Six-pulse Converter Research Articles

Modeling and exergy analysis of an integrated cryogenic refrigeration system and superconducting magnetic energy storage

Superconducting magnetic energy storage (SMES) systems widely used in various fields of power grids over the last two decades. In this study, a thyristor-based power conditioning system (PCS) that utilizes a six-pulse converter is modeled for an SMES system. The main subject of this research is the generation of required helium for an SMES because for the coil to be at superconducting temperature, it needs to always be immersed in liquid helium. In the conducted simulation, the helium production system provided, in which primarily the gaseous helium temperature was reduced by heat transfer in LNG heat exchangers, and then after the sudden pressure drop, it turned into a liquid. The effect of the various firing angles is investigated, and it is found that at angles lower than 90°, at a specific angle, the output current enhances with time. In the 90°, this current remains constant, and at degrees greater than 90°, the output current reduces with time. The percentage of input flows to the expanders is investigated to find the rate of the maximum liquid helium production amount to the inlet gaseous helium. The diverted ratio of mass flow via expander 1 and expander 2 was 0.46 and 0.35, respectively. The system's work utilization of network, and liquid helium production is 67.18 MW and 12.7 kg/h. Also, the exergy analysis is done and the results show 35.7 % exergy efficiency. The efficiency of helium production has a direct relation to liquid nitrogen mass flow. However, due to the required high power for producing liquid nitrogen, with mass flow rate increment, the total system's efficiency is reduced. The results are evaluated with Aspen HYSYS, Aspen Energy Analyzer, and MATLAB. Specific work obtained from the analysis is 290,097 kW.s/kg which indicates that uses lower power in comparison with the other helium production methods which saves power and electrical costs.

Effect of vacuum drying the insulation pressboard on partial discharge characteristics under ripple voltage conditions

The object of the research is partial discharges arising in a sample of the insulation pressboard. In most modern high-voltage direct current transmission schemes based on voltage-source converters six-pulse or twelve-pulse converters are used. The signal waveform on the direct current voltage side of a high-voltage direct current transmission is not pure direct current voltage and it has alternating current component. Since the partial discharge activity under distorted voltage is much different than that under pure direct current voltage, voltage ripples and voltage harmonics are the subject of various studies. This article examines the effect of vacuum drying the insulation pressboard on partial discharge characteristics at direct voltage ripples. The insulation pressboard was dried in a vacuum chamber with a residual pressure of 1 mm Hg. Among all the characteristics of a partial discharge, the main focus has been on the apparent charge of a partial discharge. The greater is the apparent charge value, the stronger is the destructive effect on high-voltage insulation. It was shown that drying the insulation in a vacuum chamber has the greatest effect on reducing the apparent charge of a partial discharge at direct current voltage than at alternating current voltage. After drying the insulation in a vacuum chamber, the amplitude of the partial discharge pulses was decreased by 99.3 % at direct current voltage in comparison with the moistened sample. After vacuum drying, at DC voltage, rare and very low magnitude partial discharges were recorded. The conducted research contributes to the development of methods for partial discharge detection under non-standard voltage conditions.

Analysing the impact of optimally allocated solar PV-based DG in harmonics polluted distribution network

The optimal installation of a renewable distributed generation (DG) in a radial distribution network (RDN) provides a sustainable and clean solution for the future smart network. A weighted-sum multi-objective approach is applied to determine the optimal location of solar PV-DG followed by a PSO algorithm to find optimal DG size. The impact of optimal DG allocation in distorted and non-distorted distribution network is efficaciously demonstrated and validated on IEEE 33-bus RDN. The harmonic analysis in the presence of the six-pulse converter non-linear load and non-linear DG is carried out for IEEE 34-bus network. The non-linear loads are modelled as harmonic current source. As composite load model provides lowest voltage drop with decreased capital investment cost, hence, its effect and the effect of constant power load model on energy loss saving, network loss and total harmonic distortion at various load levels is being analysed. The harmonic load flow results obtained considering non-linear and linear loads are compared to other analytical methods and nature-inspired techniques to illustrate the robustness of the proposed strategy for enhancing the performance of the network. The statistical significance of the results is verified by the Wilcoxon test.

