Control of a multi-rotor wind turbine system using a central controller to calculate local control objectives

1. A control system for a wind turbine system comprising a plurality of wind turbine modules mounted to a common support structure, the control system comprising:

a local controller operable to control an operation of a respective one of the plurality of wind turbine modules, and to issue local control commands thereto to achieve a set of local control objectives; and

a central controller implementing a model predictive control (MPC) routine configured to monitor an operation of the wind turbine system and based on the operation of the wind turbine system calculate the set of local control objectives,

wherein the MPC routine employs a cost function that comprises elements directed to isolated operation of each of the respective one of the plurality of wind turbine modules and at least one element directed to a cross-coupling between at least two of the plurality of wind turbine modules,

wherein the cross-coupling includes a structural cross-coupling between at least two of the plurality of wind turbine modules.

2. The control system according to claim 1 , wherein the model predictive control routine repeatedly calculates a receding horizon trajectory for the wind turbine system and wherein the set of local control objectives is determined based on the receding horizon trajectory for the wind turbine system.

3. The control system according to claim 1 , wherein the central controller is further configured to determine a current operational state of the wind turbine system, and based on the current operational state calculate a predicted operational state trajectory of the wind turbine system, and wherein the set of local control objectives is calculated using the predicted operational state trajectory.

4. The control system according to claim 3 , wherein the current operational state of the wind turbine system is included in the calculation of the set of local control objectives as constraints.

5. The control system according to claim 1 , wherein the local controller is implemented as a control loop feedback controller.

6. The control system according to claim 1 , wherein the local controller is implemented as model predictive controller.

7. The control system according to claim 1 , wherein the structural cross-coupling between the at least two of the plurality of wind turbine modules is defined by a number of pre-determined mode shapes for movement of the wind turbine modules and the common support structure.

8. The control system according to claim 7 , wherein the number of pre-determined mode shapes is selected based on a vibrational frequency of a mode shape being less than a frequency limit.

9. The control system according to claim 7 , wherein the number of pre-determined mode shapes is selected based on a minimum level of vibrational energy being included in the selected number of pre-determined mode shapes.

10. The control system according to claim 7 , wherein the number of pre-determined mode shapes is selected based on loads incurred by a mode shape on the common support structure or elements of the common support structure.

11. The control system according to claim 1 , wherein the cross-coupling includes an aerodynamic cross-coupling between at least two of the plurality of wind turbine modules.

12. A wind turbine system comprising a plurality of wind turbine modules mounted to a common support structure, wherein each of the plurality of wind turbines modules includes a rotor and a power generation system driven by the rotor, wherein the wind turbine system further comprises:

a local controller operable to control an operation of a respective one of the plurality of wind turbine modules, and to issue local control commands thereto to achieve a set of local control objectives; and

a central controller implementing a model predictive control (MPC) routine configured to monitor an operation of the wind turbine system and based on the operation of the wind turbine system calculate the set of local control objectives,

wherein the MPC routine employs a cost function that comprises elements directed to isolated operation of each of the respective one of the plurality of wind turbine modules and at least one element directed to a cross-coupling between at least two of the plurality of wind turbine modules,

wherein the cross-coupling includes a structural cross-coupling between at least two of the plurality of wind turbine modules.

13. A method of controlling a wind turbine system comprising a plurality of wind turbine modules mounted to a common support structure, the method comprising:

controlling an operation of a respective one of the plurality of wind turbine modules to achieve a set of local control objectives;

monitoring an operation of the wind turbine system to determine a current operational state; and

calculating using a model predictive control (MPC) routine and based on the current operational state, the set of local control objectives,

wherein the MPC routine employs a cost function that comprises elements directed to isolated operation of each of the respective one of the plurality of wind turbine modules and at least one element directed to a cross-coupling between at least two of the plurality of wind turbine modules,

wherein the cross-coupling includes a structural cross-coupling between at least two of the plurality of wind turbine modules.

14. A non-transitory computer readable medium including computer program code that, when executed by one or more computer processors, performs an operation to control a wind turbine system comprising a plurality of wind turbine modules mounted to a common support structure, the operation comprising:

generating instructions to a local controller arranged to control an operation of a respective one of the plurality of wind turbine modules to achieve a set of local control objectives;

monitoring an operation of the wind turbine system to determine a current operational state; and

calculating using a model predictive control (MPC) routine and based on the current operational state, the set of local control objectives,

wherein the MPC routine employs a cost function that comprises elements directed to isolated operation of each of the respective one of the plurality of wind turbine modules and at least one element directed to a cross-coupling between at least two of the plurality of wind turbine modules,

wherein the cross-coupling includes a structural cross-coupling between at least two of the plurality of wind turbine modules.