Abstract:The technology progress plays an important role in supporting the low-carbon transition of power systems. At the same time, the development of technology should also aim at the realization of the low-carbon transition of power systems. Especially in the long-term time scale, the mutual interaction between them is more significant. China promises to achieve the goal of carbon neutrality of the whole society before 2060, and the power system will gradually achieve low-carbon or even zero-carbon emissions. The development level of key technologies such as clean energy power generation, ultra-high voltage (UHV) power transmission and energy storage has become an important factor in the economic feasibility of power system transition, and the development of the key technologies should also be accelerated with the goal of carbon neutrality. In order to quantitatively evaluate the coupling and matching relationship between the key technology progress and the economic feasibility of the low-carbon transition of power systems, a framework and a method of collaborative optimization of them are proposed. It combines the technology maturity and economy with the power system expansion planning model, and takes the 2060 long-term power planning of China as a case to study the economic feasibility of the clean low-carbon transition for the power system in different technology development scenarios, and the contribution of different technologies to the reduction of the overall unit electricity cost of the whole system is analyzed.

Abstract:With the introduction of the objective of “carbon emission peak and carbon neutrality” and the gradual completion of the carbon market system, industrial enterprises are facing tremendous pressure in the low-carbon transition and sustainable development. The vigorous development of renewable energy and the application of hydrogen energy in the transportation and industrial production have provided better opportunities for the industrial enterprises. Based on this, the use of renewable energy and hydrogen energy industry chains to reshape the industrial energy system is a major means to promote industrial development. By taking the low carbon, green, environmental protection, and energy saving as the main considerations, a coupling complex system consisting of “green power, hydrogen energy and industry” is built, and the advantages of the coupling system are compared and analyzed from two perspectives of energy flow and carbon flow. Through the construction of environmental protection, energy saving and economic evaluation models, the feasibility of the construction of the coupling system is quantitatively explained. By analyzing the development status of iron and steel industry in China, the green development potential of iron and steel industry is calculated according to different development speeds. The results show that the green development of iron and steel industry will greatly promote the development and application of the green hydrogen, the gradual maturity of the hydrogen energy industry chain will also speed up the green transformation of iron and steel industry,and they complement each other.

Abstract:The integration of distributed generators and a massive amount of customer-side adjustable resources makes it possible to improve system energy efficiency, save electricity costs and achieve clean energy transition through demand-side response. However, the uncertainty and intermittency of distributed generation as well as the random fluctuation of customer load make the model-driven regulation methods that rely on forecasted data have the problems of poor regulation results due to forecast errors. To address the above problems, a data-driven real-time economic regulation method for the household energy is proposed. The method first establishes a mathematical model of the household energy system, and then uses historical data to construct a training sample dataset based on the model-driven approach. The constructed training dataset will be used for the supervised learning of the artificial neural network to build a data-driven regulation decision model. Afterwards, when a new scenario arrives, the model outputs the regulation results and imposes equipment constraints to obtain regulation decisions. Simulations demonstrate that the proposed method can coordinate the operation of the electrical appliances and the energy storage system based on the change of electricity price, which can achieve the economic operation while ensuring the safe operation of the electrical appliances and the energy storage system.

Abstract:In order to realize the selection and quantitative evaluation analysis of energy trading schemes between multi-microgrid systems, a co-governance decision-making method for coordinated transaction of multi-microgrid energy is proposed. Each microgrid in the multi-microgrid system is regarded as an equivalent energy management entity. Each microgrid can propose an energy trading scheme or score and evaluate the scheme, thereby constructing a decentralized decision-making and distribution energy management architecture without a central management entity. In order to verify the effectiveness of the proposed framework, three trading schemes of contract, price and peer-to-peer are designed for reference and analysis. The proposed optimization scheme is evaluated and scored by the remaining microgrids using economy, fairness, environmental protection and safety as evaluation indicators. Subjective and objective weights are determined by using analytic hierarchy process and entropy evaluation method. The optimal execution scheme is selected through comprehensive decision-making using the combination weighting method, so as to realize the co-governance decision of coordinated transaction for multi-microgrid energy . The simulation of the calculation example shows the results of the optimization schemes in the co-governance mode. The schemes are compared and analyzed according to the evaluation indicators, and the transaction execution scheme is selected through comprehensive evaluation, which verifies the effectiveness of the proposed method.

