Voltage Problems Research Articles

Power Quality Enhancement in Solar PV and Battery Integrated UPQC Grid Connected System

This paper discusses a distributed generation system consisting of grid-connected solar PV and a battery-integrated Unified Power Quality Conditioner (UPQC). Embedded in the PV array, the UPQC consists of a series and shunt converter connected back through a common DC link. In this system, power quality problems of clean energy, such as harmonics, voltage drops, ripples, are compensated by injecting active energy into the power grid. The shunt converter is controlled to maintain a constant DC link voltage and harmonic compensation of the load current. The main voltage problem is compensated by a series converter that injects the voltage during sag and swell. The advantages of integrating renewable energy sources and enhancing power quality are brought together in this system. The performance of the system is analyzed during voltage sag, swell condition and under unbalance condition for nonlinear load along with power flow analysis through the enhancement of dc bus voltage. Finally, the simulation results are shown for the estimation of dynamic performance of PV, battery integrated UPQC system during unbalanced condition

A bi-level optimization method for voltage control in distribution networks using batteries and smart inverters with high wind and photovoltaic penetrations

In electrical distribution systems, the voltage quality problem considers the most restrictive issue that hinders high photovoltaic (PV) and wind integration. Therefore, this study aims at providing a reliable control method for the voltage problem in distribution networks embedded with high PV and wind sources. The proposed voltage management strategy consists of two controlling stages. The first stage uses battery energy storage systems (BESS), while the second stage employs the smart PV inverters' reactive power injection capability. For BESS operation, a bi-level optimization method based on metaheuristic optimization algorithms (MOA) is developed to regulate the voltage levels by governing the batteries charging/discharging rates. The bi-level optimization problem aims to maximize PV and wind energy exploitation while improving the voltage profile. In this study, a detailed comparison is conducted between three MOA: Social Spider Optimization, Particle Swarm Optimization, and Cuckoo Search Optimization. In addition, considering the uncertainty associated with PV system generation, a PV generation forecast is embedded in the voltage control strategy to reinforce the decision-making process of BESS operation. The efficacy of the proposed method is deployed on a modified IEEE-34 bus test feeder with real-world load and PV and wind power generation data. Experimental results show the effectiveness of the proposed method and indicate that proper coordination between the BESS and smart PV inverters is beneficial for distribution system operations that seamlessly integrate PV and wind energy. Overall, the proposed voltage management strategy can be used to control the voltage to any desired range at different locations.

Quantifying the benefits of shared battery in a DSO-energy community cooperation

Local energy communities are forming as a way for prosumers and consumers to invest in distributed renewable energy sources, community storage and share electricity. Meanwhile, several distribution grids have voltage problems at certain hours of the year. Local energy communities consisting of generation and storage units might be valuable flexible assets that the distribution system operator (DSO) can make use of. This article aims to study how a battery in an energy community can provide services to the distribution grid, by creating a linear optimisation model which includes power flow constraints and a battery degradation model. First, we investigate how the battery operation of an energy community impacts the voltage in the nearby buses. We find that when including the degradation model, the voltage limits are violated much less than when not including the degradation model. Next, we investigate how the battery operation differs when the energy community cooperates with an active DSO to share the battery use, and quantify how much the DSO should remunerate the energy community. We find that the energy community should get 15 € per year due to an increase in electricity and degradation costs, which equals an increase of 0.12%, compared to when the community is not providing a service. Finally, a sensitivity analysis is performed to determine which parameters are more important to consider. We find that voltage violations in the grid are sensitive to the battery replacement cost, electric vehicle charging peak and the average spot price, while the remuneration from the DSO is sensitive to the battery replacement cost. For small battery sizes and a low power-to-energy ratio, the community is not able to improve the voltage at all hours of the year.

Network-Aware Coordination of Aggregated Electric Vehicles Considering Charge–Discharge Flexibility

This paper presents a novel framework for network-aware coordination of aggregated electric vehicles (EVs) via transactive control in distribution networks considering the operating constraints of the network. The proposed framework facilitates participation of EVs in local energy markets through aggregators, while their preferences and privacy are preserved. The flexibility of EVs in charging-discharging is employed to resolve the congestion and voltage problems in distribution networks. To this end, in addition to the market price, a flexibility price is considered to encourage EVs to contribute to the congestion and voltage management in the network. The performance of the proposed method is evaluated in various case studies conducted on the IEEE 55-node, 100-node and 302-node LV European test systems. Simulation results and a comparative study demonstrate the effectiveness of the proposed framework in terms of achieving high-quality congestion and voltage management, satisfying EV owners’ preferences, and computation efficiency.

