Power Semiconductors for Voltage Source Converters in HVDC and STATCOM Applications

• With a steady increase in electricity consumption in both developed and developing regions combined with demand for sustainable energy infrastructure, trends towards more renewable energy sources and more open electricity markets are becoming more prominent. High Voltage DC (HVDC) connections and Static Synchronous Compensators (STATCOM) are two technologies that play a part in fulfilling this increasing demand. HVDC is beneficial in cases where production and consumption are geographically separated or for sub-sea cable transmissions. STATCOM helps to increase the capacity of AC transmission in addition to enhancing ac-grid voltage quality. A key component in both HVDC and STATCOM converters are the semiconductor switching devices. Switching devices have a fundamental impact on performance levels that can be obtained in terms of efficiency, reliability and functionality. This paper serves two purposes. The first is to give a historical overview of switching devices employed in HVDC transmission systems and STATCOMs. This starts with the use of mercury arc valves some 100 years ago and it continues with the semiconductor switching devices that are currently being employed in HVDC and STATCOM applications. A second purpose of this paper is to indicate developments in switching technology that are of interest for HVDC and STATCOM. In order to do this in a structured manner, the technologies are compared in terms of efficiency, reliability and functionality. Developments that are discussed in this paper are the emergence of Silicon Carbide (SiC) devices and the improvement of Insulated Gate Bipolar Transistor (IGBT) and Integrated Gate Commutated Thyristor (IGCT) devices in silicon. Currently, applications are based on silicon based thyristors or IGBT technology. Line commutated converters based on thyristors are cost-effective and efficient; however, due to lack of controlled turn-off capability, functionality is limited. Using voltage source converter technology with semiconductors having turn-off capability, such as the IGBT, increased functionality is obtained. The IGCT, a gate controlled thyristor with turn-off capability, has lower conduction losses compared to an IGBT with the same active area. In case a modular multilevel converter is used, the switching frequency of the individual switches can be reduced for the same performance. This leads to a shift towards the importance of having low conduction losses as opposed to low switching losses. A further shift can be achieved by using soft-switching techniques. Regarding SiC devices, different maturity is reached for unipolar and bipolar devices. Unipolar devices in SiC have been marketed successfully at low voltages (≤ 1700V). An example is SiC Schottky diodes for power factor correctors. For the voltages typically applied in HVDC and STATCOM, the drift region resistance would impose serious limitations on efficiency (if high current densities are used). Bipolar devices such as SiC IGBTs and IGCTs have been demonstrated in laboratory setups and results have been published; however, reliable operation is currently impeded due to the propagation of crystal lattice defects which causes rapid degradation of such devices.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik -- Annan elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering -- Other Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

Nyckelord

IGCT

IGBT

HVDC

STATCOM

Si

SiC

Electrical Engineering

Elektro- och systemteknik

Energy Technology

Energiteknik

Publikations- och innehållstyp

vet (ämneskategori)

kon (ämneskategori)