Showing papers on "AC power published in 2020"
TL;DR: The concepts of narrow versus broad band signals are first recalled along with the limitation of the meaning of apparent power, power factor and reactive power, and the adequacy of the phasor representation of voltages and currents waveforms are discussed.
126 citations
TL;DR: A five-level common ground transformerless inverter with reduced output harmonic content for PV systems is proposed and it presents a maximum dc-voltage utilization in opposition to half-bridge-based topologies.
Abstract: Transformerless inverters are extensively employed in grid-connected photovoltaic (PV) generation systems due to its advantages of achieving low cost and high efficiency. However, the common-mode voltage issues have been motivated the proposition of new topologies, control, and modulation schemes. In common ground PV inverters, the grid neutral line is directly connected to the negative pole of the dc bus. Therefore, the parasitic capacitances are bypassed and the leakage current can be eliminated. In this paper, a five-level common ground transformerless inverter with reduced output harmonic content for PV systems is proposed. In addition, the proposed inverter can process reactive power and it presents a maximum dc-voltage utilization in opposition to half-bridge-based topologies. The operation modes of the proposed inverter, a simple modulation strategy, as well as the design guidelines are analyzed in detail. Finally, experimental results demonstrate the feasibility and good performance of the proposed inverter.
126 citations
TL;DR: A number of experimentally verified non-isolated and isolated microinverters have been carefully reviewed and compared in terms of their corresponding efficiency, power density, reliability, and cost.
Abstract: The power processing and the presence of the electrical isolation between the PV module and the grid is a very crucial aspect in determining the performance requirement, as well as the utility operator’s specifications for the PV microinverter design. The grid-connected PV microinverter design can be classified into four categories: 1) nonisolated single-stage topologies; 2) isolated single-stage topologies; 3) nonisolated double-stage topologies; and 4) isolated double-stage topologies. Typically, a microinverter’s performance can be enhanced by the use of nonisolated topologies to be more efficient, more compact, less bulky, and less costly than the isolated topologies. Whereas, the use of a transformer in microinverter topologies provides high-power quality as well as galvanic isolation to eliminate the safety issues, which in return meet the grid standards. The power processing (boosting the dc voltage of PV panel, extracting the maximum power and converting it to ac power), which can be achieved either via single stage or double stage, has a significant impact on the microinverter performance. This paper reviews and compares experimentally verified microinverter topologies in terms of their corresponding efficiency, power density, reliability, and cost. The most efficient topology in each category is designed and simulated in comparison with a benchmark. The topologies are then compared in terms of their component count, input voltage range, modular structure, soft-switching implementation, and battery integration.
111 citations
TL;DR: The graph theory, stochastic theory and Lyapunov functional approach are employed to derive the stability and convergence analysis of the proposed dynamic event-triggered conditions considering noise interferences.
Abstract: This paper proposes a stochastic distributed secondary control scheme for both frequency/voltage restoration and optimal active power sharing (e.g., minimize the total generation cost) of ac microgrids by employing event-triggered communication mechanism in noisy environments. Compared with existing ideal and periodic communication among distributed generations (DG), the proposed stochastic distributed secondary control scheme can achieve mean-square synchronization for frequency and voltage restoration of DGs and the optimal active power sharing for their economic operation through a sparse communication network, even though the communication channels are susceptible to noise interferences and limited bandwidth constraints. The stochastic distributed control protocols are designed to be employed into the secondary control stage for microgrids, which is a fully distributed control paradigm. With the proposed control protocols, control deviations of frequency and voltage produced during the primary control stage can be well remedied and the optimal active power sharing for their economic operation can be well achieved simultaneously. Furthermore, the graph theory, stochastic theory and Lyapunov functional approach are employed to derive the stability and convergence analysis of the proposed dynamic event-triggered conditions considering noise interferences. Simulation results on an islanded microgrid test system are presented to demonstrate the effectiveness of the proposed control protocols.
104 citations
TL;DR: A novel pre-synchronization control method is proposed to eliminate the phase jump while meeting the requirements in case of closures or re-closures of generation units and the feasibility of the proposed methods is verified by simulations on a microgrid consisting of parallel VSG and SG units.
