JPS6031193B2 - 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.

FIG. 1 shows an example of a conventional control system for an induction motor. In the figure, an AC power input is converted by a forward converter 1 at around 1l, and the forward converted DC output is sent to a DC reactor 2.
The AC signal is supplied to the inverter 3 via the inverter 3, where it is inversely converted and an AC output of a desired frequency is taken out, which drives the induction motor IM.

Describing the configuration of the control device for the induction motor IM 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 output of the speed generator 4, that is, the detected value (r)d of the rotational speed of the IM and the set value (r)s of the rotational speed and extracts the deviation signal. An amplifier with a speed control limiter takes the output as an input and amplifies it. 7 is the output of the amplifier with a limiter 8. and the output (of r) d of the speed generator 4
9 is a set value (of the slip angle frequency) based on the output (s) d of the matching circuit 7 and the output of the amplifier 6. 10 is a matching circuit for supplying the deviation output to the amplifier 8;
of the output. 11 is a voltage-to-frequency converter that converts the voltage to a frequency signal 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; 12 is a distributor that converts the output of the amplifier 6 into a secondary current; A multiplication circuit for calculating the square of the set value (12) s, 13 a multiplication circuit for calculating the square of the no-load current IM (constant), and 14 the output of the multiplication circuit 12 and the output of the multiplication circuit 13. 15 is a square root calculator to which the output of the adder circuit 14 is supplied and sends out the output as the set value (1.) S of the primary current; 16 is a forward converter 1 The primary current (1) d detected by the DC current transformer 17' provided on the output side of the square root calculator 15 and the output (1,) s of the square root calculator 15 are supplied, and the deviation output is sent to the amplifier 17 with a limiter. The matching circuit 18 is 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 control system for a subordinate transfer motor, and the difference from FIG. 1 is that the detected speed value (r
) d and S of the output of the amplifier with a transmitter 6 are added to the adder circuit 19.
of the deviation output obtained by adding.

The voltage-to-frequency converter 101 is supplied with the voltage-to-frequency converter 101, and the other components are the same as those in FIG. 1 or those having the same functions are designated by the same reference numerals. The first of the above
The induction motor control systems shown in FIGS. and 2 have the following problems.

That is, [1} 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. '2) For current type, the current frequency (including phase) should be specified, but the voltage frequency is specified.

In a transient state, there is a change in the power factor angle, and this change becomes a problem. '3} In the method shown in Fig. 2, there is no time delay in the slip angular frequency and the current control system has a time constant, so the ratio of the secondary current to the slip angular frequency is not constant in a transient state.

The present invention aims to solve these conventional problems, and will be explained 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 same figure, the set value of rotational speed (mountain r) s
and the speed set value (r)d of the induction motor IM by the speed generator 4 in the matching circuit 5, and the deviation obtained is amplified by the first amplifier with limiter 6, and its output is equal to the secondary current. Setting value (12) S and slip angle frequency setting value (
s). The limiter in the limiter amplifier 6 is set so that the slip does not exceed the maximum torque. In the secondary current control loop, the secondary current calculation circuit 2 is used to convert the secondary electric log 2 into the primary current 1, (here, the primary current (1,) d detected by the DC current transformer 17' is used). ,
Calculated from the slip angular frequency s (here we use (s)d, which is the output of the matching circuit 21), and other quantities that can be directly detected (for example, terminal voltage V, power supply frequency i, etc.), and ( 12) Let it be c.

This secondary current calculation method will be described later. The matching circuit 22 takes the output (12) c of the secondary current calculation circuit 20 and the secondary current setting value (12) s, which is the output of the amplifier with a transmitter 6.
The deviation output obtained by matching the two is taken out as the primary current set value (1,)s via the second limiter equipped amplifier 23 and inputted to the matching circuit 24. In order to suppress the primary current to a limit value, this set value (1,)s is limited by an amplifier 23 with a limiter. The matching circuit 24 matches the primary current (1,) d detected by the DC current transformer 17' with the set value (1,) s, and outputs the deviation from the output via the amplifier 17 with a limiter to the phase adjuster. 18, and the output of this phase adjuster 18 controls the thyristor gate of the forward converter 1 to set the primary current to the set value. Next, in the control loop of the slip angular frequency s, the set value (s) of the slip angular frequency s and the detected value (w
s) and d are matched by a matching circuit 25, and the deviation output thereof is amplified by a third amplifier with a limiter 26 to obtain a frequency signal of the primary current.

