In this paper, large-scale energy storage system(ESS) is taken as the research object to conduct study of business models on the participation of ESS in electricity spot market with liberalization. First, based on the typical market clearing mechanism at home and abroad, the clearing method, clearing calculation process and so on in day-ahead market and real-time balance market are analyzed, and a joint clearing mechanism suitable for large-scale ESS to participate in the spot market is proposed, including bidding method, billing method and clearing method, etc. Then, in order to fully explore the market value and other added value of large-scale ESS, to enhance cluster effect and to solve the problem of idle ESS capacity, business models suitable for large-scale ESS to participate in the spot market are proposed, including independent (single investment entity, single service model), alliance (diversified investment entities, single service model), and shared (diversified investment entities, diversified service models) models. The game relationship in the market transaction chain is analyzed, of which the electric energy value, the ancillary service value, and other added value are quantified. On this basis, a bilevel clearing model paradigm for ESS to participate in the spot joint market of different business models is constructed based on the master-slave game. In the upper-level model, large-scale ESS is the leader to participate in market competition with the goal of maximizing profits, while the dispatching and trading center in the lower-level model are followers to jointly clear the market with the goal of maximizing social welfare. Finally, the validity and feasibility of the proposed business models are verified by taking typical transaction scenarios as examples based on the improved IEEE30 node system.
Electromagnetic detection is the main method of marine oil and gas resources exploration, and marine electromagnetic transmitter is the key equipment of marine electromagnetic detection system. At present, when the underwater towed body of the marine electromagnetic transmitter operates for a long time, the switch devices will be damaged. First, the commutation process of the transmitting bridge with unidirectional controlled-source circuit is analyzed. It is found that the feedback energy of the transmitting dipole parasitic inductor makes the secondary bus generate impulse voltage, which increases the voltage stress of the switch devices. Then, the operating mode of bidirectional controllable source circuit is analyzed, and a dual variable decoupling control strategy is proposed. Based on the model established at the front and back of the transformer, the original coupling nonlinear system is globally linearized into two single input single output systems, so as to obtain the functional relationship of the sliding mode controller. The simulation and experimental results show that the designed controllable source circuit can significantly reduce the impulse voltage of bus capacitor and the voltage stress of switch device, and improve the dynamic performance and efficiency of the system.
In order to achieve the dual carbon goal of “carbon peak and carbon neutrality”, it is of great significance to promote the electric and hydrogen complementary integrated energy system. However, with the gradual increase of the penetration rate of renewable energy, the inertia level of the system decreases, and the frequency security is threatened. Aimed at the problem that the traditional optimization scheduling method cannot guarantee the frequency stability of the system, a coordinated optimization scheduling method of electric-hydrogen complementary multiple buildings considering the frequency stability constraint is proposed. First, the architecture of the electric-hydrogen integrated energy system with the building as the ground floor unit is established, and the renewable energy generator sets in the system are controlled by the virtual synchronous generator technology to improve the inertia level of the system. Then, aimed at minimizing the total operating cost of the system in the scheduling period, and considering the inertia requirements of the system in different operation modes of grid-connected and islanding, an optimal scheduling model considering the system frequency stability constraint is established. Finally, an example is given to verify the effectiveness, economy, and environmental protection of the proposed method for frequency stability of the system.
Virtual power plant (VPP) with a carbon capture system provides a new path to improve energy efficiency and achieve the target of carbon peaking and carbon neutrality. At the same time, flexible coordination of multiple uncertainties in the VPP system is a key premise to realize low-carbon operation of the system. A low-carbon economic dispatch model of VPP considering ladder-type carbon trading in multiple uncertainties is proposed. The carbon capture system and demand response are modeled, and a carbon trading mechanism is introduced into the optimal dispatch model to build a ladder-type carbon trading cost model to restrict system carbon emissions. A variety of uncertain factors in VPP is modeled, including wind power generation, photovoltaic, load and electric vehicle, and a low carbon economic dispatch model of VPP is established considering opportunity constraints. The uncertainty of electric vehicles is dealt with by using adjustable robust optimization. Based on the sequence operation theory, the uncertain model with opportunity constraints is transformed into a mixed integer linear programming model. The decision optimization technology CPLEX solution is used to verify the effectiveness of the proposed model in an actual VPP example.
Wind power generation is different from traditional power generation in which wind power output is highly stochastic and spatio-temporally dependent. In the optimal scheduling problem of wind power grid-connected power system, ensuring the optimal execution of power scheduling in different wind power scenarios is the key of the decision-making problem. Therefore, high quality wind power scenario generation is of great importance. The spatiotemporal correlation of the output power of wind power plants are characterized based on Gaussian stochastic process and spatiotemporal covariance function, and the joint probability distribution is established by the Pair Copula model, and specific scenarios are implemented by the method of empirical probability inverse transformation. A variety of scene metrics of the generated scene are generated, which verifies the superiority of the generated scene. Finally, based on the modified IEEE 6-bus system, a mixed integer programming model for the unit output of the power system is established to solve the problems in different scenarios and verify the economic advantages of the scenario generation method in the dispatching problem of wind power grid connection.