Abstract: In recent years, the increasing penetration of distributed generation in microgrids challenges the control and coordination of energy resources. Especially in microgrids with virtual synchronous generator (VSG)-controlled converters and conventional synchronous generators (SG), the inherent inertia difference (i.e., the VSG and SG) results in a poor transient performance when the VSG and/or loads are cut in/out. Thus, this paper explores the transient performance of microgrids with parallel VSG and SG systems. More importantly, a novel pre-synchronization control method is proposed to eliminate the phase jump while meeting the requirements in case of closures or re-closures of generation units. A small-signal dynamic model is presented, and accordingly, the VSG inertia and its damping can be designed considering the capacity ratio of VSG and SG units. In addition, with the power angle stability analysis, an active power provision strategy is introduced to suppress the transient power oscillation due to the inertia difference. Finally, the feasibility of the proposed methods is verified by simulations on a microgrid consisting of parallel VSG and SG units.
96 citations
TL;DR: The proposed control can operate in a distributed fashion where each bus makes its decision based on local voltage measurements and communication with neighboring buses, always satisfy the reactive power capacity constraint, drive the voltage magnitude into an acceptable range, and minimize an operational cost.
Abstract: In this paper, we propose a distributed voltage control in power distribution networks through reactive power compensation. The proposed control can operate in a distributed fashion where each bus makes its decision based on local voltage measurements and communication with neighboring buses, always satisfy the reactive power capacity constraint, drive the voltage magnitude into an acceptable range, and minimize an operational cost. We also perform various numerical case studies to demonstrate the effectiveness and robustness of the controller using the nonlinear power flow model.
95 citations
TL;DR: The proposed strategy is demonstrated on the IEEE 33-node test case, and the simulation results show that the power supply pressure can be obviously relieved by introducing the coordinated charging/discharging behavior of EV, ensuring the safe and economical operation of the distribution system.
Abstract: Based on the large-scale penetration of electric vehicles (EV) into the building cluster, a multi-objective optimal strategy considering the coordinated dispatch of EV is proposed, for improving the safe and economical operation problems of distribution network. The system power loss and node voltage excursion can be effectively reduced, by taking measures of time-of-use (TOU) price mechanism bonded with the reactive compensation of energy storage devices. Firstly, the coordinate charging/discharging load model for EV has been established, to obtain a narrowed gap between load peak and valley. Next, a multi-objective optimization model of the distribution grid is also defined, and the active power loss and node voltage fluctuation are chosen to be the objective function. For improving the efficiency of optimization process, an advanced genetic algorithm associated with elite preservation policy is used. Finally, reactive compensation capacity supplied by capacitor banks is dynamically determined according to the varying building loads. The proposed strategy is demonstrated on the IEEE 33-node test case, and the simulation results show that the power supply pressure can be obviously relieved by introducing the coordinated charging/discharging behavior of EV; in the meantime, via reasonable planning of the compensation capacitor, the remarkably lower active power loss and voltage excursion can be realized, ensuring the safe and economical operation of the distribution system.
94 citations
TL;DR: Simulation results show that the proposed HC-VVC method is overall superior in minimizing power loss and voltage deviation and the coordination model is solved by a scenario-based stochastic optimization approach with probabilistic uncertainty modeling.
Abstract: Photovoltaic (PV) inverters can provide fast and flexible reactive power support for voltage regulation and power loss reduction in distribution networks. Conventionally, central and local voltage/VAR control (VVC) strategies are separately determined, lacking a cross-hierarchy coordination. This paper proposes a novel hierarchically-coordinated VVC (HC-VVC) method where central hierarchy dispatches the inverter reactive power output to minimize network power loss and local hierarchy responds to real-time voltage deviation through a linear droop controller. The proposed method simultaneously optimizes inverter reactive power output setpoints for the central dispatch and droop functions for the local control so that the two control hierarchies are optimally coordinated under stochastic PV power generation and load variations. The coordination model is solved by a scenario-based stochastic optimization approach with probabilistic uncertainty modeling where real-time variations of the uncertainties are fully addressed. Simulation results show that, compared with existing methods, the proposed HC-VVC method is overall superior in minimizing power loss and voltage deviation.
