Most view articles
2020, 35(4):128-132.
DOI: 10.19781/j.issn.16739140.2020.04.017
Abstract:
The LLC resonant converter can achieve softswitching while it operates in highfrequency and then improves the power density and efficiency of power supply. The fundamental approximation and mode analysis are two classic analysis methods of LLC resonant converter, but the comparative studies in the voltage gain accuracy, efficiency and application is not intensively discussed. On this background, the principle of the above methods is illustrated firstly. Then, the operation mode of LLC resonant converter is analyzed in PSIM simulation environment. Based on the operation modes, the voltage gain accuracy of the two methods is compared in simulation. Finally, the resonant parameters are selected based on the peak voltage gain, and a 1.5 kW/28 V prototype is set up. The experimental results show that actual gain is higher than the gain curve based on FHA 10% to 15% below the resonant zone, and have high accordance with the voltage gain based on the mode analysis in whole frequency range. And the iterative parameters based on mode analysis have higher efficiency with the experimental prototype.
The LLC resonant converter can achieve softswitching while it operates in highfrequency and then improves the power density and efficiency of power supply. The fundamental approximation and mode analysis are two classic analysis methods of LLC resonant converter, but the comparative studies in the voltage gain accuracy, efficiency and application is not intensively discussed. On this background, the principle of the above methods is illustrated firstly. Then, the operation mode of LLC resonant converter is analyzed in PSIM simulation environment. Based on the operation modes, the voltage gain accuracy of the two methods is compared in simulation. Finally, the resonant parameters are selected based on the peak voltage gain, and a 1.5 kW/28 V prototype is set up. The experimental results show that actual gain is higher than the gain curve based on FHA 10% to 15% below the resonant zone, and have high accordance with the voltage gain based on the mode analysis in whole frequency range. And the iterative parameters based on mode analysis have higher efficiency with the experimental prototype.
2020, 35(4):3-12.
DOI: 10.19781/j.issn.16739140.2020.04.001
Abstract:
The disordered planning and unreasonable allocation of electric vehicle charging stations have a serious impact on the safty，stability and economy of the distribution network operation．To solve this problem, this paper constructs an optimal planning model of electric vehicle charging stations based on the voltage stability index of distribution network．The model not only could balance the construction investment of charging stations，the economic operation of distribution system and the quality of power supply，but also take full account of the demand and convenience of the electric vehicle charging．The improved adaptive particle swarm optimization (APSO) algorithm with fast speed and high accuracy is adopted to solve the nolinear optimization problem with multiple constraints. Finally, the simulation results based on IEEE33bus system show the effectiveness of the proposed method.
The disordered planning and unreasonable allocation of electric vehicle charging stations have a serious impact on the safty，stability and economy of the distribution network operation．To solve this problem, this paper constructs an optimal planning model of electric vehicle charging stations based on the voltage stability index of distribution network．The model not only could balance the construction investment of charging stations，the economic operation of distribution system and the quality of power supply，but also take full account of the demand and convenience of the electric vehicle charging．The improved adaptive particle swarm optimization (APSO) algorithm with fast speed and high accuracy is adopted to solve the nolinear optimization problem with multiple constraints. Finally, the simulation results based on IEEE33bus system show the effectiveness of the proposed method.
2020, 35(1):31-39.
DOI: 10.19781/j.issn.16739140.2020.01.004
Abstract:
Before the spot electricity market is established, electrical energy is traded through forward contracts in the current medium and longterm electricity market in China. A reasonable balancing and settlement mechanism for electrical energy deviation is conducive to the smooth transition from the mediumand longterm electricity market to the spot market. Given this background, an assessment mechanism is presented for contract energy deviation in a mediumand longterm electricity market. First, the deviation settlement mechanism of the basic rules for the mediumand longterm electricity market is examined, and a generationside deviation balancing mechanism suitable for the current electricity market environment proposed. Then, considering the differences of the marketoriented electricity proportion and the differences in the capabilities of various users in controlling contract deviations, the risk of the electrical energy deviation penalty imposed on demand customers is analyzed. A fixedratio energy deviation settlement method is next designed for nontotal electrical energy transaction, and a staged assessment mechanism of demandside energy deviation proposed. Simulations based on actual deviation assessment data from a provincial electricity market in China show that the proposed energy deviation assessment mechanism is effective in the mediumand longterm electricity market.
