Turn-on delay compensator for motor control

A method to be used with a PWM generator which receives first, second and third command voltages from a controller and uses the command voltages to generate associated first, second and third terminal voltages at, and first, second and third currents through, motor terminals, the method for substantially eliminating turn-on delay distortions in the terminal voltages and associated current by modifying the command voltages, the method comprising the steps of:

• sensing the first, second and third terminal currents and providing an first, second and third amplitude signals indicative of the first, second and third current amplitudes;
• comparing the first, second and third amplitude signals to upper and lower limit values which define a current range to determine when the first, second and third amplitude signals are within the range;
• and
• altering the first command voltage as a function of the first terminal current when the first amplitude signal is within the current range, altering the second command voltage as a function of the second terminal current when the second amplitude signal is within the current range and altering the third command voltage as a function of the third terminal current when the third amplitude signal is within the current range.

A method for tuning a turn-on delay compensator using a closed loop current controller during a commissioning procedure to essentially eliminate turn-on delay distortions in first, second and third terminal voltages at motor terminals during subsequent control using an open loop controller, the closed loop controller provides both d and q-axis voltages and associated command voltages for controlling a PWM generator and provides three phase current feedback signals corresponding to the three phase terminal voltages, the compensator receives the feedback currents, adjusts the currents using a compensator gain and generates correction voltages to be added to the command voltages by comparing the adjusted amplitudes to upper and lower limit values, when an adjusted amplitude exceeds the upper limit value, the compensator sets the correction voltage equal to an upper threshold value, when an adjusted amplitude is less than the lower limit value, the compensator sets the correction voltage equal to a lower threshold value and when the adjusted amplitude is between the upper and lower limit values, the compensator sets the correction voltage equal to an amplitude which is between the upper and lower threshold values and which is dependent on the adjusted amplitude, the compensator tunable by adjusting a compensator gain, the method comprising the steps of:

• (a) receiving first, second and third feedback currents and providing first, second and third amplitude signals indicative of the first, second and third current amplitudes;
• (b) mathematically combining the first, second and third amplitude signals and the gain to provide first, second and third adjusted amplitudes;
• (c) monitoring the d-axis voltage, when the d-axis voltage exhibits minimum distortion, skipping to step f;
• (d) modifying the variable gain;
• (e) repeating steps a through d;
• and
• (f) storing the gain as a tuned gain for the compensator.