92 citations
TL;DR: Zuo et al. as mentioned in this paper modeled the electric heating and cooling system of the integrated energy system in the coastal area in coastal area and provided the accurate analysis of the coupling relationship.
Abstract: Zuo, X; Dong, M; Gao, F, and Tian, S, 2020 The modeling of the electric heating and cooling system of the integrated energy system in the coastal area In: Yang, Y; Mi, C; Zhao, L, and Lam, S (eds), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering Journal of Coastal Research, Special Issue No 103, pp 1022–1029 Coconut Creek (Florida), ISSN 0749-0208The accurate analysis of the coupling relationship of the electric heating and cooling system is the basis of its load calculation Because the current method does not consider the analysis of the coupling relationship of the electric heating and cooling system in the design, the accuracy of the load calculation results is low In order to solve this problem, the load modeling of the electric heating and cooling system of the comprehensive energy system in the coastal area is studied Through the calculation of power network, natural gas network and comprehensive energy flow, the power flow value of electric heating and cooling system of comprehensive energy system is obtained On this basis, according to the energy conversion efficiency of the equipment included in the energy hub and the distribution ratio of electric energy and gas, the coupling relationship of the electric heating and cooling system is obtained According to the coupling relationship of the electric heating and cooling system, the load model of the electric heating and cooling system is constructed, and the optimal solution of the model is calculated by Grey Wolf algorithm to complete the modeling research of the electric heating and cooling system of the comprehensive energy system in the coastal area The simulation results show that the model designed in this paper can obtain the accurate calculation results of the active power and reactive power of the electric heating and cooling system, and the calculation of the load of the electric heating and cooling system is time-consuming, accurate and reliable
91 citations
TL;DR: In this article, a salp swarm algorithm (SSA) was used to solve the OPF problem in two electric grids such as IEEE 57- and 118-bus electric networks.
Abstract: A new attempt of employing salp swarm algorithm (SSA) to tackle the optimal power flow (OPF) problem is demonstrated in the current study. This aforementioned problem has four fitness functions to be optimized such as (1) the sum of generating units’ fuel costs, (2) total network real power losses, (3) entire sum of voltage deviation of load buses, and (4) static voltage stability (VS) of electric power systems. At initial stage, these objective are solved one by one, and at a later stage, different vector objective functions are solved simultaneously by the SSA. The VS study based on a modal analysis is taken into consideration as an objective function. In this issue, the eigenvalues and eigenvectors of a reduced Jacobian matrix due to the reactive power change are figured. The smaller magnitude of eigenvalues indicates the vicinity to system voltage instability. As the magnitude of eigenvalues increases, the incremental voltage decreases, which means strong VS. The output active power of generating units, their voltages, transformers tap setting, and capacitor devices represent the search field. Two electric grids such as IEEE 57- and 118-bus electric networks are demonstrated to examine the performance of the SSA. The effectiveness of the SSA–OPF methodology is compared with that obtained by using other competing optimization methods. Furthermore, statistical performance measures comprising parametric and nonparametric tests are made and the simulation results are extensively verified which indicate a competition of the SSA with others algorithms in solving the OPF problem.
89 citations
TL;DR: Current and future challenges, feasible solutions and subsequent research prospects are detailed and some key principles that should underlie future changes of wind integrated energy systems are suggested and further research directions are addressed.
TL;DR: A bi-level programming approach for the collaborative management of an active distribution network (ADN) with multiple VPPs by designing comprehensive prices for active and reactive power.
