Showing papers on "Base load power plant published in 2014"

Participation of wind power plants in system frequency control: Review of grid code requirements and control methods

Abstract: Active power reserves are needed for the proper operation of an electrical system. These reserves are continuously regulated in order to match the generation and consumption in the system and thus, to maintain a constant electrical frequency. They are usually provided by synchronized conventional generating units such as hydraulic or thermal power plants. With the progressive displacement of these generating plants by non-synchronized renewable-based power plants (e.g. wind and solar) the net level of synchronous power reserves in the system becomes reduced. Therefore, wind power plants are required, according to some European Grid Codes, to also provide power reserves like conventional generating units do. This paper focuses not only on the review of the requirements set by Grid Codes, but also on control methods of wind turbines for their participation in primary frequency control and synthetic inertia.

Analyzing operational flexibility of electric power systems

Abstract: Operational flexibility is an important property of electric power systems and plays a crucial role for the transition of today's power systems, many of them based on fossil fuels, towards power systems that can efficiently accommodate high shares of variable Renewable Energy Sources (RES). The availability of sufficient operational flexibility in a given power system is a necessary prerequisite for the effective grid integration of large shares of fluctuating power in-feed from variable RES, especially wind power and Photovoltaics (PV). This paper establishes the necessary framework for quantifying and visualizing the technically available operational flexibility of individual power system units and ensembles thereof. Necessary metrics for defining power system operational flexibility, namely the power ramp-rate, power and energy capability of generators, loads and storage devices, are presented. The flexibility properties of different power system unit types, e.g. load, generation and storage units that are non-controllable, curtailable or fully controllable are qualitatively analyzed and compared to each other. Quantitative results and flexibility visualizations are presented for intuitive power system examples.

Optimal Operation of Independent Storage Systems in Energy and Reserve Markets With High Wind Penetration

Abstract: In this paper, we consider a scenario where a group of investor-owned independently-operated storage units seek to offer energy and reserve in the day-ahead market and energy in the hour-ahead market. We are particularly interested in the case where a significant portion of the power generated in the grid is from wind and other intermittent renewable energy resources. In this regard, we formulate a stochastic programming framework to choose optimal energy and reserve bids for the storage units that takes into account the fluctuating nature of the market prices due to the randomness in the renewable power generation availability. We show that the formulated stochastic program can be converted to a convex optimization problem to be solved efficiently. Our simulation results also show that our design can assure profitability of the private investment on storage units. We also investigate the impact of various design parameters, such as the size and location of the storage unit on increasing the profit.

Reactive power injection strategies for single-phase photovoltaic systems considering grid requirements

Abstract: As the development and installation of photovoltaic (PV) systems are still growing at an exceptionally rapid pace, relevant grid integration policies are going to change consequently in order to accept more PV systems in the grid. The next generation PV systems will play an even more active role like what the conventional power plants do today in the grid regulation participation. Requirements of ancillary services like Low-Voltage Ride-Through (LVRT) associated with reactive current injection and voltage support through reactive power control, have been in effectiveness in some countries. Those advanced features can be provided by next-generation PV systems, and will be enhanced in the future to ensure an even efficient and reliable utilization of PV systems. In the light of this, Reactive Power Injection (RPI) strategies for single-phase PV systems are explored in this paper. The RPI possibilities are: a) constant average active power control, b) constant active current control, c) constant peak current control and d) thermal optimized control strategy. All those strategies comply with the currently active grid codes, but are with different objectives. The thermal optimized control strategy is demonstrated on a 3 kW single-phase PV system by simulations. The other three RPI strategies are verified experimentally on a 1 kW singe-phase system in LVRT operation mode. Those results show the effectiveness and feasibilities of the proposed strategies with reactive power control during LVRT operation. The design and implementation considerations for the characterized strategies are also discussed.

A Hybrid Power Control Concept for PV Inverters with Reduced Thermal Loading

Abstract: This letter proposes a hybrid power control concept for grid-connected photovoltaic (PV) inverters. The control strategy is based on either a maximum power point tracking control or a constant power generation (CPG) control depending on the instantaneous available power from the PV panels. The essence of the proposed concept lies in the selection of an appropriate power limit for the CPG control to achieve an improved thermal performance and an increased utilization factor of PV inverters, and thus, to cater for a higher penetration level of PV systems with intermittent nature. A case study on a single-phase PV inverter under yearly operation is presented with analyses of the thermal loading, lifetime, and annual energy yield. It has revealed the trade-off factors to select the power limit and also verified the feasibility and the effectiveness of the proposed control concept.

