Given the wide application of DC grids,the protection equipment of power grids must be improved during the fault period.This study proposes an integrated multiport flexible voltage clamp circuit breaker with a DC chop...Given the wide application of DC grids,the protection equipment of power grids must be improved during the fault period.This study proposes an integrated multiport flexible voltage clamp circuit breaker with a DC chopper acting on the receiving end converter to solve the DC short circuit fault and surplus power because of AC low-voltage fault;it has a modular design.As a DC circuit breaker,the device utilizes the voltage-clamping principle and thyristor semi-control to remove faults.As the fault current increases,the branch circuit outputs different voltage levels by selecting different gears,thereby controlling the voltage-clamping effect.This device can distinguish between different fault types to prevent secondary shocks in the system.As a DC chopper,the voltage at both ends of the energy dissipation resistor is varied by switching submodules,consuming surplus power to complete AC low-voltage faults and minimizing the impact of low-voltage faults on the system’s transmission capacity.Finally,the effectiveness and applicability of the equipment are verified using wind turbines connected to a flexible DC transmission three-terminal power grid model in PSCAD/EMTDC,and two fault simulation types are analyzed.A comparison of the electrical quantities(fault current,system voltage and branch voltage)of the proposed circuit breaker with other similar equipment shows that due to the efficiency of the proposed equipment,the peak fault current is reduced by at least 35.8%.The required voltage stress of key power electronic equipment is reduced by at least 71.5%.Therefore,the equipment ensures that the per-unit voltage of the DC system does not exceed 1.05 during AC fault crossing.展开更多
Multi-objective optimal dispatching schemes with intelligent algorithms are recognized as effective measures to promote the economics and environmental friendliness of microgrid applications.However,the low accuracy a...Multi-objective optimal dispatching schemes with intelligent algorithms are recognized as effective measures to promote the economics and environmental friendliness of microgrid applications.However,the low accuracy and poor convergence of these algorithms have been challenging for system operators.The bird swarm algorithm(BSA),a new bio-heuristic cluster intelligent algorithm,can potentially address these challenges;however,its computational iterative process may fall into a local optimum and result in premature convergence when optimizing small portions of multi-extremum functions.To analyze the impact of a multi-objective economic-environmental dispatching of a microgrid and overcome the aforementioned problems of the BSA,a self-adaptive levy flight strategy-based BSA(LF-BSA)was proposed.It can solve the dispatching problems of microgrid and enhance its dispatching convergence accuracy,stability,and speed,thereby improving its optimization performance.Six typical test functions were used to compare the LF-BSA with three commonly accepted algorithms to verify its excellence.Finally,a typical summer-time daily microgrid scenario under grid-connected operational conditions was simulated.The results proved the feasibility of the proposed LF-BSA,effectiveness of the multi-objective optimization,and necessity of using renewable energy and energy storage in microgrid dispatching optimization.展开更多
Aiming at the diversity and nonlinearity of the elevator system control target, an effective group method based on a hybrid algorithm of genetic algorithm and neural network is presented in this paper. The genetic alg...Aiming at the diversity and nonlinearity of the elevator system control target, an effective group method based on a hybrid algorithm of genetic algorithm and neural network is presented in this paper. The genetic algorithm is used to search the weight of the neural network. At the same time, the multi-objective-based evaluation function is adopted, in which there are three main indicators including the passenger waiting time, car passengers number and the number of stops. Different weights are given to meet the actual needs. The optimal values of the evaluation function are obtained, and the optimal dispatch control of the elevator group control system based on neural network is realized. By analyzing the running of the elevator group control system, all the processes and steps are presented. The validity of the hybrid algorithm is verified by the dynamic imitation performance.展开更多
To realize the efficient transient simulation of a grid-connected power generation system based on multiple inverters, this paper proposes a hybrid simulation method integrating the models of electromagnetic transient...To realize the efficient transient simulation of a grid-connected power generation system based on multiple inverters, this paper proposes a hybrid simulation method integrating the models of electromagnetic transient and dynamic phasors. Based on a demonstration of the concepts and properties of dynamic phasors, the models of single-phase and three-phase inverters described by dynamic phasors are established first. Considering the numerical compatibility problem between dynamic phasors and instantaneous values, an interface scheme between dynamic phasors and instantaneous values is designed, and the efficiency and precision differences of various transformation methods are compared in detail.Finally, by utilizing MATLAB/Simulink, a hybrid simulation platform of a multi-inverter grid-connected system is built, and the efficiency and accuracy of the hybrid simulation are validated via comparison with the full electromagnetic transient simulation.展开更多
基金supported by National Natural Science Foundation of China(U2066208).