Ripple Voltage Suppression of Dual Active Bridge Converter in Electric Locomotive Using H∞ Loop Shaping Control Method

The next-generation electric locomotive drive system has the problem of double grid frequency ripple voltage in the DC side of a single-phase PWM rectifier. In this paper, the intermediate stage dual-active-bridge DC-DC converter is studied, and an H∞ loop shaping ripple voltage suppression control strategy is proposed to restrain the harmonic voltage and optimize the dynamic and robust performance of the closed-loop system. Firstly, the mathematical model of the DAB closed-loop control system with fluctuating input voltage is established. Then, based on the H∞ loop shaping control theory, the dynamic performance, the ability of ripple voltage suppression, and the robust performance of the system are analyzed in the frequency domain. According to the results, a reasonable compensator is selected to reconstruct the magnitude frequency characteristic curve of the nominal system. After reconstruction, the solution of the robust stability margin of the corrected object is transformed into the H∞ robust control problem under the coprime factor uncertainty. The suboptimal H∞ robust controller is solved to obtain the best robustness boundary of the constructed system. Finally, the H∞ loop shaping ripple voltage suppression controller is obtained by combining the H∞ controller with the compensator. The experimental environment is set up in MATLAB-Simulink software. Compared with the traditional voltage loop control method and the input voltage feedforward control method, the dynamic performance of the proposed control strategy is slightly improved, and while within the allowable robust boundaries of the system, it has better ripple voltage suppression performance. When the system magnitude frequency curve is outside the tolerant robust stability margin, the ripple voltage suppression performance fails, but the harmonic content of output voltage is still far less than the other two control methods. The experiment results also prove the correctness of the theoretical analysis and that the proposed control method is effective and proper.

P2P flexibility markets models to support the coordination between the transmission system operators and distribution system operators

The increasing integration of Distributed Energy Resources (DER) in the distribution network has brought more importance to Peer-to-Peer (P2P) markets. However, energy traded in P2P markets can lead to voltage and congestion constraints in distribution networks operated by Distribution System Operators (DSOs). At the same time, Transmission System Operators (TSOs) may need to solve system problems, requesting the participation of DERs in frequency regulation services. To ensure competitive participation in P2P markets, as well as to ensure a correct operation of distribution networks and to contribute to mitigate problems at the system level, coordination mechanisms between the P2P market and the System Operators (SOs) are required. This paper introduces a set of mathematical models considering P2P flexibility trading at the distribution system, while assisting the DSO and TSO in solving the congestion, voltage and frequency problems, respectively. The models are assessed on an IEEE 37-bus distribution network with high DER penetration. The first and second models are based on product differentiation to avoid violating the lines’ thermal limits and the nodes’ voltage limits, respectively. The second model also considers reactive power control in order to impact voltage constraints. The third model uses a virtual load, connected to the TSO network (before the power transformer), to model frequency regulation services. The last model proposes the integration of all methods. Results showed that each model was effective in solving its constraint. However, they do not dismiss the use of the peers’ flexibility assets to assure an overall feasible techno-economic solution. The use of the methodology proposed in the present paper can significantly facilitate the adoption of full P2P markets as well as the confidence of the system operators in the integration of these markets.

Coordinated optimization of source–storage–load in distribution network based on edge computation

A large number of distributed photovoltaics are linked to the distribution network, which may cause serious power quality problems. Based on edge computing, this article put forward a strategy that aggregates multiple distributed resources, such as distributed photovoltaics, energy storage, and controllable load to solve this problem, emphasizing the coordination and optimization between distributed resources. Firstly, an edge computing architecture that can be fully applicable to the coordination of source–storage–loads is constructed. Based on this architecture, the distributed photovoltaic, energy storage and interruptible loads are optimized with the minimum operating cost of edge computation nodes as the objective function. Combined with the operation requirements of the distribution system, lessen the system network loss and make sure the stable and safe operation of the net; Finally, the model is changed with a second-order cone model and verified in an improved IEEE 33 node example. The results show that this method can effectively reduce the loss cost of the system, and can effectively solve the problem of system voltage exceeding the limit, reduce the voltage fluctuation, and maintain the safe and stable operation of the system.

