Additional Control Strategies Research Articles

Control Strategies for Mitigating Power Quality Issues in Renewable Energy coordinated Microgrid - A Comprehensive Review

Abstract Renewable Energy technologies are becoming more and more common for generating electricity because they are environmentally friendly and can meet local electricity needs. They reduce network congestion and also lighten the load on conventional based power plants. Over the past few decades, grid-connected renewable energy systems have seen a rise in the significance of Power Quality issues, particularly as a result of the extensive usage of nonlinear electronics and the intermittent nature of these systems. With the emergence of power electronic converters through powerful control technology, renewable energy systems be interconnected to a large extent with the power grid or used as isolation systems in remote areas. Using additional competent control strategies can enhance not only improve the concert of these systems, but also caliber the quality of energy generated, distributed and used at the load side of Power System. Hence, this paper reviews various control strategies adopted for alleviation of power quality staples of renewable energy coordinated microgrid system and further recommendations are provided to solve power quality issues as future research.

Fast excitation structure for improving the transient time of magnetic controlled reactors

With the increasing proportion of renewable energy usage, the randomness and volatility of renewable energy have led to a corresponding increase in the demand for reactive power regulation in the power system. Magnetic controlled reactor (MCR) is one of the technical and economic means used to solve problems such as reactive power compensation and voltage regulation in the power system. However, the transient time of traditional MCR is relatively long compared to other reactive power compensation devices, which limits the further application of MCR. At present, most methods for optimizing the dynamic response time of MCR are to add additional circuits or change control strategies, which will increase the difficulty of MCR control and reduce stability. Therefore, without adding additional circuit structure and control difficulty, this paper proposes a three-phase MCR fast excitation structure that changes the winding connection method, which can improve the DC voltage in the control circuit and reduce the transient time of the MCR. A magnetic circuit model in the MCR core under the fast excitation structure is built and analyzed, based on which, the transient time of the MCR is mathematically calculated. A fast excitation MCR simulation model was constructed based on MATLAB/Simulink platform for dynamic response test simulation. Compared with typical MCR simulation results, the transient time was reduced from 400 ms to 37.1 ms. Dynamic response tests were conducted on a three-phase MCR prototype of 35 kV/18 Mvar, and drop test indicates that the fast excitation structure could reduce the transient time of the three-phase MCR prototype to 36.6 ms, which substantiate the precision of mathematical and simulation results and the efficacy of the fast excitation structure.

A triple‐LC‐based DC/DC converter with wide input voltage gain in both under‐resonance and over‐resonance frequency regions

AbstractIn recent years, wide voltage range DC/DC converters have been widely used in telecom power, solar generation and electric vehicle charger applications. Based on this, a new multi‐resonant converter with wide input voltage is proposed here. Compared with the traditional LLC converter, the proposed converter can maintain the output voltage within a narrow frequency regulation range in both under‐resonance and over‐resonance areas. Thus, a wide voltage range can be realized without additional switch components or complex control strategies. The topology and the corresponding working principle of the proposed converter are introduced. In addition, the equivalent model by considering the fundamental wave is established and the influence of the resonance parameters on the voltage gain characteristic is analysed in detail. With these considerations, the resonance parameters are designed. Finally, a 500 W experiment platform is established to verify the effectiveness and feasibility of the proposed converter.

Towards humanlike grasp in robotic hands: mechanical implementation of force synergies

In the field of robotic hands, finger force coordination is usually achieved by complex mechanical structures and control systems. This study presents the design of a novel transmission system inspired from the physiological concept of force synergies, aiming to simplify the control of multifingered robotic hands. To this end, we collected human finger force data during six isometric grasping tasks, and force synergies (i.e. the synergy weightings and the corresponding activation coefficients) were extracted from the concatenated force data to explore their potential for force modulation. We then implemented two force synergies with a cable-driven transmission mechanism consisting of two spring-loaded sliders and five V-shaped bars. Specifically, we used fixed synergy weightings to determine the stiffness of the compression springs, and the displacements of sliders were determined by time-varying activation coefficients. The derived transmission system was then used to drive a five-finger robotic hand named SYN hand. We also designed a motion encoder to selectively activate desired fingers, making it possible for two motors to empower a variety of hand postures. Experiments on the prototype demonstrate successful grasp of a wide range of objects in everyday life, and the finger force distribution of SYN hand can approximate that of human hand during six typical tasks. To our best knowledge, this study shows the first attempt to mechanically implement force synergies for finger force modulation in a robotic hand. In comparison to state-of-the-art robotic hands with similar functionality, the proposed hand can distribute humanlike force ratios on the fingers by simple position control, rather than resorting to additional force sensors or complex control strategies. The outcome of this study may provide alternatives for the design of novel anthropomorphic robotic hands, and thus show application prospects in the field of hand prostheses and exoskeletons.