Abstract: Virtual power plants (VPPs) have become an effective technique to manage a growing number of flexible resources, which have posed great technical challenges to distribution system operators (DSOs). This article proposes a bi-level programming approach for the collaborative management of an active distribution network (ADN) with multiple VPPs by designing comprehensive prices for active and reactive power. The upper layer aims to minimize the overall operation cost of the ADN considering the system security and economic operation and the interactions among the power market, ADN and VPPs. The lower layer aims to maximize the benefits of each VPP agent considering various flexible resources. Then, the bi-level model is transformed into a tractable single-level problem by using a linearization method, the Karush–Kuhn–Tucker (KKT) optimality conditions, the Fortuny-Amat transformation and the strong duality theorem. Case analyses indicate that the proposed strategy can effectively enhance the system security and improve the system economic performance by introducing reactive power pricing. The implementation effect and superiority of the proposed strategy are profoundly analyzed under different scenarios and conditions, which indicates its promising application value in the industrial field.
TL;DR: This work proposes a compatible hierarchical control structure that enables operation and seamless transition between islanded and grid-connected modes and achieves voltage and frequency regulation and grid synchronization in the islanded mode.
Abstract: Virtual oscillator control (VOC) is a nonlinear time domain controller that achieves significantly faster primary control response in islanded microgrids, compared to droop or virtual synchronous machine (VSM) control. Despite its superior performance, adoption of VOC is limited due to the lack of compatible secondary regulation or grid synchronization techniques. This is attributed to the nonlinear nature of VOC that complicates secondary control design, and the third-harmonic component in VOC output voltage that severely restricts grid-tied operation. To leverage the faster primary control response characteristics of VOC, we propose a compatible hierarchical control structure that enables operation and seamless transition between islanded and grid-connected modes. In the islanded mode, the controller achieves voltage and frequency regulation and grid synchronization; in the grid-tied mode, notch filters are used to suppress harmonic currents and tertiary level power reference tracking is achieved. The proposed controllers are validated through a series of real-time hardware-in-the-loop tests and hardware experiments using laboratory inverter prototype and state-of-the-art controls and communications hardware.
TL;DR: An enhanced genetic algorithm (EGA) that combines the merits of genetic algorithm and local search to find the optimal placement and capacity of the simultaneous allocation of DGs/SCs in the radial systems is proposed.
Abstract: Controlling active/reactive power in distribution systems has a great impact on its performance. The placement of distributed generators (DGs) and shunt capacitors (SCs) are the most popular mechanisms to improve the distribution system performance. In this line, this paper proposes an enhanced genetic algorithm (EGA) that combines the merits of genetic algorithm and local search to find the optimal placement and capacity of the simultaneous allocation of DGs/SCs in the radial systems. Incorporating local search scheme enhances the search space capability and increases the exploration rate for finding the global solution. The proposed procedure aims at minimizing both total real power losses and the total voltage deviation in order to enhance the distribution system performance. To prove the proposed algorithm ability and scalability, three standard test systems, IEEE 33 bus, 69 bus, and 119-bus test distribution networks, are considered. The simulation results show that the proposed EGA can efficiently search for the optimal solutions of the problem and outperforms the other existing algorithms in the literature. Moreover, an economic based cost analysis is provided for light, shoulder and heavy loading levels. It was proven, the proposed EGA leads to significant improvements in the technical and economic points of view.
TL;DR: This paper presents a Hybrid Shunt Active Power Filter (HSAPF) optimized by hybrid Particle Swarm Optimization-Grey Wolf Optimization (PSO-GWO) and Fractional Order Proportional-Integral-Derivative Controller (FOPIDC) for reactive power and harmonic compensation under balance and unbalance loading conditions.
