JP3507235B2 - Inverter device for driving induction motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for driving an induction motor having a function of controlling a flux linkage and an output torque of the induction motor, respectively. 2. Description of the Related Art Generally, there is known an inverter for driving an induction motor having a function of controlling a flux linkage and a torque of the induction motor and controlling a speed of the induction motor.
This is as shown in FIG. FIG. 2 shows a conventional example, in which 1 is a DC power supply, 2 is a DC voltage detector, 3 is a three-phase inverter circuit, 4 is an output voltage detector for each of U, V and W phases, and 5 is U, V output current detectors for each phase, 6 is a motor (hereinafter simply referred to as a motor), 7 is a speed detector, 8 is a speed command operation circuit, 9 is a speed control circuit, 10 is a torque limiting circuit, and 11 is a magnetic flux command. A setting circuit, 12 is a torque control circuit, 13 is a magnetic flux control circuit, 14 is a PWM generation circuit, 15 is a magnetic flux calculation circuit, and 16 is a torque calculation circuit. In FIG. 2, an inverter circuit 3 obtains a DC power supply 1 and drives a motor 6. In addition, the speed control circuit 9 uses the deviation between the speed command N * set by the speed command calculation circuit 8 and the actual rotation speed N detected by the speed detector 7 to determine the torque command TR1. The torque command TR1 is limited by the torque limiting circuit 10 to a range in which the electric motor 6 can output, and is converted into a torque command TR2. A torque control circuit 12 calculates a torque component voltage command Tv from a deviation between the torque command TR2 and the actual torque T obtained by the torque calculation circuit 16. On the other hand, the magnetic flux control circuit 13 calculates the magnetic flux component voltage command φv from the deviation between the primary interlinkage magnetic flux command φR1 given from the magnetic flux command setting circuit 11 and the magnitude of the primary interlinkage magnetic flux vector φ1 obtained by the magnetic flux calculation circuit 15. Calculate. Here, the magnetic flux calculation circuit 15 calculates a primary interlinkage magnetic flux vector φ1 from the output voltage vector V0 obtained by the output voltage detector 4, and calculates a torque calculation circuit.
In the case of 16, the primary linkage flux vector φ1 and the output current detection circuit 5
The actual torque T is calculated from the output current vector I0 obtained by the above. [0005] The PWM generation circuit 14 generates a torque component voltage command T
The gate signals Su, Sv, and Sw for each phase of U, V, and W are calculated from v and the magnetic flux component voltage command φv, and given to the inverter circuit 3. Therefore, the three-phase AC voltage output from the inverter circuit 3 which is acted on by the gate signals Su, Sv, Sw is applied to the electric motor 6. Here, the speed back electromotive voltage of the electric motor 6 is proportional to the magnitude of the primary linkage flux vector φ and the actual rotation speed N. If the speed back electromotive voltage is larger than the voltage that can be output from the inverter circuit 3, the above-described control becomes impossible. Therefore, the primary interlinkage magnetic flux command φR1 indicates that the speed back electromotive voltage is equal to the inverter speed at the rated rotation speed of the motor 6. The magnetic flux command setting circuit 11 sets the voltage to be smaller than about 90% of the output voltage of the circuit 3. However, when the voltage of the DC power supply 1 drops significantly below the rated voltage, the voltage that can be output from the inverter circuit 3 drops in proportion, so that the speed back electromotive voltage becomes larger and control becomes impossible. . Therefore, in the speed command calculation circuit 8, the speed command N * is adjusted as shown in FIG. 3 using the DC voltage VDC obtained by the DC voltage detector 2. FIG. 3 shows the limit value of the speed command when the DC voltage drops,
Nr is the rated rotation speed of the electric motor 6. That is, when the DC power supply voltage becomes 90% or less of the rated voltage, the speed command is limited to a value or less that is proportional to the DC power supply voltage. In the prior art of this type, when the DC power supply voltage drops to 90% or less of the rated voltage, the rotational speed of the motor always becomes a value proportional to the DC power supply voltage. Therefore, there is a problem that the speed cannot be controlled to an intended speed. It is an object of the present invention to provide an induction motor driving inverter device capable of minimizing a decrease in the rotation speed of the motor even when the DC power supply voltage is reduced. