Patent Description:
Actuators, which comprise an electric motor in connection with a controller for controlling operation of the electric motor, are used in many areas of application where parts need to be actuated by the electric motor in a controlled fashion. Particularly, in applications where mechanical parts need to be actuated into defined positions and/or orientations, actuators are equipped with controllers that are configured to determine the current motor position of the electric motor and to control operation of the electric motor, such as to move the electric motor or the actuated part, respectively, to a set target position and/or orientation. Examples of application include actuating and positioning dampers or shutters of fluid ducts or ports, regulating members of valves, e.g. balls in ball valves or discs in disc valves, or the like. In scenarios and situations where there is dynamically changing external influences and forces affecting the actuated parts, e.g. wind on the shutter of an air intake port, varying pressure in a fluid transportation system, etc., the current position of the electric motor or the actuated part, respectively, must be monitored continuously and readjusted, if necessary, in order to maintain a set target position. Maintaining the target position of the electric motor or the actuated part, target position. Maintaining the target position of the electric motor or the actuated part, respectively, in the presence of external forces and influences on the actuated parts may require significant amounts of electric energy. For the actual operation of the electric motor an inherent cogging torque is a further undesirable influential factor. Cogging torque of electrical motors is produced as a result of the interaction between permanent magnets of the rotor and the stator slots. The cogging torque is especially prominent at lower speeds and can be observed as stuttering or jerky movement.

<CIT> describes a brushless direct current motor with cogging torque.

In the field of couplings for transmitting rotation, clutches and brakes, <CIT> describes an electric brake for motor vehicles. The electric brake of <CIT> has a blocking brake function produced by pronounced stator and rotor poles and applying defined blocking current to bring poles into latching position.

<CIT> in particular relates to an electromechanical brake in motor vehicles. The brake contains an electric motor having a holding brake function. To generate the holding brake function, an electric motor with salient stator poles and rotor poles is provided. The motor is acted upon by a defined holding current in such a way that the poles of the motor thereby are brought into a locked position and held there, or are held in a locked position. In addition, after activation of the holding brake function and after a locked position has been reached, the current delivered to the motor for braking is very substantially decreased. The electrical brake can optionally act on the brake caliper with a spindle and a linkage, the electric motor driving and braking the spindle.

<CIT> describes a method and actuation control for stopping an electrical drive, by means of closed-loop position control, in a predetermined nominal position.

<CIT> describes a safety drive for a flap or a valve. The safety drive comprises an actuator with a controllable electric motor and a capacitive energy storage, configured to power the electric motor to a specified safety position, in case of a power failure.

It is an object of this invention to provide an actuator with an electric motor and a method of controlling the electric motor to drive an actuated part of an HVAC system to a target position and maintain a current position. In particular, it is an object of the present invention to provide an actuator with an electric motor having cogging torque, and a method of controlling the electric motor to drive an actuated part of an HVAC system to a target position and maintain a current motor position, whereby at least some electric energy required for maintaining a target position can be reduced.

According to the present invention, the above-mentioned objects are achieved by features as defined in the independent claim <NUM>.

In an embodiment, the circuit is configured to reduce the motor torque as long as the current motor position is within the defined range around the selected stable position.

In a further embodiment the circuit is configured to keep the motor torque at zero when the motor torque has been reduced to zero and the current motor position is within the defined range around the selected stable position.

In an embodiment, the circuit is configured to increase the motor torque to return the motor position within the defined range around the selected stable position when the current motor position has moved outside the defined range around the selected stable position.

In a further embodiment, the circuit is configured to record a value of the motor torque when the current motor position has reached a boundary of the defined range around the selected stable position, to increase the motor torque to return the motor position within the defined range around the selected stable position, and to reduce the motor torque as long as the current motor position is within the defined range around the selected stable position, using the recorded value of the motor torque for determining a limit of reducing the motor torque.

In an embodiment, the circuit is configured to determine the set of stable positions by controlling the electric motor to move in incremental steps, determining the motor torque to maintain the motor position at the incremental steps, and determining the set of stable positions from the incremental steps requiring the smallest motor torque to maintain the motor position.

In a further embodiment, the actuator further comprises an electrical energy store configured to drive the electric motor to a defined safety position in case of a power failure.

In addition to the actuator, the present invention also relates to a damper for an HVAC system comprising a damper blade and the actuator coupled to the damper blade for moving the damper blade.

