JPH047674Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a control circuit that performs feedback control of the rotational speed of an AC motor.

[Prior art]

Conventionally, there has been a control circuit of this type as shown in FIG. In FIG. 1, numeral 1 is an arithmetic unit which inputs the reference speed signal ω _r ^* and the speed signal ω _n to be fed back and generates the torque component current command signal i _1q ^* , and 2 is the reference magnetic flux signal φ ₂ ^*. is input and generates a command signal i _1d ^* of magnetic flux component current, and has a transfer function (1+sL ₂ /R ₂ )/M. However, S is a differential operator, and M, L ₂ , and R ₂ are the mutual inductance between the primary and secondary windings, the self-inductance of the secondary winding, and the resistance of the secondary winding, respectively. 3 is a divider that divides the command signal i _1q by the reference magnetic flux signal φ ₂ ^* , 4 is the input of the output of divider 3, and the transfer function
an arithmetic unit having MR ₂ /L ₂ and outputting a command signal ω _s ^* of the slip frequency; 5 generates a corrected command signal ω _p ^* by adding the command signal ω _s ^* and the speed signal ω _n ; adder; 6 is a converter that inputs command signals i _1q ^* , i _1d ^* , ω _p ^* and generates AC current command signals i _u , i _v , i _w for each phase; 7 is a command signal i _u , i _v , i _w and drive current i _ub , i _vb ,
An amplifier 8 outputs command signals i _ua , i _va , i _wa which are controlled by determining the _deviation of i _{wb and} have a polarity that makes this deviation _zero . _{9 is an induction motor driven by the drive currents i ub , i vb , i wb ; 10} is an induction motor 9;
This is a detector that detects the rotation of the motor and outputs a speed signal ω _n .

Next, the operation will be explained. The induction motor 9 is driven by drive currents i _ub , i _vb , i _wb , and its rotation is detected by a detector 10 and inputted to the calculator 1 as a speed signal ω _n . Arithmetic unit 1 calculates the deviation between the reference speed signal ω _r ^* and the speed signal ω _n , and generates a command signal according to this and controlled with a polarity that makes this deviation zero.
Print i _1q ^* . The calculator 2 receives the reference magnetic flux signal φ ₂ ^* and generates the command signal i _1d ^* based on the transfer function (1+sL ₂ /R ₂ )/M. The command signal i _1q ^* is divided by the reference magnetic flux signal φ ₂ ^* in the divider 3, and then becomes the command signal ω _s ^* by the arithmetic unit 4 having the transfer function MR ₂ /L ₂ . The adder 5 obtains the command signal ω _p ^* by adding the command signal ω _s ^* and the speed signal ω _n . The converter 6 receives the command signals i _1q ^* , i _1d ^* and ω _p ^* obtained in this way.
command signals i _u , i _v , i _w for each phase are output.
The command signals i _u , i _v , i _w are applied to the induction motor 9 via the amplifier 7 and the power converter 8 to drive currents i _ub , i _vb , i _wb
It is supplied as follows.

Since the amplifier 7 performs current control as described above, the induction motor 9 receives a torque component current command signal.
i _1q ^* and a current that matches the command signal i _1d ^* of the magnetic flux component current is supplied. At this time, the following equation holds between the secondary magnetic flux φ ₂ of the induction motor 9 and the command signal i _1d ^* . (Reference: New Drive Electronics, published by Denki Shoin, pp196) φ ₂ = M/1 + sL ₂ /R ₂ i _1d ^* …(1) The calculator 2 sends a reference magnetic flux signal φ ₂ ^* to the induction motor 9.
In order to generate a secondary magnetic flux φ ₂ equal to , a command signal i _1d ^* is calculated and output from a reference magnetic flux signal φ ₂ ^* using the following equation, which is an inverse function of equation (1).

i _1d ^* = 1 + sL ₂ /R ₂ /Mφ ₂ ^* ...(2) The conventional control circuit is configured as described above, and combines the generated torque T _M of the induction motor with the command signal i _1q ^* of the torque component current and the reference magnetic flux. It is proportional to the product of signal φ ₂ ^* , that is, T _M −αφ ₂ ^* i _1q ^* …(3), and by considering the linear relationship between current and torque as in the speed control of a DC motor, , which attempts to realize good speed control of an induction motor. Such a control method is called slip frequency type vector control of an induction motor (see the above-mentioned document pp. 205).

