Unbalanced Operation Research Articles

Decentralized management of unbalanced multi‐agent distribution systems: A transactive approach leveraging ADMM framework

AbstractThe emergence of multi‐agent systems and significant integration of distributed energy sources (DESs) are transforming distribution networks. This necessitates a decentralized management strategy for unbalanced operation in multi‐agent distribution systems (MADSs) due to the autonomous nature and potential for unbalanced injection of single‐phase DESs. Accordingly, this paper proposes a novel approach for decentralized management of unbalanced operation in MADSs. The approach leverages a customized alternating direction method of multipliers to facilitate decentralized decision‐making, while incorporating transactive energy signals aligned with the alternating direction method of multiplier framework to enable independent agent operation. In this scheme, independent agents would optimize their operating costs considering the announced transactive signals, which model the power prices and power loss in the grid. The decentralized structure enables agents to apply stochastic and condition value at risk methods to address the uncertainty and associated risk in scheduling resources. Furthermore, without violating the privacy concerns of agents, the developed transactive‐based scheme facilitates minimizing the asymmetrical condition, caused by the unbalanced integration of DESs, in the power request at the connection point of MADSs and transmission networks. Finally, the proposed methodology is simulated on 37‐bus and 123‐bus test‐systems to study its effectiveness in managing the MADSs with unbalanced integration of DESs.

A Three-Phase Four-Leg Neutral Point Clamped Photovoltaic Inverter With Decoupled Active & Reactive Power Control and DC Link Voltage Ripple Minimization Under Unbalanced Grid Operation

A Three-Phase Four-Leg Neutral Point Clamped Photovoltaic Inverter With Decoupled Active & Reactive Power Control and DC Link Voltage Ripple Minimization Under Unbalanced Grid Operation

Optimal Clean Energy Resource Allocation in Balanced and Unbalanced Operation of Sustainable Electrical Energy Distribution Networks

Optimal Clean Energy Resource Allocation in Balanced and Unbalanced Operation of Sustainable Electrical Energy Distribution Networks

Effect of decision-making principle on P2G–CCS–CHP complementary energy system based on IGDT considering energy uncertainty

As one of the most promising large-scale de-fossilization technologies currently available, Power-to-Gas (P2G) is expected to promote utilization of renewable sources and mitigate the effects of greenhouse gas. Through the coupling of P2G, Combined Heat and Power (CHP) as well as Carbon Capture and Storage (CCS), the P2G–CCS–CHP microgrid energy system could achieve hierarchical energy transfer and green-powered interconversion of gas, electricity and heat flows. However, the conversion of multiple energy shapes between different facilities is deeply intertwined with renewable energy sources, greatly increasing risk of unbalance operation and impacting the overall robustness and economic viability of system. To address these challenges, this study proposes a decision-making framework based on Information Gap Decision Theory (IGDT) method for a P2G–CCS–CHP system. The real-time balancing of heat & power loads and supply, the mechanism of gas-electricity-heat interaction, as well as recycling pattern of synthetic fuel within the system are carefully addressed to achieve optimal operation. Different scheduling schemes are obtained by setting up two separating decision principles, namely risk-seeking (RS) and risk-avoiding (RA), to solve these uncertainties and ensure robust decision making. Meanwhile, adaptability of decision-making methodology is analyzed based on several criteria including share of recycled green-powered fuel, ecological friendliness, carbon trading benefit, etc. Results show that adding of P2G module enables a 12.6% reduction in carbon emissions and generates 1252.2 kg of green powered gas, highlighting the eco-friendly nature of the multi energy system (MES). About 21.5% of the renewable energy flows participate the interconversion of electric-heat-gas and about 17.7% of total carbon flow is circulated as synthetic fuel within the system. In addition, conservative tendency is witnessed in the case of risk-seeking decision mode, leading to an approximate 13.22% increase in the operation costs, compared with risk-avoiding mode. The proposed IGDT decision strategy has shown significant compatibility in dealing with the impact of multiple uncertainties.

