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This paper analyzes the influence of non-dispatchable energy sources on the dynamic stability of stand-alone MicroGrids (MGs) with autonomous control of frequency and voltage based on inverters. The analysis considers the use of eigenvalue techniques. Although this methodology is well known, the contribution of this paper is twofold. First, it proposes an algorithm for designing the inverter interface to meet the requirements associated with the harmonic distortion (THD) and dynamic performance of the inverter. Second, it provides an analysis of the dynamic stability of MG considering different levels of penetration of non-dispatchable energy sources, variations in the network parameters and the presence of dynamic loads (i.e., induction motors). [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a method for PSS parameter tuning. The proposed method is based on the system identification using a Kalman filter. To eliminate the influence of inaccuracies of the mathematical model due to incomplete data of the system parameters, this paper proposes a procedure for identifying system parameters based on a Kalman filter. The identified system is the basis for determining the eigenvalue sensitivity function. PSS tuning is carried out based on the eigenvalue sensitivity analysis of changes of PSS parameters. In order to obtain the eigenvalue sensitivity function on the PSS parameter in a wider range of parameter values, it has been proposed to determine eigenvalues on the basis of the Bairstow method for solving polynomial equations. The entire procedure can be applied on-line, so the PSS structure and settings can be adaptive. Experimental tests carried out on a synchronous generator connected to an AC system demonstrate the effectiveness of the proposed method. Performance of the PSS tuned by using the proposed method was compared with the performance of the PSS tuned by using eigenvalue sensitivity. [Copyright &y& Elsevier]

Abstract: When an inter-area mode dominates a low-frequency oscillation in a stressed condition, control of the active power flow of interface lines, with compensating devices, can effectively reduce the electromechanical power oscillations. In general, interface lines in which inter-area oscillations are large are considered to be good locations for installation of compensating devices. A sensitivity analysis with respect to change in active power flow can provide an important factor in electric power system operation. This paper proposes a new methodology to calculate the damping sensitivity with respect to change in active power flow, which can be useful for accurate selection of critical lines from the viewpoint of small-signal stability. In the proposed methodology, a damping sensitivity index is used to select the critical lines to damp power system oscillations. This paper describes how to derive the damping sensitivity for the selected mode and illustrates an example applying the proposed algorithm to a simple two-area system and the New England 39-bus test system. [Copyright &y& Elsevier]

Abstract: Use of power electronic equipment has increased and introduced new dynamical phenomena in power systems. For example, new electric rail vehicles (locomotives) equipped with modern power electronic traction chains have caused situations of low-frequency power oscillations and instability in single-phase railway power supply systems. This paper presents the development and implementation of an instantaneous value model and simplified fundamental frequency (RMS) models of such an advanced electric rail vehicle in order to investigate their representation of low-frequency dynamics. The dynamical behaviour is studied by use of both time-domain simulations and linear analysis (eigenvalues) and the degree of simplifications regarding controller dynamics and power system dynamics are presented and discussed. An enhanced RMS model is tested in order to account for the impact of fast current dynamics on the low-frequency behaviour. The results show that this enhanced model is corresponding more closely to the instantaneous value model than what can be obtained by the traditional RMS simplifications and indicate that current dynamics should be included in stability studies involving power electronic inverters. [Copyright &y& Elsevier]

Increasing amounts of wind turbines are connected to electrical power systems. This affects many aspects of their operation and behaviour. In this paper, the impact of large scale wind power generation on power system oscillations is treated. The three main types of power system oscillations, namely oscillations of a group of generators against a strong system and intra- and inter-area oscillations are studied. To this end, test systems are used. The effect of wind power on the oscillations is investigated by gradually replacing the power generated by the synchronous generators in the system by power from either constant or variable speed wind turbines, while observing the movement of the eigenvalues through the complex plane. From the results, it is concluded that the effect of wind power on power system oscillations depends on the wind turbine concept (constant or variable speed) and on the wind power penetration. In most cases, an increase in frequency and damping of power system oscillations was observed. This observation is caused by a relative reduction in size of the synchronous generators that engage in power system oscillations, which is equivalent to strengthening their mutual coupling. Further, it was shown that constant speed wind turbines damp power system oscillations more than variable speed turbines. This is caused by the damping effect of the squirrel cage induction generator used in constant speed wind turbines. [Copyright &y& Elsevier]

Advancement of power electronic technologies makes ac systems to be more adaptive and flexible as new forms of power controller emerges in recent years. Though not yet well developed, underpinned research suggests that unified power flow controller (UPFC) is a promising power system controller. This paper proposes a method to coordinate UPFC with power system stabilizer (PSS) so as to damp down oscillations caused by small signal disturbance. It starts by deriving a mathematical model of UPFC, with which its linearized differential equations are integrated to design an overall control strategy for enhancing small signal stability of the so connected power systems. The approach is to identify the eigenvalue of the largest real part and then minimize it as a nonlinear optimization problem. In order to ensure the robustness of the control system, different operating conditions are simultaneously considered in the parameter optimization process. Results of a case study on the New England test system show that the model is correct and the method is promising for coordinating the model parameters to enhance the small signal stability of the complex power system. [Copyright &y& Elsevier]

• Eigenvalue stability analysis of SSTI applying accurate MMC state space model. • Significant risk of SSTI between MMC HVDC and nuclear plant generators. • Conclusions contrary to previous studies on MMC and two level VSC. • Comprehensive analysis of operating conditions and controller parameters. • Different impact of PLL gains on rectifier and inverter. This paper presents a comprehensive analytical eigenvalue stability study of subsynchronous torsional interactions between the 1 GW Eleclink MMC HVDC and the 1.12 GW Gravelines turbine-generator in north France. It revalidates the conclusions of previous studies on VSC-based HVDC systems by showing that the risk of SSTI may be of significance when the HVDC is based on the MMC and not the two level VSC technology. The study demonstrates that in the case of the weak French grid and the rated HVDC power flow from France to England, the HVDC can destabilize the dominant low frequency, 6.3 Hz, torsional mode. The analysis also expands the work of previous studies on MMC and reveals that the case of the HVDC power flow from the English to the French grid may also introduce the risk of destabilizing the lower frequency mode. Furthermore, it also reveals a noticeable impact of the PLL and that increasing the gains has an opposite effect on the two HVDC power flow directions. Moreover, participation factors are analyzed for the 6.3 Hz mode indicating that the main cause of the torsional interactions is the HVDC power control loop. The main findings are verified on the detailed EMTP model. [ABSTRACT FROM AUTHOR]