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Hybrid ac/dc microgrid (HMG) comprises ac and dc microgrids (MGs) interconnected through an interlinking converter (IC). In islanded operation mode of HMG, a coordinated control structure must be implemented to realize voltage and frequency control in ac MG, voltage control in dc MG, active and reactive power sharing among ac sources, active power sharing among dc sources, global active power sharing among dc and ac sources, and reactive power sharing among ac sources and IC. To realize these objectives, a new coordinated control based on master–slave approach is proposed in this paper. In this method, the master source of each MG broadcasts its relative power loading as a common signal to the slave sources of the same MG and IC through a unidirectional low-bandwidth communication network. Based on this information, the slave sources and the IC adjust their operating point. The proposed method provides accurate power sharing as well as zero voltage and frequency deviation. It does not require a centralized control unit and features plug and play capability. The derivation of the proposed method is thoroughly discussed in this paper. Time domain simulation results based on CIGRE benchmark MG are presented to validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

The ancillary services are becoming more important due to the increasing integration of non-dispatchable and intermittent renewable energy sources. Such behavior under deregulation necessitates the procurement of these services suitably. This paper presents the multi-objective procurement of voltage control ancillary service in a dynamic pool deregulated system that is contingent to wind and solar power generation uncertainties. The shunt capacitors bid to supply this service and their switchings, although restricted due to life expectancy, depend on locational marginal prices. An improved multi-objective artificial electric field algorithm, which adopts the concept of Pareto-based non-dominated sorting, is presented to co-optimize total cost and voltage deviation. The particle's positions are updated through randomly picked Pareto solution to enhance exploitation capability. The sign and reorder mutation operations are employed to maintain diversity in the population, improve exploration, and evade local optima trap. The performance is investigated for different levels of wind and solar penetration on IEEE 30-bus and IEEE 118-bus test systems. The convergence of presented algorithm is analyzed and compared with other algorithms through statistical metrics and associated boxplots. [ABSTRACT FROM AUTHOR]

In order to meet global energy efficiency and environmental objectives, production costs of these key devices, and other similar, must be reduced. Back-to-back VSC systems are essential for wind power generation and industrial machine drivers. Sensor elimination is a viable path to achieve such goal, as long as the control is adequate and does not impair the main converter functions. This paper presents the results of an academic-industrial research work aiming at a new control technique capable of reducing the number of sensors from 13 to only 6, using a single PID feedback loop for each VSC based on the monitoring the DC-link power. This leads to an easy-to-implement control scheme which preserves all functions required by AC/DC/AC conversion systems, such as DC voltage control, active power flow, and reactive power generation in each AC port. The results obtained demonstrate the suitable performance and advantages of this timely proposed technique for medium-power Back-to-Back VSC systems. Finally, four cases of study are fully discussed and supported by simulation and experimentation through a laboratory prototype. [ABSTRACT FROM AUTHOR]

The uncertainty of solar generation is a challenging issue for the operation and control of distribution systems. Also, because of the large number of control and operation variables in advanced distribution networks, the centralized optimization technique requires high computational capabilities. In this paper, a distributed voltage regulation approach in a distribution system based on the predictor corrector proximal multiplier (PCPM) algorithm has been presented. This paper focuses on the voltage rise in distribution systems with high penetration of photovoltaics. The proposed method uses a clustering approach to divide the network into partitions based on the coupling degrees among different nodes. The optimal reactive power control strategy is conducted in each partition and integrated using PCPM. The proposed method is tested on 69 and 123 nodes IEEE distribution test systems. The results confirmed that the proposed method achieves the optimal solution with the same accuracy as the centralized method but in a much shorter computation time. [ABSTRACT FROM AUTHOR]

A design procedure for an RLC damping branch applied at a voltage source inverter followed by an LCL output filter is carried out in this paper. The main purpose of the proposed methodology is to allow the system to operate properly in both grid-connected (GC) and islanded (IS) modes with smooth transitions between them. The usage of passive damping methods to smooth the resonating filters effects is well known. However, the design procedure of the damping branch is specific for either the GC or IS mode, and usually, the parameters tuned for an operation mode are unsuitable for the other one. Thereby, this paper contributes to presenting a methodology design of an RLC branch aimed to achieve damping effect for both operation modes, thus allowing the continuous operation with no hazardous transients during transitions. By means of the proposed approach, the passive elements are adequately designed in order to provide easy controller synthesis. Therefore, a two-loop control strategy is adopted where the inner loop controls the capacitor voltage and ensures the system stability for both operation modes; meanwhile, an additional outer loop controls the grid current for GC mode allowing active and reactive power flows. Experimental results for a 2-kW prototype are presented in order to validate the proposed design methodology and control strategy. [ABSTRACT FROM AUTHOR]

