Digital Current Mode Control Tuning in GaN-based Multiphase Boost Converters for Ultra-fast Transient

Controller tuning based on linear small-signal models often results in poor closed-loop bandwidth in a boost converter in which there exists a right-half-plane (RHP) zero. This is because of the fact that small-signal models often ignore fast switching dynamics; thus the performance improvement cannot be fully explored. This paper proposes a geometry tuning in a digitally current mode controlled multiphase boost converter operating under a fixed-frequency digital pulse-width modulator (DPWM) throughout. This achieves proximate time optimal transient recovery for load step transients using a normalized load current feedforward. The latter results in near load invariant regulation; thus, a small integral gain is sufficient for minimizing the steady state error. A GaN-based 4-phase boost converter prototype is made for 48 V rated output voltage, and the measured efficiency is found to be around 97% for the input voltage range of 12 to 36 V. Test results demonstrate nearly a ten fold improvement in the (load) transient response using the proposed tuning over a conventional linear tuning. All the digital controllers are implemented using an FPGA device.