Method and apparatus for control of current in a motor winding
First Claim
1. In a method for controlling the flow of current in an inductive load to cause the current to follow a certain command waveform having a rapidly decaying portion, comprising the steps of:
- connecting the inductive load across a power supply for flow of current through the inductive load in a first direction;
connecting first and second current modulators in series with said inductive load and on opposite sides of said load, for modulating the flow of current through the inductive load;
connecting a first diode in parallel with the series connection of the inductive load and said second current modulator, and in reverse polarity to the first direction of current flow, for allowing the current to circulate through the inductive load and the second current modulator in the first direction when the current flow to the inductive load from the power supply is interrupted by said first current modulator;
connecting a second diode in parallel with the series connection of the inductive load and said first current modulator, and in reverse polarity to the first direction of the current flow, for allowing the current to circulate through the inductive load in the first direction, and through the power supply and the first diode in the opposite direction, when the current is interrupted by both said first and second current modulators, whereby the circulating current in said inductive load is caused to decay rapidly;
sensing the flow of current through said second current modulator;
sensing the flow of current through said first diode;
comparing the sensed currents with the command waveform to derive an error signal;
controlling said first current modulator in response to the error signal, derived from the comparison of the sensed current flow through said second current modulator so as to cause the modulating current to follow the command waveform;
sensing loss of current control when the first current modulator can no longer cause the current through the inductive load to decay rapidly enough to follow the decaying portion of the command waveform; and
cutting off the current flow through both of said first and second current modulators in response to sensing loss of current control, to cause the current to circulate through the power supply in the opposite direction, and through the inductive load in the first direction, whereby the current in the inductive load in the first direction is caused to decay rapidly.
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Accused Products
Abstract
A current driver circuit for an inductive load, such as a motor winding, provides unidirectional, controlled current through the winding by use of two pulse width modulator switches on opposite sides of the winding or bidirectional current control by use of two pairs of pulse width modulated switches; each pair straddling the winding relative to the power supply. Each pair of switches is modulated in two different modes to control current during two different operating conditions. The first mode of modulation is used for all but rapidly decaying winding current conditions and a second mode provides control for rapidly decaying winding current. In the first mode, unidirectional current to the winding from the power supply is pulse width modulated while the companion switch of the pair is on. In the second mode of operation for rapidly decaying current control, current from the power supply to the winding is shut off by one switch while the companion switch is pulse width modulated to cyclically switch winding, circulating current back through the power supply in the reverse direction to allow rapid decay of the circulating current. In this manner, increased efficiency is obtained while reducing electromagnetic interference.
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Citations
10 Claims
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1. In a method for controlling the flow of current in an inductive load to cause the current to follow a certain command waveform having a rapidly decaying portion, comprising the steps of:
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connecting the inductive load across a power supply for flow of current through the inductive load in a first direction; connecting first and second current modulators in series with said inductive load and on opposite sides of said load, for modulating the flow of current through the inductive load; connecting a first diode in parallel with the series connection of the inductive load and said second current modulator, and in reverse polarity to the first direction of current flow, for allowing the current to circulate through the inductive load and the second current modulator in the first direction when the current flow to the inductive load from the power supply is interrupted by said first current modulator; connecting a second diode in parallel with the series connection of the inductive load and said first current modulator, and in reverse polarity to the first direction of the current flow, for allowing the current to circulate through the inductive load in the first direction, and through the power supply and the first diode in the opposite direction, when the current is interrupted by both said first and second current modulators, whereby the circulating current in said inductive load is caused to decay rapidly; sensing the flow of current through said second current modulator; sensing the flow of current through said first diode; comparing the sensed currents with the command waveform to derive an error signal; controlling said first current modulator in response to the error signal, derived from the comparison of the sensed current flow through said second current modulator so as to cause the modulating current to follow the command waveform; sensing loss of current control when the first current modulator can no longer cause the current through the inductive load to decay rapidly enough to follow the decaying portion of the command waveform; and cutting off the current flow through both of said first and second current modulators in response to sensing loss of current control, to cause the current to circulate through the power supply in the opposite direction, and through the inductive load in the first direction, whereby the current in the inductive load in the first direction is caused to decay rapidly. - View Dependent Claims (2, 3, 4, 5, 6)
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7. In a motor-drive circuit for causing the current in the motor winding to follow a certain command waveform having a rapidly decaying portion comprising
current supply means for supplying a flow of current in a first direction; -
a motor winding connected across said current supply means for flow of current from said current supply means through said motor winding for driving said motor; first and second current modulator means connected in series with said motor winding and on opposite side of said winding for modulating the flow of current through said winding; a first diode means connected in parallel with the series connection of said motor winding and said second current modulator means, and in reverse polarity to said first direction of current flow, for allowing current to circulate through said motor winding and said second current modulator means in the first direction when the current flow to said motor winding from said power supply means is interrupted by said first current modulator means; a second diode means connected in parallel with the series connection of said motor winding and said first current modulator means and in reverse polarity to the first direction of current flow for allowing the current to circulate through said motor winding in the first direction, and through said power supply means and said first diode means in the opposite direction, when the current is interrupted by both said first and second current modulator means, whereby the circulating current in said motor winding is caused to decay rapidly; first sensing means for sensing the flow of current through said second current modulator means to derive a first sensed output; comparator means for comparing said first sensed current output with the command waveform to derive a first error signal output; said first current modulator means being responsive to said first error signal output, for causing the current flowing through said motor winding and said second current modulator means to follow the command waveform; control sensing means including means for sensing loss of control over the current in said motor winding and means for producing a loss of control output when said first current modulator means can no longer cause the current through said motor winding, to decay rapidly enough to follow the rapidly decaying portion of the command waveform; and said second current modulator means being responsive to said loss of control output, for modulating current flow therethrough and for causing current to circulate through said motor winding in the first direction, through said second diode, power supply means, and first diode means in the opposite direction, and to cause the circulating current in said motor winding to decay rapidly. - View Dependent Claims (8, 9, 10)
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Specification