Reactive Power Disturbance Research Articles

Robust Direct Power Control of Three-Phase PWM Rectifier with Mismatched Disturbances

To effectively eliminate the impacts of both matched and mismatched power disturbances in a three-phase PWM rectifier, this paper proposes a robust direct power control (RDPC) method with a single-loop control structure. Firstly, a nonlinear power model of the three-phase PWM rectifier is established. Then, using the exact feedback linearization method, a linearized power model including matched and mismatched power disturbances is derived and achieves the decoupling of active and reactive power. Secondly, to regulate the DC bus voltage, a sliding-mode controller (SMC) combined with a nonlinear disturbance observer (NDO) is proposed. The proposed SMC combined with an NDO (SMC + NDO) method features a single-loop control structure, which enables a faster response and simpler structure compared to the dual-loop DPC method. By incorporating estimated mismatched power disturbance into the sliding-mode surface, it overcomes the SMC’s defect in incompletely suppressing mismatched disturbances and enables the simultaneous regulation of voltage and active power. Additionally, it effectively reduces sliding-mode chattering. To regulate reactive power, a sliding-mode controller based on the exponential convergence law is designed to suppress matched reactive power disturbances. Finally, the simulation and experimental comparative results demonstrate that the proposed controller exhibits stronger robustness against matched and mismatched power disturbances, as well as a better performance under the constant power load (CPL).

An Islanding Detection Method Based on the Reactive Power Disturbance for Multiple Inverter-Based DG Systems

In this paper, an islanding detection method for multiple inverter-based distributed generation systems is proposed, which is based on perturbing reactive power output. An asymmetric form of positive and negative reactive power disturbance is presented so that there always exists a certain total amount of disturbance in the system. To decrease the disturbance amplitude without expanding the non-detection zone, a positive feedback of frequency difference is added to the disturbance. A reactive power disturbance synchronization method without communication among inverters is proposed so that the averaging effect caused by unsynchronized reactive disturbances can be eliminated and the island can be detected in a multiple-DG system. Additionally, the islanding detection criterion is improved by establishing the relationship between the direction of disturbance and the numerical symbol of frequency difference, so there is no misjudgment of islanding detection in a weak grid. Finally, an experimental platform consisting of three 6kW three-phase grid-connected inverters and a 99.9kVA islanding detection test device is established. The experimental and simulation results indicate that the proposed method performs fast and precise islanding detection for the multiple-DG system with small NDZ and little impact on power quality. Additionally, no misjudgment happens in a weak grid.

Hybrid Wind-Solar System with UPQC

The hybrid wind-solar system is a combination of renewable energy sources, specifically wind and solar, that is utilized for power generation. While wind power has historically been used for various purposes such as sails, windmills, and wind pumps, it is now predominantly used for electricity generation. This system incorporates solar panels and small wind turbine generators to produce electricity. The advantage of hybrid systems is that they can generate electricity as needed, taking into account the varying peak working hours of solar and wind systems throughout the year. To ensure a stable power system, UPQC (Unified Power Quality Conditioner) is employed. This multipurpose power conditioner serves multiple functions, including preventing harmonic load current from entering the power system, rectifying voltage fluctuations, and compensating for voltage disturbances from different power sources. It is specifically designed to minimize interference with sensitive or critical loads. With its series and shunt compensation capabilities, UPQC effectively manages power flow, reactive power, harmonics, and voltage disturbances. In this paper, the work addresses the issue of electricity quality that arises from the installation of wind turbines in the grid. To get over this issue, the suggested course of action demonstrates how to install a BESS and a unified power quality conditioner (UPQC) at the connection point. Even though wind power fluctuates, the use of battery energy storage technology helps to provide a constant power supply. With the power system block established in MATLAB/SIMULINK, one can simulate the UPQC control method of a grid-connected wind energy generating plant. As a result, the power's quality will increase. When the recommended approach lowers the load's and the induction generator's reactive power requirements, it is successful. Furthermore, the plan for raising the grid's power quality criteria and developing the grid coordination rule are also provided.

