Papers by Lasantha Meegahapola
Investigation of frequency stability during high penetration of CCGTs and variable-speed wind generators in electricity networks
Variable-speed wind generators (VSWGs) are being extensively deployed as the main wind power gene... more Variable-speed wind generators (VSWGs) are being extensively deployed as the main wind power generation technology around the world. However, when the VSWGs are integrated to gas turbine based (e.g. combined-cycle gas turbines (CCGTs) and open-cycle gas turbines (OCGTs)) electricity networks, potentially threatening dynamic interactions could occur during frequency excursions. This is due to the fact that gas turbines depict unique frequency response characteristics, while VSWGs exhibit either no or emulated inertial response during system frequency events. Thus, stability issues will arise when both technologies have significant penetration levels in electricity networks. This study shows that frequency stability concerns could become more severe due to the non-coherent inertial power release and recovery response of VSWGs equipped with emulated inertial response which can coincide with the unique frequency response characteristics of CCGTs. Therefore, special care must be taken by the system operator to avoid any potentially threatening VSWG and CCGT combinations during system operation.
Low-voltage ride-through characteristics of microgrids with distribution static synchronous compensator (DSTATCOM)
This paper investigates the low-voltage ride-through (LVRT) characteristics of microgrid with DST... more This paper investigates the low-voltage ride-through (LVRT) characteristics of microgrid with DSTATCOMs and microgrid capability to support the utility grid during external faults. Two approaches are taken in order to investigate the LVRT behaviour of a grid connected microgrid as a single entity. A distribution static synchronous compensator (DSTATCOM) is installed at different locations of the microgrid, and the voltage and reactive power support to the external grid is analysed. The grid connected microgrid is subjected to different operating conditions and the impact of DSTATCOM is investigated. DSTATCOM operation in a multi-microgrid environment is also investigated in this paper.
Impact of battery storage on residential energy consumption: An Australian case study based on smart meter data
Renewable Energy, 2022
IEEE Transactions on Industry Applications, 2017
The high penetration level of wind energy, and non-responsive nature of power electronic interfac... more The high penetration level of wind energy, and non-responsive nature of power electronic interfaced wind energy conversion system (WECS) during frequency variations may create significant stress on conventional generators in a wind-diesel hybrid remote area power supply (RAPS) system. Hence, it is a necessity for WECS to provide frequency support. However, conventional frequency control strategies being used for WECS may impose a severe stress to wind turbines. In this paper, an enhanced frequency response strategy is proposed for the permanent magnet synchronous generator (PMSG) based WECS to regulate RAPS system frequency jointly with its integrated ultracapacitors. The proposed frequency response strategy utilizes the droop control and virtual inertial techniques while suboptimal power point tracking (SOPPT) is implemented in WECS. It can effectively regulate RAPS system frequency while alleviating high rate of change of power (ROCOP) and thus torque stress on both the conventional generators and wind turbines under frequency disturbances.
Impacts of Residential PV and BESS on Distribution Network Performance
Iet Generation Transmission & Distribution, May 1, 2017
Voltage stability in general is of paramount importance with increasing penetration levels of var... more Voltage stability in general is of paramount importance with increasing penetration levels of variable-speed wind power generators (VSWGs) in power systems. Limited knowledge exists considering the impact of VSWGs on long-term voltage stability (LTVS) of power systems, focusing on doubly fed induction generators and full-converter wind generators. This paper presents the results of a comprehensive study on the impact of VSWGs on LTVS. Integration of wind generators while operating the existing synchronous generators improves the LTVS. However, it is unlikely that power systems will retain all existing synchronous generators operating, with high wind penetration levels. Therefore, this study compares the capability of the synchronous generators and VSWGs on LTVS by considering the dynamic reactive power capabilities. The significance of overload capability of synchronous generators on LTVS is highlighted. It is also illustrated that integrating wind farms at remote and local locations from load centres has distinct impacts on LTVS. Replacement of synchronous generators located in close proximity to load centres has a detrimental effect on LTVS. Furthermore, this study demonstrates the impact of different wind generator loading levels on LTVS. The study outcomes highlight several distinct factors which influence the LTVS of power systems with high wind penetration levels.