Abstract: This paper presents a Hybrid Shunt Active Power Filter (HSAPF) optimized by hybrid Particle Swarm Optimization-Grey Wolf Optimization (PSO-GWO) and Fractional Order Proportional-Integral-Derivative Controller (FOPIDC) for reactive power and harmonic compensation under balance and unbalance loading conditions. Here, the parameters of FOPID controller are tuned by PSO-GWO technique to mitigate the harmonics. Comparing Passive with Active Filters, the former is tested to be bulky and design is complex and the later is not cost effective for high rating. Hence, a hybrid structure of shunt active and passive filter is designed using MATLAB/Simulink and in real time experimental set up. The compensation process for shunt active filter is different from predictable methods such as (p-q) or (i
d
-i
q
) theory, in which only the source current is to be sensed. The performance of the proposed controller is tested under different operating conditions such as steady and transient states and indices like Total Harmonic Distortion (THD), Input Power Factor (IPF), Real Power (P) and Reactive Power (Q) are estimated and compared with that of other controllers. The parameters of FOPIDC and Conventional PID Controller (CPIDC) are optimized by the techniques such as PSO, GWO and hybrid PSO-GWO. The comparative simulation/experiment results reflect the better performance of PSO-GWO optimized FOPIDC based HSAPF with respect to PSO/GWO optimized FOPIDC/CPIDC based HSAPF under different operating conditions.
TL;DR: The main contribution of this paper is the formulation of the multi-objective function that can address daily active power loss and voltage deviation under 24-h load pattern including grouping of residential, industrial and commercial loads.
Abstract: The increase in plug-in electric vehicles (PEVs) is likely to see a noteworthy impact on the distribution system due to high electric power consumption during charging and uncertainty in charging behavior. To address this problem, the present work mainly focuses on optimal integration of distributed generators (DG) into radial distribution systems in the presence of PEV loads with their charging behavior under daily load pattern including load models by considering the daily (24 h) power loss and voltage improvement of the system as objectives for better system performance. To achieve the desired outcomes, an efficient weighted factor multi-objective function is modeled. Particle Swarm Optimization (PSO) and Butterfly Optimization (BO) algorithms are selected and implemented to minimize the objectives of the system. A repetitive backward-forward sweep-based load flow has been introduced to calculate the daily power loss and bus voltages of the radial distribution system. The simulations are carried out using MATLAB software. The simulation outcomes reveal that the proposed approach definitely improved the system performance in all aspects. Among PSO and BO, BO is comparatively successful in achieving the desired objectives. The main contribution of this paper is the formulation of the multi-objective function that can address daily active power loss and voltage deviation under 24-h load pattern including grouping of residential, industrial and commercial loads. Introduction of repetitive backward-forward sweep-based load flow and the modeling of PEV load with two different charging scenarios.
TL;DR: The proposed control strategy is based on distributed consensus algorithm, which is developed to achieve the accurate reactive power sharing and dc current sharing in ac and dc MGs.
Abstract: The controller of the interlinking converter (ILC) in a hybrid ac/dc microgrid (MG) system plays an important role of maintaining power sharing between ac and dc MG systems. The coordination control between the ILC controllers and the secondary controllers in each MG should be considered to maintain proper power sharing among two MGs and improve power qualities of hybrid MG system. This paper proposes a distributed coordination control strategy for the hybrid ac/dc MG. The proposed control strategy not only regulates accurate dc current and reactive power sharing among DGs in ac and dc MGs, but also maintains power sharing among two MGs and restores the ac frequency and dc voltage to their nominal values. The hierarchical control of the ILC, comprised of primary and secondary control layer, is proposed to regulate power sharing between ac and dc MGs. The proposed control strategy is based on distributed consensus algorithm, which is developed to achieve the accurate reactive power sharing and dc current sharing in ac and dc MGs. The feasibility of the proposed control strategy is validated by the laboratory prototype hybrid MG system. A comparison study on the proposed control and the conventional control is presented to show the effective of the proposed control strategy.
TL;DR: This paper presents a novel fast frequency response and power oscillation damping control by large-scale PV plants controlled as STATCOM, termed PV-STATCOM, to simultaneously enhance frequency regulation and small signal stability of power systems.
