JPS596789A - Drive device for induction motor - Google Patents

Abstract

PURPOSE:To maintain magnetic flux constant even at transient time by calculating a slip frequency command from a magnetic flux current command and a primary current amplitude detected value under slip frequency control system vector control, thereby controlling the primary current frequency. CONSTITUTION:An induction motor 5 is driven by a converter 2 and an inverter 4, a magnetic flux current command Iphi, and a torque current command IT are inputted to an arithmetic circuit 10, which outputs the primary current amplitude command I1S, which is subtracted by the signal from a current detector 6, thereby controlling the converter 2. On the other hand, the command Iphi and the signal from a current detector 6 are inputted to arithmetic circuits 20, 21, thereby obtaining a slip frequency command fS1, and a transient slip frequency command fS2, which are added by the signal from a speed detector 7, thereby controlling the inverter 4. Accordingly, the detected current value is inputted to the arithmetic circuits 20, 21, thereby maintaining the magnetic flux constant even if a delay exists in the primary current amplitude control system, and obtaining preferable controlling performance.

Description

[Detailed Description of the Invention] As a high-speed response control method for induction motors, vector control, which controls magnetic flux and torque independently, is widely practiced. The basic concept is to consider the magnetic flux current that is generated separately and the torque current that is orthogonal to each other, and to control both independently. In implementation, the key is to know the direction of the magnetic flux, and this can be done by using a magnetic flux detector attached to the motor body or by the direct method, which is determined from various electrical quantities such as primary current and voltage.
There is an indirect method that calculates indirectly from the relationship between the primary current amplitude and frequency ◇ The latter is well known as slip frequency control method vector control, and the present invention relates to an improvement of this method, and the following is based on the drawings. The contents of the present invention will be explained in detail below.〇Figure 1 is a block diagram of an example of vector control using the conventional slip frequency control method.・1
2 is an AC power input terminal, and 2 is a converter that converts this AC voltage into DC, and the DC output voltage is controlled by a signal from the converter control circuit 16.

Reference numeral 4 denotes an inverter that converts direct current to alternating current, and controls the frequency of the alternating current output current by a signal from the inverter control circuit 19. The output of the converter 2 is sent to an inverter 4 via a DC reactor 3, and the output of the inverter 4 is connected to an induction motor 5 to be controlled. A DC reactor 3 is connected to an OC converter 2 which reduces the pulsating component of the induction motor primary current. DC reactor 3. Inverter 4. Converter control circuit 16 and inverter control circuit 19 are well known as current source inverter devices.

6 is a current detector, which together with the current detection circuit 13 controls the primary current amplitude of the induction motor 5! Detect. A pulse generator 7 mechanically connected to the induction motor 5 detects the rotation frequency fm of the induction motor 5 together with a speed detection circuit 17 .

8 is the input terminal of the magnetic flux current command ■φ, 9 is the torque current command I
At the input terminal of T, magnetic flux current command ■φ, torque current command IT
are both sent to arithmetic circuits 10, 11, and 12, and each arithmetic circuit receives the primary current amplitude command ■18. A slip frequency command fj1 and a transient slip frequency command fsm are calculated.

The subtracter 14 subtracts the primary current amplitude 11 detected by the current detection circuit 13 from the primary current amplitude command 11s and sends the output to the current control circuit 15, and the converter control circuit 16 is operated by the current control circuit 15 output. Thus, the detected value of the primary current amplitude If is controlled to match the primary current amplitude command Its.

Adder 18 adds slip frequency command fat, transient slip frequency command fi11, and rotational frequency afM detected by speed detection circuit 17 to generate primary current frequency command fl to control inverter control circuit 19.

The operation of the conventional device configured as described above is well known and will not be described in detail, but the arithmetic circuits 10, 1
1 and 12, a primary current amplitude command 118t slip frequency command fllll and a transient slip frequency command fsm are calculated from the magnetic flux current command Iφ and torque current command IT using the following equations, respectively.

Il, = FT■ ・・・・・・・・・・・・(1
) However, T2 is the secondary time constant of the induction motor. It has the following drawbacks. That is, the calculation of the primary current frequency command fI in the adder 18 and the inverter control circuit 1 based on this result.
9 controls the frequency of the inverter 4 with almost no time delay, whereas the primary current amplitude Is is controlled due to a delay in the amplitude change caused by the DC reactor 3, a dead time delay in phase control in the converter 2, etc. causes a time delay with respect to the primary current amplitude command 118. Therefore, during a transient period, a predetermined magnetic flux current command Iφ and torque current command IT are generated to command the primary current amplitude command 118 and the primary current frequency command fl. However, since the actual primary current amplitude 1 is different from the command, the actual magnetic flux and torque are also different from the command, and the independence of the two is lost, causing vibrations caused by magnetic flux changes. A phenomenon may occur.

