Method of controlling an actuator system and aircraft using said method

1. A method of controlling an actuator system comprising a plurality of k actuators, wherein said actuators are configured as individual propulsion units of a multiactuator aerial vehicle, the method comprising:

sending, by a controller, a control input u i to each of said actuators during operation, and each of the actuators receiving the control input u i , wherein index i denotes a particular one of the actuators,

determining the control input u i depending on a weight matrix W comprising a weighting factor w i for each said actuator and depending on at least a physical maximum control limit u i max for each of the actuators,

actively changing both said weighting factor w i and said physical maximum control limit u i max during operation of the actuator system when a first comparison, for at least some of the actuators, of said control input u i or a function ƒ(u i ) thereof with a set first threshold value)) (ƒ i (u i avail ) yields that said control input u i or said function ƒ(u i ) thereof exceeds said set first threshold value (ƒ i (u i avail )),

augmenting a first counter (t i avail ) whenever said first comparison yields that said control input u i or said function ƒ i (u i ) thereof exceeds said first set threshold value (ƒ i (u i avail )), and adjusting at least the weight matrix W based on a value of a weighting function (wf1) that is dependent on the current value of said first counter (t i avail );

repeating said first comparison over time during operation of the actuator system; and

determining a new control input u i from both an adjusted weighting factor w i and an adjusted physical maximum control limit u i max and applying the new control input u i to the actuators.

2. The method of claim 1 , wherein said control input u i is determined based on a pseudo control input u p , wherein u p =Du, D being an allocation matrix dependent on at least u i max, wherein determining u includes solving an equation u=D −1 u p , D −1 being an inverse allocation matrix and defined as D −1 (W,u max ), W being said weight matrix, wherein the inverse allocation matrix D −1 is adjusted according to adjusted values of W and u i max ; and

wherein the new control input u i is determined from the adjusted inverse allocation matrix D −1 and applied to the actuators.

3. The method of claim 1 , wherein said first threshold value (ƒ i (u i avail )) comprises an available control limit (u i avail ) for each said actuator, said available control limit (u i avail ) being a control input at which a given one of the actuators functions continuously without overload.

4. The method of claim 1 , further comprising augmenting a second counter (t i max ) whenever the first comparison and any successive comparisons yield that said control input u i or said function ƒ i (u i ) thereof exceeds said corresponding set threshold value (ƒ i (u i max )), and adjusting at least the weight matrix W based on a current value of said second counter (t i max ).

5. The method of claim 4 , wherein the adjusting of at least the weight matrix W based on the current value of said second counter (t i max ) is based on a value of a second weighting function (wf2) that is dependent on said current value of said second counter (t i max ).

6. The method of claim 4 , wherein the weight matrix W is adjusted based on the current value of at least one of the first counter or the second counter, only when at least one of the first counter or said second counter does not exceed its respective set threshold value (ƒ i (u i avail ), ƒ i (u i max )).

7. The method of claim 4 , wherein u i max is adjusted to a lower value, said lower value being an available control input (u i avail ) at which a given actuator can function continuously without overload, when said first counter (t i avail ) exceeds a set first counter threshold ( t i avail ).

8. The method of claim 1 , further comprising:

augmenting a first counter (t i avail ) whenever said first comparison yields that said control input u i or said function ƒ i (u i ) thereof exceeds said first set threshold value (ƒ i (u i avail )), and adjusting at least the weight matrix W based on a current value of said first counter (t i avail ), and

actively changing W and u i max during operation of the actuator system based on a second comparison, for at least some of the actuators, of the control input u i or said function ƒ i (u i ) thereof with at least a second set threshold value (ƒ i (u i max )) for said control input u i or said function ƒ i (u i ) thereof, when said second comparison yields that said control input u i or said function ƒ i (u i ) thereof exceeds said second set threshold value (ƒ i (u i max )), and when a second counter (t max ), which second counter (t max ) is augmented whenever said second comparison yields that said control input u i or said function ƒ i (u i ) thereof exceeds said second set threshold value (ƒ i (u i max )) exceeds a set second counter threshold ( t i max ), whereupon u i max is adjusted to a lower value available control input (u i avail ), said lower value available control input (u i avail ) being the control input (u i avail ) at which a particular one of the actuators functions continuously without overload, said second comparison being repeated over time during operation of the actuator system, wherein said second set threshold value (ƒ i (u i max )) comprises the maximum control limit (u i max ) for each said actuator, said maximum control limit (u i max ) being the control limit (u i max ) at which a particular one of said actuators functions only during a limited amount of time without overload.

