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The shift from traditional fossil fuel-based power systems to renewable energy sources heightens the importance of frequency regulation. The lack of inertia in this new generation increases the risk of low-frequency oscillatory events, a significant concern in power systems stability. To mitigate these stability problems, it is crucial to study the effectiveness of damping controllers. This paper delves into the analysis of three damping controllers: the power system stabilizers (PSS) installed in synchronous generators, and two Power Oscillation Damping (POD) controllers, one with active power modulation (POD-P) and the other with reactive power modulation (POD-Q), typically installed in environments with high renewable penetration.The main objective is to critically evaluate the comparative advantages of PSS, POD-P, and POD-Q controllers in local and inter-area oscillations by exploring their flexibility and performance under various initial conditions and oscillatory scenarios. The proper choice of damping controllers will ensure the stability of the grid in future scenarios of high renewable production, thus allowing the definition of future technology needs. This research is of utmost importance as it aims to dampen different oscillations by employing uniform control parameters in the PSS, POD-P, and POD-Q controllers. Five scenarios are defined on a system based on the IEEE 39 Bus New England System model and simulated by DIgSILENT PowerFactory. The results are analyzed methodically per scenario, facilitating a comparative evaluation of the controllers and reaching promising conclusions.

• Evaluate PSS, POD-P, and POD-Q's efficiency, flexibility, and performance. • Comparative advantages and potential limitations of each control strategy. • Consider various oscillatory scenarios of a power system with renewables. • POD-P has a superior ability to manage oscillations across multiple scenarios. • PSS effectively damps inter-area oscillations with proper parameterization. The shift from traditional fossil fuel-based power systems to renewable energy sources heightens the importance of frequency regulation. The lack of inertia in this new generation increases the risk of low-frequency oscillatory events, a significant concern in power systems stability. To mitigate these stability problems, it is crucial to study the effectiveness of damping controllers. This paper delves into the analysis of three damping controllers: the power system stabilizers (PSS) installed in synchronous generators, and two Power Oscillation Damping (POD) controllers, one with active power modulation (POD-P) and the other with reactive power modulation (POD-Q), typically installed in environments with high renewable penetration. The main objective is to critically evaluate the comparative advantages of PSS, POD-P, and POD-Q controllers in local and inter-area oscillations by exploring their flexibility and performance under various initial conditions and oscillatory scenarios. The proper choice of damping controllers will ensure the stability of the grid in future scenarios of high renewable production, thus allowing the definition of future technology needs. This research is of utmost importance as it aims to dampen different oscillations by employing uniform control parameters in the PSS, POD-P, and POD-Q controllers. Five scenarios are defined on a system based on the IEEE 39 Bus New England System model and simulated by DIgSILENT PowerFactory. The results are analyzed methodically per scenario, facilitating a comparative evaluation of the controllers and reaching promising conclusions. [ABSTRACT FROM AUTHOR]

To allow the large-scale integration of renewable energy sources into the grid, VSC-HVDC is commonly utilized. However, with greater integration, several power system stability issues arise. In this study, we examined the small-signal rotor angle stability of a model of the Australian power system with embedded VSC-based HVDC links. A simplified model of the Australian power network was used to connect the potential geothermal resources in the region of Innamincka using a 1100 km HVDC link. We observed that the introduction of the new source of geothermal power generation had an adverse impact on the damping performance of the system. Therefore, two forms of stabilization are examined here: (i) generator power system stabilizers (PSS) fitted to the synchronous machines, which are used to convert geothermal energy to electrical power; and (ii) power oscillation damping controllers (PODs) fitted to the VSC-HVDC link. In the case of the PODs, two types of stabilizing input signals are considered: (i) local signals such as power flow in adjacent AC lines, and (ii) wide-area signals such as bus voltage angles at key nodes in the various regions of the system. It was concluded that the small-signal rotor angle stability of the interconnected AC/DC system can be greatly enhanced by employing the designed damping controllers. [ABSTRACT FROM AUTHOR]

Grid-forming power converters (GFMC) have been widely adopted in power systems as an attractive solution against the challenges imposed by the ever-increasing penetration of renewables. Despite its versatility, GFMC is employed only to provide islanded operation, grid regulations, and synthetic inertia. To further extend the use of GFMC in enhancing power system stability, this paper proposes a multi-rotor virtual machine (MRVM) controller to attenuate sub-synchronous oscillations. Driven by the formulation of a virtual synchronous machine (VSM), the proposed MRVM implements a VSM-based GFMC with several virtual rotors whose electromechanical characteristics can be individually adjusted to target specific oscillatory modes in the system. In this work, the MRVM’s working principle is described in detail and tuning guidelines are proposed to simplify the selection of control parameters by using frequency-domain techniques and the eigenvalue locus analyses. To validate the performance of the MRVM, an IEEE benchmark grid model is adopted namely, the three-machine-infinite-bus system. It is evident from the results that the MRVM (i) provides higher degrees of freedom when dealing with sub-synchronous oscillations, and (ii) outperforms conventional GFMC, especially in damping intra-area power oscillations.