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a speed setting section for setting a rotation speed of an electric motor, and a primary or secondary side of the electric motor. A magnetic flux setting section for setting a command value of the linkage flux, a torque limit setting section for setting a limit value of the output torque of the motor, and an output torque command based on a speed command value of the output of the speed setting section and the actual rotation speed of the motor. A speed control unit that calculates the value, a magnetic flux control unit that controls the primary or secondary linkage flux of the motor to follow the magnetic flux command obtained from the magnetic flux setting unit, and an output torque that follows the torque command value And a torque control unit and a flux linkage command that are proportional to the power supply voltage and inversely proportional to the rotation speed of the motor when the power supply voltage supplied to the inverter circuit falls below the rated value. When And means for controlling the above. [0010] With this solution, the following effects can be obtained. That is, when the DC voltage is reduced, the output torque limit value is controlled so as to be proportional to the DC voltage and inversely proportional to the rotation speed of the motor, so that the load torque of the motor is smaller than the output torque limit value. The torque command is not limited to the torque limit value, and the rotation speed of the electric motor can be controlled according to the speed command. Also, when the load torque of the motor is larger than the output torque limit value, the output torque is limited and the rotation speed of the motor decreases, but if the rotation speed of the motor decreases, the output torque limit value increases. The motor is operated at a rotational speed at which the load torque of the motor and the output torque limit value match. Furthermore, since the command value of the linkage flux is also controlled so as to be similarly proportional to the DC voltage and inversely proportional to the rotation speed of the motor,
The back electromotive voltage of the motor does not exceed the maximum output voltage of the three-phase inverter circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specifically, in particular, a coefficient calculation circuit which receives a DC power supply voltage and an actual rotation speed of a motor as signal inputs, and a primary circuit obtained by multiplying an output of the coefficient calculation circuit by an output of a magnetic flux command setting circuit. A first multiplier for generating a linkage flux command signal in the magnetic flux control circuit; and a second multiplier for generating in the torque limit circuit a torque limit signal obtained by multiplying the torque limit value by the coefficient operation circuit output. It is. Further, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of the present invention in a manner similar to FIG. 2, wherein 8 'is a speed command operation circuit, 10' is a torque limiting circuit, and 17 is a coefficient operation circuit. , 18, and 20 are multipliers, and 19 is a limit value setting circuit. That is, in FIG. 1, the speed control circuit 9 uses the deviation between the speed command N * set by the speed command calculation circuit 8 'and the actual rotation speed N detected by the speed detector 7 to determine the torque command TR1. Desired. Here, the torque command TR1 is limited to the torque limit value TL2 by the limit value setting circuit 19 and the multiplier 20 by the torque limiting circuit 10 'and converted into the torque command TR2'. The torque control circuit 12 calculates a torque component voltage command Tv from the deviation between the torque command TR2 'and the actual torque T obtained by the torque calculation circuit 16. On the other hand, the magnetic flux control circuit 13 calculates the magnetic flux based on the deviation between the primary linkage flux command φR2 given by the magnetic flux command setting circuit 11 and the multiplier 18 and the magnitude of the primary linkage flux vector φ1 obtained by the magnetic flux calculation circuit 15. Calculate the divided voltage command φv. Here, the magnetic flux calculation circuit 15 calculates the primary interlinkage magnetic flux vector φ1 from the output voltage vector V0 obtained by the output voltage detector 4, and the torque calculation circuit 16 obtains the primary interlinkage magnetic flux vector φ1 and the output current detection circuit 5. The actual torque T is calculated from the output current vector I0 to be obtained. The PWM generation circuit 14 generates a torque component voltage command T
The gate signals Su, Sv, and Sw for each phase of U, V, and W are calculated from v and the magnetic flux component voltage command φv, and given to the inverter circuit 3. Therefore, the three-phase AC voltage output from the inverter circuit 3 which is acted on by the gate signals Su, Sv, Sw is applied to the electric motor 6. Here, the primary interlinkage magnetic flux command φR1 is set by the magnetic flux command setting circuit 11 so that the speed counter electromotive voltage is smaller than about 90% of the voltage that can be output from the inverter circuit 3 at the rated speed of the motor 6. ing. The primary flux linkage command φR2 is converted to the primary flux linkage command φR1 by a coefficient calculation circuit.
