2017, 41(14):2-9. DOI: 10.7500/AEPS20170218001
Abstract:The increasing peak-valley differences, air conditioners and renewable energy sources bring new challenges to the smart grid in China. Demand response(DR)is regarded as one of the most important solutions to the above problems. A new round of electricity market reform is being carried out in China, which provides a good opportunity for developing DR. Under this background, this paper analyzes the development of DR in different electricity market environments. A business model and a market framework of DR, which suit to China's national conditions, are put forward. There are two stages: in the first stage, an ancillary service market which contains DR and is relatively separate with the energy market should be developed; in the second stage, an ancillary service market which contains DR and is collaboratively optimized with the electricity market should be developed. Moreover, product types, price clearing methods, assessment methods and settlement methods of DR are analyzed separately in the two stages. With the development of electricity market in China, DR will play more important role to the stability and economy of the power system.
2017, 41(14):10-23. DOI: 10.7500/AEPS20170220014
Abstract:With the advent of smart grids and continuous restructuring of power industry, modern power systems have gradually evolved into complex cyber-physical systems which are characterized with high renewable energy penetrations, distributed facilities, advanced metering and communication technologies, as well as ever-increasing customer awareness. In an electricity retail market, these new development trends pose significant challenges for electricity retailers and call for innovative decision-making methods. Meanwhile, China has begun to establish competitive electricity retail markets in the new round of in-depth reforms for the power industry. In order to provide a beneficial reference for constructing complete competitive electricity retail markets in China, and also to help researchers and engineers have a better overview of the state-of-the-art on the business process and decision-making schemes of electricity retailers, this paper first introduces the development history of electricity retail markets around the world. Then, it elaborates the business process of electricity retailers in Australia and Finland, and surveys the latest progress on decision-making of electricity retailers, including retail energy forecasting, energy procurement strategies and retail pricing strategies for electricity retailers, and risk management in retail markets. Finally, some critical and open issues in this field are discussed.
2017, 41(14):24-29. DOI: 10.7500/AEPS20170218006
Abstract:Demand response can effectively make better load curve and system reliability. A method for translational load to participate in demand response is proposed based on the block model. For the case of the short duration load segment has to bear the high cost of power generation, an optimization model of load segment combination is proposed. In the model, the load agent integrates the load as a long duration segment to get cheaper purchase. On this basis, a market clearing model is proposed. To solve the problem of electricity purchase cost allocation, the bilateral Shapley value(BSV)method of game cooperation is used. The method is applied to an actual case. The results show that the integration of load can reduce the cost of generation, get a cheaper buy, and achieve a win-win situation for both power producers and users.
2017, 41(14):30-36. DOI: 10.7500/AEPS20170219003
Abstract:With the launch of a new round of electricity market reform in China, a large number of electricity retailers have been set up. As a new participant in electricity market, electricity procurement and sale strategies have become core issues for electricity retailers. In view of the increasing demand response ability, a bi-level model of electricity procurement and sale strategies for electricity retailers is proposed by taking user demand response into account. The upper-level model takes maximum retailers' profit as its objective, while the lower-level model takes maximum users' utility as its objective. Besides, the penalty mechanism of the bilateral contract is considered and the user's electricity utilization response behavior is modeled. Moreover, the mechanism of electricity retailers representative users' demand response resources is adopted to interact with the real-time market. Finally, this model is verified with PJM market's data. Results show that the proposed model can provide an optimal electricity procurement and sale strategy to both electricity retailers and the users.
2017, 41(14):37-44. DOI: 10.7500/AEPS20170217005
Abstract:The reform of electricity sales is an important part of power system reform, whose focus is electricity retailers. In the electricity market environment, selling electricity purchased from market to users is the responsibility of electricity retailers. The development of the distributed generator and adjustable load has given electricity retailers more choices in addition to power purchased from market. How to meet the need of users and increase operation profit is a problem demanding prompt study in a competitive environment. Distributed generator and adjustable load are considered in the optimal dispatching model of electricity retailers whose objective is to maximize the day-ahead operation profit. The security constraints on the distribution network are also considered in the model. This paper is intended to relax the non-convex constraints on the model in order to solve the model in second-order cone programming. Finally, the modified IEEE 33-bus distribution system is used as a test case. The results of a case study show that distributed generator and adjustable load is an effective supplement to the power supply mode of electricity retailers to maximize operation benefits in the market environment while ensuring the safety of the system.