Control strategy optimization for energy efficiency and harmonic mitigation in multi-series converters

To provide electrical power for the Research System of Superconducting Magnets (RSSMs) including the background field superconducting magnet and the tested superconducting objects, the high power phase-controlled converter will be used to develop the power supply system. However, because of its inner nonlinear feature, the current harmonics and the reactive power are injected into the AC power supply system. To improve the quality of the power supply system for RSSMs, an improved synchronous control strategy is suggested for the superconducting magnet power supply system, which comprises four series-connected six-pulse converters fed by a phase-shifting transformer, respectively. According to the proposed control strategy, the basic unit is two 12-pulse converters and the control method will be changed in terms of load fluctuations which are represented by the per unit value of converter output voltage. As a result, harmonic is greatly reduced but the power factor is also high.

Small Signal Frequency-Domain Model of a LCC-HVDC Converter Based on an Infinite Series-Converter Approach

In this paper, an improved analytical small signal model of the line commutated converter (LCC) is developed in direct-quadrature-zero coordinates based on the assumption of infinite six-pulse converters. The dynamics of the commutation inductance and transportation delays during commutation are included in the model, and the sampling of the measurement of firing and extinction angles is added to accommodate actual converters with a finite pulse number (e.g., 12-pulse). The model is validated by comparing the frequency response with one obtained by frequency scanning in an electromagnetic transients (EMT) simulation. The model is shown to be effective in investigating system stability when the LCC is connected to an arbitrary external network. To do this, the frequency response of the combined system is plotted, and the generalized Nyquist stability criterion is applied. This stability result is validated by a time domain simulation on an EMT program using the first CIGRE HVDC benchmark system and the IEEE 14-bus system. Compared to the traditional LCC model, the proposed model is shown to have significantly better accuracy in system stability determination.

Total Harmonic Distortion Factor Evaluation in Shipboard Electrical Networks

Electric propulsion systems for modern civil and military ships, as well as the growing number of electric consumers on board, are a topical issue in terms of onboard electric power quality. In this respect, a growing number of high power static converters are used, which inevitably leads to the appearance, in the electricity distribution network, of voltage and current harmonics with very high weights. Through this work, the authors made a study of these harmonics for two classical cases encountered aboard a ship, namely a nonlinear consumer and a consumer powered by a static six-pulse converter. Also, the highlight of these harmonics has been made in both shore and onboard power supplies. As a result of these measurements, some conclusions were drawn regarding the analyzed situations.

Performance Analysis of Transient Current Limiters in a Distribution System

This paper deals with the performance evaluation of a three-phase transient current limiter in distribution systems. A simulation model based on mathematical model of a three-phase, transient current limiter has been developed. The problem is formulated to justify the stable and harmonic free twelve-pulse and six-pulse converter based transient current limiter. Firstly, conventional methods like Bode Plot, Nyquist Plot and Nichols Chart are used to investigate the stability of twelve-pulse and six-pulse converter based transient current limiter. Next, a comparative analysis using fast Fourier transform is used to check the system harmonics using MATLAB simulation. The proposed design is found to be more efficient in making the system stable and harmonic free.

Performance Analysis of Transient Current Limiters in a Distribution System

This paper deals with the performance evaluation of a three-phase transient current limiter in distribution systems. A simulation model based on mathematical model of a three-phase, transient current limiter has been developed. The problem is formulated to justify the stable and harmonic free twelve-pulse and six-pulse converter based transient current limiter. Firstly, conventional methods like Bode Plot, Nyquist Plot and Nichols Chart are used to investigate the stability of twelve-pulse and six-pulse converter based transient current limiter. Next, a comparative analysis using fast Fourier transform is used to check the system harmonics using MATLAB simulation. The proposed design is found to be more efficient in making the system stable and harmonic free.

Stability and harmonic analysis of a transient current limiter in distribution system

This paper proposes a methodology to investigate the stability of transient current limiter (TCL) in distribution systems. The problem is formulated to justify the performance of 12-pulse and six-pulse converter and make an unstable system to stable condition. The proposed approach explicitly deals with stability as well as minimization of total harmonic distortion. Firstly, the conventional methods of Nichols Chart, Nyquist Plot and Bode Plot used to investigate the stability of the network using TCL. In the next stage, a modified TCL circuit is inserted in the network system to make the system completely stable. A comparative analysis using Fast Fourier Transform (FFT) is shown to make the system harmonic free using MATLAB simulation. The proposed design is found to be more efficient in making the system stable and harmonic free.