The increasing incorporation of renewable energy in power systems is causing growing concern about system stability. Renewable energy sources are connected to the grid through power electronic converters, reducing system inertia as they displace synchronous generators. New grid-forming converters can emulate the behavior of synchronous generators in terms of inertia provision and other grid services, like power-frequency and voltage-reactive regulation. Nevertheless, as a consequence of synchronous generator emulation, grid-forming converters also present angle oscillations following a grid disturbance. This paper proposes two novel power stabilizers for damping low-frequency oscillations (LFOs) in the power system. The first power stabilizer provides power oscillation damping through active power (POD-P), and it is implemented in a grid-forming converter, using the active power synchronization loop to damp system oscillations by acting on the converter angle. The second one provides power oscillation damping through reactive power (POD-Q), and it is implemented in a STATCOM, using the voltage control loop to damp system oscillations. Both proposals are first assessed in a small-signal stability study and then in a comprehensive simulation. Moreover, two cases are considered: damping the oscillations of a single machine connected to an infinite bus through a tie-line, and damping the inter-area oscillations in a two-area system. Simulation results, as well as the stability study, demonstrate the ability of both stabilizers to damp power system oscillations, being the POD-P more effective than the POD-Q, but at the cost of requiring some kind of energy provision at the DC bus.

Fundamental sensor feedback limitations for improving rotor angle stability using local frequency or phase angle measurement are derived. Using a two-machine power system model, it is shown that improved damping of inter-area oscillations must come at the cost of reduced transient stability margins, regardless of the control design method. The control limitations stem from that the excitation of an inter-area mode by external disturbances cannot be estimated with certainty using local frequency information. The results are validated on a modified Kundur four-machine two-area test system where the active power is modulated on an embedded high-voltage dc link. Damping control using local phase angle measurements, unavoidably leads to an increased rotor angle deviation following certain load disturbances. For a highly stressed system, it is shown that this may lead to transient instability. The limitations derived in the paper may motivate the need for wide-area measurements in power oscillation damping control. [ABSTRACT FROM AUTHOR]

The increasing share of renewable generation leads to new challenges in reliable power system operation, such as the rising volatility of power generation, which leads to time-varying dynamics and behavior of the system. To counteract the changing dynamics, we propose to adapt the parameters of existing controllers to the changing conditions. Doing so, however, is challenging, as large power systems often involve multiple subsystem operators, which, for safety and privacy reasons, do not want to exchange detailed information about their subsystems. Furthermore, centralized tuning of structured controllers for large-scale systems, such as power networks, is often computationally very challenging. For this reason, we present a hierarchical decentralized approach for controller tuning, which increases data security and scalability. The proposed method is based on the exchange of structured reduced models of subsystems, which conserves data privacy and reduces computational complexity. For this purpose, suitable methods for model reduction and model matching are introduced. Furthermore, we demonstrate how increased renewable penetration leads to time-varying dynamics on the IEEE 68-bus power system, which underlines the importance of the problem. Then, we apply the proposed approach on simulation studies to show its effectiveness. As shown, similar system performance as with a centralized method can be obtained. Finally, we show the scalability of the approach on a large power system with more than 2500 states and about 1500 controller parameters. [ABSTRACT FROM AUTHOR]

The coordination of the offshore wind farm (OWF) and high-voltage direct current (HVDC) links to provide ancillary power oscillation damping (POD) services may become a mandatory requirement from the transmission system operators in the near future. However, the performances of the POD controllers (PODCs) are vulnerable to the power system uncertainties and random communication delays of the wide-area signals. To address these issues, this paper proposes the design of the coordinated PODCs by using the deep reinforcement learning (DRL) method. The DRL-based PODCs employ one of the state-of-the-art DRL algorithms, proximal policy optimization, which can learn to adapt to the system uncertainties and time-varying communication delays by interacting with the power system continuously. A detailed simulation model of an OWF connected to the IEEE-39 bus AC grid via the modular multilevel converter based HVDC link has been built as a simulation platform, and the efficacy of the proposed DRL-based PODCs has been validated across a broad spectrum of operating conditions, disturbances, and communication latency. [ABSTRACT FROM AUTHOR]

Modern electrical grids face serious challenges to maintain healthy operational conditions. The nominal voltage and frequency, for instance, are affected by huge load changes and renewable energy integration. Renewable energy conversion systems are traditionally installed to provide active power. Fortunately, advanced renewable energy conversion systems have the ability to provide other facilities such as reactive power control and harmonic mitigation. In fact, recent grid codes obligate renewable energy systems to serve other duties such as generating reactive power rather than just simply supply active power, participate in fault ride through, for instance. This paper presents a comprehensive study on the doubly fed induction generator (DFIG)-based wind energy conversion system (WECS), which provides ancillary services to the grid along with performing its regular duties. These services include reactive power control, voltage ride through, power quality improvement, frequency control, and power oscillation damping. The literature survey and comparative studies show that the DFIG-based WECS has the ability to support electrical grid during normal and transient conditions, and it can also help in the large-scale renewable energy penetration to the power grid. The effect of different industrial and nonlinear controllers on DFIG performance in extracting grid ancillary services is highlighted.

