Method and apparatus for controlling induction motor

Abstract

When actuating again in induction motor rotating inertially by applying power to the induction motor from an inverter capable of changing both of its output frequency and output voltage, the power is once supplied to the induction motor to increase the residual voltage if the residual voltage of the induction motor is not sufficient, and the frequency of an initial impressed voltage that is in agreement with the rotating speed of the induction motor is determined.

What is claimed is: 
     
       1. In a method of actuating an induction motor rotating inertially by supplying power to said induction motor from power conversion means capable of changing both the output frequency F 1  and the output voltage V 1  thereof, a control method of an induction motor comprising the steps of: (a) a tentative power supply step for applying power necessary for said induction motor to generate a residual voltage above a predetermined value V 2  for a predetermined period Ta, to said induction motor during a later-appearing power supply interruption step;   (b) said power supply interruption step for interrupting the power supply to said induction motor after said tentative power supply step;   (c) a residual voltage frequency detection step for detecting the frequency fm of a residual voltage of said induction motor within said period Ta after the interruption of power supply in said power supply interruption step; and   (d) a real power supply step for supplying power having a frequency corresponding to the frequency fm of said residual voltage determined by said residual voltage frequency detection step, to said induction motor from said power conversion means.   
     
     
       2. A control method of an induction motor according to claim 1 wherein said real power supply step supplies a voltage whose initial frequency is fm and which is lower than C×fm, where Fr is a rated frequency of said induction motor and C is Vr/Fr with Vr representing a rated voltage of said induction motor, from said power conversion means to said induction motor, and said voltage is gradually increased towards C×fm while the frequency thereof is kept constant. 
     
     
       3. A control method of an induction motor according to claim 1, wherein said real power supply step supplies a voltage whose initial frequency is fm and which is lower than C×fm, where fm is the frequency of said residual voltage determined by said residual voltage frequency detection step, C is Vr/Fr, Fr and Vr are rated frequency and rated voltage of said induction motor and Fs is an output set frequency of said power conversion means, from said power conversion means to said induction motor, then the voltage is gradually increased towards C×fm while the frequency thereof is kept substantially constant, the frequency is thereafter increased towards Fs and moreover, the voltage is gradually changed to a value corresponding to said frequency Fs. 
     
     
       4. A control method of an induction motor according to claim 1 wherein said residual voltage frequency detection step detects the frequency and the phase of said residual voltage, and said real power supply step supplies power corresponding to said phase from said power conversion means to said induction motor. 
     
     
       5. In a method of actuating an induction motor by supplying, from power conversion means, power capable of changing both the output frequency F 1  and the output voltage V 1  to said induction motor rotating inertially, a control method of an induction motor comprising the steps of: (a) a tentative power supply step for increasing gradually said output voltage V 1  from a predetermined value to a value necessary for said induction motor to generate a residual voltage above a predetermined value V 2  for a predetermined period Ta in a later-appearing power supply interruption step while the output of said power conversion means is being applied to said induction motor;   (b) said power supply interruption step for interrupting the supply of power to said induction motor from said power conversion means, after said tentative power supply step;   (c) a residual voltage frequency detection step for detecting the frequency fm of the residual voltage of said induction motor within said period Ta after the interruption of the supply of power, during said power supply interruption step; and   (d) a real power supply step for supplying power having a frequency corresponding to the frequency fm of said residual voltage determined by said residual voltage frequency detection step, to said induction motor from said power conversion means.   
     
     
       6. A control method of an induction motor according to claim 5 wherein said output frequency F 1  is also increased gradually in said tentative power supply step. 
     
     
       7. A control method of an induction motor according to claim 6 wherein said output frequency F 1  and said output voltage V 1  are increased gradually while keeping the ratio V 1  /F 1  constant in said tentative power supply step. 
     
     
       8. A control method of an induction motor according to claim 6 wherein said output frequency F 1  and said output voltage V 1  are increased gradually while keeping the condition V 1  /F 1  =Vr/Fr in said tentative power supply step where Fr is a rated frequency and Vr is a rated voltage of said induction motor. 
     
     
       9. A control method of an induction motor according to claim 6 wherein said output frequency F 1  and said output voltage V 1  are gradually increased to Fr and Vr, respectively, from V 1  =a positive predetermined value when F 1  =0, in said tentative power supply step where Fr is a rated frequency and Vr is a rated voltage of said induction motor. 
     