Modeling and Simulation of Superconducting Magnetic Energy Storage Systems

This paper aims to model the Superconducting Magnetic Energy Storage System (SMES) using various Power Conditioning Systems (PCS) such as, Thyristor based PCS (Six-pulse converter and Twelve-pulse converter) and Voltage Source Converter (VSC) based PCS. Modeling and Simulation of Thyristor based PCS and VSC based PCS has been carried out. Comparison has also been carried out based on various criteria such as Total Harmonic Distortion (THD), active and reactive power control ability, control structure and power handling capacity. MATLAB/Simulink is used to simulate the various Power Conditioning Systems of SMES.

Influence of interphase transformers and ac line reactances on the thyristor bridges' current sharing in 18-pulse rectifiers

In this paper, computer simulation models of two different topologies of 18-pulse rectifiers are presented. Each rectifier topology consists of three parallel, three-phase six-pulse full-bridge thyristor converters connected via interphase transformers. The influence of the interphase transformer's layout and AC line reactances variations on the particular thyristor converter current sharing is analysed. Various configurations of 18-pulse rectifiers are examined by simulating operation with symmetric input voltage supply, as well as in the cases of different levels of voltage supply asymmetry, at unequal input conductors impedance, and at different thyristor voltage drops. According to computer simulation results, an optimal 18-pulse rectifier circuit topology is recommended. The optimal topology has three AC line reactances with two input current-balancing interphase transformers. These added AC reactances are also involved with the current commutation process between thyristors. Application of the recommended optimal topology of an 18-pulse rectifier could enable the reduction of the AC line reactances number from nine to three, while the dissipated power of the AC/DC converter's most loaded thyristor could be reduced by approximately 11 %. During the simulation of the nominally loaded 18-pulse rectifier, in all considered cases the effective value of the output signal ripple below one promil of total current and voltage values has been achieved.

Synthetic Test Circuit for Thyristor Valve in HVDC Converter with New High-Current Source

Synthetic test circuit (STC) for thyristor valve test consists of a low-voltage high-current source to provide the forward current during turn-on state and a low-current high-voltage source to provide the reverse and forward voltage during turn-off state. This paper proposes a new low-voltage high-current source for STC that has a six-pulse thyristor converter and a two-phase chopper with an auxiliary switch. The operation of STC with a new low-voltage high-current source was verified through theoretical analysis and computer simulations with PSCAD/EMTDC. Based on computer simulation results, a scaled hardware system for the proposed circuit was built and tested to confirm the feasibility of implementing a real-size STC.

Effect of Field-Voltage Source Impedance on Load-Rejection Test Results of Large-Rating Synchronous Generators

This paper presents a technique to determine the effect of the field-voltage circuit during the load-rejection test of a large-rating salient-pole synchronous generator. Once the circuit powered by a six-pulse converter connected to the excitation transformer of the generator unit corresponds to a power-supply voltage not constant immediately after the load rejection, a careful evaluation of the resulting signals is necessary to extract rotor and stator parameters from the comparison with theoretical expressions derived under the assumption of constant-field terminal voltage and excluding external effects. The results obtained in the load-rejection test of a 179-MVA, 13.8-kV generating unit at Nova Ponte power plant show the parameters that are more affected by the external impedance in series with the rotor circuit and how to compensate them.

Grid Connected Based Six-Pulse Converter Applied A Self-Excited Induction Generator for Wind Turbine Applications

Abstract This paper the electrical power conversion system presents developed for a self-excited induction generator for wind turbine applications. In the wind energy conversion system a self-excited induction generator converts the mechanical energy into electrical energy. A B6 rectifier and inductor are utilized to maintain constant dc link current. The average power is converted entirely by the six-pulse converter, it's consists of a B6 current-source inverters. Line side current-source inverter supply currents into the utility line by regulating the dc link voltage. The active power is controlled by firing angle of converter with operated at inverter mode. The performance improvement of this proposed system by experiment using a 1 kW four pole self excited induction generator. The overall control system is implemented on six-pulse converter board. Experimental results are illustrated in order to validate performance of the proposed system.

