Abstract
Recently, three-phase series-resonant converters (SRCs) have been proposed for high power applications. Three-phase SRCs can achieve zero-voltage-switching (ZVS) of the primary power switches and regulate the output voltage by pulse-frequency modulation. The interleaving technique is also a conventional method for DC-DC converters to achieve a high power level, reducing the output voltage ripples due to operating out of phase at the same frequency between the two converters. However, an interleaved three-phase SRC cannot easily synchronize switching instants between the two modules due to the component tolerances of circuits. In the proposed control method, phase shift modulation (PSM) is used to solve the output current imbalance caused by component tolerances. The power switches of the converter can also maintain synchronizing switching instants between the two modules. Therefore, the lower output voltage ripple can be achieved. A detailed analysis and design of this new control method for interleaved three-phase SRCs are described. Finally, prototype converters with a 2.4 kW total output were built and successfully tested to verify the feasibility of the current sharing modulation.
Highlights
In the past decades, the resonant converter has been widely used in many applications such as laptop adapters, server power supply units and battery chargers
The resonant converter is not suitable in high power and large output current applications because the secondary-side rectifiers do not use stored energy inductors such as an LLC resonant converter; the secondary-side current is larger compared with other DC-DC converters
The conventional interleaving control for pulse-width modulation (PWM) cannot be directly applied to the resonant converters because they use pulse-frequency modulation (PFM) to regulate output voltage and the operational frequency of each module must be synchronized for the interleaved operations
Summary
Legs; switches a–S240 f are controlled at a 0.5 dutytransformers ratio and three legs exhibit phase shi at 0 , 120 S and. √ Lr Cr. Equation (2) can explain the elements that can use the phase shift degree φ and switching frequency fsw to regulate output power Po. Figure 4 depicts the relationship. To explain the relationship among the voltage gain, phase shift degree φ and switchTo explain the relationship among the voltage gain, phase shift degree φ and switching from Equation (2) where n is the turn ratio of the primary-side to the secondary-side of ing frequency f sw, the voltage gain is defined as nVo/Vin and Equation (3) can be derived fsw ,the voltage again is defined aso/V nVino=/V from in and thefrequency transformers, assuming voltage gain nV. When increasing the phase shift degree φ or decreasing the normalized quency fn, the voltage gaingain obviously frequency fn , the voltage obviously nV rises.
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