Inherent Interaction Analysis for Harmonic Oscillations in the Multi-Paralleled Grid-Connected Inverter System Using a Sum Type Criterion: Global Admittance (GA)

Abstract

With the extensive use of power electronics converters, harmonic oscillation issues in the multiparalleled grid-connected inverter system have drawn much attention. Apart from the stability analysis using the impedance-based stability analysis method, the interaction analysis is aimed at revealing the changing process of the system state under the variation of some parameters such as the grid impendence, the number of grid-connected inverters and the control parameter of the inverter current control, etc. In this paper, after comparing the ratio type stability criterion and the sum type stability criterion, the interaction analysis using global admittance is presented in two frequency-domain dimensions. It shows that the harmonic instability depends on both the imaginary part of global admittance which determines the appearance of the resonance point and the real part of global admittance which reflects the property of such resonance point. The essence of this approach is to reveal the appearance of the resonance point and its influence on the system stability. The inherent changing rules of the resonance point are illustrated in the following typical occasions: different grid impendence, different number of grid-connected inverters and different control parameters of the current control loop. Finally, detailed simulations and experimental results validate the effectiveness of the proposed approach. INDEX TERMS Harmonic oscillations, stability criterion, interaction analysis, global admittance, resonance point, point of common coupling (PCC).

Impedance Characteristics and Harmonic Analysis of LCL-Type Grid-Connected Converter Cluster

“…As can be seen from Equation (27), G V_ff (s) is a second-order differential transfer function; it is then easy to introduce high-frequency noise interference into the control system. In this case, the power grid voltage can be low-pass filtered before the feedforward algorithm is implemented.…”

“…In [26], the stability of the grid-connected photovoltaic inverter is analyzed, and the resonance problem of the grid-connected inverter is discussed through the zero-pole distribution characteristic of the system. A sum type criterion is proposed to analyze the harmonic oscillation in the multiple grid-connected inverter systems, and based on the criteria, the stability can be predicted [27,28]. The phenomenon of equal amplitude oscillations of current sometimes occurs in power systems with power electronics.…”

Electromagnetic Oscillation Origin Location in Multiple-Inverter-Based Power Systems Using Components Impedance Frequency Responses

“…Based on the components aggregation procedures in Fig. 3, several impedance aggregation methods have been reported in the existing literature, which can mainly be grouped into the following five breeds [13], [16]- [19], [23], [36]- [39], [45]- [49]. In IBSC #1, the NC is performed one time at a certain node, e.g., PCC, with calculating RHP poles of the minor loop gain (MLG) and encirclement number of its Nyquist plot around (−1, j0), where the RHP poles of the MLG are identified from the theoretically-derived formulas of the load impedance and source admittance models [13], [16], [19], [45]- [47].…”

“…However, only local stability, i.e., stability of grid current, can be obtained in IBSCs #1, #2, and #3. In IBSC #4, the NC is performed at all nodes to assess stability of grid current and output currents of all GCIs with calculating RHP poles of the MLGs and encirclement numbers of their Nyquist plots around (−1, j0), where the RHP poles of the MLGs are identified from the theoretically-derived formulas of the load impedance and source admittance models [17], [48], [49]. In IBSC #5, the NC is performed sequentially at all nodes to assess stability of grid current and output currents of all GCIs without calculating RHP poles of the MLGs.…”

Responsibility Division for Harmonic Instability in the Multi-Paralleled Grid-Connected Inverters System Based on Impedance Analysis

“…Most research works on harmonic instability in the multiparalleled grid-connected inverters system mainly focuses on predicting system stability and exploring various measures to improve system stability, such as deriving stability criteria based on impedance analysis [7][8][9], or redesigning the control strategy of each inverter to achieve oscillation suppression [10][11][12][13][14][15]. However, the overall parallel system may still experience resonance or even instability even if all inverters individually meet the stability criteria [2,6,11].…”