Abstract:With the rapid development of its national economy, China has become a major producer and consumer of energy. To guarantee the sustainable development of power industry and national economy, China should exploit fossil and renewable energy efficiently according to the development situation of generation resources. Firstly, this paper analyzes the utilization status of main generation resources in China, such as coal, hydropower and wind energy. Secondly, this paper illustrates the STEP model, which analyzes some issues for China’s generation resource utilization from political, economic, social and technological aspects. For example, the resource distribution is inconsistent with electricity demand, the renewable energy power output is intermittent, and there is some disruption in coal mining. Finally, combined with the utilization status and issues, this paper presents some improvement approaches from the perspectives of cost, efficiency and external influence.

Abstract:Aspects of terrestrial microgrids and ship power systems are examined. The work exposes a variety of technical synergies from these two power systems to effectively advance their technologies. Understanding their overlap allows congruent efforts to target both systems; understanding their differences hinders conflict and redundancy in early-stage design. The paper concludes by highlighting how an understanding of both systems can reduce the investment in research resources.

Abstract:A novel optimal scheduling method considering demand response is proposed for power systems incorporating with large scale wind power. The proposed method can jointly dispatch the energy resources and demand side resources to mitigate the fluctuation of load and wind power output. It is noticed in practical operation that, without customer’s satisfaction being considered, customers might reject the too frequent or violent demand response all together. In this case, two indices that measure the customer satisfaction are then introduced as constraints to reduce the impact to end-users and avoid extreme demand adjustment. To make the model solvable, a proximate decoupling technique is used to dispose the concave constraint introduced by the customer satisfaction constraints. Results from the case studies show that the proposed model can significantly reduce the operation cost of power system while the demand response meets customer satisfaction. Especially, the total start-up costs of conventional thermal units decreases dramatically due to less startup times. Moreover, compared to the consumption way satisfaction constraint, the payment satisfaction constraint has a heavier influence on the cost.

Abstract:Global warming and climate change are two key probing issues in the present context. The electricity sector and transportation sector are two principle entities propelling both these issues. Emissions from these two sectors can be offset by switching to greener ways of transportation through the electric vehicle (EV) and renewable energy technologies (RET). Thus, effective scheduling of both resources holds the key to sustainable practice. This paper presents a scheduling scenario-based approach in the smart grid. Problem formulation with dual objective function including both emissions and cost is developed for conventional unit commitment with EV and RET deployment. In this work, the scheduling and commitment problem is solved using the fireworks algorithm which mimics explosion of fireworks in the sky to define search space and the distance between associated sparks to evaluate global minimum. Further, binary coded fireworks algorithm is developed for the proposed scheduling problem in the smart grid. Thereafter, possible scenarios in conventional as well as smart grid are put forward. Following that, the proposed methodology is simulated using a test system with thermal generators.

Abstract:This paper proposes a novel frequency aware robust economic dispatch (FARED) approach to exploit the synergistic capability of accommodating uncertain loads and renewable generation by accounting for both the frequency regulation effect and optimal participation mechanism of secondary regulation reserves for conventional units in response to uncertainties in the robust optimization counterpart of security constrained economic dispatch. The FARED is formulated as a robust optimization problem. In this formulation the allowable frequency deviation and the possible load or renewable generation curtailments are expressed in terms of variable uncertainty sets. The variables in the formulation are described as interval variables and treated in affine form. In order to improve the computational tractability, the dominant constraints which can be the candidates of tight transmission constraints are determined by complementarity constraints. Then the robust optimization problem is simplified to a bilinear programming problem based on duality theory. Finally, the effectiveness and efficiency of the proposed method are illustrated based on several study cases.

Abstract:Future power systems face several challenges. One of them is the use of high power converters that decouple new energy sources from the AC power grid. This situation decreases the total system inertia affecting its ability to overcome system frequency disturbances. The wind power industry has created several controllers to enable inertial response on wind turbines generators: artificial, emulated, simulated, or synthetic inertial. This paper deals with the issues related to the emulated inertia of wind turbines based on full-converters and their effect on the under-frequency protection schemes during the recovery period after system frequency disturbances happen. The main contribution of this paper is to demonstrate the recovery period of under-frequency transients in future power systems which integrate wind turbines with emulated inertia capability does not completely avoid the worse scenarios in terms of under-frequency load shedding. The extra power delivered from a wind turbine during frequency disturbances can substantially reduce the rate of frequency change. Thus it provides time for the active governors to respond.

