A method for controlling brushless d.c. motors and apparatus for carrying out the method

Claim 1

A method for controlling a brushless d.c. motor having at least two phase windings which are supplied with current pulses whose frequency and duration are steered with driving pulses which are synchronized with the rota­tion of the rotor of said motor and the frequency of which driving pulses is related to the motor speed, each driving pulse including two or more pulse-width-modulated part-­pulses (P1, P2, P3 and P4, P5, P6 respectively) which occur at a given part-pulse frequency and with which each part-pulse period comprises a part-pulse followed by a pulse pause, and which method comprises monitoring the motor current for the purpose of detecting the possible occurrence of a maximum current state during a part-pulse within which the motor current has reached a highest per­mitted value and in which method, upon detection of a maximum current state, the pulse-pause/pulse ratio is increased in those part-pulse periods within which said maximum current state was detected, characterized in that upon detection of a maximum current state (Ö1-Ö5) during a part-pulse the part-pulse concerned is inhibited from a given first time point during the remainder of the part-­pulse period, irrespective of whether the maximum current state ceases during this part-pulse period or not; in that if the maximum current state has ceased at the commence­ment of the next part-pulse period in sequence the intro­duction of the next part-pulse takes place at the begin­ning of this period; and in that if it is detected that said maximum current state still prevails at the beginning of the next part-pulse period, the next part-pulse is introduced at that point in time at which the maximum current state ceases to exist.

Claim 2

A method for controlling a brushless d.c. motor having at least two phase windings which are supplied with current pulses whose frequency and duration are steered with driving pulses which are synchronized with the rota­tion of the rotor of said motor and the frequency of which driving pulses is related to the motor speed, each driving pulse including two or more pulse-width-modulated part-­pulses (P1, P2, P3 and P4, P5, P6 respectively) which occur at a given part-pulse frequency and with which each part-pulse period comprises a part-pulse followed by a pulse pause, and which method comprises monitoring the motor current for the purpose of detecting the possible occurrence of a maximum current state during a part-pulse within which the motor current has reached a highest per­mitted value and in which method, upon detection of a maximum current state, the pulse-pause/pulse ratio is increased in those part-pulse periods within which said maximum current state was detected, characterized in that upon detection of a maximum current state (Ö1-Ö5) during a part-pulse the part-pulse concerned is inhibited from a given first time point during the remainder of the part-­pulse period, irrespective of whether the maximum current state ceases during this part-pulse period or not; in that if the maximum current state has ceased at the commence­ment of the next part-pulse period in sequence the intro­duction of the next part-pulse takes place at the begin­ning of this period; and in that if it is detected that said maximum current state still prevails at the beginning of the next part-pulse period, the next part-pulse is introduced at that point in time at which the maximum current state ceases to exist.

Claim 7

A method according to any of claims 3-5, characterized in that detection of a minimum current state is instigated solely when the motor speed exceeds a given value.

Claim 8

A system for controlling a brushless d.c. motor (1) having at least two phase windings (2ʹ, 2ʺ, 3ʹ, 3ʺ, 4ʹ, 4ʺ) said system comprising a power unit (5) which is operative in sending to the phase windings current pulses whose frequency and duration are steered by driving pulses delivered to the power unit (5); a control unit (6) for generating driving pulses that are synchronized with the rotation of the rotor of said motor, the frequency of which driving pulses is in relation with the speed of the motor and each of the driving pulses normally comprises two or more regularly occurring pulse-width-modulated part-pulses (P1, P2, P3 and P4, P5, P6 respectively) followed by pulse pauses; sensing means (8) for monitoring the motor current to detect the possible occurrence of a maximum current state in which the motor current has reached a highest value permitted for the prevailing point in time, the control unit (6) being intended to increase the pulse- pause/pulse ratio during those part-pulse periods within which a maximum current state is detected, characterized in that the control unit includes an arrangement (6; 1C; 6.2; 6.3) which, upon detection of a maximum current state during the generation of a part-pul­se, is operative in shortening the part-pulse supplied to the power unit by the whole of that part of the part-pulse which would normally remain from a given first time point, irrespective of whether or not the state of maximum cur­rent ceases during the remainder of the part-pulse period, and an arrangement (6; 1A; 6.3; 6.4) which, subsequent to the detection of a maximum current state, is operative in instigating the generation of the next-following part-pul­se at the normal commencement of the next part-pulse period if the maximum current state has ceased at this point in time, or to delay the generation of said next following part-pulse to the time point at which the maxi­mum current state ceases if the maximum current state still prevails at the beginning of the next part-pulse period.

Claim 9

A system for controlling a brushless d.c. motor (1) having at least two phase windings (2ʹ, 2ʺ, 3ʹ, 3ʺ, 4ʹ, 4ʺ) said system comprising a power unit (5) which is operative in sending to the phase windings current pulses whose frequency and duration are steered by driving pulses delivered to the power unit (5); a control unit (6) for generating driving pulses that are synchronized with the rotation of the rotor of said motor, the frequency of which driving pulses is in relation with the speed of the motor and each of the driving pulses normally comprises two or more regularly occurring pulse-width-modulated part-pulses (P1, P2, P3 and P4, P5, P6 respectively) followed by pulse pauses; sensing means (8) for monitoring the motor current to detect the possible occurrence of a maximum current state in which the motor current has reached a highest value permitted for the prevailing point in time, the control unit (6) being intended to increase the pulse- pause/pulse ratio during those part-pulse periods within which a maximum current state is detected, characterized in that the control unit includes an arrangement (6; 1C; 6.2; 6.3) which, upon detection of a maximum current state during the generation of a part-pul­se, is operative in shortening the part-pulse supplied to the power unit by the whole of that part of the part-pulse which would normally remain from a given first time point, irrespective of whether or not the state of maximum cur­rent ceases during the remainder of the part-pulse period, and an arrangement (6; 1A; 6.3; 6.4) which, subsequent to the detection of a maximum current state, is operative in instigating the generation of the next-following part-pul­se at the normal commencement of the next part-pulse period if the maximum current state has ceased at this point in time, or to delay the generation of said next following part-pulse to the time point at which the maxi­mum current state ceases if the maximum current state still prevails at the beginning of the next part-pulse period.

Claim 11

A system according to any of claims 7 or 8, characteri­zed in that the sensing means (8) for monitoring the motor current are also arranged to monitor for the eventuality of a minimum current state in which, during a part-pulse period within which a maximum current state has been detected, the value of the motor current lies at an abso­lute pre-set minimum for the duration of this part-pulse period; and in that an arrangement (6.10, 6.11, 6.12, 6.13) is provided for shortening an occurrent part-pulse period upon the detection of a minimum current state while retaining an ordinary period length (T) for subsequent part-pulse periods.