Dan Wang

The effect of small impedance branches on the convergence of the Newton Raphson power flow

This paper investigates the process of the Newton Raphson (N-R) method with flat voltage start when it is used for systems with small impedance branches. And find out that the divergence occurs in the cases which both ends of the small impedance branch are connected to PQ buses. Even under the cases with the divergence problem the Jacobian matrix is still nonsingular and the equations are solvable, and the results from the equations are very precise but unreasonable. So this paper draws a conclusion that it is not the numerical instability but the characteristic of the equations of the N-R method that cause the divergence. Further investigation shows that the improvement of voltage start can avoid the divergence problem. Based on the theoretical analysis, a method to prevent the N-R method from divergence by improving voltage start is presented. Experimental results validate the convergence analysis and illustrate the effectiveness of the proposed method.

Convergence analysis on the power flow methods for distribution networks with small impedance branches

The small impedance branch is a primary factor that results in the divergence of the power flow methods. The study of the methods of power calculation in Newton-Raphson (N-R) method and backward/forward sweep (BFS) method indicates that the method of power calculation together with small impedances may result in the convergence problem. The impact of small impedance branches on the convergence of the two power flow methods is different because the two methods are different in mechanism. So the ways to improve the convergence performance of the power flow methods are also different. Based on theoretical analysis, a branch dividing method is presented which divides a transformer with small impedance into a transformer with normal impedance and a capacitive line. The proposed method can conveniently and effectively deal with the convergence problem in the BFS method caused by small impedance transformer branches, and experimental results illustrate the effectiveness of the method.

The Effect of Transformer Representation on the Convergence of the Backward Forward Sweep Method for Distribution Power Network

The small impedance branch has a great significant effect on the convergence of the power flow methods. Whether the power flow converges or not when it used for systems with small impedance branches not only depends on the power flow methods but also the representation of the network elements. The backward forward sweep (BFS) method which is widely used for distribution networks is discussed in the paper. When the BFS method is applied to systems with small impedance transformer branches, the divergence of power flow may occur. The transformer representation affects the convergence property of the BFS method greatly. The Pi equivalent circuit usually causes the divergence of the BFS method, while the standard equivalent circuit with an ideal transformer does not. The results of an experimental system validate our conclusion.

Diagnosis of Actuator Lock-in-place for Flight Control Systems

In this paper, the diagnosis problem of actuator lock-in-place is studied. Based on multiple-model structure, an adaptive unknown input observer (UIO) approach is developed to detect and isolate aircraft actuator faults. Existing multiple-model FDI (fault detection and isolation) approaches assumed that the model for each fault case is known a priori. However, in the cases of lock-in-place, the locked position is unknown and varies in the range of maximum deflections. Thus, there exists an infinite family of models which is impossible to model exhaustively. To solve this problem, we developed an adaptive approach to estimate the unknown parameters on-line. The proposed adaptive algorithms guarantee that both the residual signals and the estimation errors of the unknown parameters converge exponentially when a model matches the system. To the best of our knowledge, this is the first adaptive UIO presented.

Design and Research on Ballast Anti-Heeling System for the Crane/Pipe-Laying Vessel Based on DP3 Requirements

To ensure the stability of the crane/pipe-laying function in different working conditions, the redundancy of ballast system of a certain crane/pipe-laying vessel is designed according to the relative requirements of the third class dynamic positioning (DP3) in regulations and the characteristics of the vessel arrangement. The DP3 requirements of the redundancy of ballast system for the vessel are satisfied by means of the arrangement of ballast pumps and the redundancy configuration of the piping systems. Simultaneously, the ballast anti-heeling system is able to fulfill different working conditions.

The Reliability Modeling of Marine Power Station

Through the prediction based on reliability counting method, identified weak links of automatic control system, achieved the reliability modeling of marine power station and structured reliability block diagrams and the reliability mathematical models, the reliability and mean time between failures (MTBF) of marine power station are obtained under different work conditions. The marine power station reliability modeling acquired from different work conditions accords with the actual operating mode, and all these work can supply more scientific theoretical support for study on reliability of marine power station.

Study of a Fuzzy Decision Making Based Energy-Saving Controller for Marine Power System

In order to realize energy-saving for marine power system, combining the fuzzy set theory with the traditional PID control technology, the marine power system energy-saving controller was designed, which control ship power grid frequency and voltage collaborative reduction within a certain scope and scale. As several prototypes testing, the application of the energy-saving controller, which control the ship power grid frequency from 60Hz dropping to 57Hz, and the voltage from 450V collaborative falling to 425.5V, and meet the Ship Building Standard, can save 9.85% of electric energy and 9.53% of fuel.