JPS6039372A - Circulating current type cycloconverter device - Google Patents

Abstract

PURPOSE:To maintain the reactive power of a power receiving terminal of a cycloconverter at a constant value by varying and controlling the sum of the output currents of converters to the prescribed value or the predetermined value in response to a load state. CONSTITUTION:The output currents I1, I2, I3 of converters are respectively detected by output current detectors CT1, CT2, CT3, and load currents IU, IV, IW are calculated as load current detected values. A sum current command value IT* is provided by a sum current setter TCR, while the output current IT=I1+ I2+I3 of the converters SS1, SS2, SS3 are obtained, and the sum current command value IT* and the sum current detected value IT are compared by a comparator CT. Then, the sum IT of the output currents of the converters is slightly varied and controlled to the prescribed value of the predetermined value in response to the load state. Thus, the reactive power value of the power receiving terminal of the cycloconverter can be maintained constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a circulating current type triangularly connected cycloconverter device in which the reactive power at the power receiving end is kept approximately constant.

TECHNICAL BACKGROUND OF THE INVENTION A cycloconverter is a frequency conversion device that directly converts alternating current power of one frequency to alternating current power of another frequency, and is widely used as a drive power source for induction motors and synchronous motors.

The triangular connection cycloconverter has three AC/DC power converters (
A commonly used cycloconverter (a cycloconverter in which a positive group and a negative group converter are paired to form one phase of output ), it has the advantage of requiring half the number of converters (converters), and has recently been attracting attention. In particular, circulating current type triangular-connected cycloconverters have small harmonics on the output side and It has the advantage of being able to control reactive power at the receiving end using current, and can be widely used as a drive power source for induction motors and synchronous motors. (Patent Application 1983-1)
58692) [Problems with Background Art] A known example of a triangular connection cycloconverter is the above-mentioned Japanese Patent Application No. 56-158692, which has the following problems.

a) In order to control the reactive power at the power receiving end of the cycloconnoser overnight in the conventional device, a reactive power detector at the power receiving end is first required. It was necessary to provide a transformer for detecting voltage and a current transformer for detecting three-phase alternating current, and also a reactive power calculator for calculating reactive power from the voltage and current. Therefore, the configuration of the device becomes complicated and the system has to be expensive.

b) Furthermore, the output signal from the reactive power control circuit is used as a command value for the circulating current of the cycloconverter, and the actual circulating current of the cycloconverter is controlled to match the command value, but if the load current is This caused a disturbance in the circulating current control system, making accurate control impossible.

C) Furthermore, it is difficult to accurately detect the circulating current of the triangularly connected cycloconverter, and examples of such a detector are shown in FIGS. However, especially the line current IU)
Signals SG, , SG2. S.G.

It is difficult to obtain the current Io+Iv+Iw
The pulsation of the signal disturbs the signal, causing problems such as difficulty in detecting the circulating current. Although other methods of detecting the circulating current are conceivable, all of them require complicated arithmetic circuits, lower the reliability of the device, and become economically expensive.

OBJECT OF THE INVENTION] The present invention has been made in view of the above-mentioned problems, and uses a reactive power detector at the receiving end and a circulating current detector of a cycloconverter to detect reactive power at the receiving end of the cycloconverter. An object of the present invention is to provide a circulating current type cycloconverter device that can maintain a substantially constant value.

[Summary of the invention]

In order to achieve the above object, the present invention provides a circulating current type cycloconverter main body connected to a three-phase load and triangularly connected by at least three AC/DC power converters, and a current to be supplied to the three-phase load. a load current control circuit that controls the sum of the output currents of the converters, a sum current control circuit that controls the sum of the output currents of the respective converters, and a firing phase of each converter according to output signals from the load current control circuit and the sum current control circuit. A circulating current type cycloconverter device comprising a phase control circuit for controlling the sum current control circuit according to the state of the three-phase load, and adjusting the sum current command value of the sum current control circuit to reduce the reactive power at the receiving end of the cycloconverter. This is a circulating current type cycloconverter device characterized in that the current is kept almost constant.

[Embodiments of the invention]

FIG. 1 is a configuration diagram showing an embodiment of a circulating current type cycloconverter device of the present invention.