Before the spot electricity market is established, electrical energy is traded through forward contracts in the current medium and longterm electricity market in China. A reasonable balancing and settlement mechanism for electrical energy deviation is conducive to the smooth transition from the mediumand longterm electricity market to the spot market. Given this background, an assessment mechanism is presented for contract energy deviation in a mediumand longterm electricity market. First, the deviation settlement mechanism of the basic rules for the mediumand longterm electricity market is examined, and a generationside deviation balancing mechanism suitable for the current electricity market environment proposed. Then, considering the differences of the marketoriented electricity proportion and the differences in the capabilities of various users in controlling contract deviations, the risk of the electrical energy deviation penalty imposed on demand customers is analyzed. A fixedratio energy deviation settlement method is next designed for nontotal electrical energy transaction, and a staged assessment mechanism of demandside energy deviation proposed. Simulations based on actual deviation assessment data from a provincial electricity market in China show that the proposed energy deviation assessment mechanism is effective in the mediumand longterm electricity market.
2022, 37(5):80-87.
DOI: 10.19781/j.issn.1673-9140.2022.05.009
Abstract:
The conventional frequency-controlled LLC resonant converter suffers from wide frequency regulation range and low conversion efficiency, so that it is unsuitable for wide voltage range applications with a wide voltage range. In order to solve these problems, a PWM control strategy of the full-bridge LLC resonant converter is proposed in this paper, which realizes the gain adjustment by adjusting the duty cycle of the switch The switches of two lower arms of the resonant converter are controlled by a fixed frequency, and the switching frequency is equal to the resonant frequency, while the switches of the two upper arms are controlled by PWM to adjust the output voltage. With the method, the frequency variation range of the resonant converter is significantly narrowed. In addition, the switches of primary circuit and the rectifier diodes of secondary circuit could achieve zero voltage switching (ZVS) and zero current switching (ZCS), respectively, which effectively reduces the switching losses of the converter. Finally, the 1.5 kW simulation and experimental prototype with 400 V input voltage, 250~500 V output voltage are established to verify the effectiveness of the proposed PWM control strategy.
The conventional frequency-controlled LLC resonant converter suffers from wide frequency regulation range and low conversion efficiency, so that it is unsuitable for wide voltage range applications with a wide voltage range. In order to solve these problems, a PWM control strategy of the full-bridge LLC resonant converter is proposed in this paper, which realizes the gain adjustment by adjusting the duty cycle of the switch The switches of two lower arms of the resonant converter are controlled by a fixed frequency, and the switching frequency is equal to the resonant frequency, while the switches of the two upper arms are controlled by PWM to adjust the output voltage. With the method, the frequency variation range of the resonant converter is significantly narrowed. In addition, the switches of primary circuit and the rectifier diodes of secondary circuit could achieve zero voltage switching (ZVS) and zero current switching (ZCS), respectively, which effectively reduces the switching losses of the converter. Finally, the 1.5 kW simulation and experimental prototype with 400 V input voltage, 250~500 V output voltage are established to verify the effectiveness of the proposed PWM control strategy.
2022, 37(6):3-16.
DOI: 10.19781/j.issn.1673-9140.2022.06.001
Abstract:
Commutation failure, DC blocking and near AC short-circuit fault of HVDC transmission system would lead to transient overvoltage of sending-end power grid, restrict transmission capacity and threaten safe and stable operation of system. For this reason, this paper firstly gives the similarities and differences of the transient overvoltage generation mechanism of DC sending-end power grid under three typical fault conditions of commutation failure, DC blocking and near-field AC fault are analyzed systematically, and the main influencing factors of transient overvoltage are clarified. Secondly, the existing transient overvoltage suppression strategies and their advantages and disadvantages are summarized. Finally, in view of the shortcomings of the existing research, it is analyzed that the three aspects of analyzing the transient overvoltage mechanism of different new energy transmission scenarios, revealing the coupling law of multiple influencing factors of transient overvoltage, and constructing a multi-temporal and spatial scale transient overvoltage collaborative suppression system are the focus of future research on transient overvoltage of HVDC sending-end power grid.
