Commutation failure is one of the common faults of DC system,continuous commutation failure or multiple HVDC commutation failure will seriously endanger the stable operation of the AC and DC systems,and thus commutation failure judgment is a very important issue.Electromechanical transient program often has simple models,large simulation scale,short computation time,and it's simulation accuracy can meet the power system calculation requirements,so it is often used for large AC-DC hybrid grid commutation failure research.This paper describes the commutation failure mechanism and its influencing factors first,then analyzes the DC models and commutation failure criterion of electromechanical transient program.Finally,compare the simulation results of the most commonly used electrome-chanical transient program BPA and PSS/E through an example,and analyze the scope of these two programs for commutation failure research.

As the Ultra HVDC transmission system established,DC power declined several times abnormally,which brought about obvious effects on inversion side AC/DC grid,especially the generators nearby.In order to validate the simulation and system modeling the fault is analyzed in detail.DC system with real control blocks,as well as the inversion side 525/230 kV AC system models are built on EMTDC/PSCAD platform,and at the rectification side,the discharge transient process of DC voltage divider in measuring unit is simulated.The results of simulation is well coincide with the fault recording,which shows the accuracy of electromagnetic simulation and system modeling.

Parameter sensitivity indices of power system stabilizer(PSS) are introduced and sensitivity computation function are implemented in SSAP power system software package by two approaches;(i) the sensitivity computation function of eigenvalues associated with oscillation modes and their damping ratios via PSS controller parameters;and(ii) the sensitivity computation function of the eigenvalues of oscillation modes and their damping ratios via PSS parameters subject to the condition of constant equivalent AC gain.Low frequency oscillation damping is optimized in both approaches.The 600 MW generator in Honghaiwan power station is taken for case study.The parameter of PSS is optimized by sensitivity analysis subject to constant equivalent AC gain.The optimized results well coincide with the oscillograms recorded during the on site experiment.The sensitivity analysis by SSAP is validated not only by theoretic analysis but also by engineering practice.

To analyze the effect of stochastic parameters in power system on dynamic simulation, a novel method based on the two-point estimation method (TPEM) was presented for dynamic voltage stability analysis. The method evaluated the dynamic voltage stability through the TPEM and quasi-steady state analysis. Considering the compensation effect of STATCOM on voltage stability, the proposed method was used to study the system with STATCOM, and the indexes of bus voltage in stochastic faults were calculated. Numerical analysis verifies the accuracy of this algorithm and fast calculation, which can provide the guidance to the power system planning and design.

Considering nonlinear power system with the form of differential algebraic system, we proposed a new nonlinear STATCOM controller structure which contains multi machine power system applying the generalized Hamiltonian system and relevant control strategy. The power injection based STATCOM model was the object in controller design. And the STATCOM controller in multi machine power system was obtained to improve the system robustness, which had precise mathematical and physical meaning. Simulation results of a 3-machine and 9-node system with STATCOM verify that the controller proposed in this paper is effective to power system voltage stability.

The static synchronous compensator (STATCOM) is well known as a reactive power compensator with the best performance in the power system recently, which is used in power systems to regulate the line voltage, enhance the power transmission capacity and extend the transient stability margin. STATCOM is conventionally realized by a voltage-source converter; however, being a current injection device, its performance can be improved when realized by a current-source converter (CSC) that can generate a controllable current directly at its output terminals. A STATCOM based on the current-source converter topology is proposed. The nonlinear model of the current-source converter, which is the source of the difficulties in the controller design, has been modified to a linear model through a novel modeling technique. The proposed modeling technique is not based on the linearization of a set of nonlinear equations around an operating point. Instead, the power balance equation and a nonlinear input transformation are used to derive a linear model independent of the operating point. This model acts as the basis for the design of a decoupled state-feedback controller. The proposed STATCOM has been simulated using the PSCAD/EMTDC package. The simulation results show that a CSC-based STATCOM can result in excellent current and voltage waveforms as well as very short response time while operating at a low switching frequency. This makes the proposed scheme suitable for high power applications. Ill. 6, bibl. 11 (in English; summaries in English, Russian and Lithuanian).

Bifurcation analysis based on the power flow equation model is a useful tool for static analysis of power system voltage stability,where the saddlenode bifurcation and limit-induced bifurcation associated with the power flow equation are two kinds of different bifurcation phenomena that result to voltage collapse.This paper discusses the similarities and differences of these two kinds of bifurcations from their mathematical and physical aspects for better understanding and identification of voltage collapse phenomena due to them.Numerical simulations on IEEE 57-bus and IEEE 118-bus systems are used to illustrate our theoretical results.