Detailed modeling of droop-controlled multi-energy systems under unbalanced operation

Considering the residential sector, greenhouse gas emissions can be effectively reduced by the widespread deployment of distributed renewable energy sources (DRESs) in low-voltage (LV) electrical networks (ENs). Through the electrification and the integration of different energy systems, the exploitation of the locally generated renewable energy can be further increased, acting also as an efficient countermeasure to the technical challenges in ENs posed by the intermittent nature of DRESs. This work deals with the modeling of multi-energy systems (MESs) consisting of unbalanced ENs and district heating networks (DHNs), formulated based on existing EN and DHN models. The developed model is enhanced by the incorporation of a thermal droop control scheme into the controllable sources of DHN, i.e., heat pumps (HPs). The validity of the proposed model is assessed via time-series simulations on a MES composed of a benchmark unbalanced LV EN and a real DHN. It is shown that the integrated droop control scheme can act as a means towards overvoltage mitigation, temperature control and reduced MES losses, improving the operational reliability and exploitation of the DRES potential. Therefore, the proposed model could be useful for system operators and decision makers for the efficient planning and operation of MESs.

Disturbance-rejection control for unbalanced operation of microgrids: Invariant-set approach

In microgrids, voltage imbalance control is crucial to preserving the required level of power quality. The article presents a tracker design that mitigates the unbalance in the microgrids. The proposed microgrid model includes positive and negative sequences, whereby the positive sequences are controlled, and the negative sequence is treated as an external disturbance (whose effect must be attenuated). The uncertainty in the external disturbance is modelled in the norm-bounded form. The suggested control is based on attracting (driving) the state trajectory into a small region, including the origin (attracting ellipsoid-set). The effect of the negative sequence components is attenuated by minimizing the ellipsoid volume. When the state trajectory enters that region, it will never leave it for the future time (termed invariant-set). Two theorems were formulated for tracker synthesis that follows the desired reference and reduces the negative sequence impact. These theorems are the invariant-set method and the H∞ approach. The validity of the suggested control is demonstrated via testing the system under various operational unbalanced scenarios, such as unbalances or faults at the load side or in the transmission lines. The simulations show the superiority of the suggested method in terms of accuracy and dynamic response when compared with the H∞ . Additionally, a comparison is made between the suggested tracker and Active Disturbance Rejection Control (ADRC).

Unbalanced operation of integrated power distribution system for optimal energy flow using LSO-vCANNs approach

Unbalanced operation of integrated power distribution system for optimal energy flow using LSO-vCANNs approach

An Effective Charging Torque Elimination Method for Dual-Channel Electric-Drive-Reconstructed Onboard Chargers

The idea of electric-drive-reconstructed onboard charger (EDROC) systems, along with the concept of dual-channel charging, offers a novel design, thought to enhance the integration and fault tolerance of the charging system of electric vehicles (EVs). This article investigates a dual-channel EDROC incorporating an asymmetrical six-phase permanent magnet synchronous machine (ASPMSM). A unique operation mode, called the unbalanced charging voltage operation mode, exists in this topology, in case the voltages of the two batteries are unequal. This unbalance results in different winding currents following through two channels, leading to an undesired charging torque in the machine. To ensure the safety of the system, an effective charging torque elimination method, based on dual-channel winding current balance, is proposed, which achieves a dot-shaped current path of torque generation-associated subspace (i.e., α–β subspace) by balancing the dual-channel charging power. Eventually, a controller is designed for the system and a prototype is created, to validate the effectiveness of the proposed method.

Decentralized restoration of distribution systems with coupling neighboring microgrids

In this study, a multi-agent system (MAS) is incorporated in a decentralized strategy to restore distribution systems while taking into account coupling neighboring microgrids (CNMGs). This provides modeling for renewable energy sources (RESs), electric vehicles (EVs), battery storage systems (BSS) and load. The desired and most favorable restoration path is found by the MAS, in which zone agents are dispersed across the distribution system. The MAS can also manage microgrids (MGs) overloaded as the unbalance operation of RESs, BSS, EVs, and load. This is realized by making a bridge between MGs and neighboring non-overloaded MGs. The suggested method adheres to voltage and power flow restrictions while operating according to expert system standards. The recommended approach is put to the test using a 33-bus radial distribution system. MATLAB calculations on agents and power flow are carried out in order to verify the validity of the choices made by agents. The proposed restoration plan is able to obtain the best power supply path with a low number of switching in the event of a fault so that the voltage magnitude is higher than 0.9 p.u. and free capacity is available for the distribution lines. The smart charging strategy of EVs reduces 93% of their turn off compared to the non-smart charging strategy. However, if the CNMG plan is established, all vehicles can be powered.

