Passivity-Based Analysis and Performance Enhancement of a Vector Controlled VSC Connected to a Weak AC Grid

Abstract

Despite attempts to increase the active power capability of vector-controlled voltage source converters (VSCs) connected to very weak grids, the interaction between the control dynamics and physical system is not completely understood. The result is often complex strategies that are difficult to implement. This paper proposes an intuitive modification of the VSC control based on physical considerations and dynamics of existing control. Several physical variables as seen from the point of common coupling (PCC) are found to contribute to the detrimental behavior of the VSC under weak connections. Hence, eliminating the impacts of these variables through feedforward eliminates their influence and significantly improves the active power capability. Notably, the basic structure of the vector controlled VSC is kept and its output-impedance is effectively reshaped. The proposed modification is validated through nonlinear time-domain simulations in MATLAB/Simulink Simscape Power System and results demonstrate the simplicity and intuitiveness of the modified structure.

Impedance Decomposition for Design-Oriented Analysis of Grid-Forming Voltage-Source Converters

“…In such a system, Zg is strictly passive, while ZVSC may be non-passive in specific frequency bands. The passivity of ZVSC can be checked by the positive realness of the passivity index [43], which is the minimum eigenvalue of the Hermitian matrix of ZVSC, i.e.,…”

Grid–Following DVI–Based Converter Operating in Weak Grids for Enhancing Frequency Stability

“…The network with SCR≥3.0 is known as a strong grid while SCR<3.0 represents a weak grid condition [18]. Herein, we consider two SCRs, 2.5 and 1.0.…”

Comparative Study of Small-Signal Stability Under Weak AC System Integration for Different VSCs

“…Limited by space, the derivations of the AC impedance models are provided in the Appendix, and the detailed derivation process can be referred to [11]- [13]. The impact of the DC-side network is neglected [10] [12] [28] by setting the small-signal expressions for the DC current or DC active power to be zeros. The dq impedances of VSCs and the AC system are denoted as:…”

“…Retuning of the control parameters can be useful for stability improvement. In [26]- [28], the speeding up of the AC voltage controller and the slowing down of PLL are suggested for the VSCs under DC voltage and AC voltage control mode. While in this paper, the VSCs are under a different control mode.…”