2017, 41(14):45-53. DOI: 10.7500/AEPS20170203002
Abstract:With the development of smart grids and promotion of demand responses, intelligent energy management at the demand side has attracted extensive attention. The advanced automation level and vast energy consumption of an industrial load makes it a good choice for implementing intelligent energy management. Given this background, a framework of an intelligent energy management system for industrial loads is presented first, with different types of power demands and management of photovoltaic power generation taken into consideration. Then, based on the state task network, power demand models are developed for production devices and temperature-controlled devices with thermal comfort of the production environment considered. On this basis, an optimal operation model of the intelligent energy management system is presented with the energy-purchasing cost and energy-selling income of the industrial load concerned taken into account. Finally, a typical industrial load is employed to demonstrate the essential characteristics of the developed method, and its demand response performance and benefits of the presented intelligent energy management system are addressed as well.
2017, 41(14):54-60. DOI: 10.7500/AEPS20170104004
Abstract:In order to promote the user's flexible load resources to participate in the demand response effectively, load aggregators can be employed to arrange load resources to participate in the grid dispatch. By dividing the user's loads into several categories, a hierarchical dispatch model is proposed that consists of the power grid company, load aggregators, and residential users. In day-ahead bidding, the game model is formulated based on maximizing load aggregators' profit, load aggregators' bidding behavior is analyzed with non-cooperative game, and the existence of Nash equilibrium is also given mathematically. In the real-time scheduling, for promoting load aggregators' profit without affecting users' comfortableness, the minimum error between real-time scheduling and bidding results is taken as a goal to schedule users' loads with constraints on three kinds of loads in physical characteristics. A case study validates the effectiveness of the proposed hierarchical dispatch model on demand response of flexible load. And simulation results show that the power network company, load aggregators, and residential users can all benefit simultaneously.
2017, 41(14):61-69. DOI: 10.7500/AEPS20170104005
Abstract:Virtual power plant(VPP)is an energy service provider integrating load and distributed energy, which is also a new type of online market transaction mode. On one hand, internal members of VPP have independent property and on the other, electricity price and electricity quantity bidding act in order. After taking into account the above-mentioned essentials, a bidding model for VPP based on the dynamic game theory is developed using the Stackelberg game theory. Considering the output fluctuation and forecasting error of wind turbine, photovoltaic and load, the electricity price bidding model and electricity quantity bidding model are built, respectively. Based on the principal and subordinate hierarchical relation between the two submodels, the equilibrium solution of the model is obtained using the first-order optimality condition and the particle swarm intelligence optimization algorithm. Thus the transaction price and dispatching scheme of the VPP are determined. Finally, the model is simulated, the revenues from electricity price and electricity quantity bidding results in different scenarios are discussed to verify the validity of the model.
2017, 41(14):70-77. DOI: 10.7500/AEPS20160726006
Abstract:As traditional price-based demand response(DR)may increase the electricity cost for some customers with small flexible loads this paper presents a dynamic pricing DR scheme for active distribution network(ADN)with the help of Stackelberg model to ensure cost saving for users in the DR program. The loads of users are divided into two types, namely, fixed loads and shiftable loads. Shiftable loads are assumed to be aggregated by DR agents and the Stackelberg model is formulated to capture the interaction between the ADN and DR agents where ADN is the leader and DR agents are the followers. The existence of a unique Stackelberg equilibrium that provides optimal energy demand and optimal pricing is demonstrated. Numerical results show that the proposed DR design is effective in helping customers save cost.
