Showing papers on "Transient (oscillation) published in 2019"
TL;DR: It is shown that transient instability can occur to the droop-controlled VSC when its current is saturated under large disturbances and a stability enhanced P-f droop control is proposed to deal with this instability problem.
Abstract: In the modern power grid, distributed generators are widely connected to the grid via voltage source converters (VSCs). Analyzing the transient stability of VSCs under large disturbances is useful for maintaining the security of the grid. However, this topic is very little studied. In this paper, the transient stability behavior of the droop-controlled VSC is theoretically explained. In particular, it is shown that transient instability can occur to the droop-controlled VSC when its current is saturated under large disturbances. In addition, the dynamics of the VSC under voltage sags that could incur instability problem is elaborately studied to consider special non-fault disturbances. To deal with this instability problem, a stability enhanced P-f droop control is proposed. Simulations and hardware-in-the-loop experiments verify the validity of the transient stability analysis and the effectiveness of the proposed control scheme.
254 citations
200 citations
TL;DR: Transient angle stability of a VSG is investigated by Lyapunov’s direct method and an enhanced control strategy is presented to improve the transient angle stability by adjusting the reference power.
Abstract: With an increasing number of distributed energy resources integrated into the power system, inverters need to take on the corresponding responsibility for the security and stability of the system. Virtual synchronous generators (VSGs) are proposed to mimic dynamic characteristics of traditional rotational synchronous generators (RSGs) to compensate for the loss of inertia and reserve capacity. Similar to RSGs, VSGs will experience transient angle instability under certain conditions, which likely threatens the system security. In this paper, transient angle stability of a VSG is investigated by Lyapunov’s direct method. The deteriorative effect of reactive power control loop on transient angle stability is first analyzed and then voltage variation is incorporated into an approximate Lyapunov’s direct method. In this method, the inverter internal voltage is treated as a parameter rather than a state variable. Moreover, the influence of different parameters on transient angle stability is studied. Finally, an enhanced control strategy is presented to improve the transient angle stability by adjusting the reference power. Numerical simulation results are presented to validate the effectiveness of the proposed method and the enhanced control.
192 citations
TL;DR: A fault identification method based on the difference of square of transient voltages to identify the faulted lines for DC grids using overhead lines and a line protection scheme including detection activation, fault identification, faulted pole discrimination, and post-fault re-closing is designed.
Abstract: Fast and reliable DC fault detection is one of the main challenges for modular multilevel converter (MMC) based DC grid with DC circuit breakers (DCCBs). This paper extracts the high-frequency components in transient voltages by wavelet transform and proposes a fault identification method based on the difference of square of transient voltages to identify the faulted lines for DC grids using overhead lines. Meanwhile, a faulted pole discrimination method based on the difference between the change of positive and negative pole voltages is presented. A line protection scheme including detection activation, fault identification, faulted pole discrimination, and post-fault re-closing is designed. Using only the local measurements, the scheme can realize the protection of the whole line without communication and has the capability of fault resistance endurance and anti-disturbance. The proposed method is tested with a four-terminal MMC-based DC grid in PSCAD/EMTDC. The selection methods of threshold values are presented and the impact of DCCB operation on the reliability of DC fault protection is analyzed. Simulation results verify the fast detection and reliability of the designed DC line protection scheme.
160 citations
TL;DR: In this article, the impact of low voltage ride-through (LVRT) and dynamic voltage support (DVS) capability on short-term voltage stability and Fault-Induced Delayed Voltage Recovery (FIDVR) was investigated.
Abstract: This paper investigates the impact of: 1) the Low Voltage Ride-Through (LVRT) and Dynamic Voltage Support (DVS) capability; 2) the active current recovery rate; 3) the local voltage control; and 4) the plant-level voltage control of large-scale PhotoVoltaic (PV) systems on Short-Term (ST) voltage stability and Fault-Induced Delayed Voltage Recovery (FIDVR). Moreover, the influence on transient and frequency stability is studied briefly. To evaluate FIDVR, a novel metric, the so-called Voltage Recovery Index (VRI), is defined. The studies are performed with the WECC generic PV system model on an IEEE voltage stability test system, namely the Nordic test system. The results show that without LVRT capability the system is ST voltage and transient unstable. Only the LVRT and DVS capability help to avoid ST voltage and transient instability. Considering voltage and frequency dynamics, an active current recovery rate of 100%/s shows the best performance. To further enhance voltage dynamics, plant-level voltage control together with local coordinated reactive power/voltage control should be applied. Moreover, the VRI provides useful information about the FIDVR and helps to compare different ST voltage controls.