Commutation failure, DC blocking and near AC short-circuit fault of HVDC transmission system would lead to transient overvoltage of sending-end power grid, restrict transmission capacity and threaten safe and stable operation of system. For this reason, this paper firstly gives the similarities and differences of the transient overvoltage generation mechanism of DC sending-end power grid under three typical fault conditions of commutation failure, DC blocking and near-field AC fault are analyzed systematically, and the main influencing factors of transient overvoltage are clarified. Secondly, the existing transient overvoltage suppression strategies and their advantages and disadvantages are summarized. Finally, in view of the shortcomings of the existing research, it is analyzed that the three aspects of analyzing the transient overvoltage mechanism of different new energy transmission scenarios, revealing the coupling law of multiple influencing factors of transient overvoltage, and constructing a multi-temporal and spatial scale transient overvoltage collaborative suppression system are the focus of future research on transient overvoltage of HVDC sending-end power grid.
2020, 35(1):40-49.
DOI: 10.19781/j.issn.16739140.2020.01.005
Abstract:
The wellestablished contract for difference (CfD) is a middleor longterm financial contract. When the CfD is applied in the electricity market, the electricity price can be fixed and the risk associated with the fluctuated electricity price in the spot market avoided. In recent years, with the advance of the power industry restructuring and the expansion of the pilot scope in China, the electrical energy CfD is included in the designed electricity market mechanisms in several provinces. Currently the implemented CfD contracts for electricity in provincial electricity markets in China are actually electrical energy contracts rather than electrical power ones, and hence it is necessary to decompose the contracted electricity energy into dispatchable electrical power demand curves. A brief overview of the electrical CfD is first presented, and the existing theories and methods from the perspectives of the rolling correction and optimization models based decomposition algorithms for definite contracted electrical energy are presented and compared. Finally, some problems associated with the decomposition of the contracted electrical energy in this round of power industry restructuring are prospected, and possible solved methods addressed.
The wellestablished contract for difference (CfD) is a middleor longterm financial contract. When the CfD is applied in the electricity market, the electricity price can be fixed and the risk associated with the fluctuated electricity price in the spot market avoided. In recent years, with the advance of the power industry restructuring and the expansion of the pilot scope in China, the electrical energy CfD is included in the designed electricity market mechanisms in several provinces. Currently the implemented CfD contracts for electricity in provincial electricity markets in China are actually electrical energy contracts rather than electrical power ones, and hence it is necessary to decompose the contracted electricity energy into dispatchable electrical power demand curves. A brief overview of the electrical CfD is first presented, and the existing theories and methods from the perspectives of the rolling correction and optimization models based decomposition algorithms for definite contracted electrical energy are presented and compared. Finally, some problems associated with the decomposition of the contracted electrical energy in this round of power industry restructuring are prospected, and possible solved methods addressed.
2024(1):1-12.
DOI: 10.19781/j.issn.1673-9140.2024.01.001
Abstract:
To address the challenges posed by the large-scale integration of electric vehicles and new energy sources on the stability of power system operations and the efficient utilization of new energy, the integrated photovoltaic-energy storage-charging model emerges. The synergistic interaction mechanisms and optimized control strategies among its individual units have also become key issues urgently needing resolution in smart grid development. Due to the characteristics of integrated generation, load, and storage, mutual complementarity of supply and demand, and flexible dispatch, the photovoltaic-energy storage-charging (PV-ESS-EV) integrated station micro-grid (ISM) mode, incorporating "PV- PV-ESS-EV + intelligent building" features, has become a focal point for energy conservation, carbon reduction, and energy transition in China. In consideration of the challenges faced by the operational mode of microgrids, such as the strong uncertainty of distributed energy sources and the unclear interaction mechanisms during islanded and grid-connected operation, various aspects of the PV-ESS-EV ISM are reviewed, including its unit modules, key technologies, and operational states. Additionally, the current research status of PV-ESS-EV is summarized while future development trends are discussed, and the challenges that need to be addressed are examined. The research findings have important theoretical and practical implications for exploring the regulatory potential of various demand-response resources under economic incentives, ensuring the reliability of power grid supply, and serving as valuable references for both theory and practice.
To address the challenges posed by the large-scale integration of electric vehicles and new energy sources on the stability of power system operations and the efficient utilization of new energy, the integrated photovoltaic-energy storage-charging model emerges. The synergistic interaction mechanisms and optimized control strategies among its individual units have also become key issues urgently needing resolution in smart grid development. Due to the characteristics of integrated generation, load, and storage, mutual complementarity of supply and demand, and flexible dispatch, the photovoltaic-energy storage-charging (PV-ESS-EV) integrated station micro-grid (ISM) mode, incorporating "PV- PV-ESS-EV + intelligent building" features, has become a focal point for energy conservation, carbon reduction, and energy transition in China. In consideration of the challenges faced by the operational mode of microgrids, such as the strong uncertainty of distributed energy sources and the unclear interaction mechanisms during islanded and grid-connected operation, various aspects of the PV-ESS-EV ISM are reviewed, including its unit modules, key technologies, and operational states. Additionally, the current research status of PV-ESS-EV is summarized while future development trends are discussed, and the challenges that need to be addressed are examined. The research findings have important theoretical and practical implications for exploring the regulatory potential of various demand-response resources under economic incentives, ensuring the reliability of power grid supply, and serving as valuable references for both theory and practice.