This paper presents an application for the control of a voltage source converter (VSC) through the synchronverter approach. The objective is to show that such an approach is pertinent to handle this type of converters, especially important nowadays that such devices are practically permeating small as well as large electrical networks. The paper helps to demonstrate that the proposed control strategy is capable of satisfying the requirement that a modern VSC must contribute to the Volts/Var regulation problem in the smart grid, which represents a significant challenge. The application is carried out in the context of the hardware-in-the-loop using Matlab/Simulink. The results state the VSC performance under different operating conditions and become quite relevant. [ABSTRACT FROM AUTHOR]

Encouraged by the increasing electric energy consumption, the distributed generation has been widely included in the electrical power system. However, renewable energy resources have intermittent characteristics. When the distributed generation is high at certain times of the day, the energy generation at distribution systems can become higher than the required power. The surplus energy is returned to the transmission system, giving rise to active distribution networks. This paper proposes an approach to optimally managing the existing distributed generation and voltage control devices. The management is performed by solving an optimal power flow problem, aiming to find an operating condition for the system in which the losses are minimized, and the voltage profiles are improved. A combined transmission and distribution system is proposed. Some scenarios are considered to assess the impact of distributed generation insertion and the contribution of these sources in support of reactive power. The results indicate the need for adequate active distribution networks management, which depends on the distribution generation insertion level and the generation sources' power factor. [ABSTRACT FROM AUTHOR]

Virtual synchronous generators (VSGs), with the operational characteristics of synchronous generators (SGs), have been employed in renewable energy generation grid-connected systems to solve the problem of insufficient equivalent inertia, which is caused by the high permeability of distributed generation systems in the grid. However, a VSG does not possess low voltage ride-through (LVRT) capability. A novel LVRT control strategy for a VSG based on virtual self-inductive flux linkage is proposed in this paper. First, the electromagnetic transient response mechanism of a SG under grid faults is analyzed in detail. Then, a memory and retention strategy are proposed to simulate the effect of the switch law. Furthermore, the virtual q-axis armature self-inductance is introduced into the VSG and a virtual self-inductive magnetic chain is utilized to block the change of the transient fault current. This helps the inverter adjust the output voltage quickly. In addition, under the premise of meeting the reactive power margin, the reactive power compensation strategy is optimized to achieve a quick response in terms of the reactive power compensation of grid faults, which is helpful for realizing the LVRT of a VSG. Finally, the feasibility and effectiveness of the proposed LVRT method are verified by thorough simulation results. [ABSTRACT FROM AUTHOR]

Voltage regulation issue in the distribution network is considered as a challenge that is associated with high penetration of the distributed generations (DGs). The widespread of the DGs led to influence the operation of the reactive power compensation (RPC) devices and the on-load tap-changers (OLTCs) and significantly affected the voltage profile. Therefore, obtaining the suitable control settings for the OLTC and the RPC should be reconsidered considering the impact of the DGs. This paper proposes a strategy for coordinating the operation of the OLTC and the RPC with DGs in the distribution networks. The proposed coordination strategy obtains the optimal values of the active power generated from the DGs, the reactive power injected from the switched capacitors (SCs), and the tap settings of the OLTC by using the multi-objective particle swarm optimization (MOPSO). The objective function is to minimize the total active power losses for all lines and the total voltage deviation for all nodes in the distribution network. The proposed coordination strategy is tested on the modified IEEE 33-node test feeder and a practical distribution feeder extracted from the North Delta Electricity Distribution Company in Egypt. A MATLAB code is built in this paper for simulation of the case studies and for determining the optimal parameters. A comprehensive comparison between the proposed MOPSO and the mixed-integer linear programming (MILP) method for different operating conditions of the distribution network is made. The results demonstrate that, the proposed strategy decreases the power losses, improves the voltage regulation and provides efficient coordination of DG with the voltage regulating devices; SCs and OLTC. [ABSTRACT FROM AUTHOR]

The increasing participation of wind turbines based on doubly fed induction generator (DFIG) in the power system around the world is motivating the investigation of novel strategies to enhance the reliability of DFIG and power system connection. This paper proposes the use of a new hybrid multilevel back-to-back converter on DFIG wind turbine to improve its fault ride-through capability and power system transient stability. The proposed topology is built adding single-phase full-bridge inverters in series with each phase of traditional three-phase inverter. This converter is able to generate higher voltages in rotor circuit whenever it is required, which can effectively protect power converter and at the same time contribute with grid transient performance. Simulation results, using PSCAD®, are presented for a 2 MW DFIG machine submitted to symmetrical faults in single machine—infinite bus and three-bus system. Results show that the proposal is effective as a protection and works well as an alternative to traditional solutions, limiting currents and maintaining power control during voltage dips. It is also effective in contribution with the improvement of transient stability margin by the possibility of reactive power injection. [ABSTRACT FROM AUTHOR]

