Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
  • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
  • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
  • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
  • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
  • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
  • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
  • H02M7/53873—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with digital control
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
  • G05F1/10—Regulating voltage or current
  • G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
  • G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
  • G05F1/565—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M1/00—Details of apparatus for conversion
  • H02M1/0003—Details of control, feedback or regulation circuits
  • H02M1/0009—Devices or circuits for detecting current in a converter
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M3/00—Conversion of dc power input into dc power output
  • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
  • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
  • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
  • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
  • H02M3/1555—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only for the generation of a regulated current to a load whose impedance is substantially inductive

Definitions

• the present invention generally relates to actuators.
• the present invention relates to a current control loop for controlling torque produced by an actuator.
• actuators are used in heating, ventilating, and air- conditioning (HVAC) systems to actuate a variety of loads, such as opening and closing dampers and valves.
• HVAC heating, ventilating, and air- conditioning
• an actuator is designed with a rating that specifies a maximum torque at which the actuator is capable of actuating the load.
• the actuator is capable of generating the rated maximum torque, but is also configured not to exceed the rated maximum torque. If the rated maximum torque is exceeded, it is possible for the actuator to damage the load and/or the gear train or linkage connected between the actuator shaft and the load.
• Actuators can use one or more feedback loops to control the actuator during actuation.
• some actuators use a positional feedback loop, which monitors a position of an actuator's motor relative to a desired end position. The error between the actuator's present position and the desired end position is 25 calculated by a controller, which uses this error to direct the actuator's motor to the desired end position.
• Other actuators employ a velocity feedback loop, which monitors a velocity at which an actuator's motor is currently operating. An error between the actuator's current velocity and desired velocity is calculated by a controller, which 30 then uses this error to speed or slow the velocity of the actuator as desired.
• a typical actuator used in an HNAC system includes a spring return to drive a load such as a damper or valve coupled to the actuator back to an initial or closed position.
• the spring return includes a spring that is wound by the actuator's motor as the actuator opens the damper, and the energy stored in this spring is used to return the damper to the initial position upon loss of power.
• some HNAC actuators typically called modulating actuators
• modulating actuators are configured to stop at positions between the fully closed and fully open stops. Such actuators must therefore develop sufficient torque to, for example, overcome the spring returns incorporated into the actuators, while opening or holding at the intermediate position short of the fully open stop.
• Control of the rated maximum torque and positioning and velocity of an actuator can be complicated by variances in the tolerances between actuators, as well as by the need to overcome the spring return. In addition, control can be complicated by the necessity in modulating actuators to stop at intermediate positions between fully open and fully closed stops. While the positional and velocity types of feedback control loops for actuators are sufficient for some applications, the prior art control designs for actuators do not always provide the desired efficiency and precise control needed. Therefore, it is desirable to provide new systems and methods for controlling the actuation of an actuator.
• the present invention generally relates to actuators.
• the present invention relates to a current control loop for controlling torque produced by an actuator.
• the invention relates to systems and method for providing current control loops for actuators.
• the invention relates to systems and methods for calibrating, sampling, and/or regulating a torque produced by an actuator, such as a maximum torque.
• the actuators are used as part of a heating, ventilating, and air-conditioning (HVAC) system.
• HVAC heating, ventilating, and air-conditioning
• Figure 1 is a block diagram illustrating an example system including an embodiment of an actuator coupled to a power source and load made in accordance with the present invention
• Figure 2 is a schematic diagram of an example actuator including an example current sampling circuit made in accordance with the present invention
• Figure 3 is a schematic diagram of an example current control loop made in accordance with the present invention and incorporating the example current sampling circuit shown in Figure 2
• Figure 4 is a flow diagram illustrating an example method for setting a maximum command current of an actuator in accordance with the present invention
• Figure 5 is a flow diagram illustrating another example method for setting a maximum command current of an actuator in accordance with the present invention
• Figure 6 is a flow diagram illustrating an example method for providing a current control loop clipped at a maximum command current in accordance with the present invention.
• the present invention generally relates to actuators.
• the present invention relates to a current control loop for controlling torque produced by an actuator. While the invention is not so limited, a greater understanding will be achieved through review of the following specification and attached drawings.
• the example spring return actuator 100 includes an electric motor 120 driven by a drive circuit 125, which is in turn powered by a power source 110.
• the example actuator 100 also includes a spring 140, which biases a load 150, coupled by a gear train 127 to the electric motor 120, to a first position.
• the example actuator 100 also includes a microcontroller 130 coupled to the drive circuit 125 and the electric motor 120 to commutate the electric motor. When power from the power source 110 to the actuator 100 fails, the spring 140 returns the load to the first position.
• the actuator 100 and the load 150 are part of a heating, ventilating, and air-conditioning (HNAC) system, such as an HVAC system in a building or house.
• the load 150 can be, for example, a damper used to control airflow through one or more ventilation ducts, or a valve, such as a hydronic valve, used to control the flow of a liquid or gas through a pipe.
• the actuator 100 can be used to actuate the load 150 to one or more desired positions, such as to open and close the damper or valve.
