JPS6031194B2 - Control method of induction motor - Google Patents

Description

[Detailed description of the invention] The present invention relates to a control method for an induction motor.

Figure 1 shows an example of a conventional control system for a transfer motor. The AC signal is supplied to the converter 3, inversely converted in the inverter 3, and an AC output of a desired frequency is taken out to drive the induction motor IM.

Describing the configuration of the control device for the induction motor M driven by the inverter device having the forward converter 1 and the inverse converter 3 as described above, 4 is a speed generator that detects the rotational speed of the induction motor IM, and 5 is a speed generator. A matching circuit 6 is supplied with the rotational speed detection value (mountain r) d and the rotational speed setting value (scream) s of the speed generator 4 and takes out a deviation signal thereof; 6 inputs the output of the matching circuit 5; An amplifier with a speed control limiter 7 amplifies the output of the amplifier with a limiter 8. and the slip detection speed (■r)d of the speed generator 4 are supplied,
A matching circuit 9 that sends out the deviation output (S) d is supplied with the output (■S) d of the matching circuit 7 and the set value (S) s of the slip angle frequency based on the output of the amplifier 6. a matching circuit 1 for supplying the deviation output to the amplifier 8;
0 is a voltage-to-frequency converter that converts the output o of the amplifier 8 into a frequency signal, 11 is a distributor that controls the thyristor gate of the inverse converter 3 based on the output of the voltage-to-frequency converter 10, and 12 is the aforementioned A multiplication circuit receives the output of the amplifier 6 as a set value (12)s of the secondary current and calculates its square; 13 a multiplier circuit receives the no-load current IM (constant) and calculates its square; and 14 a multiplication circuit. An adder circuit 15 is supplied with the output of the circuit 12 and the output of the multiplier circuit 13 and takes out the sum thereof, and 15 is supplied with the output of the matching circuit 14, and sends out the output as the primary current setting value (1,)s. A square root calculator 16 is supplied with the primary current value (1,) d detected by a DC transformer 17' provided on the output side of the forward converter 1 and the output (1·) s of the square root calculator 15. , a matching circuit that sends the deviation output to the amplifier 17 with a limiter, and 18 a phase adjuster that controls the thyristor gate of the forward converter 1 based on the output of the amplifier 17. FIG. 2 shows another example of a conventional induction motor control system, and the difference from FIG. 1 is that the detected speed value (mountain r) d, which is the output of the speed generator 4,
The deviation output o obtained by matching the output s of the amplifier with a transmitter 6 with the matching circuit 19 is converted to the voltage-frequency converter 1.
0, and the other configurations are as follows.
Components that are the same as those in the figure or have the same functions are designated by the same reference numerals.

The above-described control systems for induction motors shown in FIGS. 1 and 2 have the following problems.

That is, '1- It is necessary to detect the rotation speed of the induction motor.

'2} Since the primary current 1 is specified instead of the secondary current 12, even if the primary current reaches the specified value, the secondary current does not necessarily reach the specified value. In a transient state, the excitation component and the effective component are not allocated as expected. '31 For current type, the frequency (including phase) of the current should be specified, but
Specifies the voltage frequency.

In a transient state, there is a change in the power factor angle, and this change becomes a problem. [41 In the method shown in Figure 2, there is no time delay in the slip frequency control system, and there is a time constant in the current control system, so
In transient conditions, the ratio of secondary current to slip angular frequency is not constant.

The present invention aims to solve these conventional problems and improve control performance (improvement in stability and response speed), and will be described below using examples.

FIG. 3 shows an embodiment of an induction motor control system according to the present invention, and the same reference numerals are used for the same parts or parts having the same functions as in FIG. 1.

In the figure, the output voltage of the inverter 3 is detected as a primary voltage by an instrument transformer 20, and the detected value (V,) d is input to a slip angular frequency calculation circuit 21.

