Dechang Yang

An Industrial DC Power Supply System Based on an Inductive Filtering Method

This paper proposes a new direct current (dc) power supply system based on an inductive filtering method for one industrial dc load. The operating mechanism of the new inductive filtering method is analyzed, and then, the harmonic model and the equivalent model are established. Moreover, the impedance conditions for the implementation of the inductive filtering method are presented, and the influence of the filtering loops impedance on the filtering performance is clarified. Both the simulation and the experimental study on one practical inductive-filtering-based industrial dc supply system for chemical electrolysis are used to validate the theoretical analysis. The research results show that the inductive filtering method not only greatly reduces the harmonic magnetic flux in the rectifier transformer but also prevents harmonic currents from flowing into the primary (grid) winding of the rectifier transformer. It presents good filtering and reactive power compensating performances to public networks and also increases the operating efficiency of the industrial dc power supply system itself.

Harmonic Transfer Characteristics of a New HVDC System Based on an Inductive Filtering Method

This paper presents a new HVDC system improved by an inductive filtering method, and afterward proposes a unified equivalent circuit model and a corresponding mathematical model for the calculation of the harmonic transfer characteristics of the new HVDC system. First, according to the special topology of the new HVDC converter station, an equivalent circuit model described by the fundamental and the harmonic impedances is established. Second, via the mathematical modeling of this new HVDC system, a harmonic transfer model is also established, which can be used to express the effect of inductive filtering method on the harmonic distribution characteristics. Moreover, by the theoretical analysis on the commutation process of the HVDC converter, a time-domain expression of the valve current is obtained to represent the harmonic characteristics of the converter. Finally, an experimental study validates the established analytical model and illustrates the harmonic transfer characteristics of the new HVDC system.

Wide-area time-delay damping control to prevent power oscillations in HVDC/AC interconnected power systems

In this paper, a robust high voltage direct-current (HVDC) wide-area time-delay damping control strategy is proposed to prevent the potential low-frequency power oscillation and enhance the power stability of HVDC/AC interconnected power systems. Firstly, the basic design concept and the related design flow are presented. Then, the general wide-area power system model with the time-delay characteristic is described by the linearization modeling method. The practical reduced-order algorithm is introduced to further obtain the reduced system state-space model that maintains the low-frequency oscillation mode. Furthermore, considering the inevitable time delay in the wide-area feedback control signals transmitted by the wide-area measurement system (WAMS), the improved linear matrix inequality (LMI) method is applied to design the robust supplementary damping controller associated to the HVDC converter pole-control. Such controller can efficiently suppress the negative effect of time delay of the wide-area control signals on the oscillation damping performance. In addition, the iterative algorithm is proposed to search the optimal overall gain matrix for the state feedback control, and the state observer is also designed based on the classic pole-placement method to realize the observability on the state variables of the reduced system. Finally, a case study on a benchmark system of small signal stability study is performed to validate the proposed HVDC wide-area time-delay damping control strategy.

Analysis of Low Frequency Oscillations using improved Hilbert-Huang Transform

As a non-linear and time-varying tool, Hilbert-Huang Transform (HHT) has been widely used to analyze Low Frequency Oscillation (LFO) signals in power systems. It utilizes Empirical Mode Decomposition (EMD) to decompose the LFO signals into a collection of Intrinsic Mode Functions (IMFs), and then the instantaneous parameters including magnitude, frequency of every IMF can be calculated by applying the Hilbert Transform. However, HHT suffers from a number of shortcomings. In order to dispose the inherent problems of conventional HHT, an improved HHT is proposed based on Symmetrical Extrema Extension (SEE) method and frequency heterodyne technique. In this paper, SEE method is employed to expand the original signal during the processing of EMD and frequency heterodyne technique is used to overcome the mode-mixing phenomena. Next, the principle and influences of different shifting frequency factors are introduced. Based on these, the steps and flow chart of improved HHT are proposed. The results of testing signals and simulation model show that the improved HHT not only diminishes the influences of End Effect, but also expands the application of HHT. It is feasible and effective to overcome special mode-mixing problem.

LMI-based robust wide-area time-delay damping control of SSSC-type FACTS device for stability enhancement of power system

This paper presents a linear matrix inequality (LMI) method for the design of the wide-area time-delay damping (WATDD) controller of static synchronous series compensator (SSSC)-type flexible ac transmission system (FACTS) device to enhance the power stability of the interconnected power systems. Firstly, in order to reveal the single-input multi-output (SIMO) characteristic of the open-loop power system with SSSC-type FACTS device, the prediction error estimation (PEE) algorithm based system identification method is applied to fit a special SIMO linear model. Then, based on the robust control theory and LMI method, the identified linear model is formulated as the standard control problem with the time-delay of the input signals of the WATDD controller, and combined with the designed state observer for the input state variables of the WATDD controller, the control parameters are optimized by the LMI iterate solution algorithm. Finally, the nonlinear simulation on the typical 2-area 4-machine system installed with SSSC-type WATDD controller is performed to verify the LMI-based design method and the proposed SSSC-type WATDD controller.