A Novel Decentralized Frequency Regulation Method of Renewable Energy Stations Based on Minimum Reserve Capacity for Renewable Energy-Dominated Power Systems

In this paper, we propose a novel decentralized frequency regulation method for renewable energy-dominated power systems. First, the system is modularized into unified frequency regulation modules composed of synchronous generators(SGs) and renewable energy stations. Then, based on the aggregation model of the module, a renewable energy station frequency regulation method based on robust control barrier functions(RCBFs) is proposed to ensure that the frequency deviation is limited, and an additional switching control strategy is complemented to avoid the long-term suspension of over-high quasi-steady-state frequency. The proposed method is still applicable under the coordination of multiple renewable energy stations. Each renewable energy station deploys decentralized control based on local information, which can support fast frequency response. The robustness of frequency response time constants of renewable energy stations and frequency dead zone are considered, which makes the control method easy to implement. A module transient frequency stability margin index based on reserve capacity is proposed, which can be used to guide the system planning and operation. Finally, simulation results validate the applicability of the proposed method, demonstrating its efficacy in regulating frequency in renewable energy-dominated power systems.

Optimization of the Fast Frequency Regulation Strategy for Energy Storage-Assisted Photovoltaic Power Stations

Photovoltaic (PV) power generation is characterized by randomness and intermittency, resulting in unpredictable fluctuations in output power. This presents a significant challenge to the stable operation of the grid. To address this issue, the integration of energy storage systems provides a solution to mitigate the volatility of PV output, ensuring stability and precise control. In this study, we propose an ASS-Elman-based equivalent droop control strategy for PV power stations participating in grid frequency regulation. Furthermore, a joint PV-energy storage frequency regulation system is developed. For energy storage power stations actively engaged in grid frequency regulation, we employ an adaptive droop control strategy to enhance the traditional droop control method by incorporating additional frequency control strategies. We validate the effectiveness of the proposed strategies through simulation using MATLAB/SIMULINK. The results demonstrate that these strategies maximize the potential of energy storage and PV systems to comprehensively regulate frequency and significantly improve primary frequency regulation performance.

Research on fast frequency response to AC grid of a battery‐free MVDC system incorporating a high proportion of distributed photovoltaic generation units with reserve capacity

AbstractWith the fast development of renewable energy, system operators intend to require renewable energy generation to have more grid support capabilities. This paper studies the grid‐connected control strategy of a battery‐free medium‐voltage direct current (MVDC) system with distributed photovoltaic generation units (DPVGUs), aiming to realize the rapid grid support function to AC grid frequency. Firstly, a scheme for the MVDC system can keep some reserve capacity is provided. At this moment, DPVGUs execute a master‐slave coordinated control strategy, that is, the master DPVGU adopts an improved DC constant voltage control strategy to maintain the MVDC bus voltage, and the remaining DPVGUs adopt an improved droop control strategy to quickly provide corresponding power. Secondly, when the frequency deviation of AC grid exceeds the deadband of primary frequency control, fast frequency response (FFR) control strategy of the modular multilevel converter is proposed, aiming to actively transmit some or all of the reserved power of the MVDC system to the AC grid and can quickly provide frequency support to AC grid. In FFR control strategy, an additional control strategy is added on the vector control strategy. Finally, simulation studies are carried out in RTDS to verify the effectiveness of the proposed control scheme.