A current (1,) d of the DC circuit detected by the DC current transformer 17' is inputted to the slip angular frequency calculation circuit 21 as a primary current. Further, as the detected value of the angular frequency, v of the angular frequency signal of the primary voltage, which will be described later, is used, and v of the angular frequency signal of the primary voltage is input to the slip angular frequency calculation circuit 21. The slip angle frequency calculation circuit 21 calculates these primary current detection values (1,) d and primary voltage detection values (V,
)d, calculate the slip angular frequency using Y of the angular frequency signal of the primary voltage, and let the calculated value be (S)c. A matching circuit 22 matches the primary voltage angular frequency set value (v) s and the primary voltage angular frequency signal v corresponding to the detected value, and outputs the bound deviation signal to an amplifier 23 with a limiter for frequency control.
The output is set as the secondary current setting value (12) s and the slip angle frequency setting value (shame) s. in this case,
The limiter in the limiter amplifier 23 is set so that the slip does not exceed the maximum torque value. In the secondary current control loop, in the secondary current calculation circuit 24, the secondary firewood 8
2, the primary current 1, (here we use the primary current (1,) d detected by the DC current transformer 17') and other directly detectable quantities and the slip angular frequency s (here we use the slip angular frequency calculation) (using the calculated value (s)c which is the output of the circuit 21), etc., and set it as (12)c.

This secondary current calculation method will be described later. The matching circuit 25 outputs (12) oc and I of the secondary current calculation circuit 24.
The secondary current setting value (1
2) The deviation output obtained by matching the values s and s is taken out as the primary current set value (1,)s via the limiter equipped amplifier 26 and inputted to the matching circuit 27. In order to suppress the primary current below the limit value, the set value (1,)s is set below the limit value by the limiter in the limiter amplifier 26. A matching circuit 27 matches the primary fin current (1,) d detected by the DC current transformer 17' with the set value (1,) s, and the phase of the deviation output is adjusted via the amplifier 17 with a limiter. m by the output of this phase adjuster 18.
The thyristor gate of the converter 1 is controlled to bring the primary current to the set value. Next, in the control of the slip angular frequency, the set value of the slip angular frequency (■s) s and the calculated detected value of the slip angular frequency (s) which is the output of the slip angular frequency calculation circuit 21 are used.
)c are matched by a matching circuit 28, and the deviation output thereof is amplified by an amplifier with a limiter 29 to make it similar to the angular frequency signal of the primary current.

The power factor angle differential value calculation circuit 30 is a slip angle frequency circuit 21
The time differential value of the power factor angle is calculated based on the output (S)c of . A method for calculating the time differential value of the power factor angle will be described later. The angular frequency signal of the primary voltage is added to the adder circuit 3.
1, it is obtained by adding i of the angular frequency signal of the primary current and the time differential value of the power factor angle. The reason for this is that in a steady state, the primary current angular frequency and the primary voltage angular frequency are equal, but in a transient state due to load fluctuations, etc., they differ. This situation is shown in FIG. 11. For example, in a steady state, it is assumed that the power factor angle is the same, and that the primary current and the primary voltage have waveforms shown by solid lines and {ii), respectively. Here, let us consider a case where the primary voltage becomes the waveform shown by the chain line 'iii'' due to load fluctuations, and the power factor angle changes to 2 and becomes worse. In order for the power factor angle to change to 2, the angular frequency of the primary voltage must increase. The amount of change in the angular frequency becomes the differential value of the change in the power factor angle, and this can be expressed by the formula: ■v2=V, 10. v, , v2 are the primary voltage angular frequencies before and after the change, respectively. By the way, since v is the value before the change, that is, in the steady state, it is equal to the primary current angular frequency. Therefore, the angular frequency of the primary voltage is the sum of the angular frequency of the primary current and the time derivative of the power factor angle. The angular frequency signal v of this primary voltage is used as the detected angular frequency value instead of the detected value of the rotational speed. of the signal corresponding to the angular frequency of the primary current, is the voltage-frequency converter 1
0' is input and controls the thyristor gate of the inverter 3 via the distributor 11. Here, the secondary current 12
The time constants of the limiter amplifiers 26 and 29 are adjusted so that the ratio of s to the slip angular frequency is always constant including the transient state.