Let us consider this phenomenon mathematically below. +11 above
, (2) , (3) For the primary current amplitude command 118*slip frequency command rst and transient slip frequency command f3 calculated using equations 118 and 3, each actual component is controlled equally to these commands, including during transient times. If so, the actual magnetic flux current (IQ) and torque current (IQ) will also be equal to the magnetic flux current command Iφ and torque current command IT. However, the slip frequency and transient slip frequency are Even if the control is performed according to the value, the primary current amplitude ■1 will be different from the primary current amplitude command Iss during the transient period due to the control delay described above.0 At this time, the magnetic flux current I- and the torque current (2) L is a value that satisfies each of the following equations, with I18 in equation (1) being 1.

11=65m ・・・・・・・・・・・・(4)
From equations (2) and (5) or equations (3) and (6), it follows that (t) and (4).

Similarly, o+ is obtained from equations (4) and (7).

(81, as is clear from equation (9), the primary current amplitude 1
1 differs from the primary current amplitude command IIB, the magnetic flux current I-, ) torque current also differs from the magnetic flux current command ■φ and the torque current command IT by the ratio.

An induction motor has a winding that carries a magnetic flux current I2 and a torque current I
Instead of having a separate winding that flows the current, the component current is supplied from the same primary winding, and the torque current error is supplied from the primary winding force by electromagnetic induction to the secondary winding. There is 0 Therefore,
In vector control, which requires coordination, the magnetic flux is kept constant even during torque control transients, and only the torque current proportional to the torque is changed to avoid electromagnetic phase interference due to changes in magnetic flux. However, in the device shown in FIG. 1, even if the magnetic flux current command Iφ is kept constant as described above, the actual magnetic flux current I; fluctuates, so the magnetic flux is not constant.
There are adverse effects such as torque vibration phenomena caused by the second-order time constant.

The present invention has been made to eliminate these drawbacks and realize a simple and higher-performance slip frequency control method vector control, which makes it possible to maintain t magnetic flux constant during transients and obtain good control characteristics. Figure 2 is a block diagram of an embodiment of the improved vector control using force 1 according to the present invention. Command fs! The calculation circuits 20 and 21 for calculating are all the same as those in FIG. The detected value of the primary current 9 and the width width 1 is input to the calculation circuits 20 and 21 in FIG. 2, and the following calculation is performed.

Considering the actual magnetic flux current I2 and torque current tsubo in this case, s II e I s satisfies equation (4), and the following equation holds true, setting flll in equation (5) and α1 to be equal. .

(4), From formula 04・”, I'φ=Iφ ・・・・・・・・・
- Song a1 is established.

Similarly, (t), (41, (ta formula, IO becomes.

a3. As is clear from the α4 equation, in the device shown in Figure 2, although the torque current is different from the torque current command IT, the magnetic flux current - is equal to the torque current command φ, and the magnetic flux is kept constant. Also, (6) When formula (4) is transformed using formula (11), it becomes equal to formula 19, which proves the validity of the arithmetic circuit 21.

As explained in detail above, in the vector control of the apparatus shown in FIG. 2 according to the present invention, the magnetic flux is kept constant even when there is a delay in the primary current amplitude control system, and the independent control of magnetic flux and torque is the essence of vector control. Good control performance can be obtained without loss of properties.

Moreover, in the embodiment shown in FIG. 2, the primary current amplitude ■! which becomes the input signal of the arithmetic circuits 20 and 21! is detected from the input current of the motor, but since there is a certain relationship between the input and output currents of the inverter, it is detected at the input side of the inverter, and this is used as one input signal of the arithmetic circuit. You may use it.

Note that although the above explanation uses a current source inverter as an example, it is not limited to current source inverters, but also applies to the primary current amplitude and frequency of induction motors such as cycloconverters and voltage source inverters that perform current control type pulse width modulation. As long as it can be controlled, it can be similarly applied to other power converters, and the arithmetic circuits 10, 20, 21, etc. do not need to be independent, but can be implemented using the same hardware as the microcombi Goto. Needless to say, the software may be used to perform various calculations.

[Brief explanation of the drawing]

\J' Fig. 1 is a block diagram of an example of conventional vector control based on slip frequency control, and Fig. 2 is a block diagram of an embodiment of improved vector control according to the present invention. 1...AC power input terminal, 2...Converter, 3...DC reactor, 4...Inverter, 5...Induction motor, 6... ...Current detector, 7...Pulse generator, 8...
- Magnetic flux current command input terminal, 9...Torque current command input terminal, 10, 11, 12, 20, 21...
... Arithmetic circuit, 13 ... Current detection circuit, 14
...subtractor, 15...current control circuit,
16...Converter control circuit, 17...
・Speed detection circuit, 18... Adder, 19...
...Inverter control circuit □ Day 1 82

Claims (1)

[Claims] In order to separate the primary current of an induction motor into two components, a magnetic flux current that contributes to secondary flux linkage generation and a torque current that contributes to torque generation, and to control them independently, the primary current is calculated from the magnetic flux current command and the torque current command. Calculate the amplitude command and feedback control the primary current amplitude, calculate the slip frequency command from the magnetic flux current command and the detected value of the primary current amplitude, and add the rotation frequency detected by the speed detection circuit to the calculated signal. An induction motor drive device characterized in that the primary current frequency is controlled by: