Method and system for control power in remote DC power systems

1. A control power supply system comprising:

a first conductor configured to carry a direct current (DC) electrical current from a source to a load; a second conductor configured to carry the DC electrical current from the load to the source; an electrical device electrically coupled in series to at least one of said first and second conductor, said electrical device comprising a plurality of diodes coupled in series with at least one of said first conductor and said second conductor, wherein: each diode of said plurality of diodes coupled in a forward bias direction with respect to a flow of the DC electrical current in said first conductor and said second conductor; and said electrical device configured to only fail in a shorted condition such that failure of said electrical device maintains a DC ring bus comprising said first conductor and second conductor; and a control power circuit electrically coupled in parallel with a portion of said electrical device such that a DC voltage across said portion of said electrical device provides a DC voltage supply to said control power circuit.

2. A control power supply system in accordance with claim 1 , wherein said electrical device comprises at least one semiconductor device.

3. A control power supply system in accordance with claim 1 , wherein said plurality of diodes comprises a press pack housing.

4. A control power supply system in accordance with claim 1 , wherein said control power circuit comprises an active switching device to facilitate converting the DC voltage at a first level to a DC voltage at a second level different from the first level.

5. A control power supply system in accordance with claim 1 , wherein said control power circuit comprises an active switching device controllable to operate at a voltage less than a forward voltage drop of said portion of said electrical device.

6. A control power supply system in accordance with claim 1 , further comprising a capacitive voltage divider configured to supply start-up power to said control power circuit and a second auxiliary power supply configured to supply operating power to said control power circuit.

7. A control power supply system in accordance with claim 6 , wherein said second auxiliary power supply is configured to harvest AC ripple from a switched DC converter.

8. A method of supplying control power supply from a direct current (DC) power cable, said method comprising:

transmitting a DC power current from a sending station to a load station located remotely from the sending station through a DC power cable;

dropping a DC voltage across one or more electrical devices, wherein the one or more electrical devices includes a plurality of diodes coupled in electrical series with the sending station and the load station through the DC power cable, the plurality of diodes further coupled in a forward bias direction with respect to a direction of flow of the DC power current through the DC power cable; and

generating a control power voltage using an active semiconductor switch coupled in electrical parallel with the one or more electrical devices.

9. A method in accordance with claim 8 , further comprising: filtering an AC ripple voltage from the DC power cable, the AC ripple voltage induced onto the DC power cable by a switching action of a plurality of electrical devices; and transmitting the filtered AC ripple voltage to the control power supply.

10. A method in accordance with claim 8 , further comprising supplying a startup power to the AC control power supply using a capacitive voltage divider.