Multiple Distributed Generation Research Articles

A New Improved Voltage Stability Assessment Index-centered Integrated Planning Approach for Multiple Asset Placement in Mesh Distribution Systems

This paper offers a new improved voltage stability assessment index (VSAI_B)-centered planning approach, aiming at the attainment of technical and cost related objectives with simultaneous multiple asset deployment in a mesh distribution systems (MDS). The assets such as multiple distributed generation (DG) and distributed static compensator (D-STATCOM) units have been utilized; aiming at voltage stabilization, loss minimization, and associated objectives. The proposed planning approach incorporates expressions of VSAI_B aiming at initial simultaneous assets placement followed by loss minimization conditions (LMC) for appropriate asset sizing, which is further utilized for performance evaluations. The VSAI_B-LMC-based integrated planning approach is applied to configured MDS models such as a 33-bus test distribution system (TDS) for detailed analysis. The performance evaluations with the presented approach have been conducted for different cases along with respective scenarios considering various technical and cost-economic performance metrics. First, three cases referring to multiple DGs sitting and sizing for various power factors have been presented, followed later by two cases of multiple DGs and D-STATCOMs with respective evaluation scenarios. Finally, benchmark analysis is conducted on a 69-bus TDS for validity demonstration of the proposed approach. The comparison of achieved results in comparison with the available literature points out toward the validity and improved performance of the proposed approach.

Optimal incorporation of multiple distributed generation units based on a new system maximum loadability computation approach and vortex searching algorithm

In this paper, the optimal incorporation of distributed generation (OIDG) units for the maximization of the system‟s loadability is investigated (based on sizing and siting). To this end a new computational approach for computing maximum loadability of the system is developed. This approach has been compared with the classical one on different radial test systems (RTS) and is found to be faster and more accurate. The OIDG problem is formulated mathematically as an optimization problem with the objective function to maximize system‟s loadability, the imposed constraints are; voltage limits, thermal limits and DG penetration level. The optimization algorithm used is to solve the OIDG problem is the Vortex searching algorithm (VS). The tested radial distribution systems are the standard 33-bus and 69-bus systems. This paper also discusses some other interesting findings about VS algorithm.

Optimal incorporation of multiple distributed generation units based on a new system maximum loadability computation approach and vortex searching algorithm

In this paper, the optimal incorporation of distributed generation (OIDG) units for the maximization of the system‟s loadability is investigated (based on sizing and siting). To this end a new computational approach for computing maximum loadability of the system is developed. This approach has been compared with the classical one on different radial test systems (RTS) and is found to be faster and more accurate. The OIDG problem is formulated mathematically as an optimization problem with the objective function to maximize system‟s loadability, the imposed constraints are; voltage limits, thermal limits and DG penetration level. The optimization algorithm used is to solve the OIDG problem is the Vortex searching algorithm (VS). The tested radial distribution systems are the standard 33-bus and 69-bus systems. This paper also discusses some other interesting findings about VS algorithm.

Optimal incorporation of multiple distributed generation units based on a new system maximum loadability computation approach and vortex searching algorithm

In this paper, the optimal incorporation of distributed generation (OIDG) units for the maximization of the system‟s loadability is investigated (based on sizing and siting). To this end a new computational approach for computing maximum loadability of the system is developed. This approach has been compared with the classical one on different radial test systems (RTS) and is found to be faster and more accurate. The OIDG problem is formulated mathematically as an optimization problem with the objective function to maximize system‟s loadability, the imposed constraints are; voltage limits, thermal limits and DG penetration level. The optimization algorithm used is to solve the OIDG problem is the Vortex searching algorithm (VS). The tested radial distribution systems are the standard 33-bus and 69-bus systems. This paper also discusses some other interesting findings about VS algorithm.