2022, 37(5):17-24.
DOI: 10.19781/j.issn.1673-9140.2022.05.002
Abstract:
With the fast development of the economy and society, the reliable supply of electricity has triggered a wide range of concerns. On 15th, February, 2021, a large-scale power outage occurred in Texas, USA due to the extremely cold weather. More than 4.8 million users are affected. This accident has a serious impact on industrial production and people's lives. Firstly, the general situation of the power system in Texas is briefly introduced, and then the specific process of the blackout is described in chronological order. After that, the causes of the blackout event are analyzed from three aspects: grid adequacy, regional support capability, and the market mechanism. Finally, from the perspective of the construction of China's new power system, some inspirations are proposed for the meteorological forecasting technology applications, the power supply structure of the new power system, the flexible resource and integrated operation of the source-grid-load-storage system, and the construction of the grid structure of the power grid. This work provides a reference to help guarantee the adequacy of the power supply in China's new power system.
With the fast development of the economy and society, the reliable supply of electricity has triggered a wide range of concerns. On 15th, February, 2021, a large-scale power outage occurred in Texas, USA due to the extremely cold weather. More than 4.8 million users are affected. This accident has a serious impact on industrial production and people's lives. Firstly, the general situation of the power system in Texas is briefly introduced, and then the specific process of the blackout is described in chronological order. After that, the causes of the blackout event are analyzed from three aspects: grid adequacy, regional support capability, and the market mechanism. Finally, from the perspective of the construction of China's new power system, some inspirations are proposed for the meteorological forecasting technology applications, the power supply structure of the new power system, the flexible resource and integrated operation of the source-grid-load-storage system, and the construction of the grid structure of the power grid. This work provides a reference to help guarantee the adequacy of the power supply in China's new power system.
2020, 35(3):135-140.
DOI: 10.19781/j.issn.16739140.2020.03.018
Abstract:
In order to reduce the induced voltage at the metal sheath of cables, as well as the circulation current of sheath in the cross interconnected grounding mode, the grounding mode of sheath is modified for the reconstruction of cable lines. Based on the defects of cross interconnection grounding in t he practical application, three kinds of the optimization scheme for grounding protection are proposed. There are the grounding of one side of the protective layer through the compensating inductance, single terminal grounding through the cross connection, and grounding at each section. The simulation models are built by utilizing PSCAD simulation software to study the voltage and circulation current at sheaths under different schemes. Theoretical analysis and simulation results show that those three kinds of cable sheath grounding can effectively suppress the metal sheath end induction high voltage. The sheath circulation current produced after the line reconstruction can be reduced. The optimization schemes for cable sheath grounding can be utilized as the engineering practice in the future direction of promotion.
In order to reduce the induced voltage at the metal sheath of cables, as well as the circulation current of sheath in the cross interconnected grounding mode, the grounding mode of sheath is modified for the reconstruction of cable lines. Based on the defects of cross interconnection grounding in t he practical application, three kinds of the optimization scheme for grounding protection are proposed. There are the grounding of one side of the protective layer through the compensating inductance, single terminal grounding through the cross connection, and grounding at each section. The simulation models are built by utilizing PSCAD simulation software to study the voltage and circulation current at sheaths under different schemes. Theoretical analysis and simulation results show that those three kinds of cable sheath grounding can effectively suppress the metal sheath end induction high voltage. The sheath circulation current produced after the line reconstruction can be reduced. The optimization schemes for cable sheath grounding can be utilized as the engineering practice in the future direction of promotion.
2021, 36(2):31-39.
