Study On Speed-senseless Control System Based On Three-level SVM Under 120° Coordinate

Induction motor is main driving equipment in our country and its annually power consumption occupies almost half of total power we generated.How to improve power utilization rate is very important and one way is popularize VVVF technology.High-performance VVVF IM is badly depends on the detection of rotor speed to realize dynamic response.But it increases cost and complexity and reduces the robust of the system no matter which method you use,speed sensors or optical-electricity encoder.The development of speed-senseless control system is the best solution.This paper has studied several high-performed IM speed-senseless control systems in aspects of circuit topology,modulation strategy,VVVF method and speed identification.The validity of the system has been analyzed by theoretical modeling and been proved by simulation and experimental test.Firstly several three-level topologies and modulation strategies are listed and CHB SPWM and NPC SVM are chosen to be studied.Traditional three-level space vector modulation algorithm will restrict the performance because of the massive triangular and square root computation it contains.This paper proposes a novel SVM algorithm based on 120° coordinate to avoid such drawbacks.Simulation shows its superiorities.Secondly,this paper studies scalar control method and vector control method in speed-senseless system.Equivalent circuit of IM and static mathematical model is derived as well as V/F control method.Owing to the oscillation and static speed error traditional V/F consists,an improved algorithm based on V/F method in which stator current signal is collected to compensate slip frequency and restrain oscillation,is proposed to solve these problems.Nonlinearity and multivariable mathematical model of IM and coordinate transformation theory is studied in vector control system.Rotor flux orientation is adopted and current closed-loop,flux closed-loop and speed closed-loop make up the double close-loop system to realize decoupling.Stator flux observation is based on current model and MRAS is used to acquire the rotor speed of IM.Similarly,simulation is implemented to verify the validity of the method.Lastly,experimental system of IM is set up in order to conduct the experimental test of speed-senseless vector control system based on three-level SVM under 120° coordinate.The validity of the system has been proved by experimental test.