Modified Chameleon Swarm Optimization Algorithm to Improve the Power System Stability

Power system stability has been difficult due to the occurrence of low frequency oscillation in the modern power system. Oscillation is mainly due to sudden changes of frequency, load, voltage, active power and reactive power. In this paper we provide a damping solution to oscillate the low frequency by using modified chameleon optimization algorithm. Damping performance and stability analysis of system is done by proposed modified chameleon Swarm Algorithm compared with conventional chameleon Swarm algorithm and Genetic algorithm with different operating condition in terms of Real power, Reactive power and Load disturbances. The comparative results confirmed that the proposed controller exhibit higher damping ratio, and better damping of deviations in speed and power angle to improve the stability of the system.

Active Power Sharing Control Strategy of Photovoltaic Microgrid Based on Adaptive Droop

An error of active power distribution will occur with a traditional resistive droop control, due to the difference of the output line impedance of parallel inverters, during the operation of island photovoltaic microgrid. Aiming to this issue, a control strategy for regulating the droop coefficient automatically is proposed. The active power and reactive power output by inverters as the feedback values are lead into the droop control equation in the strategy, and the active power is employed into the reactive frequency equation; the small disturbances will be produced in reactive power, and it can be employed to compute the sharing error of the active power, the process of clearing up reactive power disturbance, which is equal to the process of regulating the droop coefficient automatically, which can greatly improve the accuracy of active power sharing. Simulation and experiment results show that, by using the proposed strategy, the precision of active power sharing can be improved and the circulating currents between inverters are suppressed.

Control of Offshore Wind Turbines Connected to Diode-Rectifier-Based HVdc Systems

Diode-rectifier-based high voltage dc (DR-HVdc) systems can be a promising low-cost solution for exporting wind power from remote offshore wind farms to onshore power systems. Industrializing the offshore DR-HVdc requires technical maturation, achievable through in-depth studies and pilot experiments. Deployment of offshore DR-HVdc systems may entail a fundamental change of control philosophy in wind turbine (WT) converters from grid-following control to grid-forming. This article proposes a new grid-forming control for DR-connected offshore WT converters. The proposed controller uses two sequential control loops to regulate WTs' active power, and maintain the frequency and voltage of the offshore ac network. The first control regulates the active-power mismatch of each WT into a voltage angle deviation, which leads to a frequency change. The second control adjusts the WT's alternating voltage magnitude to counteract the frequency change. An internal current control loop is used to limit the fault current and eliminate high-frequency resonances in the system. The proposed control is verified by electromagnetic transient simulations, including fault-ride through, WTs power change, reactive power disturbance, and WTs outage.

A Novel Hybrid Islanding Detection Method for Grid-Connected Microgrids With Multiple Inverter-Based Distributed Generators Based on Adaptive Reactive Power Disturbance and Passive Criteria

In order to obtain the benefits of both passive and active methods, a well-designed hybrid islanding detection method for grid-connected microgrids with multiple inverter-based distributed generators (IBDGs) is presented in this paper. Considering that IBDGs located at different positions can detect the same frequency variation (FV) characteristics, linear reactive power disturbance (RPD) is utilized, which can guarantee the synchronization of RPDs added on different IBDGs in the microgrid without the need for communication. In addition, the disturbance slope can change adaptively to reduce the disturbance in grid-connected mode and enlarge the reactive power mismatch during islanding for effective and rapid detection. Setting principles of slope values for IBDGs operating at the unity power factor and those generating active and reactive power simultaneously are analyzed in detail. Considering different conditions that may occur after islanding, three passive criteria, including voltage variation, voltage unbalance, and rate of change of frequency, are sufficiently utilized to activate disturbance slope adjustment, further shortening the detection time. Moreover, the correlation factor between the RPD and FV is also designed as another frequency-related criterion, and the slope adjustment logic is provided. This method is simple and easy to implement with excellent performance regardless of the IBDG power factor, parallel number, and connection mode. According to the anti-islanding test system recommended by IEEE Std.929-2000 and IEEE Std.1547-2003, the method effectiveness has been validated with several test cases in the power systems computer-aided design (PSCAD)/electromagnetic transients including DC (EMTDC) environment.

