Control of three phase converters as source for microgrid
Rasool, Akhtar (2017) Control of three phase converters as source for microgrid. [Thesis]
Three-phase power electronic converter is the main component which plays the role of interconnection between a source(s) and a micro-grid or power-grid. The control of the power converter is very crucial in obtaining a reliable operation of a distributed generator or a source-converter in varying conditions of the grid. The control of converter is actually dependent on the control of its switching matrix. The DC to AC converter has three independent control inputs, and in a majority of control approaches, the goal is stated as the control of the current (specified in an orthogonal frame of references) or the power (active and reactive), thus having two dimensional control error. This leads to an underutilization of the capabilities of the switching converter. Thus, one more control requirement along power control has been defined to achieve a novel control solution for the power-converter. The additional control requirement is based on the difference of the zero-component of voltage (or current) on the grid and the converter's output side, which makes the proposed controller a valid solution for both the balanced and unbalanced conditions of the grid. Two orthogonal components are not enough in unbalanced grid conditions requiring either the zero-component or the respective positive and negative components be introduced. Hence, a simple grid-current control method is also developed, which satisfies the positive sequence power requirements and eliminates the necessary negative sequence components causing double frequency oscillations in power. The main contributions of this dissertation are; the development of a general control solution for power flow while utilizing the zero-voltage component of the grid and the improvement of an existing grid current control method for unbalanced grid voltage conditions.
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