System for regulating above-synchronous speed of an a.c. motor

Claim 1

IN A REVERSIBLE DRIVE SYSTEM EMPLOYING AN A.C. MOTOR WHICH FOR A PARTICULAR DIRECTION OF MOTOR TRAVEL PROVIDES REGENERATIVE BRAKING WHEN THE MOTOR IS TRAVELING IN SAID DIRECTION AT ABOVE-SYNCHRONOUS SPEED AND THE MOTOR IS EXCITED WITH THE PARTICULAR SENSE OF EXCITATION REQUIRED TO DRIVE THE MOTOR IN SAID DIRECTION AT SUBSYNCHRONOUS SPEED, AND WHEREIN 1ST AND 2ND ADJUSTABLE EXCITATION MEANS SUPPLY 1ST AND 2ND EXCITATION SENSES, RESPECTIVELY, TO SAID MOTOR TO OPERATE THE MOTOR IN RESPECTIVE OPPOSITE DIRECTIONS, CONTROL MEANS HAVING 1ST AND 2ND SELECTABLE MODES, MEANS RESPONSIVE TO SAID 1ST AND 2ND MODES FOR RESPECTIVELY PROVIDING 1ST AND 2ND OPPOSITELY SENSED REFERENCE SIGNALS, MEANS FOR PROVIDING A SPEED RESPONSIVE SIGNAL WHICH IS A FUNCTION OF THE SPEED OF SAID MOTOR AND WHOSE SENSE IS DEPENDENT ON THE TRAVEL DIRECTION OF THE MOTOR, MEANS RESPONSIVE TO SAID CONTROL MEANS IN SAID FIRST MODE FOR PROVIDING TO EACH OF SAID EXCITATION MEANS A FIRST RESULTANT CONTROL FORCE PRODUCED BY A COMBINATION OF SAID 1ST REFERENCE SIGNAL AND SAID SPEED RESPONSIVE SIGNAL IN OPPOSITION TO EACH OTHER, ANY GIVEN SENSE OF SAID RESULTANT FORCE HAVING OPPOSITE CONTROL EFFECTS ON SAID 1ST AND 2ND EXCITATION MEANS, WHEREBY A PARTICULAR SENSE OF SAID 1ST RESULTANT DRIVES ONLY ONE OF SAID EXCITATION MEANS UPWARD, AND THE OPPOSITE SENSE OF SAID 1ST RESULTANT DRIVES ONLY THE OTHER OF SAID EXCITATION MEANS UPWARD, AND MEANS RESPONSIVE TO SAID CONTROL MEANS IN SAID SECOND MODE FOR PROVIDING TO ONLY SAID ONE EXCITATION MEANS A SECOND RESULTANT CONTROL FORCE PRODUCED BY A COMBINATION OF SAID 2ND REFERENCE SIGNAL AND SAID SPEED RESPONSIVE SIGNAL IN OPPOSITION TO EACH OTHER, SAID ONE EXCITATION MEANS BEING DRIVEN UPWARD IN RESPONSE TO SAID SECOND RESULTANT BEING OF SAID OPPOSITE SENSE.