis of the main circuit in the chopper cascade speed control system.Based on the steady-state analysis of the main circuit,the parallel topology,parallel IGBT synchronization,low sense laminated bus of high-power chopper unit are optimized.The optimization scheme of high-power chopper unit is proposed for the first time,and verified in the domestic maximum power(5400kW)cascade speed control project,which solves the key problems of the application of chopper cascade speed control system in high-power motor.3.The loss of chopper reactor is studied deeply.According to the theory of core loss and the analysis of working current characteristics of reactor,the mathematical model of core loss of chopper reactor is established based on the modified Steinmetz empirical formula,which is verified on the high-power simulation load experimental platform,providing theoretical basis and engineering methods for the design and selection of chopper reactor.4.Based on the steady-state analysis and the direct correlation between the parameters and the performance of the speed control system,four main performance parameters of the speed control system and five key parameters that affect the performance of the speed control system are identified.The influence of key parameters on the performance of the system is systematically analyzed.From the overall situation of the speed control system,the comprehensive optimization scheme of the system is put forward to realize the comprehensive optimization of the speed control system in three aspects of speed control performance,reliability and economy,which provides the comprehensive optimization method and practical application scheme for the design of the chopper speed control system.5.The power factor of the chopper cascade speed regulation system is studied,the reasons for the low power factor is analyzed,and a low-voltage integrated reactive power compensation scheme is proposed.In view of the practical problem of inverter subversion when low-voltage reactive power compensation is switched on and off,the mechanism is analyzed and the solution is proposed.Based on the principle of reducing the harmonic at the rotor side to improve the power factor,the improvement scheme of capacitance absorption of rectifier unit is proposed.