Fixed-frequency control method of full-bridge LLC resonant converter

Abstract

The invention provides a fixed-frequency control method of a full-bridge LLC resonant converter. The full-bridge LLC resonant converter is composed of a direct-current input source Vin, a primary sidesquare-wave generator I, a primary side LLC resonant circuit II, a transformer III, a secondary side full-bridge rectifying circuit IV, an output filter capacitor Co and an output resistance load Ro.The primary side square wave generator I is composed of a primary side first switch tube S1, a primary side second switch tube S2, a primary side third switch tube S3 and a primary side fourth switchtube S4. The primary side LLC resonance circuit II is composed of a resonance capacitor Cr, a resonance inductor Lr and an excitation inductor Lm. The primary side second switch tube S2 and the primary side fourth switch tube S4 are controlled through a pair of fixed-frequency complementary pulses, a duty ratio is 50%, and a switch frequency is equal to a series resonant frequency of the resonantcapacitor Cr and the resonant inductor Lr. Switch pulses of the primary side first switch tube S1 and the primary side third switch tube S3 are controlled through output voltage feedback, and duty ratios of the switch pulses of the primary side first switch tube S1 and the primary side third switch tube S3 are complementary.

Description

technical field [0001] The invention relates to a fixed-frequency control method for a full-bridge LLC resonant converter, especially applied to an isolated DC-DC power converter, and belongs to the technical field of power electronic power converters. Background technique [0002] Isolated DC-DC converters are currently widely used, including data center server power supplies, electric vehicle on-board chargers, photovoltaic DC microgrids, fuel cells, LED drive circuits, etc. The high efficiency and high power density of converters have always been the focus of people the goal that is pursued. The LLC resonant converter has a simple structure and can realize zero voltage switching (ZVS) and zero current switching (ZCS). It has excellent characteristics such as high efficiency, low electromagnetic interference, good voltage regulation performance, and current isolation. It is easy to achieve high efficiency at the resonance frequency Power density has become a research hots...

AI Technical Summary

Problems solved by technology

The first method adds an auxiliary switching device and uses pulse width modulation (PWM) to adjust the voltage gain, but the added auxiliary power device increases the circuit complexity and design cost, and the additional PWM control increases the complexity of the control

Another method improves the control strategy, but there are disadvantages such as complex control circuit, limited voltage gain, and low efficiency.

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