Abstract

It is well known that traditional line-commutated converter (LCC) based high voltage direct current (HVDC) system is not able to control its reactive power and terminal AC voltages. This paper investigates the reactive power and AC voltage control at the inverter side of the LCC HVDC system with controllable capacitors. The system's ability of operating under negative extinction angle is utilized to achieve a wide range of reactive power control and, in particular, the ability of exporting reactive power. In connection with the inverter AC terminal voltage or reactive power control, among different control possibilities at the rectifier side, active power control is desirable since large variations of active power transfer is very unfavorable. Detailed theoretical analysis is carried out first to show the reactive power controllability, and the capacitor voltage level is selected based on the desired control range. In addition, a new extinction angle measurement approach is proposed for negative extinction angle measurements. The effectiveness of the reactive power/voltage control capability for the proposed system is validated through simulation results using Real-Time Digital Simulator (RTDS). To verify the effectiveness of the reactive power and voltage control, CCC HVDC and LCC HVDC with SVC are also set up in RTDS, and simulation comparisons are made. Furthermore, contribution to AC voltage control in power system using the proposed method is demonstrated through simulation results of the modified two-area four-machine AC power system.

Highlights

  • TRADITIONAL Line-Commutated Converter (LCC) based High Voltage Direct Current (HVDC) technology has played an important role in long distance bulk power transmission around the world since its first application 60 years ago

  • This paper investigates the reactive power and AC voltage control at the inverter side of the LCC HVDC system with controllable capacitors

  • It should be mentioned that compared with Capacitor Commutated Converter (CCC) HVDC, since the controllable capacitors are mainly inserted into the circuit during commutation period, valve voltage stress is slightly increased, and is comparable to the original LCC HVDC system [22]

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Summary

INTRODUCTION

TRADITIONAL Line-Commutated Converter (LCC) based High Voltage Direct Current (HVDC) technology has played an important role in long distance bulk power transmission around the world since its first application 60 years ago. The reactive power requirement originates from the firing of thyristors after commutation voltage becomes positive, which in effect delayed the current waveforms with respect to the voltage waveforms [1] Both rectifier and inverter sides of the system absorb reactive. The minimum extinction angle controller will advance its firing angle which leads to a higher reactive power consumption and causes further AC voltage drops. These operational characteristics are clearly unfavorable, and FACTS devices such as STATCOM and SVC, etc may be needed to mitigate the problem. This paper focuses on achieving the aforementioned desired inverter performances by further exploiting the reactive power control capability of the previously proposed LCC HVDC system with controllable capacitors [22].

System Configuration
Insertion Strategy
Capacitor Voltage Balancing
THEORETICAL ANALYSIS OF REACTIVE POWER CONTROLLABILITY
Commutation Overlap i1
Pre-insertion of Capacitors
Power Factor
Capacitor Voltage Level
Reactive Power Controller
AC Voltage Controller
Rectifier Active Power Control
SIMULATION RESULTS
Reactive Power Control
AC Voltage Control
CONCLUSION
VIII. BIBLIOGRAPHY
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