Review of FACTS technologies and applications for accelerating penetration of wind energies in the power system

AbstractConventional energy resource problems made power system planners apply more renewable energy sources (RESs) in the power system. RESs have a significant impact on fulfilling the world's energy demand, protecting the environment at least in the exploration phase, and providing energy reliability as well as security for the new generation of power grids. In this regard, wind power generation is considered a promising solution. However, by increasing the share of wind power generation units in the power sector, some challenges, such as voltage problems, transient stability, increasing system losses, and line congestions can occur. Consequently, an alternative solution is required to accelerate wind power units' connections to the grid by preventing the problems caused by the penetration of wind power. In this regard, Flexible Alternating Current Transmission Systems (FACTS) devices can play an important role while they can improve power grid dynamic performance. This paper presents a review of the optimization techniques applied to accelerate the penetration of wind energy by exploiting FACTS devices. The topic identifies the objectives and optimization formulations, as well as schemes and models available in the published literature. This survey gives noteworthy insights to the researchers to cover available solutions in these regards. The literature in the field is summarized in different aspects, such as FACTS technology, objective functions, constraints, optimization methods, planning or operation purposes, and load flow types. At each aspect, a comparison is derived to recognize the most important issues. The result of the review is the finding of future work and contributions which can be done in the field of wind energy integration acceleration using FACTS devices and the output of the paper can be used as a guide for researchers to find a new path for research in this area.

Comprehensive Solution Method Considering Load Distribution for Determining Low‐Voltage Network Configurations

AbstractSignificant photovoltaic (PV) penetration accelerates voltage problems in distribution networks. We have so far studied what kind of low voltage system configurations are desired in the planning stage. In our previous studies, possible equipment measures were classified into several categories, formulating the ‘low‐voltage system configuration determination problem’; in addition, a solution algorithm based on the practical priorities of classified measures was proposed. In this study, we propose a more efficient and comprehensive solution method while considering load distribution. Several numerical simulations were conducted to verify the performance of the proposed method. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Capacitance balance control strategy for three-phase four-switch open-winding permanent magnet synchronous motor

The open-winding permanent magnet synchronous motor (OWPMSM) system is a novel high-cost system that uses dual-inverters to control both sides of the stator to improve the performance of the motor. To save the system cost, the three-phase four-switch open-winding permanent magnet synchronous motor (TPFS-OWPMSM) system is proposed to replace the general three-phase six-switch OWPMSM system, but it brings the problem of bridge arm capacitor voltage offset. To solve the instability problem caused by capacitance, this paper carries out the state analysis and offset source analysis of the inverter capacitor voltage, and proposes a dual-inverters capacitor voltage balance control strategy. The capacitor balance control converts unstable capacitor offset voltage into current and injects the currents into the stator current loop through closed-loop correction. And this strategy includes the optimal control of different capacitors under dual-inverters with the goal of system stability. The effectiveness of the balancing strategy is verified by the simulation of various motor working conditions.

A five-level inverter based on differential structure

Due to the advantages of low harmonic, low pollution to the power grid, and easy filtering, multilevel inverters have attracted more attention in recent years. In this paper, a five-level inverter based on the differential structure is proposed. It doesn’t need an additional bridge arm to change the polarity of the output voltage, but synthesize the structure of generating multiple voltages and changing the polarity of the output voltage. In addition, the special symmetrical structure of the inverter solves the problem of unbalanced capacitor voltage. The proposed five-level inverter is simulated by MATLAB/Simulink and the prototype is made to experiment.

Wavelet analysis and consensus algorithm-based fault-tolerant control for smart grids

In this paper, the voltage and frequency regulation problems are investigated for smart grids under the influence of faults. To solve those problem, a wavelet analysis and consensus algorithm-based fault-tolerant control scheme is proposed. Specifically, the wavelet analysis technique is introduced to determine whether there exist faults or not in the smart grids. Then, a distributed fault estimator is designed to estimate the attack signals. Based on this estimator state, a distributed fault-tolerant controller is designed to compensate for the faults. It is theoretically shown that the developed method can achieve the voltage regulation and frequency objectives. Finally, a smart grid with four distributed generations is constructed in MATLAB/Simulink for simulation to validate the effectiveness.