2017, 41(14):78-86. DOI: 10.7500/AEPS20160605007
Abstract:Distributed generators(DG)and loads can form coalitions for energy supply and consumption in the distribution network, as well as participate in the local electricity market. Compared with working alone, such coalition helps DG and load whose market capabilities are weak to participate in the electricity market. Therefore, improving the direct power purchase between themselves encourages the formation of distribution electricity market. In the meantime, such coalition could also guide the production and usage of distributed electricity power with price signals, enhancing the incentives of DG and load in a deregulated electricity market by enabling them to make more profits. The conditions for the existence of such a coalition trading mode are studied. Based on the role of the utility grid and the cooperative game theory, corresponding price models are developed. Moreover, for the aggregator, an optimization decision model is built to maximize its profit, whose outputs are the optimal formulation of the coalition and price of energy traded inside the coalition. Simulation results show the theoretical feasibility of such a coalition trading mode and the effectiveness of the proposed optimization decision model in different scenarios.
2017, 41(14):87-91. DOI: 10.7500/AEPS20160929008
Abstract:In order to solve the three-phase load unbalance and power peak load highlighted in a distribution network, a non-cooperative game model of electricity consumption behavior of single-phase power consumers based on the dynamic game theory is proposed by using the signal transmission mechanism of game theory. The power consumer of each phase is takes as a game player. The optimization objective is to minimize the power consumption cost for each consumer in a whole period. The three-phase unbalance suppressing and peak load shifting are taken into account in the cost function. The particle swarm optimization algorithm is used to find the Nash equilibrium solution. The simulation results show that the proposed method is able to suppress the three-phase unbalance, while achieving peak load shifting and reducing the difference between peak and valley loads.
2017, 41(14):92-98. DOI: 10.7500/AEPS20170219001
Abstract:A reasonable transmission and distribution price is important for the construction and promotion of the electrical retail market. With a new round of China's electric power reform, the transmission and distribution pricing method has become a part of demanding prompt study. On the basis of summarizing the development trend of the allocation and pricing methods for transmission and distribution costs, a pricing method based on the peak-load theory is devised. A further study on the application of the model for the data missing case is proposed, and a numerical case is used to prove that the method proposed is feasible. The method can reflect the amount of transmission and distribution resources occupied by different users, ensure the revenue of the total transmission and distribution cost and make it available in case of missing data, which meets the need of electrical revolution.
2017, 41(14):99-104. DOI: 10.7500/AEPS20170219002
Abstract:With steady liberalization of the electricity market, competition has been introduced into the sale of electricity. Providing quality customers with quality power supply service appears to be particularly important. The voltage sag insurance mechanism is exactly an effective way to improve users' satisfaction. Based on an analysis of the loss risk characteristics of voltage sag, the control type and financial type loss risk management modes are compared and discussed. Three voltage sag insurance mechanisms of financial risk management mode are set. By introducing the grey system theory and making comprehensive quantitative assessment of different insurance mechanisms through synthesizing the views of different entities, the most suitable and feasible insurance mechanism for the loss risk of voltage sag has been obtained. Finally, according to an empirical analysis of three high-tech customers in a high-tech park in China, the applicability and rationality of the method is proved.
2017, 41(14):105-111. DOI: 10.7500/AEPS20161228006
Abstract:Integration of flexible and controllable load resources into power system scheduling and operation will increase the risk of grid congestion, and pose new challenges to power system dispatching regulation ability. The traditional power grid eliminates congestion mainly through capacity-increase, load transfer and orderly power utilization. With the upgrading of the interactive capabilities of “source-grid-load”, flexible loads participating in grid scheduling plays a very cost-effective role in solving grid congestion problems. Based on flexible loads involved in demand response scheduling, a comprehensive optimal scheduling model for integration of power generation and consumption considering network constraints is developed to make comprehensive benefits of interaction maximum. By forming the optimal pricing and incentive scheme, the model realizes coordinated scheduling of the integration of power generation and consumption. On the basis of effectively mitigating grid congestion, it has optimized the satisfaction and interaction costs. The optimization model is proved economical and effective with the example of an IEEE14-node system.
