Power electronics and the energy transition
Power electronics convert electricity between forms efficiently using fast semiconductor switches. They connect solar panels, batteries, electric vehicles, and modern loads to the grid.
What power electronics do
Power electronic converters change voltage levels, convert between AC and DC, and control frequency by switching semiconductors rapidly on and off, rather than burning excess energy in resistors. Rectifiers convert AC to DC, inverters DC to AC, DC-DC converters change DC levels, and variable-frequency drives control AC motor speed.
Switching devices
Power converters use MOSFETs for lower voltages and high frequencies, insulated-gate bipolar transistors (IGBTs) for high voltages and currents, and thyristors in very high power systems such as HVDC. Wide-bandgap semiconductors, silicon carbide (SiC) and gallium nitride (GaN), switch faster with lower losses and tolerate higher temperatures, enabling smaller, more efficient chargers and electric-vehicle drives.
DC-DC converters
A buck converter steps DC voltage down by switching an input on and off and smoothing the result with an inductor and capacitor; ideally \(V_{out} = DV_{in}\), where D is the duty cycle. A boost converter steps voltage up: ideally \(V_{out} = \frac{V_{in}}{1 - D}\). Switching at tens of kilohertz to megahertz keeps components small, and efficiencies above 90% are common, far better than linear regulators.
Inverters
Inverters create AC from DC by switching transistors in patterns, typically using pulse-width modulation to synthesise a sinusoidal average, followed by filtering. Solar inverters convert panel output to grid AC while tracking each panel string's maximum power point; electric-vehicle inverters drive traction motors at variable frequency; and uninterruptible power supplies use inverters to run equipment from batteries during outages.
Batteries and storage
Lithium-ion battery costs fell by roughly 90% between 2010 and 2023, according to BloombergNEF price surveys, making electric vehicles and grid-scale storage practical. Grid batteries smooth renewable output, provide fast frequency response within milliseconds, and shift solar energy into the evening. Pumped hydro remains the largest form of grid storage worldwide by capacity.
Electric vehicles and charging
Electric vehicles use battery packs of roughly 40 to 100 kWh or more, inverters, and efficient motors. Home charging typically supplies 3 to 11 kW of AC, converted by an on-board charger; DC fast chargers deliver 50 to 350 kW directly to the battery. A car using about 15 to 20 kWh per 100 km on a 60 kWh pack travels roughly 300 to 400 km.
Grid integration
Inverter-based resources such as solar, wind, and batteries lack the spinning inertia of traditional generators, which naturally steadies grid frequency. Grid-forming inverters, faster frequency response, smart grids with two-way communication, demand response that shifts flexible loads, and expanded transmission help grids remain stable as renewable shares rise.
Worked example
A buck converter turns 12 V into 5 V for USB devices. The ideal duty cycle is \(D = \frac{5}{12} \approx 0.42\). Delivering 2 A at 5 V (10 W) with 92% efficiency, it draws about \(\frac{10}{0.92} \approx 10.9\) W, or 0.9 A from 12 V, wasting 0.9 W. A linear regulator would draw 2 A at 12 V, 24 W, wasting 14 W as heat, which is why switching converters dominate.
Key takeaways
Power electronics convert electricity by fast switching: rectifiers, inverters, DC-DC converters, and variable-frequency drives. Switches include MOSFETs, IGBTs, and thyristors; SiC and GaN wide-bandgap devices cut losses and size. Buck converters give V_out = D V_in and boost converters V_out = V_in / (1 - D), at over 90% efficiency. Inverters synthesise AC with PWM for solar, EVs, and UPSs, with maximum power point tracking for panels. Lithium-ion costs fell about 90% from 2010 to 2023, enabling EVs and grid batteries; pumped hydro is still the largest storage. EVs charge at 3 to 11 kW AC or 50 to 350 kW DC. Grids integrate inverter-based renewables with grid-forming inverters, fast response, smart grids, and transmission.
Flashcard
Efficient conversion by fast switching
Check your understanding
Why are switching DC-DC converters preferred over linear regulators for dropping 12 V to 5 V at high current?