PV Distribution Network Planning Method Considering the Cost and Effectiveness of Voltage Control

The large-scale grid connection of distributed power sources can save energy, reduce emissions, and improve the flexibility of the power supply, but the volatility and uncertainty of its power output lead to voltage fluctuations and power quality problems, among which voltage problems have become an important factor inhibiting the large-scale access of distributed power sources, posing new challenges to the grid planning and operation. To address the grid voltage crossing problem after PV grid connection, firstly, a multi-time scale voltage control model based on voltage control coefficients is established to achieve maximum network safety and economic satisfaction; the problem is then solved using a variety of group traction differential evolutionary algorithms with the objective function being the minimum annual integrated cost and the maximum percentage of clean energy generation. This method offers a strong theoretical and technical guarantee for the planning of distributed power access to the distribution system.

Research on Load State Sensing and Early Warning Method of Distribution Network under High Penetration Distributed Generation Access

Aiming at the problems of power flow fluctuation and voltage exceeding standard caused by high permeability distributed power supply access, this paper proposes a load state perception early warning method for distribution networks. Firstly, the random behavior characteristics and voltage early warning mechanisms of power supply and load in distribution networks are analyzed, the dynamic model of distribution networks based on complex network theory is established, and the risk index of voltage exceeding limits under the conditions of high permeability distributed power supply access is put forward. Secondly, the random power flow of distribution networks based on the Monte Carlo method is studied by sampling and analyzing the dynamic model of distribution networks. Then, the risk calculation and safety assessment of voltage exceeding limits are carried out on the currently extracted model, and the risk control strategy of distribution network operation is put forward. Finally, an improved IEEE30-node distribution network topology is proposed. Through simulation analysis, it is proven that the load situation awareness early warning method of distribution networks can effectively predict, improve the security of distribution networks, and provide timely early warning information for maintenance personnel.

Comparison of Control Techniques for Harmonic Isolation in Series VSC-Based Power Flow Controller in Distribution Grids

The application of power electronics equipment in medium voltage (MV) distribution grids can provide new management solutions for power flow control, load balancing and voltage problems. A series MV VSC-based power flow controller has recently been presented to interconnect two radial distribution feeders performing active and reactive power transfers to improve the flexibility and utilization of these circuits in a controlled and secure way. Although not previously explored, this power flow controller can integrate the functionality of a series power filter, accomplishing independent control of the fundamental power flow while isolating the harmonic content between the two interconnected feeders. This prevents harmonic pollution from one feeder from propagating to the other, improving the voltage quality. To implement the harmonic isolation, several control strategies can be used. Therefore, this paper provides a comparative analysis between two of the main harmonic control techniques found in the literature: the Synchronous Reference Frame (SRF) controller and the Proportional Resonant (PR) controller. Assessments are conducted both through simulations and experimental results in a meshed network at 13.8 kV with different types of non-linear loads. In the simulation cases, both algorithms showed similar results; however, in the experimental cases, the PR-based solution exhibited better performance in isolating the harmonics from one feeder to the other.

Innovative AVR-LFC Design for a Multi-Area Power System Using Hybrid Fractional-Order PI and PIDD2 Controllers Based on Dandelion Optimizer

In this article, the problem of voltage and frequency stability in a hybrid multi-area power system including renewable energy sources (RES) and electric vehicles has been investigated. Fractional order systems have been used to design innovative controllers for both load frequency control (LFC) and automatic voltage regulator (AVR) based on the combination of fractional order proportional-integral and proportional-integral-derivative plus double derivative (FOPI–PIDD2). Here, the dandelion optimizer (DO) algorithm is used to optimize the proposed FOPI–PIDD2 controller to stabilize the voltage and frequency of the system. Finally, the results of simulations performed on MATLAB/Simulink show fast, stable, and robust performance based on sensitivity analysis, as well as the superiority of the proposed optimal control strategy in damping frequency fluctuations and active power, exchanged between areas when faced with step changes in load, the changes in the generation rate of units, and the uncertainties caused by the wide changes of dynamic values.