Decomposition of unbalanced operation incremented active power loss in distribution network

Decomposition of unbalanced operation incremented active power loss in distribution network

A Comprehensive Review of Compensation Control Techniques Suitable for Cascaded H-Bridge Multilevel Inverter Operation with Unequal DC Sources or Faulty Cells

A cascaded H-bridge multilevel converter topology is the ultimate solution for energy conversion in various industrial applications due to its exceptional features, such as high modularity and fault-tolerant capability. However, two circumstances can lead to unbalanced operation of the inverter, potentially causing a decrease in its reliability and survivability: unequal DC voltage sources and faulty cells. In recent decades, scientists and engineers have conducted intensive research and meaningful studies to propose control solutions capable of maintaining the stable and continuous operation of the inverter under these operational concerns. Typically, each challenge is addressed separately using a distinct compensation control scheme in the existing literature. The paper aims to offer a comprehensive review of the existing compensation control schemes appropriate for CHBMIs operating under unbalanced conditions. It overviews the most popular control schemes and summarizes their usefulness in such scenarios. The theoretical foundations of each control scheme are presented and discussed, including their operating principles, implementation schemes, advantages, and disadvantages. The paper concludes with suggested future trends that require further research for CHBMIs’ continued growth and adoption in various industrial applications.

A Simple Method for Detection of Voltage Sags and their Mitigation using a Dynamic Voltage Restorer

Power quality is the major focus of progressive nations.In the era of smart grid,power quality receives a lot of thrust at all voltage levels namely,medium ,high and low.The objective of this paper is to present a simple and cost effective method of sag detection and mitigation in three phase systems at the consumer's end. The use of the concept of space vector representation of three phase quantities, effectively in the detection ,quantification and mitigation of short duration voltage disturbances such as sags in three phase supply systems under both balanced and unbalanced conditions of operation is presented.Three phase balanced quantities can be represented by a synchronously rotating space vector of constant magnitude .The two phase equivalent of which on a stationary reference frame are orthogonal to each other.When balanced sags occur,the magnitude of the rotating space vector obtained as a resultant of its orthogonal components is sensed for magnitude deviations from its constant nominal value.A trigger signal of varying amplitude is generated in proportional response to the detection of the deviation in its magnitude . In case of sags occurring on one or two phases of the supply, (unblanced),the positive sequence components of the unbalanced three phase quanities are determined using mathematical transformations and the magnitude of the resultant is found out. This resultant is sensed and its deviations from nominal value are measured and used to generate the trigger after processing.The trigger thus generated, initiates the control system of a Dynamic Voltage Restorer(DVR).When a sag is detected,the trigger signal generated, switches on the control circuit of the inverter which uses the space vector pwm control using sampled phase amplitudes of the control signal to generate the modulating wave in proportion to the deviation of the sag voltage from the reference value.The fundamental component of the output voltage which in proportion to the deviation from the nominal value is injected in series with the three phase disturbed signal through a transformer of suitable gain .The results show the successful operation of the DVR in maintaining nominal value of the voltage across the load through out the duration of the disturbance for all cases of balanced and unbalanced operation. The paper presents the detection algorithm as well as the control algorithm for restoration of voltage which are simple and easy to implement .

Zero-sequence controller requirements and comparison for a delta-CHB STATCOM under unbalanced operation

Delta-configured Cascaded H-Bridge (DCHB) topology is a suitable alternative for Static Synchronous Compensator (STATCOM) applications. However, under unbalanced voltage and/or current conditions, zero-sequence current needs to be injected to guarantee dc-link capacitor voltage balancing. The control loop of this zero-sequence current is analyzed in this paper, in order to determine the requirements that the implemented controller must fulfill. Considering these requirements, appropriate transient response and stability margin indicators are defined to quantify and evaluate the performance of different controllers that could be employed —Proportional-Resonant controller (PR), PR controller with delay compensation (PRd), and Vector Proportional-Integral controller (VPI) are proposed and analyzed for this application in this paper. Based on the defined indicators, the VPI is the most appropriate among the studied control techniques. Experimental results validate the analytical model of the controllers and their performance.

