| Doubly Salient Electromagnetic(DSEM)machine has many advantages such as simple structure,high reliability,adjustable field regulation and low cost,exhibiting good prospect in aircraft power system,automobile and industrial application.DSEM machine is similar to Switched Reluctance Motor(SRM)in terms of stack structure,whereas the operating principle is significantly different.The control methods of traditional brushless DC motor and SRM are hard to be adopted in DSEM motor directly due to different back-EMF and inductance characteristics and the introduction of field current.In addition,the torque capacity of DSEM machine can not been fully exploited.In this paper,the torque production mechanism and characteristics of DSEM machine are investigated based on which a novel control method with fully use of torque for DSEM is proposed.The output torque and efficiency of DSEM machine are improved by the proposed control method.At first,the torque production mechanism of DSEM machine is studied based on the electromechanical energy conversion principle and inductance characteristics.The characteristics of mutual torque,reluctance torque and cogging torque of DSEM machine are analyzed in detail.Three basic motoring modes SRM,DSM1 and DSM2 for DSEM machine are provided and analyzed.The maximum torque output capability of DSEM machine is investigated based on static torque characteristics analysis.Hence,the Static Maximum Torque(SMT)control method is proposed.The torque ripple of DSEM machine is investigated and the suppression methods are discussed.The advantages and disadvantages of the existing Standard Angle Control(SAC),Advanced Angle Control(AAC)and Three Phase Six States(TPSS)control methods are analyzed systematically and studied in depth.As an optimization scheme,the Three Phase Nine States(TPNS)control method is provided.In the TPNS method,the inductance variation regions are fully utilized to produce torque so that the output torque of the motor is improved.Based on the SMT method,a better control method Asymmetrical Current Control(ASCC)method is provided.In the ASCC method,not only the inductance variation regions are fully used but also the reluctance torque is utilized.Hence,the torque output capability is improved to a higher level and the torque ripple is suppressed effectively.The influence of key structure parameters such as air gap length and rotor pole arc on the torque output capacity of DSEM machine are studied,which provides a good reference for the optimization of motor structure.The back electromotive force(EMF)of DSEM machine is analyzed and the uniform formulas for generating and motoring mode are derived.The No-chopping Current Control(NCC)method is provided.In the NCC method,the back-EMF of DSEM machine is adjusted by angle control parameters and field current.The number of phase current chopping decreases due to the balance between back-EMF and DC bus voltage.The efficiency of both motor and inverter are improved.Hence,the driving system efficiency is improved dramatically.In order to analyze and validate the control method proposed in this paper,a finite element analysis(FEA)model of DSEM machine is set up.The dedicated simulation pack for DSEM machine is developed by C language in Simplorer software.The similar-sized DSEM prototype machine and controller are developed with reference to the technical requirements of a 1.3k W induction motor driving system used in the electric forklift.The driving system experimental platform is constructed and the console software is developed by Lab VIEW software.With the adoption of proposed control method,the power and efficiency of DSEM machine are improved significantly.The overload capacity is up to 2.3 times and the system efficiency of the main working region reaches between 75% and 87%.The performance of the prototype fully satisfy the requirements of the electric forklift drive system which reveals that DSEM machine has a prosper prospect for the application in electric vehicles. |
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