Voltage and current limiting method and apparatus for a voltage/frequency drive
First Claim
1. An apparatus for use with a system including a variable speed AC motor, a controller and an inverter, the inverter linked to and drawing direct current from a DC bus and linked to and supplying alternating current to the motor, the controller linked to the inverter and receiving and using an output frequency signal to control inverter frequency and thereby motor speed, the apparatus for regulating inverter frequency to maintain DC bus voltage and a supply line current amplitude below a voltage limit and a current limit, respectively, the apparatus comprising:
- a DC bus voltage error determiner linked to the DC bus for generating a voltage error signal to indicate when the DC bus voltage exceeds a threshold voltage level, periods during which a voltage error signal is generated being voltage limit periods and other periods being non-limit periods;
a slew rate determiner for generating a decelerating slew rate signal, the slew rate being a rate of motor frequency change;
a selector linked to the error determiner and the rate determiner for selecting the error signal during limit periods and selecting the slew rate signal during non-limit periods for determining the inverter frequency; and
a modifier liked to the rate determiner for modifying the slew rate signal as a function of the durations of the limit and non-limit periods.
1 Assignment
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Accused Products
Abstract
A method and apparatus for maintaining both a DC bus voltage and a motor current within limit values wherein, when a voltage limit condition occurs, a voltage error (i.e. DC bus voltage limit minus DC bus voltage) is used to increase an inverter output frequency until the voltage limit condition subsides, and, wherein during a current limit condition a current error signal (i.e. motor current limit minus motor current) is used to reduce inverter output frequency until the current limit condition subsides, a slew rate used to control the output frequency when neither a current nor a voltage limit condition exists, the slew rate decreased as a function of the voltage limit period durations and increases a function of the current limit period durations.
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Citations
27 Claims
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1. An apparatus for use with a system including a variable speed AC motor, a controller and an inverter, the inverter linked to and drawing direct current from a DC bus and linked to and supplying alternating current to the motor, the controller linked to the inverter and receiving and using an output frequency signal to control inverter frequency and thereby motor speed, the apparatus for regulating inverter frequency to maintain DC bus voltage and a supply line current amplitude below a voltage limit and a current limit, respectively, the apparatus comprising:
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a DC bus voltage error determiner linked to the DC bus for generating a voltage error signal to indicate when the DC bus voltage exceeds a threshold voltage level, periods during which a voltage error signal is generated being voltage limit periods and other periods being non-limit periods;
a slew rate determiner for generating a decelerating slew rate signal, the slew rate being a rate of motor frequency change;
a selector linked to the error determiner and the rate determiner for selecting the error signal during limit periods and selecting the slew rate signal during non-limit periods for determining the inverter frequency; and
a modifier liked to the rate determiner for modifying the slew rate signal as a function of the durations of the limit and non-limit periods. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for use with a system including a variable speed AC motor, a controller and an inverter, the inverter linked to and drawing direct current from a DC bus and linked to and supplying alternating current to the motor, the controller linked to the inverter and receiving and using an output frequency signal to control inverter frequency and thereby motor speed, the method for regulating inverter frequency to maintain DC bus voltage and a supply line current amplitude below a voltage limit and a current limit, respectively, the method comprising the steps of:
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generating a voltage error signal to indicate when the DC bus voltage exceeds a threshold voltage level, periods during which a voltage error signal are generated being voltage limit periods and other periods being non-limit periods;
generating a decelerating slew rate signal, the slew rate being a rate of motor frequency change;
selecting the error signal during limit periods and selecting the slew rate signal during non-limit periods for determining the inverter frequency; and
modifying the slew rate signal as a function of the durations of the limit and non-limit periods. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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22. An apparatus for use with a system including a variable speed AC motor, a controller and an inverter, the inverter linked to and drawing direct current from a DC bus and linked to and supplying alternating current to the motor, the controller linked to the inverter and receiving and using an output frequency signal to control inverter frequency and thereby motor speed, the apparatus for regulating inverter frequency to maintain DC bus voltage and a supply line current amplitude below a voltage limit and a current limit, respectively, the apparatus comprising:
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a determiner means linked to the DC bus for generating a voltage error signal to indicate when the DC bus voltage exceeds a threshold voltage level, periods during which a voltage error signal are generated being voltage limit periods and other periods being non-limit periods;
a slew rate means for generating a decelerating slew rate signal, the slew rate being a rate of motor frequency change;
a selector means linked to the determiner means and the rate means for selecting the error signal during limit periods and selecting the slew rate signal during non-limit periods for determining the inverter frequency; and
a modifier means linked to the rate means for modifying the slew rate signal as a function of the durations of the limit and non-limit periods. - View Dependent Claims (23, 24, 25, 26, 27)
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Specification