In addition to the actuator and the HVAC damper, the present invention also relates to a method of controlling an electric motor to drive an actuated part of an HVAC system to a target position and maintain a current motor position. The method comprises a controller determining the current motor position of the electric motor, the controller determining from a set of stable positions, defined by cogging torque of the electric motor, a selected stable position closest to the current motor position, and the controller controlling a motor torque of the electric motor to maintain the motor position within a defined range around the selected stable position.

In an embodiment, the controller reduces the motor torque as long as the current motor position is within the defined range around the selected stable position.

In a further embodiment, the controller keeps the motor torque at zero when and if the motor torque has been reduced to zero and the current motor position is within the defined range around the selected stable position.

In an embodiment, the controller increases the motor torque to return the motor position within the defined range around the selected stable position when and if the current motor position has moved outside the defined range around the selected stable position. In a further embodiment, the controller records a value of the motor torque when the current motor position has reached a boundary of the defined range around the selected stable position, the controller increases the motor torque to return the motor position within the defined range around the selected stable position, and the controller reduces the motor torque as long as the current motor position is within the defined range around the selected stable position, using the recorded value of the motor torque for determining a limit of reducing the motor torque.

In an embodiment, the controller determines the set of stable positions by controlling the electric motor to move in incremental steps, determining the motor torque to maintain the motor position at the incremental steps, and determining the set of stable positions from the incremental steps requiring the smallest motor torque to maintain the motor position.

In addition to the actuator, the HVAC damper, and the method of controlling the electric motor, the present invention also relates to a computer program product comprising a non-transient computer readable medium. The computer program product or the non-transient computer readable medium, respectively, has stored thereon computer program code configured to control a processor of an actuator such that the processor controls an electric motor of the actuator to drive an actuated part of an HVAC system to a target position and maintain a current motor position, by determining the current motor position of the electric motor, determining from a set of stable positions, defined by cogging torque of the electric motor, a selected stable position closest to the current motor position, and controlling a motor torque of the electric motor to maintain the motor position within a defined range around the selected stable position.

The present invention will be explained in more detail, by way of example, with reference to the drawings in which:.

In <FIG>, reference numeral <NUM> refers to an actuator comprising an electric motor <NUM>, specifically an electric motor <NUM> which has cogging torque, e.g. a brushless direct current motor, and a motor controller <NUM> comprising a control circuit <NUM>. The actuator <NUM> is an HVAC actuator configured to drive an actuated part of an HVAC system to a target position, i.e. a set actuation position or actuated position within a range of actuatable positions, e.g. in a range from a fully closed to a fully open position, or from a defined minimum position to a defined maximum position. As illustrated in <FIG>, the actuator <NUM> further comprises an energy store <NUM>, e.g. a battery or a capacitor, e.g. a supercapacitor (SC) such as a Lithium-ion capacitor (LIC). The energy store <NUM> is configured to power the electric motor <NUM>, specifically in an emergency situation with power failure, such as to drive the electric motor <NUM> and an actuated part actuated by the electric motor <NUM> to a defined safety position. For example, in an emergency situation, the energy store <NUM> powers the electric motor <NUM> to drive a damper to a closed or fully open position, depending on the respective application and scenario. The control circuit <NUM> comprises a programmable processor, an application specific integrated circuit (ASIC), or another electronic circuit configured to control the electric motor <NUM>. In the configuration involving a programmable processor, the actuator <NUM> further comprises or is connectable with a computer program product, which comprises a non-transient computer readable medium, having stored thereon programmed software modules with computer program code configured to control the processor, such that the processor controls the electric motor <NUM> to maintain a current motor position as described below in more detail.

As illustrated in <FIG>, the control circuit <NUM> comprises various functional modules which are implemented as electronic sub-circuits or programmed software modules controlling a processor, respectively. The functional modules include a position controller <NUM>, a speed controller <NUM>, a holding torque controller <NUM>, a limiter <NUM>, a current controller <NUM>, and a position feedback module <NUM>. The position controller <NUM> is configured to control the electric motor <NUM> or motor current, respectively, to move to a set target position, defined by a number of motor rotations, or an angle or position of an actuated part. The speed controller <NUM> is configured to control the speed of the motor according to a set motor speed. The holding torque controller <NUM> is configured to control the motor current or torque, respectively, such as to maintain a current motor position, as explained below in more detail with reference to <FIG>. The limiter <NUM> is configured to control the motor current within set limits of power, current, torque, and/or motor temperature. The current controller <NUM> is configured to control the motor current depending on control signals from the position controller <NUM>, the speed controller <NUM>, the holding torque controller <NUM>, and/or the limiter <NUM>. The position feedback module <NUM> is configured to determine and provide the current position of the electric motor <NUM> and/or its actuated part, respectively.

