Voltage Sag Research Articles

Boosting a practical Li-CO2 battery through dimerization reaction based on solid redox mediator

Li-CO2 batteries offer a promising avenue for converting greenhouse gases into electricity. However, the inherent challenge of direct electrocatalytic reduction of inert CO2 often results in the formation of Li2CO3, causing a dip in output voltage and energy efficiency. Our innovative approach involves solid redox mediators, affixed to the cathode via a Cu(II) coordination compound of benzene-1,3,5-tricarboxylic acid. This technique effectively circumvents the shuttle effect and sluggish kinetics associated with soluble redox mediators. Results show that the electrochemically reduced Cu(I) solid redox mediator efficiently captures CO2, facilitating Li2C2O4 formation through a dimerization reaction involving a dimeric oxalate intermediate. The Li-CO2 battery employing the Cu(II) solid redox mediator boasts a higher discharge voltage of 2.8 V, a lower charge potential of 3.7 V, and superior cycling performance over 400 cycles. Simultaneously, the successful development of a Li-CO2 pouch battery propels metal-CO2 batteries closer to practical application.

Power Control Strategies During Voltage Sags According to Spanish Grid Code

In order to connect any power converters into the grid there are some grid requirements to insure the safe operation of the grid. So, the control of the converters especially during abnormal condition-e.g. during voltage sags- is a very important key to guarantee the good behavior of the distributed generation system. In this paper four control strategies,will be stated in the literature, are discussed in order to ensure their ability to match the grid requirements when unsymmetrical voltage sags are produced in the network. The Spanish grid code did not give any information about the negative sequence, and it only represents the positive sequence components. Therefore, the main contribution of this paper is to verify the grid code with not only the positive sequence but also with the negative sequence. Moreover, the system is tested by simulation to show that the results cope well with the analytical equations.

Implementation of a New Method for an Improved Voltage Dips Evaluation by the Italian Power Quality Monitoring System in Presence of VT Saturation Effects

The paper deals with a recent measurement improvement introduced into the Italian power quality monitoring system, concerning voltage dips detection and their proper evaluation in the presence of voltage transformer VT saturation phenomena. Saturation effects, essentially on network operated with isolated neutral, can give origin to “false” voltage dips, which can affect the on-line voltage monitoring during a few specific events (i.e. single line-to-ground faults). The “false dip” problem, on the other hand, can be considered negligible in compensated neutral networks. A new criterion has been developed in cooperation with the Polytechnic of Turin, based on the detection of a second harmonic component in the measured voltages, which, once provided with the proper setting parameters, can succeed in identifying “false” dips. The criterion effectiveness has been evaluated on field. The major advantage of the filter implementation in the monitoring system is that, from now on, network operated with isolated neutral could be considered quite similar to those operated with neutral compensation from the point of view of voltage dip performance.

Environment and Power Quality International Conference on Renewable Energies and Power Quality (ICREPQ’09) Valencia (Spain), 15th to 17th April, 2009 Evaluation of Different Methods for Voltage Sag Source Detection Based on Positive-Sequence Componen

This paper evaluates methods for voltage sag source detection, which are based either on energy, current or impedance criteria. It is shown that some methods known from the literature do not work well, particularly in cases of asymmetrical voltage sags. Furthermore, some methods require measurements of instantaneous values, which is not always feasible. Therefore, symmetrical component transformation is applied, whereas only positive-sequence components are used. All the discussed methods were tested by applying extensive simulations and field tests. The obtained results show that all methods which are based on positive-sequence components are highly effective also in cases of asymmetrical voltage sags.

