Power Flow Conditions Research Articles

Evaluating the performance of reaching laws in the sliding mode control of the Unified Power Flow Controller (UPFC)

This paper evaluates reaching laws in sliding mode control (SMC), encompassing constant rate, exponential, and power rate reaching laws. The performance of the proposed controller is assessed using a Unified Power Flow Controller (UPFC) as the test subject. The Unified Power Flow Controller system is in order to improve the stability of a power system hence providing security under increased power flow conditions. The sliding mode control, utilizing reaching laws, is designed to ensure the Unified Power Flow Controller system closely follows the reference power. Comparative simulation results with a traditional PID controller demonstrate superior performance with sliding mode control. Specifically, the sliding mode control Reaching law with power rate effectively controls the Unified Power Flow Controller system for active power, Various simulations have given very satisfactory results and we have successfully improved the active and reactive power flows on a line of transmission. achieving an overshoot of approximately 0.5411%, with a setting time of 0.1009 seconds and a rising time of 4.0720*10^-4 seconds.

Complex plane based adaptive method for protection of series compensated transmission line using phasor measurement unit data

Though differential relays are preferred for the protection of series-compensated transmission line (SCTL), they may mal-operate during current inversion, high resistance internal faults and current infeed/outfeed situations. Therefore, a new protection scheme for SCTL using Phasor Measurement Unit data, that adaptively manages the operating region in the current ratio complex plane according to the percentage compensation level, is presented. Boundaries of the operating region are determined adaptively based on the estimated impedance value of the series compensation. Usefulness of the technique is confirmed by generating cases covering wide range of fault parameters, compensation level, and load angle on an existing 400 kV Indian SCTL using PSCAD software as well as through Hardware in Loop simulation employing the Real Time Digital Simulator. Reported outcomes reveal the ability of the suggested algorithm in sensing all types of internal faults. Its performance remains unaffected during current/voltage inversion, operation of MOV and/or airgap during high fault current conditions, current infeed/outfeed situation, and external fault with current transformer saturation condition. Impact of the presence of noise in the acquired signals is also analyzed. The suggested technique is applicable for SCTLs having different voltage levels and power flow conditions. The proposed method has higher responsiveness during high resistance internal faults up to 500 Ω and better steadiness during external faults compared to numerous prevailing methods.

Intelligent controller based WECS fed unified power flow conditioner for PQ enhancement

<p>The dominance of non-linear loads, sustainable energy sources and power electronic devices in modern power system has in turn compromised the system stability by introducing numerous power quality (PQ) issues. A wind energy conversion system (WECS) fed unified power flow conditioner (UPFC) architecture is suggested in this work since maintaining optimal PQ is important for both the supply authorities and customers. The proposed approach supports both clean energy generation and PQ enhancement. The UPFC aids with accomplishing control over reactive power flow, active power flow, phase angle, impedance and voltage. The reference current for the UPFC is generated using DQ theory. Moreover, a shunt and series compensators of an UPFC are controlled using cascaded fuzzy logic controller (CFLC). The stability of the DC voltage obtained from doubly fed induction generator (DFIG) based WECS is also controlled using a CFLC. The simulation model for the presented WECS fed UPFC is developed in MATLAB and its performance is evaluated.</p>

A Consensus-Based Distributed Secondary Control Optimization Strategy for Hybrid Microgrids

In this paper, a new consensus-based distributed secondary control (DSC) strategy is proposed for frequency control, dc-voltage regulation, and optimal dispatch (OD) in isolated hybrid ac/dc-microgrids (HMGs). At the same time, all the units are maintained within limits. The proposed control scheme dispatches the distributed generators (DGs) within the microgrid in compliance with the Karush-Kuhn-Tucker (KKT) conditions of a linear optimal power flow (OPF) formulation. Furthermore, the power through the interlinking converters (ICs) is also dispatched to help minimize the total operation cost of the microgrid. The controllers rely on local measurements and information from neighbouring devices at both sides of the microgrid (DGs and ICs). Thus, unlike conventional methods, the microgrid is considered a single entity and not as three independent systems interacting with one another, and the OD is calculated considering both the ac-DGs and dc-DGs. Extensive simulations demonstrate a good performance of the controller amid load step changes and unit congestion, driving the system to an optimal economic operation.