Comparative Study of Different Approaches for Islanding Detection of Distributed Generation Systems

The issue of unintentional islanding in grid interconnection still remains a challenge in grid-connected, Distributed Generation System (DGS). This study discusses the general overview of popular islanding detection methods. Because of the various Distributed Generation (DG) types, their sizes connected to the distribution networks, and, due to the concern associated with out-of-phase reclosing, anti-islanding continues to be an issue, where no clear solution exists. The passive islanding detection technique is the simplest method to detect the islanding condition which compares the existing parameters of the system having some threshold values. This study first presents an auto-ground approach, which is based on the application of three-phase, short-circuit to the islanded distribution system just to reclose and re-energize the system. After that, the data mining-decision tree algorithm is implemented on a typical distribution system with multiple DGs. The results from both of the techniques have been accomplished and verified by determining the Non-Detection Zone (NDZ), which satisfies the IEEE standards of 2 s execution time. From the analysis, it is concluded that the decision tree approach is effective and highly accurate to detect the islanding state in DGs. These simulations in detail compare the old and new methods, clearly highlighting the progress in the field of islanding detection.

Modified amplitude adaptive control algorithm for power quality improvement in multiple distributed generation system

This study deals with the modified amplitude adaptive notch filter (AANF)-based control algorithm for managing the generated power from different energy sources in an autonomous microgrid. In this study, the autonomous microgrid consists of a wind energy conversion system, photovoltaic array and a storage battery. The main objective of the proposed modified AANF (MAANF)-based control algorithm is to control the flow of active and reactive powers among the different energy sources and the load, along with the regulation of the point of common coupling (PCC) voltages and mitigation of the source current harmonics. The advanced features of proposed control algorithm are the DC-offset rejection from the input signal and fast frequency estimation, which enable the MAANF control algorithm to rapidly and accurately estimate the fundamental components of the distorted load currents. Therefore, the estimated reference source currents remain immune to the DC offset and various harmonic currents. The active power balance is achieved by regulating the DC-link voltage using a bidirectional DC–DC converter, which is connected between the DC link of the voltage source converter and a storage battery. Test results have validated the control algorithm under various steady-state and dynamic operating conditions.

A Novel ANFIS-Based Islanding Detection for Inverter-Interfaced Microgrids

This paper presents a new islanding detection strategy for low-voltage inverter-interfaced microgrids based on adaptive neuro-fuzzy inference system (ANFIS). The proposed islanding detection method exploits the pattern recognition capability of ANFIS and its nonlinear mapping of relation between inputs. The ANFIS monitors seven inputs measured at point of common coupling (PCC), namely root-mean square (RMS) of voltage and current (RMS U and RMS I ), total harmonic distortion (THD) of voltage and current (THD U and THD I ), frequency ( ${f}$ ), and active and reactive powers ( ${P}$ , ${Q}$ ) that are experimentally obtained based on practical measurement in a real-life microgrid. The proposed method is composed of passive monitoring of the mentioned inputs. It does not influence power quality (PQ) and considerably decreases non detection zones (NDZs). In order to cover as many situations as possible, minimize false tripping and still remain selective; type and number of samples are introduced. Here, one of the primary goals is reducing NDZ while keeping PQ in order. Based on the sampled frequency and number of samples, we find that the proposed method has less detection time and better accuracy when compared to the reported methods. Simulations performed in MATLAB/Simulink software environment and several tests performed based on different active load conditions and multiple distributed generation, prove the effectiveness, authenticity, selectivity, accuracy and precision of the proposed method with allowable impact on PQ according to UL1741 standard.

Distributed Control Strategy to Achieve Synchronized Operation of an Islanded MG

To seamlessly transition a microgrid (MG) from islanded to grid-connected mode, it is necessary to synchronize the magnitude, frequency, and phase of the MG voltage to the voltage of the main grid. In this paper, we propose a distributed control strategy to achieve synchronized operation of an islanded MG supported by multiple controllable distributed generators (DGs). The proposed method utilizes a pinning-based consensus algorithm to ensure explicit coordination between magnitude, frequency, and phase angle regulation while ensuring proportional power sharing. System frequency is regulated by all the DGs in proportion to their capacity, while a selected DG eliminates the phase and magnitude regulation errors. Controller design criteria is based on small-signal stability analysis. The proposed control strategy is implemented in hardware controllers and its effectiveness is demonstrated using a real-time hardware-in-the-loop MG testbed.

