| With the development of automotive electronics industry,new energy vehicle industry in recent years has a significant growth momentum.Further driven by the rapid progress of Power Semiconductor technology,automotive applications of DC-DC converter products in the new energy vehicles is playing an important role.For automotive DC-DC converter design trends of high power density,high reliability and low EMI,the Four-switch Buck-Boost converter with wide input range is well suited for automotive battery output voltage regulator applications and battery management applications.In this thesis,multi-mode operation and mode switching of the Four-switch Buck-Boost converter are investigated.Based on the low EMI design and fast transient response requirements,a peak current mode PWM control scheme is used.Peak-Buck Peak-Boost control is used for multi-mode switching.The stepdown operation is in Buck mode and the Stepup operation is in Boost mode.For the Buck-Boost mode,where is Input voltage is close to Output,Buck-Boost on Buck Mode(B~2Buck Mode)and Buck-Boost on Boost(B~2Boost Mode)sub-mode control are used,which can realize seamless mode switching in the wide input range.And based on the classical Ridley model,the small signal modeling in each operating mode is carried out,and the small signal transfer functions of loop gain is given in each mode.A ramp compensation strategy with a constant quality factor is proposed to achieve full-range loop stability and reliability.Due to the requirement of high efficiency and low EMI for automotive DC-DC converter systems,this thesis introduces the key technologies needed in the design of Buck-Boost converter controller chips.This thesis briefly investigates the Pseudo-random Spread-spectrum Frequency Modulation(SSFM)technique and analyzes the spectral characteristics of Up-spread type Triangular Modulation.The advantages of the Pulse Skipping Mode in low EMI design and light load efficiency optimization are explained.For the fixed-frequency control sheme,inductor current surge problem occurs during the soft-start process,a frequency reduction technique for soft-start based on the Pulse Skip Mode is presented to solve this promblem.Based on the research above,a Buck-Boost converter controller chip with high switching frequency and wide input voltage range is designed in the 0.18μm BCD process platform.The design and simulation of each sub-module are completed using Spectre simulator.The simulation results show that the output voltage overshoot is 177m V,48 m V and 136 m V when transfering from Buck to B~2Buck mode,from B~2Buck to B~2Boost mode and from B~2Boost to Boost mode,respectively.After spectral spreading,the peak spectral amplitude of the switch node decreases by 12.53 d B near the harmonics.The peak efficiency achieves 91.36%for fixed output 12 V and different input and load currents. |
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