In <FIG>, reference numeral <NUM> refers to a damper, specifically a damper for a Heating, Ventilating, and Air Conditioning (HVAC) system. As illustrated in <FIG>, the damper comprises an actuated part <NUM>, specifically a damper blade <NUM> for adjusting the orifice of the damper <NUM> and thereby the flow of fluid, e.g. air, through the damper <NUM>. As further illustrated in <FIG>, the actuated part <NUM>, i.e. the damper blade <NUM>, is mechanically coupled to the actuator <NUM> by way of a mechanical coupling <NUM>, e.g. a drive shaft, for actuation by the actuator <NUM> or its electric motor <NUM>, respectively. The actuator <NUM> or its motor <NUM>, respectively, drives or moves the actuator part <NUM>, i.e. the damper blade <NUM>.

<FIG> shows in the upper graph the course of the magnetic energy E of the electric motor <NUM>, as a function of or depending on the motor angle Φ (or the motor position, respectively). The lower graph of <FIG> shows the course of the cogging torque C of the electric motor <NUM>, as a function of or depending on the motor angle Φ (or the motor position, respectively). As indicated in <FIG>, the position or angle Φ of the electric motor <NUM> has stable positions P1, P2 and (stable) ranges R1, R2 around these stable positions P1, P2 where positive (+) cogging torque C and negative (-) cogging torque C draws the electric motor <NUM> towards the stable positions P1, P2; whereas in (instable) ranges around instable positions P3 positive (+) cogging torque C and negative (-) cogging torque C pulls the electric motor <NUM> away from the instable positions P3.

As illustrated in <FIG>, in preparatory step S0, the motor controller <NUM> or its circuit <NUM>, respectively determines the stable positions P1, P2 of the electric motor <NUM> (position or angle Φ). Furthermore, the motor controller <NUM> or its circuit <NUM>, respectively determines defined ranges R1, R2 around the stable positions P1, P2, e.g. as portion of the distance or difference d between two consecutive stable positions P1, P2, d=P2-P1, e.g. a range R of R=[P-<NUM>%·d; P+<NUM>%·d] around a stable position P. For example, in a motor configuration where stable positions P1, P2 occur every <NUM>°, i.e. d=<NUM>°, the range R around a stable position P is defined by R=[(P-<NUM>°)<Φ; Φ>(P+<NUM>°)], e.g. around P1: R1=[-<NUM>°<Φ; Φ<<NUM>°], or around P2: R2=[<NUM>°<Φ; Φ<<NUM>°]. Specifically, the stable positions P1, P2 (and ranges R1, R2) are stored in a data store of the motor controller <NUM> or its circuit <NUM>, respectively. Depending on the embodiment and/or configuration, the stable positions P1, P2 (and ranges R1, R2) are determined by performing a calculation, based on a known configuration of the magnetic poles of the stator and the rotor of the electric motor <NUM>, specifically based on the number of magnetic poles on the stator (e.g. an internal stator with nine magnetic poles) and the number of magnetic poles on the rotor (e.g. an external rotor with six magnetic poles) of the electric motor <NUM>, or by performing a measurement run of the electric motor <NUM>. For example, the calculation is performed "off-line" for the particular type and (magnetic) configuration of the electric motor <NUM> and stored in the motor controller <NUM> at manufacturing time or a later point in time. In case of the measurement run, the circuit <NUM> of the motor controller <NUM> controls the electric motor <NUM> to move in incremental steps, e.g. a rotation of one degree or of a partial degree, and determines the motor torque required to maintain the motor position at the incremental steps. Subsequently, the set of stable positions are determined as those incremental steps which require the smallest motor torque to maintain the motor position.

In step S1, the motor controller <NUM> or its circuit <NUM>, respectively, receives or sets a target position for the electric motor <NUM> or a target value that relates to a target position for the electric motor <NUM>. Depending on the application and/or installation, the target position or target value is defined and set by a building control system or a user terminal communicatively connected to the electric motor <NUM>.

