Patent ID: 8547073

Claim:
A DC power supply system of a step-up type comprising: series-connected first, second, third and fourth switching elements each having an anti-parallel-connected diode, a first reactor with one end thereof connected to a point between the series-connected first switching element and the second switching element, a second reactor with one end thereof connected to a point between the series-connected third switching element and the fourth switching element, a DC power supply with one end thereof connected to another end of the first reactor and with another end thereof connected to another end of the second reactor, a first capacitor connected in parallel to the series-connected first switching element and the second switching element, and a second capacitor connected in parallel to the series-connected third switching element and the fourth switching element; a DC output voltage of the DC power supply system being a voltage of a series-connected circuit of the first capacitor and the second capacitor, and the DC power supply system having output terminals of a positive terminal at one end of the first capacitor, a neutral terminal at a point of series-connection of the first capacitor and the second capacitor, and a negative terminal at one end of the second capacitor; the DC power supply system being configured to operate in a first mode and a second mode, wherein in the first mode, the DC power supply system operates under conditions in which a voltage across the first capacitor and a voltage across the second capacitor are lower than a voltage of the DC power supply, electric current in the first and second reactors flows in a discontinuous mode, and the voltage across the first capacitor is higher than the voltage across the second capacitor, and through a procedure in which the second switching element is turned ON to make electric current flow successively through the DC power supply, the first reactor, the second switching element, the second capacitor, the diode of the fourth switching element, and the second reactor, then the second switching element is turned OFF to transfer magnetic energy stored in the first and the second reactors to the first and the second capacitors to charge the first and second capacitors, and then the first and the fourth switching elements are turned ON to discharge the first capacitor down to a voltage at a value before the second switching element is turned ON; and in the second mode, the DC power supply system operates under same conditions as in the first mode except that the voltage across the first capacitor is lower than the voltage across the second capacitor, and through a same procedure as in the first mode except that the third switching element is turned ON and OFF in place of the second switching element and the fourth switching element is turned ON and OFF in place of the first switching element.