Assessing the Impact of Organic and Chemical Herbicides on Agronomic Parameters, Yield, and Weed Control Efficiency in Lentil (Lens culinaris Medik.) under a Direct-Seeding System: A Comparative analysis

Lentil is characterized by low weed competitiveness due to its small size and slow development, resulting in the reduction of quality and quantity of production. Controlling these weeds with biological alternatives is necessary because lentils are phytotoxic to most herbicides. To address this gap, a field experiment was carried out at the pedagogical research farm of the National School of Agriculture in Meknes, Morocco, for two years, to evaluate the effectiveness of two weeds control strategies; chemical and agroecological. Three treatments, including a Nettle aqueous extract (T3) and two herbicides (Bentazone (T2) and Pyridate (T1)), were compared to the control (T0) in a complete randomized block design with four replications. All treatments resulted in effective weed management in terms of density and biomass, and significant improvement in agronomic parameters compared to the control. However, both herbicides used had a phytotoxic effect on the lentil plants, and the minimum yield was achieved in plots untreated (6.61Qx/ha) followed by plots treated with Pyridate. In contrast, Nettle aqueous extract had no phytotoxic effect, with the highest protein content in the lentil’s seeds, the highest economic grain, and a yield almost similar to that of Bentazone. Our study highlights the advantages of using organic Nettle treatment over herbicides for weed control, promoting sustainable agricultural practices. However, further research is needed to explore additional weed control strategies in lentil crops comprehensively.

Antagonistic Magneto-Rheological Actuators with Inherent Output Boundedness: An Ideal Solution for High-Performance and Human-Safe Actuation

This paper studies the working principles of antagonistic magneto-rheological (MR) actuators, i.e., a combination of an electric motor and a pair of MR clutches in an antagonistic configuration, for compliant actuation in robotics. The study focuses on the unique boundedness property exhibited by MR actuators, which limits the output torques delivered to the load, independent of the received input torque and/or control commands. This inherent property is of significant importance for ensuring human safety in human–robot interaction applications. Through a comprehensive analysis, we provide analytical proof of the inherent output boundedness of antagonistic MR actuators and validate our findings through experimental results. Our research demonstrates that these actuators are well-suited for safe operations in robotic applications, eliminating the need for additional sensor measurements or complex control strategies. This promising capability enables the avoidance of trade-offs between actuator performance, complexity, and cost. The insights gained from this study contribute to advancing compliant actuation technology, paving the way for high-performance and human-safe robotic systems.

Strategies for the Biological Control of Parthenium hysterophorus L. in Eastern Pakistan

Abstract The arrival of the invasive agricultural weed parthenium, Parthenium hysterophorus , in Pakistan was first noted in the Gujrat district of the Punjab Province in 1980. The plant has now spread further in the Punjab Province as well as into Khyber Pakhtunkhwa (KP), the Islamabad Capital Territory (ICT) and Azad Jammu and Kashmir. The heartlands of parthenium infestation are in the central and northern districts of Punjab, the ICT and KP, and the weed is moving into the southern parts of Punjab and north-eastern KP. Given parthenium’s highly invasive nature, it is likely that it has already spread into the southern parts of Punjab, especially as the area is home to extensive irrigated farming, and it is possible that the plant has even reached Sind and Baluchistan provinces in the south and south-west of Pakistan. To date, two biological control agents for parthenium have reached Pakistan without being introduced deliberately, most likely arriving from India or Nepal: Zygogramma bicolorata – the Mexican or parthenium leaf beetle – and Puccinia abrupta partheniicola , or winter rust. This case study assesses the effectiveness of these existing biological control agents in Pakistan, the potential of redistribution projects to increase their impact and whether artificially inducing Z. bicolorata to emerge from diapause early could further stem parthenium growth in spring. The second part of the case describes the importation of the stem-boring weevil Listronotus setosipennis into a quarantine facility for host range testing. The plan is to boost Pakistan’s biological control programme by releasing the weevil in areas where parthenium occurs. Finally, the case also recommends additional biological control agents and strategies for the future. Adapted from: The biological control of Parthenium hysterophorus L. in Pakistan: Status quo and future prospects'. Management of Biological Invasions (2021), Volume 12, Issue 3: pages 509-526. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International - CC BY 4.0). Information © CAB International 2023

Control of fully heat-integrated pressure-swing distillation with strict pressure manipulation: A case study of separating a maximum-boiling azeotrope with small pressure-induced shift

