Use of fuzzy techniques for analysis of dynamic loads in power systems

Presents the use of fuzzy techniques for analysis of dynamic load characteristics of power systems to identify the voltage stability (collapse) of a weak bus and concludes from the consistent results obtained that this is a useful tool for analysis of load charactersitics of sophiscated power systems and their components.

DAMAGE TOLERANCE ANALYSIS ON HOLLOW AXLES OF HIGH SPEED MOTOR TRAINS

According to the rules of UIC515-3, the service loads of the axles are defined, which include some different loads cases as follows： the static loads; the impact loads resulted from running through the rail joints and unevenness rails; the loads through curves and from braking. Through the calculating and analysis, the stress distribution of the hollow axles is obtained for 200 km/h high speed motor trains used in China. At the same time, the fatigue crack growth of hollow axles is studied, and the initial surface cracks of 2 mm depth caused by hard objects strike or the other causes are discussed. On the basis of the linear elastic fracture mechanics theory, the stress intensity factor of the crack of the geometry transition outside the wheel seat is also studied. Associated with fatigue crack propagation equation and the corresponding crack propagation threshold, the crack propagation characteristics under different shapes are calculated. Then the running distances are educed with different shapes propagating to the critical length, and the estimation of the residual lives about hollow axles which are the reference values of examine and repair limit of the hollow axle is given.

Determination of conditions for stable operation of induction motor resistance load using load flow and fuzzy techniques

Discusses the significance of induction motor constant resistance (IM R) load on the lower part of the PV curve of a power system and determines the conditions for stable operation of IM R load using fuzzy techniques and load flow.

Study on load performance of electric motor system used in hybrid electric vehicle

The performance of the power assist, global optimization solved by dynamic programming （DP） method, Chery and Insight control strategies are analyzed using the mild parallel hybrid electric vehicle （PHEV） model based on Insight structure. The influence of the four control strategies to the load power of the electric motor system used on parallel hybrid electric vehicle is studied. It is found that 80 percent of the motor load power points are under 1/5 of the electric peak power. The motor load power of the power assist control strategy is distributed in the widest range during generating operation, and the motor load power of the global optimization control strategy has the smallest one.

A 6n-Order Low-Frequency Mathematical Model of Multiple Inverters Based Microgrid

Microgrid stability analysis is a critical issue especially due to the inverters’low-inertia nature.The voltage and current control loops influences on stability are researched frequently most of which focus on medium and high-frequency characteristic.Although the complete state-space model aims at low-frequency characteristic,it is too complicated and the calculation amount is huge with the scale of the microgrid increasing.One available reduced-order model of an inverter is simple,but it is suitable for only single inverter without network dynamic in microgrid.To fill in these gaps,a novel modeling method is proposed in this paper to investigate the low-frequency instability phenomenon and describe the whole DG connected system including network.In consideration of the high penetration level of induction motor(IM)loads and constant power(CP)loads in practical applications,the low-frequency mathematical model of IM and CP loads on the basis of static load is also built in this paper.Simulation and experimental results verify the effectiveness of the proposed model.