The usage of open communication infrastructure for transmitting the control signals in the Load Frequency Control (LFC) scheme of power system introduces time delays. These time delays may degrade the dynamic performa...The usage of open communication infrastructure for transmitting the control signals in the Load Frequency Control (LFC) scheme of power system introduces time delays. These time delays may degrade the dynamic performance of the power system. This paper proposes a robust method to design a controller for multi-area LFC schemes considering communication delays. In existing literature, the controller values of LFC are designed using time domain approach which is less accurate than the proposed method. In proposed method, the controller values are determined by moving the rightmosteigenvalues of the system to the left half plane in a quasi-continuous way for a preset upper bound of time delay. Then the robustness of the proposed controller is assessed by estimating the maximumtolerable value of time delay for maintaining system stability. Simulation studies are carried out for multi-area LFC scheme equipped with the proposed controller using Matlab/simulink. From the results, it has been concluded that the proposed controller guarantees the tolerance for all time delays smaller than the preset upper bound and provides a bigger delay margin than the existing controllers.展开更多
The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen.The results show that the fracture toughne...The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen.The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicone oil,i.e.stress corrosion cracking,decrease linearly with the increasing applied electric field,either positive or negative.For the PZT-5 ferroelectric ceramics,delayed fracture in silicone oil under sustained positive or negative field can occur,and the threshold field for delayed fracture under sustained positive or negative field decreases linearly with applied stress intensity factor.The combined effect of electric and mechanical loading on delayed fracture in silicone oil includes fieldenhancing delayed fracture under sustained load and stress-enhancing delayed fracture in silicone oil under sustained field.展开更多
This study aims to determine the improvement effect on the delay margin if fractional-order proportional integral(PI) controller is used in the control of a singlearea delayed load frequency control(LFC) system. The d...This study aims to determine the improvement effect on the delay margin if fractional-order proportional integral(PI) controller is used in the control of a singlearea delayed load frequency control(LFC) system. The delay margin of the system with fractional-order PI control has been obtained for various fractional integral orders and the effect of them has been shown on the delay margin as a third controller parameter. Furthermore,the stability of the system that is either under or over the delay margin is examined by generalized modified Mikhailov criterion.The stability results obtained have been confirmed numerically in time domain. It is demonstrated that the proposed controller for delayed LFC system provides more flexibility on delay margin according to integer-order PI controller.展开更多
Considering the escalating usage of renewa-ble energy and rising frequency of extreme meteorological events,the risk of emergency load shedding(ELS)in power grids due to faults is increasing.The existing ELS strategie...Considering the escalating usage of renewa-ble energy and rising frequency of extreme meteorological events,the risk of emergency load shedding(ELS)in power grids due to faults is increasing.The existing ELS strategies fail to provide users with advance warnings and blackout preparation time.To address this issue,an in-novative strategy called warning and delayed load shed-ding is proposed in this study.In this approach,when it becomes necessary to shed load for emergency control,users are immediately notified with a power outage warning.Subsequently,energy storage and other regula-tory resources are employed to substitute for load shed-ding,thus postponing the execution of the load shedding command.This delay equips users with the ability and time to respond and prepare.To implement this strategy,the operational principles supported by energy storage and backup power are further discussed.Five perfor-mance indexes are utilized to evaluate the delayed load shedding capability.Moreover,the delayed load shedding switch function and energy storage power balance equa-tion are constructed to determine the relationship be-tween energy storage,backup power sources,and load shedding time.Subsequently,two optimized load shed-ding models supported by energy storage are established,i.e.,maximum and flexible delayed models.For compar-ison,improvements are made to the conventional load shedding model without delay by incorporating energy storage.An IEEE 30-node network with energy storage is used to test the three load shedding models.Accordingly,the evaluation indexes are calculated and compared.The results of the performance indexes and comparative analysis validate the effectiveness of the proposed meth-ods,indicating that by using energy storage,users can be notified with advance power outage warnings and prep-aration time.展开更多
文摘The usage of open communication infrastructure for transmitting the control signals in the Load Frequency Control (LFC) scheme of power system introduces time delays. These time delays may degrade the dynamic performance of the power system. This paper proposes a robust method to design a controller for multi-area LFC schemes considering communication delays. In existing literature, the controller values of LFC are designed using time domain approach which is less accurate than the proposed method. In proposed method, the controller values are determined by moving the rightmosteigenvalues of the system to the left half plane in a quasi-continuous way for a preset upper bound of time delay. Then the robustness of the proposed controller is assessed by estimating the maximumtolerable value of time delay for maintaining system stability. Simulation studies are carried out for multi-area LFC scheme equipped with the proposed controller using Matlab/simulink. From the results, it has been concluded that the proposed controller guarantees the tolerance for all time delays smaller than the preset upper bound and provides a bigger delay margin than the existing controllers.
基金This work was supported by the National Natural Science Foundation of China(Grant No.50131160738).
文摘The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen.The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicone oil,i.e.stress corrosion cracking,decrease linearly with the increasing applied electric field,either positive or negative.For the PZT-5 ferroelectric ceramics,delayed fracture in silicone oil under sustained positive or negative field can occur,and the threshold field for delayed fracture under sustained positive or negative field decreases linearly with applied stress intensity factor.The combined effect of electric and mechanical loading on delayed fracture in silicone oil includes fieldenhancing delayed fracture under sustained load and stress-enhancing delayed fracture in silicone oil under sustained field.
文摘This study aims to determine the improvement effect on the delay margin if fractional-order proportional integral(PI) controller is used in the control of a singlearea delayed load frequency control(LFC) system. The delay margin of the system with fractional-order PI control has been obtained for various fractional integral orders and the effect of them has been shown on the delay margin as a third controller parameter. Furthermore,the stability of the system that is either under or over the delay margin is examined by generalized modified Mikhailov criterion.The stability results obtained have been confirmed numerically in time domain. It is demonstrated that the proposed controller for delayed LFC system provides more flexibility on delay margin according to integer-order PI controller.
基金supported by the National Natural Sci-ence Foundation of China(No.52077017).
文摘Considering the escalating usage of renewa-ble energy and rising frequency of extreme meteorological events,the risk of emergency load shedding(ELS)in power grids due to faults is increasing.The existing ELS strategies fail to provide users with advance warnings and blackout preparation time.To address this issue,an in-novative strategy called warning and delayed load shed-ding is proposed in this study.In this approach,when it becomes necessary to shed load for emergency control,users are immediately notified with a power outage warning.Subsequently,energy storage and other regula-tory resources are employed to substitute for load shed-ding,thus postponing the execution of the load shedding command.This delay equips users with the ability and time to respond and prepare.To implement this strategy,the operational principles supported by energy storage and backup power are further discussed.Five perfor-mance indexes are utilized to evaluate the delayed load shedding capability.Moreover,the delayed load shedding switch function and energy storage power balance equa-tion are constructed to determine the relationship be-tween energy storage,backup power sources,and load shedding time.Subsequently,two optimized load shed-ding models supported by energy storage are established,i.e.,maximum and flexible delayed models.For compar-ison,improvements are made to the conventional load shedding model without delay by incorporating energy storage.An IEEE 30-node network with energy storage is used to test the three load shedding models.Accordingly,the evaluation indexes are calculated and compared.The results of the performance indexes and comparative analysis validate the effectiveness of the proposed meth-ods,indicating that by using energy storage,users can be notified with advance power outage warnings and prep-aration time.
