Control Analysis for Grid Tied Battery Energy Storage System for SOC and SOH Management

Frequency regulation is an important part of grid ancillary services in the UK power system to mitigate the impacts of variable energy resources and uncertainty of load on system frequency. The National Grid Electricity Transmission (NGET), the primary electricity transmission network operator in the UK, is introduced various frequency response services such as firm frequency response (FFR) and the new fast enhanced frequency response (EFR), which are designed to provide real-time response to deviations in the grid frequency. Flexible and fast response capabilities of battery energy storage systems (BESSs) make them an ideal choice to provide grid frequency regulation. This thesis presents control algorithms for a BESS to deliver a charge/discharge power output in response to deviations in the grid frequency with respect to the requisite service specifications, while managing the state-of-charge (SOC) of the BESS to optimize the availability of the system. Furthermore, this thesis investigates using the BESS in order to maximize triad avoidance benefit revenues while layering UK grid frequency response services. Using historical UK electricity prices, a balancing service scheduling approach is introduced to maximize energy arbitrage revenue by layering different types of grid balancing services, including EFR and FFR, throughout the day. Simulation results demonstrate that the proposed algorithm delivers both dynamic and non-dynamic FFR and also EFR to NGET required service specifications while generating arbitrage revenue as well as service availability payments in the balancing market. In this thesis, a new fast cycle counting method (CCM) considering the effect of current rate (C-rate), SOC and depth-of-discharge (DOD) on battery lifetime for grid-tied BESS is presented. The methodology provides an approximation for the number of battery charge-discharge cycles based on historical microcyling SOC data typical of BESS frequency regulation operation. The EFR and FFR algorithms are used for analysis. The obtained historical SOC data from the analysis are then considered as an input for evaluating the proposed CCM. Utilizing the Miner Rule’s degradation analysis method, lifetime analysis based on battery cycling is also provided for a lithium-titanate (LTO) and lithium-nickel-manganese-cobalt-oxide (NMC) battery. The work in this thesis is supported by experimental results from the 2MW/1MWh Willenhall Energy Storage System (WESS) to validate the models and assess the accuracy of the simulation results

Scheduling of grid tied battery energy storage system participating in frequency response services and energy arbitrage

Battery energy storage systems (BESS) are widely used to smooth power fluctuations and maintain the voltage and frequency of the power feeder at a desired level. T he National Grid Electricity Transmission (NGET), the primary electricity transmission network operator in the UK, has introduced various frequency response servic es that are designed to provide a real - time response to deviations in the grid frequency. In this study , a control algorithm is developed which generates a charge/discharge power output with respect to deviations in the grid frequency and the requisite service specifications. Using historical UK electricity prices, a new balancing service scheduling approach has also been developed to maximize energy arbitrage revenue by layering different types of balancing services throughout the day . Simulation result s show that the proposed algorithm delivers both dynamic and non - dynamic firm frequency response (FFR) and also enhanced frequency response (EFR) to NGET specifications while generating arbitrage revenue as well as service availability payment s in the balancing market. A comparative study is also presented to compare the yearly arbitrage revenue obtained from the work presented in this paper and a previous reference study . Finall y, exper imental results of a grid - tied 2MW /1MWh BESS have been used for verification purposes