Research On OS Induction Motor And Its Variable-frequency Drive System

Energy saving and emission reduction(ESER)has been set as a national priority in china since the 11th five-year plan(2006?2010)due to the increasing energy demand and environmental degradation caused by booming economic growth.Nowadays,efficiency and power density improvement of induction motor as well as topology simplification of its drive are important tasks in the "motor system energy efficiency(MSEE)project" which is one of the "ten key energy efficiency projects" in ESER plan.So far,there are lots of effective measures in the literature to either improve the efficiency and power density of induction motor or simplify the topology of its drive.As the MSEE project progresses,more and more attentions has been paid to the performance optimization of the induction motor and its drive.However,the traditional concept that the distribution of magnetic field in the air-gap of induction motor must be sinusoidal has hindered the further improvement of induction motor and its drive.This dissertation broke through this "sinusoid" restriction,and treated induction motor and its drive as a whole in the design and optimization progress.Then,the air-gap field distribution waveform best for the power density of induction motor was discussed,followed by the conclusion that a quasi-square(QS)distribution air-gap field can not only improve the efficiency and power density of induction motor but also simplify the topology of its drive when compared to the traditional sinusoidal one.As a new concept in induction motor drive system,the QS air-gap field technology provides another effective approach to improve the performance of the induction motor and its drive.First of all,impact of the air-gap field distribution waveform on the power density of induction motor,as well as the influence of harmonics in the field on the motor performance were analyzed in the dissertation.Based on these analysis results,an approach to generate the QS air-gap field was provided,and the conclusion that a QS air-gap field is much more suitable for induction motor than a sinusoid one was made correspondingly.The relationships between the rise time of the QS field waveform,during which the magnetic field is reversed between the peak value(Bp or-Bp)and zero,and the amount of field harmonic content,the magnetizing current value as well as the distribution of magnetic field in the core were investigated respectively.Thereafter,rise time values suitable for most applications were given accordingly.An easy and effective method to generate QS air-gap field was proposed in the dissertation,which is applying a set of symmetric QS voltages to stator windings of induction motor.Experiments that show a 19%improvement in power density and a 0.7 percentage point increasing in efficiency of an induction motor with QS phase voltage supply while compared to a traditional induction motor consuming almost the same material verified the feasibility of the method proposed.Secondly,expressions for parameters,such as resistance,inductance of both stator and rotor,of induction machine with QS field(QSIM)were derived based on the analysis of the MMF along the air-gap.It is shown that these parameters(in matrix form)are real symmetric circulant matrices,and they are diagonalizable according to matrix theory.Then,a special real matrix which can diagonalize these parameters was introduced,and a transmission based on this special matrix was established accordingly to transform variables to a multi-dimension dq reference frame which consists of several orthogonal dq-planes.Thereafter,a mathematical model of QSIM under the multi-dimension dq reference frame was developed successfully after deriving expressions of parameters in this reference frame.This model is simple and easy to use because of the elimination of coupling between different stator phases and the one between different rotor loops.In fact,it is suitable for analyzing induction motor supplied by any kind of sources,such as asymmetrical supplies,harmonic injection,with the use of fourier decomposition and symmetrical components method.Then,design principles were given according to the features of QSIM which are different from the traditional induction motor.Design of an induction motor is a tedious job,so only the parts which are essential to the design of a QSLM were described in this dissertation.The characteristics of various slot types of rotor were analyzed,and all the analysis justifies an unshakable view that the best slot type for QSIM are those tapered shaped slots,such as kite-shaped slot,round-bottom slot and pear-shaped slot,so that the teeth between rotor bars are of uniform section;Expressions of the core loss in the teeth and the yoke of QSIM were derived,which proves that thinner silicon laminations are much more suitable for both stator and rotor core of QSIM;Skin effect in the stator windings of QSIM was discussed,and the conclusion shows that the skin effect is too significant too ignore,so it would be an effective measure to adopt the so called rectangular twisted enamel insulated wire to manufacture stator windings;Impact of the magnetic wedge on Carter's coefficient and slot leakage inductance was analyzed,resulting in a conclusion that employ of magnetic wedge is good way to reduce the magnetizing current.Finally two prototypes of QSIM were manufactured according to the design principles proposed,one of which is 660V/99kW,and the other is 6kV/450kW.Finally,a parallel QSIM drive topology for low-voltage applications and a series QSIM drive topology for high-voltage applications were introduced in the dissertation.Two prototypes of the drive for QSIM based on these two topologies introcued were manufactured accordingly.The prototype with parallel topology uses capacitors together with the charactic that the motor stator current lags the motor stator voltage to produce the inclined section of the QS waveform directly,while the prototype with aeries topology adopts the QS-PWM to produce the QS waveform,and uses the startor windings of the QSIM to achieve the voltage balance of IGBTs connected in series.The feasibilities of both the parallel and series topology present were verified by experiments.Thereafter,control strategies for QSIM drives were discussed,as examples,the optimizing method for the v/f control strategy and the implementation of the vector control strategy were present.