However, in the conventional control circuit, since the arithmetic unit 2 that calculates the command signal i _1d ^* from the reference magnetic flux signal φ ₂ ^* includes a differential element, there are the following drawbacks. This will be explained using a diagram.

When starting the induction motor 9, the reference magnetic flux signal φ ₂ ^* is given stepwise from 0 to a certain value as shown in FIG. 3-a. At this time, the computing unit 2 outputs a command signal i _1d ^* necessary to cause the induction motor 9 to generate a secondary magnetic flux that matches the reference magnetic flux signal φ ₂ ^* , which is expressed by equation (2). Since the transfer function includes a differential element, the command signal i _1d ^* reaches the upper limit of the output of the calculator 2 as shown by the solid line in Figure 3-b for inputs that change rapidly, such as step signals. I get saturated.

Therefore, as shown in FIGS. 3-a and 3-c, the reference magnetic flux signal φ ₂ ^* and the secondary magnetic flux φ ₂ of the induction motor 9 do not match. In Fig. 1, the reference magnetic flux signal φ ₂ ^* is used to obtain the command signal ω _s of the slip frequency, but as mentioned above, φ ₂ ^* does not match the secondary magnetic flux φ ₂ , so here The command ω _s ^* obtained by is also not appropriate.

For the above reasons, in the conventional control circuit, the torque generated by the induction motor 9 is not proportional to the product of the command signal i _1q ^* and the reference magnetic flux signal φ ₂ ^* , resulting in poor control linearity and poor speed control. There is a drawback that there are cases.

On the other hand, since the upper limit value of the arithmetic unit 2 is determined by the current capacity of the power converter, a power converter with an extremely large current capacity is required to prevent saturation, and increasing the size of the device increases costs. Further, when the arithmetic unit 2 is configured with an analog circuit, there is a drawback that since it includes a differential element, it is susceptible to pulse noise and control becomes unstable.

[Summary of the idea]

This invention was made to eliminate the drawbacks of the conventional ones as described above. By providing a transfer function that includes a first-order delay element to the circuit section that processes the reference magnetic flux signal, it is possible to eliminate the saturation of the output of this circuit section. It is an object of the present invention to provide a control circuit for an AC motor that prevents mismatch between a reference magnetic flux signal and a secondary magnetic flux caused by the oscilloscope, provides good control characteristics, and is less susceptible to pulse noise.

[Example of idea]

An embodiment of this invention will be described below with reference to the drawings. In FIG. 2, the same symbols as in FIG. 1 indicate the same parts. The reference magnetic flux signal φ ₂ ^* is supplied to the positive input of the subtracter 12 via the amplifier 11 with a gain of K, and the first-order lag transfer function 1/1+sL ₂ /KR ₂ (constant of K>1)...(4 ), and the signal φ ₂ ^* , which is the output of this calculator 13, is sent to an amplifier 14 with a gain of K-1.
is supplied to the negative input of the subtractor 12 via the subtracter 12. The subtracter 12 subtracts the output of the amplifier 14 from the output of the amplifier 11 and outputs the corrected command signal i _1d ^* by passing the output through the amplifier 15 with a gain of 1/M. This command signal i _1d ^* is input to the converter 6.

The signal φ ₂ ', which is the output of the arithmetic unit 13, is sent to the divider 16.
The command signal inputted to and outputted from the calculation unit 1
A corrected command signal ω _s ^* is output by dividing i _1q ^* and passing it through an amplifier 17 with a gain MR ₂ /L ₂ . The command signal ω _s ^* is added to the speed signal ω _n in an adder 5 , and the corrected command signal ω _p ^* is input from the adder 5 to a converter 6 .

With the configuration of the above embodiment, the transfer function from the reference magnetic flux signal φ ₂ ^* to the command signal i _1d ^* is as shown in the following equation.

i _1d ^* (s)/φ ₂ ^* (s)-1/M[K+K-1/1+
s(L ₂ /KR ₂ )]=1/M・1+s(L ₂ /R ₂ )/1+s
(L ₂ /KR ₂ )...(5) The transfer function from the command signal i _1d ^* of the magnetic flux component current to the actual secondary magnetic flux φ ₂ of the induction motor 9 is φ ₂ (s)/i _1d ^* (s )=1/1+s(L ₂ /R ₂ )...(6) Also, the transfer function from the reference magnetic flux signal φ ₂ ^* to the secondary magnetic flux φ ₂ is obtained by dividing equation (5) by equation (6). It becomes as follows.