This article proposes a flexible control scheme (FCS) of a photovoltaic (PV) power plant to support the voltage stability and provide fast recovery after the grid faults in a power system with high penetration renewable energy sources (RES). To achieve these goals, the proposed FCS includes two control loops: a reactive current (IQ) injection loop and a frequency-damping control (FDC) loop. The IQ injection loop injects IQ in proportion to the terminal voltage of the PV during a fault. After the fault clearance, the FDC loop provides active and/or reactive power modulation to stabilize system frequency; then, the FDC loop puts the system recovery forward by damping out the remaining synchronous machines' frequency oscillations. The FDC loop comprises active power damping function without PV power curtailment and reactive power damping function. We verified the proposed FDC's performance in a two-area system for various penetration levels of inverter-based resources using a PSCAD simulator. We investigated the control schemes' effectiveness by comparing the efficiency and the response in mitigating the post-fault oscillations and restoring the voltage regulation. [ABSTRACT FROM AUTHOR]

To allow the large-scale integration of renewable energy sources into the grid, VSC-HVDC is commonly utilized. However, with greater integration, several power system stability issues arise. In this study, we examined the small-signal rotor angle stability of a model of the Australian power system with embedded VSC-based HVDC links. A simplified model of the Australian power network was used to connect the potential geothermal resources in the region of Innamincka using a 1100 km HVDC link. We observed that the introduction of the new source of geothermal power generation had an adverse impact on the damping performance of the system. Therefore, two forms of stabilization are examined here: (i) generator power system stabilizers (PSS) fitted to the synchronous machines, which are used to convert geothermal energy to electrical power; and (ii) power oscillation damping controllers (PODs) fitted to the VSC-HVDC link. In the case of the PODs, two types of stabilizing input signals are considered: (i) local signals such as power flow in adjacent AC lines, and (ii) wide-area signals such as bus voltage angles at key nodes in the various regions of the system. It was concluded that the small-signal rotor angle stability of the interconnected AC/DC system can be greatly enhanced by employing the designed damping controllers.

This study aims to improve oscillation damping and the rate of integration of wind energy into the grid. To this end, this study focuses on selecting the optimal location of flexible alternating current transmission system (FACTS) devices, such as the static synchronous series compensator, the static synchronous parallel compensator, and the unified power flow controller (UPFC). This study proposes new methods to determine the optimal locations of FACTS devices in the transmission system. To further improve power oscillation damping and the rate of integration of wind energy, FACTS devices were combined with a multiband power system stabiliser (MBPSS) at each synchronous machine. The MBPSS is an advanced power system damping controller that offers clear advantages over conventional power system stabilisers in the damping of low‐frequency oscillatory modes. A comparative study was performed on the two‐zone, four‐machine (Kundur) multi‐machine test network containing a wind farm to select the best combination of FACTS devices with the MBPSS. The results indicate that a combination of UPFC with MBPSS is favourable in terms of improving stability and increasing the rate of integration of wind energy into the grid. [ABSTRACT FROM AUTHOR]

This paper aims to compare two strategies for damping low-frequency electromechanical oscillations in multi-machine power systems through Static Synchronous Compensators (STATCOM) with a multi-band controller. STATCOM is represented by a controllable voltage source behind an impedance and the multi-band controller acts as a power oscillation damper that modulates parameters of the voltage source in the transient period. In the first strategy, the multi-band controller acts on the voltage-control loop through the voltage modulation. In the second one, the controller acts on the real power-control loop to modulate the phase angle of the voltage source. The coordinated design of multi-band controllers and power systems stabilizers is performed through an optimization approach taking into account several operation conditions. • Comparison of two modulation strategies for STATCOM for oscillation damping. • Multi-band power oscillation damper for STATCOM. • Robust and optimal design of power oscillation damper and power system stabilizers. [ABSTRACT FROM AUTHOR]

Power oscillation damping (POD) is one of the ancillary services expected from high‐voltage direct current (HVDC) converters. When providing POD to the ac side, converters draw power from the dc side, which can cause distortion to the dc voltage especially in the case of limited dc capacitance. In meshed/multi‐terminal HVDC grids, where dc voltage regulation is distributed using a dc voltage droop control strategy, the distortion due to the POD controller action is propagated to other connected ac grids because of the droop action. This propagation can be reduced by using the inherent energy storage capability of the modular multilevel converter (MMC), which is a common converter topology for HVDC. Different methods to utilise the energy stored in the MMC for the purpose of POD have been proposed in the literature. This study presents a detailed analysis and experimental validation of one of these methods, referred to as virtual capacitance support, which increases the effective dc grid capacitance by using the stored energy of multiple MMCs connected in the same grid. The experiments, which were carried out using power hardware in the loop setup, demonstrated the effectiveness of the method. [ABSTRACT FROM AUTHOR]