DOI: 10.19781/j.issn.1673-9140.2021.02.004
Abstract:
As the voltage level of the power system increases, the DC component influence on the breaking capacity of the circuit breaker has been closely concerned. However, there are few studies on the calculation method of DC component of short circuit current in the circuit breaker branch. In this paper, a calculation method is proposed for the DC component of branch short-circuit current and its decay time constant based on transfer impedance. Firstly, in the case of knowing the impedance matrix of the original network and considering the characteristics of the network when the system is short-circuited, the network is transformed based on the principle of forming the node impedance matrix using the branch-adding method.Then, the transformed network can easily calculate the DC component of the short-circuit current and the decay time constant of each branch. In addition, a unified algorithm for forming the node impedance matrix is concluded when considering the changes of the network topology. It has the advantages of fast calculation speed, clear physical concept, and it is easy to program so as to achieve scanning calculations. The accuracy of the proposed method is verified by EMTP simulation. Compared with results from PSS/E, the superiority of the proposed method is also verified.
As the voltage level of the power system increases, the DC component influence on the breaking capacity of the circuit breaker has been closely concerned. However, there are few studies on the calculation method of DC component of short circuit current in the circuit breaker branch. In this paper, a calculation method is proposed for the DC component of branch short-circuit current and its decay time constant based on transfer impedance. Firstly, in the case of knowing the impedance matrix of the original network and considering the characteristics of the network when the system is short-circuited, the network is transformed based on the principle of forming the node impedance matrix using the branch-adding method.Then, the transformed network can easily calculate the DC component of the short-circuit current and the decay time constant of each branch. In addition, a unified algorithm for forming the node impedance matrix is concluded when considering the changes of the network topology. It has the advantages of fast calculation speed, clear physical concept, and it is easy to program so as to achieve scanning calculations. The accuracy of the proposed method is verified by EMTP simulation. Compared with results from PSS/E, the superiority of the proposed method is also verified.
2020, 35(4):13-19.
DOI: 10.19781/j.issn.16739140.2020.04.002
Abstract:
With the construction of smart grid, power companies gradually use unmanned aerial vehicles (UAV) to replace manual inspection of transmission lines. This paper proposes a method for processing aerial images of transmission line insulators captured by UAV. Firstly, the threshold and range of RGB components in the color model are used to segment the target and background areas. Secondly, mathematical morphology and nonoverlapping window texture features are applied to roughly mark the target area. Finally, a minimum circumscribed horizontal rectangular frame is generated. Then the texture features of all the patterns within the minimum circumscribed horizontal rectangular frame are identified to locate the minimum horizontal rectangular area of the aerial image of the insulator string. In the end, we use two images to verify the algorithm and compare with the algorithms in the literature. The results show that the algorithm proposed in this paper can better identify the position of insulator strings.
With the construction of smart grid, power companies gradually use unmanned aerial vehicles (UAV) to replace manual inspection of transmission lines. This paper proposes a method for processing aerial images of transmission line insulators captured by UAV. Firstly, the threshold and range of RGB components in the color model are used to segment the target and background areas. Secondly, mathematical morphology and nonoverlapping window texture features are applied to roughly mark the target area. Finally, a minimum circumscribed horizontal rectangular frame is generated. Then the texture features of all the patterns within the minimum circumscribed horizontal rectangular frame are identified to locate the minimum horizontal rectangular area of the aerial image of the insulator string. In the end, we use two images to verify the algorithm and compare with the algorithms in the literature. The results show that the algorithm proposed in this paper can better identify the position of insulator strings.
2020, 35(4):42-48.
DOI: 10.19781/j.issn.16739140.2020.04.006
Abstract:
The effect of the oscillating wave on the interfacial and internal defects of cable from the perspective of the electric field is studied in order to understand the test results of the oscillating wave voltage method for different defects in cables. Firstly, an oscillating wave test platform is set up to partial discharge tests the artificial defective models including longitudinal knife defects and external semiconductor lap defects. Then, the excitation characteristics of oscillation wave are analyzed primarily by PDIV and PRPD. Furthermore, the electric field distribution of cables with defects are simulated by utilizing a finite element simulation software in threedimension. Artificial defects with different sizes are fabricated to represent the diversity of the defect site and the characteristics of defective discharges are explained by the electric field distortion at the defects. Experimental and simulation results show that: it is hard to detect the internal defects due to the filling of hard grease by using the oscillation wave voltage method, whereas interfacial defects of poor connection of outer semiconductor has better characterization results.
