A7 Power Electronics

Topic

Power electronics deals with the large-scale conversion and control of electrical energy, relying on the same pulse-width modulation technique previously described in the context of switched-mode power supplies: controlling the effective average voltage by rapidly varying the fraction of time a source remains connected to the load, rather than continuously varying the voltage itself. This is the fundamental technique behind variable-speed motor drives, electric vehicle traction systems, and the inverters that convert solar energy into usable alternating current.

The Insulated-Gate Bipolar Transistor (IGBT) is currently the dominant power switch for high-voltage, high-current applications because it combines the best attributes of two technologies previously discussed separately: it is voltage-controlled at the gate—like the MOSFET described in an earlier model—yet maintains a low voltage drop during conduction, similar to the bipolar transistor covered in another model.

Energy losses in a power switch like this stem from two distinct sources: conduction losses, which are proportional to the current flowing while the switch is closed; and switching losses, which occur during every turn-on or turn-off transition and increase with the switching frequency—reflecting the same trade-off between frequency and losses previously outlined regarding switched-mode power supplies. Conduction losses dominate at low frequencies, while switching losses dominate at high frequencies.

Consequently, this module—which begins by revisiting the established pulse-width modulation technique—concludes by highlighting how wide-bandgap semiconductors (such as silicon carbide and gallium nitride, previously described in the advanced devices model) enable the construction of converters that are more compact, lightweight, and efficient than traditional silicon-based ones. These materials are better suited to the high-voltage and high-frequency conditions necessitated by the aforementioned loss trade-off, making them the key technology behind today’s fast chargers for electric vehicles and state-of-the-art photovoltaic inverters.

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