84 citations
TL;DR: A relay coordination scheme is proposed for the faulted section isolation in a dc ring bus microgrid and the maloperation of a relay due to the communication failure in the unit protection scheme can be averted by applying the proposed method using local data.
Abstract: A fast and accurate protection scheme for a dc microgrid enhances the service reliability and improves the power quality. A fault in any section of a dc microgrid results in oscillation in current, where its frequency is a function of fault position. The frequency and associated transient power of the first cycle of the oscillation are used for fault detection and faulted section identification, respectively. Based on the inverse-time transient power, a relay coordination scheme is proposed for the faulted section isolation in a dc ring bus microgrid. The maloperation of a relay due to the communication failure in the unit protection scheme can be averted by applying the proposed method using local data. The performance of the method is tested using data obtained from PSCAD/EMTDC simulations for numerous cases including bidirectional power flow situation, high fault resistance, and different fault types. The proposed algorithm is also validated on a scaled-down hardware setup in the laboratory.
69 citations
TL;DR: The simulation results demonstrate that the proposed technique exhibits high reliability and leads to faster detection of islanding condition as compared to the existing passive islanding detection methods not only for zero active and reactive power mismatch conditions, but also for transient events caused due to nonlinear loads.
Abstract: In this paper, transient response of the microgrid caused due to unintended switching events and faults have been investigated in distributed generation (DG) system. The proposed technique is based on two new criteria transient index value (TIV) and positive sequence superimposed current angle at point of common coupling. The proposed method utilizes three phase voltage signals at DG end to compute the TIV. The performance of the proposed integrated approach has been evaluated on a sample test system and a practical distribution network consisting of combined heat and power plant, wind turbine generators, and photovoltaic system. The simulation results demonstrate that the proposed technique exhibits high reliability and leads to faster detection of islanding condition as compared to the existing passive islanding detection methods not only for zero active and reactive power mismatch conditions, but also for transient events caused due to nonlinear loads.
69 citations
27 May 2019
TL;DR: dVOC is a promising decentralized control strategy that requires only local measurements to induce grid-forming behavior with programmable droop characteristics and is dispatchable–i.e., the inverters can vary their power generation via user-defined power set-points and guarantees strong stability.
Abstract: This paper presents an analysis and experimental validation of dispatchable virtual oscillator control (dVOC) for inverter-dominated power systems. dVOC is a promising decentralized control strategy that requires only local measurements to induce grid-forming behavior with programmable droop characteristics. It is dispatchable–i.e., the inverters can vary their power generation via user-defined power set-points and guarantees strong stability. To verify its feasibility, a testbed comprising multiple dVOC-programmed inverters with transmission line impedances is designed. With an embedded synchronization strategy, the dVOC inverters are capable of dynamic synchronization, black start operation, and transient grid voltage regulation with dynamic load sharing, and real-time-programmable droop characteristics for backward compatibility. All these features are experimentally verified.
68 citations
TL;DR: The proposed lead-lag controlled BESS manifests better transient performance than BESS with PI-lead and traditional PI controller, in the event of divergent temporary and permanent faults.
Abstract: This paper investigates the enactment of battery energy storage system (BESS) and static compensator (STATCOM) in enhancing large-scale power system transient voltage and frequency stability, and improving power export capacity within two interconnected power systems. A PI-lead and lead-lag controlled BESS is proposed for multimachine power system to provide simultaneous voltage and frequency regulation within the defined battery state-of-charge ranges and an equivalent Finnish transmission grid is used to evaluate the system performance. According to Australian National Electricity Market grid requirements, the performances of the proposed control schemes are compared with conventional PI controlled BESS and STATCOM under multiple temporary and permanent fault conditions. In addition, two adjacent disturbance events are also applied to evaluate system performance with BESS and STATCOM. Through simulation results, it is shown that when there is a ${\text{44}\%}$ increase in power export and the STATCOM fails, incorporating BESS improves the performance and justifies the novelty of this study. Moreover, the proposed lead-lag controlled BESS manifests better transient performance than BESS with PI-lead and traditional PI controller, in the event of divergent temporary and permanent faults.
