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Posted on 02 July 2019

From Mercury-Arc to Hybrid Breaker (part 2)

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100 years in power electronics – Part 2

2013 marks the centenary of ABB’s involvement in power electronics. Power electronics have become ever-present in a vast range of applications ranging from large high-voltage direct current (HVDC) installations - transmitting gigawatts over thousands of kilometers - to everyday household devices. The development of power electronics was driven by the desire to convert electricity from one frequency or voltage level to another without having to resort to moving, maintenance-intensive mechanical parts. In the early days, converters used mercury-arc rectifiers, which were replaced by semiconductors in the 1950s and 1960s. Throughout its 100 year history, ABB has been a pioneer of both power electronic technology and its applications.

By Andreas Moglestue and Christoph Holtmann, ABB Switzerland Ltd.

< Here is the second part of “From Mercury- Arc to Hybrid Breaker”, continued from Bodo’s Power Systems, May 2013. >

Semiconductors

The elements of the periodic table are generally divided into metals and nonmetals. In their pure form, metals conduct electricity, whereas nonmetals (mostly) do not. There is, however, an interesting group of nonmetals that perform intermediate levels of conductivity. These are the semiconductor materials, most notably germanium and silicon. Some hybrid crystals such as gallium arsenide and silicon carbide have semiconductor properties, too.

A simple example of a semiconductor device is a diode. A p-zone adjoins an n-zone on the same crystal. Current can flow from the p- to the n-zone (ie, in the p-zone holes flow towards the p-n junction, and in the n-zone, electrons flow towards the junction, with the two types of carriers recombining at the junction). If a reverse voltage is applied, charge carriers are depleted from the junction area and conduction ceases.

In order to create switchable valves, a method was required to externally trigger conductivity. The first transistor was created by Bell Laboratories in 1947. It used an electric field to control the availability of charge carriers in a germanium crystal, meaning that the current through it was determined by a control voltage.

The invention of the transistor kicked off a rapid and highly visible development culminating in the remarkable revolution in communications and data processing, whose fruits are highly visible today. Maybe less obvious but equally spectacular is another semiconductor revolution that occurred in parallel in the domain of power electronics: Today electricity can be transformed, controlled and converted in ways which only some decades ago would not have been considered possible. For example today’s ubiquitous data and communications devices and their highly integrated microprocessor chips would be of little use without powerelectronic circuits delivering the power, charging their batteries and keeping the data centers and communications links running without which social networks and other online services could not function. Similarly, today’s boom in renewable energy and the resultant reduction of emissions would not be possible without power-electronic converters assuring reliable and affordable grid connectivity.

It took many decades of development to make this feasible. Both BBC and ASEA commenced semiconductor development in the early 1950s, with BBC’s first rectifier diodes (rated 100 V, 100 A) coming onto the market in 1954 (Figure 1). These and other early semiconductors were made of germanium (some manufacturers used selenium), but the material was found to be unsuitable for power applications due to constraints in terms of blocking voltage and temperature. It was soon displaced by silicon.

ABB developed the first germanium diodes in 1954

Thyristor

Transistor applications in analog amplifiers (such as in radios and telecommunications) are well known. However, the demands of power electronics are different: Switches should ideally either be on or off, with the transition period being kept as short as possible because of the losses in the device.

An early switchable power semiconductor was the thyristor, whose principle was proposed by William Shockley in 1950. A thyristor is similar to the pn-diode described previously, but with additional layers inserted between the outer p- and n-zones. These layers normally prevent conduction, but the injection of current at a third contact called the gate floods this area with charge carriers, enabling current to flow if a forward voltage exists between anode and cathode. Once triggered, the replenishment of charge carriers is self-sustaining, meaning the trigger current can be removed. Conduction does not cease until the current drops below a critical value. The device can thus be used for line-commutated inversion (Figure 2), but not for self-commutation.

First locomotive using ABB silicon thyristors, 1967

Between 1960 and 1980, the maximum blocking voltage and power handling per device increased in a roughly linear fashion, from about zero in 1960 to 6,000 V and 600 kW, respectively, in 1980 (Figure 3).