This paper presents a novel fast frequency response and power oscillation damping control by large-scale PV plants controlled as STATCOM, termed PV-STATCOM, to simultaneously enhance frequency regulation and small signal stability of power systems. Frequency deviations typically occur together with power oscillations in large power systems. The proposed controller comprises: first, power oscillation damping controller based on reactive power modulation and second, fast frequency response controller based on real power modulation, both of which are applied to the plant level controller of PV-STATCOMs. The proposed composite control is shown to successfully reduce frequency deviations, damp power oscillations, and provide voltage regulation both during over-frequency and under-frequency events. The proposed smart inverter control makes effective utilization of the PV inverter capacity and available solar power. For large power flows, the proposed control is shown to be superior than the conventional droop control recommended by North American Electric Reliability Corporation for generating plants. MATLAB/Simulink-based simulations are conducted on two-area power system using generic PV plant dynamic models developed by Western Electricity Coordinating Council, for a wide range of system operating conditions. Such grid support functionality is expected to bring new revenue making opportunities for PV solar farms. [ABSTRACT FROM AUTHOR]

This paper focuses on the methods that ensure the rotor angle stability of electric power systems, which is most frequently analyzed with small-signal models. Over the past several decades, power system stabilizers (PSSs) for conventional excitation systems were the main tools for improving the small-signal stability of electromechanical oscillatory modes. In the last decade, power oscillation damping (POD) control implemented in photovoltaic (PV) inverters has been considered an alternative to PSSs. As PV generation undergoes massive rollout due to policy directions and renewable energy source integration activities, it could potentially be used as a source of damping, which is crucial for sustaining the rotor angle stability of the remaining in-service synchronous generators. Several studies have already been dedicated to the development of different damping strategies. This paper contributes to the existing research in power system stability by providing a comprehensive review of the effects of PV generation on small-signal stability, as well as the recent evolution of POD control through PV inverters. The features and impacts of the various ways to realize POD controllers are assessed and summarized in this paper. Currently, detailed information and discussions on the practical application of PV inverter PODs are not available. This paper is, thus, intended to initiate a relevant discussion and propose possible implementation approaches concerning the topic under study.

Synchronous generation is being displaced by renewable energy sources and high-voltage direct current (HVDC) interconnectors. These factors will lead to a diminishing provision of ancillary services. Conventional services tendered to provide network support rely on the availability of synchronous generation and because of this, future power system operators will have to develop new ways to obtain the ancillary services required. A technology rapidly gaining in popularity is voltage source converter (VSC)-based HVDC and further advances in the technology have led to the modular multilevel converter (MMC). Due to the design of an MMC there is intrinsic electrostatic energy that could potentially be utilised to provide ancillary services. This study determines the electrostatic energy available from a typical grid-scale MMC VSC for network support during disturbances and for power oscillation damping. Supporting simulations are provided to ascertain the impact that this electrostatic energy could have on network performance if utilised. This study displays that although an MMC possesses intrinsic energy, utilising it for frequency response would provide negligible system benefits. However, for POD, the available intrinsic MMC energy did improve system stability which leads to the potential of using multiple MMCs to increase the energy and further improve system stability.

This paper presents a novel control of photovoltaic (PV) solar system as a FACTS device STATCOM, termed PV-STATCOM, for power oscillation damping (POD) in transmission systems. In the proposed control, as soon as power oscillations due to a system disturbance are detected, the solar farm discontinues its real power generation function very briefly (few tens of seconds) and makes its entire inverter capacity available to operate as a STATCOM for POD. As soon as power oscillations are damped, the solar farm restores real power output to its pre-disturbance level in a ramped manner, while keeping the damping function activated. This results in much faster restoration than that specified in grid codes. During nighttime, the solar farm performs POD with its entire inverter capacity. It is shown from EMTDC/PSCAD simulations that the proposed control provides significant increase in power transfer capacity on a 24/7 basis in systems that exhibit both local inertial and interarea oscillatory modes. The proposed PV-STATCOM is about 50–100 times cheaper than an equivalent STATCOM for providing POD at the same location. This novel control can potentially bring large savings for transmission utilities and open up a new revenue making opportunity for solar farms for providing POD. [ABSTRACT FROM AUTHOR]

Synchronous generation is being displaced by renewable energy sources and high-voltage direct current (HVDC) interconnectors. These factors will lead to a diminishing provision of ancillary services. Conventional services tendered to provide network support rely on the availability of synchronous generation and because of this, future power system operators will have to develop new ways to obtain the ancillary services required. A technology rapidly gaining in popularity is voltage source converter (VSC)-based HVDC and further advances in the technology have led to the modular multilevel converter (MMC). Due to the design of an MMC there is intrinsic electrostatic energy that could potentially be utilised to provide ancillary services. This study determines the electrostatic energy available from a typical grid-scale MMC VSC for network support during disturbances and for power oscillation damping. Supporting simulations are provided to ascertain the impact that this electrostatic energy could have on network performance if utilised. This study displays that although an MMC possesses intrinsic energy, utilising it for frequency response would provide negligible system benefits. However, for POD, the available intrinsic MMC energy did improve system stability which leads to the potential of using multiple MMCs to increase the energy and further improve system stability. [ABSTRACT FROM AUTHOR]

