Abstract
The major merits of the fixed structure sliding mode control (FSSMC) are being able to preserve the robust performance of the traditional variable structure sliding mode control without changing the control system structure and meanwhile able to eliminate the unwanted chattering phenomenon. Moreover, owning to its fixed structure nature, the corresponding implementation becomes much more easier. Since the major research goal of this thesis is to improve the robustness of induction motor drives, the FSSMC theory is used to design the current and speed controllers of the induction motor drives simultaneously in order to achieve a doubly effective robust control. In fact, the title of the controller, namely, “double fixed structure sliding mode controller,” comes from this philosophy.Basically, the contributions of this thesis may be sum-marized as follows. First, a double fixed structure sliding mode controller is proposed for the robust control of both electrical and mechanical subsystems of induction motor drives and the chattering effect are eliminated simultaneously. Besides, the closed forms of the system eigenvalues are explicitly derived, which render the proposed controller design considerably simple and straightforward. Second, an “input re-gulator” in the electrical subsystem is separated from the dynamic system to convert the current control signals into voltage control signals without the time delay of dq-axes coupling effect. Another distinguishing feature of this input regulator is its ability to regulate the control parameters with the variation of the rotor flux speed to achieve the same dynamic performances under different operating conditions. Finally, a prototype is also constructed to verify the feasibility of the proposed control. The proposed controller is implemented fully digitally with a digital signal processor (DSP) TMS320F240 to reduce the number of hardware components, the volume and to simplify the maintenance problems.