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Showing papers on "Voltage sag published in 2014"


Journal ArticleDOI
TL;DR: In this article, the LVRT capability of three mainstream single-phase transformerless PV inverters under grid faults is explored in order to map future challenges, and control strategies with reactive power injection are also discussed.
Abstract: Transformerless photovoltaic (PV) inverters are going to be more widely adopted in order to achieve high efficiency, as the penetration level of PV systems is continuously booming. However, problems may arise in highly PV-integrated distribution systems. For example, a sudden stoppage of all PV systems due to anti-islanding protection may contribute to grid disturbances. Thus, standards featuring with ancillary services for the next-generation PV systems are under a revision in some countries. The future PV systems have to provide a full range of services as what the conventional power plants do, e.g., low-voltage ride-through (LVRT) under grid faults and grid support service. In order to map future challenges, the LVRT capability of three mainstream single-phase transformerless PV inverters under grid faults is explored in this paper. Control strategies with reactive power injection are also discussed. The selected inverters are the full-bridge (FB) inverter with bipolar modulation, the FB inverter with dc bypass, and the Highly Efficient and Reliable Inverter Concept (HERIC). A 1-kW single-phase grid-connected PV system is analyzed to verify the discussions. The tests confirmed that, although the HERIC inverter is the best candidate in terms of efficiency, it is not very particularly feasible in case of a voltage sag. The other two topologies are capable of providing reactive current during LVRT. A benchmarking of those inverters is also provided in this paper, which offers the possibility to select appropriate devices and to further optimize the transformerless system.

307 citations


Journal ArticleDOI
TL;DR: In this article, a phase-locked loop (PLL)-based seamless transfer control method between grid-connected and islanding modes in a three-phase gridconnected inverter is proposed.
Abstract: This paper proposes a phase-locked loop (PLL)-based seamless transfer control method between grid-connected and islanding modes in a three-phase grid-connected inverter. The PLL is used to synchronize the phase of the load voltage to a grid voltage in grid-connected operation, and to generate an angle with the desired frequency in islanding operation. The stability of both the grid current loop for grid-connected operation and the load voltage control loop for islanding operation is analyzed. The phase and magnitude of the load voltage are successively matched to the grid voltage for a seamless transfer from islanding to grid-connected operation. When grid voltage sag occurs, an operating sequence including a PLL operation is suggested in order to transfer smoothly to islanding operation and to provide a stable and seamless voltage to a sensitive load under the voltage sag condition. The simulation and experimental results are carried out to verify the effectiveness of the proposed algorithm.

162 citations


Journal ArticleDOI
TL;DR: In this article, different voltage injection schemes for dynamic voltage restorers (DVRs) are analyzed with particular focus on a new method used to minimize the rating of the voltage source converter (VSC) used in DVRs.
Abstract: In this paper, different voltage injection schemes for dynamic voltage restorers (DVRs) are analyzed with particular focus on a new method used to minimize the rating of the voltage source converter (VSC) used in DVR. A new control technique is proposed to control the capacitor-supported DVR. The control of a DVR is demonstrated with a reduced-rating VSC. The reference load voltage is estimated using the unit vectors. The synchronous reference frame theory is used for the conversion of voltages from rotating vectors to the stationary frame. The compensation of the voltage sag, swell, and harmonics is demonstrated using a reduced-rating DVR.

157 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented a comprehensive theoretical analysis and experimental verification of dead-time effect in the isolated bidirectional full-bridge dc-dc converter (IBDC) with all operation states.
Abstract: As the development of isolated bidirectional full-bridge dc-dc converter (IBDC), the dead-time effect has become an apparent issue. This paper presents a comprehensive theoretical analysis and experimental verification of dead-time effect in the IBDC. Besides the internal power transfer and phase drift phenomena mentioned in previous works, there are also many other novel phenomena caused by the dead time, such as voltage polarity reversal and voltage sag phenomena, etc. The paper gives a detailed switching characterization of the IBDC with dead-time effect in all operation states. On this basis, the transmission power characterization is analyzed comprehensively. Compared to the traditional theoretical model, the transmission power model with dead-time effect is not a strictly monotone increasing function, the relation curve is not symmetric around the median axis, and the zero point is not achieved at zero phase-shift ratio. In addition, in different operation states, the characterization is also different. Finally, experimental results verify the theoretical analysis.

