Jukka Turunen

Comparison of Three Electromechanical Oscillation Damping Estimation Methods

This paper describes three data driven methods to monitor electromechanical oscillations in interconnected power system operation. The objective is to compare and contrast the performance of the methods. The accuracy of damping ratio and frequency of oscillations are the measures of the performance of the algorithms. The advantages and disadvantages of various techniques and their limitations to measurement noise have been considered while assessing performance. The target frequency and damping are computed using the Nordic power system simulation model.

Experiences and future plans in monitoring the inter-area power oscillation damping

This paper first describes what kind of inter-area oscillations there exist in the Nordic power system and in what kind of situations they affect the power transfer capacity. The paper also describes the actions already taken in order to improve the damping of the oscillations and the efforts at online-monitoring of the damping level. The results of a two yearpsilas monitoring period imply that one should have different approaches to frequent small and infrequent large power oscillations. The first one of these is more difficult in nature and requires system-wide synchronised phasor measurements combined with a solid mathematical method to reliably calculate the damping level. Some plans are presented that are based on using several input signals measured from different points of the grid and using a known probing signal to excite oscillations during the normal operation of the power system.

Selecting wavelets for damping estimation of ambient-excited electromechanical oscillations

This paper discusses aspects related to a wavelet transform and random decrement technique based method developed for estimating power system electromechanical oscillation damping from ambient-excited oscillations. The main focus of this paper is in finding the optimal wavelet functions for the damping estimation method. General selection criteria for the wavelet functions are defined, the selection criteria are specified quantitatively for the Nordic power system and the wavelet functions fulfilling the criteria are presented. Damping of a simulated Nordic power system case is analyzed with the damping estimation method and with different wavelet functions. The damping estimation results show that when the mother wavelet is selected according to the specified criteria, the damping estimates are better than by using other wavelets.

Performance of wavelet-based damping estimation method under ambient conditions of the power system

The paper discusses performance evaluation of damping estimation methods and specifically evaluates the performance of a wavelet-based damping estimation method. The focus is on the damping estimation under the ambient conditions of the power system. Damping estimation results are reviewed in case of the simulated data because then real damping is known and can be compared with the estimated damping. Various degrees of complexity of the simulation models are used: linear single and double pole pair models, and a detailed nonlinear system model of the Nordic power system. In the linear models, the real damping of the modes can be analytically calculated and compared with the estimated damping. Damping estimation performance is studied in different operating conditions of the studied simulation models. The main results are: frequency estimates are better than the damping estimates, other oscillation modes may affect the damping estimation, poor damping can be estimated more accurately than high damping, and the performance of the method is nearly similar regardless of the complexity of the simulation model.

Modal analysis of power systems with eigendecomposition of multivariate autoregressive models

Analysis of electromechanical modes provides substantial information regarding the power system stability. This paper introduces a novel approach to the measurement based modal analysis of power systems by using a multivariate autoregressive model (MAR). The MAR model utilizes data that are simultaneously measured from several locations in the power system through a wide area monitoring system (WAMS). The performance of the MAR model is analyzed by applying it to data generated with a 39-bus New England test system. In addition, the model is utilized for analyzing data generated with a detailed simulation model of the Nordic power system. The results indicate that the frequencies and damping ratios of electromechanical oscillatory modes can be accurately analyzed with the eigendecomposition of the MAR model. Thus, the MAR model is a promising identification technique for wide-area monitoring of electromechanical oscillations.

Measured faults during lightning storms

Lightning storms may only last some hours, but the number of faults during these storms can represent a considerable share of the annual disturbances. In this paper, six identified lightning storms were the main interest. In general, single-phase earth faults are the most typical fault type. However, in the lightning storms we researched, short circuits represented the majority of faults. The majority of faults, both during lightning storms and in normal conditions, are cleared by high-speed auto reclosure. In addition, it was observed that during lightning storms coincident faults and fault types that develop into another fault type before the opening of the circuit breaker occurred repeatedly. When observing the influence of overvoltage protection type on faults, the results encourage the use of surge arresters.

Analysis of electromechanical modes using multichannel Yule-Walker estimation of a multivariate autoregressive model

Stability of power systems can be analyzed by monitoring the electromechanical oscillatory modes. This paper investigates the use of multichannel Yule-Walker (YW) estimation of a multivariate autoregressive model (MAR) for the measurement based modal analysis of power systems. The proposed YW-MAR method utilizes data that are simultaneously measured through a wide area monitoring system (WAMS). The performance of the method is analyzed by applying it to data generated with the New England test system. The results indicate that the frequencies and the damping ratios of electromechanical oscillatory modes can be accurately analyzed by using the YW-MAR method and the method is not significantly affected by measurement noise or losing a measurement signal.

Recent developments in modal estimation of power system electromechanical oscillations

This paper presents three data-driven methods to monitor electromechanical oscillations in power systems during ambient operation. The characteristics of the methods are compared and the differences in the characteristics are explained. The results indicate that all three methods are suitable for estimating the damping and frequency of electromechanical oscillations. The paper also studies the validity of the assumption that the load variations in power systems are Gaussian distributed. This is a common assumption in damping estimation methods. The assumption is shown to be valid for the studied loads.

Robustness and performance of a multi-objective Model Predictive Static Var Compensator controller

This paper presents the robustness and performance study of a wide-area multi-objective optimization based Model Predictive Control (MPC) strategy for Static Var Compensator (SVC). Many MPC control strategies presented in the literature have been based on single-objective optimization and focused merely on damping of the electromechanical oscillations. In this paper, the MPC controller is designed both for the oscillation damping and voltage control using multi-objective optimization approach. With this approach, the controller can improve the system stability in various operating conditions where either the damping or voltage stability is more important. The performance of the proposed MPC controller is compared with a local SVC controller using nonlinear time domain simulations. A simplified model of the power system in the Northern parts of Finland and Norway is used. The conducted study indicated that the proposed MPC controller could improve the system stability in varying operating conditions.

Multi-objective Model Predictive Control for damping inter-area power oscillations

This paper introduces a multi-objective optimization based Model Predictive Control (MPC) strategy for damping inter-area oscillations in power systems. The previous MPC control strategies presented in the power system literature have been based on single-objective optimization, but this paper extends the approach to multi-objective optimization. The controller is designed using a linear discrete time state space model and calculates control signals in centralized fashion for local control devices. The optimal control sequence is calculated as a solution to a multi-objective optimization problem with two objective functions. The controller is combined with a Kalman filter state estimator using voltage angle measurements. The performance of the proposed multi-objective optimization based MPC controller is compared against a single-objective optimization based MPC controller using New England New York test system model.