In the figure, BUS is a three-phase AC power supply electric line CAP is a phase advance capacitor, TR is a power transformer, CC is a three-phase output cycloconverter body, and M is a three-phase AC motor (load).

It consists of three AC/DC power converters (con 7 (-ta) 881.SS2+SS3 and DC reactors LH, L2 + Ls).Power converter (con 7 (-ta) -ta) ss, , 882
．． The 88° AC input sides are insulated from each other by a power transformer TR, and the DC side is connected to a DC reactor L1. so that a unidirectional circulating current ZX flows. They are connected Δ via L, , L3. It constitutes a so-called triangular circulating current type cycloconverter. DC reactor L1.
L2. The center tap of L is connected to the three-phase winding of a three-phase AC motor M.

On the other hand, the control circuit includes current transformers CT□+ c'r2', c'r3 that detect the output current of the converter 7, sum current command circuit TCR, and comparators CT, CL+, Cv, Cw1.
Current control compensation circuit, GT, G, , Gv, GW, adders A1 to A, and phase city 1] control circuit PH□, PH2, P
H3 is used.

FIG. 2 shows an equivalent circuit of the cycloconverter CC and the load (motor M) of the device shown in FIG.

The operating principle of the device shown in FIG. 1 will be explained below using the equivalent circuit shown in FIG. 2.

The voltage equation for the main circuit can be calculated from the equivalent circuit shown in Figure 2 as follows. However, p = d/d t is a differential operator.

v, = (R, +L, p) ・i, +M,, ・p−
i, +M3□-p-i3+ vtIv,, (1)V
x=(”y+ L2P) ・i!+M1. m p−i
I+M21 +pe i, +Vvw −(2)V3
== (RB + L2p) ・I 3+MB, ・
p-i 1 +M135・p-1t+ VWU...
(3) Vo=(RL+LLp)・ju+Voo +++
++・++++++ (4) vv=(Rr, +Lr, p)
・iv + Vav −−−・−(5) Vw=(RL+
Lhp)jw+Vow ＋＋＋＋・＋＋＋＋＋＋＋ (
6) Here, R1, R,, R, ... resistance value of the DC reactor, L,, L, ...... l self-inductance value M, , M, , Ma.・−・ Mutual inductance value RL of 〃 ...Resistance value LL for one phase of load ...... l Inductance value vo
UIvovIvOw...This is the back electromotive force of the motor.

Further, "UVI" VWIvwU is the line voltage of the load, and there is the following relational expression between it and each phase voltage MU +VV +VW.

Vov = Vu Vv ・---・(7)vvw ””
My vw ””””' (s)vwu = vw
VU """"' (9) Also, converter output current i,, i,, ig and load current +1J+IV+IW
The following relational expression holds true.

1U=i, -i, ...... (1st season 1y=i
2-i, ...... En IW = is-i, ・
.....alpha. This is not related to the presence or absence of a circulating current in the cycloconverter.

Here, R1 = gift = R, -8 ri, -L, , , L, = L Ml - Toki = Ms: M vg + vy + vw = 0, and when formula (1) - (3) is inserted, v + −vs=(
R+bp)-(it-is)-M-p(1!-1s)+
2Vu ”*'v %'w = (R+ (LM) ・p) (1, -13) 4
3Vu=(R+(LM)p)iU+3((几り十LLp)・iU+VoU)=3・[FV
3+RL+((LM)/3+LL)I)), it+
+3vOυ ......(1■) Therefore, to control the load current ig (13)
It can be seen that the voltage v1 vs can be controlled using the relationship in the equation. At this time, the back electromotive force V. Since this enters our current control system as a disturbance, it is necessary to add in advance a compensation amount of the above voltage V+Vsl to cancel it.

Similarly, by subtracting equation (2) - equation (1) and equation (3) - (2), the following are obtained.

V, vl = 3 [R/3+RL+ ((LM)/
3+L L) p) ・t v+34 Vr3 y
・・・・・・αa Vs-V2:3[R/3-IL+((L-M)/3+L
L)! ])・iW+3−VOW・・・・・・(151 From the relationship of equation (L4), to control the load current lv, it is sufficient to control the voltage V!−v□, and It can be seen that in order to control the load current, it is sufficient to control the voltage V, -v.

The load current control circuit shown in FIG. 1 uses the above principle.