The power factor angle differential value calculating circuit 27 calculates the time differential value of the power factor angle based on the detected value (S)d of the slip angle frequency which is the output of the matching circuit 21. A method for calculating the time differential value of the power factor angle will be described later. The adder circuit 28 adds the time differential value of the power factor angle to the frequency signal of the primary current to obtain v of the frequency signal of the primary voltage, and calculates v of the angular frequency signal of the primary voltage and the detected speed value (r). d is matched by a matching circuit 21, and a detected value (of s) d of the slip angular frequency is obtained as the deviation. A signal peak corresponding to the angular frequency of the primary current is input to a voltage-to-frequency converter (abbreviated as V/F) 10, and is passed through a distributor 11 to an inverter 3.
controls the thyristor gate. Next, the reason why the angular frequency signal of the primary voltage is expressed as the sum of the angular frequency signal of the primary current and the time differential value of the power factor angle is that in a steady state, the angular frequency of the primary current and the angular frequency of the primary voltage is the same, but becomes different when transient conditions occur due to load fluctuations, etc. This situation is shown in FIG. 12. For example, in a steady state, the power factor angle is , and the primary current and primary voltage have waveforms shown by solid lines 'i) and 'ii), respectively. Let us now consider a case where the primary voltage takes on the waveform shown by the chain line {iii} due to load fluctuations, and the power factor angle changes from 2 to 2 and becomes worse. The power factor angle is,
In order to change from 2 to 2, the angular frequency of the primary voltage must increase. The change in angular frequency becomes the differential value of the change in power factor angle, and this can be expressed in the formula v2=
v, ten.也v, , are the primary voltage angular frequencies before and after the change, respectively. Incidentally, since the peak V is a value in a state of change, that is, in a 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. Here, the amplifier with limiter 23 and the amplifier with IJ limiter 26 are adjusted so that the ratio between the secondary current 12 and the slip angular frequency s is constant including the transient state.

Next, the method of calculating the secondary current and the method of calculating the time differential value of the power factor angle described above will be described in detail below.

[1] Calculation method of secondary current {1- Calculated from the relationship between primary current and secondary current.

SM,. ,…,． , {1,12=
〉L+SZM+LSe1. Here, r2: Resistance of the secondary circuit M: Mutual inductance between the primary circuit and the secondary circuit L2: Secondary circuit leakage inductance Secondary current 12' is determined from the primary current 12 and the slip angle frequency.

Formula [1} is further set as SM
=F(■S)-1. ......■, and in order to obtain 12 from this, as shown in FIG. By inputting and multiplying by the primary current 5, the secondary current 12 is obtained.

The s-F(ws) curve is shown in FIG. ■ Determined from the relationship between active power and secondary current.

P = bad life 1〆 ...... [
3} ○Results are ignored, and the power loss in the primary circuit is ignored.

If we rewrite the '3} formula, we get I2 echo.・・・．・・・． - Since the side active power P is the time average of the product of the instantaneous values of the induced voltage Vm and the primary current 1, it can be obtained as shown in FIG.

In FIG. 8, -Vm and 1 are multiplied by a multiplier 31, and the output is passed through a filter 32 to obtain the active power P.
Multiply this by wS in the multiplier 33, input it to the divider 34, divide it by sail, multiply the output by 1'r2 in the amplifier 35, find the square eye in the square root operator 36, and divide this by The secondary current is assumed to be 12.

The operational amplifier 32 is used as a filter; 32a is an amplifier, 32b and 32d are resistors, and 32c is a capacitor.

Note that the induced voltage is obtained by subtracting the primary voltage drop from the primary terminal voltage V, and is determined as Vm=V, 1 (r, 10 PL.) 1.

Here, r. is the primary resistance, L is the primary leakage inductance, and P is the differential operator.

A circuit diagram showing how to obtain this Vm is shown in FIG. 11. In FIG. 11, 44 inputs 1 and outputs -(
An operational amplifier 45 is a matching circuit for calculating r, 1PL)1. In the operational amplifier 44, 44a is an amplifier, 44b and 44c are resistors, and 44d is a capacitor.
In the matching circuit 45, 45a and 45b are resistors;
5c is an amplifier. However, the induced voltage is approximately substituted by the primary terminal voltage. ■ Approximate by the effective part of the current.

Since the secondary current is mostly an effective component, the effective component (lp) of the primary current can be used instead.

Therefore, lp=P/Vm [5] The effective component lp of the secondary current 12, that is, the primary current 1, 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. 9. In FIG. 9, 37 is a multiplier that multiplies 1 and -Vm; 38, 3;
9 is a filter circuit, 4 active power P is Vm (average value)
It is a divider that divides by. In the filter circuits 38, 39, 38a, 39b are amplifiers, 38b, 38c, 39b,
39c is a resistor, and 38d and 39d are capacitors.

[B] 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 equation.

SM of r2
2-2. ．．・{6-That is, in steady state, it is a function only of the slip angle frequency.

The time derivative of the power factor angle is equal to = ±{r2 end vocal cord retention similar/small ・-…
-dt, so it can be found as a function of the scream and its time derivative.