The operation of the integrated energy system is one of the hot spots in the current energy research field. With the reform of the energy field mechanism, the integrated energy system with multi-micro-energy grids poses great challenges to the operation of the power grid. Aimed at the economic and operational problems caused by the integration of multi-micro-energy grid integrated energy systems into the upper distribution network, a multi-temporal and spatial scale optimization operation strategy for integrated energy of micro-energy grid considering demand response is proposed. Moreover, a multi-dimensional energy supply and demand balance model from the perspective of energy is constructed. Furthermore, a multi-time-space scale operation model with upper, middle, and lower layers of collaborative optimization is established. The upper layer adopts day-ahead scheduling, the middle layer adopts intraday scheduling, and the lower layer adopts real-time scheduling with replaceable, transferable, and curtailable loads for demand response optimization. Calculation examples show that this strategy can realize the co-ordination and complementation of multi-dimensional energy sources, realize the coordinated operation of multiple energy sources at different time and space scales, and improve the economy of system operation.
In order to reduce the forecast output error caused by the randomness and volatility of renewable energy in microgrid operation, a microgrid energy management strategy considering carbon quota guided demand response is proposed. A two-layer model predictive control (MPC) energy management model is constructed. The upper layer guides electric vehicles to participate in the demand response of microgrid by constructing a carbon emission quota mechanism to realize the economic operation of microgrid and reduce carbon emissions. The lower layer uses the model predictive control rolling optimization and the power fluctuation caused by the prediction error of renewable energy is suppressed by the short time scale model predictive control. The results of calculation analysis show that the proposed energy management strategy can effectively guide electric vehicles or other controllable loads to participate in demand response and realize low-carbon economic dispatch and stable operation of microgrid.
Stepwise inertial control (SIC) provides a step-increase of power after load fluctuation, which can effectively prevent system frequency decline and ensure the safety of grid frequency. However, in the power recovery stage, secondary frequency drop (SFD) is easy to occur. Therefore, it is necessary to optimize SIC to obtain a better frequency regulation effect. The traditional method has the disadvantages of high calculation dimension and long consuming time, which is difficult to meet the requirements of providing the optimal control effect in different scenarios. In order to realize the optimal stepwise inertial fast control of wind power frequency regulation in load disturbance events, this paper introduces the deep learning algorithm and proposes a stepwise inertial intelligent control of wind power for frequency regulation based on stacked denoising autoencoder(SDAE) and deep neural network(DNN). First, sparrow search algorithm (SSA) is used to obtain the optimal parameters, and SDAE is used to extract the data features efficiently. Then, DNN is used to learn the data features, and the accelerated adaptive moment estimation is introduced to optimize the network parameters to improve the global optimal parameters of the network. Finally, the stepwise inertial online control of wind power frequency regulation after disturbance event is realized according to SDAE-DNN. The simulation analysis is conducted for a single wind turbine and a wind farm in the IEEE 30-bus test system. Compared with the results obtained by the traditional method, shallow BP neural network and original DNN network, it is found that the proposed network structure has a better prediction accuracy and generalization ability, and the proposed method can achieve a great effect of stepwise inertia frequency regulation.
The optimal Latin hypercube experimental design method is used to refine the vortex generator parameters, determine the test scheme, simulate and calculate the thrust and torque of the wind turbine, and obtain the experimental data. Based on the back propagation (BP) neural network, the aerodynamic performance model of the wind turbine vortex generator optimized by genetic algorithm is constructed. The reliability of the aerodynamic performance model is verified by calculating the error and root mean square of the predicted and simulated values of the aerodynamic performance model. Coupling the fish swarm algorithm and the aerodynamic performance model of the wind turbine vortex generator, an optimization method of the wind turbine vortex generator is established, and the height, length, and installation angle of the vortex generator are solved iteratively to realize the optimization of the vortex generator. The results show that compared with the original vortex generator scheme, the flow separation of the wind turbine blade section optimized by the vortex generator is effectively restrained and delayed, the surface fluid separation phenomenon is improved, the power of the wind turbine is increased by 1.711%, and the thrust of the wind turbine is decreased by 0.875%.
