JP2547824B2 - Induction motor controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control device for an induction motor driven via an inverter.

[Conventional technology]

FIG. 3 is a block diagram showing a conventional example of such a control device. In the figure, 1 is a three-phase AC power source, 2 is a converter, 3 is a capacitor, 4 is an inverter, 5 is a comparator, and 6
Is a carrier wave signal generation circuit, 7 is an induction motor (hereinafter also simply referred to as a motor), 8 is a variable flow path (current detector), 9A and 9B are coordinate converters, 10A is a torque current regulator (ACR), and 10B is Exciting current regulator (ACR), 11A and 11B are output limiting circuits (limiters), 12 is a divider, and 13 is an arithmetic circuit.

This regards the motor current, voltage, etc. as vector quantities,
These quantities, which are AC quantities when observed from the stator winding, are converted to DC quantities by observing from the rotating magnetic field of the motor and separated into a component parallel to the magnetic flux and a component orthogonal to this. Control independently of each other, which is well known as a so-called vector control method.

Now, the torque command value τ ^*, a secondary magnetic flux command value φ ₂ ^*
Then, the command value of the current component (excitation current) parallel to the magnetic flux
i _M ^* is p: d / dt (differential operator), T ₂ : Motor secondary time constant, M: Mutual inductance, and the command value i _T ^* of the component (torque current) orthogonal to the exciting current is i _T ^* = It is given as τ ^* / φ ₂ ^* ... (2).

Therefore, the arithmetic circuit 13 calculates the equation (1), and the divider
The division of formula (2) is executed by 12. The coordinate converter 9A converts the quantities (i _u , i _v , i _w ) of the stator coordinate system detected by the current detector 8 into the quantities (i _T , i _M ) of the secondary magnetic flux coordinate system. Then, assuming that the angle formed by, for example, the a-phase winding of the stator and the secondary magnetic flux in the motor is φ ₂ , conversion is performed by the following equation (3).

Torque current command value i _T ^* and torque current detection value i _T , exciting current command value i _M ^* and exciting current detection value i _{M obtained as above}
The torque current regulator 10
Input to A and exciting current controller 10B. The torque current controller 10A and the excitation current controller 10B are so-called PI controllers having a proportional operation term and an integral operation term, and the torque current command value
The deviation between i _T ^* and the detected torque current value i _T is calculated by the torque current controller.
Input the torque voltage command value V _T ^* to 10 A and input the deviation between the excitation current command value i _M ^* and the excitation current detection value i _M to the excitation current controller 10 B to input the excitation voltage command value V _M ^{Get *} Further, the current regulators 10A, 10B are provided with output limiting circuits (limiters) 11A, 11B for limiting the output of the regulator when the regulator is saturated and improving the recovery characteristic from the saturation. Coordinate converter 9B, the current regulator 10A, quantities of secondary flux coordinate system output by ^{_{10B (V T *, V M}} *) and quantities of the stator coordinate system (V _u ^*, V _v ^* , V _w ^* ), and the conversion formula is shown by the following formula.

Three-phase voltage command value (V _u ^* , V converted according to equation (4)
By comparing _v ^* , _Vw ^* ) and the three-phase waveform signal output from the carrier signal generation circuit 6 by the comparator 5, the pulse width modulation (PWM) signal for controlling the inverter 4 can be obtained. can get. The inverter 4 receives the DC intermediate voltage V _{dc which} is converted by the converter 2 from the AC voltage supplied from the AC power supply 1 and smoothed by the capacitor 3. The inverter 4 pulse-width modulates the DC intermediate voltage V _dc in accordance with the PWM signal described above, and supplies it to the motor 7.

[Problems to be Solved by the Invention]

In the conventional technology, when the DC intermediate voltage fluctuates due to a momentary power failure,
There is a problem that the current overshoots. This will be described below.

FIG. 4 shows a block diagram of the torque current control system of FIG. 3, and FIG. 5 shows an operation waveform diagram of FIG.