Development of switching power of the three major power semiconductor device types

GTO

Production of gate turn-off thyristors (GTOs) commenced in the mid 1980s. A GTO is a thyristor that can be turned off by applying a current to the gate in the reverse direction. The ability to produce devices that were able to switch off without an artificial zero crossing helped expand the scope of application of power semiconductors, enabling for example DC-DC converters and self-commutated inverters. Furthermore, multiple switching cycles during an AC half-wave can make the AC output less rectangular in shape.

Semiconductor production

BBC’s early semiconductor production was at Ennetbaden, Switzerland. BBC established a modern semiconductor factory at Lampertheim in the late 1960s and sought to concentrate all manufacturing there. However, some of the production at Ennetbaden (mostly development activities and pilot production, but also modest levels of production) was transferred to Birr, Switzerland. These activities were moved to a new factory at Lenzburg, Switzerland, in 1981.

Inauguration of expanded production facility at ABB Semiconductors in Lenzburg, Switzerland, 2010

Following the merger of ASEA and BBC to form ABB in 1988, the Lampertheim site was sold to IXYS. ASEA’s factory at Västerås, Sweden, was closed and all production concentrated at Lenzburg. ASEA’s strength laid in thyristors and rectifier components, whereas BBC’s strength laid in diodes, GTOs and thyristors. Although there was some overlap, the different ranges were largely complementary.

At the time, semiconductor manufacturing was not recognized as a business in its own right within ABB, but was perceived as an activity required for the support of other product areas, such as drives or HVDC. Product development and investment were thus largely driven by the needs of ABB’s other businesses. In the early 1990s the business changed into a standalone activity, directly competing with other semiconductor manufacturers on the outside market. In 1995, the Lenzburg factory was a finalist in the European Quality Award, and in 1996 it was awarded the “Supplier of the Year Award” by General Electric.

IGBT

A new BiMOS factory opened in Lenzburg in 1998, specifically tailored for the manufacture of insulated gate bipolar transistors (IGBTs). The introduction of IGBTs represented a fresh leap in terms of manufacturing complexity and the technologies involved, but at the same time also represented a step change in device performance and capability. An IGBT is a power semiconductor controlled by voltage rather than current as for a GTO - this also reduces the power and space requirements of the gate unit (the external drive unit that turns the switch on or off via the gate), permitting more compact and lightweight converters. IGBTs are also more inherently stable than GTOs, reducing the need for protective circuitry, and are furthermore capable of faster operation, permitting higher switching frequencies.

IGCT

To also make hard-switching capability available for higher power classes, ABB pioneered the integrated gate-commutated thyristor (IGCT) in the mid 1990s. Developed on the basis of GTO technology, the new device was capable of much faster switching than conventional GTOs. In this it was supported by an integrated low-inductance gate unit. This development was remarkable as it occurred at a time that other manufacturers were withdrawing from GTO development, assuming the technology had no future.

ABB further strengthened its market presence with the acquisition of the Czech semiconductor company, Polovodièe, in 2010. This gave ABB a second manufacturing site (in Prague). At the same time, capacity at Lenzburg was again increased with the construction of a further factory (Figures 4&5).

ABB Semiconductors’ current high-power Bipolar and IGBT product range

BiGT

The latest development of the IGBT family is the bi-mode insulated gate transistor (BiGT), an IGBT that integrates the reverse conducting diode in a highly space saving manner. The BiGT is an important technology for one of ABB’s most significant announcements of recent decades: the hybrid HVDC breaker.

The hybrid HVDC breaker is yet a further example of semiconductors finding their way into entirely new uses. The range of applications of power electronics is growing in ways that only some years ago would have seemed unimaginable.

Further reading

  • H.R. Zeller, The winning chips: History of power semiconductors at ABB, ABB Review 3/2008, pages 72-78
  • S. Linder, Power semiconductors: Part one, Basics and applications, ABB Review 4/2006, pages 34-39
  • S. Linder, Power semiconductors: Part two, Housing technology and future developments, ABB Review 1/2007, pages 62-66

 

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