144 citations


Journal ArticleDOI
TL;DR: In this paper, a new algorithm to generate reference voltage for a distribution static compensator (DSTATCOM) operating in voltage-control mode is proposed, where the reference voltage is arbitrarily taken as 1.0 p.u.
Abstract: This paper proposes a new algorithm to generate reference voltage for a distribution static compensator (DSTATCOM) operating in voltage-control mode. The proposed scheme exhibits several advantages compared to traditional voltage-controlled DSTATCOM where the reference voltage is arbitrarily taken as 1.0 p.u. The proposed scheme ensures that unity power factor (UPF) is achieved at the load terminal during nominal operation, which is not possible in the traditional method. Also, the compensator injects lower currents and, therefore, reduces losses in the feeder and voltage-source inverter. Further, a saving in the rating of DSTATCOM is achieved which increases its capacity to mitigate voltage sag. Nearly UPF is maintained, while regulating voltage at the load terminal, during load change. The state-space model of DSTATCOM is incorporated with the deadbeat predictive controller for fast load voltage regulation during voltage disturbances. With these features, this scheme allows DSTATCOM to tackle power-quality issues by providing power factor correction, harmonic elimination, load balancing, and voltage regulation based on the load requirement. Simulation and experimental results are presented to demonstrate the efficacy of the proposed algorithm.

135 citations


Journal ArticleDOI
TL;DR: The topic of voltage support is open for further research, and the control scheme proposed in this paper can be viewed as an interesting configuration to devise other control strategies in future works.
Abstract: Static synchronous compensators have been broadly employed for the provision of electrical ac network services, which include voltage regulation, network balance, and stability improvement. Several studies of such compensators have also been conducted to improve the ac network operation during unbalanced voltage sags. This paper presents a complete control scheme intended for synchronous compensators operating under these abnormal network conditions. In particular, this control scheme introduces two contributions: a novel reactive current reference generator and a new voltage support control loop. The current reference generator has as a main feature the capacity to supply the required reactive current even when the voltage drops in amplitude during the voltage sag. Thus, a safe system operation is easily guaranteed by fixing the limit required current to the maximum rated current. The voltage control loop is able to implement several control strategies by setting two voltage set points. In this paper, three voltage support control strategies are proposed, and their advantages and limitations are discussed in detail. The two theoretical contributions of this paper have been validated by experimental results. Certainly, the topic of voltage support is open for further research, and the control scheme proposed in this paper can be viewed as an interesting configuration to devise other control strategies in future works.

129 citations


Journal ArticleDOI
TL;DR: In this paper, a fault-location method based on smart feeder meters with voltage sag monitoring capability is proposed, where the main idea is to explore voltage measurements from monitors placed in different buses of distribution systems to estimate the fault location.
Abstract: This paper proposes a fault-location method based on smart feeder meters with voltage sag monitoring capability. The main idea is to explore voltage measurements from monitors placed in different buses of distribution systems to estimate the fault location. The estimation is achieved by relating the voltage deviation measured by each meter to the fault current calculated based on the bus impedance matrix, considering the fault in different points. In order to improve the method accuracy, the loads are represented by constant impedance models and included into the bus impedance matrix. The performance of the proposed method is demonstrated by using a real distribution system. Sensitivity studies results show that the method is robust since it has good performance for different values of fault resistance, quantity, and location of the smart meters.

122 citations


Journal ArticleDOI
TL;DR: In this paper, a control scheme for DVR topologies with an ac-ac converter, based on the characterization of voltage sags, is proposed to mitigate voltage sag with phase jump.
Abstract: Voltage sag remains a serious power-quality (PQ) problem by being the most common and causing more economic losses. The dynamic voltage restorer (DVR) is a definitive solution to address the voltage-related PQ problems. Conventional topologies operate with a dc link, which makes them bulkier and costlier; it also imposes limits on the compensation capability of the DVR. Topologies with the same functionality, operating without the dc link by utilizing a direct ac-ac converter, are preferable over the conventional ones. Since no storage device is employed, these topologies require improved information on instantaneous voltages at the point of common coupling and need flexible control schemes depending on these voltages. Therefore, a control scheme for DVR topologies with an ac-ac converter, based on the characterization of voltage sags is proposed in this paper to mitigate voltage sags with phase jump. The proposed control scheme is tested on an interphase ac-ac converter topology to validate its efficacy. Detailed simulations to support the same have been carried out in MATLAB, and the results are presented. The results of real-time testing of the scheme on a single-phase model of the topology to compensate various sag types using DSPF28335 are also presented.

