Switching Frequency is Not the Limit: Multiphase Coupled Inductor FCML Converter Tracking Signals Above the Switching Frequency

Switching frequency is usually considered the main limiting factor for reducing the passive component size and improving the control bandwidth of power converters. The switching frequencies of semiconductor devices and passive components are usually the same in typical power electronics systems. Multi-level, multi-phase, and magnetically coupled circuits utilize a large number of low-frequency semiconductor devices to drive a few high-frequency passive components, enabling reduced ripple, reduced dc energy storage, miniaturized volume, and improved transient performance. This paper presents a 1 MHz four-phase, five-level coupled inductor flying capacitor multilevel (FCML) converter that tracks signals at and above the switching frequency. Combining multiple voltage levels, multiple phases, and coupled inductors, the effective switching frequency and achievable control bandwidth are multiplied by 16× to 16 MHz. A printed circuit board (PCB) embedded planar coupled inductor is designed to intrinsically balance the flying capacitor voltages, minimize output distortion, minimize output voltage/current ripple, and improve the transient performance. Spread spectrum pulse-width modulation (PWM) is implemented to mitigate high frequency harmonics.