The rapid increase of converter-based generation in grids causes significant changes in system dynamic characteristics. These changes require verification and testing of the reliability, optimization, and functionality of power system elements and controllers, which become more important for guaranteeing a secure operation. This paper first introduces a hardware-in-the-loop setup of an automatic voltage regulator (AVR) control system and then proposes a software-in-the-loop (SiL) setup for the parameterization of an IEEE standard AVR/excitation system model and a power oscillation damping (POD) controller of synchronous condenser. The AVR hardware is interfaced with a simulated grid in real-time digital simulator (RTDS) using EMT simulation to evaluate its control functions. Parameter optimization for the POD and the AVR simulation model by SiL simulation is implemented in a closed loop between RTDS and MATLAB/Simulink interfaced through OPC to satisfy the optimization objectives. By the tests executed on the future Western Danish power system, parameter optimization of the POD and IEEE standard AVR model, and the function of AVR hardware are successfully implemented and verified. [ABSTRACT FROM AUTHOR]

This paper considers power oscillation damping (POD) using active power modulation of high-voltage dc transmissions. An analytical study of how the proximity between interarea modal frequencies in two interconnected asynchronous grids puts a fundamental limit to the achievable performance is presented. It is shown that the ratio between the modal frequencies is the sole factor determining the achievable nominal performance. To illustrate the inherent limitations, simulations using a proportional controller tuned to optimize performance in terms of POD are done on a simplified two-machine model. The influence of limited system information and unmodeled dynamics is shown. The analytical result is then further validated on a realistic model with two interconnected 32-bus networks. [ABSTRACT FROM AUTHOR]

• A novel energy storage system based oscillation damping scheme; • A novel PSS/POD node selection approach based on controllability Gramian; • A unit load energy function averaging approach based ESS sizing; • Enhanced system performance under high wind power penetration. This paper proposes a novel power oscillation damping approach for transient stability enhancement of a power system with high penetration of wind power, where the energy storage system (ESS) is utilized to assist the damping of power oscillation with power system stabilizer and power oscillation damper. First of all, the ESS-based power system stabilizer and power oscillation damper structures are proposed to enhance the flexibility of power input and output of the wind turbines and the synchronous generators. Subsequently, the effect of installing ESSs for the enhancement the SGs and WTs' damping torque is analyzed. In the meantime, we proposed an optimal allocation approach to decide the installation nodes of the ESSs by minimizing the Euclidean distance of the system's uncontrollable oscillation modes to its controllability Gramian, along with the optimal sizing approach of ESSs via a novel unit load energy function averaging approach. Simulations are conducted to validate the effectiveness of the proposed scheme, and the superior performance of the proposed approach is also proven via comparative studies. [ABSTRACT FROM AUTHOR]

An active power oscillation damping (APOD) control is one of the representative unbalanced fault compensation strategies. Recently, various studies have been performed on the effect of the APOD with the internal power dynamic analysis of a Modular Multilevel Converter (MMC); however, most of the papers have considered only the active power component for analyzing the internal dynamics of the MMC. During the APOD operation, while reactive power is supplied to the grid for the voltage compensation, phase-leg power imbalance can be aggravated. To enhance stability and reliability, the phase-leg power imbalance phenomenon should be sufficiently considered at the development stage of the controller. This research discovers that the phase-leg power imbalance rate could be determined by the magnitude and phase of the negative sequence component of the grid voltage and the amount of reactive power. In addition, the unbalanced power component can be accurately calculated only based on the grid voltage information and the reactive power reference. Also, this paper proposes a phase-leg power equalization method (PPEM) using unbalanced power component estimation. Furthermore, an improved control structure is also proposed to achieve more accurate phase-leg power equalization using the internal leg-energy dynamics analysis. The effectiveness of the proposed methods is verified through high-fidelity PSCAD/EMTDC time-domain simulations using Point-to-Point (PTP) MMC-HVDC system and Hardware-in-the-Loop Simulation (HILS) with the MMC-MVDC system. • The phase-leg power imbalance phenomenon occurs by the current component corresponding to the reactive power in MMC system under APOD strategy. • The phase-leg power imbalance rate is related to the amount of the reactive power and the grid voltage imbalance rate. • The tendency of the phase power imbalance according to reactive power and voltage dip factor is analyzed under the APOD strategy. • Based on the analysis of the phase-leg power imbalance phenomenon, a phase-leg power equalization method that can achieve precise phase-leg power balancing is proposed. • The effectiveness of the proposed methods is verified through high-fidelity PSCAD/EMTDC time-domain simulations and the HILS test platform. [ABSTRACT FROM AUTHOR]