The effect of the oscillating wave on the interfacial and internal defects of cable from the perspective of the electric field is studied in order to understand the test results of the oscillating wave voltage method for different defects in cables. Firstly, an oscillating wave test platform is set up to partial discharge tests the artificial defective models including longitudinal knife defects and external semiconductor lap defects. Then, the excitation characteristics of oscillation wave are analyzed primarily by PDIV and PRPD. Furthermore, the electric field distribution of cables with defects are simulated by utilizing a finite element simulation software in threedimension. Artificial defects with different sizes are fabricated to represent the diversity of the defect site and the characteristics of defective discharges are explained by the electric field distortion at the defects. Experimental and simulation results show that: it is hard to detect the internal defects due to the filling of hard grease by using the oscillation wave voltage method, whereas interfacial defects of poor connection of outer semiconductor has better characterization results.
2020, 35(4):147-153.
DOI: 10.19781/j.issn.16739140.2020.04.020
Abstract:
When itoccurs load mutation in cophase power supply system, conventional detection method in detecting the fundamental active current and reactive current will exist a time buffer, which in turn directly affects the detection effect of fundamental active current and reactive current at power grid side. It may lead to not timely compensate the reactiveand harmonic current in load side. Based on the above problems, this paper proposed a Scott balance transformer combined balance transform device of cophase traction power supply system mode. The twophase voltage and current analysis Through the special power supply mode of the twophase balance transformer. According to the instantaneous reactive power theory of twophase circuit, the whole singlephase fundamental wave active and reactive current signals aredetected.Theactive current in the whole singlephase circuit is decomposed. Thus,the amount of negative sequence can be obtainedin the case of mutation, and then the positive sequence under the condition of fundamental wave stability is recombined with the negative sequence. Therefore, the dynamic performancegets greatly improved when it occurs load mutation. Simulation and theoretical comprehensive analysis verify the rationality of this method.
When itoccurs load mutation in cophase power supply system, conventional detection method in detecting the fundamental active current and reactive current will exist a time buffer, which in turn directly affects the detection effect of fundamental active current and reactive current at power grid side. It may lead to not timely compensate the reactiveand harmonic current in load side. Based on the above problems, this paper proposed a Scott balance transformer combined balance transform device of cophase traction power supply system mode. The twophase voltage and current analysis Through the special power supply mode of the twophase balance transformer. According to the instantaneous reactive power theory of twophase circuit, the whole singlephase fundamental wave active and reactive current signals aredetected.Theactive current in the whole singlephase circuit is decomposed. Thus,the amount of negative sequence can be obtainedin the case of mutation, and then the positive sequence under the condition of fundamental wave stability is recombined with the negative sequence. Therefore, the dynamic performancegets greatly improved when it occurs load mutation. Simulation and theoretical comprehensive analysis verify the rationality of this method.
2020, 35(4):66-75.
DOI: 10.19781/j.issn.16739140.2020.04.009
Abstract:
In the traditional electromagnetic transient simulation, the computation speed of SVC (Static Var Compensator) and TCSC (Thyristor Controlled Series Compensation) is relatively slower. In order to overcome this deficiency, a new method of fast simulation for the electromagnetic transients of SVC and TCSC is proposed. For the fact that the state equations of SVC and TCSC are unchanged when the state of TCR (Thyristor Controlled Reactor) branches stay the same, the piecewise timeinvariant state equations of SVC and TCSC are developed firstly. Then, auxiliary variables are introduced and the model is transformed from a set of nonhomogeneous linear equations into homogeneous ones to obtain the unified expression suitable for varied working conditions. Finally, the scaling and squaring method is utilized to compute the matrix exponent and the response of the model is obtained. The feasibility and high efficiency of the proposed method is verified by comparing with the results from classical electromagnetic transient simulations using the PSCAD/EMTDC software package.
In the traditional electromagnetic transient simulation, the computation speed of SVC (Static Var Compensator) and TCSC (Thyristor Controlled Series Compensation) is relatively slower. In order to overcome this deficiency, a new method of fast simulation for the electromagnetic transients of SVC and TCSC is proposed. For the fact that the state equations of SVC and TCSC are unchanged when the state of TCR (Thyristor Controlled Reactor) branches stay the same, the piecewise timeinvariant state equations of SVC and TCSC are developed firstly. Then, auxiliary variables are introduced and the model is transformed from a set of nonhomogeneous linear equations into homogeneous ones to obtain the unified expression suitable for varied working conditions. Finally, the scaling and squaring method is utilized to compute the matrix exponent and the response of the model is obtained. The feasibility and high efficiency of the proposed method is verified by comparing with the results from classical electromagnetic transient simulations using the PSCAD/EMTDC software package.
2020, 35(4):181-182.