86 citations


Journal ArticleDOI
TL;DR: This paper deals with a three-phase hybrid transformer (HT) without dc energy storage to compensate voltage sags and swells and to protect sensitive loads against the rapid and extensive changes in supply voltage amplitude.
Abstract: The parameters of electrical energy such as voltage amplitude are very important, particularly from the viewpoint of the final consumer and sensitive loads connected to the grid. The dynamic states in the power grid-deep voltage sags and swells-might cause faults and defects in sensitive loads. This paper deals with a three-phase hybrid transformer (HT) without dc energy storage to compensate voltage sags and swells and to protect sensitive loads against the rapid and extensive changes in supply voltage amplitude. The analyzed HT contains two main units: the first one is the conventional electromagnetic transformer, realizing an electromagnetic coupling, and the second one is the buck-boost matrix-reactance chopper, realizing an electrical coupling in the HT unit. In the presented solution, output voltage is transformed in two ways-electromagnetically and electrically. This paper presents an operational description, the theoretical analysis, and the experimental test results from a 2-kVA laboratory model. On the basis of the authors' research, it can be stated that the HT makes it possible to compensate deep voltage sags (deeper than 50% of nominal source voltage) and overvoltages (up to 140% of nominal source voltage) while maintaining good dynamic properties. The main advantages of the proposed solution, in comparison to other conventional solutions, are the ability to control the output voltage in the range of 0.66-3.5 US, good dynamics (transient state during source voltage uS amplitude change is shorter than 10 ms), and galvanic separation between source and load (such as in the case of the conventional electromagnetic transformer).

81 citations


Journal ArticleDOI
TL;DR: In this paper, a multilevel inverter-based dynamic voltage restorer (DVR) was proposed to improve the quality of output voltage in both deep and shallow voltage sags.
Abstract: Dynamic voltage restorer (DVR) is a power electronic converter-based custom power device used to compensate for voltage variations. The inverter used in the DVR structure can have different topologies. Multilevel inverters are a good candidate to be used in the DVR structure especially in higher voltage level. This study proposes a new scheme for DVR based on a multilevel inverter. In the proposed DVR, a dc-dc converter is attached to the multilevel inverter. The dc-link voltage is regulated by the dc-dc converter considering the voltage sag magnitude. In this way, the output voltage of the multilevel inverter has always its maximum possible number of levels. This results in better quality of output voltage in both deep and shallow voltage sags. It is important to emphasise that the existing inverter-based DVR topologies do not have this capability. Also, in the proposed DVR, there is no need for an output filter. Moreover, the fundamental frequency control method for the multilevel inverter can be used instead of pulse width modulation-based methods. This can result in lower switching losses and lower switching stresses. The mathematical analysis of the operation range of the proposed DVR is given in detail. The simulation results using Power System Computer Aided Design/Electromagnetic Transient including DC (PSCAD/EMTDC) as well as the experimental results from a laboratory prototype verify the proposed DVR scheme.

79 citations


Journal ArticleDOI
TL;DR: In this paper, a sag-based design for phase-angle control for UPQC (UPQC-SPAC) is proposed to mitigate a given value of voltage sag, and the same is used during a healthy operating condition in order to provide reactive power compensation of a distribution network.
Abstract: This paper presents an investigative study on the impact of unified power-quality conditioner (UPQC) allocation on radial distribution systems. A design approach for UPQC, called sag-based design for phase-angle control for UPQC (UPQC-SPAC) is proposed. The phase-angle shifting of the load voltage required to mitigate a given value of voltage sag is determined and the same is used during a healthy operating condition in order to provide the reactive power compensation of a distribution network. To study the impact of the UPQC-SPAC allocation on distribution systems, it is placed at each node, except the substation node, one at a time. The load-flow algorithm for radial distribution systems is suitably modified to incorporate the UPQC-SPAC model. The simulation results show that a significant amount of power-loss reduction, under voltage mitigation, and the enhancement of voltage stability margin can be obtained with an appropriate placement of the UPQC-SPAC in a distribution network. The performance comparison of the UPQC-SPAC with one previously reported design approach shows that it is more efficient in undervoltage mitigation. An appropriate allocation of the UPQC-SPAC is also found to be beneficial for the networks with distributed-generation units.