Abstract:With more and more wind power generation integrated into power grids to replace the conventional turbine-generator (T-G) units, how the subsynchronous resonance (SSR) of conventional T-G units is affected becomes an important technical issue. In this paper, a group of T-G units are interconnected with a series compensated transmission line, and some units are substituted by a nearby DFIG-based wind farm (WF). Under such circumstances, the SSR of power systems would change accordingly. This paper establishes the mathematical model to analyze the torsional interaction (TI) and the induction generator effect of the T-G units. Both eigenvalue analysis and time domain simulations demonstrate the impact of DFIG-based WF on SSR of power systems and how the control parameters of wind farms can affect the SSR.

Abstract:Large-scale wind power penetration can affect the supply continuity in the power system. This is a matter of high priority to investigate, as more regulating reserves and specified control strategies for generation control are required in the future power system with even more high wind power penetration. This paper evaluates the impact of large-scale wind power integration on future power systems. An active power balance control methodology is used for compensating the power imbalances between the demand and the generation in real time, caused by wind power forecast errors. The methodology for the balance power control of future power systems with large-scale wind power integration is described and exemplified considering the generation and power exchange capacities in 2020 for Danish power system.

Abstract:This paper focuses on the day-ahead allocation of operation reserve considering wind power prediction error and network transmission constraints in a composite power system. A two-level model that solves the allocation problem is presented. The upper model allocates operation reserve among subsystems from the economic point of view. In the upper model, transmission constraints of tielines are formulated to represent limited reserve support from the neighboring system due to wind power fluctuation. The lower model evaluates the system on the reserve schedule from the reliability point of view. In the lower model, the reliability evaluation of composite power system is performed by using Monte Carlo simulation in a multi-area system. Wind power prediction errors and tieline constraints are incorporated. The reserve requirements in the upper model are iteratively adjusted by the resulting reliability indices from the lower model. Thus, the reserve allocation is gradually optimized until the system achieves the balance between reliability and economy. A modified two-area reliability test system (RTS) is analyzed to demonstrate the validity of the method.

Abstract:A probabilistic equivalent method for doubly fed induction generator (DFIG) based wind farms is proposed in this paper. First, the wind farm equivalent model is assumed to be composed of three types of equivalent DFIGs with different dynamic characteristics. The structure of equivalent model remains constant, whereas the parameters change with the migration of different scenarios in the wind farm. Then, historical meteorological data are utilized to investigate the probability distribution of key equivalent parameters, such as capacity, wind speed and electrical impedance to the point of common coupling. Each type of equivalent DFIG is further clustered into several groups according to their active power output. Combinations are created to generate representative scenarios. The probabilistic equivalent model of wind farm is finally achieved after removing invalid combinations. Most matched representative scenarios can be predicted according to the real-time measurement. The equivalent model is applied to the probabilistic power flow calculation and the stability analysis of test systems.

Abstract:In the condition of connecting large scale doubly-fed induction generators (DFIGs) into weak grid, the closely coupled interactions between wind generators and power grid becomes more severe. Some new fault characteristics including voltage phase angle jump will emerge, which will influence the power quality of power system. However, there are very few studies focusing on the mechanism of voltage phase angle jump under grid fault in a weak grid with wind turbine integration. This paper focuses on the scientific issues and carries out mechanism studies from different aspects, including mathematical deduction, field data analysis and time domain simulation. Based on the analysis of transient characteristics of DFIGs during the grid fault, this paper points out that the change of terminal voltage phase angle in DFIGs is an electromagnetism transition process, which is different from conventional synchronous generator. Moreover, the impact on transient characteristics of voltage phase angle are revealed in terms of fault ride through (FRT) control strategies, control parameters of current inner-loop of rotor-side converter and grid strength.