Next, the method for calculating the secondary current, the method for calculating the slip angular frequency, and the method for calculating the time differential value of the power factor angle will be described in detail below. [1] Calculation method of secondary current The secondary current is calculated from the primary current 1, other forces that can be directly detected, and the slip angle frequency using one of the following calculation methods m to [3].

○} Method for determining secondary current from primary current and slip angular frequency Secondary current Ima・2=Zoza+Geijibata M×Lrl・---(1}Here, r2: Resistance of secondary circuit M: Primary Mutual inductance between the circuit and the secondary circuit (L2: leakage inductance of the secondary circuit) is given by Z.

Therefore, if we set ■SM F(s): zo r20 S2(M+L)2, we get 12=F(wS)・1,...■.

F (mountain s) is obtained using a polygonal line approximation function generator or the square root of the sum of squares. Here, for the slip angle frequency s, a calculated detected value, which will be described later, is used. As shown in FIG. 5, the secondary electrical toy 2 inputs the slip angular frequency s to the polygonal line approximation function generator 32 to obtain F(s), and inputs this to the multiplier 33 to obtain the primary current 1
, to obtain the secondary current 12.

The SF (s) curve is shown in FIG. {21
A method for determining the secondary current 12 from the active power P, the primary voltage angular wave number v, and the slip angular frequency s.

The active power P transferred from the primary circuit to the secondary circuit is p=22.122...{3
It is given as '00S.

When calculating 12 from this '3' formula, I2: Dasuma
．． ...It becomes '4'.

The active power P is the total active power minus the power loss in the primary circuit. Therefore, the active power P is the time average of the product of the instantaneous values of the induced voltage Vm and the primary current 1, and the induced electromotive force Vm is the primary terminal voltage V, minus the primary voltage drop, Vm = V, - (r, 10PL.)L, is obtained. Here, r. is the primary resistance, L is the primary leakage inductance, and P is the differential operator. Therefore, the secondary current 12 can be found from FIG.

In FIG. 7, numeral 34 is an operational amplifier which inputs primary current 1 and outputs (r, 10PL) 1 as output J output, and 35
3 is a matching circuit which inputs the primary terminal voltage y, and -(r, 10PL.)1, and sends out the deviation output -Vm;
6 is the output (1 Vm) of the matching circuit 35 and the primary current 1,
37 is a filter inputting the output of the J multiplier 36 to obtain the active power P; 38 is a multiplier that multiplies the active power P by s; 39 is a filter of the multiplier 38; A divider which divides the output by v and sends out ±; 40 is a square root calculator which calculates the square root of the two outputs of the divider 39;
The output of this square root calculator 40 is assumed to be the secondary current 12. Here, wS uses a calculated value of the slip angular frequency, which will be described later. In addition, in the operational amplifier 34, 34 is an amplifier, 34b, 3
4c is a resistor, and 34d is a capacitor. In the matching circuit 35, 35a is an amplifier, and 35b to 35d are resistors. In the filter 37, 37a is an amplifier, 37b and 37c are resistors, and 37d is a capacitor. For simplicity, the induced voltage Vm may be replaced by the primary terminal voltage V, and in this case, V, and 1 may be input directly to the multiplier 36 in FIG. {3' Method of calculating the secondary voltage method 52 by substituting the effective component of the current.Since the secondary current is almost the effective component, the effective component IP of the primary current is substituted.

P...[5'IP=
The effective portion IP of the 12 secondary currents (1 primary current) is obtained by dividing the active power P by the time average value Vm of the induced voltage.