A Bidirectional Grid-Tied ZVS Three-Phase Converter Based on DPWM and Digital Control

In this paper, a bidirectional grid-tied ZVS three-phase converter is proposed. The circuit operation principle in both the rectifier and inverter modes was analyzed. The proposed topology could achieve zero-voltage switching in the six main switches and the auxiliary switch both in the rectifier mode and inverter mode. In addition, the reverse recovery current of body diodes in the main switches was also suppressed. Furthermore, in order to realize the ZVS control scheme under the grid-tied bidirectional power flow condition and reduce the number of switchings, a modified carrier-based discontinuous PWM was proposed to fit the bidirectional switching sequence. Finally, a 3 kW prototype was constructed. Some simulation and experimental results are presented to verify the validity of the proposed circuit topology and PWM control scheme.

Cascading Failure Propagation and Mitigation Strategies in Power Systems

In this article, we investigate the local and nonlocal failure propagation patterns in power systems and propose effective mitigation strategies. It is widely acknowledged that the sequence of failure events of component overloading is determined by power flow redistribution. To understand the power flow redistribution process, we analyze the prefault power flow condition using network flow theory and by clustering the system into several regions with balanced local power flow. We observe that faults triggering local power imbalance would lead to remote power transfer and faults causing no local power imbalance would lead to local power redistribution. The improved understanding of the failure process permits us to develop effective mitigating strategies consisting of adaptive power balance restoration and selective edge protection for cascading failure propagation. In addition, we propose a set of indexes to measure the local and nonlocal propagation risks of cascading failures. Numerical simulations on the IEEE 118- and 300-bus systems demonstrate that the proposed mitigation strategies can significantly reduce the blackout sizes and are tolerant to incorrect transmission line tripping.

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

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

Evaluation method of congestion frequency considering changes in power flow conditions due to wind turbine installation

With the recent introduction of renewable energy sources, the shortage of the transmission line capacity (i.e., grid congestion) in Japan is a major concern. To maximize the output of wind turbines (WTs), the installation area is determined by considering the grid congestion frequency and wind conditions when installing new WTs. However, determining the appropriate area may be challenging for some power producers in terms of the limitation of accessible information and construction of an evaluation platform as detailed information on the power system and power flow calculations is required. Therefore, this study assumes that the system operator shares the information of acceptable additional generation in each area without grid congestion based on past actual power flow data. Furthermore, using this information, a simple evaluation method is proposed for power generators to evaluate the frequency of grid congestion after the introduction of new WTs. To verify the usefulness of the proposed method, numerical experiments are conducted for several scenarios introducing WTs in a simplified power system model of the northern area of the Tohoku region. The results indicate that the proposed method can accurately estimate the frequency of grid congestion in the evaluation scenarios.

Application of data models in power grids for loss reduction and disaster anticipation

This paper addresses the critical objective of optimizing power flow within a region, particularly focusing on the Mangystau region, amidst evolving energy demands and the integration of renewable resources. The escalating challenges associated with maintaining both system stability and economic viability underscore the significance of this research, as suboptimal power flow conditions can exacerbate climate change. To expedite the solution to the optimal power flow problem, machine learning algorithms are explored. Initially, load data from the region is analyzed, and various supervised learning algorithms are tested using simulation data to predict power flow patterns. The primary concern in the Mangystau region lies in the aging infrastructure of oil companies, which operates under suboptimal conditions. This study employs neural networks in Matlab to simulate the electrical system’s parameters, unveiling the intricate relationship between optimal system parameters and those of the examined system. Comparing these results with analytical grid modeling, the study reveals that system optimization aligns with target values, particularly concerning optimal receiver replacement schemes.