Multi-objective optimal sizing of distributed generation by application of Taguchi desirability function analysis

Distributed Generation (DG) is modular power generating technology. DG has beneficial impact on tail end voltages, line losses and operating cost. The sizing and location of DG in distribution system is a vital undertaking. In this paper Taguchi Desirability Function Analysis (TDFA) is presented. The remarkable highlight of TDFA is the skillful handling of simultaneous optimization of nearly thousand objectives and its ability to generate multiple optimal solutions. It facilitates the effortless addition of each objective. TDFA is used for finding the optimal size of single as well as multiple DG. Size estimation is carried out for multiple objectives of minimizing the line losses, improving the voltage profile and improving voltage stability index (VSI). The objectives may be minimized, maximized or assigned target values simultaneously. In the scope of this paper more than nine objectives have been optimized simultaneously. TDFA has been implemented to determine optimal size of DG for different load conditions. The proposed approach is tested and verified on IEEE 33-bus and IEEE 85- bus radial distribution system (RDS).

A novel islanding detection technique using modified Slantlet transform in multi-distributed generation

In this paper, a new hybrid islanding detection scheme based on a combination of a modified Slantlet Transform (MSLT) and machine learning is applied to a passive time frequency islanding detection of multiple distributed generation units. A Harmony Search Algorithm (HSA) is used to optimally specify suitable scales of Slantlet transform and Slantlet decomposition levels for accurate islanding classification. Slantlet transform is utilized to derive the features in the required detection parameters measured from islanding and non-islanding events using identified Slantlet scales. In order to automate classification process, machine learning classifiers are utilized to detect islanding and non-islanding conditions with an objective of increasing the detection rate and avoiding nuisance distributed generation tripping during non-islanding situations. Islanding and non-islanding events are simulated for a multi-distributed generations system and used to assess the performance of the proposed anti-islanding protection method. The numerical results showing the efficiency of the proposed islanding detection technique are explained and conclusions are drawn.

Adaptive Droop Based Virtual Slack Control of Multiple DGs in Practical DC Distribution System to Improve Voltage Profile

This paper proposes an adaptive droop based virtual slack (ADVS) control for multiple distributed generations (DGs) to improve voltage stability of a practical DC distribution system. Although there have been many researches for optimal sizes of multiple DGs, their solutions are valid only in the particular operating point. Additionally, a previous study proposed a voltage control based optimal operation method, its performance depends on measurement accuracy in practice. The proposed ADVS control operates the system based on the current sensitivities between the DGs and loads, so that it can regulate the system voltages without a large computational effort. This is effective even if measurements are noisy and biased. All DGs contribute to voltage regulation by current control even though they do not directly control voltages. As an additional effect, they effectively share the load. To verify the proposed method, the DC system is modeled based on the real distribution system of the Do-gok area in Seoul, Korea. Then, the Levenberg-Marquardt algorithm determines its operation point. The proposed method is verified based on the electromagnetic transient (EMT) simulation with random loads.

A Planning Framework for Optimal Partitioning of Distribution Networks Into Microgrids

This paper proposes a novel methodology for the optimal design of microgrids in distribution systems with multiple distributed generation units (DGs). Following the IEEE Standard 1547.4-2011, the operation and control of large distribution networks can be enhanced by dividing these networks into multiple virtual microgrids. The proposed planning framework incorporates the necessary conditions for microgrids to operate efficiently in grid-connected operating mode and successfully during islanding. To obtain a robust design, the clustering process considers three objectives: maximizing the self-adequacy of the designed microgrids, maximizing microgrid islanding success probability, and a combination of both targets. For this purpose, the PG&E distribution system with 69 buses is selected as a test case. Backtracking search optimization algorithm, a probabilistic load flow approach, and graph-based theories are used to accomplish this research. Simulation results demonstrate the effectiveness of combining the self-adequacy and the islanding success probability objectives in the clustering process. Compared with other strategies present in the previous literature, the proposed framework results in more self-sufficient and successful islands assessed in terms of active and reactive power adequacy as well as voltage constraints. Next, the effects of increased penetration level of DGs and installation of both distributed energy-storage units and distributed reactive sources on the design process are examined. Finally, a comparison with other microgrid design objectives applied in previous researches reveals that the resultant design is sensitive to the system's reliability, security, and economic requirements.