The control system plays an important role in the high-voltage direct-current transmission system. An improved particle swarm optimization algorithm is proposed and employed to design the optimal proportional-integral controllers in high-voltage direct-current system in this article. Simulation examples were implemented on the CIGRE HVDC Benchmark Model [Szechtman, M., Wess, T., and Thio, C. V., First benchmark model for HVDC control studies, CIGRE WG 14.02 Electra, No. 135, pp. 54-73, 1991], and the results of the standard particle swarm optimization algorithm and stable boundary law method were also given as contrasts. Simulation results showed that the proportional-integral controller designed by the proposed method can satisfy the requirements of stability and dynamic response performance indexes of high-voltage direct-current transmission system.

In order to enhance the dynamic stability of AC/DC power system, a novel adaptive chaos particle swarm optimization (ACPSO) algorithm is presented and applies to design optimal coordinated HVDC modulators for the multi-infeed HVDC system. According to the proposed ACPSO algorithm, the diversity of the particle swarm is enhanced by using the ergodicity of the chaos motion to initialize the swarm; a part of particles are chosen on the basis of their fitness value and optimized by chaos optimization algorithm to help the inert ones jump out the local extremum region at each iteration; the capability of global and local search is improved by introducing an adaptive inertia weight factor for each particle to adjust its inertia weight factor adaptively in response to its fitness. Simulation is implemented on a three areas dual-infeed HVDC system, in which the active power deviation of the AC inter-ties and the rotor angle deviation of all generators are selected to form the objective function, and the ACPSO algorithm is used for searching the global optimal parameters of each bilateral frequency-difference HVDC modulator. The simulation results show that the proposed ACPSO algorithm can realize optimization and coordination of HVDC modulation and enhance dynamic stability of AC/DC interconnected power system more effectively than the traditional PSO algorithm and genetic algorithm, and can be a promising method for parameters' optimal coordination of HVDC modulators in multi-infeed HVDC power system.

This paper proposes a novel method for analyzing the zero-sequence signal of three-level voltage-source inverter based on vector diagram partition. The inherent relation between carried-based PWM and SVPWM is demonstrated. It is shown that the two method can work equivalently through proper selection of active time for the redundant vector in the case of space vector modulation, or zero-sequence signal injections in the case of carried-based modulation. Both simulation and experimental results verify the effectiveness of proposed approach.

An adaptive particle swarm optimization(APSO)algorithm which can overcome the disadvantages of frequent trapping in local optimum in the traditional PSO algorithm was presented in order to optimize the design for HVDC PI controllers.According to the presented APSO algorithm,the inertia weight coefficient of each particle changes adaptively based on its current fitness function value in the optimization process.So,the particles with good fitness function value trend to make fine search in the vicinity of the colony's optimal solution,and the ones with poor evaluation function value will do rough detection with larger step size in the whole feasible region to discover new better solution.Therefore,the new algorithm has a good effort to adjust the dynamic balance between colony's convergence and individual's diversity,and effectively overcomes the problem of local optimal resolution.A systematic modeling and optimization method of design the HVDC PI controllers was proposed based on the APSO algorithm.Simulation examples were implemented on the CIGRE HVDC Benchmark Model,and the result of the Stable Boundary Law design method was also given as a contrast.The feasibility and validity of the proposed method are proved by the simulation results.

This paper introduces the average circuit models for the cascaded H-bridge (CHB) multilevel inverter for shunt compensation of electric distribution systems, such as DSTATCOMs and active filters (AFs). These CHB-based shunt compensators achieve dynamic reactive power and harmonic compensation, which is particularly appreciated for power quality (PQ) enhancement for the high-power applications. Nevertheless, digital simulation and controller synthesis of these CHB-based shunt compensators is rather complex due to the sophisticated switching topologies introduced by the pulse-width modulation (PWM) process. To simplify the difficulty for theoretical investigation and accelerate digital simulation, the state-space averaging (SSA) technique is utilized to derive the approximate model of the CHB-based inverters. The proportional-resonant (PR) controller is adopted for the current tracking control of the inverter, and the average dc-link voltage is controlled using a proportional-integral (PI) controller to regulate the active power flow of the DSTA TCOM Besides, the voltage balancing controller (VBC) is adopted to achieve equal reactive power loading among individual H-bridges by using separate PI regulators to control the difference voltage between the individual dc-link voltage and the average dc-link voltage. Extensive simulation results are presented to validate the theoretical analysis and the devised control strategies. Furthermore, the experimental results obtained from a four modules CHB-based DSTA TCOM are also presented for verification. The consistency between the simulation and experimental results further verifies the validity and the effectiveness of the proposed technique. Copyright (C) 2009 Praise Worthy Prize S.r.l - All rights reserved

The main obstacle to the wide application of the measurement-based load modeling approach(MBLMA) lies in the serious insufficiency of the effective data provided by disturbance normally occurring in a power system.This is because the currently used MBLMA can only identify the load parameters from three-phase symmetric disturbance.But most of the faults occurring in a power system are asymmetric,and it is hard to get permission to do field test.An approach to load dynamic modeling during asymmetric disturbance(LMAD) is proposed.The problem of insufficient data is solved by applying Park's equations in solving the induction motor's dynamic process.And the problem of divergence in MBLMA is solved with the modified immune algorithm in the optimization of the model parameters instead of the least square estimation(LSE) method.Finally,the identified load model's influence on the critical clearing time(CCT) in Shanghai Power Grid is discussed.