Abstract:The accuracy of the existing three-phase power flow linearization models in distribution networks decreases obviously under heavy load, which limits its application. Therefore, an improved hybrid data-physical-driven linearization method for three-phase optimal power flow is proposed. First, the three-phase linear power flow model is obtained based on the physical characteristics of distribution networks. Then, the linearization error model is obtained by using the data-driven method of partial least squares regression to correct the physical-driven model. Compared with the fully data-driven method, the three-phase linear power flow model retains the line information and can be used to describe branch constraints in the optimal power flow. Compared with the fully physical-driven model, the three-phase linear power flow model can obtain the linear relationship between the linearization error and the node load by making full use of the optimization fitting ability of data-driven approach. Because the error correction term contains more multidimensional global information, the accuracy of the linearization model is improved, and the accuracy of the proposed method is still high enough under heavy load. The proposed method has better applicability, which can deal with the three-phase transformers and the load models with various connection modes, and the distributed generator model considering the coupling between phases. Based on the IEEE standard cases, the proposed method is compared with other linearization methods that can be used for optimal power flow. The results show that the proposed method still has high accuracy under heavy load.

Abstract:The coupling of heating, cooling and power energy keeps increasing, and the integrated operation optimization of multi-energy systems is a key concern. Under the background of park-level integrated energy system (PIES) connecting to the active distribution network, this paper studies the coordinated dispatching of the PIES and active distribution network. Firstly, a dispatching model of PIES is established, with integrative cost as the optimization objective. Secondly, a multi-source coordinated dispatching model of the active distribution network is established. The model contains PIES, distributed generators, energy storage equipment, and flexible loads. The objective functions are dispatching cost, variance of load curves and abandoned renewable energy power. Thirdly, the model is solved by using analytical target cascading method combined with the particle swarm algorithm. Finally, numerical test on the modified IEEE 33-bus system verifies the effectiveness of the model and solving method.

Abstract:With the continuous growth of clean energy, such as photovoltaic power, wind power, etc., the electricity-heating hybrid system will be the development trend of the integrated energy system in the future. Firstly, an equivalent relationship between the electric power of the power system and the fluid mass flow rate of the heating network system is built to ensure that the electric power flow and heating power flow can be analyzed on the same time-domain scale. On this basis, the average temperature response model of the heating network system and the external characteristic model of the electric boiler are respectively constructed, thereby confirming the response status of the heating network system and the interactional variables between the electric and heating power flows. Based on the fundamental principles of the Newton method and hydraulic calculation of the heating network system, the power flow correction equations of the electricity and heating network system are deduced as well as its Jacobian matrix, thus developing a static power flow analysis method for the electricity-heating hybrid system considering the variation of the electric heating efficiency with the system operation environment. Finally, the case analysis is given to demonstrate the feasibility and practicability of the proposed method.

Abstract:This paper analyzes the effect of the flexible distribution network (FDN) on the accommodation of intermittent distributed generator (DG) from the perspective of source-grid-load matching. Firstly, the concept of DG and load matching is proposed to measure the degree of power balance between them. In order to better explain the accommodation results, the accommodation ratio is divided into source-load matching accommodation ratio and source-grid-load matching accommodation ratio. The source-load matching accommodation ratio ignores the network constraint. Secondly, a method to calculate the source-load matching accommodation ratio from the matching degree is proposed. This paper presents a DC-based time-series production simulation model, and a voltage calibration and result correction method to calculate the source-grid-load matching accommodation ratio. Finally, three typical scenarios are designed based on the matching relationship between DG and load, and the accommodation ratios of FDN and traditional rigid distribution network (RDN) are compared and analyzed to obtain the accommodation mechanism of FDN and suggestions for operation and planning.

Abstract:Source-load-storage interaction is an important technical method to deal with flexibility shortage of power systems with high proportion of renewable energy. Quantifying the influence of energy storage on source-load-storage interaction to enhance system flexibility is beneficial to optimizing the configuration of the energy storage resources. Based on the economic dispatch optimization model of the system with energy storage and flexible loads, considering the stochastic variation of wind power output, the duality theory is used to generate cut-plane constraints excluding infeasible points, the three-dimensional domain interval with storage and load regulation interval and the acceptable wind power fluctuation range is calculated, then the influence of configuring energy storage resources on improving the acceptability for wind power of the system is quantified. In the IEEE 30-bus system, three-dimensional domain interval is utilized to visually portray the wind power accommodation fluctuation range of the system cooperated with the multi-typical flexibility of the system. The numerical examples indicate that using the proposed model to simulate the impact on the ability of system to cope with random changes in wind power output by source-load-storage interaction, which is generated by the spatial distribution and capacity rationing relationship between energy storage, wind power and flexible loads, and could improve the economics of energy storage configuration planning.