Coupled Inductor Based Voltage Balancing in Dual-Output CLL Resonant Converter for Bipolar DC Distribution System

Bipolar dc distribution systems face imbalances in voltages when unbalanced loads are connected at the outputs. To address imbalances in bipolar voltage levels, dedicated voltage balancers are required. However, they add extra active and/or passive components; including, magnetics, capacitors, etc. This increases the cost, reduces the conversion efficiency, and power density of dual-output converters. Therefore, to tackle the imbalances in output voltages without adding any extra active and/or passive components, this article presents coupled inductor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CI</i> ) based voltage balancing in dual-output <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLL</i> resonant converter. The main features of the proposed method are as follows: since <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CI</i> is the result of already present resonant inductors of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLL</i> tank circuit, therefore, it does not require extra magnetic components to balance the output voltages; with no additional components, it does not increase the magnetic volume, component count, cost, and complexity of the converter; due to the direct coupling, a half of circuit inductances are integrated to achieve the respective resonant inductance of the tank circuit; and it can also avoid complex control schemes applied to voltage balancing. Besides, with the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CI</i> , the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLL</i> converter maintains all of its good features including; zero-voltage and zero-current-switching (ZVZCS). The detailed analysis of the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CI</i> with different load conditions is discussed. Moreover, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> or Type-12 resonant tank circuit is presented to validate ZVZCS operation in the reverse power flow condition. To verify the effectiveness of the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CI</i> based voltage balancing, a 3.6-kW hardware prototype has been built and tested.

A new method for online evaluation of the effects of PV panels and comparison with MVDI in electrical power distribution networks

With the increasing penetration of PV, LV distribution networks experience the condition of reverse power flow and also voltage increase in a part of the network. As a result, the capacity of the installed feeders is approximately within the range of the nominal value defined for them. Therefore, the proper assessment of the impact of PV in distribution networks seems necessary. In this paper, we have investigated the effect of PV systems in low-voltage and medium-voltage (MV) distribution system, and suitable online strategies were presented to alleviate these problems. In this regard, comprehensive modeling and analysis for LV and MV distribution networks have been performed. Therefore; this will allow the proper allocation of PV systems in the network. Using the approach as mentioned above, PV networks can be modeled for medium-voltage three-wire systems and low-voltage four-wire systems, which include Y-Δ transformers and ground impedance. PV systems modeling based on temperature , and ambient radiation data, inverter efficiency, PV panel parameters and V-I feature will be done. By using the above approach, it will be possible to optimally allocate PV systems in LV and MV distribution networks. In addition, a suitable method for carrying out load flow in distribution systems along with PV systems is provided, and in this regard, a suitable design will be proposed to analyze the effect of PV systems in distribution networks. Based on this plan, which was based on stabilizing the voltage of the network feeders at a nominal value, it was shown that the changes in the working conditions for PV systems in the presented algorithm and structure cannot have a negative impact on the network performance.

Robust control of adaptive power quality compensator in Multi-Microgrids for power quality enhancement using puzzle optimization algorithm

The primary purpose of this paper is to design a novel multi-microgrid connection that uses power compensation methods to improve voltage profiles and reduce harmonic distortions using specific compensation devices in low inertia systems. The utilized compensation device is an adaptive power quality compensator (APQC) which includes series and shunt compensators. Thyristor controlled series capacitor (TCSC) is used as a series compensator to alleviate the dynamic voltage profile as well as diminish transient voltage. A shunt active power filter (SAPF) is utilized as a shunt compensator to improve the power factor and lessen voltage and current harmonics. The TCSC has a power level of error of the PID controller, while the SAPF has a dynamic multi-level of errors of the PID controller. Further, the recent swarm intelligence-based puzzle optimization algorithm is employed to get the best self-tuning of the PID controller gains to reveal the act of the APQC typology. The efficacy of the presented APQC with the multi-level mechanism approach, assessed using Matlab/Simulink time-domain simulations, has been compared with the recently reported literature. Two operation modes are addressed, one for the island mode and the other for the grid-connected mode with significant renewable generation penetration and nonlinear loads. APQC successfully enhances the power quality of multi-microgrids (MMGs), according to theoretical research and simulation statistics. Finally, three comparative study assessments of numerous optimization approaches, with a unified power flow conditioner (UPFC), and with other series-shunt compensators like distributed power condition controller (DPCC) are proposed to attain efficacy and strength of the compensator.