The modular multilevel converter (MMC) suffers from low output level and high harmonic distortion in medium-/low-voltage applications such as direct current (DC) distribution networks. In addition, the capacitor voltage of MMC is coupled with DC bus voltage in the traditional modulation method, leading to large fluctuations of capacitor voltages and deviation from the rated value under DC bus voltage margin. In order to solve the problems above, this paper proposes an improved nearest level control method, which can increase the output level of medium-/low-voltage MMCs by introducing a step wave correction. Based on the proposed modulation method, a capacitor voltage feedback control is thus proposed to limit the range of capacitor voltage fluctuations and improve equipment safety. The effectiveness of the proposed method is verified by MATLAB/Simulink simulation and real-time digital simulation system hardware-in-the-loop test.
Due to the considerable number and the characteristics of energy storage, it is possible for electric vehicles (EVs) to participate in the operation and regulation of power system to provide reserve service. In view of this, a multi-objective optimal scheduling model is established based on the wishes of electric vehicle users, with the objectives of the economic benefits of electricity collectors, microgrid power fluctuations and user satisfaction. Considering the uncertainty of load demand, the optimal scheduling analysis of multi-time scale scenes with the day-ahead time scale and the intra-day real-time correction time scale is conducted. The mainstream multi-objective intelligent optimization algorithm NSGA-III algorithm is adopted in the solution method, and the NSGA-II and MOEA/D algorithms are used for comparison. The optimal dispatching scheme is selected through comparative experiments and scenarios where EVs provide spare capacity are analyzed. The simulation results verify the feasibility and effectiveness of the proposed model.
Aimed at the problem of uncertainties in the regional development stage and the difficulties in quantifying regional investment demand in different development stages, a robust optimization method for power grid investment decision-making considering regional development stage uncertainties is proposed to promise the matching degree between power grid investment decisions and development needs, and to improve the ability of decision-making results to deal with portfolio risks and uncertainties in regional development stage. First, investment risk constraints are constructed based on the modern portfolio theory. Then, a box uncertainty set is used to characterize uncertainties in regional development stage, and a robust optimization model for power grid investment decision-making considering uncertainties in development stage is established. In the optimization model, the outer minimization problem is used to solve the uncertain variables in regional development stage in the worst scenario, while inner maximization problem is used to obtain the decision-making plan that can maximize investment return in the worst scenario. Furthermore, according to the strong duality theory, the double-layer optimization model is transformed into a single-layer model that can be solved directly, and the big-M method is used to solve the model proposed. Finally, an actual example of 13 cities in an eastern coastal province verifies the applicability and effectiveness of the power grid investment decision-making model.
Serious earthquake disasters not only cause power outages in distribution network, but also destroy transportation networks, which hinders the transportation of resources for restoration of distribution network and slows down the restoration. This paper proposes an improved resilience evaluation method and a resilience enhancement strategy of distribution network considering the effects of seismic attack on transportation networks. First, a seismic attack model is established to describe the relation between earthquake disasters and failure probability of transportation-distribution networks based on peak ground acceleration. The impact of earthquake disasters on transportation-distribution networks is quantified, and the failure scenarios are generated. Then, a resilience evaluation index is proposed by introducing the waiting time for road repair of emergency repair teams. Afterwards, a bi-level optimization model for distribution network restoration considering the fault line repair, the road repair, and the emergency resource scheduling is established and solved. The upper layer aims at the minimum power loss load, while the lower layer takes the minimum waiting time of the repair team as the goal. Finally, case studies on a coupling example of a 12-node transportation network and an IEEE 33-node distribution network verify the feasibility of the improved resilience index and the effectiveness of the proposed method. The results show that the resilience index considering seismic attack on transportation networks is accurate, and the restoration strategy can effectively enhance the resilience of distribution network in earthquake disasters.
High penetrated renewable energy has brought great challenges to the flexibility of the power system due to its volatility and intermittency. To improve the capacity of renewable energy accommodation, the flexibility reformation of thermal power units, the construction of gas-fired units, and the electrical energy storage installation are considered as effective solutions. Thus, an optimization model for power system planning scheme considering multi-type flexible resources with their different output characteristics is established. The simulation results on a modified IEEE 24-bus power system and 12-node natural gas system demonstrate the effectiveness of the proposed model. In addition, the applicability of different flexible resource planning schemes is comprehensively evaluated from the perspectives of economy, accommodation capacity, and carbon reduction, so as to meet the different planning goals.
The passivity-based control (PBC) based on energy function has been studied for grid-connected converters to achieve a better performance. However, traditional PBC method relies on the accurate mathematical model of grid-connected inverter. In previous studies on PBC, the effect of digital control delay is rarely considered and the stability under grid impedance uncertainties is not discussed, especially in the capacitive grid or complex weak grid. To address these issues, this paper proposes an improved PBC method to reshape the output admittance for LCL-filtered grid-connected inverters. The system passive region is expanded up to the Nyquist frequency by adding a capacitor current feedback loop which can achieve active damping control of LCL resonant frequency under the wide range of grid impedance changes. The parameter design method is also presented for the proposed PBC control. To verify the correctness of the theoretical analysis, both simulation and experiments are conducted on a 3 kW grid-connected inverter prototype.