Sideband Harmonic Suppression Analysis Based on Vector Diagrams for CHB Inverters Under Unbalanced Operation

Unexpected sideband harmonics of the cascaded H-bridge (CHB) inverters will appear in unbalanced conditions among cells and may result in harmonic pollution and even harmonic resonance. The linear controller to suppress the output voltage distortion is destined to be ineffective due to the non-linear characteristic of sideband harmonics. Focus on this problem, this article proposes a closed-loop harmonic suppression method by adjusting the phase-shift angles for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -cells CHB inverter. The harmonics suppression mechanism is revealed from a vector synthesis point of view. No complicated trigonometric function calculations and optimization algorithms are required. This method can achieve the suppression of the harmonic distortion around any multiplicative switching frequency. Phase-shift angles are adjusted continuously in real-time. The superior harmonic performance achieved by the proposed method is verified by the simulation and experiment results.

Hybrid AC/DC OPF Model for Unbalanced Operation of Bipolar HVDC Grids

Hybrid AC/DC OPF Model for Unbalanced Operation of Bipolar HVDC Grids

Analysis of the Mechanism and Control of the Unbalanced Operation of Three-Phase Four-Wire Inverters

In this paper, a solution is proposed to the problem of the unequal phase imbalance of output voltage caused by a three-phase, four-wire, split capacitor inverter when the load is unbalanced. First, the triple-loop control strategy was used to solve the unequal amplitude problem. This method used the feedforward + feedback composite control strategy on the inductor current inner-loop and voltage mid-loop to decrease the disturbance of the power and load. And the Root Mean Square (RMS) of voltage on the outer-loop completed the control of amplitude for the three-phase voltage. Second, to solve the imbalanced phase problem, the imbalance operation mechanism of the three-phase four-wire inverter was analyzed. It is known from the analysis that the phase imbalance is related to the DC-side splitting capacitance. The function relations between the DC-side capacitance and phase angle between each phase was simulated by MATLAB. But, it was too complicated to calculate the magnitude of the capacitance value through the functional relationship. In order to simplify the design of the DC-side splitting capacitor, the relations among the imbalanced current, the voltage fluctuations of the DC-side capacitor and the harmonics of load voltage were analyzed. In addition, by following the requirement of the national standard about the harmonics of load voltage, a DC-side capacitor design was mentioned to decrease the influence of imbalanced phase. Finally, simulation and experimental results show that the three-phase load voltage is stable, the THD value is less than 3%, and three-phase voltage unbalance is less than 2%, thus verifying the effectiveness of the proposed DC-side split capacitor design and control strategy.

How subjectivities and subject-making influence community participation in climate change adaptation: the case of Vietnam

Critical scholars on power relations and climate change adaptation have highlighted the lack of community participation as a consequence of unbalanced power operations. Evidence about how unequal power relations and subject formation constrain public participation, however, is under-studied. In this paper, we utilised the intersection between community participation and the subjectivities lens to examine how a hierarchical political structure systematically operates to influence community engagement in adaptation and how and why local communities are included or excluded from adaptation as a result of subject-making, using Vietnam as a case study. Using 66 semi-structured interviews and ten focus group discussions involving policymakers, practitioners, local authorities, and communities, we examined how the key respondents stereotyped local roles and capacity in agricultural adaptation activities. Applying content analysis, we found that the general population in Vietnam is often framed as lacking knowledge and capacity to respond to climate impacts. Reflected through a traditional government-led model in two agricultural adaptation projects, the study showed that subtle but pervasive subjectivities and subject-making processes constrain community participation by affecting perceptions and, subsequently, actions of key stakeholders, undermining local roles and capacity in undertaking adaptation. These perpetuate the power imbalance between local communities and government entities. The findings contribute to the prevailing scholarship of climate change adaptation that, under an authoritarian regime, local capacity is undermined not only by powerholders but also by community members as they consent to government decisions.