Sliding Mode Observer-Based Load Angle Estimation for Salient-Pole Wound Rotor Synchronous Generators

Synchronous generator load angle is a fundamental quantity for power system stability assessment, with possible real-time applications in protection and excitation control systems. Commonly used methods of load angle determination require additional measuring equipment, while existing research on load angle estimation for wound rotor synchronous generator has been limited to the estimator based on the generator’s phasor diagram and estimators based on artificial neural networks. In this paper, a load angle estimator for salient-pole wound rotor synchronous generator, based on a simple sliding mode observer (SMO) which utilizes field current, stator voltages, and stator currents measurements, is proposed. The conventional SMO structure is improved with use of hyperbolic tangent sigmoid functions, implementation of the second order low-pass filters accompanied with corresponding phase delay compensation, and introduction of an adaptive observer gain proportional to the measured field current value. Several case studies conducted on a generator connected to a power system suggest that the proposed estimator provides an adequate accuracy during active and reactive power disturbances during stable generator operation, outperforming the classical phasor diagram-based estimator by reducing mean squared error by up to 14.10%, mean absolute error by up to 41.55%, and maximum absolute error by up to 8.81%.

Novel islanding detection method for inverter‐based distributed generators based on adaptive reactive power control

Here, a novel active islanding detection method for inverter-based distributed generators (IBDGs) is presented. In order to reduce the disturbance in grid-connected mode and realise rapid and effective detection during islanding, the linear reactive power disturbance is utilised in the proposed method and its slope can change adaptively. The voltage variation and correlation factor between reactive power disturbance and frequency variation are proposed as criteria for disturbance slope adjustment. In addition, considering IBDGs located at different positions can detect the same frequency variation characteristics, the value of the frequency is used as the criteria to control the disturbance values, which can guarantee the synchronisation of disturbances added on different IBDGs without the need of communication. According to the anti-islanding test system recommended in IEEE Std.929-2000, the effectiveness of the method has been validated with several case studies in the power systems computer-aided design (PSCAD)/EMTDC environment.

Analysis on the Impact of Geomagnetic Storm on Reactive Power and Voltage in Extrahigh Voltage Power Grid

With the growing scale of the power grid and the improvement of the voltage level, the geomagnetically induced currents (GICs) generated by geomagnetic storms has become one of the leading factors that cause large-scale power outages in power grid. Considering the global simultaneity characteristic of geomagnetic storms, this paper presents the concept of mass reactive power disturbance for the first time, analyzes the mechanism of GIC reactive power loss of transformer and reveals the mechanism of mass reactive power disturbance’s influence on voltage. Finally, combined with the practical situation of 750kV EHV power grid in China, the reactive power loss and voltage distribution under the geomagnetic storms at various intensities are calculated, with the grid operating in two typical modes, and the impact of the geomagnetic storm on voltage is illustrated, which provides the theoretical basis for the study of voltage stability.

Coded Switching Scheme for Monitoring the Operation of Distribution Capacitors

A novel scheme is proposed to monitor the operation of capacitors scattered in MV distribution systems. It first codes each capacitor with a distinctive switching character by setting a unique combination of a three-phase switching order and time interval. As a result, the transient of the three-phase reactive power during capacitor switching will appear in a unique way. Then, the reactive power disturbances monitored in the substation are decoded to identify which capacitor is being switched on and off . A detailed decoding method is developed to realize this identification without being impacted by the switching interference of loads and other reactive power compensation devices. Moreover, the implementation of the proposed scheme in the field is elaborated, and the resultant three-phase voltage unbalance is analyzed in this paper. Compared with existing methods, this scheme only requires one power quality monitor located at the substation to monitor the operations (energizing or de-energizing) of downstream distribution capacitors without extra communication devices. The operation information is valuable for tackling power quality problems caused by capacitor switching and optimizing the distribution grid operation.

Additional reactive power control and emergency control of the ±1100 kV UHVDC system with a hierarchical connection mode

This paper proposes an additional reactive power control strategy and an emergency control strategy for ±1100 kV ultra-high voltage direct current (UHVDC) system with a hierarchical connection mode, in which the inverter station connect to two AC systems with different voltage levels. Firstly, the relationship between reactive power and DC voltage is analysed. Then, an additional reactive power control strategy is proposed to solve the voltage fluctuation caused by reactive power disturbance. Next, the reactive power emergency control strategy is proposed when a short-circuit fault occurs. Reactive power compensation devices will be inputted into the fault-free AC system to provide reactive power support through coupling relationship between two AC systems in the inverter side. Simulation results show that the additional reactive power control strategy can suppress reactive power disturbances without affecting the active power. Moreover, the reactive power emergency control strategy can reduce the probability of commutation failure in converters connected to the fault AC system while a short-circuit fault occurs.