DC-Link Current Minimization Control for Current Source Converter-Based Solid-State Transformer

This article proposes a fast predictive control method and a small dc-link inductor to minimize the dc-link current in current-source converter (CSC) based solid-state transformer. The dc-link current minimization can significantly reduce power loss and improve efficiency. The challenge of this problem is on improving both steady-state and dynamic performance. PI control methods and large dc-link inductors are conventionally used in the CSC but have limited dynamic performance. A model predictive control (MPC) method is proposed to achieve switching-cycle-level settling time, and the dc-link inductor is sized for 40% ripple to enable fast current change. Importantly, this article also proposes to minimize the dc-link current by varying the current even within a line cycle under single-phase load to improve the steady-state performance, in contrast with the reduction to a constant value in the literature. The proposed MPC features a constant switching frequency without weighting factors. The MPC does not have a high computational burden and is implemented in a regular digital controller for a prototype of soft-switching solid-state transformer (S4T) with reduced conduction loss. The effectiveness of the proposed method has been experimentally verified on the SiC S4T prototype during steady-state and dynamics under different multiport power flow conditions up to 2 kV peak. The dc-link current in the experiments is close to the minimum current with a short zero-vector duration, which further verifies the performance of the proposed method.

Analisis Penentuan Lokasi Gangguan Hubung Singkat Pada Saluran Transmisi Di Sulawesi Tenggara

The electricity system often experiences disturbances, especially short circuit disturbances on transmission lines. This short circuit disturbance is caused by various things such as lightning surges, fallen trees, animals, and other conditions. The interconnected Southeast Sulawesi power system cannot be separated from this short circuit problem. Therefore, determining the location of this short-circuit fault must be done quickly so that the cause of the disturbance can be immediately identified. This study aims to analyze the determination of the location of short circuit faults using the Takagi Method. Simulations were carried out using ETAP 16.0.0 software to see the condition of the Southeast Sulawesi system power flow. This Takagi method analyzes the location of the disturbance using the conditions before and after the disturbance occurs based on the recorded data at the substation. The results of the analysis carried out on the Southeast Sulawesi transmission line show that the percentage of accuracy in determining the location of a single-phase short-circuit fault to ground using the Takagi method is better, with a distance difference of 0.368-0.581 km (1.49%) when compared to the reading results on recordings of 10,173-9,960 km (31.58%) from the fault location occurred after inspection of the Lasusua-Kolaka transmission line. Disturbances on lines 1 and 2 Kolaka-Lasusua produce an error value of 1.533 km (9.24%) and 1.547 km (9.32%) when compared to fault locator readings of 3.212 km (19.36%) and 1.812 km ( 10.92%). Meanwhile, the Unaaha-Kolaka transmission line produces a distance difference of 0.709 km (3.29%) when compared to the fault locator reading of 4.323 km (20.12%). The results of the power flow simulation produce an installed generating capacity of 188 MW, a total active power of 116.780 MW and a reactive power of 29,944 Mvar. Thus, it can be concluded that the Takagi Method has a better accuracy value in reading fault locators.

Design and implementation of a PI-PBC to manage bidirectional power flow in the DAB of an SST

The interest of moving towards more sophisticated power grids and the possibility of having more efficient and reliable power semiconductor devices have enabled the introduction of new concepts in power systems, such as solid-state transformers (SSTs). SSTs are considered to be one of the most relevant elements in the future of smart grids since their functionalities allow for the appropriate integration of distributed generation, renewables, energy storage systems, among others, with traditional power grids. One of the main stages of an SST (a DC-DC stage) includes a dual active bridge (DAB) that enables bidirectional power flow, which is regarded as one of the main advantages over traditional power transformers. This work focuses on proposing a current control strategy based on PI passivity in order to regulate the power flow in a DAB. The proposed controller guarantees the system's stability in a closed loop, keeping its passive properties. In addition, it preserves the simplicity of a PI controller, with high performance and robustness, and it does not depend on the converter's parameters. The performance and effectiveness of the proposed controller is validated through time-domain simulations and experimental results under different power flow conditions, including bidirectional power flow. The results show that the proposed controller has a better performance than classical PI controllers.

