Font Size: a A A

Research On Key Components In Hybrid Energy Systems

Posted on:2009-06-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:H YangFull Text:PDF
GTID:1102360272477846Subject:Motor and electrical appliances
Abstract/Summary:PDF Full Text Request
Due to the shortage of fossil fuel, the environmental crisis and the limitations of concentrative power generation, hybrid energy system (HES) has attracted more and more attention. HES has two remarkable features compared with normal distribution generation systems, one is the complementary advantage achieved by the rational allocation of microsources and energy storage systems, and the other is the load leveling control strategy which could make balance between the customers' high level demand and the real power supply. As the key components to realize the two features of HES, the energy storage system and the grid-connected converter are the main research issues in this dissertation. In order to establish a typical HES prototype, some theoretical problems are analyzed and summarized in this dissertation, such as HES configuration, selection and modeling of components, main circuit design and so on. Next the flywheel energy storage system and the multifunctional grid-connected converter are further studied by theoretical analysis, simulation and experimental validation.First of all, based on the comparison and the summary on some indexes of different energy storage systems and the requirements of the HES prototype, flywheel and sodium-sulfur battery are selected as the energy storage systems in the HES prototype. Then the concept of multifunctional converter is presented according to the load leveling control strategy, and the topology selection for the multifunctional converter in three-phase four-wire power system is made. As per modeling and quantitative analysis of three-leg split-capacitor topology, four-leg topology and three single-phase full bridge topology, the appropriate topology is finally proposed.Secondly, after the components selections and their function orientation are defined, a comprehensive analysis is elaborated on the characteristics of photovoltaic battery, sodium-sulfur battery and flywheel energy storage system (FESS). According to this analysis, the equivalent circuit model, the thermal model, the evaluation indexes, the electromechanical state equation as well as the corresponding power electronic interfaces are consequently presented. The transfer function for grid-connected converter is also given. These models are verified by simulation results. Therefore the main circuit deign for HES is completed.Concerning FESS, some advices on material, shape and processing technology for high strength flywheel are given, and some different types of driving motors for high speed flywheel are discussed. In terms of the solution for the bearings in FESS, two novel bearing configurations for both vertical and horizontal flywheel are proposed. For the three-pole inverter-fed active magnetic bearing, the state equation for magnetic force on rotor is presented on the basis of equivalent magnetic circuit, and the analytical results are verified by finite element analysis (FEA) simulation. Owing to the decoupled analytical model, a control method with PID displacement control in the outer loop and hysteresis current control in the inner loop is proposed. The performance of the control method is verified by advanced simulator coupling technology. For interleaved permanent magnet thrust bearing, based on the current sheet model, a simple form analytical solution for the analysis and design of permanent magnet (PM) thrust bearing is proposed. It could be used for magnetic force calculation of single or multiple pairs PM arrays or PM rings. The accuracy of the analytical solution is verified by 2D and 3D FEA simulation. According to the analytical solution, a prototype PM thrust bearing with the proposed configuration is designed and fabricated, whose performances are experimentally validated on the FESS test platform.When load leveling control strategy is applied in multifunctional grid-connected converter, the realization in hardware and software will change accordingly. Based on the analysis of control structure feature and main circuit configuration feature in multifunctional grid-connected converter, the harmonics detection and interface circuit between converter and grid are further studied. The phase lock loop detection error and the time delay often occur in the digital control circuit for harmonics detection. In order to minimize their bad influences, the performance of the harmonics detection method without phase lock loop is discussed, and meanwhile the effect of the time delay on the reference compensation current signal is investigated based on universal instantaneous power theory. Then an improved synchronous reference frame method for harmonics and reactive currents detection is proposed in the dissertation, which applies no phase lock loop and takes the time delay into account. The simulation results have proved its accuracy and feasibility. Then a LCL filter formed by traditional LC filter and the short circuit impedance of isolation transformers is proposed, which has better filter characteristics. And some design principles for the LCL filter are also given. Last but not least, the control circuit accomplishment and the software flow chart are introduced, and the fabrication of a 15kVA three single-phase full bridge multifunctional grid-connected converter prototype is finally completed.
Keywords/Search Tags:Hybrid energy system, Load leveling, Energy storage system, grid-connected converter, Flywheel, Permanent magnet bearing, Active magnetic bearing, Harmonics detection, LCL filter
PDF Full Text Request
Related items