Pressure-swing distillation (PSD) is an alternative configuration used to separate pressure-sensitive azeotropes and avoid product contamination(s) in extractive or heterogeneous azeotropic distillation via the entrainer(s). Full heat integration between high- and low-pressure columns (HPC and LPC) can provide significant energy savings compared to the conventional case, while it also loses the control degree of freedom, trim condenser or reboiler heat load, via the integrated condenser/reboiler exchanger. Typically, the pressure of HPC is left uncontrolled, and additional pressure-compensated control strategies are implemented, which may create safety issues. To address this, the study proposes adding an auxiliary cooling-water-driven condenser to the fully heat-integrated PSD system, providing an extra manipulated variable to regulate the pressure of HPC. Compared to the conventional PSD system, the new modified process could achieve a 26.31% reduction in total annual cost. The research uses the maximum-boiling azeotropic mixture of acetone/chloroform as a case study which makes the distillation system characterized by high reflux ratios and a large recycle flow rate, leading to the unwelcome snowball effect. To achieve effective process control, robust control structures are proposed that rigorously regulate the pressure of the column by manipulating the heat removal in the trim condenser, attenuating or eliminating potential overpressure issues. Product purity and other evaluation indicators, such as product transient deviations, offsets, integral absolute error, and oscillation degrees, are also considered. Results show that the proposed control schemes can efficiently control the pressure of HPC, weaken the snowball effect, and maintain product purity. This study highlights the importance of pressure control for fully heat-integrated PSD systems, particularly for pressure-sensitive azeotropes with small pressure-induced shifts.

Multicell nonisolated resonant modular multilevel dc‐dc converter with self‐voltage balancing and step‐up conversion

SummaryWith the rapid development of renewable energy power generation technologies in high‐voltage direct‐current (HVDC) system, the high step‐up ratio dc‐dc conversion plays an important role to connect dc grids with different voltage levels. This paper presents a multicell nonisolated resonant modular multilevel dc–dc converter (MMDC) for medium‐ and high‐voltage applications. The converter exhibits expandability without using transformer. Moreover, by adding additional switched‐inductor (SL) cells, switched‐capacitor (SC) cells, and the upper arm submodules (SMs), the proposed converter can obtain high gain with low voltage stresses on switches and diodes. The operating states of SMs is regulated by the carrier phase‐shifted pulse width modulation (CPS‐PWM) to guarantee the number of inserted SMs is constant to support the high‐side load at any moment. The converter is operated in resonant mode with resonance between SM capacitors and arm inductor. The step‐up ratio could be regulated by adjusting the number of SL cells, SC cells, and upper arm SMs; thus, more flexible voltage regulation can be realized. In addition, the proposed converter has the voltage self‐balancing capability of capacitors in SMs and SC‐cells without additional balancing control strategy. The topology configuration, parameter design guideline, operating principle, and comparison with other MMDCs are presented. Finally, the theoretical analysis is verified by the simulation and bench‐scaled experimental prototype results.

Ivermectin as a novel malaria control tool: Getting ahead of the resistance curse

Reduction in malaria clinical cases is strongly dependent on the ability to prevent Anopheles infectious bites. Vector control strategies using long-lasting insecticidal nets and indoor residual spraying with insecticides have contributed to significantly reduce the incidence of malaria in many endemic countries, especially in the Sub-Saharan region. However, global progress in reducing malaria cases has plateaued since 2015 mostly due to the increased insecticide resistance and behavioral changes in Anopheles vectors. Additional control strategies are thus required to further reduce the burden of malaria and contain the spread of resistant and invasive Anopheles vectors. The use of endectocides such as ivermectin as an additional malaria control tool is now receiving increased attention, driven by its different mode of action compared to insecticides used so far and its excellent safety record for humans. In this opinion article, we discuss the advantages and disadvantages of using ivermectin for malaria control with a focus on the risk of selecting ivermectin resistance in malaria vectors. We also highlight the importance of understanding how ivermectin resistance could develop in mosquitoes and what its underlying mechanisms and associated molecular markers are, and propose a research agenda to manage this phenomenon.

A ground fault section location method based on active detection approach for non-effectively grounded DC distribution networks

Identifying and locating the single-pole-to-ground fault for the non-effectively grounded DC distribution networks is highly challenging due to the topology arrangement limitations and the grounding mode. To solve this problem, a ground fault section location method based on active detection approach is proposed. Firstly, an approach based on an additional control strategy in coordination with a resonant branch setup is proposed to inject the detection signals. Then, the parameters of the resonant branch and the detection signals to be injected are obtained after careful consideration to ensure the optimal distribution characteristics of the injected signals. Finally, a protection principle based on a coordinating time interval scheme is proposed to locate and isolate the fault section according to the single terminal information. Simulation results show that the proposed method achieves excellent performance.