DOI: 10.19781/j.issn.16739140.2020.04.025
Abstract:
Based on the analytical expression of the static voltage stability limit derived from apparent power, this paper gives an index to identify the weak point of static voltage stability, and proposes an improved engineering calculation method for the static voltage stability limit. The power system simulation software is mainly used in the project to calculate the static voltage stability. This method simulates the load growth in the stability calculation program, and solves the problem of limit misjudgment caused by the difficulty of the convergence of the operating point near the static voltage stability limit in the ordinary power flow algorithm. In the power flow calculation program, the PV node of the generator in the region is modified to a PQ node, which solves the problem of excessive output of reactive power caused by the dynamic calculation characteristic of the generator in the stable calculation program. Finally, a certain district power grid in Beijing is used as an example to verify the adaptability of the calculation method.
Based on the analytical expression of the static voltage stability limit derived from apparent power, this paper gives an index to identify the weak point of static voltage stability, and proposes an improved engineering calculation method for the static voltage stability limit. The power system simulation software is mainly used in the project to calculate the static voltage stability. This method simulates the load growth in the stability calculation program, and solves the problem of limit misjudgment caused by the difficulty of the convergence of the operating point near the static voltage stability limit in the ordinary power flow algorithm. In the power flow calculation program, the PV node of the generator in the region is modified to a PQ node, which solves the problem of excessive output of reactive power caused by the dynamic calculation characteristic of the generator in the stable calculation program. Finally, a certain district power grid in Beijing is used as an example to verify the adaptability of the calculation method.
2020, 35(4):91-98.
DOI: 10.19781/j.issn.16739140.2020.04.012
Abstract:
Windthermal bundling external power transmission use thermal power to suppress the fluctuation of wind power and improve the utilization rate of the line. It is an important way to absorb wind power on a large scale. Therefore, the choice of windthermal bundling external power transmission lines and supporting thermal power is crucial. And the transmission capacity of the external power transmission line is related to its cross section and environmental temperature. Considering the line heat capacity or namely the influence of environmental temperature, this paper proposes a method to optimize transmission line crosssection and thermal power capacity of windthermal bundling external power. This method comprehensively considers the impact of wind power and thermal power income, total cost of thermal power, line investment cost, and wind curtailment cost on social benefits. The calculation example shows that this method can give full play to the transmission capacity of the line and increase social benefits compared with the method without considering the thermal load capacity.
Windthermal bundling external power transmission use thermal power to suppress the fluctuation of wind power and improve the utilization rate of the line. It is an important way to absorb wind power on a large scale. Therefore, the choice of windthermal bundling external power transmission lines and supporting thermal power is crucial. And the transmission capacity of the external power transmission line is related to its cross section and environmental temperature. Considering the line heat capacity or namely the influence of environmental temperature, this paper proposes a method to optimize transmission line crosssection and thermal power capacity of windthermal bundling external power. This method comprehensively considers the impact of wind power and thermal power income, total cost of thermal power, line investment cost, and wind curtailment cost on social benefits. The calculation example shows that this method can give full play to the transmission capacity of the line and increase social benefits compared with the method without considering the thermal load capacity.
2023, 38(4):1-14.
DOI: 10.19781/j.issn.1673-9140.2023.04.001
Abstract:
The non?technical losses caused by electricity theft in the power system have always been a pressing issue for power grid companies to urgently address. With the deployment of a large number of smart meters in the power grid, the use of user?side data collected by the power metering automation system to accurately detect electricity theft has attracted widespread attention from researchers and power grid companies. Firstly, the basic classification of users' electricity stealing behavior, evaluation indicators and existing electricity theft detection data sets are introduced. Then, from the four aspects of grid state analysis, machine learning, game theory and hardware, the existing detection methods of electricity theft behavior are comprehensively sorted, analyzed and compared, and the basic ideas, advantages and disadvantages of each method are summarized. Finally, the current challenges in the field of electricity theft behavior detection are deeply analyzed, and a prospective outlook on the focus of future research work is provided.
The non?technical losses caused by electricity theft in the power system have always been a pressing issue for power grid companies to urgently address. With the deployment of a large number of smart meters in the power grid, the use of user?side data collected by the power metering automation system to accurately detect electricity theft has attracted widespread attention from researchers and power grid companies. Firstly, the basic classification of users' electricity stealing behavior, evaluation indicators and existing electricity theft detection data sets are introduced. Then, from the four aspects of grid state analysis, machine learning, game theory and hardware, the existing detection methods of electricity theft behavior are comprehensively sorted, analyzed and compared, and the basic ideas, advantages and disadvantages of each method are summarized. Finally, the current challenges in the field of electricity theft behavior detection are deeply analyzed, and a prospective outlook on the focus of future research work is provided.