Abstract: This paper presents a novel fast frequency response and power oscillation damping control by large-scale PV plants controlled as STATCOM, termed PV-STATCOM, to simultaneously enhance frequency regulation and small signal stability of power systems. Frequency deviations typically occur together with power oscillations in large power systems. The proposed controller comprises: first, power oscillation damping controller based on reactive power modulation and second, fast frequency response controller based on real power modulation, both of which are applied to the plant level controller of PV-STATCOMs. The proposed composite control is shown to successfully reduce frequency deviations, damp power oscillations, and provide voltage regulation both during over-frequency and under-frequency events. The proposed smart inverter control makes effective utilization of the PV inverter capacity and available solar power. For large power flows, the proposed control is shown to be superior than the conventional droop control recommended by North American Electric Reliability Corporation for generating plants. MATLAB/Simulink-based simulations are conducted on two-area power system using generic PV plant dynamic models developed by Western Electricity Coordinating Council, for a wide range of system operating conditions. Such grid support functionality is expected to bring new revenue making opportunities for PV solar farms.
TL;DR: This work presents a survey of different meta- heuristic techniques applied for solution of ORPD problems in power transmission system, and proposes a new meta-heuristic Sine-Cosine algorithm to solve the problem.
TL;DR: The chaotic bat algorithm (CBA) is applied to solve the optimal reactive power dispatch (ORPD) problem taking into account small-scale, medium-scale and large-scale power systems, revealing the effectiveness and robustness of the CBA for solving the ORPD problem.
Abstract: In this paper, the chaotic bat algorithm (CBA) is applied to solve the optimal reactive power dispatch (ORPD) problem taking into account small-scale, medium-scale and large-scale power systems. ORPD plays a key role in the power system operation and control. The ORPD problem is formulated as a mixed integer nonlinear programming problem, comprising both continuous and discrete control variables. The most outstanding benefit of the bat algorithm (BA) is its good convergence for optimal solutions. The BA, however, together with other metaheuristics, often gets stuck into local optima and in order to cope with this shortcoming, the use of the CBA is proposed in this paper. The CBA results from introducing the chaotic sequences into the standard BA to enhance its global search ability. The CBA is utilized to find the optimal settings of generator bus voltages, tap setting transformers and shunt reactive power sources. Three objective functions such as minimization of active power loss, total voltage deviations and voltage stability index are considered in this study. The effectiveness of the CBA technique is demonstrated for standard IEEE 14-bus, IEEE 39 New England bus, IEEE 57-bus, IEEE 118-bus and IEEE 300-bus test systems. The results yielded by the CBA are compared with other algorithms available in the literature. Simulation results reveal the effectiveness and robustness of the CBA for solving the ORPD problem.
TL;DR: A novel model predictive power control scheme to control and coordinate the dc–dc converter and inverter for grid-connected PV systems with energy storage systems (ESS) can support the power grid to maintain stable voltage and frequency and improve the power factor.
Abstract: The cascaded control method with an outer voltage loop and an inner current loop has been traditionally employed for the voltage and power control of photovoltaic (PV) inverters. This method, however, has very limited power regulation capability. With the fast increasing penetration of PV power generation systems in the distribution network, the voltage rise/drop has become a serious problem impacting negatively on the power quality and grid stability. Therefore, flexible power regulation is highly desired for PV inverters to provide ancillary services. This paper proposes a novel model predictive power control (MPPC) scheme to control and coordinate the dc–dc converter and inverter for grid-connected PV systems with energy storage systems (ESS). By regulating the dc-bus voltage and controlling the active and reactive power flows, MPPC can support the power grid to maintain stable voltage and frequency and improve the power factor. Numerical simulation and controller hardware-in-the-loop (CHIL) testing have been conducted on a PV-ESS system to verify the capability and effectiveness of the proposed control strategy.
TL;DR: From the experimental analyses, distributed voltage deviations can be mitigated using active power curtailment and volt-watt control systems, and the over-frequency of an electric power grid can be reduced using frequency-Watt control method.
TL;DR: A new five-level transformerless inverter topology is presented in this study that is able to boost the value of the input voltage and can remove the leakage current problem through a common-ground architecture.
