Problem Of Low-frequency Oscillations Research Articles

Research on additional damping control strategy of flexible distribution transformer

Disturbances to the power system may lead to relative swing between synchronous generator rotors, causing low-frequency oscillation problems in the absence of damping. In this article, based on the single-machine infinity system containing flexible distribution transformer and synchronous generator, the linearized state equations of the system is deduced by the small-signal modeling. The mechanism of flexible distribution transformer on the rotor speed of synchronous generator is analyzed. The influence factors of flexible distribution transformer on the rotor speed of synchronous generator are analyzed. The equation of the additional damping provided by the flexible distribution transformer to this system is constructed. It was concluded that by controlling the output voltage of the regulating converter in the flexible distribution transformer, the rotor speed of the synchronous generator can be varied to increase the system damping. An additional damping control strategy for flexible distribution transformer is proposed. The simulation verifies that the proposed control strategy can effectively suppress the oscillation amplitude of each electrical quantity and shorten the oscillation duration when the system is subjected to large and small perturbations. The proposed additional damping control strategy of flexible distribution transformer can effectively improve the damping of the system and alleviate the problem of low frequency oscillation.

Power System Stability Improvement by LQR Approach and PSS Considering Electric Vehicle as Disturbance

Low frequency oscillations result due to heavy loading conditions line faults, sudden change of generator output and also due to poor damping of interconnected power systems. There are different types of disturbances in the power system like sudden change of load, generation, faults, switching of lines. This hampers the power transmission capacity of the lines and the stability of the system There are significant impacts on the system stability during the charging and discharging operation of Electric Vehicle (EV). In the present work the charging operation of EV is considered as a load disturbance. The introduction of these vehicles in the system creates the problem of low frequency oscillation and endanger the system stability and security. In the present work the Single machine infinite bus system (SMIB) is first developed using mathematical modelling with consideration of EV disturbance. The LQR approach from optimal control theory is then applied in the system to damp the system oscillations, improving the system eigenvalues and enhancing the stability. The stability is seen in the system after LQR from various figures. In the second work the plotting of variation of different state variables is done using three different methods which are the transfer function model method, using code and then using state space representation of the system. The work is further extended by adding Power system stabilizer (PSS) to the system, again considering the EV disturbance. The time domain simulation results showed the improvement in stability using PSS device. Thus, in the present work the oscillations problems created due to the introduction of electric vehicles are solved by two methods. The first is implementing LQR approach from optimal control theory in the system and the second method is by adding PSS device in the same system.

Low-frequency oscillation suppression strategy considering dynamic power characteristics of energy storage system

Aiming at the problem of low-frequency oscillation in the weak power grid, a low-frequency oscillation suppression strategy considering the dynamic power characteristics of the energy storage system (ESS) is proposed in this paper. Firstly, the principle of low-frequency oscillation in the power system is analyzed by using a single machine infinite bus system. Secondly, considering the dynamic characteristics of the ESS output active power, a controller for the ESS to suppress low-frequency oscillation is designed, which can provide positive damping for frequency oscillation of the power grid. Finally, the simulation analysis and experimental results of an actual weak grid are carried out to verify the effectiveness and feasibility of the proposed method. The results show that the suppression effect of the low-frequency oscillations is related to the ESS location in the weak power grid.

Research on improving low frequency oscillation characteristics of wind power system with DFIG-PSS-VI

The new energy represented by strong random wind power connecting to the power system may make the problem of inter-area low-frequency oscillation more serious. In this paper, a DFIG-PSS controller based on virtual impedance is constructed to solve the low-frequency oscillation problem in the wind power system. The step response of PSS-VI was carried out to test the effect of the controller to verify the advantages of PSS-VI than traditional PSS. The input signal of PSS-VI which is a controller based on PSS installed virtual impedance is the active power of DFIG. The output signal of PSS-VI is added to the reactive power control loop of rotor side controller of DFIG. DFIG-PSS-VI was built in Digsilent/Powerfactory software, and the simulation was carried out on the system of 4 machines and 2 regions. It is verified that PSS-VI can improve the low-frequency oscillation of wind power system.

Enhancement of Small Signal Stability of SMIB System with Robust Power System Stabilizer

As power system experiences low frequency oscillations due to disturbances, these low frequency oscillations are related to the small signal stability of a power system. The phenomenon of stability of synchronous machine under small perturbations is explored by examining the case of an SMIB system. The analysis of SMIB gives physical insight into the problem of low frequency oscillations. The SMIB system is predominant in local mode low frequency oscillations. These oscillations may sustain and grow to cause system separation if no adequate damping is available. The damping is provided by adding Power System Stabilizer for Synchronous Machine. In addition, as power system is nonlinear in nature, application of robust control techniques is mandatory to face the challenge of dynamic conditions. Hence, this work aims to design robust Power System Stabilizer for Synchronous Machine in order to damp the rotor speed deviations.

Review on Mechanism and Analysis Methods of Low Frequency Oscillation in Power System

Low frequency oscillation caused by system interconnection has been the main factor to threat the secure operation of power grid. It’s significant to research on the problem of low frequency oscillation. This paper summarizes the generation mechanism and analysis methods of low frequency oscillation. Each analysis method has both advantages and disadvantages.