Corrective Voltage Control Scheme Considering Demand Response and Stochastic Wind Power

Abstract: This paper proposes a new approach for corrective voltage control (CVC) of power systems in presence of uncertain wind power generation and demand values. The CVC framework deals with the condition that a power system encounters voltage instability as a result of severe contingencies. The uncertainty of wind power generation and demand values is handled using a scenario-based modeling approach. One of the features of the proposed methodology is to consider participation of demand-side resources as an effective control facility that reduces control costs. Active and reactive redispatch of generating units and involuntary load curtailment are employed along with the voluntary demand-side participation (demand response) as control facilities in the proposed CVC approach. The CVC is formulated as a multi-objective optimization problem. The objectives are ensuring a desired loading margin while minimizing the corresponding control cost. This problem is solved using e-constraint method, and fuzzy satisfying approach is employed to select the best solution from the Pareto optimal set. The proposed control framework is implemented on the IEEE 118-bus system to demonstrate its applicability and effectiveness.

A survey of influence of electrics vehicle charging on power grid

Abstract: Electric vehicle (EV) industry gets into fast growth period in China, so that charging of large scale of EV will pose inevitable impacts on power grid in the future. In this article, the main factors and modeling methods of EV charging load are analyzed; The literature reviews are carried out on EV integration and impacts on power grids, including grid access capability, power quality, power economy and environment; Additionally, the benefits and realization methods of smart charging strategy are discussed. The current research on V2G (vehicle to grid) operation are summarized as well. Finally, the unresolved problems and possible future research areas are presented.

Multi-stage robust unit commitment considering wind and demand response uncertainties

Abstract: With the increasing penetration of wind power into the power grid, maintaining system reliability has been a challenging issue for ISOs/RTOs, due to the intermittent nature of wind power. In addition to the traditional reserves provided by thermal, hydro, and gas generators, demand response (DR) programs have gained much attention recently as another reserve resource to mitigate wind power output uncertainty. However, the price-elastic demand curve is not exactly known in advance, which provides another dimension of uncertainty. To accommodate the combined uncertainties from wind power and DR, we allow the wind power output to vary within a given interval with the price-elastic demand curve also varying in this paper. We develop a robust optimization approach to derive an optimal unit commitment decision for the reliability unit commitment runs by ISOs/RTOs, with the objective of maximizing total social welfare under the joint worst-case wind power output and demand response scenario. The problem is formulated as a multi-stage robust mixed integer programming problem. An exact solution approach leveraging Benders' decomposition is developed to obtain the optimal robust unit commitment schedule for the problem. Additional variables are introduced to parameterize the conservatism of our model and avoid over protection. Finally, we test the performance of the proposed approach using a case study based on the IEEE 118-bus system. The results verify that our proposed approach can accommodate both wind power and demand response uncertainties, and demand response can help accommodate wind power output uncertainty by lowering the unit load cost.

Optimal Power Scheduling for Smart Grids Considering Controllable Loads and High Penetration of Photovoltaic Generation

Abstract: The distributed generator (DG) has a huge economical and environmental potential, especially if it is based on renewable energy sources (RESs). It is very important for the future development of smart grids. However, high penetration of DGs into distribution systems can cause voltage deviations beyond the statutory range, and reverse power flow toward the substation transformer. Consequently, it can increase the distribution system losses if it is not well supervised. Thus, in order to meet smart grid objectives, DGs have to be controlled in coordination with other power resources existing in the distribution system. Controllable loads (CLs) can also help in promoting smart grids through demand response (DR) application. Therefore, this paper proposes a decision technique of an optimal reference schedule for DGs, battery energy storage system (BESS), CLs, and tap changing transformers. The main objective of the proposed optimization problem is to achieve loss reduction in the distribution system. However, other aims such as voltage control and power flow smoothing have been achieved. The optimization is performed based on predicted values of load demand and DG generation. Simulations are conducted for one operation day to illustrate the optimality of the proposed scheduling method and to assess the impact of CLs in smart grids.

A New Approach to Model Load Levels in Electric Power Systems With High Renewable Penetration

Abstract: In medium- and long-term power system models, it is a common approach to approximate the demand curve by load levels in order to make the models computationally tractable. However, in such an approach, the chronological information between individual hours is lost. In this paper, we propose a novel approach to power system models which constitutes an alternative to the traditional load levels. In particular, we introduce the concept of system states as opposed to load levels, which allows us to better incorporate chronological information in power system models, thereby resulting in a more accurate representation of system outcomes such as electricity prices and total cost. Moreover, the system states can be defined taking into account various important system features at once, as opposed to load levels which are defined using just one specific feature, i.e., demand or net demand. Therefore the system states approach better captures other results such as reserve prices, which are not driven by the usual feature used to define load levels. In a case study, we compare the newly proposed methodology to a standard load level approach, which validates that the system states approach better captures power system outcomes.

