Abstract
Due to the merits of high efficiency, high power density, high torque to inertia ratio and wide speed range, interior permanent magnet (IPM) motors have now attracted more and more industrial applications. The objective of this thesis is to design a more precise speed controller for AC motors by using phase-locked loop (PLL) technique, which is a common technique used in communication systems. Basically, the major contributions of this thesis may be summarized as follows. First, considering the inherent inertia, a novel phase frequency detector (PFD) is proposed. Depending on whether the magnitude of the speed error is large, small, or almost zero, the output of the proposed PFD is set equal to zero, linear virtual phase difference, real phase error, respectively. By this way, the generated control torque components due to speed error and phase error can be properly coordinated during the whole speed range. Second, based on the proposed PFD, a novel precise adjustable speed controller is proposed. Special merits include adopting the maximum torque per ampere control strategy to achieve fast dynamic response and being able to achieve much better accuracy. Basically, the proposed speed controller configuration comprises two control loops. One is the conventional PI speed control loop as is used in common industry and the other is the previously mentioned PFD PLL loop to achieve more robust PLL control. In addition, some design criteria are presented for fast design of the proposed controller to satisfy the specification. Third, a prototype system is constructed for a 6-pole 2-hp IPM motor based on the proposed controller by using DSP TMS320F2812 together with FPGA LFEC10E to verify the validity of the proposed controller. Experimental results of the prototype show that the corresponding IPM motor can be controlled smoothly from 482 rpm to 3122 rpm with zero speed error.