Analysis of Droop Control of BESS for VPP based Frequency Control in Distribution Network
2022 IEEE PES 14th Asia-Pacific Power and Energy Engineering Conference (APPEEC)
Multi-objective Coordinated Control of Hybrid AC/DC Power Grids
Power systems, 2022
Enhancing dynamic stability performance of hybrid ac/dc power grids using decentralised model predictive control
Electric Power Systems Research
Impact of Multiple Motor Loads on Dynamic Performance and Stability of Microgrids
2019 IEEE International Conference on Industrial Technology (ICIT)
Microgrids are becoming integral parts of the new power system structure where induction machines... more Microgrids are becoming integral parts of the new power system structure where induction machines (IMs) constitute a significant portion of the system loads. This paper investigates the dynamic behaviour of various induction machines in microgrids and their related issues such as low-frequency oscillations (LFOs). This study also compare the dynamic performance of multiple parallel small IMs with a large IM of same power rating over a wide range of operating conditions using eigenvalue analysis and non-linear dynamic simulations considering different model parameters and voltage/frequency transients across the IM terminals. The results indicate that the IM rotor resistance is the most significant parameter which affects the dynamic behaviour of the machine while voltage and frequency transients lead to LFOs in the microgrid. Furthermore, the LFO damping capability of large IMs is found to be less than the small IMs while the system frequency with single large IM has shown one dominant LFO compared to multiple low frequency modes of the system with parallel small IMs.
Investigation of Factors Affecting the Critical Clearing Time of Hybrid AC/DC Power Systems
2020 12th IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC)
Due to the large-scale integration of renewable energy sources and high-voltage direct current (H... more Due to the large-scale integration of renewable energy sources and high-voltage direct current (HVDC) links, the power grid is transforming into a hybrid AC/DC power grid. The critical clearing time (CCT) is used to evaluate the proximity of a power network to the instability point, hence can be used as a stability indicator for hybrid AC/DC power grids. Various factors influence the CCT of a hybrid AC/DC power network, especially voltage source converters (VSCs) significantly affect the CCT. This paper investigates the factors that influence the CCT of a hybrid AC/DC power grid with a VSC-HVDC link. The conventional CCT calculation procedure is exemplified with an AC power network. Subsequently, the CCT analysis procedure is carried out for a single-machine test system with a VSC-HVDC link. Influence of both controller parameters and power network parameters are investigated to assess their impact on CCT. According to the theoretical analysis and simulation results, the fault resistance, the DC bus capacitor, current controller limit and DC transmission line parameters have a significant influence on the CCT of a hybrid AC/DC power network. By selecting optimal values for the current limit of VSCs, the CCT could be improved in a hybrid AC/DC power network since others are network dependent parameters.
Adaptive Protection Scheme with Passive Islanding Detection for AC Microgrids
2022 International Power Electronics Conference (IPEC-Himeji 2022- ECCE Asia)
Correlation Analysis of Wind Farms through Short-term Probablitic Analysis
2021 IEEE PES Innovative Smart Grid Technologies - Asia (ISGT Asia), 2021
The intermittency of renewable energy resources such as wind farms is causing a significant chall... more The intermittency of renewable energy resources such as wind farms is causing a significant challenge on power grids due to possible short-term steep variations in generation. In order to properly quantify the probabilistic nature of these short-term changes, in this paper, several correlation coefficient methods are applied on the power generation data of Australian wind farms to define the correlation between their steep generation variations. The study has compared Pearson Correlation Coefficient (PCC), Sørensen-Dice coefficient (DC), Overlaps similarity (OS), and K-means clustering methods. The results show that the PCC provides better performance on long-term generation datasets, while, DC and OS show better results for short-term conditions. The Standard Deviation (SD) computed with K-means can present the interrelationship between wind farms, and this method could also split the aggregated SD into different groups to show the impact from steep variation in generation with probabilistic analysis. This study presented the feasible correlation method for different wind farms with short-term generation data and proved the “extreme” SD can cause contingency in power systems with high penetration wind farms.
Impact on rotor angle stability with high solar-PV generation in power networks
2017 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), 2017
This paper investigates the impact on rotor angle stability (both small-disturbance and transient... more This paper investigates the impact on rotor angle stability (both small-disturbance and transient rotor angle stability) with high penetration of solar-PV generation in power networks. Although a number of studies have conducted on rotor angle stability with solar-photovoltaic (PV) generation, these studies have changed more than one system parameter in the analysis, hence it is difficult to make an accurate judgement on rotor angle stability impact with solar-PV generation. In this study, a systematic methodology is followed to investigate the rotor angle stability with high solar-PV generation, by maintaining steady-state system parameters constant with solar-PV integration; these parameters include active and reactive power, and maximum rotor angle difference. Study results show that by integration of solar-PV generation, small-signal stability has improved except in the remote fault scenarios where generators with power system stabiliser (PSS) are replaced with solar-PV generation. Transient stability has worsened due to increased solar-PV penetration when a fault occurs at critical points. However, transient stability has improved when a fault occurs at less critical points, and hence fault proximity to solar-PV generation is a critical determinant of transient stability.