The influence of network characteristics and environmental conditions on voltage dip performance in MV networks

The paper is focused on the possible influence that some network characteristics (i.e. network configuration, type of neutral operation, geographical area, lines and cable length…) and environmental phenomena (lighting) may have on voltage dip performance in Medium Voltage (MV) networks. The investigation has been performed by applying both correlation techniques and Multiple Linear Regression analysis (MLR) on the voltage dips collected along several years of monitoring by the Italian MV network monitoring system QuEEN. As to the network characteristics and environmental factors used in the performed analysis they are referred to the data supplied in the past for the monitoring system and to the lighting data provided by the Italian lightning location system SIRF1. The percentage contribution of each network and environmental factor to the voltage dips statistic, irrespective of the other parameters, have been evaluated by multiple linear regression methods. The results of these analysis confirm that the overhead line length has got a significant influence on the phenomena while cable lines length has, as expected, only a negligible effect. The influence of lightning seems to be not so critical as expected and this happen also with the neutral type of operation while voltage dips performances depend, in a non-negligible way, on the belonging to a geographical area.

Optimal Placement and Sizing of DG for Loss Reduction,Voltage Profile Improvement and Voltage Sag Mitigation

Increasing trend in using distributed generation has motivated power sector planners to consider approaches that result in benefiting the most from investments in this field. Meanwhile subjects such as power loss reduction, voltage profile improvement and voltage sag mitigation has significant role in lessoning imposed expenditures to utility companies. Loss reduction is important for utility companies as it directly increases company benefit in a competitive electricity market, beside reaching power quality standards is too important as it has vital effect on customer orientation. In this paper an optimization algorithm is developed to gain these goals all together. In order to evaluate sag mitigation capability of the proposed algorithm, voltage in voltage sensitive buses is investigated. An existing 20KV network has been chosen as test network. Results show the efficiency of the proposed algorithm in reducing power loss, improving voltage profile and mitigating voltage sags in voltage sensitive buses.

A First Approach on the Impact of Distributed Generation on Voltage Sags

An analysis of the distributed generation (DG) impact on studies of voltage sags caused by system faults is presented. The simulation of 62 case studies of phase-to-ground faults on 13.8, 69, 138 and 230 kV transmission lines were performed and the voltage of a 380 V sensitive industrial busbar client was monitored. These lines are part of the electrical system of the city of Goiania, Brazil. For each case study, different fault positions were simulated by considering different DG levels connected to the consumer busbar. Long-term simulation scenarios were obtained by the Monte Carlo method and analyzed based on their cumulative distribution functions and probability density curves of voltage sags. This is one major contribution of this work.

Comparison of different voltage dip detection techniques

To accurately determine the beginning and the end of voltage sags is very important for the actuation of a system that is connected to the grid and must have ride-through capability. This paper analyses four voltage sag detection methods, comparing both detection speed and reliability, not presenting false detections and providing a consistent signal during all the gap duration. In particular, it has been analysed the behaviour of the detection methods when voltage waveforms present harmonics due to power electronics switching.

Voltage Disturbances and Inrush Current of DC Power Supplies

The potential damaging effects of high inrush currents occurring after power quality disturbances on switch-mode dc power supplies (SMPS’) have been reported, but have not been studied in detail. This paper presents a new analytical model for the accurate representation and calculation of inrush currents of low-power SMPS devices. This model is verified against previously developed circuit-based simulation model and compared with the only other analytical model available in existing literature. The developed analytical model is also used to investigate device protection co-ordination, in order to demonstrate two important effects of high-inrush current: nuisance tripping of protection and damage of internal SMPS components. Key words. Inrush current, load modelling, analytical representation, switch-mode dc power supply (SMPS), power quality disturbance, short interruption, voltage sag

Simulations of a possible configuration of Premium Power Park

The voltage dip and the sudden electrical energy interruption are, probably, the most important disturbances of the power quality in the electrical system. Several technical solutions exist to mitigate voltage dips, respectively at plant or system level as for example: • the installation of Custom Power (CUSPO) for a single customer; • the Premium Power Park (PPP) for a group of customers. According to the PPP concept, the tenants of an industrial or commercial office park would be provided with a guaranteed level of electrical service quality made possible by Custom Power devices, such as the Dynamic Voltage Restorer (DVR), the Distribution Static Compensator (DSTATCOM – Distribution STATCOM), the medium voltage Static Transfer Switch (STS). The paper summarizes the Premium Power Park idea and a possible configuration of it, studied by ERSE, including the system aspects and the analysis of the combined operation or interaction of the Custom Power.