Aiming at the problem of weakly or negatively damped low-frequency oscillations caused by cross-zone transmission of electricity from large wind farms, this paper proposes a fast terminal sliding-mode additional damping controller based on the Lyapunov stability theory. By investigating the flexible power regulation characteristics and the capability of dynamic frequency response to damping regulation of doubly-fed wind turbines (DFIG), a rotor magnetic chain controller is designed according to the relationship between the applied voltage and magnetic chain of DFIG rotor and the sliding mode variable structure control method. When low-frequency oscillations occur in the system, the desired magnetic chain value will deviate from the actual magnetic chain value. The additional damping controller outputs an adaptive control signal for the rotor-side power control link to increase the active output of the wind farm and suppress low-frequency oscillations in the system. A simulation model of the wind power grid-connected system is established in MATLAB/Simulink for off-line simulations, and a real-time simulation experiment of a large wind farm cross-zone transmission model based on real time digital simulation system is conducted. The results of both off-line and real-time simulations show that when low-frequency oscillations occur in the system, the proposed control method can quickly regulate the active power emitted by the DFIG and enhance the damping level of the system, which is effective in suppressing low-frequency oscillations in the system.
Aimed at the impact of extreme weather on the stable operation of microgrid, an optimal configuration strategy of microgrid based on fuzzy scene clustering is proposed. Using historical weather data, a fuzzy scene clustering method is used to deal with the problem of new energy output fluctuations caused by random weather on the source side, and a robust optimization model is established on the load side to deal with load fluctuations within a certain range. Using scenes of 8 760 hours in a year, typical scenes and extreme scenes are obtained by distinguishing the unique membership characteristics of fuzzy scene clusters. Considering the impact of extreme scenarios on the optimal configuration of the microgrid, a two-stage robust model with the smallest comprehensive cost is established, which is decomposed by the column and constraint method, and is finally solved iteratively by Cplex solver. The effectiveness and feasibility of the proposed optimal configuration strategy are verified by simulation analysis.
To promote the optimal allocation of resources across the country, China is actively developing inter-provincial electricity transactions, and will gradually form an inter-provincial and intra-provincial electricity market operation mode. In this context, a two-stage day-ahead, and intraday economic dispatch framework considering inter-provincial and intra-provincial bi-level market coordinated operation is proposed. In the day-ahead dispatch stage, an inter-provincial and intra-provincial bi-level economic dispatch model is constructed. In the intraday dispatch stage, an economic dispatch model considering the forecast error of source-load is constructed. To further deal with the influence of the uncertainty of source-load forecast on economic dispatch, a two-stage day-ahead and intraday distributionally robust economic dispatch model and its solution method are proposed, realizing the economic dispatch under random scene ambiguity set. Finally, a multi-sending ends and multi-receiving ends interconnected test system is constructed using IEEE 39-bus and 118-bus systems. The effectiveness of the proposed model and method is verified by simulation.
Miniaturization, lightweight, and high power density are development trends of vehicle-mounted inverters. The existing vehicle mounted single-phase inverter with DC 110 V input voltage adopts two-stage independent modulation between Boost circuit and full bridge inverter circuit, which has the problems of low efficiency and low power density. To solve these problems, a two-stage cooperative modulation between Boost circuit and full-bridge inverter circuit is studied. According to the relationship between the absolute value of input voltage and output voltage, the Boost circuit and the full-bridge inverter operate with different modes in the proposed method, which optimizes the insulated gate bipolar transistor(IGBT) switching state and diode on-off state to reduce the loss of the inverter and improve the efficiency of the inverter. At the same time, the output harmonics of the full-bridge inverter circuit can be reduced to decrease the size of the filter and improve the power density of the inverter. A 2.75 kV·A prototype is designed and fabricated. Experiments are conducted to verify the correctness and feasibility of the proposed method.
The time resolution of scheduling plan refers to the length of each time interval in the scheduling plan. With the increasing proportion of climate-sensitive renewable energy sources (RES), the volatility of net load during the dispatch interval is significantly enhanced, resulting in an insufficient system climbing capacity and abnormal frequency. Therefore, the setting of time resolution at different renewable energy penetration rates becomes an urgent problem to be solved at present. A global sensitivity-based day-ahead dispatch time resolution selection optimization method is proposed to select the time resolution for different volatility grids. To achieve a balance between the degree of refinement and the accuracy of load prediction, the global sensitivity analysis method based on Sobol' method and sparse chaos expansion is used to evaluate the impact of net load volatility and uncertainty on dispatch at different time resolutions, and an appropriate time resolution is chosen to optimize the scheduling effect. The analysis and simulation results show that the choice of time resolution is mainly determined by the net load fluctuation rate. The appropriate time granularity is chosen according to the net load fluctuation rate, which minimizes the unbalanced power, and the purpose of improving the optimal scheduling effect and reducing the dispatching cost is achieved.