Abstract:The large-scale application of the line commuted converter based high voltage direct current (LCC-HVDC) transmission systems makes the harmonic and resonance problems of AC/DC hybrid power grids increasingly prominent. The harmonic state estimation is the premise of power grid harmonic management, but existing studies mainly focus on AC grids. Even if the DC system is considered, it is only regarded as a harmonic current source. And existing methods cannot achieve the unified harmonic state estimation that takes into account the harmonic interaction between AC and DC systems. Based on the wide-area broadband synchronous monitoring system, and treating the AC/DC hybrid power grid as an organic whole, a unified harmonic state estimation model for the AC/DC hybrid power grid with LCC-HVDC is developed. Then, taking into account economy, redundancy and robustness, a comprehensive model for the optimal placement of broad-band phasor measurement units (bPMUs) and its staged solution method are proposed, which significantly improve the rationality of the placement and the computational efficiency. Furthermore, the robust least squares method is used to solve the unified harmonic state estimation value of the AC/DC hybrid power grid with LCC-HVDC. Finally, a simulation model of the AC/DC hybrid power grid based on PSCAD/EMTDC is established. The simulation results verify the effectiveness and accuracy of the proposed method.

Abstract:Broadband carrier communication technology has greatly increased the frequency and breadth of data collection for electricity consumption information, and in-depth exploration of the application value of metrology big data is a current research hotspot. First, aiming at the low-voltage distribution network with a radial topology, this paper constructs a circuit model with two-stage virtual loop impedance, that is, the user's virtual trunk line impedance and virtual branch line impedance; and achieves accurate calculation of two types of virtual impedances by eliminating the interference of the three-phase imbalance and adopting a multi-constraint linear regression model. Then, the operation mechanism of several typical abnormal operation conditions in the distribution station area is analyzed, such as topology abnormality, electricity theft by users, and line abnormality. And an analysis method for the abnormal operation condition perception of distribution stations is proposed, forming a combination diagnosis strategy based on timing stability of virtual loop impedance and spatial similarity to effectively support the equipment maintenance and power consumption inspection task of the power grid company. Finally, a power supply station in Hebei Province of China is taken as an example, and engineering application analysis and on-site verification are carried out, which fully verify the effectiveness of the proposed method.

Abstract:When multiple fixed-ratio electricity-theft users exist in one distribution station area, the non-technical loss (NTL) of the station area will be jointly determined by the amount of electricity stolen by this group of electricity-theft users. Current detection methods ranked according to the strength of the NTL correlation are likely to fail in this scenario. First, to solve this problem, this paper finds an incremental phenomenon in the correlation between the NTL of the station area and meter data of the fixed-ratio electricity-theft users, and argues a sufficient condition for this phenomenon to hold. Based on this, a method of electricity theft detection based on covariance analysis is proposed. The correlation between NTL and users’ electricity consumption is measured by normalized covariance, and the search for an fixed-ratio electricity-theft users is realized by solving a combinatorial optimization problem. Then, the operational framework and detection scheme of the method in the practical application are designed. Finally, the effectiveness of the proposed method is verified based on the actual measurement data provided by a provincial power company in China and the electricity theft data generated by the electricity theft simulation experiment platform.

Abstract:Adaptive reclosing should not only have the ability to distinguish fault types but also further optimize the reclosing time after the transient fault, which requires the identification of fault arc extinction time. Firstly, by analyzing the dynamic characteristics of grounding fault arc, the nonlinear characteristics of fault arc and adaptive simulation of arc extinction time are realized. Secondly, the transient and steady state characteristics of fault pole voltage of true bipolar flexible DC line before and after arc extinction are analyzed. It is revealed that the changing trend of fault pole voltage before arc extinction mainly depends on the zero input response component, showing an attenuation trend, while the fault pole voltage after arc extinction mainly depends on the zero state response component, showing an upward trend. Finally, an integral ratio algorithm is proposed to effectively extract the characteristic difference of fault extreme voltage before and after arc extinction. If the integral ratio is not lower than the threshold in the cycle judgment time, the fault arc extinction is judged, and the time when the threshold is exceeded for the first time is output as the detected arc extinction time. PSCAD/EMTDC simulation results verify the effectiveness and reliability of the proposed strategy.