2017, 41(14):112-118. DOI: 10.7500/AEPS20161028004
Abstract:In order to meet the demand of voltage stability and operation economy, an improved small disturbance voltage stability index is introduced into the optimized power flow model of microgrid, and a multi-period dynamic optimal power flow algorithm considering load fluctuation is studied. The transformation ratio and high order terms from transformation ratio are eliminated by adding the voltage of the dummy nodes in the on-load tap changer transformer model. In consideration of the influence of the distributed generation and energy storage unit, a new dynamic optimized microgrid second-order model is established in the rectangular coordinate system. The traditional interior point method is improved by keeping the higher order terms during Taylor expansion of the Lagrange equation and numbering of nodes with the adaptive minimum degree(AMD)algorithm. The constant coefficient Hessian matrix used in calculation is combined with the improved interior point method to find the constant coefficient Hessian matrix interior point method. Thus the contradiction between the calculation precision and efficiency of iteration is solved effectively. The microgrid model is established with ETAP software, and the optimal power flow is carried out with the proposed algorithm. The results show that the model and the algorithm can satisfy the requirement of operation economy and voltage stability of microgrid under the constraint on the improved small disturbance voltage stability index.
2017, 41(14):119-125. DOI: 10.7500/AEPS20160627002
Abstract:There are usually only three types of nodes, viz, the slack node, active power-voltage node and active power-reactive power node in the traditional power flow calculation based on Newton-Raphson method. So it is difficult to calculate the power flow of microgrid with droop controlled distributed generators using the traditional Newton-Raphson method directly. A novel power flow calculation method similar to Benders decomposition is proposed. The power flow calculation of islanded microgrid under decentralized droop control strategy is decomposed into a traditional Newton-Raphson power flow calculation sub-problem and a droop control node updating sub-problem, while solving the original problem via the alternative iteration of two sub-problems. In this algorithm, the complex original problem is decomposed into two simple sub-problems, which makes solving the original problem efficient and fast. By the simulation tests on case studies, the feasibility and validity of the proposed methodology are proved.
2017, 41(14):126-132. DOI: 10.7500/AEPS20161025008
Abstract:Electric vehicles with the characteristics of cleanliness and energy storage have broad application prospects. However, in order to solve the drawback of short driving mileage, electric vehicle charging stations should be available on the expressways. The battery-swapping mode is employed in the electric vehicle charging stations for centralized management of batteries. Firstly, a bi-level economic dispatch model is developed. The objective function is to minimize the total cost in the upper level, and optimize the network loss in the lower level, respectively. Secondly, based on the proposed model, a new method is presented. In the upper level, the total output of the centralized charging stations and the thermal power units are optimized for every moment using the particle swarm optimization method. The power output of each thermal power unit is allocated for every moment by the integrative sensitivity. In the lower level, the power output of each centralized charging station is optimized for every moment and allocated by network loss sensitivity. Finally, numerical examples based on an improved IEEE 30-bus tested system show that the method proposed is accurate and effective, which can satisfy the economic requirements while obviously improving the calculation speed.
2017, 41(14):133-139. DOI: 10.7500/AEPS20161125005
Abstract:The phasor measurement unit(PMU)can directly obtain measurement data such as the rotor angle of generators in the dynamic process. However, considering random noises in the real-time measurement data, it is necessary to filter out the noises in the measurement data to get more accurate information on generator states. This paper presents a novel method based on the unscented particle filter(UPF)to dynamically estimate the states of synchronous generators. Firstly, dynamic state estimating models of the generators are developed based on the fourth-order dynamic equations. Secondly, in the framework of the particle filter(PF), the proposed method obtains the important density function of PF by using unscented Kalman filter(UKF). The proposed method takes the latest measurement information into consideration in the process of generating predictive particles, which makes the distribution of particles much closer to the posterior probability distribution of the true states. Finally, the performance of the proposed method is compared with UKF and PF both in American Western Systems Coordinating Council(WSCC)3-machine 9-bus system and an actual grid. Simulation results show that, compared with PF and UKF, the UPF performs better in estimation precision and robustness to measurement noise.
2017, 41(14):140-146. DOI: 10.7500/AEPS20160819002
Abstract:With the wide adoption of phasor measurement unit(PMU)in energy management systems, research on dynamic state estimator for synchronous machine based on PMU is attracting more and more attention. Should there exist bad data, the effect of filtering would be seriously affected. First, an algorithm for dynamic state estimation based on unscented Kalman filter is described. But as the PMU data is of poor quality, to solve problem, the time-varying residual threshold is found by deriving the residual equation. Then, the position of bad data measuring point is determined by an iterative detection method. The corresponding measurement of the bad data is ruled out and repeated for correction of the estimation. Simulation results show that the proposed algorithm can effectively restrain the influence of bad data on state estimation.