A novel approach to biological risk surveillance in occupational hygiene: A case study on the use of quantitative microbial risk assessment to determine occupational risks for wastewater treatment plants workers in Costa Rica

Wastewater treatment is essential for preventing infectious diseases and water pollution. To perform this process, workers operate and maintain wastewater treatment plants (WWTPs); thus, they are exposed to the many pathogens in domestic wastewater. Consequently, it is necessary assess occupational exposure to pathogens in WWTPs. Quantitative microbial risk assessment (QMRA) is an approach for estimating the risk posed by a specific pathogen which can be useful for occupational hygiene assessments of biological risk. In this study, we applied QMRA, informed by occupational field surveillance, to estimate the potential risk for WWTP workers. Furthermore, we used simulations to test additional control strategies such as personal protective equipment (PPE). The QMRA was conducted for three WWTPs in Costa Rica with data collected between May 2020 and May 2021. Observation in each workplace showed a need for more consistent application of risk reduction strategies in the work environment, especially in behavior, infrastructure, and use of appropriate PPE. Cryptosporidium sp., Giardia sp., norovirus, and enterovirus genus were measured and detected in the WWTPs, and the treatment performance was unsatisfactory. As a result, the total health disease burden was higher than the benchmark for drinking water recommended by WHO (1.00 × 10−6 DALY per person per year) by between one and three magnitudes orders in all WWTPs for the three exposure scenarios (operation, maintenance, and visitors). The simulation demonstrated that using PPE could reduce the estimated disease burden by nearly two orders of magnitude. Still, this control measure did not reach a level below the benchmark risk (less than 1.00 × 10−6 DALY per person per year) for the WWTP workers. This study highlights the importance of using PPE with other control measures, such as automation or barriers, to isolate exposure sources. However, this study employed an uncommon approach in occupational health and hygiene, which combined field inspections, survival analysis, and QMRA, using field surveillance to understand the occupational environment and potential exposure routes, which is crucial for hazard identification and risk assessment. In addition, exposure modeling and QMRA were used to simulate different control scenarios, providing a robust estimate of potential risks associated with occupational exposure.

Differential impact of dual-active ingredient long-lasting insecticidal nets on primary malaria vectors: a secondary analysis of a 3-year, single-blind, cluster-randomised controlled trial in rural Tanzania

Gains in malaria control are threatened by widespread pyrethroid resistance in malaria vectors across sub-Saharan Africa. New long-lasting insecticidal nets (LLINs) containing two active ingredients (dual active-ingredient LLINs) have been developed to interrupt transmission in areas of pyrethroid resistance. We aimed to evaluate the effectiveness of three dual active-ingredient LLINs compared with standard pyrethroid LLINs against pyrethroid-resistant malaria vectors in rural Tanzania. In this study, we did a secondary analysis of entomological data from a four-group, 3 year, single-blind, cluster-randomised controlled trial carried out between Feb 18, 2019, and Dec 6, 2021. We conducted quarterly indoor mosquito collections using the Centers for Disease Control and Prevention light trap, in eight houses in each of the 84 study clusters in the Misungwi district, northwestern Tanzania. Anopheles vectors were then tested for malaria parasites and identified at species level, to distinguish between sibling species of the Anopheles gambiae and Anopheles funestus groups, using molecular laboratory techniques. The primary outcomes were density of different malaria vector species measured as the number of female Anopheles collected per household per night, the entomological inoculation rate (EIR), an indicator of malaria transmission, and sporozoite rate. Entomological outcomes were assessed on the basis of intention to treat, and the effect of the three dual active-ingredient LLINs was compared with the standard pyrethroid LLINs at household level. Dual active-ingredient LLINs had the greatest effect on Anopheles funestus sl, the most efficient vector in the study area, with comparatively weak effect on An arabiensis. An funestus density was 3∙1 per house per night in the pyrethroid LLIN group, 1∙2 in the chlorfenapyr pyrethroid LLIN group (adjusted density ratio [aDR]=0∙26, 95% CI 0∙17-0∙14, p<0∙0001), 1∙4 in the piperonyl-butoxide pyrethroid LLIN group (aDR=0∙49, 0∙32-0∙76, p=0∙0012), and 3∙0 in the pyriproxyfen pyrethroid LLIN group (aDR=0∙72, 0∙47-1∙11, p=0∙15). Malaria transmission intensity was also significantly lower in the chlorfenapyr pyrethroid group, with 0∙01 versus 0∙06 infective bites per household per night in the pyrethroid LLIN group (aDR=0∙21, 0∙14-0∙33, p<0∙0001). Ecological niche models indicated that vector-species distribution was stable following LLIN intervention despite the reductions observed in An funestus sl density. Chlorfenapyr pyrethroid LLINs were the most effective intervention against the main malaria vector An funestus sl over 3 years of community use, whereas the effect of piperonyl-butoxide pyrethroid LLIN was sustained for 2 years. The other vector, An arabiensis, was not controlled by any of the dual active-ingredient LLINs. Additional vector control tools and strategies targeted to locally prevalent vector species evading dual active-ingredient LLINs should be deployed to further reduce malaria transmission and achieve elimination. The Department for International Development, UK Medical Research Council, Wellcome Trust, the Department of Health and Social Care, and The Bill & Melinda Gates Foundation via the Innovative Vector Control Consortium.