A circuit diagram showing how to obtain this is shown in FIG. 8. In FIG. 8, 42 is a multiplier for multiplying the primary current 1 by 1 Vm;
3 and 44 are filter circuits, and 45 is a divider that divides the active power P by Vm (average value). In the filter circuits 43, 44, 43a, 44a are amplifiers, 43b, 43c, 4
4b and 44c are low resistance resistors, and 43d and 44d are capacitors. Note that the induced voltage Vm is obtained by subtracting the primary voltage drop from the primary terminal voltage V (see FIG. 7), but for simplicity, the primary terminal voltage may be substituted. [B] Calculation method of slip angle frequency (lEEEVolIA-11, M
．． 5 P. 483 (1975)) Since the rotational speed is not directly detected, the slip angular frequency is calculated from the primary voltage and current.

In a small slip range, the slip angular frequency S is expressed by the following equation.

r2P. ．． Fence-like = (
Here, P is the active power transferred from the primary circuit to the secondary circuit as described above, that is, the total active power minus the power in the primary circuit.

Therefore, P is determined as the time average of the product of the induced voltage Vm and the instantaneous value of the primary current.

The induced voltage Vm is the primary terminal voltage V, minus the primary voltage drop. Therefore, the slip angular frequency signal s can be obtained using a multiplier/divider as shown in FIG.

In FIG. 9, 46 is the primary current 1. The operational amplifier 46 is an operational amplifier which receives -(r, 10 PL.)1 as an output and is composed of, for example, an amplifier 46a, resistors 46b and 46c, and a capacitor 46d. 47 is the output of the operational amplifier 46 - (r. 1PL)1. The matching circuit 47 inputs the primary terminal voltage V, and outputs the deviation output -Vm. The matching circuit 47 includes, for example, an amplifier 47a and resistors 47b to 47d.

48 is a multiplier that multiplies -Vm and 1. 49 is multiplier 4
This filter circuit 49 uses the output of the amplifier 49 as an input to obtain the effective power P.
a, resistors 49b and 49c, and a capacitor 49d.

The multiplier 51 is a filter circuit that receives the output of the multiplier 50 as an input and sends out 1 Vm2 (average value) as an output.This filter circuit 51 consists of, for example, an amplifier 51, resistors 51b and 51c, and a capacitor 51d. It consists of

52 is a divider that divides -Vm2 (average value) which is the output of the filter circuit 51 by v of the frequency signal of the primary voltage, and 53 is a divider that divides the output of the filter circuit 49 by the output of the divider 52 to calculate the slip angle frequency sail. This is the divider you are looking for.

[m] Calculation method of time differential value of power factor angle **The power factor angle of the primary current based on the induced voltage is expressed by the following formula. T2 twist COS = zo r220 S2 (MFT vs vr20 S2
The force-time derivative of the L2 power factor angle is .・・・・・・
...(7) r22M {r22-wS2-other ten L2)}
Since the group = ± { et al. 20 others + L2) 2} M + means sail x , it can be found as a function of the power factor angle and its time derivative.

Here, G (S of S)-d Yo ・
It can be rewritten as - side.

Therefore, the time differential value of the power factor angle is obtained as shown in FIG. In FIG. 10, 54 inputs ws and calculates G (scream), for example, a polygonal line approximation function generator, 55
This is a differentiator for deriving the time/minute value of s, and this differentiator 55 includes, for example, an amplifier 55a, a resistor 55b, and a capacitor 55c. 56 is a multiplier that multiplies the power of the differentiator 55 by G (■S), which is the output of the broken line approximation generator 54, to obtain the d-core.

As described above, calculation of the secondary current, calculation of the slip angle frequency, and calculation of the time differential value of the power factor angle are performed.

FIG. 4 shows another invention of a control system for an induction motor, in which a set value (s) s of the slip angular frequency and a calculated detected value (s) c of the slip angular frequency are matched by a circuit 28. The deviation signal obtained by matching is amplified by an amplifier with a limiter 29 to obtain the angular frequency signal v of the primary voltage, and Y of the angular frequency signal of the primary voltage is the detected angular frequency value instead of the detected value of the rotation speed. used as.

