Performance Analysis of Phase Controlled Unidirectional and Bidirectional AC Voltage Controllers ABDUL SATTAR LARIK*, MUKHTIAR AHMED MAHAR **, AND ABDUL RASHID SHAIKH*** RECEIVED ON 14.09.2010 ACCEPTED ON 03.01.2011 ABSTRACT AC voltage controllers are used to vary the output ac voltage from a fixed ac input source. They are also commonly called ac voltage regulators or ac choppers. The output voltage is either controlled by PAC (Phase Angle Control) method or on-off control method. Due to various advantages of ac voltage controllers, such as high efficiency, simplicity, low cost and ability to control large amount of power they efficiently control the speed of ac motors, light dimming and industrial heating, etc. These converters are variable structure systems and generate harmonics during the operation which will affect the power quality when connected to system network. During the last couple of years, a number of new semiconductor devices and various power electronic converters has been introduced. Accordingly the subject of harmonics and its problems are of great concern to power industry and customers. In this research work, initially the simulation models of single phase unidirectional and bidirectional ac voltage controllers were developed by using MATLAB software. The harmonics of these models are investigated by simulation. In the end, the harmonics were also analyzed experimentally. The simulated as well as experimental results are presented. Key Words: AC Voltage Controllers, Phase Control, Unidirectional Converter, Bidirectional Converter, Harmonics. * Associate Professor, Department of Electrical Engineering, Mehran University of Engineering and Technology, Jamshoro. *** Assistant Professor, Department of Electrical Engineering, Mehran University of Engineering and Technology, Jamshoro *** Regular Visiting Faculty, Department of Electrical Engineering, Pakistan Navey Engineering College, NUST, Karachi. 1. INTRODUCTION T he ac-ac conversion technology has been developing very rapidly because of its high efficiency and compactness. It is achieved by cycloconverters, dc link converters and ac voltage controllers [1-4]. The last one is simplest topology, control only output voltage, while its output frequency remains constant. This topology has many attractive features such as: simple controller designing as compared to other converter topologies, low volume and weight, and low cost due to less number of active and passive devices [4- 10]. Because of its smart features, AC voltage controller has recently drawn attention of many researchers. It is a well known fact that ac voltage controllers are periodic variable structure systems due to their switched operation. MEHRAN UNIVERSITY RESEARCH JOURNAL OF ENGINEERING & TECHNOLOGY, VOLUME 30, NO. 1, JANUARY, 2011 [ISSN 0254-7821] 151