Hig efficiency AC-DC converter

An AC-DC converter system comprising:

• A sinusoidal AC voltage source with its first terminal and second terminal;
• A bridge circuit consists of a first bridge arm and a second bridge arm, each said bridge arm consists of a first switch at high side and a second switch at low side, the negative terminal of the first switch and the positive terminal of the second switch of each said bridge arm are connected together respectively to form a switching node of each said bridge arm, the negative terminal of the second switch of said two bridge arms are connected together to form a power ground of said bridge circuit, the positive terminal of the first switch of said first bridge arm is connected to the first terminal of said AC voltage source, and the positive terminal of the first switch of said second bridge arm is connected to the second terminal of said AC voltage source;
• A transformer with its first winding and second winding, a capacitor with its first terminal connected to the switching node of the first bridge arm and second terminal connected to the second terminal of the first winding of said transformer, the first terminal of the first winding of said transformer is connected to the switching node of the second bridge arm, the second winding of said transformer is connected to a rectifier circuit to convert the voltage from the secondary winding to a DC output voltage;
• wherein the switching operation employs a series resonance scheme, the switching operation of the first bridge arm and the second bridge arm is in synchronous with identical switching action for the first switch of both bridge arms and identical switching action for the second switch of both bridge arms, and the first switches and second switches are turned on and off alternatively at symmetrical duty cycle of near 50% with a small dead time inserted at each switching transition, the voltage applied to the first winding of said transformer is adjusted by varying the switching frequency of the bridge arms, to realize the function of forcing the profile of the input current from the AC voltage source to follow the reference signal, which is in synchronous and proportional to the sine wave of the AC voltage source, the amplitude of the reference signal is adjusted by voltage control loop of the system to realize the function of output voltage regulation.