Multiple DGs for Reducing Total Power Losses in Radial Distribution Systems Using Hybrid WOA-SSA Algorithm

Distributed generators (DGs) are currently extensively used to reduce power losses and voltage deviations in distribution networks. The optimal location and size of DGs achieve the best results. This study presents a novel hybridization of new metaheuristic optimizations in the last two years, namely, salp swarm algorithm (SSA) and whale optimization algorithm (WOA), for optimal placement and size of multi-DG units in radial distribution systems to minimize total real power losses (kW) and solve voltage deviation. This hybrid algorithm is implemented on IEEE 13- and 123-node radial distribution test systems. The OpenDSS engine is used to solve the power flow to find the power system parameters, such power losses, and the voltage profile through the MATLAB coding interface. Results describe the effectiveness of the proposed hybrid WOA-SSA algorithm compared with those of the IEEE standard case (without DG), repeated load flow method, and WOA and SSA algorithms applied independently. The analysis results via the proposed algorithm are more effective for reducing total active power losses and enhancing the voltage profile for various distribution networks and multi-DG units.

Adaptive decentralized output-constrained control of single-bus DC microgrids

A single-bus DC microgrid can represent a wide range of applications. Control objectives of such systems include high-performance bus voltage regulation and proper load sharing among multiple distributed generators &#x0028 DGs &#x0029 under various operating conditions. This paper presents a novel decentralized control algorithm that can guarantee both the transient voltage control performance and realize the predefined load sharing percentages. First, the output-constrained control problem is transformed into an equivalent unconstrained one. Second, a two-step backstepping control algorithm is designed based on the transformed model for bus-voltage regulation. Since the overall control effort can be split proportionally and calculated with locally-measurable signals, decentralized load sharing can be realized. The control design requires neither accurate parameters of the output filters nor load measurement. The stability of the transformed systems under the proposed control algorithm can indirectly guarantee the transient bus voltage performance of the original system. Additionally, the high-performance control design is robust, flexible, and reliable. Switch-level simulations under both normal and fault operating conditions demonstrate the effectiveness of the proposed algorithm.

Hybrid Analyzing Technique Based Active Islanding Detection for Multiple DGs

Microgrids enable integration of renewable energy resources to the utility grid through distributed generators (DGs) to cope up the increasing demand for electrical energy. Endurance of these DGs is not appreciated during unintentional islanding, due to the drawbacks of jeopardizing the system and working personnel. An active tailor made islanding detection based on d -axis current injection is suggested in this paper along with a novel hybrid analyzing technique, dedicated to microgrids with multiple and hybrid DGs to detect islanding faster and more accurate. The proposed technique is capable of distinguishing between various nonislanding and the islanding events and also very much efficient and robust for various operating conditions with less detection time. The proposed technique is validated by investigations on extensive simulations done in MATLAB R2017b, for various operating conditions.

A New Passive Islanding Detection Technique for Integrated Distributed Generation System Using Rate of Change of Regulator Voltage Over Reactive Power at Balanced Islanding

Grid integration of renewable energy sources in distributed generation (DG) is increasing day to day life due to their advantages of increasing system reliability and power quality. Ahead of their advantages, they are suffering with the problem of unintentional islanding. Islanding is caused in the DG due to problems in the main grid. It is required to detect the islanding within 2 s after islanding as per DG interconnection standards. In this paper a new passive islanding detection method for single synchronous generator based DG and multiple DG units is proposed with rate of change of exciter voltage, over the rate of change of reactive power (dE/dQ). Due to inertia, the response of these exciter voltage and reactive power are very sensitive to small changes compared to other passive parameters, because in the real world the exciter voltage and reactive power are directly depends on the excitation of the generator. The investigations are made on the Matlab/Simulink environment. This method is clearly differentiating between islanding and non islanding events. The effectiveness of this method compared with other passive methods is, it detects islanding during zero power imbalance conditions of active and reactive power.

