Zigang Lu

Bio: Zigang Lu is an academic researcher from Hohai University. The author has contributed to research in topics: Filter (signal processing) & Noise. The author has an hindex of 2, co-authored 3 publications receiving 35 citations.

A modified Kalman filter algorithm for fractional system under Lévy noises

Abstract: This paper considers the filter designing problem for discrete linear fractional order systems with non-Gaussian noises. Taking both the system noise and the measurement noise as Levy noises instead of Gaussian white noises, through the approximating transformation for Levy noises, a modified Kalman filter algorithm is proposed for discrete linear fractional order system. The developed results can be used to estimate the system states for discrete linear fractional order system under non-Gaussian Levy noises with satisfactory accuracy, which are more general than some existing results. Finally, simulation results are provided to verify and illustrate the effectiveness of the obtained results.

Power flow calculation for unbalanced three-phase distribution network with DGs based on phase-sequence hybrid modeling

Abstract: With many distributed generations (DGs) connected to distribution networks, the traditional power flow methods are difficult to deal with PQ(V)-node, PV-node and PI-node types DGs. Therefore, in this paper, a novel power flow algorithm for unbalanced three-phase distribution networks with DGs based on phase-sequence hybrid modeling is proposed. By using the phase-sequence hybrid modeling method, three-phase load models and parameter models of distribution network are established. And combined the special topological structure of distribution network and the three-sequence decoupling-compensation models of unsymmetrical branches with the path-loop circuit analysis method, an effective power flow algorithm for unbalanced three-phase distribution networks is proposed. Then, kinds of DGs are divided into PQ-node, PQ(V)-node, PV-node and PI-node types DGs, their calculation models are derived in detail and can be simply integrated into the proposed power flow algorithm of distribution networks. Test example results show that the proposed method possesses good convergence and efficiency of processing DGs, furthermore, it is verified from the simulation results that robustness and usefulness of the proposed algorithm.

Power system dynamic state estimation considering correlation of measurement error from PMU and SCADA

Abstract: It is well known that measurements from phasor measurement unit (PMU) or supervisory control and data acquisition (SCADA) are not generally independent. Since the correlation of measurement error is a very representative feature of the actual measurement system, traditional assumptions on error independency are not adequate. In this paper, taking the correlation of measurement error of both PMU and SCADA measurements into consideration, a novel correlated extended Kalman filter (CEKF) is proposed. The actual measurement configurations are analyzed with the consideration of measurement error transfer characteristics. Then, the modified measurement error covariance matrix is calculated by using the point estimation method, which will replace the traditional diagonal variance matrix. At last, IEEE 14‐bus system and 57‐bus system are provided to illustrate the effectiveness and superiority of the method, respectively.

Fault Mechanism Analysis of Voltage Transformer Caused By Iron Core Saturation

Abstract: Voltage transformer, providing primary system voltage information to secondary system to measure, monitor and protect the power grid, is a very important equipment to ensure the safe operation of power grid. In the neutral ungrounded distribution system, since the excitation inductance of electromagnetic voltage transformer has nonlinear characteristics, and the ferromagnetic resonance phenomenon are prone to occur under certainconditions, which has serious influence on safe and stable operation of the system. The ferromagnetic principle of electromagnetic voltage transformer in neutral ungrounded system and its harm are briefly analyzed and introduced. Combined with the actual case, the damage reason of 10kV bus voltage transformer in substation is analyzed and the correctness of the analysis result is verified by theoretical calculation. Finally, the countermeasures are put forward to improve the operation safety of voltage transformer in distribution network.

Design of Extreme High Voltage High Stability Test Voltage Source

Abstract: This paper designs an extreme high voltage and highstability test voltage source. First of all, the design of a highstability direct current(DC) voltage source is realized by using a high-frequency transformer and a two-stage boosting method of a voltage-doubling rectifier circuit. In this way, a voltage source with lower ripple factor and higher stability can be obtained. Then, in order to obtain a fast and free experimental platform, this paper designs an integrated voltage doubling and pressure measurement for the structure of the DC voltage source voltage equalization system, and effectively solves the problem of series voltage equalization of high-voltage silicon stacks. According to the scheme of this paper, the voltage source is designed, the output voltage is 1100kV, the ripple coefficient is 0.059%, and the stability is better than 0.05%/h. It reaches the domestic leading level which has been successfully applied to the DC voltage transformer of ±400kV sense converter station in Lhasa.

Fractional extended Kalman filtering for non-linear fractional system with Lévy noises

Abstract: In this study, the extended Kalman filtering problem is discussed for fractional-order non-linear discrete system with Levy noises. Two different approximating methods are proposed, respectively, one is to obtain the approximated system measurement noise firstly, then calculates the iterative state vector and measurement vector, the other one is to approximate state vector and measurement vector directly, which seems to be more efficient. Based on the proposed approximating methods, two novel fractional extended Kalman filter designing strategies are developed for fractional-order non-linear discrete system with Levy noises, some detailed comparisons and discussions are presented to show that the obtained results are more general. Finally, some simulation results with necessary comparisons and discussions are given to illustrate the validity and correctness of the proposed methods.

Kalman filtering for discrete-time linear fractional-order singular systems

Abstract: This study considers the optimal linear estimation problem for the discrete-time stochastic fractional-order system in its more general formulation. The system is allowed to be in singular form, rectangular, with dynamical and measurement noises correlated. First, some new conditions for the solvability, regularity and causality to discrete-time linear stochastic fractional-order singular (FOS) systems are given, and then, a new Kalman filter (KF) fractional singular KF (FSKF) is designed for such systems. This general form of filter is derived using deterministic arguments in a completely self-contained way besides the stochastic reasoning and covers the nominal singular and fractional KFs. Instead of the standard stochastic formulation, the filter recursions are obtained as a solution of a convenient organisation of the deterministic data-fitting estimate of an entire state trajectory given the measurements for both time-invariant and time-varying cases. To present the efficiency of the proposed algorithm, results of numerical simulations are presented.

Robust extended fractional Kalman filter for nonlinear fractional system with missing measurements

Abstract: Accurate and effective state estimation is essential for nonlinear fractional system, since it can provide some vital operation information about the system. However, inevitably missing measurements and additive uncertainty in the gain will affect the performance of estimation result. Thus, in this paper, in order to deal with these problems, a novel robust extended fractional Kalman filter (REFKF) is developed for states estimation of nonlinear fractional system, by which the states can be estimated accurately even with missing measurements. Finally, simulation results are provided to demonstrate that the proposed method can achieve much better estimation performance than the conventional extended fractional Kalman filter (EFKF).

Molecular Evolution Based Dynamic Reconfiguration of Distribution Networks With DGs Considering Three-Phase Balance and Switching Times

Abstract: As the problem of three-phase unbalance in a distribution network with distributed generations (DGs) is prominent, a multiobjective dynamic reconfiguration method for three-phase balance is proposed to make reconfiguration more reasonable and effective. Based on three-phase power flow calculation and reconfiguration process analysis of distribution networks with DGs, a new reconfiguration model with comprehensive optimization objectives of minimizing three-phase unbalance factor and number of switching times are established. A network connectivity discrimination method based on the algebraic connectivity of graph theory is adopted to quickly remove infeasible solutions, and a new multiobjective molecular differential evolution algorithm is designed to improve optimization depth and avoid prematurity in the optimization process, which is based on the principle of closer molecules with greater intermolecular repulsion. The multiobjective optimal dynamic reconfiguration of a modified IEEE 34-bus test feeder with DGs is carried out and the simulation results demonstrate the effectiveness and superiority of the proposed method.