JPS6013263A - Active current detector - Google Patents

Abstract

PURPOSE:To enable accurate detection of active current without use of any changeover switch by inverting the polarity of a second voltage phase signal according to the direction of output phase rotation of a multiphase AC power source unit to compute the effective current. CONSTITUTION:The phase rotation signal 93 is set at ''1'' with respect to the direction of reversing a motor 1 so that a sine wave generator 92 will read counts of a counter 7 as such added to by 1,000, for example. The sine wave generator 92 is so arranged to output -COS(omegat) for counts of 1,000 to 1,255, for example. As a result, the second voltage phase signal 90 gives -COS(omegat) when the signal 93 indicates reversion by ''1'' though counts of the couter 7 range from 0 to 255. Changes in the polarity of the second current signal generated by inverting the direction of phase rotation are cancelled by inverting the polarity of the second voltage phase signal thereby always enabling accurate detection of active current without use of any changeover switch.

Description

DETAILED DESCRIPTION OF THE INVENTION An effective current detection device for detecting an effective current flowing through a flE motor will now be described.

2. Description of the Related Art Conventionally, it is generally known that torque control of an induction motor (hereinafter referred to as a motor) is performed using a VVVF device. Now, if Tanabata's static voltage effective value is expressed as v1 phase current effective value, and the power factor is expressed as cos(θ), then the power input to the motor is expressed by the following equation (1).

p=v'了v・P−CO8(θ)・−・−・TI) Further, the torque T of the motor is roughly expressed by the following equation (2), where N is the number of revolutions.

When controlling the torque of a motor, it is a known method to control the output voltage of a VVVF device so that I/V/N is kept at a constant value. Therefore, the torque T is proportional to the value 1cos(θ) (referred to as effective current) obtained by multiplying the effective current value by the power factor. This means that when trying to operate a motor at a desired torque or rotational speed, the motor's effective J
It is an effective means to detect the WL flow and use it as a feeder control signal.

The effective current of the motor can be detected in the following way. If the motor is expressed as 5 inches (ωt), the phase current can be changed by Tpsln (ω is 10θ). However, il+ is the maximum value of the phase current, and 6 is the power factor angle. , (ω is the voltage phase. The previous i1 phase πXEiE signal is conveniently referred to as a first voltage phase signal, and the current of this phase is referred to as a first current signal.

Next, the voltage phase signal of 2ir, 2 which has a phase difference of 900 with respect to the first tχ voltage phase signal is expressed as coa (ωt), and the second voltage phase signal which has a phase difference of 900 with respect to the first current signal is expressed as coa(ωt). ifj vli; The signal is expressed as Ipcos (ωt + 10 or more, 4 ; Using 1r1 of 1Iij, C first voltage phase signal and m l'ffr tlflL IF
By multiplying the second voltage phase signal and the second current signal and adding them together, the lower lie
As expressed by equation (3), a value obtained by multiplying the maximum current value by the power factor is obtained.

5in(ωsu(IF!'in(ω)
(iP cos (ωt-M January = Ip cos (0
) ・・・・・・・・・・・・(3) Also, since the above-mentioned effective current value calculation has the relationship of I=IP/σ, the above-mentioned (3
) is a value proportional to the effective current. Therefore, ip Co5(θ) is hereinafter referred to as an effective current.

The means for specifically detecting the effective current will be explained by taking as an example vvvp i i which outputs three-phase alternating current.

FIG. 1 is a block diagram showing a conventional active current detection device applied to a VVVF device, in which 1 is a motor, 2 is an inverter device, 3 is a current detector, 4 is a voltage command generator, and 5 is a It is an oscillator. 6 indicates an effective current detection device; 7
is a counter, 8.9 is a sine wave generator, and lO is 2II! I
I converter, 11.12 is a multiplier, and 13 is an adder. Reference numeral 93 indicates a phase rotation signal, 94 a changeover switch for a phase current signal, and 200 a frequency command.

