Semiconductors as Key Components in Future Smart Grid Installations

Martin Schulz, Infineon Technologies AG, Germany

2036
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Special requirements for the power electronics in use arise from the wide variety of boundary conditions as well as lifetime and availability of the installations. Depending on the location, the power plant may be subject to ambient temperatures from −30°C in cold regions to +50°C in warmer zones. Relative humidity can exceed 90%, sulfurous atmosphere, salty mists and dust in deserts are factors that have to be considered in power electronic design too. Especially components mounted in the nacelle or even the hub suffer from vibration, leading to further stress for the power semiconductors. The electrical interface between generator and grid can be designed on module- or subsystem level. The power electronic subsystem, or Stack, can be considered an off-the-shelf component, available in power ranges up to megawatts. Figure 3 gives an impression of a MODStack HD, designed for a throughput of 2MW. In this application, the most important thing to care for is robustness. The predicted lifetime is demanded to reach 20 to 25 years along with a warranted availability of 97%.

Fig. 3: Stack assembly for a wind power application with 2MW throughput.
Fig. 3: Stack assembly for a wind power application with 2MW throughput.

ENERGY TRANSPORT

One of the major challenges coming with the extended use of regenerative energy, is the geographic distance between the point of generation and the area where the energy is finally needed. Transferring energy from an off-shore windfarm in the North Sea to the industrial centers in the middle or even the south of Europe comes with two separated difficulties. Besides political aspects, the extension of the grid infrastructure is an obstacle to overcome.

Using AC-voltage to transfer energy over long distances is not a viable option. The losses that occur will make this a non-ecological approach. Starting from some hundred kilometers, High Voltage Direct Current (HVDC) transmission is to be favored. DC-transmission is most efficient in both, electrical losses and material in use as it can be done on a single-wire setup. HVDC is well established and, among others, connects England to the European continent via cable.

Core of these transfer systems are semiconductors in disc designs. Thyristors and diodes are installed to transfer energy in a GW-range using bipolar DC-voltages of up to ±800kV. Today, the converter needed to create an AC-voltage from this DC-line is based on thyristors as well. Figure 4 gives an overview on this kind of devices.

Fig. 4: Disc-shaped thyristor and diode devices
Fig. 4: Disc-shaped thyristor and diode devices

Currently, research is ongoing to use IGBT-based multilevel converters to replace the thyristors in the DC-AC converter. Here too, efficiency is the driving force. Expanding the interconnection beyond European borders would allow integrating the regions with the highest energy yield, North Africa and Middle East, into a transcontinental grid. The vision of the Desertec Project pictured in figure 5 clearly shows, that thousands of kilometers would have to be crossed. In this vision, HVDC becomes the technology of choice for the necessary long-distance connections.

Fig. 5: A transcontinental energy grid, Source: Desertec Foundation
Fig. 5: A transcontinental energy grid, Source: Desertec Foundation

CONCLUSION

Power electronics both in module and disc design, is a mostly unrecognized part of the already existing supply network. New applications in Smart Grids demand innovative approaches to enhance efficiency and increase power density to build smaller power electronic devices. Especially mobile and electric vehicle applications demand low weight and volume and even in private houses, space is not necessarily available in excess.

Furthermore, supply networks are expected to achieve a very long lifetime, especially if compared to classical consumer electronics. Robustness and longevity will be the most pressing needs to be fulfilled. Therefore, new developments in semiconductor material and the interconnection technology in use are to be expected.

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