Resonant converter and control method thereof
A resonant converter which can realize its easy design, eliminate the need for its adjustment, realize reliable soft switching operation, and increase an efficiency. A driver DRV of a main switching device uses a PLL circuit PLL to apply frequency tracking control in such a manner that a driving frequency fsw is made to track a resonant frequency fr (or 1/N thereof, N being an odd number) and that the phase of the driving frequency fsw leads the current zero phase of the resonant frequency fr always by a desired time. As a result, such an optimum condition can be kept that the main switching device is triggered immediately before the zero-cross point of a resonant current. Thus the resonant converter which can always satisfy the optimum operational conditions, realize soft switching operation, and increase an efficiency can be realized with an easy design and a manufacturing adjustment-free arrangement.
1. A resonant converter for converting a direct current to an alternating current as an alternating current output at a semiconductor switching device driven by a driving section, supplying the alternating current output to a primary side of a transformer via resonance circuit, and converting an alternating current flowing through a secondary side of the transformer to a direct current, said converter comprising:
means for making an output frequency of said driving section for driving said semiconductor switching device track a resonant frequency of said resonance circuit or a frequency corresponding to 1/(odd number) thereof.
2. A resonant converter according to claim 1 , wherein means for making the output frequency of said driving section track a resonant frequency of said resonance circuit or a frequency corresponding to 1/(odd number) thereof is provided with a PLL (Phase Locked Loop) circuit.
3. A resonant converter according to claim 1 , wherein a saturable reactor is provided in the secondary side of said transformer.
4. A resonant converter according to claim 1 , wherein a switching device to be driven by a voltage of the secondary side of said transformer is provided in the secondary side of said transformer.
5. A resonant converter according to claim 1 , wherein switching means for switchingly converting a voltage of the secondary side of said transformer to a direct current, a smoothing filter connected to an output side of said switching means and including an inductor and a capacitor, a switching device connected with such a direction as to circulate a current flowing through said smoothing filter and/or a load, and means for driving said switching device during an off period of said switching means are provided in the secondary side of said transformer.
6. A resonant converter according to claim 1 , comprising a synchronous rectification circuit provided with a center tap connected to the secondary side of said transformer and including a switching device, and means for performing PWM control over said switching device.
7. A resonant converter according to claim 1 , comprising a plurality of secondary windings of said transformer and means for converting alternating voltages of the plurality of secondary windings to direct voltages respectively.
8. A resonant converter according to claim 1 , wherein said converter comprises a plurality of transformers, and said common semiconductor switching device and said resonance circuit are connected to primary sides of said plurality of transformers to convert alternating currents flowing through secondary sides of said plurality of transformers to a plurality of direct currents and to output a plurality of direct voltages respectively.
9. A resonant converter according to claim 1 , wherein said means for making the output frequency of said driving section for driving said semiconductor switching device track the resonant frequency of said resonance circuit is arranged to track a frequency corresponding to ⅓ of said resonant frequency.
10. A resonant converter for converting a direct current to an alternating current as an alternating current output at a semiconductor switching device driven by a driving section, supplying the alternating current output to a primary side of a transformer via resonance circuit, and converting an alternating current flowing through a secondary side of the transformer to a direct current, said converter comprising:
means for making an output frequency of said driving section for driving said semiconductor switching device track a resonant frequency of said resonance circuit or a frequency corresponding to 1/(odd number) thereof, and
means for generating the output signal of said driving section with a phase leading a zero-cross point of the resonance current of said resonance circuit.
11. A resonant converter according to claim 10 , comprising a PLL (Phase Locked Loop) circuit for outputting a frequency made to track the resonant frequency of said resonance circuit or a frequency corresponding to 1/(odd number) thereof, and a delay element provided in a feedback loop of said PLL circuit; and wherein said switching device is driven on the basis of an output signal of said PLL circuit.
12. A resonant converter according to claim 10 , wherein a saturable reactor is provided in the secondary side of said transformer.
13. A resonant converter according to claim 10 , wherein a switching device driven by a voltage of the secondary side of said transformer is provided in the secondary side of said transformer.
14. A resonant converter according to claim 10 , wherein switching means for switchingly converting a voltage of the secondary side of said transformer to a direct voltage, a smoothing filter connected to an output side of said switching means and including an inductor and a capacitor, a switching device connected in such a direction as to circulate a current flowing through said smoothing filter and/or a load, and means for driving said switching device during an off period of said switching device are provided in the secondary side of said transformer.
15. A resonant converter according to claim 10 , comprising a synchronous rectification circuit provided with a center tap connected to the secondary side of said transformer and including a switching device, and control means for performing PWM control over said switching device.
16. A resonant converter according to claim 10 , comprising a plurality of secondary windings of said transformer and means for converting alternating voltages of said plurality of secondary windings to direct voltages respectively.
17. A resonant converter according to claim 10 , wherein said converter comprises a plurality of transformers, and said semiconductor switching device and said resonance circuit are commonly connected to primary sides of said plurality of transformers to convert alternating currents flowing through secondary sides of said plurality of transformers to a plurality of direct currents and to output a plurality of direct voltages respectively.
18. A resonant converter according to claim 10 , wherein said means for making the operating frequency of said driving section for driving said semiconductor switching device track the resonant frequency of said resonance circuit is arranged to track a frequency corresponding to ⅓ of said resonant frequency.
19. A method of controlling a resonant converter for converting a direct current to an alternating current as an alternating current output at a semiconductor switching device driven by a driving section, supplying the alternating current output to a primary side of a transformer via resonance circuit, and converting an alternating current flowing through a secondary side of the transformer to a direct current, said method comprising the step of:
making an output frequency of said driving section for driving said semiconductor switching device track a resonant frequency of said resonance circuit or a frequency corresponding to 1/(odd number) thereof.
20. A method according to claim 19 , wherein the output signal of said driving section is generated with a phase leading a zero-cross point of the resonance current of said resonance circuit.