Generator Output Fluctuations Research Articles

A Penalty Scheme for Mitigating Uninstructed Deviation of Generation Outputs From Variable Renewables in a Distribution Market

With rapid growth of distributed renewable generation, the establishment of electricity distribution markets has attracted widespread concerns. Different from existing transmission grid-scale electricity markets, an electricity distribution market is featured by numerous small-scale prosumers, and zero marginal cost and intermittency of renewable generation units. Against this background, this paper first extends an average pricing market (APM) mechanism for pricing renewable generation outputs with zero marginal cost in the distribution network concerned. Then, to mitigate the uninstructed volatility of renewable generation outputs and power demand, a penalty scheme is proposed for deviations between the real-time demand/output and market cleared bid/offer, with frequency regulation service (FRS) from energy storage systems (ESSs) considered. It is proved that the market volatility can be well controlled within an expected limit through properly setting the penalty prices for load demand and generation output fluctuations. Also, with this mechanism a non-negative market surplus could always be attained. Case studies are carried out to demonstrate the feasibility and efficiency of the proposed distribution market mechanism and penalty scheme.

Wind power variations during storms and their impact on balancing generators and carbon emissions in the Australian National Electricity Market

This paper examines changes in Frequency Control Ancillary Services (FCAS) generator output due to several large wind farm power variations occurring in the Australian National Electricity Market (NEM) during 2012 and 2013. Using data from actual FCAS generator output fluctuations during selected storm events and reconstructed heat rate curves for each FCAS generator, the authors address the research question of what effect such variations have on net carbon emissions from electricity generation, given balancing fossil-fueled FCAS generators will be pushed back into less efficient operating ranges. The study finds that, for all storm events evaluated, net carbon emissions decreased with each large increase in wind power, even though FCAS generator carbon intensity increased in two of the three events. This finding is consistent with the conclusions of other studies that while FCAS generators do move into less efficient operating ranges, the generation of zero carbon emission wind power displaces other fossil fuel generators and more than compensates for this efficiency reduction, creating an overall positive carbon effect. This is a significant finding as it shows that the inclusion of wind farms in the generation mix serving the Australian NEM can lower carbon emissions in both short and long time frames.

Uncertainty level of voltage in distribution network: an interval model and application in centralised storage location

Intermittent distributed generations, stochastic loads and other uncertainties have uncertain impacts on the node voltages in distribution network. To quantitatively assess the impact boundaries of uncertainties on node voltages, an interval model is proposed in this study from the perspective of linear description. The model parameters defined as the voltage influence intervals are solved for as follows: first, conduct the analysis sample collection through the affine power flow and the expected operating point estimated by point-estimate method; then, calculate the voltage influence intervals via interval regression for the above sample. To meet the different demand of solving efficiency and conservative level for parameter identification, two solution methods of interval regression based on quadratic programming and stochastic programming are proposed, respectively. To further illustrate the practical application of the interval model, an optimal location method for centralized energy storage is presented. The verification results based on the modified IEEE 33-bus system and practical 113-bus system demonstrate the interval model and its solution methods have an excellent performance in assessing the impact boundaries of uncertainties. The application case also shows that the proposed decision method can produce a global and robust location scheme with considering the bound uncertainty of distributed generation output fluctuations.

Increasing fossil power plant flexibility by integrating molten-salt thermal storage

Increasing market penetration of renewable energy sources requires measures to stabilize the electric grid. This includes reducing generator output fluctuations as well as providing control reserve. The present study investigates the use of molten-salt storage systems in fossil-fired power plants by conducting a series of numerical process simulations. Two case studies are performed: First, an incinerator representing a heat-controlled facility with fluctuating output due to varying customer steam demand. Second, a small-size lignite-fired power plant for providing control reserve, representing a power-controlled facility.The results show that the concept allows significant attenuation of fluctuations in the heat-controlled facility. For a broad range of customer steam extraction, a steady production of electrical energy could be obtained without substantial modifications to the plant. Positive and negative control reserve in the power-controlled facility can be provided through the use of a storage system with relatively low exergetic losses. However, a number of additional heat exchangers and significant modifications to the steam cycle are required.

風力発電機出力平滑化用エネルギー貯蔵装置の定格決定に関する検討

Wind turbine generator output fluctuates due to wind speed variations. Hence, wind farm output can have a serious influence on the power system frequency. Therefore smoothing control of wind generator output fluctuations is very important. With these points as background, there have been many reports so far about suppressing of the fluctuations by using energy storage system. This paper proposes an evaluation method for determining the power rating and energy capacity of Energy Storage System for smoothing the wind generator output fluctuations.

Smoothing control of wind generator output fluctuations by PWM voltage source converter and chopper controlled SMES

Since the mechanical power extracted from wind is proportional to the cube of the wind speed, the output of the wind turbine generator system fluctuates considerably due to wind speed variations. Therefore, high penetration of wind power to the power grid causes fluctuation of the grid frequency, which has adverse effects on power system stability and reliability. Since a superconducting magnetic energy storage (SMES) system has the ability to provide both active and reactive power simultaneously and quickly, the SMES system can be an effective tool to mitigate frequency fluctuations under such conditions. In the present study, a PWM voltage source converter and two-quadrant DC–DC-chopper-controlled SMES system is proposed, which can significantly decrease the voltage and output power fluctuations of the wind farm and consequently mitigate the grid frequency fluctuation. A computational method by which to determine the SMES power rating needed to minimize the grid frequency fluctuation is analyzed. Moreover, the required minimum energy storage capacity of the SMES unit is determined. The simulation analyses were performed using PSCAD/EMTDC. Copyright © 2010 John Wiley & Sons, Ltd.

A Study on the Operating Characteristics of SMES for the Dispersed Power Generation System

WPGS (Wind Power Generation System) output fluctuates due to wind speed variations and PV power generation output is changed by sudden cloudy weather conditions. Hence, if a large number of wind and PV power generators are connected to power system, their output can cause a serious influence on the power system operation, that is, frequency and voltage fluctuations. In order to solve these problems, the control of generator output fluctuations is very important. With these points as background, Superconducting Magnetic Energy Storage (SMES) is probably a key technology to overcome these fluctuations. For stabilization of power, the SMES is connected to the terminal of the WPGS. The authors compared the load side frequencies under the 1 MJ and 2.5 MJ of SMES connection, respectively. From the simulation results, it can be concluded that the SMES is a very effective device for stabilization of power system and minimization of frequency fluctuations.

新しいピッチ制御による風力発電機出力の平滑化制御

新しいピッチ制御による風力発電機出力の平滑化制御

A Suitable Load Control Method for Constant Tip Speed Ratio Operation of Stand-alone Wind Turbine-Generator Systems (Part 1: Evaluation of Power Generation Capability and Output Fluctuation)

A suitable load control method for a constant tip speed ratio operation of stand-alone systems using vertical axis wind turbines with a self-starting capability is discussed from the viewpoint of its power generation capability and output fluctuations. This study takes up a stand-alone system with a straight-wing-type turbine, which is mainly operated at a constant tip speed ratio. Two types of load control methods are considered: Method-1 wherein the load torque is controlled in proportion to the square of the rotational speed and Method-2 that adopts a feedback control of the rotational speed in response to the inflow wind speed. The computational results using the dynamic simulation model show that the decrease in the output fluctuations from Method-1 to Method-2 is much larger than the increase in the power generation capability from Method-2 to Method-1. Therefore, it is concluded that Method-1 is the suitable load control method.