Abstract The interconnection of remote large power systems, and the connection of large non-synchronous renewable power sources to AC power systems have found solutions by means of transmission in high voltage direct current (HVDC) using technology based on voltage source converters (VSC). This technology has the advantage of fast response the possibility of providing reactive power to AC systems, and the use of supplementary control signals to their automatic voltage regulators to improve stability AC systems. This paper proposes the computation of robust supplementary controller type H ∞ based on low-order models of the power system, obtained by application of N4Sid identification technique, to be installed at the VSC converter stations of a HVDC link to dampen electromechanical weak modes. The proposed model shows that using simulated input/output data by means of typical software available at utilities is possible and useful. The methodology includes the modeling of uncertainties due to the different operational points where the power system can be placed by load variations and generation dispatch. This paper also presents a methodology for the computation of robust supplementary control at VSC-HVDC stations that guarantee robustness in a wide range of operating conditions and even better to improve the damping of electromechanical oscillations. It is also proposed a methodology for defining the weighted functions based on the uncertainties theory. Likewise, it is validated with the simulation of a critical contingency in a weakly damped system obtaining an improvement in damping of electromechanical oscillations. The robust supplementary control is compared to the performance of the classical POD. Highlights • Low-order dynamic model of power systems by means of N4Sid using simulated I/O data. • An uncertainties’ estimation of the dynamic model of the power system. • Definition of weighting matrices for computing H ∞ controllers in power systems. • Application for damping weak electromechanical modes by means of VSC-HVDC converters. [ABSTRACT FROM AUTHOR]

This paper presents an ant lion optimizer (ALO) that is used to solve the robust and coordinated tuning of power system stabilizers (PSS) and the power oscillation damping (POD) controller of flexible AC transmission system (FACTS) devices in the presence of remote signals in multimachine power systems. The remote signals are used for the damping of interarea oscillation modes and are modeled by Padé approximation. The static var compensator and thyristor-controlled series capacitor, two FACTS most deployed in practical applications, were considered in this study. The ALO algorithm mimics the hunting mechanism of ant lions in nature: where four steps of hunting prey such as entrapment of ants in traps, random walk of ants, elitism and catching preys/re-building traps are implemented. The two test systems which have been used for the application of the proposed methodology for tuning of PSS and FACTS-PODs are the New England-New York 16-generator 68-bus system, and the Brazilian equivalent system modeled with 24 synchronous machines and 107 buses. Results from these simulations demonstrate the applicability of the proposal in which the efficiency of ALO is highlighted as compared to other algorithms used for design of PSS and FACTS-PODs such as particle swarm optimization and sequential quadratic programming. [ABSTRACT FROM AUTHOR]

In this paper, a robust nonlinear control scheme is proposed for voltage source converter based multiterminal HVDC grids, based on the predictive sliding mode control (PSMC). This control is a hybrid of the multivariable nonlinear model predictive control and sliding mode control. The particle swarm optimization method is applied to obtain the optimal control parameters. This control fulfills the objectives of regulating terminal dc voltage, active and reactive power, improved dynamic performance, and superior robust control operation even with plant parameter changes and external measurement disturbances. The performance of the proposed PSMC scheme is compared with the optimal synergetic control and optimal PI. The results confirm the superior transient performance and robustness of the PSMC scheme. [ABSTRACT FROM PUBLISHER]

This paper presents a variable neighborhood search (VNS) optimization algorithm for the design of the parameters of supplementary damping controllers: power system stabilizers (PSS) and the interline power flow controller–power oscillation damping (IPFC–POD) set. The objective is to insert damping to local and inter-area oscillation modes in multimachine power systems. The electric power system dynamics is represented by the current sensitivity model. Simulations were carried out using three systems: a test system known as Two-Area Symmetrical and two real systems, the New England and the Reduced Southern Brazilian. The VNS method was compared with a multi-start algorithm in terms of performance, showing better convergence rates. The proposal was also able to obtain solutions with high damping levels, that showed to be robust when changes on the operating point of the power system were considered. Finally, it has been verified that the PSS controllers were effective for damping the local mode oscillations, while the IPFC–POD set operated mainly damping the inter-area modes. [ABSTRACT FROM AUTHOR]

The advent of renewable energy sources (RESs) has posed several technical challenges related to the operation of modern power systems. These can be classified into two main categories: (a) problems at the power system level, and (b) local problems at the distribution network (DN). To solve these issues, there is a strong need for the development of innovative control schemes that can be employed by converter-based network assets, e.g., battery energy storage (BES) systems and distributed RES. In this context, a unified control system (UCS) for the provision of ancillary services (ASs) by distributed RES-BES systems within a multi-services perspective is introduced in this paper. The proposed UCS comprises different algorithms to provide ASs related to voltage regulation, voltage unbalance mitigation and frequency support. The UCS is implemented in 3-phase, 4-leg converters (3Ph4LCs) to ensure the provision of ASs in unbalanced DNs. In addition, at the dc side of the 3Ph4LC a series dc–dc converter for BES support allows the implementation of the proposed UCS in weak DNs. The transient operational performance of the proposed UCS is evaluated by conducting time-domain simulations. • A unified control system for the provision of ancillary services is introduced. • It employs voltage regulation, voltage unbalance mitigation and frequency support. • The proposed algorithms are integrated into a 3-phase, 4-leg converter. • A power oscillation damping technique is introduced to improve PLL performance. • Time-domain simulation results verify the performance of the proposed control system. [ABSTRACT FROM AUTHOR]