Enhancement of the REMix energy system model : global renewable energy potentials, optimized power plant siting and scenario validation

Abstract: As electricity generation based on volatile renewable resources is subject to fluctuations, data with high temporal and spatial resolution on their availability is indispensable for integrating large shares of renewable capacities into energy infrastructures. The scope of the present doctoral thesis is to enhance the existing energy modelling environment REMix in terms of (i.) extending the geographic coverage of the potential assessment tool REMix-EnDaT from a European to a global scale, (ii.) adding a new plant siting optimization module REMix-PlaSMo, capable of assessing siting effects of renewable power plants on the portfolio output and (iii.) adding a new alternating current power transmission model between 30 European countries and CSP electricity imports from power plants located in North Africa and the Middle East via high voltage direct current links into the module REMix-OptiMo. With respect to the global potential assessment tool, a thorough investigation is carried out creating an hourly global inventory of the theoretical potentials of the major renewable resources solar irradiance, wind speed and river discharge at a spatial resolution of 0.45°x0.45°. A detailed global land use analysis determines eligible sites for the installation of renewable power plants. Detailed power plant models for PV, CSP, wind and hydro power allow for the assessment of power output, cost per kWh and respective full load hours taking into account the theoretical potentials, technological as well as economic data. The so-obtined tool REMix-EnDaT can be used as follows: First, as an assessment tool for arbitrary geographic locations, countries or world regions, deriving either site-specific or aggregated installable capacities, cost as well as full load hour potentials. Second, as a tool providing input data such as installable capacities and hourly renewable electricity generation for further assessments using the modules REMix-PlasMo and OptiMo. The plant siting tool REMix-PlaSMo yields results as to where the volatile power technologies photovoltaics and wind are to be located within a country in order to gain distinct effects on their aggregated power output. Three different modes are implemented: (a.) Optimized plant siting in order to obtain the cheapest generation cost, (b.) a minimization of the photovoltaic and wind portfolio output variance and (c.) a minimization of the residual load variance. The third fundamental addition to the REMix model is the amendment of the module REMix-OptiMo with a new power transmission model based on the DC load flow approximation. Moreover, electricity imports originating from concentrating solar power plants located in North Africa and the Middle East are now feasible. All of the new capabilities and extensions of REMix are employed in three case studies: In case study 1, using the module REMix-EnDaT, a global potential assessment is carried out for 10 OECD world regions, deriving installable capacities, cost and full load hours for PV, CSP, wind and hydro power. According to the latter, photovoltaics will represent the cheapest technology in 2050, an average of 1634 full load hours could lead to an electricity generation potential of some 5500 PWh. Although CSP also taps solar irradiance, restrictions in terms of suitable sites for erecting power plants are more severe. For that reason, the maximum potential amounts to some 1500 PWh. However, thermal energy storage can be used, which, according to this assessment, could lead to 5400 hours of full load operation. Onshore wind power could tap a potential of 717 PWh by 2050 with an average of 2200 full load hours while offshore, wind power plants could achieve a total power generation of 224 PWh with an average of 3000 full load hours. The electricity generation potential of hydro power exceeds 3 PWh, 4600 full load hours of operation are reached on average. In case study 2, using the module REMix-PlaSMo, an assessment for Morocco is carried out as to determine limits of volatile power generation in portfolios approaching full supply based on renewable power. The volatile generation technologies are strategically sited at specific locations to take advantage of available resources conditions. It could be shown that the cost optimal share of volatile power generation without considering storage or transmission grid extensions is one third. Moreover, the average power generation cost using a portfolio consisting of PV, CSP, wind and hydro power can be stabilized at about 10 €ct/kWh by the year 2050. In case study 3, using the module REMix-OptiMo, a validation of a TRANS-CSP scenario based upon high shares of renewable power generation is carried out. The optimization is conducted on an hourly basis using a least cost approach, thereby investigating if and how demand is met during each hour of the investigated year. It could be shown, that the assumed load can safely be met in all countries for each hour using the scenario's power plant portfolio. Furthermore, it was proven that dispatchable renewable power generation, in particular CSP imports to Europe, have a system stabilizing effect. Using the suggested concept, the utilization of the transfer capacities between countries would decrease until 2050.

