Design, Analysis And Application Research Of Full Order Flux Observer For Induction Motor

Traditional V/F control method for induction motor, which is characterized by its simple principle, easy implementation and robustness to parameter variation, makes the motor loading capability weak, dynamic response slow, speed accuracy low, etc. Scalar control and speed sensorless control, under the condition of no speed sensor, solve low speed performance well for induction motor, by observing motor flux and controlling the motor voltage in observed flux oriented synchronous coordinate. Vector control and direct torque control, which realize the high performance control for induction motor, improve the dynamic performance and steady accuracy in the range from zero to super high speed. They are widely applied in high performance fields like digital control, electric locomotive, and so on. Despite of their different control structure, flux observation is necessary in these methods. Therefore, thoroughly carrying out induction motor observer design research makes sense in improving induction motor performance and enlarging speed range.Full order flux observer, simulating the practical running condition of motor, realizes the simultaneous speed identification and flux observation for induction motor by constructing motor state equation. Speed sensorless drive for induction motor as the application background, deep and systematical research is made, covering the content of full order flux observer feedback matrix design, speed adaptive law design, flux observer convergence analysis, flux observer parameter sensitivity analysis and the application of full order flux observer in speed sensorless induction motor drive.Under the condition of identifying motor speed, full order flux observer feedback matrix design is studied. The smoothness degree of transition from current model to voltage model is characterized by observer characteristic function. Full order flux observer can be divided into speed identification system and flux observation system in two-time scale. Based on them, analysis is made of the influence of feedback matrix on full order observer characteristic function, speed identification system and flux observation system. A kind of feedback matrix design is proposed, improving smoothness degree of transition and system damping ratio for full order flux observer.Deep research is carried out in speed adaptive law design for full order flux observer. Stability analysis is made of the traditional speed adaptive law based full order flux observer. The unstable range is derived by theoretical deduction, and the cause for the instability is explained. According to the unstable characteristics, speed adaptive law design rule in low speed regenerating mode is proposed. Low frequency current is injected in zero synchronous frequency and the acquisition for induced voltage, which is related with the magnetic field angle error, is introduced. Research is done on the relation between identified speed error and magnetic field position error. Corresponding induced voltage based speed adaptive law is given.Flux convergence characteristics of full order flux observer is analyzed, and compared with that of voltage model flux observer and current model flux observer. Flux observer constructed in the observed rotor flux oriented synchronous coordinate, the relation expressions between motor flux and observed flux are derived. By exploring convergence time constant for the practical flux and observed flux, analysis is carried out on the convergence characteristic in different speed acquisition methods.Parameter sensitivity of full order flux observer is analyzed, and compared with that of voltage model flux observer and current model flux observer. Identified speed expression and relation expression between practical flux and observed flux for every observer are derived in steady state. Three-dimension figures depicting the variation of speed error and flux angle error with motor speed and load are drawn, by which parameter sensitivity is explored.Stability of full order flux observer based speed sensorless control system is studied. By small signal method, the whole control system is linearized and transfer function from speed reference to practical speed is obtained. Examining pole distribution of transfer function, stability analysis is carried out. The impact of motor parameter error on speed identification system is studied. Research is made on the relation between lowering bandwidth of speed identification loop and control loop and improving speed sensorless control system stability.Experiments are done in TMS320F2407 based platform. For full order flux observer, observation characteristic in whole speed range, performance improvement by proposed feedback matrix design and sensitivity to stator resistance are tested. Stability and parameter variation rejection is explored in full order flux observer based speed sensorless induction motor drive. Comparison about the loading capacity in low speed range among full order flux observer, voltage model flux observer and current model flux observer based sensorless induction motor control system is carried out.