φ ₂ (s) / φ ₂ ^* (s) = 1/1 + s (L ₂ /KR ₂ )...(7) Also, φ ₂ used to obtain the command signal ω _s of the slip frequency from the reference magnetic flux φ ₂ ^*. According to FIG. 2, the transfer function up to ' is given by the following equation.

φ ₂ ′ (s) / φ ₂ ^* (s) = 1/1 + s (L ₂ /KR ₂ )…(8
) From the above, the waveforms of each part when starting the induction motor 9 are shown in FIG.

When the reference magnetic flux signal φ ₂ ^* is given in ^a stepwise manner, _the command signal i _1d ^* as shown in FIG. It can be seen that the waveform is as follows. Furthermore, from equations (7) and (8), the response waveforms of the secondary magnetic flux φ ₂ and the signal φ ₂ ' are the same as shown in FIG. 4-c.

By the way, the reference magnetic flux signal φ ₂ ^* is 1/K of the electrical time constant L ₂ /R ₂ with respect to the secondary magnetic flux φ ₂ of the induction motor 9.
It responds with a first-order delay with a time constant of .

Therefore, the response becomes faster as the gains K included in the arithmetic unit 13 and amplifiers 11 and 14 are increased.

However, if the gain K is made too large, the output of the amplifier 15 that outputs the command signal i _1d ^* will be saturated, so it is necessary to set it below a certain value. Since the upper limit value i _1d max of the output of the amplifier 15 and the magnitude of the reference magnetic flux signal φ ₂ ^* are known in advance,
If the gain K is adjusted so that the following equation holds true, a fast response of the secondary magnetic flux φ ₂ can be obtained within a range where the output of the amplifier 15 does not exceed the upper limit value i _1d max of the following equation and is not saturated.

i _1d max≧K・φ ₂ ^* /M (9) In addition, as mentioned above, the signal φ ₂ ' used to obtain the command signal ω _s of the slip frequency and the induction motor 9
Since the responses of the secondary magnetic flux φ ₂ to the reference magnetic flux signal φ ₂ ^* are equal, it can be seen that the optimal command signal ω _s ^* can be obtained.

Furthermore, since no differential element is included in the signal transmission path from the reference magnetic flux signal φ ₂ ^* to the magnetic flux current command signal i _1d ^* , it is less susceptible to pulse noise.

[Effect of idea]

As described above, according to this invention, since the circuit portion that processes the reference magnetic flux signal has a transfer function that includes a first-order delay element, it is possible to improve the response to the secondary magnetic flux and the characteristics against noise.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional control circuit for an AC motor, Fig. 2 is a block diagram showing a control circuit for an AC motor according to an embodiment of the present invention, and Fig. 3 is a block diagram showing a control circuit for an AC motor according to an embodiment of the present invention. FIG. 4 is a signal waveform diagram of each part when the AC motor is started by the control circuit of the present invention. 1, 2, 4, 13... Arithmetic unit, 3, 16... Divider, 5... Adder, 6... Converter, 8... Power converter, 7, 11, 14, 15, 17... ...Amplifier, 8...Induction motor. Note that in the figures, the same reference numerals indicate the same parts.

Claims (1)

[Scope of utility model registration request] a first computing unit that compares a reference speed signal with a speed signal detected from a rotating AC motor and generates a designated signal for a torque component current based on the comparison result; and a mutual inductance M between the primary and secondary windings. , a secondary winding self-inductance L ₂ , a secondary winding resistance R ₂ , and a differential operator S as constituent elements, having a first-order lag transfer function and inputting a reference magnetic flux signal; a subtracter having a reference magnetic flux signal as a positive input via a first amplifier with a gain K and an output signal of the second arithmetic unit as a negative input via a second amplifier with a gain K-1; and an output signal of the subtracter. a third amplifier that amplifies with a gain of 1/M and outputs a command signal of the magnetic flux component current; a divider that divides the command signal of the torque component current by the output signal of the second arithmetic unit; The output signal of the divider is given the gain MR ₂ /
an adder that inputs the signal through the fourth amplifier of _L2 and adds it to the speed signal to generate a designated signal of the slip frequency; a command signal of the torque component current, a command signal of the magnetic flux component current, and a command signal of the slip frequency; A converter inputs a command signal and generates a command signal for AC current for each phase, and compares the command signal for AC current for each phase with the drive current flowing to the AC motor for each phase. an AC power conversion device that is controlled by the AC voltage command signal for each phase and supplies a drive current to each phase of the AC motor; Electric motor control circuit.