     
       10. A control method of an induction motor according to claim 5 wherein said residual voltage frequency detection step detects the frequency and phase of said residual voltage, and said real power supply step supplied power corresponding to said phase from said power conversion means to said induction motor. 
     
     
       11. An apparatus for controlling an induction motor, comprising: power conversion means capable of changing both the output frequency F 1  and the output voltage V 1  and having the output terminals thereof connected to said induction motor;   frequency detection means for detecting the frequency of a residual voltage of said induction motor;   residual voltage insufficiency detection means for producing a signal representing that said residual voltage is zero or too small and said frequency detection means can not detect the frequency;   speed setting means for setting the speed of said induction motor; and   switching control means for receiving the outputs of said frequency detection means, said residual voltage insufficiency detection means and said speed setting means; increasing gradually said output voltage V 1  to a level corresponding to a frequency fm while keeping the output frequency F 1  of said power conversion means at fm when said frequency detection means detects said frequency fm; then approaching said output frequency F 1  and said output voltage V 1  to values corresponding to the output of said speed setting means; supplying the output of said power conversion means to said induction motor so that said induction motor can generate a residual voltage above a predetermined value V 2  for a predetermined period Ta during later-appearing power supply interruption when said residual voltage insufficiency detection means produces the signal representing the insufficiency of said residual voltage; and thereafter interrupting the supply of power from said power conversion means to said induction motor.   
     
     
       12. An apparatus for controlling an induction motor comprising: power conversion means capable of changing both the output frequency F 1  and the output voltage V 1  and having the output terminals thereof connected to said induction motor;   frequency detection means for detecting the frequency of a residual voltage of said induction motor;   phase detection means for detecting the phase of said residual voltage of said induction motor;   residual voltage frequency insufficiency detection means for producing a signal representing that said residual voltage is zero or too small and said frequency detection means can not detect the frequency;   speed setting means for setting the speed of said induction motor; and   switching control means for receiving the outputs of said frequency detection means, said residual voltage insufficiency detection means and said speed setting means; bringing the phase of the output of said power conversion means into agreement with α and increasing gradually the output voltage V 1  to a value corresponding to said frequency fm while keeping the output frequency F 1  at fm when said frequency detection means and said phase detection means detect the frequency fm and the phase α, respectively, then approaching gradually said output frequency F 1  and said output voltage V 1  to values corresponding to the output of said speed setting means; applying the output of said power conversion means to said induction motor so that said induction motor can generate a residual voltage above a predetermined value V 2  for a predetermined period Ta during later-appearing power supply interruption if said residual voltage insufficiency detection means produces the signal representing the insufficiency of said residual voltage; and thereafter interrupting the supply of power from said power conversion means to said induction motor.   
     
     
       13. An apparatus for controlling an induction motor comprising: power conversion means capable of changing both the output frequency F 1  and the output voltage V 1  and having the output terminals thereof connected to said induction motor;   frequency detection means for detecting the frequency of a residual voltage of said induction motor;   phase detection means for detecting the phase of said residual voltage of said induction motor;   residual voltage frequency insufficiency detection means for producing a signal representing that said residual voltage is zero or too small and said frequency detection means can not detect the frequency;   speed setting means for setting the speed of said induction motor; and   switching control means for receiving the outputs of said frequency detection means, said residual voltage insufficiency detection means and said speed setting means; bringing the phase of the output of said power conversion means into agreement with α and increasing gradually the output voltage V 1  to a value corresponding to said frequency fm while keeping the output frequency F 1  at fm when said frequency detection means and said phase detection means detect the frequency fm and the phase α, respectively; then approaching gradually the output frequency F 1  and the output voltage V 1  to values corresponding to the output of said speed setting means; increasing the output voltage V 1  of said power conversion means to a level necessary for said induction motor to produce a residual voltage above a predetermined value V 2  for a predetermined period Ta even during later-appearing power supply interruption while applying the output of said power conversion means to said induction motor when said residual voltage insufficiency detection means produces the signal representing the insufficiency of the residual voltage; and thereafter interrupting the supply of power from said power conversion means to said induction motor.   
     
