A Simplified Dynamic Model And Small Signal Stability Analysis Of Six-phase Electrically Excitation Synchronous Wind Generators

Six-phase electrically excited synchronous wind generator(SP-EESWG) is a special kind of variable speed constant frequency wind turbine. SP-EESWG has many preferable characteristics, such as-low unit cost, high power generation efficiency, small rotational torque pulsation as well as high reliability-and has been applied to some wind farms in Chongqing, Shandong and Neimeng, etc. However, compared with Double-Fed Induction Generator(DFIG) and Direct-Drive Permanent Magnet Synchronous Generators(D-PMSG), less researches on SP-EESWG have been carried out, dynamic modeling and dynamic performance analysis are, therefore, very limite.This paper studies SP-EESWGs’ dynamic modeling, power flow and small signal performance. The main contributions are as follows:a. A simplified dynamic model of SP-EESWG is presented. Based on the mathematic models of wind turbine, gearbox, generator, AC-DC-AC conversion, a simplified dynamic model is presented ignoring the dynamics and harmonics within rectifying and inverting, choosing the proper basic values and fitting the steady active-reactive power relationship of uncontrollable rectifier. And in order to determine the initial state of the dynamic model, a steady-state model of SP-EESWG is proposed. The simplified model is tested on a single-machine infinite bus sample system, by comparing its dynamic responses with those of the Simulink model of the same sample system.The steady-state model of SP-EESWG is further applied to power flow analysis. A single-machine infinite-bus system and the IEEE14-bus system including SP-EESWGs is used to verity the model proposed. Simulation results also proved that the widely used simplified power flow models for wind generators, especially the first-order and the second-order model, cannot be applied to steady-state analysis of SP-EESWG because of the large errors presented, while the third-order model and the exponential model can be used as alternatives of the model proposed only for the steady state under or near the rated wind speed.b. A state-space model of SP-EESWG is presented and applied to small signal analysis.No literatures on stability analysis of SP-EESWG have been found so far. By linearizing the simplified model of SP-EESWG presented, a state-space model of SP-EESWG is established. Based on eigenvalue analysis method, the influences of wind turbine mechanical parameters, generator electrical parameters, DC capacitance and PI control parameters on small signal stability are studied. Results demonstrated a) the wind turbine inertia time constant and DC capacitance have great influence on the small signal stability of SP-EESWG, since all of the eigenvalues are shifted torward right as they increased; b) either large or small value of the shaft rigidity coefficient and stator resistance will deteriorate the small signal stability of SP-EESWG; c) the proportion coefficient and integral coefficient of PI control shows opposite effects on the small signal stability of SP-EESWG.