Ultra Short-term Load Optimal Dispatching Method for Micro Grid Considering Demand Side Response

With the development of the economy, the electricity demand is also increasing. However, the traditional micropower supply bears the problems of excessive load growth and unstable voltage. Therefore, this paper takes power generation as the research object. First, the principle of output optimization based on schedulability, reserve capacity, and intermittent operation frequency of units is analyzed. Then, the relationship between the optimal solution and the minimum power consumption time is calculated by establishing a mathematical model to solve the algorithm, and the difference between the two results is compared. Finally, the power system is simulated on Matlab software, and the method and effect are verified by numerical simulation. The simulation results show that with the same microgrid power configuration, there is a 3.5% load transfer at time-sharing prices and a 6.4% load transfer at real-time prices through price-based demand response. The optimization objective of demand response, namely the cumulative sum of the difference between new energy power generation and load, is 15312 kW · h per year when the fixed price is implemented, 54134 kW · h is for the time of use price, and 451645 kW · h is for real-time price. The response effect of real-time price is optimal.

Robust Distributed Secondary Control for AC Microgrids With Time-Varying Delay

Non-smooth, nonuniform, and even unbounded communication time delays, which are called irregular time delays, are unavoidable in many practical systems. Currently, there is no available approach that can solve the secondary voltage and frequency restoration control problem for an ac microgrid (MG) in the presence of such unknown irregular time delays. In this brief, we propose a resilient secondary control scheme to solve the problem. To ensure system stability and achieve asymptotic voltage and frequency restoration, sufficient conditions are established in the form of algebraic gains using a multidimensional small gain approach. Simulation and experimental case studies validate that the proposed control scheme can effectively solve this problem in a tested ac MG.

Virtual inertia coordination control strategy of DFIG-based wind turbine for improved grid frequency response ability

The capability of the inertia response of the Double fed induction generator (DFIG) is mainly achieved at the cost of its economic benefits. As such, this study proposes a coordinated control strategy with frequency modulated inertia layered optimization while considering the inertia response of DFIG direct current (DC) side capacitor. According to the disturbance size of the system, the inertia control task is dynamically assigned to the DFIG DC capacitor and speed inertia control module to reduce the startup times of speed control and improve the operation economy. On this basis, we propose a dynamic recovery of DC capacitor voltage based on State of charge (SOC) self-recovery to solve the problem of voltage clamping after the inertia response of DFIG DC capacitor at its stable operating boundary and thus cannot participate in subsequent inertia control. Aiming at the frequency secondary disturbance caused by DFIG speed recovery, a variable coefficient droop control method based on logistic regression function is proposed to realize the dynamic ordered recovery of DFIG speed. Simulation results show that, compared with the traditional synchronous control with the simulation time sequence of 280 s, the proposed timing optimization coordinated control strategy reduces the rotor start times by 12 times, and the wind energy capture increases by 3.6%.

Cooperative Operational Planning Model for Distributed Energy Resources With Soft Open Point in Active Distribution Network

In this paper, optimal cooperative operational planning of distributed energy resources (DER) in an active distribution network (ADN) with soft open points (SOP) has been investigated. To do so, a new two-layer coordinated optimization framework ADN has been proposed considering SOP. In the upper layer, the location and sizing of the DERs and SOPs has been optimised. While inner layer executes simultaneous optimal functioning of volt/var control (VVC) devices, remote controlled switches (RCS), DERs, and SOPs. The main objective of proposed methodology is to reduce total investment cost of DERs and SOPs as well as operating costs of the system over the planning horizon. Besides, objective function considers the cost of energy not served (ENS), the cost of substation-purchased electricity, and the cost of carbon emissions. Meanwhile, a stochastic module has been employed to address high-level uncertainties associated to renewables and load demands. Besides, the effects of distribution network reconfiguration (DNR) and conservation voltage reduction (CVR) have been taken into account. For various instances, the suggested framework was implemented on an IEEE 119-bus distribution system and solved using a proposed hybrid optimization solver. The efficacy of proposed DER with SOP methodology has been validated on various cases and also tested on sudden external disturbances such as under voltage and over voltage problem conditions. When compared to standard planning schemes, the test results show that it is beneficial in boosting system efficiency, increasing reliability, and lowering the carbon footprint of distribution systems.