Capacitors are widely used in pulsed magnet power supplies to reduce ripple voltage,store energy,and decrease power variation.In this study,DC-link capacitors in pulsed power supplies were investigated.By deriving an ...Capacitors are widely used in pulsed magnet power supplies to reduce ripple voltage,store energy,and decrease power variation.In this study,DC-link capacitors in pulsed power supplies were investigated.By deriving an analytical method for the capacitor current on the H-bridge topology side,the root-mean-square value of the capacitor current was calculated,which helps in selecting the DC-link capacitors.The proposed method solves this problem quickly and with high accuracy.The current reconstruction of the DC-link capacitor is proposed to avoid structural damage in the capacitor’s current measurement,and the capacitor’s hotspot temperature and temperature rise are calculated using the FFT transform.The test results showed that the error between the calculated and measured temperature increases was within 1.5℃.Finally,the lifetime of DC-link capacitors was predicted based on Monte Carlo analysis.The proposed method can evaluate the reliability of DC-link capacitors in a non-isolated switching pulsed power supply for accelerators and is also applicable to film capacitors.展开更多
Frequency droop control is widely used in permanent magnet synchronous generators(PMSGs)based wind turbines(WTs)for grid frequency support.However,under frequency deviations,significant DC-link voltage fluctuations ma...Frequency droop control is widely used in permanent magnet synchronous generators(PMSGs)based wind turbines(WTs)for grid frequency support.However,under frequency deviations,significant DC-link voltage fluctuations may occur during the transient process due to sudden changes in real power of such WTs.To address this issue,a current feedforward control strategy is proposed for PMSG-based WTs to reduce DC-link voltage fluctuations when the WTs are providing frequency support under grid frequency deviations.Meanwhile,the desired frequency support capability of the PMSG-based WTs can be ensured.Simulation results verify the rationality of the analysis and the effectiveness of the proposed control method.展开更多
The prominence of Renewable Energy Sources(RES)in the process of power generation is exponentially increased in the recent days since these sources assist in minimizing the environmental contamination.A grid-tied DFIG...The prominence of Renewable Energy Sources(RES)in the process of power generation is exponentially increased in the recent days since these sources assist in minimizing the environmental contamination.A grid-tied DFIG(Doubly Fed Induction Generator)based WECS(Wind Energy Conversion System)is introduced in this work,in which a Landsman converter is implemented to impro-vise the output voltage of PV without anyfluctuations.A novel GA(Genetic Algorithm)assisted ANN(Artificial Neural Network)is employed for tracking the Maximum power from PV.Among the rotor and grid side controllers,the for-mer is implemented by combining the statorflux with d-q reference frame and the latter is realized by the PI controller.The proposed approach delivers better per-formance in the compensation of real and reactive power along with the DC link voltage control.The controlling mechanism is verified in both MATLAB and experimental bench setupby using an emulated wind turbine for the concurrent control of DC link potential,active and reactive powers.The source current THD is observed as 1.93%and 2.4%for simulation and hardware implementation respectively.展开更多
DC-link capacitors play a vital role in managing ripple voltage and current in converters and various devices.This study focuses on exploring the aging characteristics of DC-link capacitors in alternating humid and th...DC-link capacitors play a vital role in managing ripple voltage and current in converters and various devices.This study focuses on exploring the aging characteristics of DC-link capacitors in alternating humid and thermal environments aligned with the operational conditions in photovoltaic and wind power applications.Adhering to relevant power equipment standards,we designed a 24-h alternating humid and thermal aging environment tailored to the requirements of DC-link capacitors.An aging test platform is established,and 20 widely used metallized polypropylene film capacitors are selected for evaluation.Parameters such as the capacitance,equivalent series resistance(ESR),and phase angle are assessed during aging,as well as the onset time and extent of aging at various intervals.This study focuses on the aging mechanisms,analyzing electrode corrosion,the self-healing process,and dielectric aging.Fitting the aging characteristics enabled us to calculate the lifespan of the capacitor and predict it under different degrees of capacitance decay.The results show that under alternating humid and thermal conditions,capacitance attenuation and ESR increase exhibit exponential nonlinearity,influenced by factors such as the oxidation and self-healing of capacitive metal electrodes,dielectric main-chain fracture,and crystal transformation.This study underscores the pivotal role of encapsulation in determining the aging decay time.展开更多
Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters (VSCs). A constant dc-link voltage is usually assumed in existing literature to estimate transi...Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters (VSCs). A constant dc-link voltage is usually assumed in existing literature to estimate transient stability of virtual synchronous generators (VSGs). However, actual power supply in the dc-side of VSGs is limited and different dc-link voltage controllers are needed to achieve power balance between DC side and AC side. Addition of dc-link voltage controller has great influence on transient behavior of VSGs, which has not been investigated by previous research. To fill this gap, this paper gives insights into the effect of dc-link voltage dynamics on transient stability of VSGs. First, two typical kinds of VSGs with dc-link voltage controllers are introduced. Then, mathematical models considering dc-link dynamics are established and the effect of dc-link voltage controllers on transient synchronization stability of VSGs is revealed through equal area criterion (EAC). It is found that dc-link voltage controller would reduce stability margin of VSGs and design-oriented transient stability analysis is carried out quantitively using critical clearing time (CCT). Finally, simulation results are given to validate correctness of theoretical analysis.展开更多
This paper proposes a grid synchronization control strategy for the grid-connected voltage source converters(VSCs)based on the voltage dynamics of the DC-link capacitor in the VSC.The voltage dynamics of the DC-link c...This paper proposes a grid synchronization control strategy for the grid-connected voltage source converters(VSCs)based on the voltage dynamics of the DC-link capacitor in the VSC.The voltage dynamics of the DC-link capacitor are used to regulate the frequency and phase angle of the inner potential of the VSC,synchronizing the VSC with grid.Firstly,in the proposed strategy,the active power regulation and grid synchronization of the VSC are combined,which are separated in the traditional control strategy.This can avoid the instability of the VSC in a weak grid with a low short circuit ratio(SCR),aroused by the dynamic interaction between the separated control loops in traditional control strategies.Secondly,the energy stored in the DC-link capacitor is directly coupled with the grid via the inner potential of the VSC,and the inertia characteristic is naturally featured in the inner potential by the proposed strategy.With the increase of the capacitance,the natural inertial response of the VSC is helpful to improve the grid frequency dynamic.Finally,simulation results are presented to validate the correctness and effectiveness of the proposed strategy in the enhancement of the grid frequency and voltage dynamic support capability.展开更多
基金supported by the National Key Research and Development Program of China(No.2019YFA0405402).
文摘Capacitors are widely used in pulsed magnet power supplies to reduce ripple voltage,store energy,and decrease power variation.In this study,DC-link capacitors in pulsed power supplies were investigated.By deriving an analytical method for the capacitor current on the H-bridge topology side,the root-mean-square value of the capacitor current was calculated,which helps in selecting the DC-link capacitors.The proposed method solves this problem quickly and with high accuracy.The current reconstruction of the DC-link capacitor is proposed to avoid structural damage in the capacitor’s current measurement,and the capacitor’s hotspot temperature and temperature rise are calculated using the FFT transform.The test results showed that the error between the calculated and measured temperature increases was within 1.5℃.Finally,the lifetime of DC-link capacitors was predicted based on Monte Carlo analysis.The proposed method can evaluate the reliability of DC-link capacitors in a non-isolated switching pulsed power supply for accelerators and is also applicable to film capacitors.
基金This work is jointly supported by the National Key R&D Programme of China(No.2017YFB0902000)the National Natural Science Foundation of China(No.U1766206)the Science and Technology Programme of the State Grid Corporation(No.52110418000P).
文摘Frequency droop control is widely used in permanent magnet synchronous generators(PMSGs)based wind turbines(WTs)for grid frequency support.However,under frequency deviations,significant DC-link voltage fluctuations may occur during the transient process due to sudden changes in real power of such WTs.To address this issue,a current feedforward control strategy is proposed for PMSG-based WTs to reduce DC-link voltage fluctuations when the WTs are providing frequency support under grid frequency deviations.Meanwhile,the desired frequency support capability of the PMSG-based WTs can be ensured.Simulation results verify the rationality of the analysis and the effectiveness of the proposed control method.
