Type of Document	Dissertation
Author	Francis, Gerald
Author's Email Address	jerryf@vt.edu
URN	etd-03192010-150706
Title	An Algorithm and System for Measuring Impedance in D-Q Coordinates
Degree	PhD
Department	Electrical and Computer Engineering
Advisory Committee	Advisor Name Title Boroyevich, Dushan Committee Chair Baumann, William T. Committee Member Burgos, Rolando Committee Member Lesko, John Jack Committee Member Tranter, William H. Committee Member
Keywords	Three Phase AC Systems Impedance Measurement D-Q Coordinates Rotating Coordinate Systems Power Electronics Transfer Functions
Date of Defense	2010-01-25
Availability	unrestricted
Abstract This dissertation presents work conducted at the Center for Power Electronics Systems (CPES) at Virginia Polytechnic Institute and State University. Chapter 1 introduces the concept of impedance measurement, and discusses previous work on this topic. This chapter also addresses issues associated with impedance measurement. Chapter 2 introduces the analyzer architecture and the proposed algorithm. The algorithm involves locking on to the voltage vector at the point of common coupling between the analyzer and the system via a PLL to establish a D-Q frame. A series of sweeps are performed, injecting at least two independent angles in the D-Q plane, acquiring D- and Q-axis voltages and currents for each axis of injection at the point of interest. Chapter 3 discusses the analyzer hardware and the criteria for selection. The hardware built ranges from large-scale power level hardware to communication hardware implementing a universal serial bus. An eight-layer PCB was constructed implementing analog signal conditioning and conversion to and from digital signals with high resolution. The PCB interfaces with the existing Universal Controller hardware. Chapter 4 discusses the analyzer software. Software was written in C++, VHDL, and Matlab to implement the measurement process. This chapter also provides a description of the software architecture and individual components. Chapter 5 discusses the application of the analyzer to various examples. A dynamic model of the analyzer is constructed, considering all components of the measurement system. Congruence with predicted results is demonstrated for three-phase balanced linear impedance networks, which can be directly derived based on stationary impedance measurements. Other impedances measured include a voltage source inverter, Vienna rectifier, six-pulse rectifier and an autotransformer-rectifier unit.
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