     
       14. A control apparatus for an induction motor comprising: power conversion means capable of changing both the output frequency F 1  and the output voltage V 1  and having the output terminals thereof connected to said induction motor;   frequency detection means for detecting the frequency of a residual voltage of said induction motor;   phase detection means for detecting the phase of said residual voltage of said induction motor;   residual voltage frequency insufficiency detection means for producing a signal representing that said residual voltage is zero or too small and said frequency detection means can not detect the frequency;   speed setting means for setting the speed of said induction motor; and   switching control means for receiving the outputs of said frequency detection means, said residual voltage insufficiency detection means and said speed setting means; bringing the phase of the output of said power conversion means into agreement with α and increasing gradually the output voltage V 1  to a value corresponding to said frequency fm while keeping the output frequency F 1  at fm when said frequency detection means and said phase detection means detect the frequency fm and the phase α, respectively, then approaching gradually the output frequency F 1  and the output voltage V 1  to values corresponding to the output of said speed setting means; increasing the output voltage V 1  of said power conversion means to a level necessary for said induction motor to produce a residual voltage above a predetermined value V 2  for a predetermined period Ta even during later-appearing power supply interruption while applying the output of said power conversion means to said induction motor when said residual voltage insufficiency detection means produces the signal representing the insufficiency of the residual voltage; and thereafter interrupting the supply of power from said power conversion means to said induction motor. .Iadd.   
     
     
       15.  A control method of an induction motor according to claim 1, further comprising prior to the tentative power supply step, the steps of determining that an initial interruption of the power supply has been finished, and determining that the residual voltage is substantially zero. .Iaddend. .Iadd.16. A control method of an induction motor according to claim 15, wherein the step of determining that the interruption of the power supply has been finished is effected prior to the step of determining that the residual voltage is substantially zero. .Iaddend. .Iadd.17. A method of controlling an induction motor when supply of power to the induction motor is interrupted, comprising the steps of: (a) temporarily supplying power to the induction motor sufficient to enable the induction motor to generate a residual voltage of at least a predetermined value when the temporary supply of power is stopped; and   (b) uninterruptedly supplying power to the induction motor in accordance with the residual voltage. .Iaddend. .Iadd.18. A method according to claim 17, further comprising detecting the residual voltage of the induction motor when the temporary supply of power is stopped, and during the uninterrupted supply of power controlling the frequency of the power in accordance with a frequency of the detected residual voltage. .Iaddend. .Iadd.19. A method according to claim 17, wherein the induction motor is supplied with power from a power source through power conversion means capable of changing an output frequency and an output voltage thereof and when the supply of power from the power source is interrupted, the step of uninterruptedly supplying power to the induction motor includes resupplying power from the power conversion means to the induction motor. .Iaddend. .Iadd.20. A method according to claim 19, wherein the step of temporarily supplying power includes supplying power to the induction motor from the power conversion means. .Iaddend. .Iadd.21. A method according to claim 17, further comprising prior to the step of temporarily supplying power, the steps of determining that an interruption of the supply of power to the induction motor has been completed and that a residual voltage of the induction motor due to inertial rotation of the induction motor is substantially zero. .Iaddend. .Iadd.22. A method according to claim 21, wherein the step of determining that the interruption of the supply of power to the induction motor has been completed is effected prior to determining that the residual voltage is substantially zero. .Iaddend. .Iadd.23. A method according to claim 22, wherein the step of temporarily supplying power is effected when it is determined that the interruption of the supply of power has been completed and that the residual voltage of the induction motor is substantially zero and when it is determined that the interruption of the power supply has been completed and the residual voltage is not substantially zero, the step of uninterruptedly supplying power to the induction motor is effected. .Iaddend. .Iadd.24. A method according to claim 17, wherein the step of uninterruptedly supplying power includes detecting the residual voltages and supplying the power to the induction motor in accordance with the detected residual voltage. .Iaddend. .Iadd.25. A method of enabling control of an induction motor when supplying of power to the induction motor is interrupted, comprising the steps of:   (a) determining that the interruption of the supply of power has been completed and that a residual voltage of the induction motor due to inertial rotation of the induction motor is substantially zero; and   (b) temporarily supplying power to the induction motor sufficient to enable the induction motor to generate a residual voltage of at least a predetermined value when the temporary supply of power is stopped so as to enable control of the induction motor. .Iaddend. .Iadd.26. A method according to claim 25, further comprising the step of detecting the residual voltage of the induction motor when the temporary supply of power is stopped for enabling control of the induction motor in accordance therewith. .Iaddend. .Iadd.27. A method according to claim 26, further comprising the step of uninterruptedly supplying power to the induction motor in accordance with the detected residual voltage. .Iaddend. .Iadd.28. A method according to claim 27, wherein the step of uninterruptedly supplying power to the induction motor includes controlling the frequency of the power in accordance with a frequency of the detected residual voltage. .Iaddend. .Iadd.29. A method according to claim 26, wherein the power supplied to the induction motor is supplied from a power source through a power conversion means capable of changing an output frequency and an output voltage thereof, the supply of power from the power source being interrupted, and the step of uninterruptedly supplying power to the induction motor includes resupplying power from the power conversion means to the induction motor. .Iaddend. .Iadd.30. A method according to claim 27, wherein the step of temporarily supplying power to the induction motor includes supplying power from the power conversion means. .Iaddend. .Iadd.31. A method of controlling an induction motor when supply of power to the induction motor is interrupted, comprising the steps of:   (a) determining that the interruption of the supply of power has been completed and that a residual voltage of the induction motor due to inertial rotation of the induction motor is substantially zero; and   (b) temporarily supplying power to the induction motor sufficient to enable the induction motor to generate a residual voltage of at least a predetermined value when the temporary supply of power is stopped.   
     