This paper introduces a new search-based method for coordinated control of voltage (Volt) and reactive power (Var) devices for conservation of voltage reduction to achieve an effective demand and power loss reduction while keeping voltage profile within limits on a distribution system. The method searches for the best control settings for the Volt–Var devices as the operating conditions change for real-time operation. The main advantage of the proposed method is that it provides global optimal solution. When the number of control devices increases on an active distribution system with distributed generation, the search space will increase combinatorially. The method has a computationally efficient search scheme to reduce the search space systematically. The computation effort is further reduced by adopting the decoupled Volt–Var approach. To demonstrate the computational efficiency of the proposed method, test results are compared with a conventional Volt–Var scheme. The control update considered is 15-min interval. The simulations are done on modified IEEE 13 node unbalanced distribution circuit by using MATLAB™ and a power flow analysis program (OpenDSS). [ABSTRACT FROM AUTHOR]

The intermittent behavior of wind power generation results in a fast variation of both frequency and voltage magnitudes of isolated microgrids with high wind power penetration. In this paper, a hybrid energy microgrid with wind energy conversion system (WECS) and diesel synchronous generators are analyzed during wind gust conditions. Superconducting magnetic energy storage (SMES) is connected at the same node of the WECS to mitigate the intermittent wind power generation. A developed fuzzy logic controller has been applied to achieve active power sharing. The damping of voltage fluctuation depends on SMES reactive power, which is controlled by a voltage source converter. The studied microgrid comprises 33 nodes, two diesel SGs, and two WECSs of squirrel cage induction generator type at 30% penetration level. The results demonstrate the effectiveness of the proposed control strategy to mitigate the frequency fluctuations during the wind speed gusts by smoothing power output from WECSs/SMES system. Moreover, voltage control is achieved by injecting reactive power from the SMES system. All simulations are performed by MATLAB/Simulink package. [ABSTRACT FROM AUTHOR]

Among the existing power quality problems, the reactive power compensation plays a key role once it helps to maintain the system stability and increases the efficiency. Currently, there are many solutions for reactive power compensation, which unfortunately present a wide variety of problems as large inrush currents, non-continuous compensation and harmonics injection in the system. The application of devices like static VAr compensator, static synchronous compensator or unified power flow controller has demonstrated to be an effective solution for reactive power compensation. However, it is important to note that these options are rarely used in distribution systems by companies that prefer to assimilate the drawbacks of switched capacitor banks instead of investing in more expensive, sophisticated and complex solutions. Despite the large number of proposed devices in distribution systems, there is a lack of solutions with emphasis on cost reduction. Therefore, this paper presents a new topology for reactive power compensation and voltage control in distribution systems. The proposed topology has several interesting features as reduced switching losses, small capacitors and simple control scheme. In addition, the proposed solution uses already existing capacitor banks which makes possible its usage in distribution companies with minimum modifications. Experimental results have been obtained on a 6-kVA prototype to demonstrate the feasibility of the proposed solution. [ABSTRACT FROM AUTHOR]

In order to minimize the power loss and to control the voltage in the power systems, the proposed momentum-based wavelet neural network and proposed momentum-based double wavelet neural network are proposed in this paper. The training data are obtained by using linear programming method by solving several abnormal conditions. The control variables considered are generator voltages and transformer taps, and the dependent variables are generator reactive powers and load bus voltages. The IEEE 14-bus system and IEEE 30-bus system are tested using the linear programming, Levenberg-Marquardt artificial neural network, proposed momentum-based wavelet neural network and proposed momentum-based double wavelet neural network to validate the effectiveness of the proposed MDWNN method. The trained neural networks are capable of controlling the voltage, and reactive power in power systems is proved by the results with the high level of precision and speed. [ABSTRACT FROM AUTHOR]

This paper presents the application of an online optimization based fast model predictive control scheme to grid-connected wind farms for reactive power and voltage control. A linear prediction model of the network was used to predict the behavior of the system for a certain prediction horizon, while a modified quadratic programming problem was used for the optimization process. The proposed controller was tested in a 5-bus test system hosting three sub-wind farms of total 36 MW active power production capacity connected in series to the external network. The controller performed its control action by changing the reactive power output of the sub-wind farms and voltage set-points of an online load tap changer transformer to respect the safety limit imposed on the bus voltages and desired reactive power exchange. [ABSTRACT FROM AUTHOR]