First, the output current detector CT, , CT! , CT3 detects the converter output current R, , x, , I3, and uses the relationship from α1 formula to
Calculate +IW and use it as the load current detection value. Of course, it goes without saying that the load electric construction υ+IV+IW may be directly detected.

The detected values IU, Iv, Iw of the load current and their respective command values io +IV +”W are sent to the comparator C1++cV.
+CW and input each deviation εU = engineering υ - engineering υ, εy = Iy
b and εW=IW Find IW.

The respective deviations εU, εV, and εW are respectively input to the current control compensation circuit ()o I evl GW. The current control compensation circuit GIJ.

Gv and Gw are usually composed of proportional elements or integral elements, and are designed to be optimal control constants in consideration of the stability and followability of the load current control system. Here, to simplify the explanation, the current control compensation circuit is considered to have only proportional elements, and the respective magnifications are assumed to be G,=KtI, Gv==, and GW=Kw.

The control deviation εU of the U-phase load current I is multiplied and input to the phase control circuit PH via the adder AI l A2, and the inverted value of the deviation −εU is multiplied by It is input to the phase control circuit PHs via the adders A, , A,. That is, in proportion to the deviation ευ, converter S8.
The output voltage v, of converter S83 increases, and conversely, the output voltage v3 of converter S83 decreases in proportion to deviation ευ. In other words, the voltage v, -v increases in proportion to the deviation εU.

Therefore, in the case of I,)IU, the deviation εU is a positive value,
The voltage V1-V increases in proportion to ευ·Kυ. Therefore, from equation (13), the load current IU increases and approaches Iυ=Iυ.

On the other hand, when engineering υ < Iu, the deviation εU becomes a negative value, and ε
, IKU, the voltage vl-v,1 also takes a negative value.

Therefore, IU also decreases from the 0th floor formula, and it is still controlled to be υ = υ.

The V-phase load current iU and the W-phase load current iy are similarly controlled.

Next, we will write the relational expression for the sum current control of the converter.

The relationship between equation (1) + equation (2) Samurai (3) is as follows.

vl+v, +v, = (R+Lp) (i, +i, +i3
)"2Mp(11+'2"'8) +vUv+vvw+vwU =((R+(L+2M)p) iT ・・・・・・・・・
・(IQ However, it is iT-i, + i, + i3.

That is, it can be seen that in order to control the sum current iy, it is sufficient to control the sum Vl-1-v2+V of the output voltages of the converters. Moreover, the transfer function of the control system is determined by the resistance value (2) of the DC reactor and the value of the inductance (L+2M), and the control system is free from external disturbances.

The sum current control circuit shown in FIG. 1 uses the relationship of equation (16) above.

A sum current setter TC gives a sum current command value IT, while output currents I, , I, of each converter.

The sum of the detected values of Is is calculated, and the sum current detected value I T = I,
I'm looking at + I, + engineering.

The sum current command value IT and the sum current detection value IT are compared by zero comparators, and a deviation ε7=I7 IT is found.

The six deviations are input to the next current control compensation circuit GT.

Again, to simplify the explanation, 0 is considered to be just a proportional element. The value of ε,− is the adder ^.

Phase control circuit PH,,PH,,P via A4,7V6
It is input to H8. Therefore, the output voltage of each converter V11
V21v3 is increased in proportion to the signal ε, , in addition to the signal from the load current control circuit.

When It>Iy, the deviation εT becomes a positive value, and εT−K
.

The voltages v, +v, +v are increased in proportion to. As a result, the sum current I shown by equation 10 increases and 1. I7=
It is controlled to become F.

Conversely, if I:<IT, ε? ＜ O,
By setting the voltage V□+V2+Vl to a negative value and decreasing the sum current IT shown by equation 10, it settles down to 1y=Iy.

Figure 3 shows the waveforms of various parts when the sum current IT is controlled to be constant. 111 ITl IN is the output current of the converter, IIJ+IV+■W is the load current, represents each waveform of the circulating current of the cycloconverter.

Assuming that the load currents Iu, Iv, and I are balanced three-phase currents, they can be expressed as follows.

■. = Im −sinωt ・・・αηIy
= Im −sin (ωt−2π/3) ・・・・・・
・α mark Iw= Im −sin (ωt + 2yr/
3) -------σ9 However, m is the wave height value.