Study on Low Frequency Oscillation of Wind Power System Based on HHT

For the output of wind power system has the characteristics of randomness, volatility and intermittence, the voltage of wind power system low frequency oscillation is one of the most common fluctuations in the system. For the problem of low frequency oscillation, the limitations of the detection methods such as the Lyapunov linearization method, the Prony method, wavelet transform method are summed up, and a new detecting method named Hilbert-huang Transform (HHT) is put forward in this paper, which can detect the oscillation accurately and timely. To solve the problem of end effect in the process of empirical mode decomposition (EMD), B-spline empirical mode decomposition based on support vector machine is applied in dealing with the end issue. an extension of the original signal is applied. Then, calculating the average curve of the signal by B-spline interpolation method. Finally getting the intrinsic mode function (IMF) by empirical mode decomposition (EMD). The practicality of the method is verified by Matlab simulation.

Influence Assessment of UHV Project on Jiangxi Power Grid

In order to face the challenge of our economy and the environment, it is needed to speed up the energy structure transition and UItra High voltage (UHV) transmission has become an inevitable choice. Researches on the influence of UHV project to Jiangxi power grid are carried out in this paper. Using advanced digital power system simulator (ADPSS), the real-time simulation model of Jiangxi power grid is build up including the UHV project. Based on the simulation model, the problem of low frequency oscillation in Jiangxi power system is studied after the UHV power transmission project accessed. The influence of the UHV transmission line faults on system stability of Jiangxi grid is also researched.

Simulation of Grid Low Frequency Oscillation Based on MATLAB

This paper describes the generation of low frequency oscillations and suppression methods briefly. Observing a phenomenon of low frequency oscillation of Gansu Grid Power and analysis its actual situation. Therefore, we need establish simplified simulation model in MATLAB environment, then do the simulation with the dual power system simulation model which add to power system stabilizer. Simulation results show that: PSS can solve the problem of low frequency oscillations in a region of Gansu steel caused rapid and effective.

Research of PSS on the Inhibiting Effect of Low Frequency Oscillation

With the continuous spreading of scale in power system and introducing of fast excitation system, the problem of low frequency oscillation which is arosed because of lacking-damping becomes worse and worse. This paper analyzes the mechanism reasons of insufficient-damping, using an auxiliary control unitpower system stabilizer (PSS) to increase the damping torque. Through established a simulation model of excitation control system on a typical single machine-infinite bus system, simulates the synchronous generators transient operating characteristics under large and small disturbances, and the simulation results show that the design can improve the system damping and the generator operating characteristics, increase power system dynamic stability.

Damping Improvement of Power System Oscillations by Using Optimal Coordinated Design between PSS and SVC-Based Stabilizer

The large expansion of electrical power systems usually results in problem of low frequency oscillations. Therefore, the conventional Power System Stabilizers (PSSs) used to solve this problem cannot provide an adequate damping of low frequency oscillations. Flexible AC Transmission System (FACTS) damping controllers are available for providing suitable damping for these oscillations. This paper, presents the simultaneous coordinated design of the multiple damping controllers between PSS and SVC-based stabilizer in a single machine infinite bus power system. The coordinated design problem of multiple damping controllers is formulated as an optimization problem. Particle swarm optimization algorithm is applied in order to search optimal controlling parameters by maximizing the objective function based on the eigenvalue. The simulation results for a wide range of operation condition show that the coordinated design able to provide better damping and stability performance.

The Study of Low Frequency Oscillations Parameters Identification in Power System Based on Improved HHT Method

The problem of low frequency oscillations (LFOs) parameters identification in power system with the method of improved Hilbert-Huang transform (HHT) is addressed. LFOs probably cause the great potential threat to the stable operation of power system, so identifying the parameters of LFOs is very important to develop the control strategies of restraining oscillations. In this paper, the LFOs signal is first processed by empirical mode decomposition (EMD) which is improved by the approach of endpoint extension used AR data prediction, stop shifting criterion and end condition via energy difference factor. The improved EMD is able to avoid the energy leakage and damping loss and also make the intrinsic mode functions (IMFs) closer to the true oscillations. Then the approach of parameters identification using least squares (LS) fitting algorithm based on the results of IMFs’ Hilbert transform is presented. Finally, case studies demonstrate the effectiveness of improved HHT process and LS parameters identification methods used in LFOs analysis of power system.

Renewed investigation on Power System Stabilizer design

Power System Stabilizer (PSS) was proposed during 1960s to solve the low frequency oscillation problem raised by the wide application of the high-gain fast-response exciters. The fundamentals of PSS design lie in the angle compensation to increase the damping torque, which, since then, has become an important principle in designing the various power system dampers, such as SVC, TCSC, UPFC. Although many papers have been dedicated to the application of this principle, it is interesting to note that in the real industry applications PSS parameters have to be carefully tuned on site in spite of its mature design theory. So does the classical PSS design theory really meet the PSS design demand? By combining the frequency domain and the time domain analysis, this paper reinvestigates the basic idea behind the classical PSS design theory. The paper clarifies the concepts of the synchronous torque as well as the damping torque and proves that the classical PSS design principles based on these concepts are not theoretically sound. Then the paper discusses the Linear Optimal Controller Design method and analyzes its relations with the conventional PID design. By doing so the paper reveals the real mechanism of the PSS and proposes to use more systematic and advanced control tools to enhance the controller performance.