HVAC actuator

Abstract

An HVAC actuator (1) comprises an electric motor (11); an energy buffer (13) configured to store electrical energy from a power supply (2), and to provide the electrical energy to the motor (11); and a power limiting circuit (12) configured to limit input power from the power supply (2) to the energy buffer (13) to a threshold lower than motor power drawn by the motor (11) from the energy buffer (13).

Claims

1. An HVAC actuator, comprising an electric motor, wherein the HVAC actuator further comprises: an energy buffer configured to store electrical energy from a power supply, and to provide the electrical energy to the electric motor; and a power limiting circuit configured to limit input power from the power supply to the energy buffer to a threshold lower than motor power drawn by the electric motor from the energy buffer, wherein the HVAC actuator further comprises a motor controller configured to monitor an operating condition of the energy buffer, to store a safety position, and to drive the electric motor to the safety position depending on the operating condition of the energy buffer, using electrical energy stored in the energy buffer.

2. The HVAC actuator according to claim 1, wherein the energy buffer is configured to accumulate and to store electrical energy during an idle time of the electric motor and to provide electrical energy to the electric motor during an active time of the electric motor.

3. The HVAC actuator according to claim 2, wherein the power limiting circuit is configured to set the threshold such that the electrical energy stored in the energy buffer during the idle time is sufficient to drive the electric motor during the active time.

4. The HVAC actuator according to claim 1, wherein the power limiting circuit is configured to set the threshold such that the electrical energy stored in the energy buffer is sufficient to feed the motor controller.

5. The HVAC actuator according to claim 1, further comprising a regulator configured to convert input voltage of the HVAC actuator to a voltage lying in a voltage range of the energy buffer.

6. The HVAC actuator according to claim 5, wherein the regulator is a switching regulator.

7. The HVAC actuator according to claim 5, wherein the power limiting circuit is configured to adjust the threshold depending on a conversion efficiency of the regulator.

8. The HVAC actuator according to claim 1, wherein the energy buffer is a Lithium-ion capacitor.

9. A system comprising a plurality of HVAC actuators according to claim 1, connected to a common power supply line, wherein the common power supply line provides input power to the HVAC actuators, the input power in each case being limited by the power limiting circuits of the HVAC actuators.

10. The system according to claim 9, wherein the power limiting circuits of the HVAC actuators are configured to adjust the thresholds depending on the number of HVAC actuators connected to the common power supply line.

11. The system according to claim 9, wherein the power limiting circuits of the HVAC actuators are configured to adjust the thresholds depending on the power of the common power supply line.

12. The system according to claim 9, wherein the common power supply line comprises a power over Ethernet line.

13. A method of operating an HVAC actuator comprising an electric motor, the method comprising: storing electrical energy from a power supply in an energy buffer of the HVAC actuator and providing the electrical energy to the electric motor; limiting by a power limiting circuit of the HVAC actuator input power from the power supply to the energy buffer to a threshold lower than motor power drawn by the electric motor from the energy buffer; monitoring, by a motor controller of the HVAC actuator, an operating condition of the energy buffer; storing, by the motor controller, a safety position; and driving the electric motor to the safety position depending on the operating condition of the energy buffer, using electrical energy stored in the energy buffer.

14. An HVAC actuator, comprising an electric motor, wherein the HVAC actuator further comprises: an energy buffer configured to store electrical energy from a power supply, and to provide the electrical energy to the electric motor; and a power limiting circuit configured to limit input power from the power supply to the energy buffer to a threshold lower than motor power drawn by the electric motor from the energy buffer, wherein for a case of zero input power to the HVAC actuator, the energy buffer is configured to operate in a battery mode for driving the electric motor during a time.

15. The HVAC actuator according to claim 14, wherein the HVAC actuator further comprises an activation switch configured to activate the HVAC actuator, from a deactivated, energy conserving state to an active state, for the case of zero input power to the HVAC actuator.

16. The HVAC actuator according to claim 14, wherein the HVAC actuator further comprises a near field communication module configured to activate the HVAC actuator, from a deactivated, energy conserving state to an active state.

17. The HVAC actuator according to claim 14, wherein the energy buffer is configured to accumulate and to store electrical energy during an idle time of the electric motor and to provide electrical energy to the electric motor during an active time of the electric motor.

18. The HVAC actuator according to claim 17, wherein the power limiting circuit is configured to set the threshold such that the electrical energy stored in the energy buffer during the idle time is sufficient to drive the electric motor during the active time.

19. The HVAC actuator according to claim 14, further comprising a regulator configured to convert input voltage of the HVAC actuator to a voltage lying in a voltage range of the energy buffer.

