Method and apparatus for detecting current delay angle from motor terminal voltage
AssigneeAllen-Bradley Company, Inc.
InventorsPeter J. Unsworth, Jinghan Tao
Life of this patent
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Abstract
A method and apparatus to be used with an inverter based motor controller for determining current phase angles for the current on a single phase of a three phase AC motor from an inverter generated high frequency phase voltage sequence. The invention detects turn on delay periods and compares phase voltages during consecutive turn on delay periods to determine phase current zero crossing times which can be used along with phase voltage zero crossing times to derive current phase angle information.
Claims15
A method to be used with a motor controller having an inverter which provides a high frequency voltage sequence on each of three phases of an AC motor, a changing average value of the voltage sequence generating a low frequency alternating voltage and an associated alternating current which lags the alternating voltage by a current angle, the inverter controlled by a series of triggering pulses characterized by turn on delay periods, the method for determining zero crossing times of the alternating current on a single monitored phase, the method comprising the steps of:
- identifying the occurrences of turn on delay periods on the monitored phase;
- sensing the voltage sequence on the monitored phase during the turn on delay periods;
- and
- determining the current zero crossings from the sensed voltage sequence during the turn on delays periods.
A method to be used with a motor controller for controlling a three phase motor, the controller including a generator and an inverter having three separate legs, each leg of the inverter receiving DC voltage from a DC voltage supply and producing a high frequency voltage sequence, a changing average value of the pulse train generating a low frequency alternating voltage and an associated alternating current which lags the alternating voltage by a current angle, the generator providing upper and lower trigger signals to each leg, each of the signals being either in an ON state or an OFF state, the signal states being generated in an alternating sequence such that when one signal is ON, the other is OFF a turn on delay period between the time when one signal goes OFF and the other signal goes ON during which both signals are OFF, during turn on delay period the alternating voltage produced by a leg being high when the alternating current is negative and being low when the alternating current is positive, the method for determining the zero crossing times of the alternating current on a single monitored phase, the method comprising the steps of:
- (a) detecting a first turn on delay period;
- (b) sampling the voltage sequence during the first turn on delay period producing a first sampled voltage;
- (c) determining the polarity of the first sampled voltage;
- (d) detecting a second turn on delay period which immediately follows the first turn on delay period;
- (e) sampling the voltage sequence during the second turn on delay period producing a second sampled voltage;
- (f) determining the polarity of the second sampled voltage;
- (g) comparing the polarities of the first and second sampled voltages and:
- where the polarities are different, storing the termination time of the first turn on delay period as a current zero crossing time and;
- where the polarities are the same, repeating steps (a) through (g) with the second turn on delay period as the first turn on delay period and the next consecutive turn on delay period as the second turn on delay period.
An apparatus to be used with a motor controller having an inverter which provides a high frequency voltage sequence on each of three phases of an AC motor, a changing average value of the voltage sequence generating a low frequency alternating voltage and an associated alternating current which lags the alternating voltage by a current angle, the inverter controlled by a series of triggering pulses characterized by turn on delay periods, the method for determining zero crossing times of the alternating current on a single monitored phase, the apparatus comprising:
- a detector for identifying the occurrences of turn on delay periods on the monitored phase;
- a sensor for sensing the voltage sequence on the monitored phase during the turn on delay periods;
- and
- a calculator for determining the current zero crossings from the sensed voltage sequence and the turn on delay periods.
Dependencies are inferred from the claim text.