Multi-machine System Research Articles

Recurrent neural network based design of fractional order power system stabilizer for effective damping of power oscillations in multimachine system

The complexity of modern power systems has risen due to the growing demand for electricity. To mitigate this problem, the role of the electric utility in supplying safe and reliable electricity has become increasingly crucial. Low-frequency oscillations (LFOs) in a power system are an inevitable aspect. Therefore, the reliability of the system requires appropriate damping to overcome these LFOs. This paper proposes a novel design methodology for a fractional-order power system stabilizer (FO-PSS) to enhance the stability of the power system network. FO-PSS is designed to effectively dampen LFOs in both single-machine infinite bus systems (SMIB) and multi-machine power systems (MMPS). Recurrent neural network (RNN) is used to predict the parameters of proposed PSSs. To evaluate the efficacy of the proposed PSS, various test cases are considered. The results are compared to those obtained from traditional PSSs and optimization based PSSs. The effectiveness of the proposed RNN-based FO-PSS is demonstrated under diverse loading conditions.

A novel method for optimal placement and tuning of the power system stabilizer in the multi-machine system

This paper introduces a new method for optimal placement of power system stabilizers (PSS) and tuning them simultaneously in the multi-machine system. This method is based on an improved genetic algorithm (GA), and the power system model is very accurate. This method determines the best place to install the stabilizers, using the least number of PSS and tuning their parameters simultaneously to move the poles to the left of the imaginary axis and maximize the damping ratio of mechanical modes. In addition, the proposed algorithm can consider any of the critical conditions, which are obtained based on sensitivity analysis, and suggest a robust setting for stabilizers. After implementing the proposed algorithm in MATLAB, the modal analysis and time-domain simulations in IEEE 9Bus and IEEE 39Bus systems were compared with other algorithms. The results confirm that the proposed algorithm can effectively improve dynamic stability margin.

LSTM based deep neural network model of power system stabilizer for power oscillation damping in multimachine system

AbstractPower system oscillation is an unavoidable threat to the stability of an interconnected modern power system. The reliable operation of a modern power system is widely related to the dampening of electromechanical low‐frequency oscillations (ELFOs). These ELFOs must be dampened appropriately to maintain the stability and reliability of the system. However, it is relatively difficult to resolve the problem of ELFOs completely with traditional power system stabilizers (PSSs). Consequently, research should be directed towards the development of efficient damping controllers, or PSSs, for power oscillation damping. Motivated from the aforementioned fact, this article presents the design of a proportional integral derivative power system stabilizer (PID‐PSS) via a long short‐term memory neural network (LSTM) based deep neural approach for damping power system oscillations in interconnected power systems. LSTM is used to train the parameters of PID‐PSS. To evaluate the performance of the proposed LSTM based PID‐PSS, diverse test cases under different operating conditions are examined. Further, the performance of the proposed LSTM based PID‐PSS is compared with traditional PSSs through time‐domain simulations. The test cases reveal the desired efficiency achieved by the proposed LSTM based PID‐PSS under diverse loading conditions.

Inter-regional unit commitment and PV scheduling considering frequency constraints

Unit commitment problem considering renewable uncertainty has received a lot of attention in recent years. The high-level penetration of renewable lowers the system inertia, posing challenges to frequency stability. This work proposes a unit commitment model considering frequency limits. The High Voltage Direct Current (HVDC) tie-line is modeled to transfer PV generation to load centers while providing frequency support. A multi-machine system frequency response model is employed to approximate frequency excursion. PV is considered semi-controllable in the scheduling model. A novel solution approach is proposed to solve the unit commitment problem with nonlinear frequency stability constraints. Case studies demonstrate the benefits and effectiveness of the proposed approach.