20. The HVAC actuator according to claim 19, wherein the regulator is a switching regulator.

21. The HVAC actuator according to claim 19, wherein the power limiting circuit is configured to adjust the threshold depending on a conversion efficiency of the regulator.

22. The HVAC actuator according to claim 14, wherein the energy buffer is a Lithium-ion capacitor.

23. A system comprising a plurality of HVAC actuators according to claim 14, connected to a common power supply line, wherein the common power supply line provides input power to the HVAC actuators, the input power in each case being limited by the power limiting circuits of the HVAC actuators.

24. The system according to claim 23, wherein the power limiting circuits of the HVAC actuators are configured to adjust the thresholds depending on the number of HVAC actuators connected to the common power supply line.

25. The system according to claim 23, wherein the power limiting circuits of the HVAC actuators are configured to adjust the thresholds depending on the power of the common power supply line.

26. The system according to claim 23, wherein the common power supply line comprises a power over Ethernet line.

27. A method of operating an HVAC actuator comprising an electric motor, the method comprising: storing electrical energy from a power supply in an energy buffer of the HVAC actuator and providing the electrical energy to the electric motor; and limiting by a power limiting circuit of the HVAC actuator input power from the power supply to the energy buffer to a threshold lower than motor power drawn by the electric motor from the energy buffer, wherein for a case of zero input power to the HVAC actuator, the energy buffer is configured to operate in a battery mode for driving the electric motor during a time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1: shows a block diagram illustrating schematically an embodiment of an HVAC actuator comprising an energy buffer and a power limiting circuit;

(3) FIG. 2: shows a block diagram illustrating schematically an embodiment of a system comprising a plurality of HVAC actuators.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) FIG. 1 shows a block diagram of an embodiment of an HVAC actuator 1 which receives electrical power from an external power supply 2 via a wire connection. The HVAC actuator 1 comprises an electric motor 11, which is used to drive an HVAC device such as a damper or a valve, etc. The input power from the power supply 2 is limited by a power limiting circuit 12 to a threshold P.sub.th. The threshold P.sub.th may be configurable by the power limiting circuit 12. The power limiting circuit 12 can comprise shunt elements and/or control circuitry. The power limited by the power limiting circuit 12 is fed to a regulator 14, which regulates supply voltage of the power supply 2, typically 24 V, to a voltage in a range of an energy buffer 13, which is arranged downstream of the regulator 14. Preferably, the regulator 14 is a switching regulator, which offers high efficiency, low power dissipation and high power density. The high power density of the switching regulator has the advantage that space requirements can be kept small inside the HVAC actuator 1. The efficiency η.sub.regulator of the switching regulator can be as high as 80% or higher. The threshold P.sub.th is lower than the electrical motor power P.sub.motor drawn by the motor 11 from the energy buffer 13 arranged in the HVAC actuator 1. The threshold P.sub.th can be adjusted depending on various circumstances, for example depending on the motor power P.sub.motor, on the power supplied by the power supply 2, etc. The energy buffer 13 is arranged downstream of the power limiting circuit 12 and is configured to store electrical energy from the power supply 2 and to provide the stored electrical energy to the motor 11. Typically, the motor 11 of the HVAC actuator 1 is driving the HVAC device during an active time t.sub.active. During the rest of the time t.sub.idle, the HVAC device stays idle and typically only residual power is consumed by the electronics of the HVAC actuator 1, for example by a motor controller 15. Therefore, the energy buffer 13 has to provide electrical energy to the motor 11 for changing the actuator position during the active time t .sub.active. During the idle time t.sub.idle, and optionally also during the active time t.sub.active, the energy buffer 13 accumulates and stores electrical energy.

(5) In an embodiment, the power limiting circuit 12 and the regulator 14 are integrated in a single power limiting unit 10, as symbolized by the dashed box.

(6) The regulator 14 outputs an electrical loading power P.sub.load which is related to the threshold P.sub.th as follows:
P.sub.load≈η.sub.regulatorP.sub.th
The loading power P.sub.load is used to load the energy buffer 13 at least during the idle time t.sub.idle, such that the electrical energy accumulated and stored at least during the idle time t.sub.idle is sufficient for the energy consumption of the motor 11 during the active time t.sub.active. Further, the electrical energy accumulated and stored at least during the idle time t.sub.idle is sufficient for the residual power consumption of the electronics of the HVAC actuator 1. The loading power P.sub.load therefore satisfies the following relation:

(7) $P_{\mathrm{load}}\ge \frac{t_{\mathrm{active}}}{t_{\mathrm{idle}}}{P}_{\mathrm{motor}}$

(8) As an example, the motor 11 exhibits a maximum motor current of 60 mA at a voltage of 3.3 V, such that the motor power is 200 mW. Assuming that the motor 11 drives an HVAC device during an active time t.sub.active which is half of the idle time t.sub.idle, the loading power P.sub.load should at least be 100 mW. Together with the motor voltage of 3.3 V this yields a loading current of 30 mA during the idle time t.sub.idle. With an efficiency η.sub.regulator of the regulator 14 of 80%, the configurable threshold P.sub.th to the input power is adjusted to ca. 125 mW in order to achieve the loading power P.sub.load of ca. 100 mW.