A Scenario-Based Approach for Energy Storage Capacity Determination in LV Grids With High PV Penetration

Abstract: In this paper a new method is proposed to determine the minimum energy storage required to be installed at different locations of a low voltage (LV) grid in order to prevent the overvoltage due to high residential photovoltaic (PV) penetration The method is based on the voltage sensitivity analysis of feasible scenarios associated with the net injected power into the grid by customers A new concept is defined based on the remaining power curve (RPC) associated with the local generation and consumption, and the uncertainties related to PV output and load consumption are modeled in some RPCs with different occurrence probabilities without involving the time-series studies problems The proposed method is capable of modeling output power of PV panels with different orientations as well as different electric vehicle (EV) charging patterns

Potential for concentrating solar power to provide baseload and dispatchable power

Abstract: Intermittency is often cited as the single greatest hurdle to making a transition from a fossil-based power system to one based on renewables. This study shows that a network of solar power plants, located in deserts, could provide significant baseload in four world regions, suggesting that decarbonization of the power system may be possible and affordable, even if no new technologies come online.

Dynamic Scheduling of Operating Reserves in Co-Optimized Electricity Markets With Wind Power

Abstract: We propose a probabilistic methodology to estimate a demand curve for operating reserves, where the curve represents the amount that a system operator is willing to pay for these services. The demand curve is quantified by the cost of unserved energy and the expected loss of load, accounting for uncertainty from generator contingencies, load forecasting errors, and wind power forecasting errors. The methodology addresses two key challenges in electricity market design: integrating wind power more efficiently and improving scarcity pricing. In a case study, we apply the proposed operating reserve strategies in a two-settlement electricity market with centralized unit commitment and economic dispatch and co-optimization of energy and reserves. We compare the proposed probabilistic approach to traditional operating reserve rules. We use the Illinois power system to illustrate the efficiency of the proposed reserve market modeling approach when it is combined with probabilistic wind power forecasting.

A Review on Impacts of Wind Power Uncertainties on Power Systems

Abstract: With the ever-increasing penetration level of wind power,its impacts on power system reliability,power quality,economical efficiency and social welfare are becoming more and more significant mainly due to the uncertainty nature of the fluctuation and intermittence of windThus,the relationships between fluctuation,intermittence and randomness are discussedThe causes and mathematical description of uncertain factors of wind power and the impacts on the acceptability of power frequency/voltage,stability and adequacy of power systems,power quality,electricity power market and emission reduction are concludedStudying the problem in the generalized congestion framework of power systems is suggestedAlso,the state-of-art and development of wind power uncertainties are reviewedThe solutions to cope with wind power uncertainties,as well as their optimization and coordination,are discussed through aspects of generation side,grid side and demand sideAnd also,the impacts caused by wind power uncertainties are considered in the three-defense-lines of power systemsThe importance of quantitative analysis and risk-based decision-making are emphasized and suggested for further researches

Impacts of High Penetration Wind Generation and Demand Response on LMPs in Day-Ahead Market

Abstract: Environmental issues in power systems operation lead to a rapid deployment of renewable wind generations. Wind generation is usually given the highest priority by assigning zero or negative energy bidding prices in the day-ahead power market, in order to effectively utilize available wind energy. However, when congestions occur, negative wind bidding prices would aggravate negative locational marginal prices (LMPs) in certain locations. The paper determines the proper amount of demand response (DR) load to be shifted from peak hours to off peaks under the Independent System Operator's (ISO) direct load control, for alleviating transmission congestions and enhancing the utilization of wind generation. The proposed mixed-integer linear programming (MILP) model is to minimize the total operation cost while incorporating explicit LMP formulations and non-negative LMP requirements into the network-constrained unit commitment (NCUC) problem, which are derived from the Karush-Kuhn-Tucker (KKT) optimality conditions of the economic dispatch (ED) problem. Numerical case studies illustrate the effectiveness of the proposed model.

Optimal Sizing and Control of Battery Energy Storage System for Peak Load Shaving

Abstract: Battery Energy Storage System (BESS) can be utilized to shave the peak load in power systems and thus defer the need to upgrade the power grid. Based on a rolling load forecasting method, along with the peak load reduction requirements in reality, at the planning level, we propose a BESS capacity planning model for peak and load shaving problem. At the operational level, we consider the optimal control policy towards charging and discharging power with two different optimization objectives: one is to diminish the difference between the peak load and the valley load, the other is to minimize the daily load variance. Particularly, the constraint of charging and discharging cycles, which is an important issue in practice, is taken into consideration. Finally, based on real load data, we provide simulation results that validate the proposed optimization models and control strategies.