Small signal stability analysis of a hybrid AC/DC microgrid with static and dynamic loads
2017 Australasian Universities Power Engineering Conference (AUPEC), 2017
Majority of the stability studies conducted on AC and DC microgrids have investigated stability w... more Majority of the stability studies conducted on AC and DC microgrids have investigated stability with only static loads in the microgrid. Dynamic loads significantly influence the stability of mirogrids due to their voltage and frequency dependent nature. Therefore, small variation in voltage and frequency can make significant impact on the stability of the microgrid with the presence of dynamic loads. Thus, it is imperative to consider the dynamic loads in the microgrid for stability studies. Moreover, stability issues become more severe if the microgrid is operated in the standalone mode. This paper characterises the small-signal stability of a hybrid AC/DC microgrid with static and dynamic loads using state-space and dynamic simulation models developed in MATLAB/Simulink. This study investigates the critical parameters of the dynamic load which significantly affect the stability of the microgrid. Subsequently, eigenvalue analysis and time-domain simulations have been carried out to investigate the small-signal stability of the hybrid AC/DC microgrid. Eigen-sensitivity analysis has revealed that induction machine rotor resistance has the highest participation on the critical modes of the hybrid AC/DC microgrid. Additionally, the controller gains of the voltage source converters may require re-tuning due to the presence of dynamic loads.
Rotor Angle Stability Analysis of AC/DC Hybrid Power Systems with a VSC- HVDC Link
2018 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC), 2018
The power network architecture is rapidly evolving with the addition of high-voltage direct curre... more The power network architecture is rapidly evolving with the addition of high-voltage direct current (HVDC) transmission links and dc distribution networks. The voltage-source converter (VSC) based HVDC (i.e. VSC-HVDC) shows advantage in rotor angle stability control due to its ability to adjust active power and reactive power independently. This paper provides a rotor angle comparison between a single-machine-infinite-bus (SMIB) system with two paralleled AC transmission lines and a SMIB with one AC transmission line and one VSC- HVDC link. A detailed analysis is conducted based on the swing equation and the damping power of the generator is critically analysed in the study. A solid three-phase fault in the systems simulated by the DIgSILENT shows the validity and accuracy of analysis. The AC/DC hybrid power system shows better dynamic performance and becomes stable more quickly than AC power system after fault. The damping and synchronizing torque coefficients are calculated for both systems to further explain the simulation results.
Adaptive Virtual Impedance Controller for Parallel and Radial Microgrids With Varying X/R Ratios
IEEE Transactions on Sustainable Energy, 2021
In this paper, an adaptive virtual impedance-based universal voltage source converter (VSC) contr... more In this paper, an adaptive virtual impedance-based universal voltage source converter (VSC) control scheme is proposed to improve the stability, and power-sharing performance of VSC interfaced distributed energy resources in hybrid AC/DC microgrids with different feeder characteristics. The proposed control scheme modulates the VSC output impedance by tracking the active and reactive power transfer difference between the inverter terminal and the point of connection to the microgrid. Firstly, the stability limits of microgrid with resistive and inductive microgrid feeders are investigated by theoretical analysis. Subsequently, influence of the feeder parameters on the stability of microgrid is evaluated. From the theoretical analysis, the proposed control scheme shows resistive inverter output impedance at low frequency, while it shows more inductive behavior at system frequency for both the low and medium voltage microgrid feeders. The effectiveness of the proposed control strategy is demonstrated through a range of scenarios for two different microgrid types. The results show that the proposed controller can autonomously vary the output impedance of the VSC and provides significantly improved damping and power-sharing performance of the microgrid.
Voltage Stability with Wind Power Generation
Handbook of Renewable Energy Technology & Systems, 2021
Impact of active power recovery rate of DFIG wind farms on first swing rotor angle stability
IET Generation, Transmission & Distribution, 2020
IET Renewable Power Generation, 2018
This paper describes a novel strategy for microgrid operation and control, which enables a seamle... more This paper describes a novel strategy for microgrid operation and control, which enables a seamless transition from grid connected mode to islanded mode, and restoration of utility supply, without loss or disruption to loads sensitive to frequency or phase angle dynamics. A simulation study is conducted on a microgrid featuring inverter connected renewable generation, and power electronic interfaced loads. Therefore, the microgrid inherently has low inertia, which would subsequently affect the dynamic characteristics of the microgrid, in particular during mode transition. The microgrid is controlled by means of synchrophasor data to achieve synchronous island operation, enabling the microgrid to track the utility frequency and phase angle. The simulation includes synchrophasor acquisition and telecoms delays, allowing for detailed investigation of the microgrid dynamics under various mode transition scenarios, including the risk of commutation failure of the inverter sources. The proposed method is demonstrated to successfully maintain a microgrid in synchronism with the main utility grid after the transition to islanded mode without significant impact on various equipment connected to the microgrid. Thus, synchronous island operation of low inertia microgrids is feasible. This study also showed that utility supply could be seamlessly restored if the microgrid is operated as a synchronous island.
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Papers by Lasantha Meegahapola