Flexible load control of new energy based on improved genetic algorithm

In the medium and low voltage distribution network, the load form of users is complex and changeable. There are a large number of single-phase and two-phase loads connected to the distribution network, resulting in a three-phase unbalanced operation of the distribution network. With the development of the new energy, the high proportion of distributed new energy will further aggravate the three-phase imbalance of the distribution network. Therefore, this paper proposes a coordinated optimization framework of droop parameters based on the multi-converter droop control, which takes the minimum loss of the distribution network as the optimization objective, and optimizes the reference point and the slope of the VSC droop hierarchically. A small-signal stability optimization dispatching method for the VSC droop slope in the DC distribution network is proposed. By adding small-signal stability constraints to the slope optimization model, the optimal slope command and slope stability region which can ensure the small-signal stable operation of the system are obtained. Experiments show that the optimization model of the VSC small-signal stability slope can make the droop control instruction significantly improve the small-signal stability of the system to adapt to the intra-day source load power fluctuations with a small economic cost. The slope stability region pre-optimization model can provide a reliable stability slope upper limit for the slope optimization problem based on ensuring the system operation economy. The research in this paper can make full use of the flexible control ability of power electronic equipment, and then suppress the three-phase imbalance, which is of great significance to improve the security and economy of the distribution system operation.

Simulation of protection against unbalanced high-voltage asynchronous drive of recycle compressor in fuel hydrotreating unit

In the oil and gas industry, continuous processes such as oil and gas refining play a great role and are sensitive to many external factors. Such processes require special procedures for stopping and restarting. In order to maintain a sustainable process, the entire system needs to be cleaned by removing of unreacted components. Rejected raw materials are often dumped into a flare leading to tangible environmental problems and significant economic disadvantages. Electrotechnical systems (ETS) play an important role in ensuring continuous technological processes in oil and gas industry. Electric motors are one of the key elements of ETS. The majority of the electrical machines used in industry today are Asynchronous motors (AM) – no less than 80 %. Ensuring their trouble-free operation is one of the key factors in the design, simulation, and analysis of asynchronous motor relay protection systems, including unbalanced conditions of their operation. These conditions can occur due to unbalanced AM connection circuits, supply voltage unbalance, or as any faults in a machine itself. Operating a motor under these conditions will result in shorter motor life, reduced power, wear and aging of the insulation. The study subject was an Asynchronous motor drive of a recycle compressor of a gasoline hydrotreating unit at the fuel hydrotreating integrated unit at the Astrakhan Gas Refining Plant (AGRP). The authors used Matlab simulations to study the facility and its protection systems/devices operation. The method of symmetrical components was selected as the main theoretical method. The authors developed a model of an asynchronous motor drive of a recycle compressor. This involved establishing a set of relay protections (RP) and developing the models of the following protections: sequence filter (symmetrical component filter) (SF), negative sequence (nps) O/C protection, and overload protection. It was demonstrated that the specified relay protection complex fully protects the motor from unbalanced operation conditions. The authors conducted a study of the protection complex operation under different supply voltage unbalances, with different motor loads. They formed a conclusion about the performance of the developed protection complex, and gave recommendations for its technical implementation in a business environment. The study findings can be used as a basis for the development and testing of relay protection components of the entire electrical system of the fuel hydrotreating unit at the Astrakhan Gas Refining Plant.

Distributed Optimal Power Flow in Unbalanced Distribution Grids With Non-Ideal Communication

The use of distributed optimization for solving optimal power flow (OPF) problems in distribution networks is increasing as the number of controllable devices and the span of service areas increase. However, the performance of the distributed optimization algorithm largely depends on the availability and quality of communication links between the computing entities. In this paper, we evaluate the performance of the alternating direction method of multipliers (ADMM) for solving the OPF problem for volt-VAr optimization (VVO) under non-ideal communication. The overall problem is formulated by considering the unbalanced operation of multi-phase distribution networks. The algorithm's performance is first analyzed, assuming there is an ideal communication between computing entities, which serves as a benchmark for further analysis. Then, two non-ideal communication models, namely (1) sporadic communication failure and (2) communication under a noisy transmission, are applied to the information exchange architecture of the ADMM. Extensive numerical experiments are conducted with two test systems, the IEEE 123-bus feeder and a 2522-bus network scaled down from the IEEE 8500-bus system; these are used to evaluate the performance of the algorithm. The results indicate that the ADMM-based distributed VVO algorithm has deteriorated performance under high levels of communication failure and high levels of noise injection. Additionally, although the centralized-VVO counterpart has some computational superiority when the overall problem is convex and no communication impairments exist, the distributed-VVO has superior immunized solution performance under realistic communication constraints.