ANALYSIS AND SIMULATION OF PHOTOVOLTAIC SYSTEMS INCORPORATING BATTERY ENERGY STORAGE

Solar energy is an abundant renewable source, which is expected to play an increasing role in the grid\u27s future infrastructure for distributed generation. The research described in the thesis focuses on the analysis of integrating multi-megawatt photovoltaics (PV) systems with battery energy storage into the existing grid and on the theory supporting the electrical operation of components and systems. The PV system is divided into several sections, each having its own DC-DC converter for maximum power point tracking and a two-level grid connected inverter with different control strategies. The functions of the battery are explored by connecting it to the system in order to prevent possible voltage fluctuations and as a buffer storage in order to eliminate the power mismatch between PV array generation and load demand. Computer models of the system are developed and implemented using the PSCADTM/EMTDCTM software

Integration of Large PV Power Plants and Batteries in the Electric Power System

The declining cost of renewables, the need for cleaner sources of energy, and environmental protection policies have led to the growing penetration of inverter-based resources such as solar photovoltaics (PV), wind, and battery energy storage systems (BESS) into the electric power system. The intermittent nature of these resources poses multiple challenges to the power grid and substantial changes in the conventional generation and electrical power delivery practices will be required to accommodate the large penetration of these renewable power plants. The impact of large solar PV penetration on both generation and transmission systems, and the use of BESS to mitigate some of the challenges due to solar PV penetration has been studied in this dissertation. One of the major challenges in evaluating the impact of inverter-based resources (IBR) such as solar PV systems is developing an equivalent model adequate to represent its operation. This work proposes a detailed solar PV model suitable for analyzing the configurations, design, and operation of multi-MW grid connected PV systems. This model which takes into account the contributions of the power electronics control and operation was used to evaluate the impact of transient changes in solar PV power on an example transmission system. The benefits of a battery system configuration connected to the grid through an independent inverter were analyzed and its operation during transient conditions was also evaluated. After developing a detailed solar PV and BESS modules for analyzing the effect of IBR on transmission systems, an innovative approach for evaluating the impact of solar PV plants on both generation and transmission system based on a practical minute-to-minute economic dispatch model was proposed. The study demonstrates that large solar PV penetration may lead to both over- and under-generation violations, and substantial changes to conventional generation dispatch and unit commitment will be required to accommodate the growing renewable solar PV penetration. The terminal voltage of a battery pack varies based on multiple parameters and cannot be modeled as a constant voltage source for a detailed analysis BESS operation. A novel approach for estimating the equivalent circuit parameters for utility-scale BESS using equipment typically available at the installation site was proposed in this dissertation. This approach can be employed by utilities for monitoring energy storage system operation, ensure safety and avoid lithium-ion battery thermal runaway . The new methods developed, configurations and modules proposed in this dissertation may be directly applicable or extended to a wide range of utility practices for evaluating the impact of renewable resources and estimating the maximum solar PV capacity a service area can accommodate without significant upgrades to existing infrastructures

Multi-MW Solar PV Pumping System with Capacity Modulation and Battery Voltage Support

Solar photovoltaic (PV) renewable energy systems are undergoing major technological developments and large-scale field deployment and electric grid integration. This paper proposes a method of expanding the capacity of an existing irrigation farm with additional pumps powered by solar PV. The system includes PV arrays and battery energy storage connected to a common dc bus, which energizes an array of variable speed inverter driven pumps. Capacity modulation is achieved by energizing an optimal number of pumps required in order to meet a particular load demand with minimum supply energy. A grid connection to the dc bus of the power electronic system is established via a bidirectional converter, such that active and reactive power demands can be both serviced. The controls and the steady-state and transient performance of the system are implemented and simulated with the PSCAD TM /EMTDC TM software

Study of Renewable Energy Penetration on a Benchmark Generation and Transmission System

Significant changes in conventional generator operation and transmission system planning will be required to accommodate increasing solar photovoltaic (PV) penetration. There is a limit to the maximum amount of solar that can be connected in a service area without the need for significant upgrades to the existing generation and transmission infrastructure. This study proposes a framework for analyzing the impact of increasing solar penetration on generation and transmission networks while considering the responses of conventional generators to changes in solar PV output power. Contrary to traditional approaches in which it is assumed that generation can always match demand, this framework employs a detailed minute-to-minute (M-M) dispatch model capable of capturing the impact of renewable intermittency and estimating the over- and under-generation dispatch scenarios due to solar volatility and surplus generation. The impact of high solar PV penetration was evaluated on a modified benchmark model, which includes generators with defined characteristics including unit ramp rates, heat rates, operation cost curves, and minimum and maximum generation limits. The PV hosting capacity, defined as the maximum solar PV penetration the system can support without substantial generation imbalances, transmission bus voltage, or thermal violation was estimated for the example transmission circuit considered. The results of the study indicate that increasing solar penetration may lead to a substantial increase in generation imbalances and the maximum solar PV system that can be connected to a transmission circuit varies based on the point of interconnection, load, and the connected generator specifications and responses