Stability analysis of multi-machine system using FACTS devices

Stability analysis of multi-machine system using FACTS devices

Analysis of the Influence of Grid-Connected Photovoltaic Power Stations with Virtual Inertia on Low-Frequency Oscillation of Power System Based on Small Signal and Prony Analysis Methods

With the virtual synchronous generator (VSG) technology gradually becoming an emerging technology for new energy consumption, its introduction has solved the problems of weak support and weak anti-interference of traditional new energy stations. However, the practice shows that the grid-connected characteristics of VSG limit its large-scale utilization, and there is little research on the interaction between VSG and a multi-machine system. In this paper, small signal models and time domain simulation models of each link of a photovoltaic(PV) power station with the PV virtual synchronous generator (PV-VSG) are first conducted, and then the influence of the grid-connected PV power station with the PV-VSG on the low-frequency oscillation of power system and its interaction mechanism with the multi-machine system are qualitatively obtained based on the small signal analysis method and prony analysis method from two dimensions of frequency domain and time domain, respectively. The analysis and simulation show that the PV power station based on VSG technology affects the dynamic characteristics of the system by changing the electromagnetic torque of each synchronous generator. Unreasonable operating conditions and parameter settings will aggravate the phenomenon of low-frequency oscillation of the system. Before the grid connection of PV power station, the operating parameters shall be reasonably set to ensure their safe and stable grid connection.

MiniGraph: Querying Big Graphs with a Single Machine

This paper presents MiniGraph, an out-of-core system for querying big graphs with a single machine. As opposed to previous single-machine graph systems, MiniGraph proposes a pipelined architecture to overlap I/O and CPU operations, and improves multi-core parallelism. It also introduces a hybrid model to support both vertex-centric and graph-centric parallel computations, to simplify parallel graph programming, speed up beyond-neighborhood computations, and parallelize computations within each subgraph. The model induces a two-level parallel execution model to explore both inter-subgraph and intra-subgraph parallelism. Moreover, MiniGraph develops new optimization techniques under its architecture. Using real-life graphs of different types, we show that MiniGraph is up to 76.1x faster than prior out-of-core systems, and performs better than some multi-machine systems that use up to 12 machines.

Study on stability margin of ultra-low frequency oscillation in hydropower system

In recent years, the ultra-low frequency oscillation of power system caused by hydropower units has occurred frequently. It is very important to study the ultra-low frequency oscillation characteristics of hydropower stations for the stable operation of power system. It is worth further research on how to determine the system stability margin in engineering practice. Based on the established model of single machine system with load, the analysis of the characteristic equation of closed-loop transfer function of single machine system shows that the ultra-low frequency oscillation will occur when the ratio of proportional parameter to integral parameter is too small. Based on the single machine with load system model and the equivalent single machine with load model of multi machine system, the ultra-low frequency oscillation mode of the system is analyzed by eigenvalue analysis method. According to the requirements of the damping ratio index, the security domain of the system ultra-low frequency oscillation is constructed, and the risk and stability margin of the system ultra-low frequency oscillation are evaluated by the characteristic values of the system ultra-low frequency oscillation mode.

Multimachine Stability Enhancement using Fuzzy- Logic based PSS tuning with Shunt FACTS Device

In Large power system network the dynamic behaviour of system is nonlinear in nature. Due to disturbance the system stability cannot be maintained, which leads to outage of power equipment. In order to restore the system parameter after perturbance, coordination control damping is essential. Coordination control damping can be achieved by using fuzzy based PSS and STATCOM in multimachine system for sever disturbance. Due to perturbance the system loss its synchronism and the system parameter deviate from the nominal value. With the effective damping control technique proposed in this article is to minimize the integral square error of speed deviation. Two area 4-Machine 11-bus test system considered and the simulation of proposed system is developed in Matlab/Simulink R2018a.

