But the vaccine fridge needed pure, stable 60 Hz. She tweaked the duty cycle, referencing Rashid’s equations for harmonic reduction. At 3:17 a.m., the fridge compressor hummed to life—a steady, beautiful sound.
“The problem isn’t the source,” she whispered, tracing a diagram of a three-phase inverter with her finger. “The problem is control.”
For six hours, she worked by headlamp. She built a makeshift inverter—a crude but functional topology from Rashid’s Figure 8.4. Her hands shook as she soldered. At 2 a.m., she connected the river turbine’s wild AC to her contraption. The diodes rectified it into bumpy DC. Then, her IGBTs, switching at 5 kHz, carved that DC into a crude square-wave AC.