2020, 35(1):75-82.
DOI: 10.19781/j.issn.16739140.2020.01.009
Abstract:
The optimal allocation of SNOP considering operation efficiency and investment of distribution network is a multiobjective problem. In this paper, a multiattribute utility mergence method is proposed. Firstly, mergence rules are identified to achieve the aggregate utility according to the internal characteristic and logic relation of optimization indexes. Then, a SNOP allocation optimization model is built with the max aggregate utility value as the object. Finally, a case study of IEEE 33bus system is included to verify the effectiveness of the proposed model and method. It is shown that the multiattribute utility method for SNOP allocation can decrease active power losses, improve the system voltage level and load balancing level and increase the distributed generation penetration with a reasonable SNOP capacity.
The optimal allocation of SNOP considering operation efficiency and investment of distribution network is a multiobjective problem. In this paper, a multiattribute utility mergence method is proposed. Firstly, mergence rules are identified to achieve the aggregate utility according to the internal characteristic and logic relation of optimization indexes. Then, a SNOP allocation optimization model is built with the max aggregate utility value as the object. Finally, a case study of IEEE 33bus system is included to verify the effectiveness of the proposed model and method. It is shown that the multiattribute utility method for SNOP allocation can decrease active power losses, improve the system voltage level and load balancing level and increase the distributed generation penetration with a reasonable SNOP capacity.
2020, 35(4):20-26.
DOI: 10.19781/j.issn.16739140.2020.04.003
Abstract:
The accuracy of the impedance model of the converter station directly affects the small interference stability analysis of the flexible DC transmission system. However, the more accurate the model, the higher the order, which increases the complexity of the analysis. To analyze the influence of the phaselocked loop on the impedance characteristics of the converter station, we firstly establish the admittance matrix of the AC side of the converter station under the two conditions of dq coordinates with and without consideration of the phaselocked loop, and then establish the same order and mirror admittance of the converter station at the static coordinates. By comparing and not considering the input admittance of the phaselocked loop, it is concluded that the influence of the phaselocked loop on the input admittance value is directly related to the cutoff frequency of the phaselocked loop transfer function. Finally, the simulation model is established in PSCAD software. We use the signal injection method to obtain the homologous and mirror admittance of the converter station to verify the correctness of the theoretical analysis.
The accuracy of the impedance model of the converter station directly affects the small interference stability analysis of the flexible DC transmission system. However, the more accurate the model, the higher the order, which increases the complexity of the analysis. To analyze the influence of the phaselocked loop on the impedance characteristics of the converter station, we firstly establish the admittance matrix of the AC side of the converter station under the two conditions of dq coordinates with and without consideration of the phaselocked loop, and then establish the same order and mirror admittance of the converter station at the static coordinates. By comparing and not considering the input admittance of the phaselocked loop, it is concluded that the influence of the phaselocked loop on the input admittance value is directly related to the cutoff frequency of the phaselocked loop transfer function. Finally, the simulation model is established in PSCAD software. We use the signal injection method to obtain the homologous and mirror admittance of the converter station to verify the correctness of the theoretical analysis.
2020, 35(4):176-181.
DOI: 10.19781/j.issn.16739140.2020.04.024
Abstract:
Aiming at the nondirectly grounded distribution network of neutral point, this paper proposes to connect the small current fault line selection device to the distribution automation system. When a singlephase ground fault occurs, through the onoff control of the intelligent switch on the line and sequential logic of singlephase grounding alarm signal to determine the fault interval.Then the method isolates the fault area through the distribution automation system, restores the power supply in the nonfault area, and realizes the singlephase ground fault selfhealing of the distribution grid. In the end, this paper verifies the effectiveness and necessity of this strategy by experiments.
Aiming at the nondirectly grounded distribution network of neutral point, this paper proposes to connect the small current fault line selection device to the distribution automation system. When a singlephase ground fault occurs, through the onoff control of the intelligent switch on the line and sequential logic of singlephase grounding alarm signal to determine the fault interval.Then the method isolates the fault area through the distribution automation system, restores the power supply in the nonfault area, and realizes the singlephase ground fault selfhealing of the distribution grid. In the end, this paper verifies the effectiveness and necessity of this strategy by experiments.