Decoupled Frequency and Voltage Control for Stand-Alone Microgrid With High Renewable Penetration

In South Korea, the stand-alone microgrid on an island has synchronous diesel generators and multiple distributed generations (DG) based on renewable energy, and energy storage systems (ESS). According to the active policy of government to develop eco-friendly microgrids with zero carbon emission, many diesel generators in stand-alone microgrids are being replaced by the DGs. It brings challenges on the operation and control of multiple DGs because this causes the lack of inertia, which is originally provided from the diesel generators. This paper proposes a new decoupled frequency and voltage controller for DGs, which is able to keep the grid frequency and voltage magnitude constant. For frequency control, a frequency recovery control loop is newly added to conventional droop and inertia control loops for both effective power sharing and stabilization of frequency response after a disturbance. For voltage control, the proposed controller regulates the grid voltage in an inertia-free mode, in which all diesel generators are disconnected, while providing the conventional reactive power-voltage droop control under a normal condition. Moreover, the adaptive power sharing strategy is newly proposed to avoid the overcharge/discharge conditions of ESSs. As the result, the proposed controller can enhance the resilience and increase the penetration of renewable energies to the stand-alone microgrid. To verify the effectiveness of proposed controller, several case studies are being carried out by using the practical data of a real stand-alone microgrid in South Korea.

Distributed Power Sharing Control of The Grid-connected AC Microgrid

This paper considers a power sharing problem of a grid-connected AC microgrid which consists of multiple dispatchable distributed generators. The microgrid is modeled by a multiagent system and the power sharing problem is formulated as a tracking issue of leader-follower system. Simulations are presented to demonstrate the effectiveness of the proposed control scheme.

Optimal Distributed Control for Secondary Frequency and Voltage Regulation in an Islanded Microgrid

This paper proposes an optimal distributed control strategy for the coordination of multiple distributed generators in an islanded microgrid (MG). A finite-time secondary frequency control approach is developed to eliminate the frequency deviation and maintain accurate active power sharing in a finite-time manner. It is demonstrated that the traditional distributed control approach with asymptotical convergence is just a special case of the proposed finite-time control strategy under the specific control parameter settings. Then, a secondary voltage control approach is presented to regulate the average voltage magnitude of all distributed generators to the desired value and achieve accurate reactive power sharing. The implementation of the proposed distributed control strategy only requires information exchange among neighboring local controllers through a sparse communication network. Simulations with an islanded MG testbed built in MATLAB/Simulink are conducted to validate the effectiveness of the proposed distributed control strategy.

Design of a Cooperative Voltage Harmonic Compensation Strategy for Islanded Microgrids Combining Virtual Admittance and Repetitive Controller

Nonlinear loads (NLLs) in three-phase systems are known to produce current harmonics at −5, 7, −11, 13,… times the fundamental frequency. However, harmonics of the same frequencies are induced in microgrid voltage thereby reducing the power quality. Dedicated equipment, such as active power filters, can be used to compensate the microgrid harmonics. Alternatively, each distributed generation (DG) unit present in the microgrid can also be used for the same. The use of the virtual admittance concept combined with a proportional integral with resonant controller (PI-RES) control structure has previously been proposed as a harmonic compensation sharing strategy when multiple DGs operate in parallel. The drawback of this methodology is that a large number of RES controllers might be required to compensate for all the harmonic components induced by NLLs, increasing the tuning complexity as well as the execution time. This paper proposes the combined use of virtual admittance control loop and repetitive controller (RC) for harmonic compensation. The main advantage of the proposed method is that only one RC is required to compensate for all the harmonic components, significantly reducing the computational burden and the design complexity. The dynamic performance of the whole system is tested under variable NLL.