Abstract: Transformerless grid-connected inverters have been extensively popular in renewable energy-based applications owing to some interesting features such as higher efficiency, reasonable cost, and acceptable power density. The major concern of such converters is the leakage current problem and also the step-down feature of the output voltage, which causes a costly operation for a single-stage energy conversion system. A new five-level transformerless inverter topology is presented in this study that is able to boost the value of the input voltage and can remove the leakage current problem through a common-ground architecture. Here, providing the five-level of the output voltage with only six power switches is facilitated through the series–parallel switching of a switched-capacitor module. Regarding this switching conversion, the self-voltage balancing of the integrated capacitors over a full cycle of the grid's frequency can be acquired. Additionally, to inject a tightly controlled current to the local grid, a peak current controller-based technique is employed, which can regulate both the active and reactive power support modes. Theoretical analyses besides some experimental results are also given to corroborate the correct performance of the proposed topology.
TL;DR: In this article, a new control strategy for suppressing power oscillation especially the oscillation excitation is proposed, which effectively suppresses the power oscillations by adding a virtual damping element for enhancing the system damping and a virtual reactance for reducing the amplitude excitation to the conventional control scheme.
Abstract: Active power oscillation is observed when two or more parallel synchronverters undergo load fluctuations, potentially impacting the safe operation of the synchronverters. This article provides a fundamental analysis for the power oscillation mechanisms and proposes a new control strategy for suppressing power oscillation especially the oscillation excitation is proposed. It is found that power oscillation is inherently caused by weak damping and large inertia of the synchronverters under the condition of undesirable instantaneous active power sharing. Then, the condition for reducing the oscillation excitation of synchronverters, which is caused by undesirable instantaneous active power sharing, is deduced. The new control strategy effectively suppresses the power oscillation by adding a virtual damping element for enhancing the system damping and a virtual reactance for reducing the oscillation excitation to the conventional control scheme without changing the basic dynamic and steady characteristics of the synchronverters. The theoretical analysis and the proposed oscillation suppression control techniques are validated with an extensive hardware-in-loop simulation study.
TL;DR: A fundamental model for defining and optimizing distributed energy flexibility in distribution buses, as well as deliverable energy flexibility as the aggregate distributed flexibility that is available for offering to the day-ahead energy market by distribution system operators (DSOs), without jeopardizing the operational constraints of the distribution network is proposed.
Abstract: This paper proposes a fundamental model for defining and optimizing distributed energy flexibility in distribution buses, as well as deliverable energy flexibility as the aggregate distributed flexibility that is available for offering to the day-ahead energy market by distribution system operators (DSOs), without jeopardizing the operational constraints of the distribution network. The distributed energy flexibility is provided by flexible loads in distribution buses, which are modeled by clustered queuing systems representing the aggregation of large population of flexible loads with different energy and service quality requirements. Further, controllable inverters interfacing distributed solar generation provide reactive power flexibility in distribution buses. The deliverable energy flexibility is optimized by the proposed model that coordinates the energy flexibility of queued flexible loads and controllable inverters to maximize DSO’s profit of participating in the day-ahead energy market, while satisfying the service quality constraints of flexible loads, the operational limits of controllable inverters, and power flow constraints of distribution network that are formulated using the branch flow model. Moreover, an index is proposed to calculate the contribution of each distribution bus in providing the deliverable energy flexibility. The proposed model is implemented on the IEEE 33-bus distribution network. The numerical results exhibit profit opportunities for DSOs from providing the deliverable energy flexibility in the day-ahead energy market.
TL;DR: In this paper, the effects of increasing Doubly-Fed Induction Generator-based Wind Energy Conversion System (DFIG-WECS) penetration in the power system have been investigated.
TL;DR: This article deals with the multimode operation of a photovoltaic (PV) array, a battery, the grid and the diesel generator (DG) set-based charging station (CS) for providing the continuous charging and uninterruptible supply to the household loads.