Abstract:The multi-terminal bipolar DC system with the earth electrode system is not allowed to operate with the large grounding current for a long time. In the operation mode of unipolar exit at the receiving end, it is necessary to reduce the grounding pole current of each converter station and compensate the power loss of the converter station with the unipolar exit condition. Based on the parallel bipolar three-terminal DC system, this paper proposes a current adjustment strategy for the converter stations under the condition of unipolar exit at the receiving end. First, the grounding current is reduced by adjusting the current at both poles of each converter station. Then, the idle DC line or the standby line is used as a metallic branch to transfer the grounding current at the receiving end with the unipolar exit to the earth electrode of the adjacent converter station. Finally, the DC current of the adjacent converter station is reduced, so that part of the power of the adjacent converter station is transferred to support the receiving end with the unipolar exit. The proposed strategy is verified by the simulation based on PSCAD/EMTDC. The simulation results show that the proposed current adjustment strategy of the converter station can control the grounding current at a safe level and reduce the DC power loss at the receiving end with the unipolar exit.

Abstract:The controller parameters of high voltage direct current (HVDC) transmission systems have an important influence on the system stability and dynamic response performance. This paper proposes a controller parameter setting method for the line commutated converter based high voltage direct current (LCC-HVDC) system based on the D-partition method. Firstly, based on the operation parameters of an actual project, an equivalent small-signal dynamic model of the LCC-HVDC system in the single-pole full-voltage operation mode is established. Then the transfer functions of constant current control and constant voltage control loops are obtained based on the Laplace transform of the model. The D-partition method is used to set the proportional-integral (PI) parameters of the constant current controller and the constant voltage controller, and obtain the controller parameter setting domain that meets the requirements of gain margin, phase margin and bandwidth limitation at the same time. The parameter setting domains at different power transmission levels are superimposed to obtain the multi-condition general controller parameter domain. The simulation results verify the accuracy of the small-signal dynamic model and the effectiveness of the proposed controller parameter setting method.

Abstract:As an increasing number of power electronic devices are integrated into modern power systems, the demand for real-time electromagnetic transient simulation with microsecond simulation steps keeps increasing. It is an important way to realize the real-time simulation of the converters by improving the computing capability of the simulation system through the field programmable gate array (FPGA). A multi-rate real-time simulation method of converters is proposed by introducing FPGA as a hardware acceleration device to optimize the real-time performance of the simulation system. Aiming at the analysis of the error caused by the multi-rate decoupling of the control system as well as the parallel computing sequence, the improved linear extrapolation algorithm combined with the Lagrange interpolation method is used to effectively reduce the delay error in the multi-rate parallel simulation sequence after the control system is decoupled. The simulation results show that, compared with the parallel computation without the extrapolation algorithm, the proposed simulation method has higher accuracy. The performance analysis verifies that the established simulation platform has certain advantages in the real-time performance and resource utilization compared with the simulation platforms established solely on CPU or FPGA.

Abstract:In order to improve the sensitivity of high-resistance grounding fault detection in distribution networks, a single-phase grounding fault detection method for tracking and monitoring parameter asymmetry of distribution lines is proposed. Aiming at the random difference characteristics of distribution parameters of lines in the distribution network, the parameters characterizing the parameter asymmetry of lines are defined, the critical conditions and flow path of generating zero-sequence current of distribution lines are demonstrated, the equivalent operation model of the zero-sequence network for the distribution network considering the asymmetric random difference of line parameters is established, and the measurement methods of parameters such as distribution line impedance to ground and asymmetry are proposed to realize single-phase grounding fault line selection, phase selection and transition resistance measurement. The fault detection scheme is optimized according to the fault types. In the case of high-resistance grounding, the zero-sequence voltage is artificially adjusted to improve the sensitivity of fault detection. In the case of a low-resistance fault, the fault is quickly detected only relying on the change of zero-sequence electrical information. Simulation experiment results verify the effectiveness of the proposed detection method.

