COMBINED DC-DC CONVERTER FOR USE IN HYBRID POWER SYSTEM
FIG6 is an equivalent circuit diagram of the hybrid power supply system in FIG2 in a fourth working mode  FIG5 is an equivalent circuit diagram of the hybrid power supply system in FIG2 in a third working mode
FIG6 illustrates an equivalent circuit diagram of the hybrid power supply system in the fourth working mode. As illustrated in FIG6, the controller 28 controls the bidirectional DC-DC converter 22 to work to provide a pulse width modulation signal to the switch transistor Q1, respectively raise the DC voltage at the two ends of the photovoltaic cell 21 to the predetermined DC bus voltage, and store, in the energy storage capacitor 23, the electric energy from the photovoltaic cell 21. The controller 28 also controls the bidirectional DC-DC converter 25 to work to provide a pulse width modulation signal to the switch transistor Q4, so as to obtain a lowered charging voltage at the input end of the bidirectional DC-DC converter 25, and meanwhile charge the rechargeable battery 24 by using the electric energy in the energy storage capacitor 23.  FIG5 illustrates an equivalent circuit diagram of the hybrid power supply system in the third working mode. As illustrated in FIG5, the bidirectional DC-DC converters 22 & 25 are connected in parallel between the rechargeable battery 24 and the energy storage capacitor 23. The controller 28 controls the bidirectional DC-DC converters 22 & 25 to work to provide pulse width modulation signals to the switch transistors Q1 & Q3, respectively raise the DC voltage at the two ends of the rechargeable battery 24 to the predetermined DC bus voltage, and meanwhile store, in the energy storage capacitor 23, the electric energy from the rechargeable battery 24. Since 6 KW electric energy is provided to the energy storage capacitor 23 via the bidirectional DC-DC converters 22 & 25 collectively, the bidirectional DC-DC converters 22 & 25 with lower power (e.g. 3 KW) may be selected.
diagram
28
controller
11
photovoltaic cell
6
is
['4. The combined DC-DC converter for use in the hybrid power supply system according to claim 1, wherein the first bidirectional DC-DC converter is the same as the second bidirectional DC-DC converter.', '7. The combined DC-DC converter for use in the hybrid power supply system according to any one of claims 1-6, wherein the combined DC-DC converter for use in the hybrid power supply system further comprises a controller used for controlling the on/off state of the switch group and the working mode of the first and second bidirectional DC-DC converter.']