An overview of the common converter topologies and power semiconductor devices © CR EA TA S IEEE INDUSTRY APPLICATIONS MAGAZINE MAR j APR 2010 WWW.IEEE.ORG/IAS BY MARC HILLER, RAINER SOMMER, & MAX BEUERMANN 22 T ODAY, THERE ARE NUMEROUS DIF- demands and special applications, thyristor converters are ferent converter topologies and power still frequently used semiconductor devices used in mediumvoltage drive systems This article provides Medium-Voltage Drives a general overview of the common converter topologies Over the past few years, a market for medium-voltage available on the market and their corresponding major drives has developed, which is growing at a rapid pace characteristics The different topologies are compared and This market is mainly driven by rising energy costs and by evaluated with respect to the number of semiconductors the energy-saving potential offered by variable-speed and the complexity drives The boom in the raw materials market has resulted Due to the power semiconductor devices that are avail- in an increased demand for medium-voltage drives over able with maximum blocking voltages of 6.5 kV, the drive the entire power and voltage range (drives for rolling market with power ratings of up to 25 MW is domi- mills, gas compressors, extraction pumps, etc.) nated by voltage-source inverters (VSIs) in The use of medium-voltage converters is not only insulated gate-bipolar transistor (IGBT) limited to applications in the high power range Especially and insulated gate-commutated in the American and Asian markets, medium-voltage transistor (IGCT) tech- drives are used in a power range down to several 100 kVA nologies For high- In the small and medium power range of approximately er power 300 kVA to MVA, the output voltage is based on the Digital Object Identifier 10.1109/MIAS.2009.935494 1077-2618/10/$26.00©2010 IEEE standard voltages available throughout the world: 2.3 and 4.16 kV in the North American and 6–6.6 kV in the Asian and Russian markets Even 10 kV drives are emerging for applications that have to operate on weak line supplies In Europe, low-voltage drives up to 690 V have become prevalent in this power range In the case of high rating drives from to 60 MVA, the output voltage can usually be freely selected and is determined by cost optimization of the whole drive system, consisting of line transformer, converter, cables, switchgear, and motor Because of the various applications, the wide voltage and power range for medium-voltage drives and the rapid development of the available power semiconductor devices, numerous different converter topologies have been developed for medium-voltage applications in recent decades Unlike the low-voltage range, where the two-level (2L) voltage-source converter has become the dominant solution, a large number of different converter topologies are available in the medium-voltage market The spectrum varies from IGBTconverters with low- and high-voltage IGBTs through IGCT converters to conventional thyristor converters Voltage-Source Inverters The VSI can be basically divided into two categories: converters in a delta connection and converters in a star Medium-Voltage Drives for Industrial Applications ∆ Star Circuit Y Delta Circuit Current-Source Inverters (CSIs) Cycloconverters (CCs) Delta Circuit ∆ • Series Connected • Self-Commutated • Three-Level Current Source H-Bridge Cells Neutral Point — Two-Level Cells Inverter (CSI) Clamped SC-HB (2L) (3L-NPC) — Three-Level Cells • Four-Level SC-HB (3L) Flying Capacitor (4L-FC) Star Circuit Y Voltage-Source Inverters (VSIs) • Load Commutated Inverter (LCI) Synchronous Motors (SMs) • Open Circuit (CC-D) • With Common Star-Point (CC-S) Induction Motors (IMs) Synchronous Motors (SMs) Induction Motors (IMs) Synchronous Motors (SMs) Main classification of the basic topologies available in the market today for medium-voltage converters in industrial applications IEEE INDUSTRY APPLICATIONS MAGAZINE MAR j APR 2010 WWW.IEEE.ORG/IAS Converter Topologies Figure provides a general overview of the converter topologies available on the market for medium-voltage applications Table shows the essential performance data and the power semiconductor devices used in the various topologies The data only refer to the basic converter configurations of the converter topologies being presented Possible parallel or tandem connections of power sections or step-up transformers at the converter output are not taken into account because this would give a misleading impression of the actual performance of each topology in conjunction with the power semiconductors being used Moreover, Table only focuses on load-side inverters Possible configurations for line-side converters have not been taken into consideration The circuit topologies generally used in mediumvoltage industrial converters can be roughly divided into three categories: n VSIs n current-source inverters (CSIs) n cycloconverters (CCs) with thyristor technology These categories not only differ in their actual circuit topology but also by the power semiconductors that are used—an essential difference In VSIs, asymmetrically blocking turn-off devices (IGBTs and IGCTs) with antiparallel free-wheeling diodes of 1.7–6.5 kV are used, whereas the 1.7-kV IGBTs are only used in cellular converters [SC-HB(2L)] For CSIs, symmetrically blocking, turn-off gate-commutated transistors (GCTs) are employed, whereas for load-commutated inverters (LCIs) and CCs, electrically fired, symmetrically blocking thyristors are used All self-commutated VSIs, CSIs, and all line-commutated CCs are basically suitable for feeding induction and synchronous motors In contrast, LCIs can only be operated in conjunction with overexcited synchronous motors since this type of motor is able to provide the reactive power necessary for the commutation of the motor-side thyristors 23 *Continuous power, without output transformer, only basic equipment (i.e., no parallel or tandem connection) Ball-and-tube mills, cement mills, marine propulsion systems, and rolling mills 0–22 Hz (50 Hz line) 1–4 kV Thyristor CC 3–25 MVA Starting converters, compressor drives, and marine propulsion systems 0–105 Hz 1.8–12 kV Thyristor LCI 2.5–70 MVA Pumps, blowers, and extruders IGCT: 4.16–6.9 kV (3L) SGCT: 2.3–6.6 kV IGCT: ... power range for medium-voltage drives and the rapid development of the available power semiconductor devices, numerous different converter topologies have been developed for medium-voltage applications... in the Asian and Russian markets Even 10 kV drives are emerging for applications that have to operate on weak line supplies In Europe, low-voltage drives up to 690 V have become prevalent in... basically divided into two categories: converters in a delta connection and converters in a star Medium-Voltage Drives for Industrial Applications ∆ Star Circuit Y Delta Circuit Current-Source Inverters