Journal ArticleDOI
TL;DR: In this paper, a phase-locked loop (PLL) is proposed to operate as an independent single-phase PLL in the context of three-phase systems, where the extracted information allows the independent control of both the active and reactive powers for each phase.
Abstract: This letter proposes a phase-locked loop (PLL) able to operate as an independent single-phase PLL in the context of three-phase systems. Its key advantage is that the extracted information allows the independent control of both the active and reactive powers for each phase. The proposed PLL utilizes moving average filters and, hence, remains robust under unbalanced and highly distorted voltages. A frequency estimator is also presented and incorporated in the PLL angle detector path to make it frequency adaptive. The performance of the proposed PLL is verified experimentally and results for frequency change, phase-angle jump, and unbalanced voltage sag are reported as a confirmation of its potential.

Journal ArticleDOI
TL;DR: In this article, an enhanced resonant control strategy for the unified power quality conditioner (UPQC) is proposed to simultaneously tackle voltage sags, unbalance and distortions on the supply side as well as current harmonics on the load side.
Abstract: This study proposes an enhanced resonant control strategy for the unified power quality conditioner (UPQC) to simultaneously tackle voltage sags, unbalance and distortions on the supply side as well as current harmonics on the load side. The proposed control strategy is developed in both the series and shunt active power filters (APFs) of the UPQC. In the series APF, a proportional-resonant controller and a resonant controller are employed to mitigate voltage sags, unbalance and distortions, whereas a proportional-integral (PI) controller and three vector PI controllers are used in the shunt APF to compensate harmonic currents. The performance of the proposed UPQC control scheme is significantly improved compared with the conventional control strategy owing to the superiority of the resonant controllers. In addition, voltage sag/harmonic and current harmonic detectors are not required in the proposed control scheme, which helps to simplify the control strategy and to improve the control accuracy. The proposed control strategy is theoretically analysed and its feasibility is validated through experiments.

Journal ArticleDOI
TL;DR: In this paper, the authors present a design method based on the analysis of oscillations in nonlinear systems, which proceeds by first developing simple and ac- curate models of the power system, second revealing the system features through an in deep analysis of the derived models, and third introducing a systematic design procedure for tuning the parameters of the control schemes.
Abstract: Three-phase inverters equipped with voltage support control schemes have been successfully used to alleviate the nega- tive impact of voltage imbalance on electric power systems. With these schemes, dc-link voltage ripple and current harmonics are significantly reduced by processing the positive and negative se- quence components separately. However, the design methods for tuning the parameters of these control schemes have one or more of the following limitations: 1) the design is a very time-consuming task, 2) it is conservative, 3) it does not guarantee the specifications for all the considered situations, and 4) the system can be unstable in some abnormal conditions. As an alternative, this paper presents a design method based on the analysis of oscillations in nonlinear systems. The method proceeds by first developing simple and ac- curate models of the power system, second it reveals the system features through an in deep analysis of the derived models, and third it introduces a systematic design procedure for tuning the parameters of the control schemes. As an example, a voltage sup- port control scheme for a three-phase inverter operating under an unbalanced voltage sag is designed and validated experimentally.

Journal ArticleDOI
TL;DR: In this article, a phase-locked loop (PLL) algorithm is employed for phase-angle detection of single-phase utility grid voltage, and a detailed stability analysis is performed, as well as its performance is evaluated under several power quality problems.
Abstract: This study proposes a phase-locked loop (PLL) algorithm employed for phase-angle detection of single-phase utility grid voltage. A detailed stability analysis is performed, as well as its performance is evaluated under several power quality problems. The proposed PLL structure is based on the instantaneous active power theory for three-phase power systems (pPLL), which is investigated into the fictitious two-phase stationary reference frame (αβ-pPLL). A non-autonomous adaptive filter (AF) operates in conjunction with the PLL, and its main function is to extract the fundamental component of the utility grid voltage allowing the rejection of voltage harmonics. The stability analysis of the proposed AF-αβ-pPLL scheme is carried out in order to provide adequate tuning procedures for choosing the parameters used in the proposed algorithm. In addition, the dynamic response and robustness of the AF-αβ-pPLL algorithm are evaluated by means of simulation and experimental tests, under utility grid disturbances, such as voltage harmonics, voltage sag, phase jumps and frequency variations. To emphasise the effectiveness of the algorithm, a comparative analysis with three other single-phase PLL schemes is carried out, such as the conventional power-based PLL (pPLL), the two-phase stationary reference frame pPLL (αβ-pPLL) and the well-known enhanced PLL (EPLL).

