Reduced Harmonics Generated and Reactive Volt-Ampere absorption of HVDC Converter Using By-Pass Switch (original) (raw)
Related papers
Fast and Continuous Control of a Modified HVDC Converter
2019
Control strategy for the modulation of the DC power for Modified HVDC Systems is proposed. A microprocessorbased firing scheme is presented which control the firing angles for modified HVDC converter with by-pass valves. Fast and continuous control of the DC voltage is possible with good operational characteristics. Using table-look-up algorithm to speed up the response, it gives a full range control of the firing angle for both rectifier and inverter modes. The algorithm is experimentally verified and is found to give a very-fast, precise and equidistant control of the thyristor triggering. Harmonic generations into the AC system and the converter reactive voltampere absorption have been reduced. The operations of modified bridge, the control algorithm and the microprocessor implementation are described. Experimental results on a laboratory model compare well with the predicted values.
Voltage control of modified series-connected HVDC bridges
Electric Power Systems Research, 1997
High voltage direct current (HVDC) power transmission systems constitute an important application of power electronics technology. This article presents a new method to control the HVDC converters by modified series-connected bridges to give a reduction in both harmonic generation and reactive volt-ampere absorption for the rectifier and inverter modes of operation. Moreover. a voltage control scheme is proposed which uses bypass thyristor valves connected to tapping points on the secondary windings of the transformer for one bridge with the other one operating as a conventional bridge. Fast and continuous control of the DC voltage are possible using the proposed scheme without the conventional on load-tap changer on the converter transformer.
Transient of modified HVDC converters
Electric Power Systems Research, 2007
The bridge circuit used in high voltage direct current (HVDC) converters may be modified by including bypass thyristor valves connected to tapping points on the secondary windings of the transformer to give a reduction in both harmonic generation and reactive volt-ampere absorption for the rectifier and inverter modes of operation. In this paper, control strategies for the transient response of the HVDC converter with either thyristor or GTO thyristor bypass valves are investigated using several types of firing angle control logic. Fast and continuous control of the DC voltage is possible using the proposed scheme without the conventional on load tap-changer on the converter transformer. Experimental results on a laboratory model compare well with the predicted values.
Electric Power Systems Research
this paper employs an amplitude modulation with sinusoidal plus third harmonic injection instead of trapezoidal modulation to operate a controlled transition bridge (CTB) converter as ac/dc and dc/ac converter terminals. With such an operation, the CTB converter may require small ac filters; thus attractive for high-voltage direct current (HVDC) transmission systems. To facilitate ac voltage control over a wide range and black-start capability, the injected 3 rd harmonic allows the cell capacitor voltages of the CTB converter to be regulated independent of the modulation index and power factor. The insertion of 3 rd harmonic into modulating signals achieves two objectives: extends the regions around voltage zeros so that the total voltage unbalanced can be distributed between the cell capacitors, thereby exploiting the bipolar capability of the full-bridge cells in each limb; and to ensure that each limb can be clamped to the positive and negative dc rails every half fundamental period independent of the modulation index to allow recharge of the cell capacitors from the active dc link. The suitability of the CTB converter for HVDC type applications is demonstrated using a two-terminal HVDC link that employs a 21-cell CTB converter, considering normal operation and ac faults.
Control of Multi-Level Converter Using By-Pass Switches
This paper describes a modification of the conventional bridge circuit under balanced conditions using two isolated-gate bipolar transistor (IGBT) bypass valves connected to tapping points on the secondary windings of the transformer. This scheme permits a wide range of voltage control with a reduction in both the harmonic generation and reactive volt-ampere absorption. This scheme should improve the efficiency of voltage control; it possibly eliminates the need for an on-load tap-changer on the converter transformer. The modified AC/DC converter is fully analyzed. A general mathematical model and the principle of operation for the modified converter have been determined. The characteristics for output DC voltage for the modified converter with two bypass IGBT valves are obtained; and the mathematical equations have been derived for different modes of operation. The supply current harmonic contents, reactive volt-ampere absorption and power factor have been compared with a conventional bridge for different converter bridge arrangements, modified bridge using one IGBT bypass valves and modified bridge with two IGBT bypass valves. Simulation results are obtained using Matlab-Simulink for a model that has a three-phase bridge converter using conventional thyristors as main valves and two IGBT as bypass valves employing a controllable digital firing angles with pulse generators maintained on a small firing angle of the main thyristors.