To solve the problems of large thermoelectric coupling in combined heat and power, high carbon emission of thermal power units, and insufficient resource flexibility on the load side in cogeneration units, a low-carbon dispatching model is established for the electricity-heat system. First, heat storage and carbon capture equipment is added on the source side while the demand response of electricity price and the heat load inertia of heating buildings are considered on the load side. Then, the sum of unit operating cost, carbon transaction cost and wind abandonment penalty cost are taken as the objective function with relevant constraints and solved by calling Gurobi solver. Finally, a comparative analysis of the economic cost, wind power consumption, and carbon emission rate of the system in different cases is conducted, which shows that the dispatching strategy proposed in this paper can improve the wind power consumption capacity while taking economy and low carbon emission into account.
To improve the stability of solar heating and reduce the high cost of air source heat pump heating, the idea of air source heat pump assisted solar stable heating was proposed. A solar vacuum tube water heater-air source heat pump system was developed and bulit in Weiling Township, Qilihe District, Lanzhou, Gansu Province. The performance of the system was compared to analyze the heat collection efficiency, heat pump coefficient of performance (COP), solar energy guarantee rate, and energy efficiency ratio under sunny, overcast, and cloudy conditions. The results show that the effective heat obtained by solar energy under sunny, overcast, and cloudy conditions is 75.5 kW·h, 4.1 kW·h, and 49.2 kW·h respectively, the system heat collection efficiency is 61.3%, 26.6%, and 55.2%, the average coefficient of performance(COP) of the solar heat pump is 3.6, 3.4, and 3.6, the average COP of the air source heat pump is 0, 2.9, and 3.1, the actual heat supply of the system is 113.4 kW·h, 125.9 kW·h, and 124.8 kW·h, the system power consumption is 33.4 kW·h, 50.5 kW·h, and 42.7 kW·h, the system solar energy guarantee rate is 66.6%, 3.3%, and 39.4%, and the system energy efficiency ratio is 3.4, 2.5, and 2.9 respectively. The research results prove that the solar vacuum tube collector-air source heat pump system is feasible for heating and provide a new way for heating in cold areas.
Fully tapping into the role of user side regulation helps reduce the energy cost of integrated energy system (IES). Demand response (DR) and electric vehicle (EV) as schedulable resources on the user side are important regulation means for optimal scheduling of IES. However, in the actual operation process, due to the influence of load aggregator (LA) economic incentives and EV travel, the economic impact of the uncertainty of user side DR on IES cannot be ignored. Based on this, this paper proposes an IES optimal operation model considering the robust stochastic optimization of EV and the participation of LA which considers the energy purchase cost of IES from the superior network and the economic loss cost of LA. First, the response rate model and EV uncertainty model based on economic incentive are constructed. Then, the robust optimization model of EV is built, and the load demand of EV travel uncertainty is analyzed. Finally, a simulation example is given to analyze the impact of user DR uncertainty and EV uncertainty on IES operation economy and power balance. The simulation results show that considering the uncertainty of DR and EV can optimize the economic operation of IES and reduce the economic loss of LA and the total cost, which verifies the effectiveness and economy of the proposed models.
With the gradual advancement of the market-oriented process of distributed generation, it is difficult to accurately distinguish the use degree of power grid assets by prosumers via pricing method of uniform calculation of network usage charge according to user access voltage. Therefore, this paper proposes a calculation method of network usage charge suitable for market-oriented trading of distributed generation. The characteristics of the peer-to-peer (P2P) trading model and the community-based (CB) trading model in distributed generation market are discussed from the perspective of prosumers. Meanwhile, the power trading models of the P2P model and the CB model are constructed. The optimal power flow model based on second-order cone relaxation is used to determine the distribution of power flow in distribution network, and the distribution locational marginal price is calculated with the economic significance of dual multiplier. Considering the transitivity of dual multipliers, calculation models of the network usage charge of the P2P trading model and the CB trading model are established by coupling the power trading model and the optimal power flow model. The limitations of the CB trading model are analyzed, and the Shapley value method is used to realize the fair allocation of network usage charge according to marginal contribution. By using the improved IEEE15 bus and IEEE123 bus test systems, the availability and feasibility of the proposed calculation method of network usage charge in distributed generation market are verified.
