Voltage transients
First Claim
1. Apparatus which protects an electrical circuit from damage caused by variations in the nominal voltage level of electrical power supplied to the electrical circuit, the electrical circuit including a motor circuit, comprising:
- power supply means for supplying direct current to said motor circuit, said direct current having a nominal direct current voltage value and as associated transient voltage component;
smoothing means for limiting the amplitude of said transient voltage component to a predetermined maximum value relative to said nominal direct current voltage value;
a motor connected across said power supply means;
pulse control means for delivering time modulated current pulses from said power supply means to said motor;
sensing means for controllably producing a fault signal in response to the amplitude and frequency of occurrence of said transient voltage component exceeding predetermined maximum values; and
override means for receiving said fault signal and responsively modifying said time modulated current pulses delivered from said pulse control means.
1 Assignment
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Accused Products
Abstract
Motor control systems having solid-state components are commonly used on industrial vehicles such as lift trucks. Such solid-state components are easily damaged by excessive transient voltages. The subject invention includes a power supply for supplying direct current to a motor circuit, wherein the direct current has a nominal direct current voltage value and as associated transient voltage component. A pulse control circuit supplies current pulses from the power supply to a motor. A sensing device controllably produces a fault signal in response to the amplitude and frequency of occurrence of the transient voltage component exceeding a predetermined maximum value. An override circuit receives the fault signal and responsively modifies the current pulses delivered from the power supply to the associated motor.
32 Citations
14 Claims
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1. Apparatus which protects an electrical circuit from damage caused by variations in the nominal voltage level of electrical power supplied to the electrical circuit, the electrical circuit including a motor circuit, comprising:
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power supply means for supplying direct current to said motor circuit, said direct current having a nominal direct current voltage value and as associated transient voltage component; smoothing means for limiting the amplitude of said transient voltage component to a predetermined maximum value relative to said nominal direct current voltage value; a motor connected across said power supply means; pulse control means for delivering time modulated current pulses from said power supply means to said motor; sensing means for controllably producing a fault signal in response to the amplitude and frequency of occurrence of said transient voltage component exceeding predetermined maximum values; and override means for receiving said fault signal and responsively modifying said time modulated current pulses delivered from said pulse control means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. Apparatus which protects a motor circuit from damage caused by a defective head capacitor, comprising:
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power supply means for supplying electrical power to said motor circuit; a head capacitor connected across said power supply means and adapted to block transient voltages from said supplied electrical power; a motor connected across said power supply means; pulse control means for delivering time modulated current pulses from said power supply means to said motor; sensing means for controllably producing a fault signal in response to said head capacitor failing to block said transient voltages; and override means for receiving said fault signal and responsively modifying said time modulated current pulses delivered from said pulse control means. - View Dependent Claims (10, 11, 12, 13)
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14. A method for monitoring a head capacitor in a motor circuit, said motor circuit including an electrical power source, a motor and head capacitor connected in parallel across said power source, and pulse control means for controllably delivering current pulses from said power source to said motor, comprising the steps of:
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continuously sensing the magnitude of transient voltage across said head capacitor; producing a trigger signal in response to each time said transient voltage exceeds a predetermined magnitude; receiving said trigger signals and producing a fault signal in response to receiving at least a predetermined plurality of said trigger signals during a predetermined period of time; and receiving said fault signal and responsively controllably modifying the current pulses delivered by said pulse control circuit from said power source to said motor.
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Specification