9. The method of claim 8 , wherein, when either said first counter (t i avail ) exceeds a set first counter threshold ( t i avail ) or said second counter (t i max ) exceeds said set second counter threshold ( t i max ), a third counter (t i cd ) is decreased and the weighting w i is set to a default value, with w i being equal to unity and u i max is set to u i avail , and when said third counter (t i cd ) has reached a third set counter threshold, said first, second, and third counters (t i avail , t i max , t i cd ) are reset to a respective initial value thereof and also u i max is set to its initial value u i max,init .

10. The method of claim 9 , wherein, based on a third comparison, for at least some of the actuators, of the control input u i or a function ƒ i (u i ) thereof with said first set threshold value (ƒ i (u i avail )) and of said third counter (t i cd ) with said third set counter threshold, when said third comparison yields that said control input u i or said function ƒ i (u i ) thereof does not exceed said first set threshold value (ƒ i (u i avail )) and that said third counter (t i cd ) has its initial value (t i cd,init ), then at least w i is set to the default value, with w i being equal to unity, said third comparison being repeated over time during operation of the actuator system.

11. The method of claim 10 , wherein, when said third comparison yields that said control input u i or said function ƒ i (u i ) thereof does not exceed said first set threshold value (ƒ i (u i avail )) and that said third counter (t i cd ) has its initial value (t i cd,init ), at least one of said first counter (t i avail ) is decreased or said second counter (t i max ) is decreased.

12. The method of claim 11 , wherein, when a subsequent comparison yields that said first counter (t i avail ) is below a first lower bound or that said second counter (t i max ) is below a second lower bound, said first counter (t i avail ) or said second counter (t i max ), respectively, is reset to its initial value thereof.

13. The method of claim 12 , wherein, when both said first counter (t i avail ) and said second counter (t i max ) have their respective initial values, then at least w i is set to the default value, with w i being equal to unity.

14. An aircraft comprising:

an actuator system including a plurality of k actuators, said actuators being configured as individual propulsion units of the aircraft, each of said actuators, during operation, is adapted to receive, from at least one flight control unit, a control input u i , wherein index i denotes a particular one of said actuators, wherein said control input u i is determined by at least one computer algorithm performed on said at least one flight control unit, the at least one flight control unit by performing said algorithm, is configured to:

determine the control input u i depending on a weight matrix W comprising a weighting factor w i for each said actuator and depending on at least a physical maximum control limit u i max for each of the actuators,

actively change both said weighting factor w i and said physical maximum control limit u i max during operation of the actuator system when a first comparison, for at least some of the actuators, of said control input u i or a function ƒ(u i ) thereof with a set first threshold value)) (ƒ i (u i avail ) yields that said control input u i or said function ƒ(u i ) thereof exceeds said set first threshold value (ƒ i (u i avail )),

augmenting a first counter (t i avail ) whenever said first comparison yields that said control input u i or said function ƒ i (u i ) thereof exceeds said first set threshold value (ƒ i (u i avail )), and adjusting at least the weight matrix W based on a value of a weighting function (wf1) that is dependent on the current value of said first counter (t i avail ):

repeat said first comparison over time during operation of the actuator system; and

determine a new control input u i from both an adjusted weighting factor w i and an adjusted physical maximum control limit u i max and applying the new control input u i to the actuators.

15. The aircraft of claim 14 , further comprising sensors configured to provide sensor data representative of a physical and operational state of the aircraft, and the least one flight control unit is configured to determine a pseudo control input u pj from said sensor data.