Power system stabilisers (PSSs) are commonly used in synchronous generators for damping low-frequency oscillations. However, many of these machines have been replaced by converter-interfaced generators (CIGs), such as those used in solar power plants. This means that CIG-based power plants should also contribute to oscillation damping. Moreover, CIGs may use both active and reactive power for power oscillation damping (POD). However, their combined use has been seldom studied in the literature. Moreover, only a few articles have addressed the adaption of POD controllers when the power system changes (e.g., after a fault). In this paper, a POD controller for CIG-based power plants is proposed that is suitable for operation in power systems exposed to reconfiguration. This controller takes advantage of both active and reactive power injection to maximise the damping of the power system. This controller is based only on local measurements so communication systems are not required. Theoretical developments were validated in a laboratory using real power converters including a 75 kVA grid emulator where the two-area benchmark model is emulated and four 15 kVA CIGs operating in parallel connection. The applicability of the proposed controller was also explored for the IEEE 39-bus system. • Power oscillation damping controller that utilises both active and reactive powers. • The control parameters are adjusted once the change in the system is detected. • Adjustment mechanism based on simple expressions defined in off-line analysis. • Theoretical developments verified in a laboratory with real hardware converters. • The applicability of the proposed solution was examined using the IEEE 39-Bus system. [ABSTRACT FROM AUTHOR]

Diode rectifiers (DRs) have elicited increasing interest from both industry and academia as a feasible alternative for connecting offshore wind farms (OWFs) to HVDC networks. However, before such technology is deployed, more studies are needed to assess the actual capabilities of DR-connected OWFs to contribute to the secure operation of the networks linked to them. This study assessed the capability of such an OWF to provide support to an onshore AC network by means of (active) power oscillation damping (POD). A semi-aggregated OWF representation was considered in order to examine the dynamics of each grid-forming wind turbine (WT) within a string when providing POD, while achieving reasonable simulation times. Simulation results corroborate that such an OWF can provide POD by means of OWF active power controls similar to those developed for OWFs connected to HVDC via voltage source converters, while its grid-forming WTs share the reactive power consumption/production and keep the offshore voltage frequency and magnitude within their normal operating ranges. Open-loop test results show that such capability can, however, be restricted at operating points corresponding to the lowest and highest values of active power output.

This paper presents two variations of the artificial bee colony (ABC) algorithm, the classical and a modified version, called GBest, for the design of the proportional-integral and supplementary damping controllers: power system stabilizers and the unified power flow controller (UPFC)-power oscillation damping set. The objective is to insert additional damping to the low-frequency oscillation modes present in multimachine electrical power systems, to guarantee the small-signal stability of the system considering different loading conditions. A new current injection formulation for the UPFC is proposed and incorporated into the current sensitivity model used to represent the dynamical operation of the electric power system. Static and dynamical analysis were performed for the New England system to validate the proposed formulation and to evaluate the performance of the optimization algorithms. The results indicate that the modified version of the ABC algorithm has superior performance for this problem, providing robust solutions, that ensure the stability of the system even when small variations of the load are considered. [ABSTRACT FROM AUTHOR]

The deregulated power system has paved the way for a significant number of distributed energy resources (DER). This results in a large installation of renewable sources in the grid. Thus large installations of PV systems are becoming more common. These Centralized PV systems can cause major issues in the existing grid if these are not adequately addressed. The significant contribution of these systems can cause problems with the dynamic stability of the power system. The intermittent and inertia-less nature of PV systems can produce significant power oscillations. At the present condition, the penetration level of PV into the grid is limited by the utilities, to prevent problems of power oscillation. Thus the PV plant capacity cannot be increased beyond the penetration limit. The penetration limit depends on several factors such as the types of loads and stability enhancement devices on the grid. The penetration limit is regulated cyclically. This paper proposes a control strategy for power oscillation damping in power systems implemented in Grid connected converters (GCC) so that the power system stability is enhanced without any additional cost of equipment. This, in turn, helps to provide a penetration margin and thereby to increase the PV capacity of the grid. [ABSTRACT FROM AUTHOR]

