| The daily lives of people have primarily relied on utilization of fossil fuels in electric power supply for many years. Because of energy shortage and environment problems caused by fossil fuel consumption, developing sustainable clean energy sources is a necessary means to solve these issues. Under this background, tidal power generation, as a renewable energy resource, has drawn considerable interests globaly. Many tidal power plant projects have been conducted or planned in the world. Global manufacturers with considerable experiences in wind turbine generator manufacturing (such as ABB and Alstom) are being actively involved in developing tidal power generation systems. However, to the best of the author's knowledge, little or no work has been done on the probabilistic modeling of tidal current speed and the reliability evaluation of power system with tidal power generation. This thesis develops a probabilistic model of tidal current speed, a probabilistic model of tidal current driven generator power output, a reliability evaluation model of tidal power generation systems, and a reliability evaluation model of battery energy storage. Based on all the proposed models, this thesis presents a reliability evaluation method for a hybrid tidal and wind power generation system with battery energy storage.The first step in reliability evaluation and probabilistic analysis of power system with tidal power generation is to determine an appropriate probability distribution for tidal current speed. This thesis proposes a Wakeby distribution to model the probabilistic characteristic of tidal current speed. The Wakeby distribution and nine other popular distributions are investigated using four years of tidal current speed data at ten different sites. Comparisons are conducted using the Kolmogorov-Smirnov test (K-S test) and root-mean-square error (RMSE) index for both posteriori and priori tests. The results verified that the Wakeby distribution not only has the best statistical performance but also is the only one of the ten selected distributions that passed the K-S test.A probability distribution model of tidal generator output power is needed to perform reliability assessment and other probabilistic analyses of a power system with tidal power generation. Based on the analysis of two random variables (tidal current speeds and seawater density) that impact the power output of tidal current generator, the thesis proposes a probabilistic model of tidal current generator output power, which is related to the tidal current speeds, seawater salinity and seawater temperature. The results of case studies indicate that seawater temperature generally has a relatively small impact on the output power of tidal current generator. A traditional deterministic average tidal current speed model may lead to significant errors in the calculation of output power of tidal current generator compared to the proposed probabilistic model.The reliability assessment of tidal power generation system, which is based on a doubly-fed induction generator with a bidirectional back-to-back converter, plays a vital role in the reliability evaluation of power system with tidal power generation. Based on the analysis of the factors related to failures of power electronic components and the studying on the operation mode of the doubly-fed induction generator, this thesis presents the models for calculating the rotor currents through the rotor side converter and grid side converter and the rotor current state related failure rates. Based on the Wakeby distribution of tidal current speed, a multistate discrete probability technique for rotor current is developed. The results of case studies indicate that the failure rates of rotor side converter, grid side converter and entire tidal power generation system are varied for diffenent tidal current speeds and different probability distributions of tidal current speed. The failure rates of tidal power generation system in the different operation modes are different from each other. The change trends in the failure rates of rotor side converter and grid side converter in the different operation modes are also different. The probability distributions of tidal current speed have significant impacts on the reliability of tidal power generation system.Reliability evaluation of a battery energy storage system plays a very important role in reliability evaluation of power system with renewable energy sources. This thesis proposes a method to analyze the reliability of a large scale battery energy storage system consisting of multiple battery modules. A health state index of a battery cell is calculated in terms of the capacity fade of cell that can be obtained using a weighted Ampere-hour throughput method. The health state index and a universal generating function based method are used to evaluate the reliability of the battery module. The reliability model of DC/AC power electronic converters is presented. The reliability assessment of the whole battery system is performed by using the reliability evaluation models of battery modules and power electronic converters. A reconfigurable battery energy storage system is also proposed in this thesis. The results of case studies indicate that the proposed reconfigurable battery energy storage system has higher reliability than a classic battery energy storage system. It is also more flexible as it deals with multistate output power levels. The results also show that the reliability of a battery module is related to the power level and the number of charging and discharging cycles that a battery has gone through. The reliability of a battery module can be improved by reducing the number of cells connected in series and/or increasing the number of cells connected in parallel.This thesis presents a method for reliability evaluation of a hybrid generation system of wind and tidal powers with battery energy storage. Such a system often exists in coastal areas and islands. A chronological multiple state probability model of tidal power generation system considering both forced outage rate of tidal power generation system and random nature of tidal current speed is developed. A chronological power output model of battery energy storage system is derived. A hybrid system of tidal and wind generation powers with a battery energy storage system is used to demonstrate the effectiveness of the proposed method. The results of case studies indicate that the studied system has different reliability levels in different seasons. Various sensitivity studies are conducted. The results show that there exists a critical turning point for the effects of all studied parameters on the studied hybrid generation system reliability. When a parameter exceeds the critical turning point, the effect becomes weak or even disappearing. Identifying the critical point values is important for selecting the parameters in the design of a power system with hybrid tidal and wind generation sources and battery storage. |
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