The voltage / current equation inside the motor is given by the following equation (5).

r ₁ : primary resistance, L σ: total leakage inductance, ω ₁ : primary angular frequency Considering the second and third terms on the right side of equation (5) as motor back electromotive force, that is, disturbance (indicated by symbol d in FIG. 4), The disturbance of this system includes d and the DC intermediate voltage V _dc which is the input of the multiplier 20. The controller detects a torque current value I _T is a control amount by the detection filter 21, the input is compared with the torque current detection value i _T and the torque current command value i _T ^* deviation .DELTA.i _T to the torque current regulator 10A To do. The torque current controller 10A executes PI (proportional / integral) calculation, and outputs a torque voltage command value V _T ^* as a result. In the PWM inverter, an output limiter is used for the purpose of limiting the output of the regulator when the current regulator is saturated and improving recovery characteristics after saturation. For the same purpose in this control system, the torque current command value V _T ^{*, which} is the output of the torque current regulator 10A, is limited by the output limit circuit 11A at the limit value V _L1.
Is limited to. Here, the value of the limit value V _L1 is set to a value that allows the electric motor to constantly exhibit maximum performance even when the DC intermediate voltage V _dc decreases. When the regulator output is limited to the limit value V _L1 , the regulator gives priority to the proportional calculation, and the integral term is limited by the limit value V _L1 minus the output value of the proportional term. The multiplier 20 calculates the torque current command value V _T ^* and the DC intermediate voltage V
The multiplication of _dc is executed, the resulting V _T and the disturbance d are added, and the result is input to the motor 7.

Here, decreasing the DC intermediate voltage V _dc at some inclination for instantaneous stop and the like at time t ₁ is generated in one steady state, again the DC intermediate voltage V _dc at the time t ₅ is returned with a slope in the t ₁ previous value The operation of each part in the case will be described with reference to FIG.

The dotted line in Fig. 5 (d) shows the torque current command value i _T ^* ,
It is always constant. The figure (a) shows the DC intermediate voltage V _dc , which decreases from V _d1 → V _d2 at time t ₁ → t ₃ and V at time t ₃ → t ₅ .
Return from _{d2 to} V _d1 . When the DC intermediate voltage V _dc begins to decrease at time t ₁ , the torque current command value V _T ^* shown in (c) of the figure begins to increase in order to keep V _T constant accordingly.
Reaches the limit V _L1 at time t _2, the subsequent is a limit to the V _L1. As a result, V _T in the figure (b) begins to decrease from t ₂ . Therefore, the controlled variable I _{T in} FIG. 9D also starts to decrease from t ₂ . The same figure (e) shows the integral term C _i in the controller, which starts to increase from t ₁ similarly to the torque current command value V _T ^* , but when the limit value V _L1 is reached, the integral term C _i is changed to the limit value V _{i. Since} it is limited to the value obtained by subtracting the proportional term from _L1, it begins to decrease as shown.

Next, when the DC intermediate voltage V _dc starts to return to V _d1 from time t ₃ , the controlled variable I _T begins to increase, and the integral term C _i also starts to increase. Here, the value of the integral term C _i in the steady state can be expressed by the following equation (6) from FIG.

(However, i _T ^* = I _T. ) On the other hand, the value of C _i when the controller is saturated is given by the equation (7).

C _i = V _L −K _p (i _T ^* −i _T ) (7) (K _p : proportional constant) In the current control system discussed here, the proportional constant K _p of the regulator is generally small. Value, while the control value of the current regulator
V _L is set to a large value so that the motor can exhibit its maximum performance even when the DC intermediate voltage V _dc constantly decreases, because it is set according to when V _dc decreases. For this reason
The value of C _i determined by equation (7) at time t _{4 when} i _T ^* = I _T
And C _1, the relationship between the value C ₀ of C _i in the steady state is likely to be a C _1> C _0. As a result, the extra C ₁ − accumulated in the integral term
Since the controller has to output C ₀ minutes, the controlled variable
Overshoot will occur at I _T.

Therefore, it is an object of the present invention to prevent current overshooting even when the power supply fluctuates due to a momentary power failure or the like.