A New Filtering Method and a Novel Converter Transformer for HVDC System
A new converter transformer and an inductive filtering method are presented to solve the existing problems of the traditional converter transformer and the passive filtering method of the high-voltage direct current (HVDC) system. It adopts the ampere-turn balance of the transformer as the filtering mechanism. A tap at the linking point of the prolonged winding and the common winding of the secondary windings is connected with the LC resonance circuit. It can realize the goal that once the harmonic current flows into the prolonged winding, the common winding will induct the opposite harmonic current to balance it by the zero impedance design of the common winding and the proper configuration of LC parameters, so there will be no inductive harmonic current in the primary winding. Moreover, the reactive power that the converter needs can be partly compensated in the secondary winding. Simulation results have verified the correctness of the theoretical analysis. The new converter transformer can greatly reduce the harmonic content in the primary winding, loss, and noise generated by harmonics in the transformer, and the difficulty of the transformer's insulation design.
Abstract—The converter transformer is a vital equipment in HVDC transmission system. It serves as an isolating device between power transformer and dc link. In converter transformer primary is not much affected where as secondary is severely affected due to super imposed DC voltage with polarity reversal and short time over voltages. This paper mainly introduces causes for the improper operation of converter transformer and provides the improved solution to overcome harmonic reduction and improvement in the commutation process. The analysis is carried out in SIMULINK/MATLAB environment.
Design of a combined converter-switch for converting existing AC transmission into HVDC (and back)
Seventh International Conference on AC and DC Transmission, 2001
The paper brief is one out of the first approaches in Turkey to popularize HVDC-light transmissions. It deals with: 1. Lab design and PSCAD modeling of a special bridge controlled AC -DC three load (star-delta) rectifier. It uses 9 group of valves (instead of 6 group valves of common bridge), three lines of former AC transmission, the earth and three DC loads between the lines and earth (or a star-delta inverter). 2. Lab design and PSCAD modeling of a special controlled bridge DC -AC star-delta inverter between three DC source and AC network. It also uses 9 group of valves (instead of common 6 group valves), three input DC lines (and the earth) and three outputs AC transmission lines. 3. Comparison of the bridges construction and modeling results of traditional HVDC-light transmission (6 valves rectifier, traditional DC line and 6 valves inverter) and designed AC-DC-AC transmission (9 valves rectifier, AC line and 9 valves inverter). The proposed star-delta rectifier and inverter can be implemented in common electrical applications such as HVDC transmission, supply of isolated loads, asynchronous grid connection, infeed of small-scale distributed generators (DG), infeed to city centers, for DC grids, converting the AC lines into HVDC light lines, etc.
Performance analysis of multi-level HVDC converter
International Journal of Electrical and Computer Engineering, 2022
The conventional three-phase alternating current (AC) to direct current (DC) converter can be modified using two isolated-gate bipolar transistor (IGBT) as bypass switches connected to tapping points on the secondary side of the transformer. This scheme yields a reduction in both harmonic contents and reactive volt-ampere absorption. This modified converter possibly eliminates the need for an on-load tap-changer on the converter transformer. The modified AC/DC converter is fully analyzed and implemented under balanced conditions using MATLAB-Simulink. The expressions of the output DC voltage are derived for different cases. The supply current harmonic contents, the reactive power absorption and the power factor have been compared for three schemes; the conventional bridge, the modified bridge using one bypass IGBT valve and the modified bridge with two bypass IGBT valves.