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Active power control response from large offshore wind farms
This thesis was submitted for the degree of Doctor of Engineering and awarded by Brunel University LondonThe GB power system will see huge growth in transmission connected wind farms over the next decade, driven by European clean energy targets. The majority of the UK’s wind development is likely to be offshore and many of these wind farms will be interfaced to the grid through power converters. This will lead to a loss of intrinsic inertia and an increasing challenge for the system operator to keep grid frequency stable. Given this
challenge, there is increasing interest in understanding the capabilities of converter control systems to provide a synthesised response to grid transients. It is interesting to consider whether this response should be demanded of wind turbines, with a consequential reduction in their output, or if advanced energy storage can provide a viable solution. In order to investigate how large offshore wind farms could contribute to securing the
power system, wind turbine and wind farm models have been developed. These have been used to design a patented method of protecting permanent magnet generator’s converters under grid faults. Furthermore, these models have enabled investigation of methods by which a wind turbine can provide inertial and frequency response. Conventionally inertial response relies on the derivative of a filtered measurement of system frequency; this introduces either noise, delay or both. This research proposes alternative methods, without
these shortcomings, which are shown to have fast response. Overall, wind farms are shown to be technically capable of providing both high and low frequency response; however, holding reserves for low frequency response inevitably requires spilling wind. Wind’s intermittency and full output operation are in tension with the need of the power system for reliable frequency response reserves. This means that whilst wind farms can
meet the technical requirements to hold reserves, they bid uncompetitive prices in the market. This research shows that frequency response market prices are likely to rise in future suggesting that the Vanadium Redox Flow Battery is one technology which could enter this market and also complement wind power. Novel control incorporating fuzzy logic to manage the battery is developed to allow a hybrid wind and storage system to
aggregate the benefits of frequency response and daily price arbitrage. However, the research finds that the costs of smoothing wind power output are a burden on the store’s revenue, leading to a method of optimising the combined response from an energy store and generator that is the subject of a patent application. Furthermore, whilst positive present value may be derived from this application, the long payback periods do not represent attractive investments without a small storage subsidy.The Engineering and Physical Sciences Research Council (EPSRC) and GE Energ
Modeling and Utilizing a Vanadium Redox Flow Battery for Easier Grid and Market Integration of Wind Power
Power grid and market integration of wind energy is a challenge due to the fluctuating and intermittent power output resulting from the variable nature of wind resource. Energy storage is a promising alternative for effective grid integration of renewable energy. One storage technology which is under the spotlight in the recent years is the vanadium redox flow battery (VRFB) which could have certain advantages when utilized at large-scale grid connected applications. In this study, a megawatt scale VRFB was modeled based on experimental data with a kilowatt scale real life unit. The dependence of the overall system efficiency on the state of charge and power was determined. By using the model, optimal number of modules for certain power levels during charging and discharging operations were estimated for megawatt scale operations. In order to evaluate the power grid integration of wind power at a single wind farm level, a second simulation model which combines the megawatt scale VRFB model and a medium sized (10 MW) wind farm was developed and the battery was utilized to compensate for the deviations resulting from the forecast errors in an electricity market bidding structure. Using an existing electricity market model based on deviation penalties and penalty multipliers, economics of the system were evaluated by determining the payback periods for a dedicated VRFB installation at this medium sized, single wind farm level
Stochastic Coordination of Joint Wind and Photovoltaic Systems with Energy Storage in Day-Ahead Market
This paper presents an optimal bid submission in a day-ahead electricity market for the problem of joint operation of wind with photovoltaic power systems having an energy storage device. Uncertainty not only due to the electricity market price, but also due to wind and photovoltaic powers is one of the main characteristics of this submission. The problem is formulated as a two-stage stochastic programming problem. The optimal bids and the energy flow in the batteries are the first-stage variables and the energy deviation is the second stage variable of the problem. Energy storage is a way to harness renewable energy conversion, allowing the store and discharge of energy at conveniently market prices. A case study with data from the Iberian day-ahead electricity market is presented and a comparison between joint and disjoint operations is discussed
Integral approach to energy planning and electric grid assessment in a renewable energy technology integration for a 50/50 target applied to a small island
