Abstract
This article proposes a modular state-space modeling framework for grid-connected voltage-source converters, where the different control loops, including the ac current control, the phase-locked loop, the dc-link voltage control, and the ac voltage magnitude control, can be modeled separately as building blocks. Moreover, the mathematical relationship between state-space models in the rotating ( dq -) frame and the stationary ( αβ -) frame is explicitly established, and, thus, the modal analysis can be performed directly in the αβ -frame, which allows intuitive interpretation of voltage and current oscillation modes in the αβ -frame. Experimental tests of a 3-kW back-to-back converter system validate the effectiveness of the unified modular state-space modeling and analysis.
Highlights
V OLTAGE-SOURCE converters (VSCs) are widely used in power grid applications, for e.g., renewable power generations [1], flexible power transmission and distributions, and energy-efficient consumptions [2], [3]
For the inner current loop, the multiple-input multiple-output (MIMO) system model can be simplified into single-input single-output (SISO) transfer functions based on complex space vectors
This SISO impedance model provides an intuitive insight into the interactions among the paralleled VSCs and weak power grids, and enables to reshape the output impedances of VSCs for stabilizing the power system [7], [8]
Summary
V OLTAGE-SOURCE converters (VSCs) are widely used in power grid applications, for e.g., renewable power generations [1], flexible power transmission and distributions, and energy-efficient consumptions [2], [3]. Those rules only apply to two subsystems with a well-defined interconnection form, whereas the control loops of VSCs are cross coupled with each other, which makes those rules difficult to apply Another modular state-space modeling approach that has been applied to power systems is the component connection method (CCM) [23], where the system is decomposed into multiple components, whose interconnections are modeled as a linear algebra matrix based on the algebraic relations of their inputs and outputs. Another major contribution of this study is to establish the mathematical relationship between the state-space models in the dq-frame and the αβframe, which allows the straightforward stability analysis and intuitive interpretation of voltage and current oscillation modes in the αβ-frame.
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