The time differential value of the power factor angle, which is the output of the power factor angle differential value calculation circuit 30, and the inter-angular wave number signal v of the primary voltage are matched in a matching circuit 57, and the power factor angle is determined from the frequency signal of the primary voltage. The angular frequency signal i of the primary current is obtained as the deviation output obtained by subtracting the time differential of 10, distributor 1
1 controls the thyristor gate of the inverter 3.

The other circuit configurations are the same as in Figure 3.
Components that are the same as those in the figure or have the same functions are designated by the same reference numerals. Here, as in Fig. 3, the secondary electric thorn 82
The time constants of the limiter amplifiers 26 and 29 are adjusted so that the ratio of s to the slip angular frequency is always constant including the transient state.

In this embodiment, a PAM type inverter is used for primary current detection, and the DC current is detected by the DC current transformer 17' from the DC circuit, but the present invention is not limited to this. If the inverter device is a PAM type inverter, the input current on the power supply side may be detected by a current transformer, or the input current of the forward converter 1 or the output current of the inverter 3 (output current of the inverter). In addition, in the case of a PAM type inverter, the output of the inverter 3 is detected by a current transformer,
It goes without saying that each of these may be used as the detected value of the primary current.

Furthermore, in this embodiment, the primary current control of the transfer motor IM is performed by adjusting the phase of the power supply side forward converter 1 by employing a PAM type inverter to control the DC current, but the present invention is limited to this. without being
In the case of a PAM type inverter, a chopper circuit may be provided in the DC circuit on the output side of the forward converter 1 to control the current flow width to control the DC current. Needless to say, it is also possible to control the flow width of step 3.

Further, FIGS. 12 and 13 are circuit diagrams each showing a part of another invention, and the configuration other than the configuration shown here is the same as the configuration shown in FIG. 3. That is, the invention shown in FIGS. 12 and 13 uses the fact that the primary voltage angular frequency is the sum of the primary current angular frequency and the time differential value of the power factor angle, and the invention shown in FIG. Among the configurations, the relationship between the output signals from the limiter amplifier 29 and the power factor angle differential value calculation circuit 30 and the input signal of the voltage-frequency converter 10 is slightly different. All of these inventions use the output signal from the amplifier with limiter 29 as a primary current angular frequency signal, and calculate the difference between this signal wi and the differential value of the power factor angle output from the power factor angle differential value calculation circuit 30. The input of the primary voltage angular frequency signal obtained by adding the angular frequency signals and the slip angular frequency calculation circuit 21 is the same as the invention shown in FIG. 3, but the invention shown in FIG. The obtained primary voltage angular frequency signal Y is inputted to the voltage-frequency displacement device 10', and the thyristor gate of the inverter 3 is controlled based on this, and the invention shown in FIG. The power factor angle differential value outputted from the angle differential value calculation circuit 30 is input to the voltage-frequency converter 1, and the thyristor gate of the inverse converter 3 is controlled based on this. By using the present invention described above, the following various effects can be achieved.

{1} Since the primary voltage frequency signal is used instead of the rotational speed detection value of the induction motor, there is an error corresponding to the slip angular frequency, but the rotational speed detection is not necessary.

(2- The time constants of the secondary current control loop and the slip angle frequency control loop can be made equal, and therefore the response speeds of the secondary current control loop and the slip angle frequency control loop can be made equal, so the secondary current and the slip angle The frequency ratio remains constant even in transient conditions.

Therefore, the magnetic flux is also constant. Although it is a side connection, since the secondary current is detected and controlled, the secondary current becomes a predetermined value.

[4'] The time differential of the power factor angle is derived and the difference between the frequency of the primary voltage and the angular frequency of the primary current is taken into account, so even if the primary current is controlled, the secondary current and excitation current are each at a predetermined value. become.

