COMBINED DC-DC CONVERTER FOR USE IN HYBRID POWER SYSTEM
FIG7 is an equivalent circuit diagram of the hybrid power supply system in FIG2 in a fifth working mode  FIG8 is an equivalent circuit diagram of the hybrid power supply system in FIG2 in a sixth working mode
FIG7 illustrates an equivalent circuit diagram of the hybrid power supply system in the fifth working mode. As illustrated in FIG7, the controller 28 controls the bidirectional DC-DC converter 22 to work to provide a pulse width modulation signal to the switch transistor Q1 to store, in the energy storage capacitor 23, the electric energy from the photovoltaic cell 21, and controls the bidirectional DC-DC converter 25 to work to provide a pulse width modulation signal to the switch transistor Q4 to charge the rechargeable battery 24 by using the electric energy in the energy storage capacitor 23.  FIG8 illustrates an equivalent circuit diagram of the hybrid power supply system in the sixth working mode. As illustrated in FIG8, the controller 28 controls the bidirectional DC-DC converters 22 & 25 to work to provide pulse width modulation signals to the switch transistors Q2 & Q4, and charge the rechargeable battery 24 by using the electric energy in the energy storage capacitor 23. Since the rechargeable battery 24 is charged by using 6 KW power 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
29
AC power supply
12
DC-DC converter
26
full-bridge inverter
['1. A combined DC-DC converter for use in a hybrid power supply system, the hybrid power supply system comprising a renewable energy power generation device, a rechargeable battery, an energy storage capacitor, and an inverter connected to the energy storage capacitor, wherein the combined DC-DC converter comprises: a first bidirectional DC-DC converter and a second bidirectional DC-DC converter, output ends of the first and second bidirectional DC-DC converters being configured to be connected to the energy storage capacitor; and a switch group configured to connect input ends of the first and second bidirectional DC-DC converters to the two ends of the renewable energy power generation device or the rechargeable battery, or respectively connect the input ends of the first and second bidirectional DC-DC converters to the two ends of the renewable energy power generation device and the rechargeable battery.', '12. The combined DC-DC converter for use in the hybrid power supply system according to claim 7, the hybrid power supply system comprising a bypass switch connected in series to an AC power supply, wherein when the renewable energy power generation device has electric energy and the electric energy in the rechargeable battery is less than a predetermined threshold, the controller is used for: controlling the switch group such that the input ends of the first and second bidirectional DC-DC converters are respectively connected to the two ends of the renewable energy power generation device and the rechargeable battery; controlling the bypass switch to be turned on such that the AC power in the AC power supply is rectified and then stored in the energy storage capacitor; and controlling the first bidirectional DC-DC converter to convert the voltage at the two ends of the renewable energy power generation device into a predetermined DC bus voltage, and controlling the second bidirectional DC-DC converter to charge the rechargeable battery by using the electric energy in the energy storage capacitor.']