Research On Dual Three-level Variable-frequency Speed Regulation System For Induction Motor

The increasing scarcity of energy supply and the deepening of govement’s requirement for creating conservation-minded society have prompted energy-saving reform of some high-power drive equipments. The traditional mode of inverter supplied by no-control or phase-control rectifiering device maked the grid quality worse. Moreover, in high-voltage high-power drive field, the application of variable frequency drive system is restricted by the current tolerance and voltage rating of power electronic devices. In this background, with the development and maturity of multi-level technology, dual three-level converter on the large capacity induction motor drive system has become a hot research in recent years.By making dual three-level converter system for induction motor as the study carrier, according to the diode clamped three-level topology, regarding three-level SVPWM modulation algorithm, three-level PWM rectifier and induction motor vector control system as the research object, the following research works are carried out in this thesis:Firstly, the thesis studies the three-level SVPWM control algorithm in depth.On this basis, the effect of different space vectors on neutral point balance is analysed, and SVPWM switching sequence is also presented which can reduce the switching losses, limit the dv/dt based on the principle of three-level converter for selecting switching state. The simulation results by Simulink verify the correctness of the three-level SVPWM algorithm.Secondly, a three-level PWM rectifier based on the feedforward decoupling double-loop control system is discussed in this thesis. At the same time, a software phase-locked loop based on dq coordinate system is designed and the dual closed loop direct current control strategy of three-level rectifier is also analysed. After that, the specific process and method for controller designing are presented, in accordance with the engineering optimum.Among vector control schemes for induction motor, much less parameters in stator flux orientation (SFO) are required than in rotor flux orientation (RFO). So the vector control system of IM based on SFO is more robustness to parameters than it based on RFO. In this thesis, the starting point and principle of the SFO have been represented in detail, the decoupling methods between flux and torque have been profound discussed, the system structure of the vector control based on SFO has been constructed. At last, a well stator flux observation result has been achieved by applying the limiting level fixed dual integrator to the stator flux observation.Finally, in the Matlab/Simulink platform, a simulation model of dual three-level variable-freqency speed regulation system is structured by combining the three-level rectifier with the vector control system of IM. Simulation results show that, the dual three-level converter system has good static and dynamic speed performance, and can carry load at zero speed. On the other hand, the system also can achieve two-way flow of energy and ensure the realization of unity power factor control on the grid side. Furthermore, a control method with active power feedback is applied to balance the DC bus voltage. The active power on the inverter side feeds into the current reference of the rectifier side, which decouples the DC bus voltage from the motor operation state. Theoretical analysis and simulations prove that the method greatly reduces the influence of sudden changes in the motor operation state on the DC voltage.