Energy is an important component of urban carbon emissions. Assessing the peak of urban energy carbon is a necessary means to implement the national “double carbon” strategy. For this reason, this paper proposes an energy carbon peaking assessment method based on Mann-Kendall trend test for carbon emission of urban energy. By constructing a carbon monitoring system covering elements such as energy carbon emissions, clean energy generation, and transportation electric energy substitution, the total energy carbon emissions of the city are calculated by combining historical data. In view of the seasonality and randomness of energy carbon emissions, the Mann-Kendall trend test was used to establish a model for determining urban energy carbon peaking and to measure regional carbon emissions in different periods. Taking an administrative region in Shanghai as an example, the peak status of energy carbon in this region is judged from the perspective of year and quarter. The results show that based on the annual data, the region has reached its peak energy carbon in 2020. Based on quarterly data, peak energy carbon has been achieved in summer and autumn, while spring and winter are still in plateau. The methods proposed in this paper can be used to assess the carbon peak status in the city, and provide a reference for examining the carbon peak process in other provinces and cities.
Driven by the carbon peaking and carbon neutrality goals, the power system is transforming to the new structure which is dominated by renewable energy and is facing a new supply-demand balance situation. Pumped storage, as the most mature energy storage technology at present, can provide flexible resources with different time scales to ensure the safety of the power system and promote the consumption of renewable energy. However, the operation strategy and cost sharing mechanism of the pumped storage station (PSS) are not clear, which hinders its further development under the new situation. In this context, the technical characteristics and functions of PSS are sorted out first. Then, the investment cost model is established from the perspective of the whole life cycle. After that, the evolution path of pricing mechanism and cost sharing mode are described in view of the different stages of electricity market development, providing a feasible scheme for the marketization of PSS. Finally, the future development of PSS is summarized and prospected.
During the production of gas diffusion layer (GDL), hydrophobic binding treatment and assembly compression lead to changes in pore structure and permeability. In this paper, a GDL model based on stochastic reconstruction is developed with binder and inhomogeneous compression. Single-phase flow of gas is simulated by utilizing the Lattice Boltzmann method and the effect of binder and compression on pore structure and permeability of GDL is explored. The results show that both the binder and the compression cause porosity to decrease and small-scale pore volume to increase, leading to the shrink of permeability. The change is basically consistent with the theoretical relationship between porosity and permeability. Moreover, the decrease of permeability caused by compression is higher than that caused by binder when porosity is similar.
The doubly-fed induction generator (DFIG) is connected to the distribution network as a distributed power source, which turns a radial single power supply system into a dual power supply system and changes the topology of the distribution network. When a short-circuit fault occurs in the distribution network, the short-circuit current of the distribution network will be affected by the access to wind power. Aimed at the problem that the short-circuit current is affected by the access capacity of the wind turbine and the location of the access point when DFIG is connected to the distribution network by distributed power sources and a three-phase short-circuit fault occurs at different points in the distribution network, a theoretical derivation and a simulation analysis are conducted by combining the control strategy of DFIG. First, relational expression of short-circuit fault current of the distribution network including wind power is theoretically derived, and the short-circuit current provided by the wind turbine is analyzed. Then, model predictive control is introduced to be compared with classical vector control to analyze the impact of different control strategies on the short-circuit current. The changes in access capacity and location are analyzed when a three-phase short-circuit fault occurs at different points in the distribution network, and the impact of DFIG on the short-circuit current of the distribution network is summarized.
Aimed at the main power tube with problems of weak driving ability, poor soft switching performance, and large switching loss in a self-excited resonant wireless power transmission (WPT) system, an analysis of the working principle of resonant main circuit is conducted, which indicates that the root cause of the problem is that two uncontrollable diodes limit the driving resistance of main power tube. Thereofre, an improved self-excited resonant circuit is proposed by using a fully controlled low power switch instead of the diode. The circuit theoretical analysis of four working modes suggests that the main power tube of the improved circuit has a stronger driving ability. To further obtain the optimal parameters of the improved system, a nonlinear programming model of the system is established by considering the tolerance limit of each parameter, and a hybrid optimization algorithm is designed to obtain the system global optimal solution. A comparison of the results of system simulation and experimental prototype shows that the improved WPT system has an excellent soft switching performance. The temperature of the switch tube is reduced by about 7 ℃, and the efficiency is increased by about 4%.
A microgrid control method based on prescribed time control is proposed to solve the cooperative control problem of distributed energy resources (DER) in DC microgrid. First, a current control method based on prescribed time control is proposed, which can allocate the power output of each DER proportionally within a pre-defined time. Meanwhile, the outlet voltage of each distributed power supply can be adjusted to be near the rated value and the observation value can be kept at the rated value. Then, the microgrid system is simulated through MATLAB/Simulink and the effectiveness of the proposed control strategy is verified in different working conditions. Afterward, the finite-time control strategy is established in the simulated system. A comparison of the conservative power quality of the system current with the estimated time of system convergence in the scheduled-time control strategy verifies the advantages of the proposed strategy.