文摘The prominence of Renewable Energy Sources(RES)in the process of power generation is exponentially increased in the recent days since these sources assist in minimizing the environmental contamination.A grid-tied DFIG(Doubly Fed Induction Generator)based WECS(Wind Energy Conversion System)is introduced in this work,in which a Landsman converter is implemented to impro-vise the output voltage of PV without anyfluctuations.A novel GA(Genetic Algorithm)assisted ANN(Artificial Neural Network)is employed for tracking the Maximum power from PV.Among the rotor and grid side controllers,the for-mer is implemented by combining the statorflux with d-q reference frame and the latter is realized by the PI controller.The proposed approach delivers better per-formance in the compensation of real and reactive power along with the DC link voltage control.The controlling mechanism is verified in both MATLAB and experimental bench setupby using an emulated wind turbine for the concurrent control of DC link potential,active and reactive powers.The source current THD is observed as 1.93%and 2.4%for simulation and hardware implementation respectively.
基金Supported by the Opening Project of State Key Laboratory of Large Electric Drive System and Equipment Technology(SKLLDJ022020004).
文摘DC-link capacitors play a vital role in managing ripple voltage and current in converters and various devices.This study focuses on exploring the aging characteristics of DC-link capacitors in alternating humid and thermal environments aligned with the operational conditions in photovoltaic and wind power applications.Adhering to relevant power equipment standards,we designed a 24-h alternating humid and thermal aging environment tailored to the requirements of DC-link capacitors.An aging test platform is established,and 20 widely used metallized polypropylene film capacitors are selected for evaluation.Parameters such as the capacitance,equivalent series resistance(ESR),and phase angle are assessed during aging,as well as the onset time and extent of aging at various intervals.This study focuses on the aging mechanisms,analyzing electrode corrosion,the self-healing process,and dielectric aging.Fitting the aging characteristics enabled us to calculate the lifespan of the capacitor and predict it under different degrees of capacitance decay.The results show that under alternating humid and thermal conditions,capacitance attenuation and ESR increase exhibit exponential nonlinearity,influenced by factors such as the oxidation and self-healing of capacitive metal electrodes,dielectric main-chain fracture,and crystal transformation.This study underscores the pivotal role of encapsulation in determining the aging decay time.
基金supported in part by National Natural Science Foundation of China(grant No.52207190)Funds for International Cooperation and Exchange of the National Natural Science Foundation of China(No.52061635104)。
文摘Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters (VSCs). A constant dc-link voltage is usually assumed in existing literature to estimate transient stability of virtual synchronous generators (VSGs). However, actual power supply in the dc-side of VSGs is limited and different dc-link voltage controllers are needed to achieve power balance between DC side and AC side. Addition of dc-link voltage controller has great influence on transient behavior of VSGs, which has not been investigated by previous research. To fill this gap, this paper gives insights into the effect of dc-link voltage dynamics on transient stability of VSGs. First, two typical kinds of VSGs with dc-link voltage controllers are introduced. Then, mathematical models considering dc-link dynamics are established and the effect of dc-link voltage controllers on transient synchronization stability of VSGs is revealed through equal area criterion (EAC). It is found that dc-link voltage controller would reduce stability margin of VSGs and design-oriented transient stability analysis is carried out quantitively using critical clearing time (CCT). Finally, simulation results are given to validate correctness of theoretical analysis.
基金supported by Science and Technology Project of Yunnan Power Grid Co.,Ltd.(No.YNKJXM20222105)。
文摘This paper proposes a grid synchronization control strategy for the grid-connected voltage source converters(VSCs)based on the voltage dynamics of the DC-link capacitor in the VSC.The voltage dynamics of the DC-link capacitor are used to regulate the frequency and phase angle of the inner potential of the VSC,synchronizing the VSC with grid.Firstly,in the proposed strategy,the active power regulation and grid synchronization of the VSC are combined,which are separated in the traditional control strategy.This can avoid the instability of the VSC in a weak grid with a low short circuit ratio(SCR),aroused by the dynamic interaction between the separated control loops in traditional control strategies.Secondly,the energy stored in the DC-link capacitor is directly coupled with the grid via the inner potential of the VSC,and the inertia characteristic is naturally featured in the inner potential by the proposed strategy.With the increase of the capacitance,the natural inertial response of the VSC is helpful to improve the grid frequency dynamic.Finally,simulation results are presented to validate the correctness and effectiveness of the proposed strategy in the enhancement of the grid frequency and voltage dynamic support capability.
