Research On Distributed SOFC Generation System Simulation And Power Flower Calculation

Electrical power demanding is increasing with the development of the whole society. More and more energy consumption causes depletion of fossil fuels comparing with their growing speed. At the same time, the whole world is facing the pressure of circumstance pollution and global warming caused by industry. To solve these issues, new energy and electricity generation are taken out to be researched and applied. In this paper, solid oxide fuel cell (SOFC) is chose to be studied for it has the best future among all fuel cells. The research includes electrical modeling SOFC, control and simulation of connecting with the main grid, and the power flow calculation of islanding systems. It aims to give a reference for analysis and control of the system with SOFC and other distributed generation resources (DGRS) widely used.Planner anode-supported high/intermediate-temperature solid oxide fuel cell (P-A-H/M-T SOFC) is studied in this paper for it is mostly popular in the power system. Firstly, the material and structure of P-A-H/M-T SOFC and its stack are introduced. Based on the principle of its power generation, the output characteristics of the cell and it control is studied with electrochemical electric potential model (ECE). With the help of linearization and equivalence principle, voltage source series resistance (VSSR) model and multi-voltage sources series resistances (MVSSRs) model are proposed for the simplification of the model application in static analysis. The linear equivalent electric circuit models proposed are simply and effective for applications of P-A-H/M-T SOFC in system control and analysis.Based on the analysis of the power generation characteristics, PI control, Pulse Width Modulation (PWM) control with current relay track as a feeder back, and other control ways are used to control the three-phased inverter of the cell stack to the main grid. With an example of a 50kW SOFC power generation system link to a main grid, the dynamic power control of the fuel cell stack is simulated with Matlab software. The simulation shows that it is possible to control the power (includes both active power and reactive power) of the distributed generation (DG) system by controlling its inverter to the main grid. And it shows that P-A-H/M-T SOFC is suitable for power supplying to basic load.Current DGRs are so limited that in an independent micro-grid, known as'islanding'system, no current DGR is big enough to balance the power demand and to stabilize the frequency of the micro-grid. It means that there is no swing bus of an islanding micro-grid can be managed as that set in the traditional calculation. Setting DGRs as slack PQ nodes, a new power flow calculation method based on the above research, is proposed to accommodate the lack of a swing bus in an islanding system. With this method, balanced power calculations are discussed with IEEE-5 bus system (ringing topological structure) and distributed 33-bus system (radial structure). It is solved with Newton-Raphson method). The method proposed is valid by comparing its results with those got with the traditional method. It shows that the new method is adapted to networks with different topological structures.Three-phase power flow of power system is normally unbalanced causing by the shifting of lines, single-phase loads and other factors. Using phase component analysis, a new power flow calculation method is proposed for unbalanced power calculation of islanding micro-grids. The phase shifting in power flow between primary and secondary windings of the transformer, caused by the transformer winding connection, and the coupling of the lines are also discussed in unbalanced three-phase power flow calculation. It is valid with IEEE-5 bus system by comparing he results with those of the traditional power flow calculation method.In the balanced/unbalanced three-phase power flow, different DG systems with various adjustment coefficients, different load demanding level, different load models with various adjustment coefficients are discussed in details. The improved method with good convergence addresses power flow results and the frequency of the whole system and is more appropriate for islanding systems with mesh topology and for micro-grid management with no swing bus. The power flow calculation shows that to improve the stability of the islanding micro-grids, especially that of an unbalanced system, P-A-H/M-T SOFC needs to work together with other DGRs which can change their power output quickly.