The electricity cost of 5G base stations has become a factor hindering the development of the 5G communication technology. This paper revitalized the energy storage resources of 5G base stations to achieve the purpose of reducing the electricity cost of 5G base stations. First, it established a 5G base station load model considering the communication load and a 5G base station energy storage capacity schedulable model considering the energy storage backup power demand of the 5G base station and the power supply reliability of the distribution network. Then, it proposed a 5G energy storage charge and discharge scheduling strategy. It also established a model for 5G base station energy storage to participate in coordinated and optimized dispatching of the distribution network. Finally, it compared the economy of optimized dispatch of 5G base station energy storage of different schemes. The analysis results show that the participation of idle energy storage of 5G base stations in the unified optimized dispatch of the distribution network can reduce the electricity cost of 5G base stations, alleviate the pressure on the power supply of the distribution network, increase the rate of new energy consumption in the system, and realize a win-win situation between the communication operator and the grid.
The flexibility of thermal loads of buildings is a valuable balancing resource for operation of the heat and electricity integrated energy system (HE-IES). Considering the characteristics of large scale and small single load capacity of the themal load, the non-intrusive data-driven method has become an effective means to quantify the flexibility of building thermal load. However, due to the inaccuracy of the model or the lack of data, this method inevitably produces errors and brings epistemic uncertainty to the optimal dispatch of the HE-IES. An optimal dispatch model of the HE-IES that is compatible with the epistemic uncertainty of demand flexibility in the thermal loads of buildings is proposed. First, a data-driven flexible demand assessment method for building thermal load is described. The measurement errors are modeled as epistemic uncertainty and the multiple error sources are combined by using the D-S evidence theory. Then, the representative scenarios are selected to represent the epistemic uncertainty of the demand flexibility based Latin hypercube sampling(LHS) method, and the scenarios are reduced by the fuzzy clustering method. Finally, the representative scenarios are embedded in the coordinated and optimized dispatch of the HE-IES to realize the comprehensive consideration of the thermal load flexibility and related epistemic uncertainty of the building. The results demonstrate that considering the epistemic uncertainties of the thermal load demand is crucial for reducing the wind power curtailments and improving the operational flexibility of HE-IES.
In order to evaluate the operation of energy consumption, environmental protection, and economy, a multi-index comprehensive evaluation model based on an improved technique for order preference by similarity to ideal solution (TOPSIS) is proposed. Based on the analysis of building operation, a multi-index evaluation system is constructed. Then, an improved TOPSIS evaluation method is introduced and a distance measure of the TOPSIS evaluation model by the gray correlation algorithm and analytic hierarchy process (AHP)-entropy weight method is determined. Next, a multi-attribute weighted evaluation model is established to analyze the building operation comprehensively. The multi-index evaluation of eight power office buildings indicates that the building comprehensive evaluation results vary with time and the energy consumption index score plays the main role in all indexes. A comparison of the evaluation results with those obtained by other evaluation methods verifies the effectiveness of the proposed building multi-index evaluation model.
Wind power generation has uncertainty due to the high fluctuation of wind speed. In traditional wind power prediction models, the uncertainty is measured by normal distribution with zero mean and constant variance. However, the variance may vary with time, which means the variance has heteroscedasticity. To improve the prediction accuracy, this paper proposes a new integrated probabilistic wind power prediction model for wind farm considering heteroscedasticity based on online least absolute shrinkage and selection operator and vector autoregression (LASSO VAR) and the exponential generalized autoregressive conditional heteroskedasticity (EGARCH) model. First, online LASSO VAR is used to forecast power output. Then, heteroscedasticity of residuals is validated by autoregressive conditional heteroskedasticity test. Considering heteroscedasticity, the news impact curve and dynamic significance line verify that positive and negative residuals affect future volatility asymmetrically. Thus, the EGARCH model is used to forecast the residuals to obtain the conditional variance of point prediction results. Finally, the probabilistic result of total power output is obtained by summing the power output of turbines in the wind farm considering the correlation of the active wind power of wind turbines. This method is applied to forecast the power output of a wind farm in East China and is proved effective in improving the prediction accuracy.
Logistics center is the key node of the logistics network, which connects the regional logistics network and the external transportation system. Its operation and management have great impacts on the overall efficiency of the logistics system. Therefore, it has always been the fundamental issue of logistics management. In recent years, with the development of e-commerce and corresponding express services, the transportation tasks undertaken by logistics companies have continued to grow, which has posed great challenges to the operation of logistics centers. In order to fulfill the national “dual-carbon” target, logistics centers urgently need to control carbon emission intensity while ensuring the efficiency of transportation. In this context, this paper takes the logistics center as the focus, integrates the concept of microgrid, and summarizes its operation management and emission reduction measures, in order to promote the energy utilization of logistics enterprises while improving the quality and efficiency, and to ensure their sustainable development.