POWER QUALITY MEASUREMENT CAPABILITIES OF “SMART” ENERGY METERS

Power quality measurement integrated in energy meters are presented as a potential benefit by some manufacturers. The Norwegian regulator has considered making minimum requirements for energy meters to include registration of interruptions. SINTEF Energy Research has performed tests on energy meters with power quality measurement capabilities. These tests include the ability to detect interruptions, supply voltage variations, voltage dips, among others. Results presented in this paper show large differences in capabilities for power quality measurement of ‘smart’ energy meters. The results also show that the power quality measurements are not according to international standards for such measurements like EN50160 [1], IEC 61000-4-30 [2] and others.

System Studies of DC Reactor Type Fault Current Limiter in Distribution Grid

A DC reactor type fault current limiter (FCL) in series with a downstream circuit breaker can be a solution to control fault current levels in electrical distribution systems. In order to integrate the DC reactor type FCL in to power grid, the performance of the DC reactor FCL should be studied. In this paper, short circuit analysis, based on the electromagnetic transient program (EMTP), has been used to investigate the behavior of the DC reactor type FCL installed in an electrical distribution grid. System studies show that the DC reactor type FCL can not only limit the fault current to an acceptable value, but also can mitigate the voltage sag. The Transient Recovery Voltage (TRV) could be damped in the presence of the DC reactor type FCL during fault clearing period, too

A First Approach on the Impact of Distributed Generation and network topology on Studies of Voltage Sags

An analysis of the distributed generation (DG) and network topology impact on studies of voltage sags caused by system faults is presented. The simulation of 62 case studies of phase-to-ground faults on 13.8, 69, 138 and 230 kV transmission lines were performed and the voltage of a 380 V sensitive industrial busbar client was monitored. These lines are part of the electrical system of the city of Goiania, Brazil. For each case study, different fault positions were simulated by considering different DG levels connected to the consumer busbar. Long-term simulation scenarios were obtained by the Monte Carlo method and analyzed based on their cumulative distribution functions and probability density curves of voltage sags. This is one major contribution of this work.

Marine Predator Algorithm-Based Optimal PI Controllers for LVRT Capability Enhancement of Grid-Connected PV Systems.

Photovoltaic (PV) systems are becoming essential to our energy landscape as renewable energy sources become more widely integrated into power networks. Preserving grid stability, especially during voltage sags, is one of the significant difficulties confronting the implementation of these technologies. This attribute is referred to as low-voltage ride-through (LVRT). To overcome this issue, adopting a Proportional-Integral (PI) controller, a control system standard, is proving to be an efficient solution. This paper provides a unique algorithm-based approach of the Marine Predator Algorithm (MPA) for optimized tuning of the used PI controller, mainly focusing on inverter control, to improve the LVRT of the grid, leading to improvements in the overshoot, undershoot, settling time, and steady-state response of the system. The fitness function is optimized using the MPA to determine the settings of the PI controller. This process helps to optimally design the controllers optimally, thus improving the inverter control and performance and enhancing the system's LVRT capability. The methodology is tested in case of a 3L-G fault. To test its validity, the proposed approach is compared with rival standard optimization-based PI controllers, namely Grey Wolf Optimization and Particle Swarm Optimization. The comparison shows that the used algorithm provides better results with a higher convergence rate with overshoot ranging from 14% to 40% less in the case of DC-Link Voltage and active power and also settling times in the case of MPA being less than PSO and GWO by 0.76 to 0.95 s.