[Means for solving the problem]

In an induction motor control device that separates a primary current of an induction motor that can be driven through an inverter into an excitation current component parallel to a secondary magnetic flux and a torque current component orthogonal to the excitation current component, and controls them independently, a torque current command Torque current adjusting means for inputting the deviation between the detected value and the detected torque current value, and torque current adjusting means for inputting the deviation between the exciting current command value and the detected exciting current value, and for outputting the exciting voltage command value Current adjusting means, output control means for limiting the output of the torque current adjusting means to at least first and second control values,
Comparing means for comparing the DC intermediate voltage value of the inverter with a preset setting value, and selecting means for selecting the limit value according to the comparison result from the comparing means are provided.

[Action]

The output limit value of the current control system is reduced when the DC intermediate voltage V _dc is a predetermined value or more, and conversely is increased when the DC intermediate voltage V _dc is a predetermined value or less, so that the current does not change even during power fluctuations such as momentary power failure. Prevents overshoot from occurring and ensures stable motor operation.

〔Example〕

FIG. 1 shows an embodiment of the present invention. As is clear from the figure, this embodiment is different from the conventional example of FIG.
4, The feature is that a switch 16 for switching (selecting) the output limit value of the comparator 15 and the current regulator is added. This change-over switch 16 is set to the V _L1 side when V _dc <V _d1 or to the V _L1 side when V _dc <V _{d1 according} to the result of the comparison between the predetermined value V _d1 set by the setter 14 and the DC intermediate voltage V _{dc. dc} ≥ V
In the case of _d1 is switched to the V _L2 side.

 FIG. 2 shows the operation waveform.

Figure 2 (a) to (e) are also DC intermediate voltage V _dc and Figure 5 prior art, the torque voltage command value V _T ^*, the multiplier output V _T, which is the control amount of torque current value I _T, the target The torque current command value i _T ^* , the detected torque current value i _T , the current regulator integral term C _i, etc. are shown. The figure (f) shows the limit value V _{L of the} current regulator.
The limit value V _L is switched when the power supply is lowered. Here, the value of the limit value V _L is set to a value V _L1 which allows the motor to exhibit its maximum performance even when the power supply is reduced, when V _dc <V _d1 by the changeover switch 16, and V _dc ≧ V
_In the case of _d1 , at time t ₄ in FIG. 2, C _i is set to a value V _L2 that is equal to the value obtained by the equation (6).

By switching the value of the limit value V _{L in} this way, at time t ₄ when the power is restored i _T ^* = I _T , C _i is steadily equal to the required value, so that the overshoot is almost zero. can do.

Although the limit value V _{L has} two values V _L1 and V _L2 here, it may be three or more depending on the case.

〔The invention's effect〕

According to the present invention, by switching the output limit value of the current control system according to the magnitude of the DC intermediate voltage, not only the maximum performance can be exerted when the power supply is constantly lowered, but also the electric motor can be operated when the power supply fluctuates such as an instantaneous power failure. Can be stably driven.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a time chart for explaining the operation, FIG. 3 is a block diagram showing a conventional example of a control device, and FIG. FIG. 5 is a block diagram showing the torque current control system, and FIG. 5 is a time chart for explaining the operation of FIG. 1 ... Three-phase AC power supply, 2 ... Converter, 3 ... Capacitor, 4 ... Inverter, 5,15 ... Comparator, 6 ... Carrier signal generation circuit, 7 ... Induction motor, 8 ... Current transformation Bowl, 9
A, 9B ... Coordinate converter, 10A ... Torque current controller, 10B ...
… Excitation current regulator, 11A, 11B …… Current limit circuit, 12 ……
Divider, 13 ... Arithmetic circuit, 14 ... Setting device, 16 ... Changeover switch, 20 ... Multiplier, 21 ... Current detection filter.

Claims (1)

(57) [Claims] 1. A control device for an induction motor, which separates a primary current of an induction motor driven through an inverter into an exciting current component parallel to a secondary magnetic flux and a torque current component orthogonal to the exciting current component and independently controls them. , The torque current adjustment means that inputs the deviation between the torque current command value and the detected torque current value and outputs the torque voltage command value, and the deviation between the excitation current command value and the excitation current detection value An exciting current adjusting means for outputting a value, an output limiting means for limiting the output of the torque current adjusting means to at least first and second limiting values, and a preset value of a DC intermediate voltage value of the inverter. A control device for an induction motor, comprising: comparing means for comparing; and selecting means for selecting the limit value according to a comparison result from the comparing means.