Abstract
In recent years, the LLC (inductor–inductor–capacitor) DC transformer has been widely used in communication and computer power supply because of its advantages of zero voltage conduction of primary switch and zero current turn off concerning the output rectifier diode. To obtain higher transmission efficiency and make the LLC DC transformer always run at the optimal operating point, the switching frequency of the LLC DC transformer should work at the resonance frequency of the circuit. In actual conditions, the optimal operating frequency of the LLC DC transformer will be changed due to the influences of the working condition on the circuit parameters and the load change. Therefore, the LLC DC transformer controlled by the fixed frequency mode will not be in the best working condition. In this paper, an adaptive frequency tracking method is used to control the circuit; when the circuit parameters change, the LLC DC transformer can always be in the best working state. Then, the influence of circuit parameters such as output power and excitation inductor on the optimal working point of the LLC DC transformer is analyzed in detail. Finally, a 1 kW LLC resonant converter prototype is designed under laboratory conditions to verify the feasibility of the control strategy.
Highlights
IntroductionThe DC (direct current) transformer is a necessary link for interconnecting DC networks of different voltage levels
The DC transformer is a necessary link for interconnecting DC networks of different voltage levels
Direct detection light load, complicated this paper analyses the driving waveform of the primary side switch when operating below the optimal detection (THD) of the resonant frequency calculation and long response resonance point, theDistortion current waveform circuit, the voltage waveform of the secondary method time side rectifier diode, and the output voltage waveform of the LLC resonant DC transformer, and the
Summary
The DC (direct current) transformer is a necessary link for interconnecting DC networks of different voltage levels. In those papers, the LLC resonant DCX (direct current transformer) and the PWM (pulse width modulation) DC–DC converter are cascaded to make the input side in series and the output side in parallel. To synchronize the operating frequency with the resonant frequency, it is necessary to add a frequency tracking control link to maximize the transmission efficiency of the circuit [15,16] and perform voltage regulation through the cascaded PWM DC–DC converter. The existing literature only proposes a frequency tracking method and does not analyze in detail the mechanism of the LLC DC transformer to achieve the optimal operating point for voltage sampling, and the impact of different operating conditions on the optimal operating point
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