A Novel Approach for Steady State Calculations of VSC-HVDC Connected PMSG Based Offshore Wind Farms Integrated into Multi-Machine Systems

Offshore wind farms equipped with Direct Drive Permanent Magnet Synchronous Generators (DD-PMSG) are drawing increased attention due to their advantage over other variable speed technologies. VSC-HVDC links are considered the most suitable option for transferring power to the onshore system. The integration of VSC-HVDC connected DD-PMSG based offshore wind farms into multi-machine systems is explored in this paper. A novel approach for power flow and initial condition calculations is proposed to facilitate dynamic analysis of the system. For three cases of the most commonly specified quantities of the wind farm, efficient methods have been described. The cases comprise combinations of data like the total output of the wind farm, the number of wind turbines, the wind speed, or the output of individual wind turbine, which are frequently given in literature. This approach enables the user to build the dynamic model of the system in any basic graphical dynamic modeler and numerical computational software without requiring power system toolboxes or electromagnetic transient packages. The proposed methods are highly effective for studies focusing primarily on the dynamic aspects and controls of the system. Case studies and simulations are conducted to verify the proposed technique.

Design Coordination of a Fuzzy-based Unified Power Flow Controller with Hybrid Energy Storage for Enriching Power System Dynamics

In power networks, operation planning has become necessary due to the continuously increased load demand. The Unified Power Flow Controller (UPFC) controls the power flow through the network and improves the dynamics of the power system. In this paper, the design application of the coordination of a fuzzy-based UPFC with hybrid energy storage has been proposed to enrich the system's dynamic performance during abnormal conditions and improve the hybrid energy storage performance during transients when the DC link voltage is insufficient to meet the converter voltage demand. The hybrid energy storage consists of a supercapacitor and a battery connected across the UPFC Vdc shunt capacitor. The proposed system to improve the UPFC performance during large disturbances on a multi-machine system was designed and tested in MATLAB/SIMULINK.

Influence of power oscillation damping assets reactive power capacity on damping low-frequency power system oscillations

Over the past ten years, the paradigm has shifted from conventional power generation to renewable generation. Large integration of these renewable energy sources (RES) into the power system poses challenges to system operators, leading them to put stringent requirements for their grid connection. Displacement of synchronous generators by RES reduces system inertia and consequently decreases the system damping capability of electromechanical oscillations. Poorly damped interarea oscillations reduce the transmission line's capacities and may damage power system components. Hence, future grid codes will require wind and solar power plants to provide damping to the system. Several papers have proposed adding an auxiliary damping controller to the wind turbine control algorithm to damp the low-frequency oscillations (LFOs) by modulating active or reactive power. However, these studies have not mentioned if small power plants can damp LFOs in a multimachine system. Therefore, this paper investigates the influence of reactive power capacity on the damping of LFOs and its effects on optimal controller parameters using a simplified SVC model connected at the midpoint of the tie line of a two-area test system. A local feedback signal is selected as the input signal to the SVC damping controller. Controller parameters are optimized using the particle swarm optimization algorithm. Time-domain simulations performed in PowerFactory software demonstrate the damping behavior of the controller at different SVC ratings. The results show a minimum reactive power capacity is required for effective damping of power system oscillations.

A Self-Regulating Virtual Synchronous Generator Control of Doubly Fed Induction Generator-Wind Farms

The inverter-driven renewable energy sources (RESs), such as wind energy conversion systems (WECS), pose major threats toward system stability due to lack of inertia. Hence, virtual inertia concepts have gained popularity, for control and improvisation of the dynamic behavior of RESs, by simulating the kinetic inertia of the synchronous generator. This article focuses on developing an improved self-regulating virtual synchronous generator (VSG) control for grid-tied doubly fed induction generator (DFIG)-wind farms (WFs). The proposed scheme provides frequency support to the system while ensuring the low-voltage ride through (LVRT) capability at transient conditions, as per grid code requirements (GCRs). This has been achieved by introducing an additional control at grid side converter (GSC). This auxiliary control consists of a combined approach of VSG control and a current limiting approach. The VSG loop that alters the inertia of the system improves the frequency of the system and the current limiting loop provides the required inductance to limit fault current. This overall loop uses a self-regulating approach, and the developed concept helps to suppress the transients in stator current. The study obtained on a multimachine system and also for a weak grid system confirms the effectiveness and viability of the modified converter control structure.