(9) The energy buffer 13 is preferably a Lithium-ion capacitor (LIC), which has the advantage of a high energy density and a low self-discharge rate. The voltage range is typically between 2 V and 3.5 V, which advantageously corresponds to the range of the motor electronics. Especially, using a motor controller 15 with a voltage range corresponding to the voltage range of the energy buffer 13, no up-conversion is necessary, which reduces the costs and the space required in the HVAC actuator 1.

(10) In the embodiment shown in FIG. 1, the HVAC actuator 1 further comprises a motor controller 15. The motor controller 15 may comprise a microcontroller. In an embodiment, the motor controller 15 comprises a motor driver IC. The energy buffer 13 provides electrical energy to the motor controller 15. The motor controller 15 drives the motor 11 and draws the motor power from the energy buffer 13. Accordingly, the loading power P.sub.load satisfies the following relationship

(11) $P_{\mathrm{load}}\ge \frac{t_{\mathrm{active}}}{t_{\mathrm{idle}}}\left(P_{\mathrm{motor}}+P_{\mathrm{control}}\right)$
such that the energy buffer 13 stores sufficient energy at least in the idle time t.sub.idle, that can be provided to the motor 11 and the motor controller 15 during the active time t.sub.active.

(12) The motor controller 15 is configured to monitor an operating condition of the energy buffer 13, which is symbolized by the double arrow d. Depending on the operating condition of the energy buffer 13, the motor controller 15 can prompt the motor 11 to drive to a safety position which is stored in the motor controller 15. This can for example be the case, if the motor controller 15 monitors the ageing of the energy buffer 13 based on, for example, the discharge rate, maximum stored energy etc., and detects that the performance of the energy buffer 13 has considerably degraded. In that case, the motor controller 15 controls the motor 11, respectively, to move to or drive an actuated part to a safety position, such that an accidental moving or driving to an erroneous position, due to a poor performance of the energy buffer 13, can be avoided. For obtaining the safety position, the energy buffer 13 is configured to provide the electrical energy to drive the motor 11 to the safety position. For example, the energy buffer 13 comprises a separate safety storage where the electrical energy, required for one-time driving the motor 11 into the safety position, is stored.

(13) In an embodiment, the HVAC actuator 1 comprises a communication unit (not shown in FIG. 1), which can be used to send out a signal to an external maintenance site or an indication unit which indicates the condition of the energy buffer 13, such that a maintenance of the HVAC actuator 1 can be initiated when the safety position is taken by the motor 11. In an embodiment, the condition of the energy buffer 13 can be monitored by a separate diagnose unit (not shown in FIG. 1).

(14) The HVAC actuator 1 further comprises a control interface 17 which receives an external control input symbolized by the arrow c. The control interface 17 transfers the external control input to the motor controller 15. Depending on the embodiment, the control interface 17 is an analogue or digital control interface. For example, the control interface 17 is based on a conventional interface for HVAC actuators, such as multi-point (MP), building automation and control network (BACnet), Modbus etc. In a variant, the control interface 17 includes a wireless network interface. In some embodiments, the control interface 17 includes an analogue interface with a control signal or operating range between 0 to 10 V or 2 to 10 V, such as for example used for spring-return actuators.

(15) During first time installation of the HVAC actuator 1, there is typically no power supply connected to the HVAC actuator 1. The input power is therefore zero. Conventionally, the person installing the HVAC actuator 1 manually drives the HVAC device into the desired starting position (for example a certain open and/or closed position for dampers or for valves), for example by using a hand wheel. Especially for HVAC actuators installed in positions difficult to access, this can be cumbersome.