A Triple Boost Seven-Level Common Ground Transformerless Inverter Topology for Grid-Connected Photovoltaic Applications

This article proposes a single-stage, seven-level (7L), switched-capacitor-based grid-connected inverter architecture with a common ground feature. This topology has the ability to boost the output voltage up to three times the input voltage. The proposed topology can diminish the leakage current in grid-connected photovoltaic (GC-PV) applications, and its capacitor voltages are self-balanced without any additional control strategies. The different operating modes are described in detail with their related mathematical expressions. The design of passive components and a detailed power loss analysis are presented. The merits of the proposed structure are demonstrated using a detailed comparative assessment. The grid-connected operation of the proposed inverter structure is simulated in the MATLAB/Simulink environment, and the results are presented. The laboratory prototype of 935 W is built and analyzed to validate the performance of the proposed structure.

Rejoinder: A formal causal interpretation of the case-crossover design.

We thank the discussants for their insightful commentary and questions. In our rejoinder, we extend our analysis to additional settings, control strategies, and sources of bias relevant to how case-crossover is often used in practice, as suggested by multiple discussants. In particular, we consider: control exposures that follow occurrence of events, settings with shared exposure trajectories (which are common in case-crossover studies of effects of air pollution), bias due to non-transient treatment effects, removing bias due to time trends in treatment using control subjects, and extending our results to the continuous time setting. We also take the opportunity to clarify an easily misinterpreted comment we made about collapsibility, which we thank Andersen and Martinussen for highlighting. Throughout, in the spirit of the discussants. contributions, we iterate between general bias formulas and simulations and numerical studies from illustrative simplified scenarios to build insight.

The additional control strategies to improve primary frequency response for hybrid power plant with gas turbines and steam turbines

Gas turbines with fast response characteristics make it possible to improve the flexibility of grid regulation. However, there are still some challenges in the connection of gas turbines. On the one hand, the difference of regulation rate between gas turbines and steam turbines causes the system to oscillate strongly. On the other hand, the connection of the gas turbine reduces the inertia of the system, thereby increasing the frequency deviation of the primary frequency response. Based on the above two problems, the additional control strategies are proposed in this paper. The strategies modify the voltage control and power control respectively, thereby improving the primary frequency response of the system. Moreover, a power plant and surrounding power grid in Taicang is chosen as the research object to validate the correctness of the additional control strategies proposed in this paper. The experimental results show that the proposed control strategy can well suppress the frequency oscillation and reduce the frequency deviation.

Transient Stability Analysis and Improved Control Strategy for DC-Link Voltage of DFIG-Based WT During LVRT

In this paper, the transient stability for dc-link voltage of doubly-fed induction generator (DFIG)-based wind turbine (WT) is studied in detail during low voltage ride-through (LVRT). Firstly, referring to the rotor swing equation of synchronous generator (SG), the nonlinear large-signal model of dc-link voltage is established. In addition, the damping power, static slip power, and dynamic slip power are derived. Consequently, the transient performance of dc-link voltage under the different operation conditions of DFIG is revealed during LVRT. Furthermore, the instability form of dc-link voltage with the moving process of equivalent power angle is analyzed by the energy function of dc-link voltage. In addition, the impacts of dc voltage control loop's parameter, the active current of the stator, and the slip on the stabilization process of dc-link voltage are studied. Analysis result indicates that the insufficient damping and large unbalanced power would deteriorate the transient behavior and steady-state level of dc-link voltage. Therefore, an additional damping and slip power feedforward control strategy is proposed, which can make the transition process of dc-link voltage smoother and significantly improve the voltage steady-state level. Finally, simulation and experimental results validate the effectiveness of theoretical analysis.