{5' Since the primary current is detected and controlled, overcurrent restriction can also be applied.

■ Since constant magnetic flux is maintained even in transient conditions, stable and responsive control can be performed.

Brief Description of the Drawings // Figures 1 and 2 are circuit diagrams showing examples of conventional induction motor control methods, and Figures 3 and 4 are circuit diagrams showing induction motor control methods according to the present invention, respectively. Figures 5 to 8 are diagrams explaining the calculation method of the secondary current, Figure 9 is a diagram explaining the calculation method of the slip angular frequency, and Figure 10 is a diagram explaining the calculation method of the time derivative of the power factor angle. FIG. 11 is a waveform diagram showing the relationship between primary current and primary voltage, and FIGS. 12 and 13 are circuit diagrams showing a part of the control method for the induction motor of the present invention.

In the figure, IM is an induction motor, 1 is a forward converter, 2 is a DC reactor, 3 is an inverse converter, 1 is a voltage/frequency converter, and 11
17, 23, 26, 29 are amplifiers with limiters, 17' is a DC current transformer, 18 is a phase adjuster, 20 is an instrument transformer, 21 is a slip angle frequency calculation circuit, 22, 25
, 27, 28, and 57 are matching circuits, 24 is a secondary current calculation circuit, 30 is a power factor angle differential value calculation circuit, and 31 is an addition circuit. Figure 7 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13

Claims (1)