Recently, the variable-speed wind turbine with doubly fed induction generator ( DFIG) has drawn significant attention because of its many advantages such as small power converter rating, the ability to control the output power, etc. Nevertheless, the large penetration of DFIG wind turbines may affect the power system dynamics. This paper provides a general review of the DFIG wind turbine's impact on power system dynamic performances such as frequency stability, transient stability, small-signal stability, and voltage stability. Besides, ancillary services from the DFIG wind turbine for the power grid, such as frequency support, reactive power, and voltage support, are explained. Especially, the survey emphasizes power oscillation damping methods by the DFIG wind turbine. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Damping contribution from wind farms (WFs) is likely to become a mandatory requirement as a part of the grid codes. For remote offshore WFs, connected through a voltage source converter (VSC)-based direct current link, the most convenient option for the onshore transmission system operator (TSO) is to modulate the reactive power at the onshore VSC within their own jurisdiction. In this paper, we show that supplementary control through the onshore VSC alone, although attractive for TSOs, could result in undesirable voltage variations in the onshore grid. On the other hand, modulation of active power output of the wind turbine generators (WTG) alone turns out to be inadequate due to the limited overload capability of the WTGs. Coordinated control over both onshore VSC and aggregated WF output overcomes the above limitations and is shown to be effective for power oscillation damping. A homotopy approach is used to design the coordinated controller, which can be implemented locally (at offshore WF and onshore converter site) using a decentralized architecture. This is a bilinear matrix inequality problem, which is solved by transforming these constraints into linear matrix inequality constraints. Case studies on two test systems show that the proposed controller yields similar system dynamic response as supplementary control through the WF alone. [ABSTRACT FROM AUTHOR]

Using a new improved harmony search‐based hybrid firefly algorithm (IHBFA), a comprehensive controller gain parameter estimation of all distributed resources‐based microgrid is proposed. To ensure a fast convergence and to endeavour less randomisation to conventional firefly algorithm (FA), diversity of population is increased by an improved harmony search (HS) algorithm. To decrease local optima searching delay, a linear incremental pitch adjustment rate and exponential decaying bandwidth is considered for proposed HS‐based hybrid FA. Photovoltaic (PV), an auxiliary battery energy storage system (BESS) with the second‐order phase‐locked loop control, is considered as a primary DG (DG1) for the proposed microgrid. Padѐ approximation delay‐based governor control is used for the diesel generator unit, considered as a secondary DG (DG2). The overall gain optimisation improves the dynamic stability limits by minimising low‐frequency network behaviour. The effectiveness of proposed IHBFA in terms of power oscillation damping and improved stability limits is clearly demonstrated for microgrid applications. [ABSTRACT FROM AUTHOR]

Primary frequency control is often added to the control system of a high-voltage DC (HVDC) transmission that interconnects two nonsynchronous ac grids. As the active-power actuation lag is typically in the range of hundreds of milliseconds, the HVDC primary frequency control can be made fast enough to permit inertia sharing among the interconnected ac grids. This reduces the maximum frequency fall after a loss-of-generation contingency (the nadir). A fast HVDC primary frequency control may affect the interarea modes of the interconnected grids. To this end, it is shown that, at least for the cases studied, the modal damping never decreases through the introduction of the mentioned control. [ABSTRACT FROM AUTHOR]

Flexible ac transmission system (FACTS) can provide control more than conventional control and achieve fast control response time, STATCOM is a shunt FACTS device it is used to voltage control and increase the performance of the system. In this paper STATCOM is used to improve the voltage magnitude and stability for the Iraqi (400KV) super grid network byusing MATLAB/SIMULINK. STATCOM is connected to Iraqi (400kv) super gridnetworkwhich is consisting of twenty four buses, eleven generators, eleven step up transformers fromeach generator side, twenty step down transformers from each load side and twenty loads.The loads variation through the seasons of the year causesdrop voltage on the buses of the network.To return the voltage to the rated value (400kv) STATCOM is used for this purpose. STATCOM provides suitable reactive power to the network to compensate the drop voltage on the buses, in the same time when the STATCOM improves the voltage there are large oscillations. These oscillations are handled by using power oscillation damping (POD) and proportional integral (PI) controller with the STATCOM.Each of thepower oscillation damping (POD) and Proportional integral (PI) controller is connected inside current regulator of the STATCOM device.The performance of the (POD) and (PI) in cancelation the oscillations is compared.

In electrical power systems there are many problems, from these problems voltage drop, over voltage and instability. These problems are solved by using FACTS technology. Flexible AC transmission system (FACTS) can provides better control than conventional control and achieves fast control time response; therefore FACTS controllers play an important role in power system stability enhancement. STATCOM is a shunt FACTS device which is used for voltage controlling and increasing the performance of the system. In this paper STATCOM is used to improve voltage magnitude and stability of electrical network by using MATLAB/SIMULINK. To show its effectiveness a prototype of electrical network has been chosen which consists of five buses, three generators and four loads. Simulation results show a robust improvement in network with STATCOM. If a three phase to ground fault occurs between buses (3&4) there are oscillations after clearing fault. To reduce these oscillations power oscillations damping (POD) has been proposed with STATCOM. Simulation results show that an enhancement of the network prototype with proposed controller (STATCOM- POD).

This paper focuses on multi-objective designing of multi-machine Thyristor Controlled Series Compensator (TCSC) using Strength Pareto Evolutionary Algorithm (SPEA). The TCSC parameters designing problem is converted to an optimization problem with the multi-objective function including the desired damping factor and the desired damping ratio of the power system modes, which is solved by a SPEA algorithm. The effectiveness of the proposed controller validates on a multi-machine power system over a wide range of loading conditions. The results of the proposed controller (SPEATCSC) are compared with the Genetic Algorithm (GA) based tuned TCSC through some operating conditions to demonstrate its superior efficiency.