65 citations
TL;DR: In this article, a segmented asymmetrical thermoelectric generator (SASTEG) is numerically investigated to optimize its electrical performance and mechanical reliability under transient and steady state conditions.
64 citations
TL;DR: In this article, the authors present an in-depth analysis on the transient stability of the PSC-VSC by means of the phase portrait, which reveals that the power synchronization control will maintain synchronization with the grid as long as there are equilibrium points after the transient disturbance.
Abstract: The power synchronization control (PSC) has been increasingly used with voltage-source converters (VSCs) connected to the weak ac grid. This paper presents an in-depth analysis on the transient stability of the PSC-VSC by means of the phase portrait. It is revealed that the PSC-VSC will maintain synchronization with the grid as long as there are equilibrium points after the transient disturbance. In contrast, during grid faults without any equilibrium points, the critical-clearing angle (CCA) for the PSC-VSC is identified, which is found equal to the power angle of the unstable equilibrium point of the postfault operation. This fixed CCA facilitates the design of power system protection. Moreover, it is also found that the PSC-VSC can still resynchronize with the grid after around one cycle of oscillation, even if the fault-clearing angle is beyond the CCA. This feature reduces the risk of system collapse caused by the delayed fault clearance. These findings are corroborated by simulations and experimental tests.
TL;DR: Comparisons to other competing recent algorithms such as satin bowerbird algorithm, grasshopper optimizer and genetic algorithm indicate the viability of the proposed ISO-based method in defining the unknown parameters of the SOFCs efficiently.
TL;DR: A three-stage workflow to remove the high-frequency motion-induced noise using the wavelet neural network (WNN) is developed, and the results provide a strong data foundation for the subsequent processing procedures.
Abstract: In helicopter-borne transient electromagnetic (HTEM) signal processing, removal of motion-induced noise is one of the most important steps. A special type of short-term noise, which could b...
TL;DR: In this article, a numerical simulation of transient hydrogen-natural gas mixture flow in a looped network is studied based on a mathematical model that considers the variation of the compressibility factor of the gas mixture with pressure under isothermal gas flow.
TL;DR: This paper presents a novel model predictive control (MPC) for the T-type single-phase three-level inverters, where the cumbersome procedure in tuning of weighting factors is eliminated and the implementation of the proposed MPC becomes easy.
Abstract: This paper presents a novel model predictive control (MPC) for the T-type single-phase three-level inverters. The cumbersome procedure in tuning of weighting factors is eliminated so that the implementation of the proposed MPC becomes easy. The constant switching frequency is achieved during the control implementation in order to facilitate the filter design. In order to optimize the distribution of the output current harmonics, multiple voltage vectors are employed in each control cycle with their application times setting inversely proportion to the respective cost function. The redundant small voltage vectors are utilized to balance the neutral point voltage of the inverter by directly regulating the upper and lower dc-link capacitors voltages. Finally, the proposed MPC algorithm is experimentally evaluated and compared with other two unfixed switching frequency MPC algorithms in terms of the steady state, transient performance, and parameter sensitivity.
TL;DR: A health index definition is proposed, which allows the condition of the insulation of an electrical apparatus to be assessed as a function of operation time, and, based on the aging and life models, the evaluation of maintenance actions and of the feasibility and extent of life extension plans to be carried out.
Abstract: Distributed generation, dc transmission and distribution, and power electronics for ac/dc/ac conversion bring the advantages of increased control and flexibility in electric power management. These advantages also introduce challenges that must be managed. An electrical environment where voltage is not anymore strictly sinusoidal implies that a new approach for the design and maintenance of electrical insulation systems has to be devised. Non-sinusoidal voltage supply often causes increased failure probability and, thus, reduced reliability and life of an electrical asset. This research addresses the implications of the transient and steady waveform distortion introduced by power electronic systems and dc supply, for which the electrical insulation was designed and tested through consolidated criteria based on sinusoidal voltage supply. Based on condition monitoring, a health index definition is proposed, which allows the condition of the insulation of an electrical apparatus to be assessed as a function of operation time, and, based on the aging and life models, the evaluation of maintenance actions and of the feasibility and extent of life extension plans to be carried out.
TL;DR: There is a growing need for detailed investigation of the top 30 to 50 meters of the subsurface, which is critical for infrastructure, water supply, aquifer storage and recovery, farming, waste dep... as mentioned in this paper.