Journal ArticleDOI
TL;DR: In this paper, a fast-converged estimation approach, which directly extracts amplitudes and phase angles of symmetrical components of desired frequencies from harmonic-distorted network voltages, is proposed.

01 Jan 2014
TL;DR: In this paper, the transient response analysis of vector proportional-integral (VPI) controllers and proportional-resonant (PR) controllers for grid-connected applications is discussed.
Abstract: This study deepens on the transient response analysis of the so-called vector proportional-integral (VPI) controllers and compares them with the popular proportional-resonant (PR) controllers for grid-connected applications. The employed methodology is based on the study of the error signal roots: both reference tracking and disturbance rejection abilities are considered for proper gain tuning. This study proves that PR controllers lead to shorter settling times than VPI controllers. A three-phase voltage source converter prototype has been implemented. Experimental results comparing the transient behaviour of VPI and PR controllers in different conditions are provided: a + 90° phase-angle jump in the current reference and a 'type C' voltage sag at the point of common coupling.

Journal ArticleDOI
TL;DR: In this paper, a new formulation of a composite, constrained objective function is put forward by considering objectives such as the cost of the power losses, the costs of the DGs and the cost for loss of load because of voltage sag and the constraints such as line flow limits, number/size of the installed DGs, and the power quality limits of the standard IEEE-519.
Abstract: The present study proposes a method of solving the distributed generations (DGs) placement problem by considering multiple aspects of a power system operation. In addition to the commonly considered objectives of reduction of the loss and improvement of the voltage profile, this study has optimised other power quality related objectives such as minimisation of the voltage sag and harmonic distortion. A new formulation of a composite, constrained objective function is put forward by considering objectives such as the cost of the power losses, the cost of the DGs and the cost of loss of load because of the voltage sag and the constraints such as line flow limits, number/size of the installed DGs and the power quality limits of the standard IEEE-519. The system under consideration is a complex one consisting of both linear and non-linear loads as well as the power factor correcting capacitors. The effect of the non-linear harmonic generating loads and the compensating capacitors on the penetration of the DGs in the distribution system is investigated. This optimisation problem is solved for several distribution systems by using several metaheuristic optimisation techniques. However, detailed results are presented on a benchmark IEEE 33 bus radial distribution system using genetic algorithm to demonstrate the effectiveness of the proposed method. A comparative performance analysis of various metaheuristic optimisation techniques is also presented to show the applicability of different optimisation techniques in solving the proposed optimisation problem.

Journal ArticleDOI
TL;DR: In this article, the transient response analysis of vector proportional-integral (VPI) controllers and proportional-resonant (PR) controllers for grid-connected applications is discussed.
Abstract: This study deepens on the transient response analysis of the so-called vector proportional-integral (VPI) controllers and compares them with the popular proportional-resonant (PR) controllers for grid-connected applications. The employed methodology is based on the study of the error signal roots: both reference tracking and disturbance rejection abilities are considered for proper gain tuning. This study proves that PR controllers lead to shorter settling times than VPI controllers. A three-phase voltage source converter prototype has been implemented. Experimental results comparing the transient behaviour of VPI and PR controllers in different conditions are provided: a + 90° phase-angle jump in the current reference and a `type C' voltage sag at the point of common coupling.

Journal ArticleDOI
TL;DR: In this paper, a new control structure is presented for considering the voltage sag as the main objective and voltage total harmonic distortion (THD) as the second objective of DVR controller.
Abstract: Dynamic voltage restorer (DVR) is one of the custom power devices for compensating power quality indices which is used. The main function of DVR that is discussed in many studies is to compensate voltage sag at times when faults occur. For the first time, a new control structure is presented for considering the voltage sag as the main objective and voltage total harmonic distortion (THD) as the second objective of DVR controller. In this strategy, a new and powerful optimisation algorithm (known as chaotic accelerated particle swarm optimisation (CAPSO)) which is an improved version of particle swarm optimisation algorithm is used for determining the coefficients of the proportional-integral controller of DVR. These coefficients are determined in a way that voltage sag is considered as the main objective of optimisation algorithm and voltage THD is considered as its second objective. By fuzzifying the objectives, an appropriate objective function is proposed for the optimisation process. Results obtained from simulation and a comparison made between these results and those of other controllers show that the proposed strategy outperforms other strategies.

