How ABB’s BORDLINE® Traction Converters Boost Efficient, Sustainable Rail Travel

Imagine the kind of power it takes to push a train along. Yet there is more to this power than raw performance. Passengers expect a smooth acceleration and deceleration. Railway companies expect cost and energy efficiency as well as reliability, day-in day-out, in all weathers. This is the job of the traction converter. Enter ABB’s BORDLINE® Compact Converter.

For a train to move precisely and reliably, its motors must be controlled accurately. They must rotate at the desired torque and speed, and this means the electrical supply that feeds them must be controlled with high precision. 

A traction converter’s main purpose is to convert electrical energy coming from the overhead catenary – or from a battery or a diesel generator – and use it to drive the traction motors. 

The voltage and frequency from the overhead catenary are constant, just as any grid supply is. But if the electricity in the motor were constant, the train could run at one fixed speed only. Instead, when the train needs to accelerate, the frequency of the motor’s supply is increased. When the train needs to do some heavy pulling, the motor needs more torque, and this means more amps. The traction converter varies and controls the electrical supply to the motors on demand and instantaneously.

It's all about power electronics

So how does the converter get from the fixed electrical supply of the catenary to the variable supply that the motors need? This question has confronted railway engineers since the earliest days of electric trains – starting in the latter part of the 19th Century. Many creative approaches were tried out, mostly involving mechanical gear with moving parts. This technology did what was required and held its own for many decades. But it had its limitations and, like any equipment with many moving parts, it required high levels of maintenance. Starting in the 1960s, a new revolution began: The power electronic converter. Power electronics is about using semiconductors to switch currents at high frequency without using moving parts. Switching patterns are used to modulate the precise frequency that the motor requires.   

Over the decades that followed, power electronics never stopped getting better and better. Semiconductors got smaller, more robust, more reliable, were able to switch faster, more precisely and with lower losses. Converters became more and more compact, meaning they occupied less space on the train, leaving more space for passengers. Today we are seeing silicon carbide semiconductors displace silicon, meaning a further boost in efficiency. 

Bringing Europe together

For historical reasons, many railways in Europe use different catenary voltages. In the past this often meant that locomotives needed to be changed when a train crossed from one country to another – a process that cost time and required manual intervention. In some cases, highly complex dual-mode locomotives were built. Using power electronics, it is much easier to design converters that can effortlessly deal with different voltages. Traction converters are bringing the cities of Europe closer together.

With equipment getting lighter and more efficient, trains are consuming less energy. Railways have always been among the most energy-efficient and sustainable modes of transportation, but these changes are leveraging that edge even further.

PEBB at the core

The core component of an ABB compact converter is the Power Electronic Building Block, or PEBB. The PEBB is the power module, containing IGBT semiconductors. Their temperature can get as high as 150°C. The main cause of the heat is the high frequency at which they are switching – up to two kilohertz or four kilohertz – and this while switching the main traction current which can be in the hundreds of amps. These processes are occurring in spaces of milliseconds. This is the highly demanding control frame of a modern traction converter. 

BORDLINE® Compact Converter

ABB’s BORDLINE Compact Converters are a family of converters for a broad power range. 

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