Research On Three-Level Resonant Capacitor Charging Power Supply

Generally, high frequency series resonant capacitor charging power supply uses two-level converter as its converter. Two-level converter has its advantages: easy control and simple structure. But this structure limits the current flowing direction and can't change the current range when working, and results in large current peak value, large load power needing and low charging precision. In order to improve the charging wave shapes and eliminate those shortcomings of two-level converter, this paper uses three-level converter instead of two-level converter. Not only three-level converter could work under half voltage mode, but also full voltage mode. In this way we could reduce current peak value, load power needing, and increase charging precision. In addition, three-level converter could be composed of high frequency switches with low endurable voltage which could increase working frequency, shrink passive components, and finally shrink the whole power supply. Series resonant capacitor charging power supply is easy to be affected by parasitic capacitor of high frequency transformer. There are two ways to overcome that bug. One way is use additional resonant circuit to eliminate the influence of parasitic capacitor, another way is use three-level ZVS resonant structure of charging circuit instead of two-level resonant structure, which could make good use of parasitic capacitor as its resonant parameter, heighten output voltage level, and shrink power supply more or less.This paper combines three-level converter with resonant charging structure and conducts a more thorough theoretical analysis and experimental study, which based on previous research results of three-level charging structure. In this paper, research contents include characteristics of three-level ZCS resonant structure and characteristics of three-level ZVS resonant structure. The former includes analysis on control methods and charging waveshapes, discusses the feasibility of working with combination method, and analyzes the feasibility of using resonant method to elimilate the influence of parasitic capacitor. The latter includes analysis on working principle of parallel resonance and control methods, compares the charging waveshapes of two control methods, analyzes different Q lead to different charging waveshapes, and designs the protection circuit. This paper finds out how to design three-level resonant capacitor charging power supply and demonstrates the feasibility, and supplys ideas and methods for the development of three-level resonant capacitor charging power supply.