Study on the Effects of the DC Bias on the Harmonic Characteristics of the New Converter Transformer

DC bias is the problem that must be faced in the course of the design of the converter transformer for the high-voltage direct current (HVDC) transmission system, especially the new converter transformer that has the unique wiring scheme. This paper will theoretically analyze the basic cause of the dc bias of the new converter, and then according to the real no-load characteristic of the new converter transformer, its simulation model, which considers the hysteresis loss of the core of the new converter transformer, will be established by the means of data fitting. Based on the established simulation model, the harmonic characteristic of the new converter transformer caused by the dc bias will be simulated and analyzed in detail. Furthermore, this paper will propose a new inductive filtering technology to suppress the harmonic caused by the dc bias. Finally, compared with the traditional converter transformer, the superiority that the new suppression scheme has will be revealed.

Comparative study of single-phase earth fault responses of FCC-HVDC and LCC-HVDC

In order to study the transient response characteristics of Filter Commutated Converter (FCC) under the condition of single-phase earth fault, in the paper, referring to the CIGRE HVDC benchmark testing model (LCC-HVDC), on the basic of non-changing the short circuit ration (SCR) and some parameters, combining the connecting features of FCC, the new testing model based on FCC (FCC-HVDC) is established in the PSCAD/EMTDC; based the two models of LCC-HVDC and FCC-HVDC, the magnetizing and harmonic characteristics are analyzed comparatively under the single-phase earth fault, the results indicated: (1) the magnetizing current of the converter transformer are both a sudden increase and unidirectional magnetization, but the magnetizing characteristics of FCC-HVDC is better than LCC-HVDC; (2) FCC-HVDC still maintains its good harmonic suppression characteristics.

Feasibility Study on Application of Voltage Source Inductive Filtering Converter in HVDC-Light Systems

This paper presents a new voltage source inductive filtering converter (VSIFC) for HVDC-light transmission system, which is mainly composed of the inductive filtering (IF) transformer and the related full-tuned (FT) branches with the commutating function for the self-commutated converter. This paper concerns on the technical feasibility on the application of VSIFC in HVDC-Light systems. Firstly, two kinds of main-circuit topologies of VSIFCs are proposed, and based on this, a typical test system for the proposed VSIFC-based HVDC-light transmission is established. Then, the study on the unique inductive filtering characteristic and the transient stability that VSIFC-based HVDC transmission system has are performed in the PSCAD/EMTDC environment. Through the comparison with the classic VSC-based HVDC system, this paper verifies the technical feasibility on the application of VSIFC in HVDC-Light systems, and further reveals a series of technical characteristics and superiorities that VSIFC-based HVDC-light system has.

Study on Harmonic Losses of Inductive Filtering Converter Transformer (IFCT) in HVDC System

Based on the wiring scheme and the operating principle of the inductive filtering converter transformer (IFCT), this paper analyzes the effect of harmonic on the converter transformer, and establishes the harmonic losses model for the traditional converter transformer (TCT) and the IFCT, respectively. Furthermore, according to the IEC61378-2 standard and the superposition principle, the harmonics losses are calculated in detail. The simulation results verify the correctness of the theoretical analysis, and show that the harmonic losses of the IFCT are lower than that of the TCT, and the implement of the inductive filtering method can reduce the losses of converter station greatly.

A class of new HVDC transmission modes improved by Inductive Filtering method

Different from the existing main-circuit topologies of the HVDC converters, this paper presents a class of improved converter structures constructed by Inductive Filtering (IF) method, which can be used to further construct different HVDC transmission modes. Firstly, the basic operating principle and the technical characteristics of the IF method based HVDC converter is theoretically analyzed. Then, on the basis of the main-circuit topologies of the traditional line commutated converter (LCC), Capacitor Commutated Converter (CCC), Controlled Series Ca-pacitor Converter (CSCC), and Voltage Source Converter (VSC), a class of new main-circuit topologies of the inductive filtering based HVDC converters, which are improved by the IF method, is proposed firstly in the paper. Furthermore, based on these pro-posed inductive filtering converters, three kinds of new HVDC transmission modes are further firstly proposed and the main-circuit topologies of these HVDC modes are also presented. Final-ly, the key technical characteristics of such three kinds of HVDC transmission modes will be compared. The research results show that the proposed new HVDC transmission modes represent a series of technical characteristics and superiorities, which is ad-vantage to the stable and efficient operation of the modern HVDC transmission system.