AC-AC Converter With Controllable Phase And Amplitude:Topologies And Control

The active and reactive power flow through an ac transmission line are the functions of the line impedance, the amplitudes of the sending-end voltage and the receiving-end voltage, and the phase difference between the two voltages. By regulating the amplitude and phase of the node voltage in a grid, the active and reactive power flow can be effectively controlled without changing the impedance of a transmission line. In this dissertation, a novel method for power transmission control? ac-ac converter with controllable phase and amplitude(ACCPA) is proposed, and a new kind of ac-ac conversion technology and its control strategy are studied.By using the concept of working quadrant, a technique is presented to construct the circuit topologies of the buck type, boost type and buck-boost type ac converters. A cascaded buck-boost ac converter and a p type buck-boost ac converter are proposed respectively, which have the functions of both voltage step-up and step-down. Moreover, the output voltage is in phase with the input voltage, and the power switches have low voltage stress. Then several mode-selection control strategies are presented for stabilizing or regulating ac voltage. Two prototypes of a cascaded buck-boost ac converter and a p type buck-boost ac converter are manufactured. The experimental results verify the effectiveness of the theoretical analysis.Based on the cascaded buck-boost ac converter, ACCPA is proposed by adding an ac component of double frequency into the duty ratio of its front-part. The ACCPA has two control variables and is able to continuously regulate the phase and amplitude of the output voltage respectively. The front-stage of single-phase ACCPA is used to adjust the phase of the output voltage lead or lag and comprises of a buck type ac converter and a 3rd harmonic trap. Its back-stage is a boost type ac converter and is used to regulate the amplitude of the output voltage with the front-stage. In relation to the input voltage, the phase and amplitude of the output voltage of single-phase ACCPA can be regulated respectively, and the maximum adjustment range of phase angle j1 is among [-30o, 30o]. The principle of single-phase ACCPA is analyzed in detail and its control strategy is obtained. To verify the validity of the theoretical analysis and the feasibility of the control strategy, a prototype of single-phase ACCPA is manufactured and its principle experiments are carried out.The topology structure of three-phase ACCPA without 3rd harmonic trap is presented by using symmetrical relationship of three-phase. Its front-stage comprises of 3 single-phase buck type ac converters and its back-stage is a three-phase boost type ac converter. By controlling respectively the duty ratio of its front-stage dy1 x and that of its back-stage Dy2, the phase angle and amplitude of the output voltage of three-phase ACCPA can be regulated respectively and continuously. The operational principle of three-phase ACCPA is studied and its control strategy of the phase angle and amplitude is developed. A 1200 VA prototype of three-phase ACCPA is manufactured to implement respective close-loop control of phase angle and amplitude, and the experiment waveforms and test data are presented.Structures of π type single-phase ACCPA and π type three-phase ACCPA are proposed. Compared with the cascaded single-phase(or three-phase) ACCPA, π type single-phase(or three-phase) ACCPA retrenches a(or 3) front-stage output filter(s). Prototypes manufactured in chapter 3 and 4 are taken as experimental platforms respectively for π type single-phase ACCPA and π type three-phase ACCPA, and their principle experiments are carried out. The experiment results are given to verify the validity of the theoretical analysis and the feasibility of control strategies.