In FIG. 1, the frequency command 200 causes the oscillator 5 to
A pulse train having a frequency that is an integral multiple of the output frequency of the vvp device is generated. At the same time, the frequency command 200 is generated by the voltage command generator 4.
The voltage proportional to the frequency is input to the inverter device 2.
command. The output pulse train of the oscillator 5 is input to the counter 7. It is input to counter 7. The counter 7 counts the input pulse train, and when it reaches a value corresponding to the length of one cycle of the output frequency of the VVVF device, it operates to make the count value zero. Therefore, by outputting a heavy pressure waveform in synchronization with the operation of this counter 7, the inverter device 2
It should be easy to infer that the f+ value corresponds to the phase of the output voltage of the VVVF blood supply. counter 7
outputs the count value as an output signal 70, which is applied to the sine wave relay generator 8 and the sine wave generator 9. Sine wave generator8.
9 is jn211+ which remembers the peak value of the sine wave waveform.
411 is formed by V'' and 'r, and the input count value of the counter 7 is regarded as a phase error signal, and a sine wave waveform corresponding to this valley phase is output. Vessel 9
Assume that the sine wave generator 8 stores a waveform having a phase difference of 90°. That is, when the sine wave (No. 71 80) which is the output of the sine wave generator 8 is fitted with 5 inches (ω), the sine wave signal 90 which is the output of the sine wave generator 9 is expressed as coS (ωt). Zuru.Mata 5in
(ωt) is called the first voltage phase signal, and cos(ωt)
will be referred to as the second voltage phase signal.

The current detector 3 detects each phase current of the motor 1 and is expressed by Tπ10. Taking the current signal 31 as a reference and calling it the first current signal, the two-axis converter IO uses the other two-phase current signals 32 and 33 and has a phase difference of 90' with respect to the first current signal! <20) Create a current signal. Specifically, as shown in equation (4) below, the current signal 32 is subtracted from the current signal 33 by n and multiplied by l//T.
(a+t-÷π→-θ)) == Ip CO8 (ω is 10) (4) The output of the two-axis converter lO is the first current signal 101 and the second current It is represented by signal 102.

Using the four types of Iha obtained as described above, (3
), the effective current flowing through the motor l can be obtained. This performance rf is 11.12
and an adder 13. The multiplier 11 multiplies the voltage phase signal 80 of nXl, that is, 5in (ω and the first current signal 101), that is, lp sin (ωt+θ), and the multiplier 12 multiplies the voltage phase signal 90 of 8112, that is, C05 ( ω, the second current signal 102 or I
When p Co5 (ω is 10) is multiplied 3114 and the respective calculation results 110 and 120 are added by the adder 13, Ipcos(θ) is obtained as the effective current result 130.

Now, in order to reverse the hh direction of the motor l, if a signal is given to the phase rotation signal 93 to change the phase rotation direction of the variable current low voltage output from the VVVF' device, the current (8 The relationship between current signals 32 and 33 with respect to No. 31 is reversed.Therefore, the polarity of the output signal of the two-axis converter IO is reversed as expressed by the following equation (5).

7(Ip 'I I n (0)l'' π10)-I
p sln (ωt+, π+6)) = −Ip
Co5 (ω is 10) ・・・・・・・・・(5) If we carry out the operation n that reduces the flow to effective 1, the operation n K1'
j is -Ip cos (2ωt+), so the correct effective current value is 1).

vvvi;' The conventionally considered method of correctly detecting the active current even if the phase rotation of the alternating current voltage output by the i position is reversed is to Switch 9 to change current signal 33
4. This is a method of switching. However, with current electronic circuit technology, it is difficult to realize a highly reliable on/off switch 94 without increasing the size of the device.

The present invention has been made with the above points in mind.

An object of the present invention is to provide an effective nLA detection device that correctly detects effective current even when changing phase rotation without using a changeover switch. Hereinafter, the present invention will be explained based on the drawings of the embodiments.