Abstract: There is a growing need for detailed investigation of the top 30–50 m of the subsurface, which is critical for infrastructure, water supply, aquifer storage and recovery, farming, waste dep...
TL;DR: This study presents a comprehensive review of related experimental studies, novel numerical methods and strategies along with transient characteristics and formation mechanisms in hydraulic-machine systems and suggestions have been made concerning the selection of simulation methods.
Abstract: Over the past decade, the use of conventional one-dimensional numerical-simulation methods has been demonstrated to be inadequate in terms of their usefulness in investigations concerning transient processes in hydraulic machines systems—their theoretical analyses and engineering applications. Consequently, numerous three-dimensional numerical methods capable of accurately simulating transient processes in hydraulic-machine systems have been proposed and improved upon in recent years. Through use of these novel methods and strategies, many researchers have investigated transient characteristics of processes occurring within hydraulic-machine systems along with corresponding formation mechanisms. This study presents a comprehensive review of related experimental studies, novel numerical methods and strategies along with transient characteristics and formation mechanisms in hydraulic-machine systems. Based on this study, suggestions have been made concerning the selection of simulation methods to be used and directions for future research have been proposed.
TL;DR: Analysis of transient voltages in the case of dc line faults in modular multilevel converter (MMC)-based HVDC grid and simulations show that the proposed protection method not only can detect faults rapidly and accurately, but is also effective in detecting large-resistance faults.
TL;DR: An analysis of permanent magnet synchronous generator (PMSG)-based WECSs under vector control and direct torque control provides the basis for combining salient features of the two control methods into a reliable and effective control system to provide enhanced machine performance.
Abstract: Fast transient and smooth steady-state performance of wind energy conversion systems (WECSs) is essential for sustained power conversion and grid code fulfilment including low voltage ride through capability. In this paper, an analysis of permanent magnet synchronous generator (PMSG)-based WECSs under vector control and direct torque control provides the basis for combining salient features of the two control methods into a reliable and effective control system to provide enhanced machine performance. The system includes two hysteresis current controllers in connection with an inverter-switching table. The proposed control provides fast transient and smooth steady-state performance for machine side converter of PMSGs, which controls dc-link voltage under grid fault conditions. Extensive simulation results on a 2-MW PMSG-based WECS demonstrate the desired performance of the proposed control system under both grid-normal and -fault conditions.
TL;DR: In this article, a rotating magnet serves as the transmitter and a bioresorbable antenna as the remote receiver, with capabilities for operation at low frequencies (<200 Hz, and the results demonstrate the elimination of impedance matching and electromagnetic radiation exposure presented with the types of radio frequency energy harvesters.
Abstract: Bioresorbable electronic technologies form the basis for classes of biomedical devices that undergo complete physical and chemical dissolution after a predefined operational period, thereby eliminating the costs and risks associated with secondary surgical extraction. A continuing area of opportunity is in the development of strategies for power supply for these systems, where previous studies demonstrate some utility for biodegradable batteries, radio frequency harvesters, solar cells, and others. This paper introduces a type of bioresorbable system for wireless power transfer, in which a rotating magnet serves as the transmitter and a bioresorbable antenna as the remote receiver, with capabilities for operation at low frequencies (<200 Hz). Systematic experimental and numerical studies demonstrate several unique advantages of this system, most significantly the elimination of impedance matching and electromagnetic radiation exposure presented with the types of radio frequency energy harvesters explored previously. These results add to the portfolio of power supply options in bioresorbable electronic implants.
TL;DR: The proposed FTFM-based reconstruction method indicates attractive prospects in the following two aspects: effective but efficient TFM learning for practical and on-line application, sound and adaptive signal reconstruction with the data-driven F TFM basis.
TL;DR: A novel optimum design of the proportional–integral (PI) controller in the power converter circuits using the water cycle algorithm (WCA) to augment the transient stability of a grid-connected wave energy conversion (WEC) system.