Abstract:In the DC system, the short-circuit current rises quickly and the peak value is high. As the voltage level and capacity of the system increase further, the short-circuit current breaking becomes a greater challenge. To reduce the breaking requirements of DC circuit breakers (DCCBs), it is crucial to consider fast fault current limiting in the breaking process. But it is difficult to combine both current limiting and breaking processes in existing DC breaking schemes. In this paper, a new DC circuit breaker topology with integrated current transfer and damping is proposed, which can achieve rapid fault current limiting while ensuring high breaking capacity and low cost. Firstly, the breaking principle of the proposed DCCB is introduced. Then the key influencing factors of the damping module and magnetic coupling transfer module are analyzed to obtain the optimal design of the parameters of the damping module and magnetic coupling module. Finally, based on the simulation model, the proposed breaking scheme is simulated and the breaking adaptability of the proposed topology under different operation conditions and on different voltage levels is verified. The effectiveness of the proposed damping DC breaking scheme is verified through experiments.

Abstract:The upstream and downstream locating of the voltage sag source plays a role in clarifying the responsibilities of both the power supplier and the consumer. Facing the problem of poor applicability of the load model in the traditional location method, based on the Thevenin equivalent model, this paper proposes a voltage sag source location method by comparing the changes of the upstream positive sequence parameters before and after the voltage sag. Firstly, the upstream positive sequence parameters are identified, and the upstream and downstream positions of the voltage sag source are determined by comparing the changes of upstream system positive sequence parameters before and after the voltage sag. Considering the influence of parameter uncertainty, calculation error and measurement error, an improved criterion based on the probability is proposed. Considering the influence of errors on the location results, a probability index is introduced into the location fuzzy area, to quantitatively analyze the responsibilities of the upstream and downstream parties that cause the voltage sag, which improves the rationality of the location results. Finally, the correctness and effectiveness of the proposed method are verified by the IEEE standard model.

Abstract:Aiming at the challenge of wind power output uncertainty to the safe and stable operation of power systems, a prevention and control method for security and stability risk of power systems with large-scale wind power integration is proposed. Considering that the optimization objective is to minimize the control cost of preventive control measures, including the control cost of adjusting the output of thermal power units and the curtailment risk of limiting the output of wind power clusters, the allowable operation risk is transformed into opportunity constraints with reference to the accident level evaluation standard of the power system. By calculating the control performance indices of thermal power units and wind power clusters, the effective control measures are selected, and the control quantities of effective control measures are classified and enumerated to obtain all possible control schemes. The control schemes are verified by parallel implicit enumeration based on the cluster parallel computing platform to obtain the control measures that meet the target function. The example analysis of a practical system verifies the practicability and effectiveness of the proposed method.

Abstract:To solve the data read-write conflict problem of microservices in edge computing terminals, a file lock based data synchronization mechanism for microservices of edge computing terminals in power distribution Internet of Things station area in the background of new power system is proposed. Firstly, a file lock based data interaction mechanism for microservices in edge computing terminals is designed to support the orderly access of microservice data. Secondly, a synchronization area partition mechanism is proposed to divide the areas for microservices and to eliminate the hidden danger of data read-write conflict of cross-area microservices. Then, an synchronization mechanism in a partition and an adjacent-area synchronization mechanism are proposed to solve the data read-write conflict of microservices in the same region and adjacent regions. Finally, the simulation analyzes the impact of the time-sequential logic structure of the microservice on the time consumption of the file lock based data synchronization mechanism. The results are compared before and after the adoption of the file lock based data synchronization mechanism, considering different microservice decomposition degrees and adopting different data synchronization mechanisms. The effectiveness of the proposed method is validated.

Abstract:At present, the research of electricity-heat integrated energy networks is mostly based on the traditional heat network and limited to the weak coupling network composed of a small number of combined heat and power units. The energy cells driven by the 5th generation district heating and cooling (5GDHC) system can realize the high-density mesh integrated electricity-heat network through the heat pump pool and change the interactive form of the electricity-heat network. This paper discusses the great opportunities and challenges brought by the 5GDHC system to the unified modeling theory of integrated energy electricity-heat coupling network, and the broad application prospect of energy cell flexibility aggregation based on the 5GDHC system. Furthermore, the research status of the 5GDHC system, the multi-energy flow modeling theory of electricity-heat coupling network, and the flexibility aggregation method of distributed resources are summarized. Aiming at the opportunity of energy cells using the heat pump pools and the heat network thermal inertia to improve the flexibility of the power grid, the research idea of energy cell network flow theory and flexibility aggregation method driven by the 5GDHC system are proposed: the interaction mechanism and feasible region analysis of thermal dynamics from heat pump pool to distribution network and hierarchical coordinated optimization method for flexible aggregation and allocation of heterogeneous smart energy cell interconnection.