[Scope of Claims] 1. In an inverter device having a forward converter and an inverse converter that drives an induction motor while keeping the ratio of secondary current and slip angle frequency constant, the detection value of the primary voltage of the induction motor and the primary A slip angular frequency calculation circuit calculates a slip angular frequency based on the detected current value and the primary voltage angular frequency signal, and a first amplifier with a limiter outputs the deviation between the primary voltage angular frequency signal and the set value of the primary voltage angular frequency. The output obtained by amplification is used as the setting value of the secondary current and slip angle frequency of the induction motor, and a secondary current calculation value is calculated by a secondary current calculation circuit based on the primary current detection value and the slip angular frequency calculation value. The deviation output between the primary current setting value and the secondary current set value is amplified by a second amplifier with a limiter, the amplified output is used as the primary current setting value, and the deviation output between the primary current setting value and the primary current detected value is amplified. The primary current adjustment element on the primary side is operated to control the primary current to the set value, and the power factor angle differential value calculation circuit calculates the power factor angle based on the slip angle frequency calculation value calculated by the slip angle frequency calculation circuit. A time differential value is calculated, and the deviation output between the calculated slip angle frequency value and the slip angle frequency setting value from the first amplifier with limiter is amplified by the third amplifier with limiter, and the obtained output is used as the primary current angle. A primary voltage angular frequency signal is obtained by adding the primary current angular frequency signal and the time differential value of the power factor angle, and this signal is input to the slip angular frequency calculation circuit. 1. A control method for an induction motor, characterized in that the inverse converter is controlled based on a frequency signal so that a ratio between a secondary current and a slip angle frequency becomes constant. 2. In an inverter device having a forward converter and an inverse converter that drives an induction motor by keeping the ratio of secondary current and slip angle frequency constant, the primary voltage detection value, primary current detection value, and primary voltage of the induction motor. A slip angular frequency calculation circuit calculates a slip angular frequency based on the angular frequency signal, and the deviation output between the primary voltage angular frequency signal and the set value of the primary voltage angular frequency signal is amplified by a first amplifier with a limiter. The obtained output is used as the set value of the secondary current and slip angular frequency of the induction motor, and the secondary current calculated value calculated by the secondary current calculation circuit based on the detected primary current value and the calculated slip angular frequency value, etc. The deviation output from the primary current set value is amplified by a second limiter amplifier, and the amplified output is used as the primary current set value. Based on the deviation output between the primary current set value and the primary current detected value, The current adjustment element is operated to control the primary current to the set value, and the power factor angle differential value calculation circuit calculates the time differential value of the power factor angle based on the slip angle frequency calculation value calculated by the slip angle frequency calculation circuit. is calculated, and the output obtained by amplifying the deviation output between the calculated slip angle frequency value and the slip angle frequency setting value from the first amplifier with limiter is used as a primary voltage angular frequency signal. While inputting this primary voltage angular frequency signal to the slip angular frequency calculation circuit, a primary current angular frequency signal is obtained by subtracting the time differential value of the power factor angle from the primary voltage angular frequency signal, and based on this signal, 1. A control method for an induction motor, characterized in that the inverse converter is controlled so that a ratio between a secondary current and a slip angular frequency becomes constant. 3 In an inverter device having a forward converter and an inverse converter that drives an induction motor by keeping the ratio of secondary current and slip angle frequency constant, the primary voltage detection value, primary current detection value, and primary voltage of the induction motor. A slip angular frequency calculation circuit calculates a slip angular frequency based on the angular frequency signal, and the deviation output between the primary voltage angular frequency signal and the set value of the primary voltage angular frequency signal is amplified by a first amplifier with a limiter. The obtained output is used as the set value of the secondary current and slip angular frequency of the induction motor, and the secondary current calculated value calculated by the secondary current calculation circuit based on the detected primary current value and the calculated slip angular frequency value, etc. The deviation output from the primary current set value is amplified by a second limiter amplifier, and the amplified output is used as the primary current set value. Based on the deviation output between the primary current set value and the primary current detected value, The current adjustment element is operated to control the primary current to the set value, and the power factor angle differential value calculation circuit calculates the time differential value of the power factor angle based on the slip angle frequency calculation value calculated by the slip angle frequency calculation circuit. is calculated, and the output obtained by amplifying the deviation output between the calculated value of the slip angle frequency and the set value of the slip angle frequency from the first amplifier with a limiter is used as a primary current angular frequency signal. , a primary voltage angular frequency signal is obtained by adding this primary current angular frequency signal and the time differential value of the power factor angle, and this primary voltage angular frequency signal is input to the slip angular frequency calculation circuit, while the primary voltage 1. A control method for an induction motor, characterized in that the inverse converter is controlled based on an angular frequency signal, so that a ratio between a secondary current and a slip angular frequency becomes constant. 4 In an inverter device having a forward converter and an inverse converter that drives an induction motor by keeping the ratio of secondary current and slip angle frequency constant, the primary voltage detection value, primary current detection value, and primary voltage of the induction motor. A slip angular frequency calculation circuit calculates a slip angular frequency based on the angular frequency signal, and the deviation output between the primary voltage angular frequency signal and the set value of the primary voltage angular frequency is amplified by a first amplifier with a limiter. The obtained output is used as the set value of the secondary current and slip angular frequency of the induction motor, and the secondary current calculated value calculated by the secondary current calculation circuit based on the detected primary current value and the calculated slip angular frequency value, etc. The deviation output from the primary current set value is amplified by a second limiter amplifier, and the amplified output is used as the primary current set value. Based on the deviation output between the primary current set value and the primary current detected value, The current adjustment element is operated to control the primary current to the set value, and the power factor angle differential value calculation circuit calculates the time differential value of the power factor angle based on the slip angle frequency calculation value calculated by the slip angle frequency calculation circuit. is calculated, and the output obtained by amplifying the deviation output between the calculated value of the slip angle frequency and the set value of the slip angle frequency from the first amplifier with a limiter is used as a primary current angular frequency signal. , a primary voltage angular frequency signal is obtained by adding this primary current angular frequency signal and the time differential value of the power factor angle, and this signal is input to the slip angular frequency calculation circuit, while the time differential value of the power factor angle is 1. A control method for an induction motor, characterized in that the inverse converter is controlled based on the value, so that the ratio between the secondary current and the slip angular frequency becomes constant.