Coordinated Protection and Control Based on Synchrophasor Data Processing in Smart Distribution Networks

Modern distribution grids are shifting toward resilient and sustainable energy networks through the use of unprecedented number of distributed generation (DG) units and renewable energy sources. However, unlike conventional grids, they are also highly integrative in the sense that, centralized control applications must support critical protective actions to reliably provide power to consumers. To achieve this goal, this paper presents a novel mechanism for coordinated protection and control of DG systems under permanent line faults in distribution networks. First, a centralized fault detector employs voltage phasors and frequency data to identify and isolate the fault within a tolerance time. Upon fault detection, a secondary control algorithm retrieves archived synchrophasor datasets to calculate real and reactive power disturbances caused by the fault isolation. In this mechanism, the secondary controller facilitates voltage/frequency recovery by adapting reference points of local controllers to the postfault conditions. Coordination is carried out based on the knowledge of the response time of protective devices and communication delays in control links. The proposed approach is a promising paradigm for reliable networked protection and improved situational awareness in smart distribution networks.

Research on Feasibility of Large-scale New Energy Islanding Detection Scheme Based on Impedance Measurement

A lot of research has been done on islanding detection of photovoltaic(PV) power system. In these schemes, islanding can be detected by schemes based on convertor control. The range of these research is islanding occurs in a single power station or distributed generation system. However, experiments proof that islanding also occurs in large-scale wind farms. Classical islanding detection schemes such as active frequency drift scheme or reactive power disturbance scheme may not suitable to this situation due to the different parameter when islanding occurs in large-scale new energy power stations. Meanwhile, islanding detection scheme based on system impedance detecion is an ideal scheme to detect islanding in large-scale new energy power stations. However, reaearch on islanding detection scheme based on system impedance only compute the impedance of the outlet end of the convertor, in other words, in a single power station and overlook the problems when the scheme is applied to large-scale new energy power stations, such as power quality problem and signal attenuation problem and so on. This artical will analyze the feasibility of using system impedance to detect islanding in large-scale new energy power stations.

An Islanding Detection Method for Inverter-Based Distributed Generators Based on the Reactive Power Disturbance

In this paper, an islanding detection method for inverter-based distributed generators (DGs) is presented, which is based on perturbing reactive power output. Two sets of disturbances are configured in this method, which have different amplitudes and duration time. The first set of reactive power disturbance (FSORPD) is periodic with small amplitudes to break the reactive power balance during islanding, whereas the magnitude of the second set of reactive power disturbance (SSORPD) is sufficient to force the frequency to deviate outside its threshold limits. Considering all the possible frequency variation characteristics with the FSORPD after islanding, three criterions are designed for switching the disturbance from the FSORPD to the SSORPD. Since DGs located at different positions have the same frequency variation characteristics, the SSORPDs can be added on different DGs at the same time without the need of communication. Therefore, synchronization of the SSORPDs can be guaranteed for the system with multiple DGs and the method can detect islanding with a zero nondetection zone property. Moreover, the method can be applied to the DG either operating at unity power factor or supplying reactive power as well for its local load. According to the antiislanding test system recommended in IEEE Std.929-2000 and IEEE Std.1547-2003, the effectiveness of the method has been validated with several case studies in the power systems computer-aided design/Electro magnetic transient in DC system environment.