Abstract: This paper introduces a novel optimum design of the proportional–integral (PI) controller in the power converter circuits using the water cycle algorithm (WCA) to augment the transient stability of a grid-connected wave energy conversion (WEC) system. The proposed system relies on the Archimedes wave swing device, which is coupled with a linear permanent magnet synchronous generator (LPMSG). The WEC system is interfaced with the power grid via a generator-side converter (GSC) and a grid-side inverter (GSI). The GSC is used to control both of the d -axis and q -axis current of the LPMSG to minimize its power losses and extract its maximum real power, respectively. The GSI is implemented to control the terminal voltage at the point of common coupling and the dc-link voltage through a complete vector control scheme. The proposed optimal WCA-based PI control strategy is applied to both converters. The optimization process depends on the simulation-based optimization approach. In the proposed approach, the criterion of integral squared error is chosen as a multiobjective function. To validate the proposed WEC system model, the simulation results are compared with the practical results, and their error reaches less than 1%. The effectiveness of the proposed WCA-based PI control strategy is tested and compared with that obtained using the genetic-algorithm-based PI control scheme under symmetrical and unsymmetrical grid fault conditions taking into account a successful and unsuccessful reclosure of circuit breakers. The validity of the proposed control strategy is extensively checked based on simulation studies in the PSCAD/EMTDC environment.
TL;DR: This paper presents the 13th-order nonlinear model of a dc/ac droop controlled inverter connected to an infinite bus to address inverter stability and aims to present the best model to use for time domain simulations and domain of attraction estimation.
Abstract: The transient stability of inverter-based microgrids is important given the low inertia of microgrids especially in islanded mode. However, as a prerequisite to understanding transient stability of such microgrids, the transient stability of individual inverters requires further analysis. To address inverter stability, this paper presents the 13th-order nonlinear model of a dc/ac droop controlled inverter connected to an infinite bus. The singular perturbation method was used to decompose the nonlinear model into 11th, 9th, 7th, 5th, 3rd, and 1st-order models. The aim of the study is to understand the accuracy and validity of the reduced order models in replicating the performance of the full order nonlinear model. The performance of each model is investigated using two different tools, time domain simulations and Lyapunov functions for the estimation of the domain of attraction. The work aims to present the best model to use for time domain simulations and domain of attraction estimation. Results show that certain reduced order models are capable of accurately reproducing the performance of the full order model while others can be used to gain insights into those areas of study. This will enable future studies to save computational effort and produce the most accurate results according to the needs of the study being performed.
TL;DR: In this paper, a positive-sequence model for photovoltaic (PV) power plants is derived from physics and controls first principles, which includes phase-locked loops (PLLs) and dc-side dynamics, which are typically unmodeled in classical transient stability studies.
Abstract: Transmission faults caused by recent wildfires in California have induced the disconnection of utility-scale converters in photovoltaic (PV) power plants. Postmortem investigations reported that tripping commands were caused by phase-locked loops (PLLs) and dc-side dynamics, which are typically unmodeled in classical transient stability studies. Since existing simulation packages rely on simplified models that neglect these dynamics, they have a limited capability to predict converter behavior during faults. To address this shortcoming, we set forth a positive-sequence model for PV power plants that is derived from physics and controls first principles. As seen on utility-scale three-phase converters, the model includes PLLs, dc-side dynamics, and closed-loop controllers. Instances of the developed model are integrated into illustrative power systems containing conventional generators. Numerical simulations of the obtained multi-machine multi-converter power systems are assessed via a suitable set of stability and performance metrics.
TL;DR: Power quality improvement for effective power transfer in a grid-integrated solar photovoltaic-wind energy hybrid system is presented and results show that scenario-III best fulfilled the dynamic compensation requirement among all cases.
TL;DR: In this article, a self-powered solid-state circuit breaker (SSCB) with a digitally controlled current-time profile for both ultrafast short-circuit protection and overcurrent protection is proposed.
Abstract: DC distribution networks are able to effectively improve the energy efficiency and easy integration of distributed generations. However, the reliable dc circuit breaker is an essential requisite for the wide application of dc power. This paper proposes a self-powered solid-state circuit breaker (SSCB) with a digitally controlled current–time profile for both ultrafast short-circuit protection and overcurrent protection. The fault detection unit detects short-circuit or overcurrent conditions by sensing the sampling resistance voltage and delivers these voltage signals to a low-cost microprocessor to realize the protection operation of the SSCB. A pulsewidth modulation (PWM) current limiting protection method with time interval $T_{d}$ is proposed to avoid nuisance tripping caused by inrush current during power electronic load startup. The time interval is properly selected based on the transient thermal properties of silicon carbide (SiC) junction gate field-effect transistors (JFETs). In order to verify the dynamic response of the SSCB, a SiC JFET-based circuit breaker prototype is designed and fabricated for result confirmation.