Abstract: This article deals with the multimode operation of a photovoltaic (PV) array, a battery, the grid and the diesel generator (DG) set-based charging station (CS) for providing the continuous charging and uninterruptible supply to the household loads. In this CS, a single voltage source converter operates the CS in an islanded mode, the grid connected mode and the DG set connected mode (DGM) and performs various tasks, such as power management among different energy sources and charging the electric vehicles (EVs), extraction of maximum power from the PV array, the regulation of voltage and frequency of the generator, harmonics current compensation of nonlinear loads and intentional reactive power compensation. The control of charging station (CS) is designed such that it primarily takes power from the PV array and a storage battery. In the absence of these two sources, the charging station takes power from the grid, and at last, it utilizes a squirrel cage induction generator-based DG set. However, the DG set is operated such that it generates up to 33% more power than its rated capacity without exceeding the rated current in windings, therefore, the size of the DG is reduced. Moreover, the voltage and frequency of the generator are regulated at its rated values without a mechanical speed governor. In all operating modes, the CS complies with the IEEE 1547 standard and the total harmonic distortion of voltage and current, is achieved less than 5%.
TL;DR: The proposed methodology is examined on a modified IEEE-33 bus test system, which demonstrates the high efficiency and importance of the proposed techniques in minimizing the hybrid ac–dc MG operation cost while all of the constraints of the network are satisfied.
Abstract: This paper aims to investigate the optimal scheduling of stochastic reconfigurable hybrid ac–dc microgrid (MG) in the presence of renewable energies and also considering dynamic line rating (DLR) constraint. DLR is a practical limitation that can potentially affect the ampacity of lines, particularly in the islanded mode when the lines reach their maximum capacity in lack of main generation source at the point of interconnection with the utility. In order to prevent overloading of the lines, the reconfiguration technique is developed to change the topology of the network by some prelocated switches. A linearization technique is adapted to address the nonlinearity of both nodal ac power flow and the DLR constraints. The unscented transform technique is utilized to model uncertainties including renewable energy generations, hourly load demands, and hourly market prices along with the DLR uncertainties such as solar radiation, wind speed, and ambient temperature. Finally, a sensitivity analysis is performed to see the effect of wind speed and solar radiation on the energy management of hybrid ac–dc MG. The performance of the proposed methodology is examined on a modified IEEE-33 bus test system, which demonstrates the high efficiency and importance of the proposed techniques in minimizing the hybrid ac–dc MG operation cost while all of the constraints of the network are satisfied.
TL;DR: The analysis shows that the proposed topology is suitable for wide range of power conversion applications (for example, rolling mills, fans, pumps, marine appliances, mining, tractions, and most prominently grid-connected renewable energy systems).
Abstract: This article presents an analysis and design of a new boost type six-switch five-level (5L) active neutral point clamped (ANPC) inverter based on switched/flying capacitor technique with self-voltage balancing. Compared to major conventional 5L inverter topologies, such as neutral point clamped, flying capacitor, cascaded H-bridge, and ANPC topologies, the new topology reduces the dc-link voltage requirement by 50%. Whilst reducing the dc-link voltage requirement, the number and the size of the active and passive components are also reduced without compromising the reactive power capability. The analysis shows that the proposed topology is suitable for wide range of power conversion applications (for example, rolling mills, fans, pumps, marine appliances, mining, tractions, and most prominently grid-connected renewable energy systems). Experimental results from a 1.2 kVA prototype justifies the concept of the proposed inverter with a conversion efficiency of around 97.5% ± 1% for a wide load range.
TL;DR: In this paper, a real-time detection algorithm of decaying dc component is first developed for a generic single-phase distorted ac signal, and fast and robust elimination of both decaying dc transient and harmonics can be performed simultaneously in three-phase grids, by adoption of moving average filters in $d$ − $q$ frame and subsequent calculations.
Abstract: Active power filters are conventionally utilized to compensate steady-state harmonic currents and reactive power in the utility, yet their capabilities are usually limited if the elimination of undesirable effects associated with decaying dc components during transients is the target, especially under the weak grid condition. In this letter, active cancellation of the typical first-order decaying dc-mode transients is explored. To this end, a real-time detection algorithm of decaying dc component is first developed for a generic single-phase distorted ac signal. Furthermore, fast and robust elimination of both decaying dc transient and harmonics can be performed simultaneously in three-phase grids, by adoption of moving average filters in $d$ – $q$ frame and subsequent calculations. Hardware-in-the-loop experiment results verified the effectiveness of the proposed technique.