Research On Speed Sensorless Direct Torque Control System For Six-Phase Induction Motor

Compared with three-phase speed control system,multi-phase speed control system has many advantages like higher power,lower torque ripple,better steady and dynamic performance.With the characteristic of high reliability,the motor can still be running with one or more open-circuited phases by adjusting control strategy.Thus,in the applications with high-reliability requirement like ship propulsion or aerospace Industry,multi-phase system is becoming more widespread.Direct torque control and vector control are the most commonly used strategies in the modern high-performance AC speed control field.Compared with vector control,direct torque control avoids rotating aixs conversion and the torque response is more rapid.Those various advantages of multiphase motor determines its application environment is relatively poor,but its requirements of reliability is very high,and the closed loop control of speed commonly used speed sensor to measure the motor speed in real time.The speed sensor is precision equipment which can be influenced by the environment,so the research of speed sensorless multiphase motor speed control system is very meaningful.Research content in this thesis is speed sensorless direct torque control system of six-phase induction motor.First of all,mathematical models of six-phase induction motor are built,by using the space vector decoupling transformation theory.Moreover,for the stator harmonic current is large in the six-phase induction motor,space vector pulse width modulation(SVPWM)algorithm based on the theory of space vector decoupling transformation is utilized to synthesize virtual voltage vector.And this thesis expands application of the fundmental voltage liner-output over-modulation algorithm,from three-phase motor speed control system to six-phase motor speed control system.And then,the theory of synthetic intermediate voltage vector is generalized to solve the problem of common mode voltage in motor control system.Validity of the algorithm is verified by simulation.Once more,the speed sensorless operation of six phase system is researched and use the artificial neural network control theory in the control of the six-phase motor speed identification.With the advantages of fast speed and high precision,the performance of six phase motor speed identification is improved.And the validity of this algorithm is also verified by simulation.At last,all the theories and algorithms above are tested on the hardware platform,and the experiments are carried out under the condition of speed sensor and speed sensorless.The experimental results prove the correctness of the theory.