Abstract
The major purposes of this thesis are to establish a parallel induction motor drive system and to perform its load sharing control. First, the possible parallel system configurations and their features are explored. In addition, some existing load sharing control strategies and also surveyed. Owing to the features of larger rating, rigid structure, brushless and possession of steep torque-speed characteristic, induction motors have been extensively employed for large equipments with parallel operation. For successfully performing its load sharing control, the basic characteristics, dynamic modeling and driving control of an induction motor are first comprehended. Then its load sharing control principle and methods are explored, and accordingly, the control method is proposed. For convenience of making performance evaluation test, a small parallel induction motor drive system driving a common load is established. Each motor is fed by its specific inverter. The master/slave current sharing approach is adopted for the proposed control method, and a simple disturbance cancellation based robust control is applied to enhance the load sharing control performance. In this thesis, a single-switch three-phase switch-mode rectifier (SMR) is designed and implemented. Circuit operation, design of circuit components and control scheme of this SMR are introduced in detail. Under well-regulated DC-link voltage, the line drawn power quality is much improved. The designed SMR is first verified its effectiveness by some simulation and measured results under resistive load. Then it is employed to serve as the front-end converter of the parallel induction motor drive. Some experimental results are provided to demonstrate the whole drive comparative performance including line drawn power quality, static and dynamic load sharing characteristics, dynamic speed response, DC-link voltage regulation characteristics, etc. Key words: Induction motor, scalar control, parallel load sharing control, master-slave method, disturbance cancellation robust control, three-phase switch-mode rectifier.