It is obtained by multiplying the coefficient K of 17 output by the multiplier 18. Further, the torque limit value TL2 is added to the torque limit value TL1 set by the torque limit value setting circuit 19 by the coefficient calculation circuit 17.
It is obtained by multiplying the output coefficient K by the multiplier 20. The coefficient K is obtained by the coefficient calculation circuit 17. Here, the coefficient K is obtained from the actual rotation speed N and the DC voltage VDC by the calculation of Expression (1). VDCr is a DC power supply voltage rated value. However, if (K> 1), then (K = 1)
And K = Nr / N.times.VDC / (VDCr.times.0.9) (1) Here, the coefficient K obtained in this manner is used as a primary interlinkage flux command value and torque limit. Even if the DC voltage is lower than the rated value by multiplying the value, the motor back electromotive voltage does not exceed the maximum outputtable voltage of the inverter circuit 3 and the load torque of the motor is smaller than the output torque limit value. The torque command is not limited to the torque limit value, the rotation speed of the induction motor can be controlled according to the speed command, and when the load torque of the motor is larger than the output torque limit value, the output torque is limited and the rotation of the motor is restricted. Although the speed decreases, the output torque limit value increases if the motor speed decreases, so that the motor is operated at a speed at which the load torque of the motor matches the output torque limit value. That. Although the embodiment has shown the example of the device for controlling the primary flux linkage, it is apparent that the same control is possible in the device for controlling the secondary flux linkage. Further, needless to say, the present embodiment may be realized by software. As described above in detail, according to the present invention, it is possible to provide an apparatus having a simple configuration capable of minimizing a decrease in the rotation speed of the electric motor even when the DC power supply voltage decreases.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram showing one embodiment of the present invention. FIG. 2 is a system diagram showing a conventional inverter device for driving an induction motor. FIG. 3 is a diagram showing a limit value of a speed command when a DC voltage drops. [Description of Signs] 1 DC power supply 2 DC voltage detector 3 Inverter circuit 4 Output voltage detector 5 Output current detector 6 Induction motor (motor) 7 Speed detector 8 Speed command calculation circuit 8 'Speed command calculation circuit 9 Speed control Circuit 10 Torque limiting circuit 10 'Torque limiting circuit 11 Magnetic flux command setting circuit 12 Torque control circuit 13 Magnetic flux control circuit 14 PWM generation circuit 15 Magnetic flux arithmetic circuit 16 Torque arithmetic circuit 17 Coefficient arithmetic circuit 18 Multiplier 19 Limit value setting circuit 20 Multiplier

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ identification code FI H02P 5/408 H (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 21/00 H02M 7/48 H02P 5 / 41

Claims (1)

(57) [Claims 1] A speed setting unit for setting a rotation speed of an induction motor, and a magnetic flux setting unit for setting a command value of a flux linkage on a primary side or a secondary side of the induction motor. A torque limit setting unit that sets a limit value of the output torque of the induction motor, a speed control unit that calculates a command value of the output torque from a speed command value output from the speed setting unit and an actual rotation speed of the induction motor, A magnetic flux control unit for controlling the primary or secondary linkage magnetic flux to follow a magnetic flux command obtained from the magnetic flux setting unit; and a torque control for controlling the output torque to follow a torque command value. An inverter device for driving an induction motor, comprising: a power supply voltage supplied to an inverter circuit, when the power supply voltage falls below a rated value, the torque is proportional to the power supply voltage and inversely proportional to the rotation speed of the induction motor. An inverter device for driving an induction motor, comprising: means for controlling a command limit value and a command value of linkage flux.