Capacitor Commutated Converters Research Articles

An active-passive capacitor-commutated converter for HVDC systems with a three-phase voltage-source PWM converter

This paper introduces a new approach to the capacitor-commutated converters (CCCs) for HVDC systems. A small-rated three-phase voltage-source PWM converter is connected between a series commutation capacitor and thyristor converter through matching transformers. The PWM converter acts as auxiliary commutation-capacitor for the thyristor converter while the series passive capacitor acts as the main commutation capacitor. The capacitance, which is the sum of the small-rated active and series passive capacitors, is variable, so that stable commutation is obtained. In CCCs, commutation failure occurs when the AC bus voltage is recovered whereas the proposed combined commutation-capacitor can achieve successful commutation for both rapidly decreasing and increasing AC bus voltages. The basic principle of the proposed active–passive capacitor-commutated converter is discussed in detail. Then, constant margin angle control with a constant firing angle of the thyristor converter is proposed using a function generator block. Digital simulation demonstrates the novelty and effectiveness of the proposed active–passive capacitor-commutated converter. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 66–75, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20030

An Active-Passive Capacitor-Commutated Converter for HVDC Systems with a Three-Phase Voltage-Source PWM Converter

This paper introduces a new approach to the capacitor-commutated converters (CCCs) for HVDC systems. A small-rated three-phase voltage-source PWM converter is connected between a series commutation capacitor and thyristor converter through matching transformers. The PWM converter acts as auxiliary commutation-capacitor for the thyristor converter while the series passive capacitor acts as the main commutation capacitor. The capacitance, which is the sum of the small-rated active and series passive capacitors, is variable, so that stable commutation is obtained. In CCCs commutation failure occurs when the ac bus voltage is recovered whereas the proposed combined commutation-capacitor can achieve successful commutation for both rapidly decreasing and increasing ac bus voltages. The basic principle of the proposed active-passive capacitor commutated converter is discussed in detail. Then, constant margin-angle control with a constant firing angle of the thyristor converter is proposed using a function generator block. Digital simulation demonstrates the novelty and effectiveness of the proposed active-passive capacitor commutated converter.

Capacitor commutated converters for long-cable HVDC transmission

An overview of the capacitor commutated converter is given, emphasising its applications in long-cable HVDC transmission schemes. Its advantages and disadvantages in comparison with the conventional HVDC Graetz bridge converter are identified, and a critical assessment of its performance is presented using a developed steady-state formulation as well as a transient simulation based analysis.

Modeling capacitor commutated converters in power system stability studies

This paper describes a capacitor commutated converter (CCC) model suitable for power flow and transient stability studies. The CCC control structure and important operational details are described. The practical advantages of the CCC as compared to the conventional HVDC converter are discussed. Results are presented for power flow, power system stability, small signal analysis and control design studies. These results clearly demonstrate the superior performance of a CCC link, when connected to a very weak AC system.

New aspects of inspecting commutation angles of high-voltage direct current systems

The conventional method of calculating high-voltage direct current (HVDC) converter commutation angles can result in very inaccurate results if the ripple of the DC is fairly high, or the HVDC link consists of capacitor commutated converters (CCC). For conventional line-commutated current source converters with a high DC ripple new analytical equations are presented for determining the commutation angles and the instantaneous values of DC DCside current at the firing instants. An iterative method for the calculation of commutation angles of CCC was also developed. The results are confirmed by digital simulation.

An AC active filter for use at capacitor commutated HVDC converters

This paper discusses the application of an AC side active filter in HVDC schemes involving capacitor commutated converters. A suitable topology and control algorithm is selected to achieve the necessary objective of filtering the lower order characteristic harmonics. The dependence of the filter's rating on parameters such as the extent of de-tuning of its passive elements is investigated. The performance of this filter in a capacitor commutated converter application is evaluated using an electromagnetic transient simulation program.