• the drive circuit 125 is coupled between the microcontroller 130 and the actuator's motor 120.
• the illustrated drive circuit 125 is coupled to coils A, B, and C of the motor 120.
• the drive circuit 125 alternates a direction of a current flowing through the coils A, B, and C to cause the motor 120 to spin and thereby generate torque.
• the drive circuit 125 includes high-side switches 272, 274, and 276, as well as low-side switches 282, 284, and 286. By alternating the state of each of these switches (i.e.
• the high-side switches 272, 274, and 276 are p-channel MOSFETs
• the low-side switches 282, 284, and 286 are n-channel MOSFETs, although other switching devices can also be used.
• the microcontroller 130 preferably controls the state of each of the switches. For example, the microcontroller 130 can turn on high-side switch 272 and low-side switch 284 while turning off low-side switch 282 and high-side switch 274, thereby causing current to flow in a first direction through the coil or coils of the motor.
• the microcontroller 130 can then turn off high-side switch 272 and low- side switch 284 while turning on low-side switch 282 and high-side switch 274, thereby causing current to flow in a second, opposite direction through the coil or coils.
• the microcontroller 130 includes a pulse width modulator (PWM) that uses pulse width modulation to drive the motor 120.
• PWM pulse width modulator
• the actuator 100 also includes the current sampling circuit 230, which is configured to sample a motor current, or the current flowing through the coils A, B, and C of the motor 120.
• the torque of a motor is proportional to motor current (see Equation 3 below). Therefore, the sampled motor current can be used to calculate the torque of the motor 120.
• the circuit 230 includes a switch 252, and a resistor 254 and capacitor 256 coupled in parallel.
• the switch 252 is controlled by the PWM of the microcontroller 130 and is turned on during the duty cycle of the pulse width modulation and turned off during the cycling off of the pulse width modulation.
• the switch 252 is turned on, the motor current flowing through the low-side switches 282, 284, and 286 is dissipated by the voltage drop across the resistor 254.
• the voltage drop across the resistor 254 is proportional to the motor current.
• the analog to digital (A/D) converter of the microcontroller 130 samples the charge on the capacitor 256.
• the charge measured by the microcontroller 130 on the capacitor 256 can be used to calculate the torque generated by the motor. It can be advantageous to measure the charge on the capacitor 256 rather than to directly measure the voltage drop across the resistor 254 so that a relatively slow and inexpensive A/D converter can be used.
• the A/D converter of the microcontroller 130 samples the motor current at intervals of 5 ms or less, more preferably between 1 and 2 ms.
• the circuit 230 is disclosed herein, other circuits for sampling the motor current can also be used. For example, a faster A/D converter that is synchronized with the PWM can be used to directly measure the voltage drop across the resistor 254.
• the current control loop 300 generally includes a summation module
• the current control loop 300 functions as follows.
• a command current typically generated by a current command controller 305 of the microcontroller 130, is provided to the summation module 310.
• the summation module 310 passes the command current to the proportional-integral filter 320, which converts the command current to a proportional voltage command.
• the voltage command is provided to control the duty cycle of the PWM, which in turn modulates the drive circuit 125 to drive the motor 120 at a desired torque.
• the sampling circuit 230 samples the motor current of the motor by charging the capacitor 256 in proportion to the voltage drop across the resistor 254.
• the A/D converter of the microcontroller 130 is used to sample the charge on the capacitor 256, and the microcontroller thereby calculates the actual motor current.
• a current error is calculated by subtracting the motor current from the command current. This current error is then negatively summed by the summation module 310 with the command current, the output of which is then fed to the proportional-integral filter 320 to drive the motor as described above. In this manner, the current control loop 300 functions to correct errors in the torque generated by the actuator.
• a first method for setting the maximum command current starts by providing a command current to drive the actuator to produce a torque greater than a desired maximum torque at operation 410. With the motor being driven at this torque, a maximum load is applied to the actuator in operation 420. Next, in operation 430, the command current is reduced to a point at which the actuator stalls. Then, the command current at the point at which the actuator stalls is recorded in operation 440.
• the command current is set as a maximum command current of the actuator in operation 450, and the maximum command current can be stored in non-volatile memory in operation 460 so that the setting is not lost upon power-off of the actuator.
• FIG 5 another method for setting the maximum command current is illustrated.
• the actuator is driven.
• a desired maximum load is applied to the actuator in operation 520.
• the motor current of the actuator while the maximum load is being applied is measured using, for example, the current sampling circuit 230 described above.
• the sampled motor current is set as the maximum command current of the actuator in operation 540.
• the maximum command current can be stored in non- volatile memory of the actuator.
• the microcontroller sets a command current for the actuator.
• decisional operation 615 the microcontroller determines whether the command current is greater than the maximum command current. If the command current does not exceed the maximum command current, control is passed to operation 620. Alternatively, if the command current does exceed the maximum command current, control is passed to operation 618, in which the command current is clipped at the maximum command current, and control is then passed to operation 620.
• the motor current is sampled using, for example, the circuit 230.
• the current error is calculated (by, for example, subtracting the motor current from the command current).
• the current error is applied to a proportional-integral filter to control the system response.
• the output of the proportional-integral filter is applied to the pulse width modulator as a duty cycle.
• the pulse width modulator is applied to the motor drive circuit to control the voltage applied to the motor. This process is repeated at a regular interval. In this manner, a current control loop is provided in which the motor current never exceeds the maximum command current because the command current is clipped at the maximum command current.

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• 2004
  • 2004-04-23 EP EP04750498A patent/EP1664963A1/de not_active Withdrawn
  • 2004-04-23 WO PCT/US2004/012463 patent/WO2005036296A1/en not_active Application Discontinuation
  • 2004-04-23 CN CN200480017707A patent/CN100592236C/zh not_active Expired - Fee Related

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