The p-q-r algorithm was proposed by many famous authors as an alternative for instantaneous reactive power theory (IRPT) for harmonic and reactive compensation. However, asymmetry or harmonics in the grid voltages degrades the performance of p-q-r algorithm. This paper proposes a novel approach to enhance the performance of p-q-r algorithm by using instantaneous symmetric component decomposition (ISCD) algorithm as pre-filter for the p-q-r method. The effectiveness of the proposed algorithm has been substantially confirmed by the simulation results.

A novel three-phase phase-locked loop (PLL) structure suitable for phase and angular frequency tracking from distorted ac utility voltages is presented. The proposed PLL has a simple structure: a conventional three-phase PLL followed by adaptive notch filtering technique and proportional integral controller. The feasibility of the PLL was confirmed by theoretical analysis, and the performance was verified through simulations. The proposed PLL system shows accurate performance under various line voltage disturbances, such as sag, unbalance and harmonics. Ill. 5, bibl. 4 (in English; summaries in English, Russian and Lithuanian).

A novel three-phase rectifier topology based on T-type active power filter (APF) is proposed. The design method of main circuit parameters is also given. The mathematical model of the T-type active power filter is deduced, and two control strategies, namely, source-side current feedback control strategy and source-side current feedback plus load current feed-forward control strategy are devised and compared. The proposed system is studied by digital simulation using PSCAD/EMTDC software and by experiments. The simulation and experimental results are consistent, which demonstrates the feasibility of the proposed topology and the effectiveness of the devised control strategies.

The Fast Fourier Transform (FFT) suffers from the deficiency of leakage effect for the harmonic and inter-harmonic analysis of electric signals. in order to overcome the leakage effect of FFT algorithm, a new desynchronized signal processing technique is proposed, which is based on poly-item cosine window (CW) interpolation. The proposed technique is consisted of a double-stage signal processing procedure. In the first stage, the harmonic components are accurately estimated via cosine window interpolations in the frequency domain and the estimated signal is subtracted from the original signal in the time domain. In the second stage, inter-harmonic components are accurately obtained via the same interpolation without the spectral leakage problems. Since the procedure does not require synchronization, a fixed sampling frequency can be utilized to simplify the data acquisition process. Meanwhile, the computational burden is remarkably reduced due to the direct utilization of the FFT on the acquired sampling signal. Extensive simulation results are provided to verify the validity and effectiveness of the proposed algorithm, which reveals that the frequencies, amplitudes and phase angles of the harmonics and the inter-harmonics are accurately calculated, even under significant fundamental frequency deviations in the input signal. Moreover, the proposed technique is found to have overwhelming advantages in terms of the improved estimation accuracy and reduced computational burden compared to the existing unsynchronized sampling techniques in literature. Copyright (C) 2009 Praise Worthy Prize S.r.l. - All rights reserved.

This paper proposes an LCL-filter-based hybrid active power filter for harmonic mitigation of a 10/0.4kV residential distribution system. Adaptive linear neuron network (ADALINE) is applied for individual harmonic component extraction from distorted nonlinear load currents, and the estimated signals are used for the selective harmonic elimination (SHE) purpose in the current-loop controller. A robust deadbeat current control law is derived based on the low frequency model of the presented topology. By using the ADALINE based SHE strategy, the current-loop controller bandwidth is significantly reduced thus the stability of whole system is ensured. Both the laboratory experiments and field tests are implemented. The feasibility and effectiveness of the proposed system have been substantially confirmed by the experimental results.

An effective control scheme for three-phase three-wire active power filter is proposed in this paper. Conventionally, the majority of existing APF control strategies in literature adopts feed-forward control scheme, which results in switching notches (sharp-rising or falling ripples) in the source-side currents at conduction instants of diode/thyristor rectifier load. The proposed method utilizes feedback control plus feed-forward control structures to achieve a smooth filtering performance. The feedback loop minimizes the steady-state error using two separate PI regulators in d-axis and q-axis respectively. The feed-forward loop serves the purpose of load disturbance rejection and it significantly enhances performance of active power filter by using synchronous frame adaptive neural network (SADALINE) algorithm. The proposed method overwhelms many existing compensation schemes in terms of simplicity, robustness and ease of implementation using DSP. The effectiveness of the proposed control scheme has been substantially confirmed by experimental results. Key-Words: harmonic contamination, active filter, power quality, SADALINE