Control and Integration Strategies for Bidirectional and Unidirectional Converters in Residential Distributed Power Systems

Reactive power compensation is important not only for power system stability but also efficient use of the power transmitted through the electric grid. Although many power electronics-based technologies such as flexible alternating current transmission systems and active power filters have emerged to overcome the shortcomings of traditional passive shunt compensation methods, they may not be the best solution for improvement of power quality of an entire power system due to high capital and operating costs, as well as additional inherent power losses. Usually, unidirectional power factor correction converters are utilized in many commercial applications as front-end circuitry in order to minimize the effects of harmonics distortion and poor power factor. Since these converters are commonly used, they have great potential as huge reactive power compensators in distribution level power systems. However, the distortion of input current as a result of reactive power compensation cannot be avoided due to intrinsic topology limitations. This drawback can be mitigated by employing bidirectional converters which would be incorporated in electric vehicles and photovoltaic systems, which are becoming increasingly available as residential distributed generation systems. The objective of this dissertation is to investigate reactive power capabilities of aggregated unidirectional converters and to propose cost-effective residential distributed generation systems with maximized local reactive power support capabilities. The proposed approaches are as follows: 1) to investigate functionalities of unidirectional converters as active power filers, 2) to analyze and design control algorithms for unidirectional and bidirectional converters in residential distributed power systems, and 3) to harmonize unidirectional and bidirectional converters in order to obtain harmonic-free reactive power support. The current distortion of the unidirectional converter under reactive power compensation is analytically explained and the performance of unidirectional converters as an active power filter is evaluated. Power control methods of bidirectional converters in photovoltaic and vehicle-to-grid systems are investigated. Finally, an integration strategy for controlling bidirectional and unidirectional converters is proposed. The outcome of this dissertation is to get free reactive power support using the existing resources without harmonic pollution in residential distributed generation systems