Modeling of a Multi-Megawatt Grid Connected PV System with Integrated Batteries

The multi-megawatt grid connected photovoltaic (PV) system studied in the paper includes parallel arrays and power electronic units, each with their own DC-DC and DC-AC converters. In one configuration, the DC-AC converters of adjacent parallel sections are connected in cascade, in order to effectively operate as a multilevel inverter, thereby reducing the filtering requirements. Grid voltage oriented control is employed for inverters and a battery is incorporated for energy storage and performance improvement. Modeling is performed with the PSCAD/EMTDC software, such that both the power electronics components, controls and subsystem aspects, and the electric grid power system issues, can be studied during steady-state and transient operation. The system simulation is demonstrated on a modified IEEE 14-bus test case

Measurement and Estimation of the Equivalent Circuit Parameters for Multi-MW Battery Systems

This paper proposes and validates through simulations and measurements, a procedure for the determining the equivalent circuit parameters of large utility-scale batteries. It is considered that a large battery includes multiple cells connected in series and parallel, and therefore, its equivalent circuit can be represented as a series-parallel network of state of charge (SOC) dependent resistors and capacitors. Tests for determining these equivalent circuit parameters are proposed. These tests involve subjecting the battery energy storage system (BESS) to multiple charge and discharge cycles, while monitoring the terminal voltage and current response. A method for post-processing and analyzing the measurements in order to obtain an equivalent circuit model that accounts for the dynamic properties of the battery system and differences between the parameters of each cell is developed. The measurements and simulations are conducted for a 1MW/2MWh BESS demonstrator located at the Louisville Gas and Electric and Kentucky Utilities (LG&E and KU) E.W. Brown generating plant

The Design and Analysis of Large Solar PV Farm Configurations with DC Connected Battery Systems

Typically, solar inverters curtail or “clip” the available power from the PV system when it exceeds the maximum ac capacity. This paper discusses a battery system connected to the dc-link of an inverter to recuperate this PV energy. Contrary to conventional approaches, which employ two dc-dc converters, one each for the battery and solar PV system, the proposed configuration utilizes a single dc-dc converter capable of simultaneously operating as a charge controller and a maximum power point tracking (MPPT) tracking device. In addition to improving the overall system capacity factor, increasing the conversion efficiencies and ensuring MPPT stability, the proposed configuration offers a simple solution for adding energy storage to existing PV installations. With this configuration, the excess power that will otherwise be curtailed due to inverter rating limitations is stored in the battery and supplied to the grid during periods of reduced irradiance. Moreover, a systematic methodology for sizing a dc-bus connected battery to minimize total PV energy curtailed was developed using an annual PV generation profile at the Louisville Gas and Electric and Kentucky Utilities (LG&E and KU) E.W. Brown solar facility at Kentucky. The detailed behavior of the proposed system and its power electronics controls and operations were validated with case studies developed in PSCADTM/EMTDCTM for variable power generation and PV output power smoothing

Modeling and Simulation of a Utility-Scale Battery Energy Storage System

This paper presents the modeling and simulation study of a utility-scale MW level Li-ion based battery energy storage system (BESS). A runtime equivalent circuit model, including the terminal voltage variation as a function of the state of charge and current, connected to a bidirectional power conversion system (PCS), was developed based on measurements from an operational utility-scale battery demonstrator. The accelerated response of the battery unit was verified by pulse discharging it from maximum to minimum SOC and its application for grid resiliency was demonstrated through an example droop control frequency response. For the purpose of validating the equivalent BESS model, experimental results retrieved from the LG&E and KU E.W. Brown solar facility, which houses a 1MW/2MWh operational BESS and a 1MVA variable load bank were compared with simulation results from an equivalent model developed in PSCAD/EMTDC software, which is a tool typically employed for transient analysis

Incorporating Battery Energy Storage Systems Into Multi-MW Grid Connected PV Systems

This paper analyzes the configuration, design, and operation of multi-MW grid connected solar photovoltaic (PV) systems with practical test cases provided by a 10-MW field development. In order to improve the capacity factor, the PV system operates at its maximum power point during periods of lower irradiance, and the power output is limited to a rated value at high irradiance. The proposed configuration also incorporates a utility scale battery energy storage system (BESS) connected to the grid through an independent inverter and benefits of the experience gained with a 1-MW 2-MWh BESS large demonstrator. The BESS power smoothing and frequency regulation capabilities are illustrated though combined theoretical and experimental studies. The behavior of the grid connected PV and BESS combined system is studied using a modified IEEE 14 bus test system implemented in PSCAD/EMTDC. This paper also includes a sizing exercise for energy storage in order to provide dispatchable PV power

Large-Scale Solar PV and Battery Energy Storage Model Study on a Proposed Benchmark Transmission System

Problem Formulation The move toward renewable energy sources has led to an increase in the penetration of inverter-based resources onto the transmission system Most literature discusses two types of models of IBRs, time-average models, which do not capture high-frequency switching effects, and detailed switching models, which are computationally expensive The IEEE 12-Bus test system was modified in PSCADTM/EMTDCTM to include a 100 MW PV facility and 100 MW battery energy storage system (BESS) connected at bus 2 The PV facility and BESS are modelled using a proposed dynamic inverter-based resource module A demonstration of the module was performed using two transient case studies showing the behavior of the BESS during real and reactive power support of the gri