In step S2, the motor controller <NUM> or its circuit <NUM>, respectively, controls the electric motor <NUM> to move to the set target position, e.g. to perform a certain number of rotations corresponding to a set rotary position (angle) or for driving an actuated part to a set (actuated) position. As illustrated schematically in <FIG>, the motor controller <NUM> uses the position controller <NUM>, the speed controller <NUM>, the limiter <NUM>, and the current controller <NUM> to control the electric motor <NUM> to reach the target position.

In step S3, the motor controller <NUM> or its circuit <NUM>, respectively, determines whether the electric motor <NUM> or the actuated part, respectively, has reached the target position. Specifically, the position feedback module <NUM> determines and indicates the current position of the electric motor and/or the actuated part driven by the electric motor <NUM>. If the target position has not been reached yet, control of the electric motor <NUM> is continued in step S2; otherwise, if the target position has been reached, a process of maintaining the current motor position is activated. For example, for that purpose, the position feedback module <NUM> or the circuit <NUM> or motor controller <NUM>, respectively, activates the holding control torque controller <NUM>.

In step S4, the holding control torque controller <NUM> or the circuit <NUM> or motor controller <NUM>, respectively, controls the electric motor <NUM> to maintain its position at the current position or target position, respectively, as described below in more detail with reference to sub-steps S41, S42, S43, S44, and S45. One skilled in the art will understand that external forces and influences, such as a wind gust on a damper blade <NUM> of an external air damper <NUM> or a pressure change inside a fluid duct, will have an impact on the motor position and will have to be compensated by adapting the motor torque or motor current, respectively, to hold against the external force or influence, such as to maintain a target position.

In step S41, the holding control torque controller <NUM> or the circuit <NUM> or motor controller <NUM>, respectively, determines the stable position closest to the target position or current position of the electric motor <NUM>.

In step S42, the holding control torque controller <NUM> or the circuit <NUM> or motor controller <NUM>, respectively, checks whether the current position of the electric motor <NUM> is within the range R1, R2 around the stable position P1, P2 determined in step S41. If the current position is within the respective range R1, R2, the process proceeds in step S43; otherwise, if the current position is outside the respective range R1, R2, processing proceeds in step S45 by increasing the motor torque or motor current, respectively.

In step S43, the holding control torque controller <NUM> or the circuit <NUM> or motor controller <NUM>, respectively, checks whether the current motor torque or the motor current, respectively, is at zero, i.e. whether the electric motor <NUM> maintains its current position without requiring any motor current and, thus, not producing motor torque. If the current motor torque or the motor current, respectively, is at zero, the torque is maintained at zero and the processing continues in step S42. Otherwise, if the current motor torque or the motor current, respectively, is not at zero, processing continues in step S44 by reducing the motor torque or motor current, respectively.

In step S44, the holding control torque controller <NUM> or the circuit <NUM> or motor controller <NUM>, respectively, reduces the motor torque or the motor current, respectively, e.g. by a predetermined amount or portion.

In an embodiment, the holding control torque controller <NUM> or the circuit <NUM> or motor controller <NUM>, respectively, determines the duration, e.g. in terms of time or number of cycles, during which the motor torque or the motor current, respectively, is not at zero. If this "non-zero torque duration" is longer than a defined threshold, e.g. one minute, five minutes or an hour, processing continues in step S0 by determining an alternative stable position. For example, the alternative stable position is the stable position that is located preceding (before) or succeeding (following) the current stable position (previously selected in step S0). This approach makes it possible to find more advantageous stable positions which require less motor torque or motor current, respectively, through "trial and error".

In step S45, the holding control torque controller <NUM> or the circuit <NUM> or motor controller <NUM>, respectively, increases the motor torque or motor current, respectively, e.g. by a predetermined amount or portion, and proceeds in step S42.

Claim 1:
An actuator (<NUM>) comprising an electric motor (<NUM>) having cogging torque (C), and a controller (<NUM>) configured to control operation of the electric motor (<NUM>) and determine a motor position of the electric motor (<NUM>), wherein the controller (<NUM>) comprises a circuit (<NUM>) configured to control the electric motor (<NUM>) to drive an actuated part (<NUM>) of a Heating, Ventilating, and Air Conditioning system to a target position and maintain a current motor position by determining from a set of stable positions (P1, P2) defined by the cogging torque (C) a selected stable position (P1, P2) closest to the current motor position, and controlling a motor torque of the electric motor (<NUM>) to maintain the motor position within a defined range (R1, R2) around the selected stable position (P1, P2).