Ride-through method and system for HVACandR chillers
First Claim
1. A method for controlling a variable speed drive to ride-through a voltage sag, comprising the steps of:
- providing a motor and a load mechanically coupled together;
providing a variable speed drive to power the motor, the variable speed drive including an active converter stage and an inverter stage electrically coupled by a DC link stage;
monitoring a DC voltage of the DC link stage;
monitoring an input parameter of the active converter stage;
regulating the DC voltage of the DC link stage with the active converter in response to a change in the monitored DC link voltage;
transferring the regulation of the DC voltage of the DC link stage to the inverter stage in response to the DC voltage being less than a predetermined first threshold voltage;
mechanically removing the load from the motor; and
controlling the DC voltage of the DC link stage with the inverter stage by reversing power flow from the motor to the DC link stage.
3 Assignments
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Accused Products
Abstract
A method of providing ride-through capability in a chiller/refrigeration system employs a variable speed drive with an active converter stage, a DC link stage and an inverter stage for providing variable frequency and voltage to power at least one motor. An induction motor is coupled to the output of the inverter stage for driving a compressor in the chiller/refrigeration system. The ride-through method comprises operating the active converter to regulate the DC link voltage of the DC link stage to a predetermined voltage level until the current through the active converter equals a predetermined current limit, then transferring regulation of the DC link to the inverter upon reaching the current limit of the converter. The compressor is unloaded, and the power flow through the inverter is reversed to maintain the voltage level of the DC link stage.
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Citations
33 Claims
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1. A method for controlling a variable speed drive to ride-through a voltage sag, comprising the steps of:
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providing a motor and a load mechanically coupled together; providing a variable speed drive to power the motor, the variable speed drive including an active converter stage and an inverter stage electrically coupled by a DC link stage; monitoring a DC voltage of the DC link stage; monitoring an input parameter of the active converter stage; regulating the DC voltage of the DC link stage with the active converter in response to a change in the monitored DC link voltage; transferring the regulation of the DC voltage of the DC link stage to the inverter stage in response to the DC voltage being less than a predetermined first threshold voltage; mechanically removing the load from the motor; and controlling the DC voltage of the DC link stage with the inverter stage by reversing power flow from the motor to the DC link stage. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for increasing voltage sag ride-through capability in a chiller system, comprising the steps of:
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providing a motor and a compressor mechanically coupled together; providing a variable speed drive to power the motor, the variable speed drive including an active converter stage and an inverter stage electrically coupled by a DC link stage; monitoring a DC voltage of the DC link stage; monitoring an input parameter of the active converter stage; regulating the DC voltage of the DC link stage through the active converter stage; regulating the motor speed through the inverter stage; transferring the regulation of the DC voltage of the DC link stage to the inverter stage in response to the DC voltage of the DC link stage being less than a predetermined first threshold voltage; mechanically unloading the compressor; disabling the active converter stage; and controlling the DC voltage of the DC link stage with the inverter stage by reversing power flow from the motor to the DC link. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A method for increasing voltage sag ride-through capability in a chiller system, comprising the steps of:
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providing a motor and a compressor mechanically coupled together; providing a variable speed drive to power the motor, the variable speed drive including an active converter stage and an inverter stage electrically coupled by a DC link stage; monitoring a DC voltage of the DC link stage; monitoring an input parameter of the active converter stage; regulating the DC voltage of the DC link stage through the active converter stage; regulating the speed of the motor through the inverter stage; transferring the regulation of the DC voltage of the DC link stage to the inverter stage in response to the DC voltage of the DC link stage being less than a predetermined first threshold voltage; mechanically unloading the compressor; regulating the DC voltage of the DC link stage through the inverter stage to a first voltage setpoint level by reversing power flow from the motor to the DC link; and additionally regulating the DC voltage of the DC link stage with the active converter stage to a second voltage setpoint level while the active converter stage is operating in a current limiting mode. - View Dependent Claims (14, 15, 16, 17)
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18. A method for controlling a variable speed drive to ride-through a voltage sag, comprising the steps of:
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providing a motor and compressor mechanically coupled together; providing a variable speed drive to power the motor, the variable speed drive including a passive rectifier stage and an inverter stage electrically coupled by a DC link stage; monitoring a DC voltage of the DC link stage; monitoring an input parameter of the passive rectifier stage; stopping control of the motor with the inverter stage in response to the DC voltage being less than a predetermined first threshold voltage; mechanically unloading the compressor; and controlling the DC voltage of the DC link stage with the inverter stage by reversing power flow from the motor to the DC link. - View Dependent Claims (19, 20, 21, 22, 23)
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24. A chiller system comprising:
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a compressor, a condenser, and an evaporator connected in a closed refrigerant loop; a motor connected to the compressor to power the compressor; and a variable speed drive connected to the motor, the variable speed drive being configured to receive an input AC power at a fixed input AC voltage and a fixed input frequency and provide an output power at a variable voltage and variable frequency to the motor, the variable voltage having a maximum voltage greater in magnitude than the fixed input AC voltage and the variable frequency having a maximum frequency greater than the fixed input frequency, the variable speed drive comprising; a converter stage connected to an AC power source providing the input AC power, the converter stage being configured to convert the input AC voltage to a DC voltage; a DC link stage connected to the converter stage, the DC link stage being configured to filter the DC voltage and store energy from the converter stage; an inverter stage connected to the DC link stage, the inverter stage being configured to convert the DC voltage from the DC link stage into the output power for the motor having the variable voltage and the variable frequency; a control panel to control operation of the variable speed drive, the control panel being configured to regulate the DC voltage of the DC link stage with the inverter stage in response to the DC voltage being less than a predetermined first threshold voltage; and wherein the control panel regulates the DC voltage of the DC link stage with the inverter stage by providing control signals to mechanically unload the compressor, and reverse power flow from the motor to the DC link stage to control the DC voltage of the DC link stage. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33)
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Specification