Effective supervisory controllers designed for optimal energy management in permanent magnet synchronous generator wind turbine with battery storage

Optimal control of large-scale wind turbine has become a critical issue for the development of renewable energy systems and their integration into the power grid to provide reliable, secure, and efficient electricity. In this article, a new supervisory control system for the optimal management and robust operation of a wind turbine generator and a battery energy storage system is presented. The proposed coordinated controller can mitigate both active and reactive power disturbances due to the intermittency of wind speed and load change. Moreover, the control strategy ensures the maximum power extraction capability of direct-drive wind turbine. This supervisory controller is made up of three subsystems. The first one is used to track the maximum power point for variable wind speeds; the control algorithm employs a fuzzy logic controller and a second-order sliding mode controller to effectively meet this target. The task of the second one is to maintain the required DC-link voltage level. This is achieved by controlling the bidirectional power flow in the storage batteries using DC–DC converter. Whereas in the last, a second-order sliding mode controller is investigated to achieve smooth regulation of grid active and reactive power quantities, which provides better results in terms of attenuation of the harmonics present in the grid courant compared with the conventional first-order sliding mode controller. Extensive simulation studies under different conditions of wind speed are carried out in MATLAB/Simulink, and the results confirm the effectiveness of the new supervisory control system.

Active Power Filtering Using the ZDPC Method under Unbalanced and Distorted Grid Voltage Conditions

In this paper, we propose a new Zero Direct Power Control (ZDPC) technique for active compensation of harmonics and reactive power, using shunt active power filter (SAPF), based on cancellation of instantaneous active and reactive power disturbances by comparison with their zero references. To separate harmonic and fundamental components of the line voltage and current a highly selective filter (HSF) has been used. Depending on the power errors and line voltage vector position, a switching table produces the appropriate control vectors leading to the active and reactive power variation required to reach the zero power references, even under grid voltage unbalanced and distorted conditions. The experimental validation of the proposed ZDPC has been performed. The results are compared to other recent techniques to demonstrate the superiority and feasibility of the proposed strategy.

A Key Strategy for Controlling the High-Power Photovoltaic Inverter

In this paper, a systematic control strategy has been proposed for specific problems with the various key performance indicators of the high-power photovoltaic (PV) inverter when it connects to the grid. it proposes fast and accurate variable-step-size perturbation and observation combined with power prediction as a Maximum Power Point Tracking-based (MPPT) control strategy. To meet the requirements for low voltage ride through (LVRT), it proposes a strategy for LVRT control. It adopts an active method used for anti-islanding detection of reactive power disturbance so as to realize anti-islanding detection quickly. Finally, it carries out testing on the control strategy by means of an experimental platform with a 500 kW PV inverter to prove the effectiveness of the proposed control strategy.

Coordinated Predictive Control of a Wind/Battery Microgrid System

This paper presents the operation and controller design of a microgrid consisting of a direct drive wind generator and a battery storage system. A model predictive control strategy for the ac-dc-ac converter of wind system is derived and implemented to capture the maximum wind energy as well as provide desired reactive power. A novel supervisory controller is presented and employed to coordinate the operation of wind farm and battery system in the microgrid for grid-connected and islanded operations. The proposed coordinated controller can mitigate both active and reactive power disturbances that are caused by the intermittency of wind speed and load change. Moreover, the control strategy ensures the maximum power extraction capability of wind turbine while regulating the point of common coupling bus voltage within acceptable range in both grid-connected and islanded operations. The designed concept is verified through various simulation studies in EMTDC/PSCAD, and the results are presented and discussed.

Risk factors for falls of older citizens

Fall prevention is a major issue in the ageing society. This study provides an overview of all risk factors for falls of older citizens. A literature search was conducted to retrieve studies of the past 25 years. All participants from the studies lived in the community or institutions and were aged 60 or older. The following key word combinations were used, limited to the title: elderly or older people or older adults and fall and risk. The risk factors were categorised as relevant and amendable, relevant but non amendable, inconclusive or unsupported. In total 30 publications were studied in 2013 in Enschede, the Netherlands. The relevant intrinsic risk factors are muscle strength, balance capacity, reactive power, dual tasking and sleep disturbance. Relevant extrinsic risk factors are home hazards, wrong use of assistive devices and bad footwear. Behaviour-related risk factors are hurrying, risk taking, physical inactivity and fear of falling. Relevant symptoms that could be caused by underlying risk factors are mobility problems, gait problems, vertigo, use of assisting devices and history of falls. Several risk factors are determined to be relevant and amendable. The provided overview could be used to create fall preventive measures for elderly.