Line Commutated Converter High Voltage Research Articles

Research on continuous commutation failure suppression strategy for multi-feed DC transmission system considering harmonic characteristic factors

Abstract Regarding the sustained issues of commutation failures in the hybrid double-fed DC system encompassing Line Commutated Converter High Voltage Direct Current (LCC-HVDC) and Modular Multilevel Converter High Voltage Direct Current (MMC-HVDC, from the perspective of harmonics, the harmonics in the voltage waveform of the AC bus on the inverter side are analyzed. Besides, a commutation failure suppression strategy for the hybrid doubly-fed DC transmission system based on the minimum shutdown area is designed, in which the setting value of the shutdown angle of the harmonic is considered in the minimum shutdown area. The reactive power is obtained by attaching the setting value to the reactive power control link of MMC-HVDC, and the simulation analysis in PSCAD verifies that the strategy can make the MMC-HVDC output more reactive power during the fault in the weak AC system. Increasing the shut-off margin of the manifold reduces the potential for continuous commutation failures in LCC-HVDC.

Correlation of traps inside XLPE and polypropylene with space charge dynamics under polarity reversal condition

Polypropylene (PP) is being considered as a suitable alternative to the cross-linked polyethylene (XLPE) insulation as the latter is prone to the space charge accumulation when subjected to the voltage polarity reversals in line-commutated converter high voltage direct current transmission. This novel contribution correlates the space charge accumulation with the trap distribution inside XLPE and PP under the polarity reversal condition. The pulse electro-acoustic and surface potential decay methods are used to measure the space charge and trap distributions, respectively. These measurements are carried at different poling durations (1 and 6 h at each polarity) and cycles of voltage polarity reversal (one and three cycles) at the electric field of 60 kV/mm. The XLPE shows more homo and hetero charge accumulation than PP. Dominant shallow traps in the XLPE are responsible for the space charge accumulation, whereas deep traps with higher trap density inhibit space charge accumulation within the PP. Furthermore, the positive and negative threshold fields for the space charge accumulation are measured. It is observed that the space charge can be easily accumulated under the negative electric field. Interestingly, the space charge decays rapidly inside the XLPE with the increased number of polarity reversal cycle. A valid theoretical model is developed to explain the space charge accumulation inside the XLPE and PP. The field-assisted ionization plays a key role in the space charge accumulation inside the XLPE.

Power Quality Improvement of High Voltage DC Link using Modified Shunt Active Power Filter

A new control strategy for active power filters is proposed, modeled and implemented in order to improve the power quality of a line commutated converter High voltage DC link. The ability of reactive power and harmonics reductions are generally met by using passive and active power filters. In this paper, modified active power filter with a modified harmonics pulse width modulation algorithm is used to minimize the source harmonics and force the AC supply current to be in the same phase with AC voltage source at both sending and receiving sides of a line commutated converter high voltage DC link. Therefore, it is considered as power factor corrector and harmonics eliminator with random variations in the load current. The modified harmonics pulse width modulation algorithm is applicable for active power filter based on a three-phase five-level and seven-level cascaded H-bridge voltage source inverter. Simulation results show that the suggested modified multilevel active power filters improve total harmonics distortion of both voltage and current with almost unity effective power factor at both AC sides of high voltage DC link. Therefore, modified active power filter is an effective tool for power quality improvement and preferable for line commutated converter high voltage DC link at different load conditions.

DC Line Ground Fault Detection Scheme for Line Commutated Converter High Voltage Direct Current Connected to Renewable Energy Source

DC Line Ground Fault Detection Scheme for Line Commutated Converter High Voltage Direct Current Connected to Renewable Energy Source

Operation and control of a Current Source Converter series tapping of an LCC-HVDC link for integration of Offshore Wind Power Plants

This work presents a series tapping station for integrating Offshore Wind Power Plants (OWPP) into a (Line Commutated Converter High Voltage Direct Current) LCC-HVDC transmission system. The tapping station allows to integrate wind power resources without building a new HVDC link and it is based on a Current Source Converter (CSC). However, the CSC requires a minimum DC current to extract the power coming from the OWPP which may not be guaranteed depending on the power conditions of the HVDC corridor. For this reason, this paper proposes a coordinated operation and control of the CSC and the OWPP. A steady-state analysis is performed to determine the appropriate AC voltage level of the CSC. A power reduction algorithm is presented to limit power extraction during a reduction in the current of the HVDC transmission system and under loss of communications between the CSC and the OWPP. The proposed algorithm and the performance of the system are validated through simulation results.

Boost inverter-based HVDC transmission system with inherent blocking capability of AC side contribution during DC side faults

Semiconductor advancements in the past three decades have positioned the voltage source converter-based HVDC (VSC-HVDC) solution as a practical and popular alternative to its line-commutated converter high voltage DC (LCC-HVDC) counterpart. The VSC-HVDC systems offer higher flexibility and system controllability features. One of the important challenges requiring careful investigation in such systems is the protection against DC side faults. Unfortunately, the VSC is inherently defenseless against such faults (DC link short circuit or DC cable short circuit). This paper proposes an HVDC system topology, namely, the boost inverter-based HVDC system (BI-HVDC), which provides complete blocking capability between the AC grid and the DC side fault. This blocking capability limits the DC fault current level to the DC capacitor discharge current. Ratings and characteristics of the proposed system compared to other existing topologies are highlighted in this work. A simulation study is conducted to check the performance of the proposed system during normal as well as abnormal operating conditions. A comparison between the performance of the conventional 2-level VSC-HVDC and the proposed system during DC side faults is also presented. The simulation results elucidate a significant decrease in the DC fault current due to the blocking capability of the BI-HVDC system during DC side faults.

Frequency Control Design for Offshore Wind Farm Grid With LCC-HVDC Link Connection

This paper considers the formal design for the grid frequency control in an offshore wind farm connected with line-commutated converter high voltage dc (HVDC) link. The control paradigm is based on using the grid frequency control to regulate the HVDC rectifier firing angle or dc-link current and hence control the power flow in the system. The dynamic behaviors of the system are verified by comparing the response from derived transfer functions and PSCAD simulations; hence the grid frequency controllers are designed. The control system performance has been validated by simulations of normal operation and fault regimes. The work provides a good basis for wider research investigation into wind farm operation.