Hair G (■S), d Yamakyou …………'8)
dt Here, G (scream) Ni± life M {r22 one S2}'s ^10 L2)} {et al.20 child (M+L2)2} {r22 ten child -2}
It can be rewritten as

Therefore, the time differential value of the power factor angle is obtained as shown in FIG. In Fig. 10, 41 is a function generator that inputs S of and calculates G (cape), 42 is a differentiating circuit that derives the time differential value of s, and 43 is the output of differentiating circuit 42. Machine equipment 41 Multiply by G (of S), which is the soil strength, da
This is a multiplication circuit that calculates a multiplier.

In the differential circuit 42, 42a is an amplifier, 42b is a resistor, and 42c is a capacitor. As described above, the calculation of the secondary current and the time differential value of the power factor angle are performed.

FIG. 4 shows a control system for an induction motor according to another invention.

In the figure, a circuit 25 matches the set value (wS) s of the slip angular frequency with the detected value (mountain s) d of the slip angular frequency.
The deviation signal obtained by matching is sent to an amplifier with limiter 26.
The signal is amplified by the angular frequency signal V of the primary voltage. In addition, the primary voltage angular frequency signal v and the rotation speed detection value (r)d are supplied to the matching circuit 21, and the deviation output is the slip angular frequency detection value (■S)d. The value (S)d is input to the power factor angle calculation circuit 27, and the time differential value of the power factor angle is derived. i of the angular frequency signal of the primary current
is obtained by subtracting the time differential value of the power factor angle from the angular frequency signal v of the voltage in the matching circuit 46. The angular frequency signal of this primary current is input to a voltage-to-frequency converter (V/F) 10 for driving an inverter.

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. FIG. 5 shows a control system for an induction motor according to still another invention, in which the set value (s) of the slip angle frequency, which is the output of the amplifier with limiter 6, is outputted by passing it through the time constant adjustment circuit 47. is the slip angular frequency S, and the rotation speed detection value (r)d is added to this by the circuit 4.
8, the added output is the angular frequency signal of the primary voltage, and the deviation output obtained by supplying V of the angular frequency signal of this primary voltage and the time differential value of the power factor angle to the matching circuit 49, that is, The angular frequency signal i of the primary current is input to the voltage-to-frequency converter l0. Here, the output of the time constant adjustment circuit 47 is input to the power factor angle calculation circuit 27 to derive the time differential value of the power factor angle. In each of the cases shown in FIGS. 3 to 5, the signal i corresponding to the angular frequency of the primary current is the input to the voltage-to-frequency converter 10, and the output of the voltage-to-frequency converter 10 is The inverter 3 is driven through the distributor 11.

In addition, by adjusting the amplifiers 23 and 26 in FIGS. 3 and 4, the amplifier 23 and the time constant adjustment circuit 47 in FIG.
By adjusting , the ratio between the secondary current 12 and the slip angular frequency s is kept constant including the transient state.

In this embodiment, a PAM type inverter is used to detect the primary current, and the DC current transformer 17' is used to detect the primary current from the DC circuit. However, 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 (input side of the forward converter 1) and the output current of the inverse converter 3 are detected by a current transformer, and if the inverter is a PWM type inverter, the input current of the inverter 3 is detected. It goes without saying that the output current of the primary current may be detected by a current transformer and used as the detected value of the primary current.

Further, in this embodiment, the primary current of the induction motor IM is controlled by adjusting the phase of the forward converter 1 on the power supply side using the PAM method to control the DC current, but the present invention is not limited to this. Alternatively, the DC current may be controlled by providing a chopper circuit in the DC circuit on the output side of the forward converter 1 using the PNM method and controlling the current flow width of the chopper circuit, or alternatively, the DC current may be controlled using the PWM method in the DC circuit on the output side of the forward converter 1. Of course, the width of the flow may be controlled.

Further, in this embodiment, the speed generator 4 is used to detect the rotational speed of the induction motor, but the present invention is not limited to this, and the rotational speed of the induction motor is detected by the number of pulses using a pulse pickup or the like, and frequency-voltage conversion is performed. Of course, it is also possible to convert it to DC voltage with a device and use it.

By using the present invention described above, the following various effects can be achieved.

{1) 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 frequency control loop can be made equal, so the secondary current and the slip angle frequency The ratio remains constant even in transient conditions.

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

'31 Since the time differential of the power factor angle is derived and the difference between the frequency of the primary voltage and the frequency of the current is taken into account, even if the primary current is controlled, the secondary current and excitation current each maintain a predetermined value.

'41 Since the primary current is detected and controlled, overcurrent limits can also be applied.