Journal ArticleDOI
TL;DR: In this article, a fast discrete S-transform (ST)-based time-frequency signal analyzer has been proposed for the detection, classification, and monitoring of power quality (PQ) disturbances varying in an electric power system.
Abstract: SUMMARY In this paper, a new fast discrete S-transform (ST)-based time-frequency signal analyzer has been proposed for the detection, classification, and monitoring of power quality (PQ) disturbances varying in an electric power system. The proposed algorithm is based on the generalized Fourier algorithm that is used to obtain the time-localized spectral characteristics of the time-varying voltage and current signals belonging to PQ events. The fast ST algorithm is realized with different types of frequency scaling, band pass filtering, and interpolation techniques based on Heisenberg's uncertainty principle resulting in a reduced computation cost. In the conventional ST, the window width decreases at higher frequencies with a reduction in frequency resolution and conversely at low frequencies with wider windows. Therefore, the time-varying PQ disturbance signal is down sampled at low frequencies and cropped at high frequencies resulting in the evaluation of a fewer samples. From the time–frequency matrix output, important features are extracted and used with a binary decision tree for an accurate classification of single and simultaneous PQ events. Further, a unified approach is presented to track the time-varying PQ disturbance waveforms like voltage sag, swell, harmonics, and oscillatory transients and produce estimation of their amplitudes and phase angles. Copyright © 2013 John Wiley & Sons, Ltd.

Journal ArticleDOI
01 Nov 2014
TL;DR: The results of the paper demonstrate that compensating and controlling the voltage THD signal in the control process has caused more improvement in the voltage sag of the sensitive load.
Abstract: Presenting self-tuning PI controller based on human brain emotional learning to control DVR.Suggesting a bi-objective structure for emotional controller to satisfy voltage sag and THD.Considering sensitivity of the controller's coefficients, they are regulated by an algorithm.TLBO algorithm is used to optimize emotional controller's parameters.Convergence speed and final answer are great better in TLBO algorithm than PSO algorithm. DVR is one of the custom power devices for compensating power quality indices. A self-tuning controller with a bi-objective structure is presented for controlling the DVR compensator in order to improve the THD and voltage sag indices of a sensitive load in the network. In this paper, the emotional controller which is based on emotional learning of human brain is proposed for controlling the DVR compensator. This controller has such a structure that makes it capable of considering a second objective in the control process of the system. So far, this capability of the emotional controller has not been used in any researches. The results of the paper demonstrate that compensating and controlling the voltage THD signal in the control process has caused more improvement in the voltage sag of the sensitive load. It was reported that the performance of the emotional controller depends on the selection of the values of its coefficients. Therefore, in order to better improve the proposed controller, these coefficients are tuned by an optimization algorithm. Teaching-learning-based optimization algorithm is considered as optimization algorithm to regulate these coefficients. According to simulation results, it works significantly better than classic PI controller and some intelligent controllers that have introduced in other researches already.

Proceedings ArticleDOI
27 Jul 2014
TL;DR: In this article, a fault-location method based on smart feeder meters with voltage sag monitoring capability is proposed, where the main idea is to explore voltage measurements from monitors placed in different buses of distribution systems to estimate the fault location.
Abstract: This paper proposes a fault-location method based on smart feeder meters with voltage sag monitoring capability The main idea is to explore voltage measurements from monitors placed in different buses of distribution systems to estimate the fault location The estimation is achieved by relating the voltage deviation measured by each meter to the fault current calculated based on the bus impedance matrix, considering the fault in different points In order to improve the method accuracy, the loads are represented by constant impedance models and included into the bus impedance matrix The performance of the proposed method is demonstrated by using a real distribution system Sensitivity studies results show that the method is robust since it has good performance for different values of fault resistance, quantity, and location of the smart meters

Journal ArticleDOI
TL;DR: In this article, the authors proposed a fault ride through strategy for inverter-based DGs to properly control in the fault condition instead of disconnecting from the grid in the case of high penetration of DGs, which leads to voltage sag problem.