FIG. 2 is a block diagram showing a further embodiment of the effective current detection device according to the present invention. Components in FIG. 2 denoted by the same reference numerals as those in FIG. 31 have the same functions.

In the present invention, the sine wave generator 92 is configured to invert the polarity of the sine wave signal according to the phase rotation signal 93 to obtain an output. The counter 7 is VV as in the conventional example shown in FIG.
One round JpJ of the output frequency of the VF device is divided into equal intervals and counted. Assume now that one cycle is divided into 256 parts. In the conventional square wave generator 9, the count value of the counter 7 is set to 417 so as to output cos(ωt) corresponding to values from 0 to 255. Sine wave generator 9 according to the invention
2, C is the phase rotation signal 9 for the forward rotation direction of the motor 1.
3 is received at “0°, and the output 90 at this time is cos(ω
t) is obtained. However, in the phase rotation with respect to the reverse direction of the motor l (-@ 93 is "lo" and r), the sine wave i
The generator 92 takes the value of n1 of the counter 7 as L″d, for example, by adding 1000.Then, the sine wave generator 92 takes −C05(ω By configuring 11'1 so as to output a value of
The second voltage phase signal 90 is -cos (ωt) ◎ Therefore, the present invention reverses the output phase rotation direction of < V V V' F as expressed by the above equation (5) By reversing the polarity of the second voltage phase signal, the change in the M& characteristic of the current signal of the silk 2 caused by this is canceled out, and the effective current can always be detected correctly.

As described above, since the effective current detection means according to the present invention does not use a changeover switch in the detection device, it is possible to provide a highly reliable effective current detection device.

Furthermore, the method of the present invention can also be applied to the detection of reactive current represented by s Ipsln (θ), and the following (
b) There is no deviation in performing the operation expressed by the formula *' @ mt
is obtained.

C08(ωt)(Ipain(ω is 10))−sin(
ωt ) (1pcO8(ω = Ip sin
(θ) −==−(6) When the phase rotation direction is reversed, in order to avoid reversing the polarity of the voltage signal of M2 and the second voltage phase signal, −1 psjnθ is obtained as the result of the operation n. Therefore, by reversing the polarity again, the correct reactive current can be obtained.

Also, for the two-axis converter 10, it is not necessary to detect all the three-phase currents of the motor l; for example, it is also possible to detect two phases of the current signal 1o, the current signal 31, and the current signal 32. It goes without saying that it is also possible to calculate from two phases.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional effective current detection device applied to a vvvi;'device; Fig. 2 is a block diagram showing an embodiment of an effective current detection device according to the present invention. l...Induction N, # machine, 2...Inverter' device, 3...11C flow detector, 4...
11 is a pressure command generator, 5... oscillator, 6... effective current detection device, 7 caranta, 8, 9.92...
...Sine wave generator, 10...Two-axis converter, II
, 12...N multiplier, 13-...Adder, 93...
Phase @ change signal, 94... Phase current signal cut-off switch, 200... Frequency command. Patent Author: Toyo↑Kyuki Seizo Co., Ltd. Representative Atsushi Doi Figure 1 Figure 2

Claims (1)

[Claims] The first current signal is synthesized using the reference first current signal among the phase currents of the induction motor connected to the multiphase or current rI device, and the 'rIk flow No. 6 of the other phase, and the first current i -g-
#! having a phase difference of 90' with respect to t! 2 current signal,
a first current signal representing a voltage phase of a phase through which the first current signal flows;
η also detects the effective current of the current flowing through the induction motor using four types of signals: pressure No. 1i and a second voltage phase signal having a phase difference of 90' with respect to the voltage phase of core section 1. In the effective current detection device, the active current is calculated by inverting the polarity of the positive phase signal (↑) of 011, Introduction 2, according to the output phase rotation direction of the multi-phase father R power supply device. An effective current detection device characterized in that it is configured to