     
        .Iaddend. .Iadd.32.  A method according to claim 31, further comprising the step of detecting the residual voltage of the induction motor when the temporary supply of power is stopped for enabling control of the induction motor in accordance therewith. .Iaddend. .Iadd.33. A method according to claim 32, further comprising the step of uninterruptedly supplying power to the induction motor in accordance with the detected residual voltage. .Iaddend. .Iadd.34. A method according to claim 33, wherein the step of uninterruptedly supplying power to the induction motor includes controlling the frequency of the power in accordance with a frequency of the detected residual voltage. .Iaddend. .Iadd.35. A method according to claim 32, wherein the power supplied to the induction motor is supplied from a power source through a power conversion means capable of changing an output frequency and an output voltage thereof, the supply of power from the power source being interrupted, and the step of uninterruptedly supplying power to the induction motor includes resupplying power from the power conversion means to the induction motor. .Iaddend. .Iadd.36. A method according to claim 35, wherein the step of temporarily supplying power to the induction motor includes supplying power from the power conversion means. .Iaddend. .Iadd.37. An apparatus for controlling an induction motor comprising: means for supplying power to the induction motor;   means responsive to an interruption of the supply of power for temporarily supplying power to the induction motor sufficient to enable the induction motor to generate a residual voltage of at least a predetermined value when the temporary supply of power is stopped; and   means for uninterruptedly supplying power to the induction motor in accordance with the residual voltage. .Iaddend. .Iadd.38. An apparatus according to claim 37, further comprising means for detecting the residual voltage of the induction motor when the temporary supply of power is stopped for enabling control of the induction motor in accordance therewith. .Iaddend. .Iadd.39. An apparatus according to claim 38, wherein the means for uninterruptedly supplying power to the induction motor supplies power in accordance with the detected residual voltage. .Iaddend.   
     
     
        .Iadd.40.  An apparatus according to claim 39, wherein means for uninterruptedly supplying power to the induction motor includes means for controlling the frequency of the power in accordance with a frequency of the detected residual voltage. .Iaddend. .Iadd.41. An apparatus according to claim 37, wherein the means for supplying power includes a power source supply power through a power conversion means capable of changing an output frequency and an output voltage thereof, and when the supply of power from the power source is interrupted, the means for uninterruptedly supplying power to the induction motor including means for resupplying power from the power conversion means to the induction motor. .Iaddend. .Iadd.42. An apparatus according to claim 41, wherein the means for temporarily supplying power to the induction motor includes means for supplying power from the power conversion means. .Iaddend. .Iadd.43. An apparatus according to claim 42, wherein the power conversion means includes switching means and the means for temporarily supplying power includes means for controlling the switching means of the power conversion means. .Iaddend. .Iadd.44. An apparatus according to claim 37, further comprising means for determining that an interruption of the supply of power to the induction motor has been completed and that a residual voltage of the induction motor due to inertial rotation of the induction motor is substantially zero, the means for temporarily supplying power being responsive to the determining means. .Iaddend. .Iadd.45. An apparatus according to claim 44, wherein the detecting means includes first means for determining that the interruption of the supply of power to the induction motor is completed and second means for determining that the residual voltage is substantially zero which is responsive to the first means. .Iaddend.