2017, 41(14):147-152. DOI: 10.7500/AEPS20161207003
Abstract:With the background and basic principle of the electrical spring(ES)described, the modulability of ES is analyzed at length by the vector diagram method, and the operation range of the line voltage under which ES can work is investigated. Besides, the malfunction mechanism is analyzed, and a new computational method for optimizing the specified value of critical load voltage is found. When the line voltage changes in the range, the critical load voltage can be stabilized on the standard value by ES, but when changes are beyond the range, the ES will break down, and the critical load voltage will deviate from the standard state, or even the system can become unstable. Given the permissible fluctuation range of the critical load voltage, the expanded safety regulation domain of the ES system can be obtained by optimizing the specified value of the critical load voltage. Finally, the analysis results are validated by simulation and experiment results.
2017, 41(14):153-158. DOI: 10.7500/AEPS20170125002
Abstract:A novel low voltage ride-through(LVRT)control scheme based on proportional-integral-resonant(PIR)controller and also applicable to current source converter based direct-drive permanent magnet synchronous generator(PMSG)wind generation system(CSC-DPMSG-WGS)is proposed. Based on the proposed method, once unbalanced grid voltage dip happens, the generator-side converter will quickly limit the power which flows to the DC-link to coordinate the grid-side and generator-side power. Meanwhile the grid-side converter adopts the PIR controller to control the positive and negative sequence current simultaneously in the positive sequence rotating coordinate system. This is intended to eliminate the power fluctuation of twice the fundamental frequency caused by unbalanced grid fault and maintain DC current stability. It is proved by simulation and experimental results that the proposed control strategy can eliminate the fluctuation of DC current and realize LVRT during balanced and unbalanced dip faults.
2017, 41(14):159-163. DOI: 10.7500/AEPS20160907034
Abstract:A multiservice model based communication strategy including data flow, signal flow and control flow is presented and applied to the simulation platform. According to the data, cross section and other communication demands in different stages of the whole simulation cycle, communication ways are designed to form a complete set of communication strategies for the multiservice simulation. Research shows that the all-new integrated simulation platform that contains communication strategy set can merge the simulation of the core applications and have them coordinated. Thus the panoramic application training simulation environment can graphically reappear to help solve the relatively simple problem of traditional simulation service.
2017, 41(14):164-170. DOI: 10.7500/AEPS20170411002
Abstract:System design for dispatching and control training simulation based on cloud computing technology is proposed for the inadequacy of the traditional dispatching and control training simulation. In the design, the specific solution of some key technologies have been proposed, such as scenarios construction based on virtualization, graph and model management based on cloud computing, distributed real-time data processing, collaborative simulation based on cloud computing, etc. The system has been pilot applied in control center. Practice shows that the system can achieve the multi-business and multi-scenario simulation in dispatching and control center. Meanwhile, the ability of long-distance interactive coordination of joint simulation is improved, and the performance and efficiency of the simulation are improved as well. The proposed system solves the inadequacy of the traditional dispatching and control training simulation system, and obtains the good application effect.
2017, 41(14):171-175. DOI: 10.7500/AEPS20161116003
Abstract:With the rapid development of grid interconnection and ultra-high voltage(UHV)AC/DC interconnected power grid, the characteristics of grid operation have undergone profound changes and new requirements have been proposed. In view of the problem that the current graphics browsing of smart grid dispatching and control system is incapable of meeting the requirements on centralized monitoring of UHA line equipment belonging to different dispatching institutions in the same picture, a method of grid graphics wide-area maintenance and browsing is proposed. The method realizes integral monitoring of crucial equipment by introducing the equipment model wide-area retrieval technology, the wide-area graphics file unified management and pushing technology, the definition and maintenance of wide-area data technology and the real-time graphics wide-area browsing technology, etc. The scheme has been pilot applied in the control center. This method can provide technical support to the operation of UHV interconnected power grid, and meet the demand for real-time monitoring of operation state and operating risk prompted by UHV DC equipment.