With the increase of the penetration rate of distributed generation (DG), lack of flexibility of distribution network has become increasingly prominent. This paper focuses on electric energy router (EER), and analyzes its impact on the flexibility of distribution network. First, the index of the transfer flexibility of distribution network is proposed to represent one aspect of distribution network flexibility. Then, the linear model of the EER and its related constraints are analyzed, and an optimization model of the transfer flexibility of the active distribution network with the EER model is constructed. Finally, based on the 94-bus alternating current distribution network, different scenarios are designed to analyze and compare the effects of different DG operation control modes and different parameters of EER on the transfer flexibility of distribution network. The effectiveness of EER in improving the transfer flexibility of distribution network is verified.
To achieve the goal of carbon peaking and carbon neutrality, it is urgent to build a new power system with renewable energy as the main body, characterized by clean energy supply and electrification of energy consumption. Considering the intermittency and randomness of wind-solar power, as well as the energy storage and flexibility of pumped storage power stations and power-to-hydrogen, a short-term production simulation model of wind-PV-hydrogen-pumped storage zero carbon power system is established based on the stochastic programming theory. In the proposed short-term production simulation model, on the basis of meeting the total demand of flexible hydrogen load, the short-term production simulation is implemented, including electricity-hydrogen production schedule, reserve capacity, pumped storage-water discharge power output and wind-solar curtailment, with the goal of maximizing green on-grid electricity. Taking Zhangbei zero carbon power system of China as an example, many operation scenarios are established to simulate the proposed model. The simulation results show that the proposed model can effectively simulate the on-grid scheme situation of green power in which the system deals with the randomness of wind-solar output in any output scenarios of wind-solar power scene set. The flexible hydrogen load and the pumped storage power station can effectively promote wind-solar energy accommodation and increase the comprehensive benefit of the combined system.
Hybrid three-level full bridge (H-TLFB) DC-DC converters increase the input voltage range by introducing a three-level bridge arm. Aimed at the problems of large power return and high current stress in the traditional dual phase shift control, a minimum return power control strategy is proposed. First, the power transmission characteristics of H-TLFB DC-DC converter are analyzed, the size of the return power value of the converter in two different operating modes is compared, and the optimal shift of the return power is calculated according to the mathematical relationship between the return power and the voltage ratio, the shift and the transmission power. The corresponding optimal shift of the return power is calculated, and the corresponding optimization control strategy is designed. Compared with the traditional dual phase shift control strategy, the return power in the minimum return power control strategy can reach the minimum value in the full power transmission range, and within a certain voltage ratio range, the return power and current stress can be optimized at the same time. Finally, the correctness and feasibility of the design control strategy are verified by experiments.
In order to evaluate the possibility of the ‘death spiral’ operation dilemma faced by the retailers with the high level penetration of distributed photovoltaic (PV) under the background of carbon neutrality, and to analyze the key factors that may lead to the ‘death spiral’, the system dynamics approach is applied for modeling. First, the model of customer-side distributed PV penetration guided by market conditions such as sales tariff is established. Then, a model of surplus of retailers is established based on the negative feedback relationship between distributed PV penetration level and the surplus of retailers. The case study evaluates the sensitivity effects of factors such as the generation of distributed PV and wholesale electricity prices on the surplus of retailers. The results show that the surplus of retailers tends to decrease slowly in the mid-long term. An extreme scenario may cause the ‘death spiral’ of retailers in which multiple factors such as transmission and distribution volumes, wholesale tariffs, and maintenance costs change significantly at the same time.
The proportion of renewable energy in the new power system is further increased, and the grid connected capacity of photovoltaic units has a trend of obvious improvement. The dynamic behavior of the photovoltaic (PV) power generation system at different permeabilities has a significant impact on the load characteristics of the power grid. However, the complex dynamic model of photovoltaic power generation grid connection and the large number of parameters to be identified increase the difficulty of practical application of the model. Therefore, a dynamic discrete equivalent model of the PV power generation model based on the physical model of the PV power generation model is established, and the parameters of the dynamic discrete equivalent model for the PV power generation model are obtained. The IEEE 14-bus system, which is subject to various PV permeabilities, is adopted to verify the superb dynamic characteristics of the proposed discrete equivalent model for the PV power generation in power system simulations. The pertinent simulation results show that the dynamic discrete equivalent model of the PV power generation system can accurately describe the dynamic characteristics of the PV power generation system with a high accuracy and an easy identification performance.