Proceedings ArticleDOI
14 Apr 2014
TL;DR: In this paper, series dynamic braking resistor (SDBR) is proposed to counteract the effect of faults in the grid side and hence prevents the voltage sag in grid side to enhance the low voltage ride through (LVRT) capability of the PV plant.
Abstract: Penetration of Photovoltaic (PV) power to the grid is increasing very rapidly. Energy regulatory body is imposing much stricter grid code due to this high penetration of the PV power. Grid connected PV system encounters different types of abnormalities during grid faults. When the fault appears in the grid side, the point of common coupling (PCC) voltage will go very low which will cause the DC link voltage very high for power balancing. This high DC link voltage may damage the inverter. Also, the voltage sag will force the PV system to be disconnected from the grid according to grid code. And shutdown of large PV plant may have adverse effect in power system operation. This study proposes series dynamic braking resistor (SDBR) to counteract the effect of faults in the grid side and hence prevents the voltage sag in grid side. Improving voltage sag by the proposed method will enhance the low voltage ride through (LVRT) capability of the PV plant. The effectiveness of the proposed method is verified by applying the most severe fault (three-phase-to-ground fault). The terminal voltage obtained with proposed protection scheme maintains the grid code, and hence the PV systems need not to be disconnected from the grid during fault.

01 Jan 2014
TL;DR: In this article, a nine-switch power conditioner is proposed to convert the topological short comings of the 9-switch converter into interesting performance advantages, and an appropriate discontinuous modulation scheme is proposed and studied in detail to doubly ensure that maximal reduction of commutations is achieved.
Abstract: The nine-switch converter has already been proven to have certain advantages, in addition to it s component saving topological feature A nine-switch power converter having two sets of output terminals was recently proposed in place of the traditional back-to-back power converter that uses 12 switches in total . Instead of accepting these tradeoffs as limitations, a nine-switch power conditioner is proposed here that virtually "converts" most of these topological short comings into interesting performance advantages. Despite these advantages, the nine-switch converter has so far found limited applications due to its many perceived performance tradeoffs like requiring an oversized dc-link capacitor, limited amplitude sharing and constrained phase shift between its two sets of output terminals. With an appropriately designed control scheme then incorporated, the nine-switch converter is shown to favorably raise the overall power quality in experiment, hence justifying its role as a power conditioner at a reduced semiconductor cost. Aiming further to reduce its switching losses, an appropriate discontinuous modulation scheme is proposed and studied here in detail to doubly ensure that maximal reduction of commutations is achieved.


Journal ArticleDOI
TL;DR: In this article, an interline dynamic voltage restorer (IDVR) is employed in distribution systems to mitigate voltage sag/swell problems, where one DVR compensates for the local voltage sag in its feeder, the other DVR replenishes the common dc-link voltage.
Abstract: An interline dynamic voltage restorer (IDVR) is invariably employed in distribution systems to mitigate voltage sag/swell problems. An IDVR merely consists of several dynamic voltage restorers (DVRs) sharing a common dc link connecting independent feeders to secure electric power to critical loads. While one of the DVRs compensates for the local voltage sag in its feeder, the other DVRs replenish the common dc-link voltage. For normal voltage levels, the DVRs should be bypassed. Instead of bypassing the DVRs in normal conditions, this paper proposes operating the DVRs, if needed, to improve the displacement factor (DF) of one of the involved feeders. DF improvement can be achieved via active and reactive power exchange (PQ sharing) between different feeders. To successfully apply this concept, several constraints are addressed throughout the paper. Simulation and experimental results elucidate and substantiate the proposed concept.

Proceedings ArticleDOI
18 May 2014
TL;DR: In this article, a theoretical analysis that traces the trajectory of state variable of the system during voltage sag is represented to justify the effect of the characteristics of symmetrical and unsymmetrical voltage sags.
Abstract: Virtual Synchronous Generator (VSG) is an inverter control structure that supports power system stability by imitating a synchronous machine. Because of the limitation in inverter power and current, their operation under disturbances should be evaluated and enhanced. In this paper, the VSG unit response to different types of faults at grid side is assessed. Besides, a theoretical analysis that traces the trajectory of state variable of the system during voltage sag is represented to justify the effect of the characteristics of symmetrical and unsymmetrical voltage sags. Knowing the critical characteristics (duration and initial point-on-wave) of each type of voltage sag created by fault, proper measures can be embedded to eliminate the hazardous consequences of voltage sags. Furthermore, three additional controllers for voltage sag ride-through enhancement are implemented and tested by experiments.

Journal ArticleDOI
TL;DR: In this paper, the standards for interconnection of wind generators to local grid during healthy and fault conditions have been discussed, and the LVRT scheme has been validated based on MATLAB-SIMULINK simulation.