This paper presents an energy planning, a grid assessment, and an economic analysis, considering three growing scenarios (Low, Base and High) in the electricity consumption, to supply the energy demand for a hybrid power system (Photovoltaics/Wind/Diesel/Battery) on a small island by 2050. The main aim of this study is to present a methodology to optimize and reduce the backup time of the battery bank, included from the hybrid power generation system selected. Also, it will compare four di ff erent battery technologies, simultaneously, without changes in the renewable energy targets settled in 50% until 2050 and without changes in the safe continuous operation of the grid. The methodology includes a grid assessment analysis to obtain a reliable, strong and safe operation response based on the grid code parameters, even in case of disturbance. In the proposed methodology the analysis is developed on the basis of the use of two simulation model tools. The First simulation model tool determines the optimal values of variables that the system designer controls, such as the mix of components (Photovoltaics/Wind/Diesel/Battery) that make up the system and the size or quantity of each variable. This model uses the multiyear analysis based on a time-domain simulation run at the energy- fl ow level with discrete time-steps of 1 h. The Second simulation model tool assumes all the variables and parameters on the grid as constants during the period of the time analyzed. The power fl ow is analyzed through a programming language command script function and re fl ects the system response at a speci fi c time with given speci fi c variables and parameters. The fi nal technical proposal and its fi nancial analysis are obtained applying and validating this methodology on a small island, as well as, the selection of the system to be installed for the renewable electricity generation. The electric grid modi fi cations and reinforcements through the years until 2050, according to the grid code and the renewable energy targets settled for the island ’ s electric power system are included.Postprint (author's final draft
Stochastic optimization for the daily joint operation of wind/PV and energy storage
This paper deals with the problem of optimal bidding in a day-ahead market of electricity for a power producer having joint operation of wind with photovoltaic power systems and storage of energy. Uncertainty, not only on electricity market prices, but also on wind and photovoltaic powers, has to be faced in order to achieve optimal bidding. The problem is viewed as a sort of a two-stage stochastic optimization problem formulated by mix-integer linear programming. A case study with data from the Iberian Peninsula is presented and a comparison between joint and disjoint operations is discussed, allowing concluding that the joint operation attenuates the economic impact of disjoint operation volatility
An approach to implement PV Self-Consumption and Ramp-Rate Control Algorithm using a Day-to-Day Forecast battery charging, with a Vanadium Redox Flow Battery
The variability of the solar resource is mainly caused by cloud passing,
causing rapid power fluctuations on the output of photovoltaic (PV) systems.
The fluctuations can negatively impact the electric grid, and smoothing
techniques can be used as attempts to correct it. However, the integration of a
PV+storage to deal with the extreme power ramps at a domestic/services scale is
not explored in the literature, neither its effective combination with other
energy management strategies (EMSs). This work is focused on using a battery
energy storage unit to control the power output of the PV system, maintaining
the ramp rate (RR) within a non-violation limit and within a battery state of
charge (SoC) range, appropriate to perform this RR management at the
domestic/services scale. For this purpose, the authors explore the vanadium
redox flow battery (VRFB) technology. Based on model simulation,
key-performance indicators (KPI) are studied and improved, and finally,
experimental validation is carried out. A comparison among three EMSs is made:
a self-consumption maximization (SCM), a SCM with ramp-rate control (SCM+RR),
and the last strategy performing also night battery charging based on the day
ahead weather forecast (SCM+RR+WF). The weather forecast allowed the battery
SoC control, preparing it to carry out the RR control the next day. The results
show that SCM+RR+WF, especially in wintertime, is an excellent approach to
manage PV+battery systems. This strategy successfully controlled 100 % of the
violating power ramps, obtaining also a self-consumption ratio (SCR) of 59 %,
and a grid-relief factor (GRF) of 61 %.Comment: Keywords: PV solar energy; energy storage; self-consumption; ramp
rate; VRF
Hybrid wind power balance control strategy using thermal power, hydro power and flow batteries
The increased number of renewable power plants pose threat to power system balance. Their intermittent nature makes it very difficult to predict power output, thus either additional reserve power plants or new storage and control technologies are required. Traditional spinning reserve cannot fully compensate sudden changes in renewable energy power generation. Using new storage technologies such as flow batteries, it is feasible to balance the variations in power and voltage within very short period of time. This paper summarises the controlled use of hybrid flow battery, thermal and hydro power plant system, to support wind power plants to reach near perfect balance, i.e. make the total power output as close as possible to the predicted value. It also investigates the possibility of such technology to take part in the balance of the Lithuanian power system. A dynamic model of flow battery is demonstrated where it evaluates the main parameters such as power, energy, reaction time and efficiency. The required battery size is tested based on range of thermal and hydro power plant reaction times. This work suggests that power and energy of a reasonable size flow battery is sufficient to correct the load and wind power imbalance
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