(16) The energy buffer 13, especially in embodiments where the energy buffer is a LIC, can operate in a battery mode for driving the motor 11 during a time t.sub.batt, during which the HVAC actuator is not connected to an external power supply. In an embodiment, the energy buffer 13 is loaded prior to first use with an initial energy sufficient to drive the motor 11 in battery mode. Therefore, a manual driving of the HVAC device into the desired starting position can be avoided at installation since the energy buffer 13 is able to provide the required initial energy. Prior to first use, the HVAC actuator 1 is preferably completely shut down, i.e. set in a deactivated, energy conserving state, in order to prevent or at least minimize discharge of the loaded energy buffer 13 during storage of the HVAC actuator 1, e.g. unused in a box. At installation time, the completely shut down HVAC actuator 1 can be activated by an activation switch (not shown in the Figures), which may comprise a manual switch (e.g. a button) or be connected to an NFC module and is configured to place the HVAC actuator 1 from the deactivated, energy conserving state to an active state where the HVAC actuator 1 is powered by the energy buffer 13 in the case of zero input power. For example, in the deactivated state, the motor 11 is electrically disconnected from the energy buffer 13 by the switch.

(17) FIG. 2 shows a block diagram of an embodiment of a system 3 comprising a plurality of HVAC actuators 1a, 1b, 1c, . . . , 1n, . . . coupled to a common power supply line 4, which supplies input power to the HVAC actuators 1a, 1b, 1c, . . . , 1n, . . . The dotted line between the HVAC actuator 1c and 1n and after the HVAC actuator 1n symbolizes further HVAC actuators, which are coupled to the same common power supply line 4, but are for simplicity not shown in FIG. 2. The HVAC actuator 1a comprises a power limiting circuit 12a, an energy buffer 13a, and an electric motor 11a. The respective power limiting circuits 12b, 12c, 12n, energy buffers 13b, 13c, 13n and electric motors 11b, 11c, 11n are shown for the HVAC actuators 1b, 1c and 1n. The power limiting circuits 12a, 12b, 12c, . . . , 12n, . . . of the HVAC actuators 1a, 1b, 1c, . . . , 1n, . . . limit input power from the common power supply line 4 to the energy buffer 13a, 13b, 13c, . . . , 13n, . . . to a threshold P.sub.th lower than motor power drawn by the motors 11a, 11b, 11c, . . . , 11n, . . . from the energy buffers 13a, 13b, 13c, . . . , 13n, . . . Typically, the threshold P.sub.th is the same for all HVAC actuators 1a, 1b, 1c, . . . , 1n. In some embodiments, the thresholds P.sub.th may vary from HVAC actuator to HVAC actuator 1a, 1b, 1c, . . . , 1n, depending on the specific application. The energy buffers 13a, 13b, 13c, . . . , 13n, . . . accumulate and store electrical energy, and provide the electrical energy to the motors 11a, 11b, 11c, . . . , 11n, . . . .

(18) The shown system 3, comprising a plurality of HVAC actuators 1a, 1b, 1c, . . . , 1n, . . . with power limiting circuits 12a, 12b, 12c, . . . , 12n, . . . , has the advantage that the power P of the common power supply line 4 can controllably be distributed to the plurality of HVAC actuators 1a, 1b, 1c, . . . , 1n, . . . coupled to the common power supply line 4. This is particularly advantageous, if the common power supply line 4 provides a power which is lower than the motor power drawn by the motors 11a, 11b, 11c, . . . , 11n, . . . from the energy buffers 13a, 13b, 13c, . . . , 13n, . . . , which is for example the case for an embodiment where the common power supply line comprises a Power over Ethernet (PoE) line. Especially, the power of the common power supply line 4 may be sufficient to supply one or a certain number n.sub.1 of HVAC actuators, but may not be sufficient, if a number n.sub.2>n.sub.1 of HVAC actuators are coupled to the common power supply line 4. By limiting the input power for each HVAC actuator, the system can operate even for the n.sub.2 HVAC actuators, without the power supply line 4 being overloaded.

(19) For the case of n HVAC actuators coupled to the common power supply line 4, the threshold P.sub.th may be set to P/n, such that an overload of the common power supply line 4 can controllably be avoided. Accordingly, the level of power required from the power supply line can be reduced, since the input power is limited by the power limiting circuits and distributed to the plurality of HVAC actuators. The limited input power P/n per HVAC actuator can be accumulated and stored in the respective energy buffers 13a, 13b, 13c, . . . , 13n, . . . at least during the idle time t.sub.idle of the motors 11a, 11b, 11c, . . . , 11n, . . . and provided to the motors 11a, 11b, 11c, . . . , 11n, . . . during the active time t.sub.active. In an embodiment, the HVAC actuators 1a, 1b, 1c, . . . , 1n, . . . are centrally controllable using control interfaces (not shown in FIG. 2), such that the thresholds P.sub.th can centrally be adjusted. This has for example the advantage that the thresholds P.sub.th can be readjusted, if one of the HVAC actuators fails (for example after the motor being driven to a safety position) or if an additional HVAC actuator is coupled to the common power supply line 4.