Low‐voltage ride‐through control strategy for flywheel energy storage system

AbstractDue to its high energy storage density, high instantaneous power, quick charging and discharging speeds, and high energy conversion efficiency, flywheel energy storage technology has emerged as a new player in the field of novel energy storage. With the wide application of flywheel energy storage system (FESS) in power systems, especially under changing grid conditions, the low‐voltage ride‐through (LVRT) problem has become an important challenge limiting their performance. In this paper, we propose a machine‐grid side coordinated control strategy based on model predictive current control (MPCC) for the insufficient LVRT capability of traditional FESS during grid faults. Excellent dynamic properties are demonstrated by the technique, which allows the grid‐side converter output current to swiftly follow the reference current instruction. The FESS's LVRT capability is increased when the grid‐side converter uses the MPCC current inner loop rather than the proportional–integral current inner loop during grid voltage dips. This greatly increases the reactive power response speed and efficiently supports the quick recovery of grid voltage. According to simulation verification carried out by Matlab/Simulink, the suggested control approach can assure the long‐term dependable operation of the FESS during voltage dips. This study can also be used as a reference for improving the FESS's LVRT capabilities in the future.

Specific Energy Concept Applied to Electronic Equipment in Industrial Processes Having Distributed Generation

Appliances used in commercial and industrial networks, being very sensitive equipment, are affected by voltage sags. Information about sensitivity is normally presented in time/voltage graphs, where the voltage is of a constant magnitude. This is not the case when distributed generation (DG) is involved, where due to the distributed generator disconnection the voltage magnitude could have one or two sharp changes. The methodology presented here, based upon the I2 t and V2 t change with time, allows the study of such phenomenon. Also the time-voltage and time-current coordination could be studied easily by using the proposed methodology

Frequency support scheme of grid‐forming based hybrid cascaded HVDC integrated wind farms

AbstractThe grid‐following control‐based hybrid cascaded high‐voltage direct current (HC‐HVDC) links may contribute to the worsening of inertia decline and instability issues, especially in situations characterized by a weak grid. To address the challenge, this paper proposes a grid‐forming (GFM) based optimal frequency support scheme (OFSS) for HC‐HVDC integrated wind farms. Firstly, a GFM control for hybrid converter is proposed and its stability under weak grid conditions is evaluated through a small‐signal model. Then, DC current–voltage droop control is introduced to the line commutated converter (LCC). This control approach ensures the consistency of reactive power in the LCC by regulating the DC voltage and current in the same direction, thereby mitigating AC voltage fluctuations. It also facilitates active power control in the LCC in response to grid frequency variations. Furthermore, the OFSS can convey the frequency of receiving‐end grid to the rectifier and wind farms without communication for precise power control. Finally, to validate the effectiveness of OFSS, a point‐to‐point HC‐HVDC and a 4‐machine test model are constructed on PSCAD/EMTDC. The OFSS significantly enhances the frequency support capability of HC‐HVDC links and improves the robustness in weak grid.

Impedance-Based Methods for Detection of Voltage Sag Sources

The research reflects impedance-based methods for detection of voltage sag sources, whereas measured voltages and currents are treated as average functions, and also as instantaneous values. Evaluation of the discussed methods has been performed by applying extensive numerical simulations and field testing. The obtained results show that all methods are very effective in the cases of symmetrical voltage sags. When instantaneous values are applied the best effectiveness is obtained also for asymmetrical voltage sags.

The Italian MV network dip performance characterization by contour charts as defined by UIE/CIGRE’/CIRED WG-C4.110

Reporting and analysis procedures play an important role in power quality monitoring systems especially for long term surveys. As far as voltage dips are concerned, the network voltage dip performance can be effectively described in many different ways depending on the aims of the data presentations at both site and system level. The paper deals with network dip performance different representation methods focussing in particular on the way of presentation proposed by the working group UIE/CIGRE’/CIRED C4.110. This method has been applied to the Italian 2009 voltage dips statistic as acquired by the Italian power quality monitoring system named QuEEN. Contour charts have been drawn for both different percentage of the monitoring sites and voltage dips types.

Assessment of Financial Losses Due to Voltage Sags Using Optimal Monitoring Schemes

The paper investigates the effectiveness of optimal placement of monitors in the assessment of financial losses due to voltage sags. Optimal sag monitoring schemes and typical power quality monitoring sites are used to perform a risk-based assessment of financial losses. The influence of the number and location of monitors on the outcome of a financial-loss analysis in voltage sag studies is also looked into. The results of the analysis are illustrated using a 295-bus generic distribution network (GDN) and considering a range of sensitive customers.