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

[Brief explanation of drawings]

1 and 2 are circuit diagrams showing examples of conventional induction motor control methods, and FIGS. 3 to 5 are circuit diagrams showing examples of the induction motor control method according to the present invention. Figures 6 to 9
Figure 11 is a diagram explaining the calculation method of secondary current, Figure 10
The figure is a diagram explaining the calculation method of the time differential value of the power factor angle.
The figure is a waveform diagram showing the relationship between primary current and primary voltage, and the side in the figure is an induction motor, 1 is a forward converter, 2 is a DC IJ factor, 3 is an inverse converter, 4 is a speed generator, 5, 21,2
2, 24, 25, 46, 49 are matching circuits, 6, 17
, 23, 26 are amplifiers with limiters, 17' is a DC transformer, 10 is a voltage-to-frequency converter, 11 is a distributor, 18 is a phase adjuster, 20 is a secondary current calculation circuit, 27 is a power factor angle differential Value calculation circuits, 28 and 48 are adder circuits, and 47 is a time constant adjustment circuit. Figure 1 Figure 6 Figure 7 Figure 2 Figure 3 Figure 4 Figure 5 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12

Claims (1)

[Claims] 1. In an inverter device having a forward converter and an inverse converter to drive an induction motor while keeping the ratio of secondary current and slip angular frequency constant, the rotational speed of the induction motor is detected by a speed detector. The output obtained by amplifying the deviation output between this and the speed setting value with the first limiter amplifier is used as the setting value of the secondary current and slip angle frequency of the induction motor, and the primary current, slip angle Amplifying the deviation output obtained by matching the secondary current calculated value calculated from each detected frequency value and the secondary current setting value with a second amplifier with a limiter,
The amplified output is set as the primary current set value, and the primary current is adjusted to the set value by operating the current adjustment element on the primary side based on the deviation output obtained by comparing the primary current set value and the detected primary current value. At the same time, the primary voltage angular frequency signal and the rotational speed detection value from the speed detector are matched in a matching circuit, and based on the deviation output, a power factor angle differential value calculation circuit is used to calculate the power factor angle of the primary current. calculate the time differential value of A primary voltage angular frequency signal obtained by adding the primary current angular frequency signal and the time differential value of the power factor angle is input to the matching circuit, and the reverse is applied based on the primary current angular frequency signal. A control method for an induction motor characterized by controlling a converter so that the ratio of secondary current to slip frequency is 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 rotational speed of the induction motor is detected by a speed detector, and the rotation speed of the induction motor is detected by a speed detector. The output obtained by amplifying the deviation output from the speed setting value with a first amplifier with a limiter is used as the setting value of the secondary current and slip angular frequency of the induction motor,
The deviation output obtained by matching the secondary current calculated value calculated from each detected value of the primary current and slip angular frequency with the secondary current set value is amplified by a second amplifier with a limiter, and the amplified output is A primary current setting value is set, and a primary current adjustment element is operated on the basis of a deviation output obtained by comparing the primary current setting value and the primary current detection value to control the primary current to the setting value. , the primary voltage angular frequency signal and the rotational speed detection value from the speed detector are matched by a matching circuit, and based on the deviation output, a power factor angle differential value calculation circuit calculates the time differential value of the power factor angle of the primary current. Calculate,
The slip angular frequency setting value and the deviation output from the matching circuit are matched, and the deviation output is amplified by a third amplifier with a limiter, and the obtained output is used as a primary voltage angular frequency signal, and this primary voltage angular frequency While inputting the signal to the matching circuit, the inverter is controlled based on the primary current angular frequency signal obtained by subtracting the time differential value of the power factor angle from the primary voltage angular frequency signal, and the secondary A control method for an induction motor characterized by keeping the ratio of current to slip angle frequency 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 rotation speed of the induction motor is detected by a speed detector, and the rotational speed of the induction motor is detected by a speed detector. The output obtained by amplifying the deviation output from the speed setting value with a first amplifier with a limiter is used as the setting value of the secondary current and slip angular frequency of the induction motor,
Amplifying the deviation output obtained by comparing the secondary current calculated value calculated from each detected value of the primary current and slip angular frequency with the secondary current setting value with a second limiter amplifier,
The amplified output is set as the primary current set value, and the primary current is adjusted to the set value by operating the current adjustment element on the primary side based on the deviation output obtained by comparing the primary current set value and the detected primary current value. At the same time, the slip angle frequency set value is input to a time constant adjustment circuit, and based on the output from this, a power factor angle differential value calculation circuit calculates the time differential value of the power factor angle of the primary current, and A signal obtained by adding the output from the time constant adjustment circuit and the rotational speed detection value from the rotational speed detector is defined as a primary voltage angular frequency signal, and the time differential value of the power factor angle is subtracted from this primary voltage angular frequency signal. A control for an induction motor characterized in that a primary current angular frequency signal is obtained and the inverse converter is controlled based on the primary current angular frequency signal so that the ratio of the secondary current to the slip frequency is constant. method.