Multiple-input DC-DC converter

1. A DC-DC converter comprising:

a converter input comprising a first input voltage electrically connected to a first bidirectional switch and a second input voltage electrically connected to a second bidirectional switch, wherein the first bidirectional switch and the second bidirectional switch each comprise a pair of controllable switches in a parallel connection;

an output of the converter input electrically connected with both an inductor and a third bidirectional switch, the third bidirectional switch connected to a ground and the inductor connected to a fourth bidirectional switch and a fifth bidirectional switch, the fourth bidirectional switch connected to the ground and the fifth bidirectional switch connected to a voltage output in connection with a capacitor, wherein the third bidirectional switch comprises a transistor and a diode in parallel, the fourth bidirectional switch comprises a transistor and a diode in parallel and the fifth bidirectional switch comprises a transistor and a diode in parallel;

wherein the first bidirectional switch and the second bidirectional switch can be on to transfer energy simultaneously to the voltage output; and

wherein the voltage output is bucked, boosted or buck-boosted relative to one of the first input voltage or the second input voltage and the voltage output is a same polarity relative to the first input voltage and the second input voltage without use of a transformer; and

wherein the converter operates bidirectionally to provide the output voltage to one of the voltage inputs and the one of the voltage inputs is bucked, boosted or buck-boosted relative to the output voltage and the output voltage is bucked, boosted or buck-boosted by turning on, turning off or switching each of the plurality of bidirectional switches.

2. The DC-DC converter of claim 1 , wherein each of the bidirectional switches is switched on substantially simultaneously with a switched signal;

each of the bidirectional switches has a duty cycle;

a voltage index i is assigned to each voltage source connected to a voltage input of plurality of the voltage inputs such that V1>V2> . . . Vn; and

each of the bidirectional switches has an effective duty cycle D eff(i) of

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3. The DC-DC converter of claim 1 , wherein the first bidirectional switch comprises two parallel MOSFETs and the second bidirectional switch comprises two parallel MOSFETs.

4. A method of operating the DC-DC converter of claim 1 in a buck mode, comprising:

providing a switching frequency with a period to the DC-DC converter;

switching the transistor of the third bidirectional switch off, the transistor of the fourth bidirectional switch off, the transistor of the fifth bidirectional switch off; and

switching at least the first bidirectional switch on for a buck duty cycle and off for a remainder of the period.

5. A method of operating the DC-DC converter of claim 1 in a boost mode, comprising:

providing a switching frequency with a period to the DC-DC converter;

switching the first bidirectional switch on;

switching the transistor of the third bidirectional switch off and the transistor of the fifth bidirectional switch off; and

switching the transistor of the fourth bidirectional switch on for a boost duty cycle and off for a remainder of the period.

6. A method of operating the DC-DC converter of claim 1 in a buck-boost mode, comprising:

providing a switching frequency with a period to the DC-DC converter;

switching the transistor of the third bidirectional switch and the fifth bidirectional switch off; and

switching at least one of the first bidirectional switch or the second bidirectional switch for a buck-boost duty cycle and off for a remainder of the period.

7. The DC-DC converter of claim 1 , wherein the third bidirectional switch comprises a third transistor and a third diode in parallel, the fourth bidirectional switch comprises a fourth transistor and a fourth diode in parallel and the fifth bidirectional switch comprises a fifth transistor and a fifth diode in parallel.

8. The DC-DC converter of claim 7 , wherein the converter operates in a buck mode when the fourth transistor and fifth transistor are off and either the converter input or the third diode conduct.

9. The DC-DC converter of claim 7 , wherein the converter operates in a buck-boost mode when either the third diode and the fifth diode conduct or the fourth transistor and the converter input conduct.

10. The DC-DC converter of claim 7 , wherein the converter operates in a boost mode when the converter input conducts and the third transistor is off and either the fourth transistor or the fifth diode conduct.

11. The DC-DC converter of claim 1 , wherein the first input voltage is selected from the group consisting of a battery, a wind power device, a solar power device, a fuel cell, a photovoltaic cell and an ultracapacitor.

12. The DC-DC converter of claim 1 , wherein the second input voltage is selected from the group consisting of a battery, a wind power device, a solar power device, a fuel cell, a photovoltaic cell and an ultracapacitor.