Modified PSO tuned two stage lead lag STATCOM control action for small signal stability enhancement of variable wind integrated power system

In this work Modified PSO (MPSO) is proposed to tune two stage lead lag control action based on STATCOM for enhancing small signal stability of an intermittent wind source penetrated power system. The Modified PSO has been compared with standard PSO and fractional PSO to tune controller parameters of STATCOM based control action. Multi machine system subjected to sudden and intermittent wind variations have been considered in this work. Subject to this wind penetration the lead lag control action with only PSO and two stage lead lag control action with fractional PSO and modified PSO has been implemented to damp the system oscillations pertaining to initial operating condition. It was found that subject to intermittent nature of wind penetration the rotor angle small signal stability is being hampered and subject to this when the modified PSO tuned two stage lead lag STATCOM control action is applied, it damps the oscillations heavily and the results have been compared with only PSO and fractional PSO control algorithms.

Research for reduction material-capacity of load-lift cranes with multi-engine electric drives on the base electromagnetic work shaft systems

This work is devoted to the study of multi-machine systems of coordinated rotation of the engines of handling equipment. The purpose of the work is to identify, by theoretical calculation, the reduction in the metal consumption of cranes equipped with multi-motor electric drives and operating on the principle of an electromagnetic working shaft, in comparison with the current ones. The analysis of the shifting moments of these systems in dynamics was made and conclusions were drawn about the reduction in the weight of the metal structures of cranes and the saving of metal in their production.

Multimachine stability improvement with hybrid renewable energy systems using a superconducting magnetic energy storage in power systems

Energy storage systems (ESS) have played a vital role in modern power systems to improve system stability and reliability in recent years. This paper describes the role of SMES in improving the power system stability of a multimachine interconnected with hybrid renewable energy systems (RES) such as wind and solar PV. It studies the transient stability of the system by creating a symmetrical fault in a multimachine system at various locations. The hybrid RES simulates an equivalent aggregated 75 MW photovoltaic array and a wind turbine with a capacity of 300 MW PMSG (permanent magnet synchronous generator). It couples a common DC link via a voltage source and dc/dc boost converters. A voltage source inverter connected with a step-up transformer and transmission line coupled to a multimachine system. The voltage source converter and inverter use a model predictive controller (MPC) for a better output voltage profile and to improve the system stability. A SMES is connected through a dc/dc converter with PID-SDC (Proportional Integrating Derivative Supplementary Damping Controller). It effectively suppresses power oscillations and smoothening during generation fluctuations. It reduces the low-frequency oscillations at the multimachine side during three-phase fault conditions at various locations in the system. The system's stability is improved by 3.36 s after clearing the fault. The effectiveness of the entire system is studied in the time domain simulations using MATLAB/SIMULINK software.

Power System Stability Improvement of FACTS Controller and PSS Design: A Time-Delay Approach

The existence of low-frequency oscillations in power systems is the cause of power angle instability, limiting the transmission of maximum tie-line power. One of the effective ways to improve the stability limits is by installing a power system stabilizer and supplementary excitation control to augment with an automatic voltage regulator (AVR) supplemental feedback stabilizing signal. This paper proposes a new strategy for simultaneously tuning the power system stabilizer (PSS) and FACTS controller, considering time delays. The design of the proposed controller is modeled as an optimization problem, and the parameters of the controller are optimized through the grasshopper optimization algorithm (GOA). The suggested controller’s efficacy is evaluated for both single-machine infinite bus systems and multi-machine power systems under various disturbances. It also investigated the performance of the proposed controller with variations in signal transmission delays. The results obtained from GOA optimized proposed controller are compared with those obtained from the differential evolution algorithm, genetic algorithm, and whale optimization algorithm. In this context, the proposed GOA optimized controller reduced the objective function value by 16.32%, 14.56%, and 13.72%, respectively, in the SMIB system and 1.41%, 9.98%, and 13.31%, respectively, for the multi-machine system compared with the recently published WOA, and the well-established GA and DE. Further, the proposed controller is found to be stable and effectively increases stability even under small disturbances.