A comprehensive design approach for a three‐winding planar transformer

In this paper, a new three-winding planar transformer design with the integrated leakage inductor is proposed for a triple-active-bridge converter. It enables two output voltage levels: a high voltage (HV) output port and a low voltage (LV) output port. The primary and secondary windings are split unevenly in both side legs while the tertiary winding is connected in parallel. The unique winding configuration enables: (i) enhanced efficiency with low volume; and (ii) suppressed parasitic capacitances. Detailed transformer reluctance and loss models are developed in the design process. The core geometry is optimized using a reluctance-model-based mathematical computation. Moreover, comprehensive high-fidelity simulations are conducted to analyse the trade-offs among parasitic capacitances, losses, and inductances. The customized core and the non-overlapping winding boards are assembled, characterized, and tested under various power flow conditions.

Review on the Techniques Used for Enhancing Performance of UPQC Structures

In a power transmitting network, a Unified Power Quality Conditioner is used to operate both shunt— connected and series-connected compensation simultaneously. Destabilize, disturbance, and sometimes even dc elements can all be found in a power distribution network. As a result, a UPQC (Unified Power Quality Conditioner) outperforms a Unified Power Flow Conditioner (UPFC) in many of these areas to offer shunt-connected or series-connected compensation. The main objective of this paper is to provide the overview, different designs given by many researchers to improve the performance of the UPQC.

A SVR Control Method with Switching Multiple LDC Parameters Using Measurement Data of Distribution Systems

The voltage regulation in distribution systems becomes more important these days due to the more complicated power flow profile caused by the integration of variable renewable energy sources such as photovoltaic (PV). Step voltage regulator (SVR) and load ratio controlled transformer (LRT) have been mainly used for the voltage regulation conventionally based on decentralized control methods using line drop compensation (LDC) logic for estimation of voltage drop at secondary side of the SVR. Here, it has been required for distribution system operator to determine LDC parameters properly to estimate the voltage drop based on locally measured information. Hence, in this paper, we proposed an advanced LDC logic in which the parameters can be flexibly switched based on the power flow conditions. The effectiveness of the proposed method was verified using 41-node distribution system model with PV.

Adaptive Power Factor Regulation Under Asymmetrical and Non-Sinusoidal Grid Condition With Distributed Energy Resource

Active and reactive power regulation, unbalanced current compensation, and harmonic current mitigation are the most significant functionalities typically embedded to a three-phase multifunctional grid-connected inverter. However, a vital control feature minimally addressed in the literature is the capability to adjust the grid power factor to the minimum value required by standards or grid codes. Hence, this paper presents an adaptive compensation approach to perform dynamic power factor regulation under varying power demand and unpredictable energy generation, also withstanding non-ideal voltage conditions. To demonstrate such an approach, a global power factor definition is first introduced, being validated upon bidirectional power flow conditions and under unbalanced and distorted voltages. Secondly, a simple algorithm is devised to attain scaling coefficients used on compensation purposes, allowing to instantaneously weigh up reference control signals to track a desired grid-side power factor value. As a result, the strategy can be used to retrofit the controllers of grid-connected inverters with little effort, limiting distribution losses and improving power quality. Simulations and analyses of a representative real study case are conducted to illustrate how the proposed approach copes with unpredictable distributed energy resources and variable load demands. Moreover, experimental results considering a grid-connected inverter prototype are shown to validate the feasibility of the control approach to real-life implementations.

Reactive power control of photovoltaic power generation systems by a wide‐area control system for improving transient stability in power systems

AbstractAs the installed capacity of renewable energy sources is increasing, the role of inverters is becoming more important in the maintenance of power system stability. Therefore, in this study, we propose the use of a wide area control system (WACS) to control the inverters of photovoltaic (PV) systems in a coordinated manner to improve transient stability. In this method, we select PV systems whose reactive power injections are deemed to suppress the acceleration of the critical generator, based on a time‐domain simulation for each possible fault before the fault occurs. When a fault occurs, we trigger the reactive current injections with the selected PV systems that is, the WACS operates as an event‐based emergency control system. Numerical simulation results demonstrate that this method can further improve transient stability compared with an autonomous reactive current support function that is applied to existing PV inverters. The proposed WACS could be a promising approach to address the transient instability phenomena under unscheduled power flow conditions by periodically updating the control table based on real‐time information.