System and method for controlling modulation of an inverter

Patent metadata

Field	Value
Publication number	US-9559630-B2
Application number	US-201414290247-A
Country	US
Kind code	B2
Filing date	May 29, 2014
Priority date	Mar 28, 2014
Publication date	Jan 31, 2017
Grant date	Jan 31, 2017

Abstract

A current measurement module is adapted to measure an observed current level for the inverter. A data processor or mode controller accesses a stored representation of first current level versus rotor speed output at which a total harmonic distortion level is less than threshold total harmonic distortion level. The data processor or mode controller enables the inverter to use SVPWM (space vector pulse width modulation) if the observed current level is less than the first current level for the measured or determined rotor speed. Further, the data processor or mode controller enables the inverter to use DPWM (discontinuous pulse width modulation) if the observed current level is greater than or equal to the first current level for the measured or determined rotor speed.

First claim

The following is claimed:

1. A method for controlling an inverter, the method comprising:
measuring a rotor speed of a motor coupled to the inverter;
measuring an observed current level at a fundamental frequency for the inverter;
accessing a stored representation of first current level, at the fundamental frequency, versus rotor speed output at which the total harmonic distortion level is less than a threshold total harmonic distortion level, where the total harmonic distortion level can be expressed as a percentage and where the total harmonic distortion level is estimated based on amplitude of one or more harmonic frequencies compared to an amplitude of the fundamental frequency;
enabling the inverter to use SVPWM (space vector pulse width modulation) if the observed current level is less the first current level for the measured rotor speed and for the fundamental frequency; and
enabling the inverter to use DPWM (discontinuous pulse width modulation) if the observed current level is greater than or equal to the first current level for the measured rotor speed and for the fundamental frequency.

2. The system according to claim 1 further comprising:
establishing the threshold total harmonic distortion (THD) level by defining the current level above which the THD while using DPWM is less than the desired limit for a particular inverter coupled to the motor or an equivalent load.

3. The method according to claim 1 wherein in the measuring of the observed current comprises measuring a commanded current.

4. The method according to claim 1 wherein the enabling of the inverter to use DPWM further comprises:
opposing or inhibiting the use of DPWM for an observed sampling period if the observed current level is greater than or equal to the first current level by less than a hysteresis amount for a sampling period and if the inverter is currently operating in the SVPWM mode for an earlier sampling period substantially immediately prior to the observed sampling period.

5. The method according to claim 1 further comprising:
determining an observed modulation index level for a sampling period; and
determining whether the observed modulation index level is greater than a threshold modulation index level for the sampling period; and
enabling the inverter to operate in the DPWM mode if the observed modulation index is greater than the threshold modulation index level for the sampling period.

6. The method according to claim 5 wherein the enabling of the inverter to use DPWM further considers a second countervailing factor of hysteresis to oppose or inhibit the use of DPWM for an observed sampling period if the observed modulation index is greater than the threshold modulation index level by less than a hysteresis amount for a sampling period and if the inverter is currently operating in the SVPWM mode for an earlier sampling period substantially immediately prior to the observed sampling period.

7. The method according to claim 5 wherein the modulation index is defined based on the active switching time for each inverter phase divided by the total switching period for that inverter phase, where the modulation index is generally equal to or between 0 and 1.

8. The method according to claim 5 wherein the modulation index is defined based on the amplitude of the direct axis voltage and the amplitude of the quadrature axis voltage.

9. The method according to claim 5 wherein the modulation index level threshold comprise a generally constant value that is associated with the observed current that decreases with increasing rotor speed.

10. The method according to claim 1 further comprising:
enabling the inverter to use SVPWM if the rotor speed is lower than threshold rotor speed.

11. The method according to claim 1 further comprising:
enabling the inverter to use SVPWM if the observed current is less than a first current level for a corresponding rotor speed, where the first current level is associated with the THD threshold level and where the observed modulation index is equal to or less than a threshold modulation index level.

12. The method according to claim 1 further comprising:
transitioning from an existing operational mode to a new operational mode, where the existing operational mode and the new operational mode are selected from the group of operating modes consisting of SVPWM and DPWM based on the determined rotor speed, an estimated THD level associated with a stored representation for a corresponding current and rotor speed, and the observed modulation index.

13. The method according to claim 1 wherein the stored representation comprises a linear equation, a quadratic equation, a curve, a region, an area, a set of data points, a look-up table, a database or a file that is established:
during a characterization process, operating the inverter in a DPWM mode;
during a DPWM mode at each rotor speed, determining a current level at which the total harmonic distortion is less than a threshold level to produce the representation.

14. The method according to claim 13 wherein the total harmonic distortion level is less than or equal to approximately ten percent total harmonic distortion.

15. The method according to claim 1 further comprising:
adding a hysteresis band associated with the representation to prevent transitioning between the SVPWM and the DPWM that exceeds a target transition speed.

16. The method according to claim 1 wherein the observed current comprises one or more of the following electrical currents: a commanded current level, an aggregate current derived from direct axis current and quadrature axis current, or a first phase current, a second phase current, and a third phase current, digital representations of any of the foregoing currents.

Assignees

• Deere & Co

Inventors

• Marohl Christopher L
• Holmburg David
• Weber Anthony
• Wu Long
• Lervik Jared

Classifications

• H02P27/085 Primary

  wherein the PWM mode is adapted on the running conditions of the motor, e.g. the switching frequency · CPC title