Series resonant converter having a circuit configuration that prevents leading current
A series resonant converter of the present invention includes an inverter circuit having at least a pair of a first and second switching device connected between two input terminals, a transformer having a primary winding and a secondary winding connected to the inverter circuit, a first and second resonant capacitor connected to a secondary side of the transformer and connected in series to each other between two output terminals, a first and second unidirectional device connected in series to each other, and a resonant induction device that is operated along with the first and second resonant capacitor and resonates in series. The first and second unidirectional device are configured such that current does not flow from the first and second resonant capacitor to the input terminal by preventing electric charge of the first and second resonant capacitor from being discharged to a primary side of the transformer.
1. A series resonant converter, comprising:
an inverter circuit including at least a first switching device and a second switching device, each of the first and second switching devices being directly connected between two input terminals connecting DC power supply, the inverter circuit including a first feedback diode arranged in parallel with the first switching device and having a reversed polarity opposite to that of the first switching device and a second feedback diode arranged in parallel with the second switching device and having a reversed polarity opposite to that of the second switching device;
a transformer, having a primary winding and a secondary winding, connected to the inverter circuit;
a first resonant capacitor and a second resonant capacitor connected in series to each other between two output terminals, a connection point of the first resonant capacitor and the second resonant capacitor being connected to one end of the secondary winding of the transformer;
a first unidirectional device and a second unidirectional device connected in series to each other between the two output terminals, a connection point of the first unidirectional device and the second unidirectional device being connected to a second end of the secondary winding of the transformer; and
a resonant induction device that is placed between the inverter circuit and the first and second resonant capacitors, wherein
the first switching device and the second switching device are configured to be turned on and off alternately with a conversion frequency, and the inverter circuit being configured to convert DC power inputted from the two input terminals and supply a DC output voltage to the two output terminals via the transformer, a length of the on durations of the first switching device and the second switching device are fixed to about one half cycle of a series resonance frequency with which inductance of the resonant induction device and an additive capacitance which adds capacitance of the first resonant capacitor and the second resonant capacitor are resonated in series,
the conversion frequency used for the inverter circuit being below the series resonance frequency, and
the DC output voltage being set equal to double the voltage of the DC power supply, and a resonance impedance (L/C) 1/2 determined by the inductance of the resonant induction device and additive capacitance being selected so that voltages of the first resonant capacitor and the second resonant capacitor are reverse phases to each other, and change up to voltage of amplitude, which is equal to the DC output voltage, from 0 V.
2. The series resonant converter according to claim 1 , wherein
the inverter circuit comprises a first feedback diode arranged in parallel with the first switching device and having a reversed polarity opposite to that of the first switching device, and a second feedback diode arranged in parallel with the second switching device and having a reversed polarity opposite to that of the second switching device.
3. The series resonant converter according to claim 1 , further comprising:
at least one reverse charge control device operative to prevent reverse direction charge of the first resonant capacitor or the second resonant capacitor, the reverse charge control device being connected in parallel with the first resonant capacitor or the second resonant capacitor, respectively.
4. The series resonant converter according to claim 1 , wherein
the inverter circuit comprises any of the following circuit configurations of:
a half-bridge circuit in which the first switching device and the second switching device are connected in series;
a full-bridge circuit connected in parallel with two switching device arms in which the first switching device and the second switching device are connected in series; and
a push-pull type circuit connecting the first switching device with the second switching device between the input terminal and two terminals of the primary winding of the transformer in which an intermediate tap is provided.
5. The series resonant converter according to claim 1 , wherein
inductance of the resonant induction device, and capacitance of the first resonant capacitor and capacitance of the second resonant capacitor are selected so that the inductance of the resonant induction device and additive capacitance which adds the capacitance of the first resonant capacitor and the second resonant capacitor are resonated in series at a resonance frequency which is substantially equal to a conversion frequency of the inverter circuit.
6. The series resonant converter according to claim 1 , wherein
the first switching device and the second switching device operate at a conversion frequency of the inverter which is below a resonance frequency fixed by the resonant induction device, the first resonant capacitor and the second resonant capacitor.
7. The series resonant converter according to claim 1 , wherein
the first unidirectional device comprises a first field-effect transistor and the second unidirectional device comprises a second field-effect transistor,
the first field-effect transistor being synchronized with the first switching device of the inverter circuit and turns ON simultaneously therewith, and
the second field-effect transistor configured to perform synchronous rectification by turning on to be synchronous with the second switching device of the inverter circuit.
8. The series resonant converter according to claim 1 , further comprising:
a smoothing capacitor, which has a higher capacitance than the first resonant capacitor or the second resonant capacitor, connected in parallel with a series circuit of the first unidirectional device and the second unidirectional device.
9. The series resonant converter according to claim 1 , further comprising:
a resonant inductor configured to impart at least a portion of the inductance of the resonant induction device connected in series with the first winding or the second winding of the transformer.
10. The series resonant converter according to claim 1 , wherein
at least a portion of the inductance of the resonant induction device comprises a leakage inductance caused by leakage flux between the first winding and the second winding of the transformer.
11. The series resonant converter according to claim 1 , wherein
the first switching device or the second switching device are turned off after energy accumulated in the resonant induction device is discharged.
12. The series resonant converter according to claim 2 , wherein
energy accumulated in the resonant induction device is supplied to the output terminal via one of the first feedback diode or the second feedback diode in the state where the first switching device or the second switching device of the inverter circuit are turned off, and
energy accumulated in the resonant induction device is returned to the input terminal and supplied to the output terminal via the first feedback diode or the second feedback diode in the state where the first switching device and the second switching device are simultaneously turned off.
13. The series resonant converter according to claim 1 , wherein
the voltage of the DC power supply at the input terminals is applied as reverse voltage to the first feedback diode or the second feedback diode, thereby preventing recovery current from flowing through the first feedback diodes or the second feedback diode.
14. The series resonant converter according to claim 1 , wherein
energy accumulated in the resonant induction device is supplied to the output terminal via one of the first feedback diode or the second feedback diode in the state where the first switching device or the second switching device of the inverter circuit is turned off, and
energy accumulated in the resonant induction device is returned to the input terminal and supplied to the output terminal via the first feedback diode or the second feedback diode in the state where the first switching device and the second switching device are simultaneously turned off.