A Coordinated Pumped Storage Dual Compensated Hydro Governor with PSS Action to Damp Electromechanical Power Oscillations

Subject to increasing penetrations of renewable sources like solar photovoltaic (SPV) and wind energy sources, power system oscillation damping is going to be a critical challenge for system operators. This work proposes a new dual compensated governor (DCG) in coordination with a power system stabilizer (PSS) of a pumped storage hydro plant for power oscillation damping subject to intermittent SPV and wind penetration for a hydro, wind, and SPV integrated power system. The phase lag provided by the hydro governor is compensated by additional phase lead contributed by the dual compensation, where speed and real power deviations brought by uncertain SPV and wind penetrations are simultaneously controlled by two lead-lag controllers before being applied to conventional Proportional-Integral-Derivative (PID) governor. Again, subject to critical oscillatory unstable conditions, the DCG is coordinated with PSS through a multiobjective function employing a new modified Differential Evolutionary-Particle swarm optimization (MDEPSO) algorithm. Different case studies with sudden and random SPV and wind penetrations being executed with the proposed controller considering a two area four machine and 39 bus multimachine system with pumped storage hydro units to observe system oscillations are considered. The proposed damping control action has been implemented to damp these oscillations, and the damped response has been analyzed with eigenvalue distributions and Bode plots with sensitivity analysis. The proposed action is found to be much more efficient in contrast to conventional PID governor and PSS damping action. Also, the usage of present hydro governors can be much improved by this coordinated controller action.

Load shedding for frequency and voltage control in the multimachine system using a heuristic knowledge discovery method

The voltage profile of different buses and the rotor dynamics of generators are adversely affected by a generator outage. Generator outages can be minimized using a variety of strategies and algorithms. An AI-based knowledge discovery approach has been reported in this article. This article proposes a technique for identifying sensitive loads and the amount of active and reactive power curtailment for rotor speed regulation and voltage management at the terminals. The MATLAB®/Simulink environment verifies and tests the method’s practicality on an IEEE-10-machine-39-bus system. Active power shedding is considered for rotor angle stability, while reactive power is also shedded for maintaining the terminal voltage at the loads. A sequential outage is considered to simulate a scenario where the two generators with the highest active and reactive power are taken out of service. The generator’s rotor speed, terminal voltage, and load are measured with and without load restriction. In all situations, the rotor and center of inertia speed are 1 p.u. The average steady-state load terminal voltage is 0.967 V. The average terminal voltage of all load buses improves from 0.933 to 0.972 and 0.936 to 0.971, case-wise. The reported results confirm and validate the effectiveness and applicability of the proposed technique.

Negative Damping Mechanism Analysis of Power System Stabilizer Based on Damping Torque

Power system stabilizer plays an important role in suppressing the low frequency oscillations, but a PSS with poorly tuned parameters may produce negative damping and aggravate the system oscillation. The purpose of this paper is to study the mechanism of damping of a PSS in multi machine system and to analyze whether the PSS has produced negative damping. This paper adopts Park model for analysis. According to the concepts of complex frequency and generalized phasor, the correlation between the damping torque phasor and the real part of the complex eigenvalue is studied. With the auxiliary of Park equivalent circuits, the damping torque provided by the excitation system is separated from the electrical torque phasor. Then, the damping torque coefficient of the PSS is defined as an indicator of the damp effect of the stabilizer. Finally, the simulation results of single machine infinite bus system and 4-machine system demonstrate the validation of the proposed method for evaluating the damping effect of PSS on the system.