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Research Of Winding Excited Synchronous Motor Based On Sensorless Vector Control Technology

Posted on:2010-02-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:W T KongFull Text:PDF
GTID:1102360278474232Subject:Power electronics and electric drive
Abstract/Summary:PDF Full Text Request
Winding excited synchronous motor (ESM) has many advantages of adjustable power factor and high efficiency, so it has been widely applied in high power apparatus. It is of great economic value and social effects for researching and developing high performance driving system of excited synchronous motor. Recently, there are mainly two control schemes used to develop high performance ESM drive system: one is direct torque control (DTC), and the other is field orientation control (FOC). Field orientation control of ESM has many merits: its control structure is very simple, the physical concepts is clear, the fluctuation of current and torque is little, the response of speed is rapid, and control strategy is easy to digitization. So, more and more people pay attention to this method in AC drive fields. However, research of vector control system about ac-dc-ac excited synchronous motor lacks full and in-depth study. The theory of vector control system has not been constructed. This paper discusses the primary theory of excited synchronous motor and carries out the practice study in detail. And then solid foundations are completed for researching the system more depth and widely in the future. This thesis has mainly the following aspects:Above all, several familiar synchronous drive systems are reviewed, and the principle of variable voltage at variable frequency about synchronous motor is analyzed. Based on this theory, the application of sesorless schemes in synchronous motor is described, and the sensorless technology is classified into two kinds. One is based on the fundamental variables, and the other is based on external exciting signal. Then the estimation methods of the initial rotor position are reviewed and these methods can be classified as: basing on the saturate effect of motor magnetic circuit, high frequency signal injection, induced voltage of stator windings, and the calculation of stator inductance etc. There are few papers investigating ESM initial rotor position estimation.Vector control theory of excited synchronous motor is studied in detail and the control structure is built up. First, three phase stationary ac signals are transformed equivalently into two phase rotated dc signals and ac motor is controlled to act as dc motor. Then voltage matrix equation, power equation and motion equation of field oriented control of salient pole synchronous motor are obtained based on Clarke and Park transformation. According to above equations, the equivalent circuits and vector diagram in dq axis are plotted out and mathematical models described by state space in dq axis are constructed.Second, according to model reference adaptive control theory, the speed of synchronous motor is estimated. Neglecting the effect of damper windings in d axis and taking the synchronous speed equal to zero, the mathematical models ofsynchronous motor inαβstationary reference frame is obtained. The equationwithout speed information is acted as reference model and the equation with speed parameter is acted as adjustable model. The rotor speed is estimated in terms of Povpov's hyperstability criterion and positive theory.Then a flux observer is designed to estimate the rotor flux according to the rotor speed identified by model reference adaptive system and realize closed-loop control of feedback flux. A reduced order state observer is adopted to reconstruct the rotor flux component, and the poles of flux observer are assigned properly by pole assignment algorithm to satisfy the performance criteria of system and to get the purpose of observing flux.To start with the basis concept of space vector, the paper analyzes the relationship of stator phase voltages and voltage vectors in space. Six active switching state vectors come from the inverter output voltages. These six active switching vectors and two zero vectors compose a set of voltage space vectors with same amplitude in different phase to approach circle rotating flux. Second, . according to the sector of voltage space vectors, adjacent switching state vectors are selected to calculate on-durations under volt-second balance principle. The questions of judging sectors and sector transition are discussed and qualitative analysis of performance is carried out. At last, an experiment is carried out according to the time duration by means of software construction method.According to the linear modulation, an overmodulation technology based on voltage space vector is proposed. The overmodulation area subdivide into two different mode by modulation index, one is mode I (0.907 < m≤0.952) and the other is mode II (0.952 < m≤1). Then the modulation character and realize theory of two overmodulation mode are analyzed in depth. When the voltage space vector is located within overmodulation mode I, the locus in the hexagon remain the circular, but the amplitude is larger than the modulus of voltage space vector to compensate the voltage distortion on the edge of hexagon; the reference voltage vector tracks the hexagon sides in the remaining. In this field the amplitude of voltage space vector is distorted and phase angle is continuous. When the voltage space vector is in the overmodulation II, the reference voltage is no longer tracking the circle of radius and holds an angle at the vertex and then moves along the hexagon. In this mode, the amplitude of voltage vector is distorted and phase angle is discrete. There is a holding angle at the vertex of hexagon. The computational formulas of six sectors in mode I are derived from above theory and an experiment is carried out on the TMS320LF2407A. The results demonstrate the overmodulation algorithm feasible.The principle about dead-time effect of inverter is clarified. And then a method to compensate voltage deviation based on the phase current polarity is proposed to improve the inverter output voltage. In this method, two stator phase currents aredetected and the components ofαβaxis in stationary coordinate plane are obtained through a finite impulse response digital filter. The stator current vector is synthesized based on theαβcomponents and the sector that current vector islocated in is judged by calculating the phase angle of current vector. Then according to polarity of three phase currents, the magnitude and direction of compensated voltage vector is determinate. The validity and feasibility of dead time compensation is proved through simulation and experiment.At last, a summary is made about the work of this paper and states the researching achievement. The content that needs further studies on this project is pointed out.
Keywords/Search Tags:Electrically Excited Synchronous Motor, Space Vector Pulse Width Modulation, Overmodulation, Model Reference Adaptive System, State Observer, Dead Time Compensation
PDF Full Text Request
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