Method of controlling operating depth of an electricity-generating device having a tethered water current-driven turbine

A method of controlling a tethered underwater device having a lift-producing hydrofoil, an adjustable pitch rotor blade-driven turbine, ballast tanks, and a lift-adjusting mechanism, comprising:

• A. sensing electrical energy output that is proportional to velocity of water current flowing past said device;
• B. sensing depth of said device;
• C. providing an initial net ballast to said device resulting in an initial positive buoyancy sufficient to remain above a maximum predetermined depth of said ballast tanks;
• D. balancing forces on said device by adjusting at least one of the parameters of:
• i. lift of said hydrofoil with a lift-adjusting mechanism,
• ii. buoyancy force of said ballast tanks by adjusting the amount of ballast held within said tanks, and,
• iii. drag force loading on said rotors by adjusting the pitch of said rotor blades, such that said device passively seeks an initial equilibrium velocity of water current, located within a chosen predetermined depth range and wherein the forces on said device are balanced, which when flowing past said device is sufficient to keep said device within said depth range;
• and,
• E. upon a condition that said initial equilibrium velocity changes to a new velocity that tends to urge said device out of said depth range, repeating step D to cause said device to operate at a new equilibrium velocity that is within said depth range.

A power-generating device comprising:

• a water current-driven turbine;
• said water current-driven turbine being tethered underwater;
• means for setting a predetermined maximum depth and a predetermined minimum depth;
• means for sensing depth of said device;
• and,
• means operative in response to said means for sensing depth of said device, for selectively invoking an ascend protocol or a descend protocol, said ascend protocol and descend protocol maintaining an operating depth of said device that is between said predetermined maximum depth and said predetermined minimum depth.

A means for controlling a tethered underwater power-generating device having an adjustable pitch rotor blade-driven turbine, ballast tanks and a lift-adjusting mechanism, comprising:

• A. means for sensing an electrical energy output that is proportional to velocity of water current flowing past said device;
• B. means for sensing depth of said device;
• C. means for providing an initial net ballast to said device resulting in an initial positive buoyancy sufficient to maintain a depth that is above a maximum predetermined depth of said ballast tanks;
• D. means for balancing forces on said device by adjusting one or more of the following parameters:
• i. lift force of said hydrofoil using a lift-adjusting mechanism
• ii. buoyancy force of said ballast tanks by adjusting the amount of ballast held within said tanks, and,
• iii. drag force loading on said rotors by adjusting the pitch of said rotor blades, such that said device passively seeks an initial equilibrium velocity of water current, located within a chosen predetermined depth range and wherein the forces on said device balance, such that water flowing past said device is sufficient to keep said device within said depth range;
• and,
• E. further adjusting means operative upon a condition that said initial equilibrium velocity changes to a new velocity that tends to urge said device out of said depth range, for adjusting said parameters to operate at a new equilibrium velocity that is within said depth range.

A power-generating device comprising:

• water current-driven turbine;
• said water current-driven turbine being tethered underwater;
• a control processor;
• a predetermined maximum depth and a predetermined minimum depth being set in said control processor;
• a depth pressure gauge connected to said control processor;
• and,
• a first procedure in said control processor responsive to said depth pressure gauge, said first procedure selectively invoking an ascend protocol or a descend protocol to maintain an operating depth of said device that is between said predetermined maximum depth and said predetermined minimum depth.

A power-generating device comprising:

• a tethered underwater turbine;
• said turbine having a lift-producing hydrofoil, adjustable pitch rotor blades, ballast tanks, and a mechanism to adjust lift produced by said hydrofoil;
• a power output sensor connected to said control processor;
• a depth pressure gauge;
• an initial net ballast being in said device resulting in an initial positive buoyancy sufficient to maintain a depth that is above a maximum predetermined depth of said ballast tanks;
• a first procedure balancing forces on said device by adjusting one or more of the following parameters:
• i. lift produced by said hydrofoil by adjusting said lift-adjusting mechanism;
• ii. buoyancy force of said ballast tanks by adjusting the amount of ballast held within said tanks, and,
• iii. drag force loading on said rotors by adjusting the pitch of said rotor blades;
• such that said device passively seeks an initial equilibrium velocity of water current, located within a chosen predetermined depth range and wherein the forces on the device balance, which when flowing past said device is sufficient to keep said device within said depth range;
• and, a lift-adjusting mechanism control;
• said first procedure further including a second procedure operative upon a condition that said initial equilibrium velocity has changed to a new velocity that tends to urge said device out of said depth range, that causes said lift-adjusting mechanism control to adjust the lift force produced by said hydrofoil to operate at a new equilibrium velocity that is within said depth range.