Faulty load detection for multi-phase electric motor

Patent metadata

Field	Value
Publication number	US-10338142-B2
Application number	US-201515321763-A
Country	US
Kind code	B2
Filing date	Jun 30, 2015
Priority date	Jun 30, 2014
Publication date	Jul 2, 2019
Grant date	Jul 2, 2019

Abstract

An electric motor is electrically commutated with the aid of circuitry, in which the phase current experiences a zero crossing at certain time points per motor phase. Owing to the inductive load portion, the time of said zero crossing of a phase current occurs at different times to the time of the zero crossing that would arise with purely ohmic loads. Without a faulty load condition, the time of said zero crossing is within an expected value range (e.g., expected time window) which can be determined by the circuitry, the ambient conditions and by diverse motor parameters. During occurrence of the a high-side and/or low-side phase connection, it is determined whether and when the current through the switched-on high-side of low-side switch becomes greater or smaller than a predeterminable threshold wherein said time measurement can extend over one or more PWM cycles.

First claim

The invention claimed is:

1. A method for obtaining an indication of a faulty load condition of a multi-phase electric brushless DC motor with electric commutation and electric drive control which is supplied by a DC voltage source, the brushless DC motor including a plurality of motor phases and having a drive unit which, per motor phase, comprises a high-side switch and a low-side switch, wherein the high-side and low-side switches of the motor phases are cyclically switched according to a switching scheme which generates time points at which a current through a motor phase experiences, in the motor phase, a zero crossing that, owing to an inductive load portion of the brushless DC motor, is temporally shifted relative to a time point of the zero crossing, wherein, without the faulty load condition, the time point of the zero crossing is within an expected value range, comprising,
detecting, during one of a predetermined high-side and low-side phase connection occurring in the switching scheme of the brushless DC motor supplied by the DC voltage source, a time when the current through one of a switched-on high-side and switched-on low-side switch becomes greater or smaller than a presettable threshold value,
measuring, from a presettable time point of the switching scheme, a time interval within which the current through the one of the switched-on high-side and switched-on low-side switch of one of the plurality of motor phases becomes greater or smaller than the presettable threshold value,
comparing one of (1) the measured time intervals of the individual motor phases among each other, and (2) the measured time intervals of each motor phase with one or more other measured time intervals from the respective motor phase and (3) the measured time intervals of the respective motor phases with presettable respective expected value ranges, and
evaluating a deviation, from presettable expected value ranges, of (a) the amount of the measured time intervals in the motor phases among each other and/or (b) the amount of the measured time intervals in one motor phase with one or more other measured intervals from the respective motor phase, as being an indication of the faulty load condition.

2. The method of claim 1 , wherein the presettable threshold value is in a vicinity of a zero crossing.

3. The method of claim 1 , wherein the presettable threshold value is determined based on at least one of the switching scheme, ambient conditions and parameters of the brushless DC motor.

4. The method of claim 1 , wherein, in case of the faulty load condition, the time point of the zero crossing is outside the expected value range, and further wherein, on a basis of a deviation from the expected value range indicates a type of the faulty load condition.

5. The method of claim 1 , wherein in the case of PWM control, the measured of the time interval extends over one or more PWM cycles.

6. The method according to claim 1 , wherein, from a type of the deviation from the expected value ranges for the individual motor phases among each other, conclusions are drawn on a type of the faulty load condition, further wherein the type of the faulty load condition is one of a shunt of motor phase toward motor phase, a shunt of motor phase toward ground, a shunt of motor phase toward supply voltage, a too high-ohmic motor phase connection, a loose contact of a motor phase, and a faulty resistance of an individual high-side or low-side switch.

7. The method of claim 1 , wherein, from a type of deviation from the expected value ranges of a measured time interval of a motor phase with one or more other measured time intervals from the motor phase, conclusions are drawn on a type of faulty load condition, further wherein the type of faulty load condition is one of a loose contact, a mechanical defect, play of a bearing, a malfunctioning motor, and further wherein a frequency of a sequentially occurring deviation indicates an exact site of the faulty load condition.

8. The method according to claim 1 , wherein, detecting a time when the current through the one of the switched-on high-side and switched-on low-side switches becomes one of greater and smaller than a presettable threshold value is performed by measuring an electrical parameter representing an amount of the current.

9. The method according to claim 8 , wherein the electrical parameter is a voltage drop across a component, further wherein the component is one of a shunt resistor and a transistor, the transistor being one of a high-side and low-side switch.

10. The method according to claim 1 , wherein, the presettable current threshold value is selected not to be equal to zero.

11. The method according to claim 1 , wherein the time interval is measured by a linear time measurement element with constant counting speed.

12. The method according to claim 1 , wherein the time interval is measured by a logarithmic time measurement element having a counting speed increasing with increasing measuring time.

13. The method according to claim 1 , wherein, instead of measuring the time interval, there is performed, merely at a fixed time point after switch-on of the one of the high-side and low-side switches, an examination for an exceeding or falling-short of the presettable current threshold value and, in accordance therewith, the measuring of the time interval is performed in a thus generated resolution.

14. The method according to claim 1 , wherein there is measured a time interval within which the current, upon a next motor phase being switched on, reaches the current threshold value again, and wherein (1) these time intervals of the individual motor phases are compared among each other or (2) the time intervals of each motor phase for itself are compared in temporal succession or (3) both, and wherein results of the comparisons are compared to expectation values valid for fault-free operation of the brushless DC motor, wherein a deviation of (a) the amount of the present time intervals among each other or (b) from the expectation values is evaluated as being an indicator of an existence of a faulty current.

15. The method according to claim 1 , wherein the expectation values for maximally allowable deviations are obtained empirically, by detecting, on one or more pre-aged reference systems with fault-free load condition, typical values, and adjusting the typical values with selectable additional allowable tolerances.

16. The method according to claim 1 , wherein the expectation values for maximally allowable deviations are—after production—obtained empirically, by detecting, on each motor system for itself with fault-free load condition, typical values, and adjusting the typical values with selectable additional allowable tolerances.

17. The method according to claim 1 , wherein the expectation values for maximally allowable deviations are, in the course of a lifetime of the brushless DC motor, provided with higher tolerances.

18. The method according to claim 1 , wherein, in case that the detected faulty load condition is generated by deviation of a commutation angle from the presettable expected value range, the drive unit then compensates for the deviation by adaptation of at least one of a drive parameter “amplitude” and a drive parameter “phase”.

Assignees

• Elmos Semiconductor Ag

Inventors

• Hartzsch Jörg

Classifications

• H02P29/027 Primary

  the fault being an over-current · CPC title

• H02P29/024

  Detecting a fault condition, e.g. short circuit, locked rotor, open circuit or loss of load · CPC title

• G01R19/16547

  voltage or current in AC supplies (switching for protection H02H; circuits for emergency power supply H02J9/00) · CPC title

• H02P29/0241

  the fault being an overvoltage · CPC title

• G01R31/343 Primary

  in operation · CPC title