Method and apparatus for standstill recognition when restarting a power converter-fed AC motor without a tachometer generator

Claim 1

A method for recognizing a standstill condition of a three-phase AC motor driven by an inverter, the method comprising the steps of: a) driving the inverter for a first time duration to induce a DC current through a phase of the three-phase AC motor; b) during the first time duration, measuring a time characteristic of a motor current and recording an energy component of the motor current and a reactive component of the motor current; c) after the first time duration has lapsed, turning off the inverter for a second time duration; d) after the second time duration has lapsed, driving the inverter for a third time duration so as to short-circuit the three-phase AC motor; e) during the third time duration, measuring the time characteristic of the motor current and recording the energy component of the motor current and the reactive current component of the motor current; f) after the third time duration has lapsed, calculating an average value from the energy component of the motor current recorded during the third time duration; g) comparing the average value to a preselected limiting value; h) comparing an upper range value of the energy component of the motor current, recorded during the third time duration, to a predefined limiting value; and i) determining that the three-phase AC motor is at a standstill if the average value during the third time duration is greater than the predefined limiting value and the upper range value is positive.

Claim 2

A method for recognizing a standstill condition of a three-phase AC motor driven by an inverter, the method comprising the steps of: a) driving the inverter for a first time duration to induce a DC current through a phase of the three-phase AC motor; b) during the first time duration, measuring a time characteristic of a motor current and recording an energy component of the motor current and a reactive component of the motor current; c) after the first time duration has lapsed, turning off the inverter for a second time duration; d) after the second time duration has lapsed, driving the inverter for a third time duration so as to short-circuit the three-phase AC motor; e) during the third time duration, measuring the time characteristic of the motor current and recording the energy component of the motor current and the reactive current component of the motor current; f) after the third time duration has lapsed, calculating an average value from the energy component of the motor current recorded during the third time duration; g) comparing the average value to a preselected limiting value; h) comparing an upper range value of the energy component of the motor current, recorded during the third time duration, to a predefined limiting value; and i) determining that the three-phase AC motor is at a standstill if the average value during the third time duration is greater than the predefined limiting value and the upper range value is positive.

Claim 10

A method for recognizing a direction of rotation of a three-phase AC motor driven by an inverter, said method comprising the steps of: applying a DC current to a phase of the motor during a first time interval; measuring a time characteristic of a motor current during the first time interval; disabling the driving of the motor and allowing the motor to run in idle operation during a second time interval; short-circuiting the motor across its terminals during a third time interval; measuring a time characteristic of the motor current during the third time interval; recording a plurality of orthogonal current components based on the measurements in said first and third time intervals, wherein recorded reactive current components of said first and third time intervals are evaluated such that it is determined that the motor is rotating in a first direction when an instantaneous value of said reactive current component at a beginning of said first time interval has a negative operational sign and an instantaneous value of said reactive current component at a beginning of said third time interval has a positive operational sign, and it is determined that the motor is rotating in a second direction when said operational signs are inverted.

Claim 11

A method for recognizing a direction of rotation of a three-phase AC motor driven by an inverter, said method comprising the steps of: applying a DC current to a phase of the motor during a first time interval; measuring a time characteristic of a motor current during the first time interval; disabling the driving of the motor and allowing the motor to run in idle operation during a second time interval; short-circuiting the motor across its terminals during a third time interval; measuring a time characteristic of the motor current during the third time interval; recording a plurality of orthogonal current components based on the measurements in said first and third time intervals, wherein recorded reactive current components of said first and third time intervals are evaluated such that it is determined that the motor is rotating in a first direction when an instantaneous value of said reactive current component at a beginning of said first time interval has a negative operational sign and an instantaneous value of said reactive current component at a beginning of said third time interval has a positive operational sign, and it is determined that the motor is rotating in a second direction when said operational signs are inverted.

Claim 13

An apparatus for recognizing a standstill condition of a three-phase AC motor driven by an inverter, said apparatus comprising: a coordinate converter; a plurality of memory units; a plurality of double switches coupled between said coordinate converter and said plurality of memory units; an evaluation unit connected to said plurality of memory units; and a sequencing control coupled to said evaluation unit, said sequencing control being coupled to a control input of each of said plurality of double switches and to a control element and a trigger element of the power converter.

Claim 14

An apparatus for recognizing a standstill condition of a three-phase AC motor driven by an inverter, said apparatus comprising: a coordinate converter; a plurality of memory units; a plurality of double switches coupled between said coordinate converter and said plurality of memory units; an evaluation unit connected to said plurality of memory units; and a sequencing control coupled to said evaluation unit, said sequencing control being coupled to a control input of each of said plurality of double switches and to a control element and a trigger element of the power converter.