文摘Given the wide application of DC grids,the protection equipment of power grids must be improved during the fault period.This study proposes an integrated multiport flexible voltage clamp circuit breaker with a DC chopper acting on the receiving end converter to solve the DC short circuit fault and surplus power because of AC low-voltage fault;it has a modular design.As a DC circuit breaker,the device utilizes the voltage-clamping principle and thyristor semi-control to remove faults.As the fault current increases,the branch circuit outputs different voltage levels by selecting different gears,thereby controlling the voltage-clamping effect.This device can distinguish between different fault types to prevent secondary shocks in the system.As a DC chopper,the voltage at both ends of the energy dissipation resistor is varied by switching submodules,consuming surplus power to complete AC low-voltage faults and minimizing the impact of low-voltage faults on the system’s transmission capacity.Finally,the effectiveness and applicability of the equipment are verified using wind turbines connected to a flexible DC transmission three-terminal power grid model in PSCAD/EMTDC,and two fault simulation types are analyzed.A comparison of the electrical quantities(fault current,system voltage and branch voltage)of the proposed circuit breaker with other similar equipment shows that due to the efficiency of the proposed equipment,the peak fault current is reduced by at least 35.8%.The required voltage stress of key power electronic equipment is reduced by at least 71.5%.Therefore,the equipment ensures that the per-unit voltage of the DC system does not exceed 1.05 during AC fault crossing.
基金supported by the National Natural Science Foundation of China (No. 52061635103)
文摘Multi-objective optimal dispatching schemes with intelligent algorithms are recognized as effective measures to promote the economics and environmental friendliness of microgrid applications.However,the low accuracy and poor convergence of these algorithms have been challenging for system operators.The bird swarm algorithm(BSA),a new bio-heuristic cluster intelligent algorithm,can potentially address these challenges;however,its computational iterative process may fall into a local optimum and result in premature convergence when optimizing small portions of multi-extremum functions.To analyze the impact of a multi-objective economic-environmental dispatching of a microgrid and overcome the aforementioned problems of the BSA,a self-adaptive levy flight strategy-based BSA(LF-BSA)was proposed.It can solve the dispatching problems of microgrid and enhance its dispatching convergence accuracy,stability,and speed,thereby improving its optimization performance.Six typical test functions were used to compare the LF-BSA with three commonly accepted algorithms to verify its excellence.Finally,a typical summer-time daily microgrid scenario under grid-connected operational conditions was simulated.The results proved the feasibility of the proposed LF-BSA,effectiveness of the multi-objective optimization,and necessity of using renewable energy and energy storage in microgrid dispatching optimization.
基金Supported by National Natural Science Foundation of China (No60874077) Specialized Research Funds for Doctoral Program of Higher Education of China (No20060056054) Research Funds for Scientific Financing Projects of Quality Control Public Welfare Profession (No2007GYB172)
文摘Aiming at the diversity and nonlinearity of the elevator system control target, an effective group method based on a hybrid algorithm of genetic algorithm and neural network is presented in this paper. The genetic algorithm is used to search the weight of the neural network. At the same time, the multi-objective-based evaluation function is adopted, in which there are three main indicators including the passenger waiting time, car passengers number and the number of stops. Different weights are given to meet the actual needs. The optimal values of the evaluation function are obtained, and the optimal dispatch control of the elevator group control system based on neural network is realized. By analyzing the running of the elevator group control system, all the processes and steps are presented. The validity of the hybrid algorithm is verified by the dynamic imitation performance.
基金supported by the State Grid Science and Technology Project (grant no. KJ2021-069)。
文摘To realize the efficient transient simulation of a grid-connected power generation system based on multiple inverters, this paper proposes a hybrid simulation method integrating the models of electromagnetic transient and dynamic phasors. Based on a demonstration of the concepts and properties of dynamic phasors, the models of single-phase and three-phase inverters described by dynamic phasors are established first. Considering the numerical compatibility problem between dynamic phasors and instantaneous values, an interface scheme between dynamic phasors and instantaneous values is designed, and the efficiency and precision differences of various transformation methods are compared in detail.Finally, by utilizing MATLAB/Simulink, a hybrid simulation platform of a multi-inverter grid-connected system is built, and the efficiency and accuracy of the hybrid simulation are validated via comparison with the full electromagnetic transient simulation.
