Flexible Control Of Micro-Grid-Based Hybrid Energy Storage And Optimized Configuration Of The Capacity

As an effective way of integrating distributed renewable energy, micro-grid technology has received widely attention in recent years due to the depletion of fossil energy and the threat of global climate change. Energy storage is an indispensable component in micro-grid, and it could provide critical support for micro-grid, such as stability support, renewable energy power fluctuations smoothing, power quality compensation, load shifting, emergency power, etc. However, due to the limitations of energy storage technologies, it is difficult for a single form of energy storage to meet all the requirements perfectly in micro-grid. Since hybrid energy storage technology is becoming feasible and economical for micro-grid application, it is very important and of great value to study hybrid energy technology in micro-grid.In order to meet various requirements of micro-grid, hybrid energy storage flexible control and storage capacity configuration techniques are mainly discussed in the dissertation, which focus on hybrid energy storage multi-port access technology, energy storage converter fault-tolerant technology, and micro-grid critical support based on hybrid energy storage technology. Based on the above discussion, hybrid energy storage capacity allocation multi-objective optimization techniques are intensively studied.In order to make up feasible hybrid energy storage, the common multi-port topology for hybrid energy storage is presented based on multi windings high frequency transformer. Power transfer principle and affecting factors are revealed. For hybrid energy storage system constituted by batteries and ultra-capacitor, the average current small-signal analysis model of three-port hybrid energy storage topology is derived based on its equivalent circuit of three-port full-bridge converter; Moreover, the given power control strategy for three-port hybrid energy storage is proposed. In view of ultra-capacitor voltage verified with its capacity, an asynchronous duty cycle regulated phase shift PWM based on given power control strategy is introduced to match voltages in different ports, which helps to improve power transmission efficiency. This study provides theoretical support for hybrid energy storage bottom layer power transmission control in micro-grid application.The reliability of the energy storage device largely depends on its DC-AC converter. A three-phase four-switch fault-tolerant topology for energy storage application is proposed to balance cost and reliability performance. The fault tolerant critical condition and switching rules are also created. Accurate and rapid accessing to the fault information of hybrid energy storage converter is the premise of the fault tolerant control. To deal with missed fault information problem, circuit state logic is used to build hybrid system dynamic model of hybrid energy storage converter; an open circuit fault diagnosis method based on residual current vector character is introduced, which can effectively increase the speed of the fault detection technology; To overcome the inner shortcoming of three-phase four-switch fault-tolerant converter, the inherent mechanism of output impedance, inverted frequency and capacitor leading to the unbalanced output are revealed. Based on the relation of modulating signal and space vector action time, an equivalent SVPWM control method with DC bus midpoint compensation is proposed, which can significantly improve symmetry of the three-phase four-switch fault-tolerant converter.Due to the reduction of power components and auxiliary devices, four-switch three-phase converter shows good application prospect in low-cost converter. Furthermore, as an effective way of compensating power quality, active power filter (APF) costs much but its function is limited. Hence, a low cost four-switch shunt APF is put forward. For APF power quality control without load harmonic detection, a direct compensation method based on the supply-side current tracking is proposed, which can be used easily. Given the potential influences of power supply voltage imbalance in micro-grid, four-switch APF current reference generation strategy based on synthetic line voltage vector is proposed.Four-switch energy storage APF could provide various flexible supports for micro-grid. The unified modes self-adaptive switching method for four-switch energy storage APF is presented, based on coordinate transformation, current references calculation method in different modes and switching critical conditions is given. To build up four-switch APF, the criteria to obtain the control parameter and calculation method are given, and a single phase software phase locking method is used to fulfill exact power current hysteresis tracking.Due to the lack of theoretical guidance and quantitative assessment criteria, hybrid energy storage capacity configurations in micro-grid mostly depend on engineering experience, so hybrid energy storage multi-objective capacity configuration optimization techniques are deeply discussed. For typical applications in micro-grid, hybrid energy storage capacity configuration multi-objective optimization model is established, which includes objects such as lowest cost, best power balance level, and best smoothing effect on renewable energy; by analyzing filtering coefficient, output power limit and charging constraints, factors affecting optimization results are given. To determine weights of each objective function and rebuild multi-objective optimization function, an average fitness deviation ranking method is presented, which can be easily solved by particle swarm optimization (PSO) algorithm. To evaluate the impact of energy storage application on micro-grid, quantitative assessment indices of energy storage multi-objective optimization are provided, which include renewable energy fluctuation index and power balance index.Hybrid energy storage (made up of ultra-capacitor and battery) capacity multi-objective optimization example is given, typical object function setting up method and PSO optimization algorithm fulfilled by MATLABare given. Based on the proposed quantitative assessment indices, single battery and hybrid energy storage multi-objective compensation effects are compared with each other. Results show that hybrid energy storage is more feasible in micro-grid application.Based on micro-grid platform, hybrid energy storage related experimental researches are carried out. Experiment devices including three-port full-bridge hybrid energy storage converter, four-switch fault-tolerant converter and four-switch APF are designed; critical parameter, software and hardware design method are also given. Hybrid energy storage given power control, fault-tolerance judge and control, direct current tracking, unified power quality compensation experiments are mainly carried out, which further show the validity of the theory.The research achievements in the dissertation have further developed the fundamental theory, analysis method and innovation techniques of hybrid energy storage in micro-grid, which will provide important reference value for hybrid energy storage design and engineering application in micro-grid.