2017, 41(14):176-181. DOI: 10.7500/AEPS20161202001
Abstract:Aiming at the influence of dead time setting on transfer power rating and efficiency of the inverter of double-sided LCC resonant wireless charging transfer(WPT)system, a dead time optimization method for metal-oxide-semiconductor field effect transistor(MOSFET)soft switching is proposed. First, the mathematical description of the double-sided LCC resonant wireless charging system is established, and the operating mode is briefly analyzed as well. The quantitative characteristic is deduced that the secondary side compensation capacitor can be adjusted to ensure that the circuit is inductive. And a dead time optimization design method is proposed to realize zero voltage switching(ZVS)of the inverter that is closely related to the performance of the WPT system. Finally, a prototype is built. The experimental results verify that dead time calculated by this optimized method can ensure the soft switching of the inverter MOSFET, and promote the wireless power transmission power and efficiency.
2017, 41(14):182-189. DOI: 10.7500/AEPS20161130003
Abstract:Based on the nonlinear relationship between the voltage and current of the DC link, a piecewise affine model(PWA)of voltage source converter based high-voltage direct-current(VSC-HVDC)system is developed. According to the characteristics of fast dynamic change of PWA system with state and input constraints, this paper makes up for the shortcomings of model predictive control(MPC)causing slowed-down system response and degraded real-time performance. Explicit model predictive control(EMPC)combined with off-line calculation and on-line analysis is used to transform repeated online rolling optimization calculation into a simple table lookup process. The output trajectory of the VSC-HVDC system by means of expected interval tracking deviation and adding the variable soft constraints is optimized. Simulation results show that the explicit model predictive controller has good dynamic performance and steady performance, while able to suppress fluctuations of output trajectory. Compared with the MPC, the dynamic response of EMPC is faster, and the real-time of EMPC is stronger.
2017, 41(14):190-196. DOI: 10.7500/AEPS20161118004
Abstract:The active power differential protection has unique advantages in dealing with distributed capacitance and high resistance faults. However, the defect of close metallic faults with small resistance limits its practical application. In order to overcome this shortcoming, a concept of virtual active power emanating from referring to the superposition principle is proposed, and the different characteristics for virtual active power under the internal fault and the external fault conditions are analyzed. On this basis, a split-phase action criterion for virtual active power differential protection is proposed and its operation characteristics are analyzed qualitatively. By using the model of 500 kV transmission lines on PSCAD, a number of simulations have been conducted for different fault locations, fault types, transition resistances, reactive elements operations and asynchronous data to evaluate the influences on the protection scheme performance comprehensively. Theoretical analysis and simulation results show that the proposed protection scheme is able to correctly identify the fault sections without dead zone for close metallic faults but a great capability against fault resistance, less data exchanges, a low requirement for synchronization and no need of capacitance compensation.
2017, 41(14):197-201. DOI: 10.7500/AEPS20160910004
Abstract:This paper analyzes the present applications of low voltage bus protection, and presents a new solution of simplified bus protection. Based on the characteristics of low voltage bus topology, the bus unit module is abstracted. Each bus unit module calculates the overcurrent condition of its incoming line and bus section by using the overcurrent of the other bus unit modules. By referring to the blocking signals from the outgoing line protection, selective tripping of weak power, incoming line or bus section is realized and fast fault clearing achieved.
2017, 41(14):202-207. DOI: 10.7500/AEPS20161103002
Abstract:In order to meet the demand of wide-area time synchronization for the rapid development of smart grid, a new wide-area time synchronization method is proposed, in which satellite clock and network clock are mutually spare. Based on an analysis of the error characteristics of satellite clock, crystal clock and network clock, the high-precision synchronous clock timing method combined with satellite clock and crystal clock is studied, and a message path delay improvement algorithm featuring IEEE 1588 protocol network clock is proposed. On this basis, a distributed autonomous wide-area time synchronization scheme focused on high-precision synchronous clock and network clock is put forward. The simulation results show that the wide-area time synchronization scheme can realize accurate and reliable time synchronization of the time nodes in the wide-area network while meeting the time synchronization requirement of the smart grid.