Impedance-Based Stability Analysis in Grid Interconnection Impact Study Owing to the Increased Adoption of Converter-Interfaced Generators

Abstract

This study investigates the emerging harmonic stability concerns to be addressed by grid planners in generation interconnection studies, owing to the increased adoption of renewable energy resources connected to the grid via power electronic converters. The wideband and high-frequency electromagnetic transient (EMT) characteristics of these converter-interfaced generators (CIGs) and their interaction with the grid impedance are not accurately captured in the typical dynamic studies conducted by grid planners. This paper thus identifies the desired components to be studied and subsequently develops a practical process for integrating a new CIG into a grid with the existing CIGs. The steps of this process are as follows: the impedance equation of a CIG using its control dynamics and an interface filter to the grid, for example, an LCL filter (inductor-capacitor-inductor type), is developed; an equivalent impedance model including the existing CIGs nearby and the grid observed from the point of common coupling are derived; the system stability for credible operating scenarios is assessed. Detailed EMT simulations validate the accuracy of the impedance models and stability assessment for various connection scenarios. By complementing the conventional EMT simulation studies, the proposed analytical approach enables grid planners to identify critical design parameters for seamlessly integrating a new CIG and ensuring the reliability of the grid.

Impedance-Based Interactions in Grid-Tied Three-Phase Inverters in Renewable Energy Applications

“…Figure 11 shows the equivalent circuit of the converter in Figure 8, when it is terminated with a non-ideal load. According to Figure 11, the original output current ô The load-affected set of transfer functions can be obtained by replacingv o in the bottom row of Equation (24) by Equation (34), and in the upper row of Equation (24) by Equation (35), respectively. These procedures yield the set of load-affected transfer functions as…”

“…The origin of the stability problems in grid-connected systems is usually the negativeincremental-resistor-like behavior at the input or output impedance of the three-phase converter [29][30][31] similarly as in DC-DC converters discussed in References [1,2]. In three-phase converters, the negative-incremental-resistor-like behavior is either the consequence of the grid synchronization [29][30][31][32][33][34][35] or the feedback control from the output-terminal variables [36][37][38][39][40][41][42][43]. In case of grid synchronization, the instability can be mitigated in some extends by lowering the control bandwidth of the phase locked loop (PLL) adaptively when the grid impedance is increasing as discussed in Reference [44].…”

Harmonic Stability Analysis for Multi-Parallel Inverter-Based Grid-Connected Renewable Power System Using Global Admittance

“…The nonlinear methods [12,13] involve intensive computations and are not suitable for large-scale grid-connected systems. In contrast, the linear methods require fewer computations and The impedance-based approach is a frequency-domain analysis technique [19][20][21][22][23][24][25][26]. This method was originally presented in [19] and was used to study the interactions between DC-DC converters and their filters.…”

“…A grid-connected inverter is modeled as a current source in parallel with an output impedance, and the loads are modeled as input impedances. The system stability at the point of common coupling (PCC) can be assessed by determining whether the ratio of the load input impedance to the inverter output impedance (defined as the minor loop gain (MLG)) satisfies the Nyquist stability criterion [21][22][23]. Compared to the eigenvalue-based approach, the formulation of the system matrix can be avoided in this method.…”

Stability Analysis of Grid-Connected Converters with Different Implementations of Adaptive PR Controllers under Weak Grid Conditions

“…In this paper, the stability issues of the VSC with different implementations of the adaptive PR controllers and different PLLs are studied and analyzed using the impedance-based method [18,[23][24][25][26][27][28]. A suggestion to choose a suitable controllers' implementation and the related PLL for the VSC with adaptive PR controllers is given.…”