System and method for improved motor drive tuning

Patent metadata

Field	Value
Publication number	US-9998053-B2
Application number	US-201514842538-A
Country	US
Kind code	B2
Filing date	Sep 1, 2015
Priority date	Sep 1, 2015
Publication date	Jun 12, 2018
Grant date	Jun 12, 2018

Abstract

An improved system for controlling operation of a motor with a motor drive is disclosed. The motor drive includes a control module having an inner control loop operable to generate a torque reference signal and a load observer operable to generate an estimate of the torque present on the motor. The torque estimate is summed with the torque reference signal to generate a modified torque reference. The bandwidth of the load observer is set wide enough to generate the estimated torque over a desired operating range of the motor. The control module may also include a low pass filter and at least one tracking notch filter. The low pass filter suppresses vibrations at high frequencies, and the tracking notch filter suppresses resonances present at frequencies above the bandwidth of the load observer and within the pass band of the low pass filter.

First claim

We claim:

1. A method for controlling operation of a motor operatively connected to a motor drive, the method comprising the steps of:
determining a bandwidth for a load observer executable in the motor drive, wherein the bandwidth is greater than or equal to an expected torque response generated from a load operatively connected to the motor;
reading a motor inertia value from a memory of the motor drive, wherein the motor inertia value corresponds to an inertia value for the motor when no load is connected to the motor;
executing a control module with a processor in the motor drive, wherein the control module includes:
a control loop receiving a reference signal and a feedback signal, wherein:
the reference signal is selected from one of a position reference, a speed reference, and a torque reference,
the feedback signal corresponds to an angular position of the motor, and

the control loop generates a first acceleration reference signal corresponding to a desired operation of the motor,
the load observer receiving the feedback signal corresponding to the angular position of the motor and a second acceleration reference signal, wherein the load observer generates an estimated acceleration signal corresponding to the load present on the motor;
a summing junction combining the first acceleration reference signal and the estimated acceleration signal to generate the second acceleration reference signal;
at least one filter configured to receive the second acceleration reference signal as an input and provide a filtered acceleration reference signal as an output; and
an inertia scaling factor set equal to the motor inertia value, wherein the inertia scaling factor is a gain applied to the filtered acceleration reference signal to generate a desired torque command for the motor; and

supplying at least one of a desired voltage and a desired current from the motor drive to the motor as a function of the desired torque command.

2. The method of claim 1 wherein the bandwidth of the load observer is a function of a drive model time constant (DMTC) and the DMTC is determined as a sum of a time constant of a current controller for the motor drive, a feedback sample period for the motor drive, a calculation delay for the motor drive, and a time constant of a velocity feedback filter for the motor drive.

3. The method of claim 2 wherein the bandwidth of the load observer is equal to the inverse of the product of 2π times the DMTC.

4. The method of claim 1 wherein the at least one filter includes a tracking notch filter and wherein a notch frequency of the tracking notch filter is set greater than or equal to the bandwidth of the load observer.

5. The method of claim 4 further comprising the steps of:
identifying at least one resonant frequency present in at least one of the desired voltage and the desired current supplied to the motor during operation of the motor; and
setting the notch frequency equal to the frequency of one of the at least one resonant frequencies having an amplitude greater than an amplitude of each of the other resonant frequencies.

6. The method of claim 1 wherein the control loop includes at least one of a position control loop and a velocity control loop and the position control loop and the velocity control loop each include a proportional controller and an integral controller.

7. The method of claim 6 wherein a bandwidth of the proportional controller of the velocity control loop is equal to the bandwidth of the load observer divided by a square of a desired damping factor and divided by four, a bandwidth of the proportional controller of the position control loop is equal to the bandwidth of the proportional controller of the velocity loop control divided by the square of the desired damping factor and divided by four, and the integral gain values for both the velocity and proportional control loops are zero.

8. A motor drive for controlling a motor operatively connected to the motor drive, the motor drive, comprising:
a DC bus having a positive rail and a negative rail, wherein the DC bus is operable to receive a DC voltage between the positive rail and the negative rail;
an inverter section having a plurality of switching elements, wherein each switching element is controlled by a gating signal and wherein the inverter section is operable to receive the DC voltage from the DC bus and provide an AC voltage at an output of the motor drive;
a memory device operable to store a plurality of instructions and a plurality of configuration parameters, wherein the configuration parameters include a motor inertia value corresponding to an unloaded state of the motor;
an input configured to receive a feedback signal corresponding to an angular position of the motor connected to the motor drive;
a controller operable to execute the plurality of instructions to:
determine a bandwidth for a load observer wherein the bandwidth is greater than or equal to an expected torque response bandwidth generated from a load operatively connected to the motor,
read the motor inertia value from the memory device,
set an inertia scaling factor equal to the motor inertia value,
receive the feedback signal from the input,
receive a reference signal, wherein the reference signal is selected from one of a position reference, a speed reference, and a torque reference,
generate a first acceleration reference signal corresponding to a desired operation of the motor with a control loop as a function of the feedback signal and of the reference signal,
generate an estimated acceleration signal corresponding to the load present on the motor with the load observer as a function of the feedback signal and of a second acceleration reference signal,
combine the first acceleration reference signal and the estimated acceleration signal at a summing junction to generate the second acceleration reference signal,
execute at least one filter configured to receive the second acceleration reference signal as an input and provide a filtered acceleration reference signal as an output, and
apply the inertia scaling factor to the filtered acceleration reference signal to generate a desired torque command for the motor; and

a gate driver module operable to generate the gating signal for each of the plurality of switching elements in the inverter section as a function of the desired torque command from the controller.

9. The motor drive of claim 8 wherein the bandwidth of the load observer is a function of a drive model time constant (DMTC) and the DMTC is determined as a sum of a time constant of a current controller for the motor drive, a feedback sample period for the motor drive, a calculation delay for the motor drive, and a time constant of a velocity feedback filter for the motor drive.

10. The motor drive of claim 9 wherein the bandwidth of the load observer is equal to the inverse of the product of 2π times the DMTC.

11. The motor drive of claim 8 wherein the at least one filter includes a tracking notch filter and wherein a notch frequency for the tracking notch filter is set greater than the bandwidth of the load observer.

12. The motor drive of claim 11 wherein the controller is further operable to:
identify at least one resonant frequency present in at least one of a desired voltage and a desired current supplied to the motor during operation of the motor, and
set the notch frequency equal to the frequency of the one of the at least one resonant frequencies having an amplitude greater than an amplitude of each of the other resonant frequencies.

13. The motor drive of claim 8 wherein the control loop includes at least one of a position co

Assignees

• Rockwell Automation Tech Inc

Inventors

• Miklosovic Robert J
• Fast Brian
• Chaffee Mark

Classifications

• H02P23/0004 Primary

  Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control · CPC title

• G05B13/02

  electric · CPC title

• H02P23/14 Primary

  Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage · CPC title

• H02P27/06

  using DC to AC converters or inverters (H02P27/05 takes precedence) · CPC title

• H02P23/12

  Observer control, e.g. using Luenberger observers or Kalman filters · CPC title