A new scheme for power factor correction and active filtering for six-pulse converters loads

A new scheme for power factor correction and active filtering for six-pulse converters loads This paper presents a novel harmonic-free power factor correction (PFC) topology based on T-type active power filter (APF), which is dedicated for power factor improvement and harmonic filtering for six-pulse converter loads. The cascaded controller structure is adopted for the proposed system, namely, the inner current loop and outer voltage loop. The current-loop control scheme is based on a decoupled state-space equations of the T-type APF using separate proportional-integral (PI) controllers in d-axis and q-axis of the synchronous rotating reference frame (SRRF) synchronized with grid voltages, respectively. The fundamental components of load-side currents are feed forwarded in the current-loop using two groups of synchronous frame adaptive linear neural networks (ADALINEs) to ensure estimation accuracy and a fast dynamic response. A separate proportional-integral (PI) controller is adopted in the outer voltage loop for balancing the active power flow of the voltage source inverter (VSI) dc-side capacitor. The experimental results confirm well with the theoretical analysis.

A Repetitive-Based Controller for the Compensation of $6\ell\pm 1$ Harmonic Components

In this paper, a repetitive-based controller for the compensation of 6 lscr plusmn 1 harmonic components is proposed. This control scheme is more appropriate for processes that involve the use of six-pulse converters or other converters that mainly produce harmonic components at those frequencies. The control scheme is based on the feedback array of two delay lines plus a feedforward path that compensates only the 6 lscr plusmn 1 multiples of the fundamental frequency, thereby reducing the possibility of reinjecting unnecessary distortion into the system. The proposed scheme is, then, plugged into a generic feedback control system where a stability analysis is carried out. In addition, the passivity properties of the proposed scheme are presented, which open the possibility of control design following the passivity-based approach. Experiments that are based on a simple digital implementation are provided to illustrate the merits of our solution. These results include the open-loop responses of the proposed scheme and the responses in a practical example to validate its effectiveness in an application. For this latter result, the proposed scheme has been used in the controller of a 2-kVA shunt active filter to compensate the current harmonic distortion.

A linearised small-signal model of an HVDC converter for harmonic calculation

In this paper a new method is presented for calculation of the harmonics in the ac current and dc voltage of a six-pulse HVDC converter. Instead of fast Fourier transform, FFT, the Fourier series is used in this method. The HVDC converter is represented by a linearised small-signal model in mixed time- frequency domain in which the effects of on and off states resistances, forward voltage drop, and snubber circuits of the thyristors are taken into account. RL series circuits are used for modeling of the converter transformer and ac system. To validate the method a comparison is made with PSCAD/EMTDC time domain simulation program.

Comparison between discrete STFT and wavelets for the analysis of power quality events

Abstract This paper deals with the comparison of signal processing tools for power quality analysis. Two signal processing techniques are considered: the wavelet filters and the discrete short-time Fourier transforms. Then, examples of the two most frequent disturbances met in the power system are chosen. It is designed an adjustable speed drive with a six-pulse converter using EMTP/ATP and it is presented normal energizing of utility capacitors. The analysis is tested on a system consists of 13 buses and is representative of a medium-sized industrial plant. Finally, each kind of electrical disturbance is analyzed with example representing each tool. A qualitative comparison of results shows the advantages and drawbacks of each signal processing technique applied to power quality analysis.

New pulse multiplication technique based on six-pulse thyristor converters for high-power applications

A new pulse multiplication technique based on six-pulse thyristor converters is proposed in this paper. With the proposed technique, 12-pulse, 18-pulse, and 24-pulse operations have been obtained both on the input current and on the output voltage. A control strategy over the whole range of phase angle is provided along with sophisticated input current and output voltage analysis. Experimental results from a laboratory prototype verify the proposed theory.

Steady-state algorithm for switching power electronic devices

Obtaining the steady-state operation of a power electronic device by means of brute force computer simulation is not feasible in many practical cases. Fast steady-state algorithms that formulate the steady-state problem as a boundary problem and solve it using Newton's method have been proposed to overcome this difficulty. These algorithms are known as shooting algorithms. An extension of the shooting algorithm for piecewise linear circuits is provided. The complete Jacobian matrix that takes into account the switching instants variation is analytically derived for a state variable formulation of the steady-state problem of a piecewise linear circuit. A computer program PWiseSS based on this algorithm is used to solve a previously proposed test circuit of difficult convergence as well as to solve a realistic six-pulse converter of interest to the power electronics engineer.