Abstract:Big wind farms must be integrated to power system. Wind power from big wind farms, with randomness, volatility and intermittent, will bring adverse impacts on the connected power system. High precision wind power forecasting is helpful to reduce above adverse impacts. There are two kinds of wind power forecasting. One is to forecast wind power only based on its time series data. The other is to forecast wind power based on wind speeds from weather forecast. For a big wind farm, due to its spatial scale and dynamics of wind, wind speeds at different wind turbines are obviously different, that is called wind speed spatial dispersion. Spatial dispersion of wind speeds and its influence on the wind power forecasting errors have been studied in this paper. An error evaluation framework has been established to account for the errors caused by wind speed spatial dispersion. A case study of several wind farms has demonstrated that even if the forecasting average wind speed is accurate, the error caused by wind speed spatial dispersion cannot be ignored for the wind power forecasting of a wind farm.

Abstract:Reducing the concentration of carbon dioxide (CO2) in the air can effectively alleviate climate change. Air capture, which captures CO2.directly from the air in an industrial process, is an alternative option to address climate change. The results of recent studies on the energy demand in CO2.capture process and the costs of CO2 transport and CO2.storage in air capture are analyzed in this paper. Considering renewable energy will not produce additional CO2.in the process of utilization, the electric energy in CO2.capture process of air capture driven by wind energy is different from that of carbon capture and storage. Taking externalities of renewable energy into account, the trading price of CO2.emission is taken to assess the cost of electric energy in CO2.capture of air capture driven by wind energy. Finally, the total cost and the total cost savings of air capture driven by wind energy under different scenarios are analyzed.

Abstract:Multi-terminal voltage sourced converter (VSC)-based high voltage direct current (HVDC) system composes of a number of VSCs connected to an HVDC grid (or dc grid). The dc grid is often configured by cable interconnections between converter stations, thus imposing resonance issues affecting harmonic interaction in the system. Based on the harmonic transfer characteristics of VSC and HVDC systems, the appearance and the interaction of inter-harmonics in the multi-terminal VSC-based HVDC system are analyzed. Simulation models are built and implemented using SimPowerSystems in MATLAB. The simulation results show that, a series of inter-harmonics are produced and tend to be dominant in low-frequency range. Especially in the dc grid, the inter-harmonic transfer can be magnified due to inter-harmonic resonances. The complex resonance issues in the dc grid are investigated in combination with interaction through the VSC, it is beneficial to harmonic filter designs as well as other harmonic mitigation methods.

Abstract:A sequential design and global optimization method is proposed to coordinately design local and widearea controllers to enhance the overall stability of largescale power system. The sequential design is used to assign the distributed local power system stabilizer (LPSS) and high-voltage direct current (HVDC) wide-area stabilizing controller (HVDC-WASC) to the concerned damping modes. The global optimization is used to simultaneously optimize all the overall control gains of LPSSs and HVDCWASC. Moreover, the optimization model, which has an adaptive ability of searching and updating dominant oscillation modes, is established. Both the linear analysis and nonlinear simulation results verify the effectiveness of the proposed design method in enhancing the stability of large-scale power systems.

Abstract:Current field calculation based on the resistance network method (RNM) and temperature field calculation based on the finite volume method (FVM) can be used to evaluate the performance of high-voltage direct-current (HVDC) grounding electrodes. The main idea of the two methods is to transform an electric and temperature field problems to equivalent circuit problems by dividing the 3D soil space near the grounding electrode into a suitable number of contiguous and non-overlapped cells. Each cell is represented as a central node connecting to the adjacent cells. The resistance network formed by connecting all the adjacent cells together can be solved to calculate the current field. Under the same conditions, the results calculated by the RNM are consistent with the result by CDEGS, a widely used software package for current distribution and electromagnetic field calculation. Based on the finite volume method, the temperature field results are also calculated using time domain simulation.

Abstract:This unique study will demonstrate a combined effect of weather parameters on the total number of power distribution interruptions in a region. Based on common weather conditions, a theoretical model can predict interruptions and risk assessment with immediate weather conditions. Using daily and hourly weather data, the created models will predict the number of daily or by-shift interruptions. The weather and environmental conditions to be addressed will include rain, wind, temperature, lightning density, humidity, barometric pressure, snow and ice. Models will be developed to allow broad applications. Statistical and deterministic simulations of the models using the data collected will be conducted by employing existing software, and the results will be used to refine the models. Models developed in this study will be used to predict power interruptions in areas that can be readily monitored, thus validating the models. The application has resulted in defining the predicted number of interruptions in a region with a specific confidence level. Reliability is major concern for every utility. Prediction and timely action to minimize the outage duration improves reliability. Use of this predictor model with existing smart grid self-healing technology is proposed.