On the other hand, the output current It)I2113 of each converter
When bias current I T/3 is added, it becomes as follows.

Surprisingly, the sum of the output currents of this converter is
I, + I, + I, = I7.

In other words, the peak value Im of the load current is (1/4) of the sum current IT.
The values of I, + I, + I3 will always be constant values unless they exceed the value of d).

At this time, circulating electricity construction was carried out. changes at a frequency three times the load side frequency. When Im≧IT/, /a, a non-circulating mode appears in part, so that the converter output current I
ll I21 The waveform of Is also changes.

The reactive power Qoo at the receiving end of such a triangular-connected cycloconverter that is controlled by the sum current can be expressed as shown in the following equation.

However, k is a proportionality constant, C8, C2, α.

is the firing phase angle of each converter.

Qoo=kq・(I+−5tnαH+ I2・sinα
2+I, ・sin α, ) ・== C23) Here,
Firing phase angle α1 of each converter. C2 and C3 are angles at which the input current of each converter lags with respect to the power supply voltage, and are controlled within a range of about 20° to 150° to perform natural commutation.

In the case of a motor load, the speed electromotive force is small at startup or at low speed, so it is operated at C1"pα2"qα8"=P90°, and the reactive power Qoo at that time is Qaokp k(2(If + Il! +'Is )2kq·'r''=''''' C24) If the sum current I is constant, Qoo is also kept almost constant.

Therefore, if a phase advance capacitor CAP is installed at the receiving end to cancel this, the power factor becomes hq1.

As the speed N of the motor increases, the above ignition phase angle α
1. C2 and C3 also vary within a range of approximately 20' to 180° with 90° as the center. Therefore, even if the sum current IT is kept constant, the reactive power Qoo becomes slightly smaller as shown in FIG. Therefore, the leading reactive power Q of the phase advancing capacitor CAP
cap is the advanced reactive power Qoo of the above cycloconverter
becomes larger, and the input power factor becomes progressive.

In FIG. 5, the sum current command value IT is changed according to the rotational speed N of the electric motor, and the summation current command value IT is slightly increased as the rotational speed N increases. As a result, the reactive power Qoo at the receiving end of the cycloconverter becomes a substantially constant value, cancels out Qcap of the phase advance capacitor, and can be operated with an input power factor of 1. The sum current command circuit TCR shown in FIG. 1 performs the above role.

〔Effect of the invention〕

As described above, the device of the present invention does not need to detect the reactive power at the power receiving end or the circulating current of the cycloconverter, and can detect the sum of the output currents of each converter at a constant value or depending on the load condition. By controlling the value by slightly changing it to a predetermined value, the reactive power value at the receiving end of the cycloconverter can be kept almost constant, and by simply installing a phase advance capacitor with a constant capacity at the receiving end, the input The power factor can be maintained at approximately 1. Therefore, there is no adverse effect on the power supply system due to reactive power fluctuations, and it is possible to provide an ideal power converter.

In addition, the transfer function of the sum current control system is determined only by the resistance and inductance of the DC reactor, as shown in equation 1e, and there is no disturbance from the load current, which was a problem in the past. Design has become extremely easy.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the device of the present invention, FIG. 2 is an equivalent circuit diagram of the main circuit to explain the operation of the device in FIG. 1, and FIG. 3 is a diagram showing each part of the device in FIG. The current waveform diagram, FIG. 4, is a diagram of the relationship between the rotational speed N of the motor and the reactive power Qoo at the receiving end (sum current I!) for explaining the operation of the device shown in FIG.
- constant), and FIG. 5 is a diagram of the relationship between N and Qoo, and shows the cases where the Waden construction T is varied. BUS...Electric line of 3-phase AC power supply CAP...Phase advancing capacitor TR...Power transformer CC...3-phase output cycloconverter body M...
3-phase AC motor (load) 88, , SS, , SS, ... AC/DC power converter (converter) Ll, L2. Ls...DC reactor CT□, CT2. CT, , ・Current detector TCR
...sum current command circuit CT +CU, cv, cW... comparator GT, GU,
Gv, Gw, , current control compensation circuits A1 to A6...adder

Claims (2)

[Claims] (1) A circulating current type cycloconverter body connected to a three-phase load and triangularly connected by at least three AC/DC power converters, and a load current control circuit that controls the current to be supplied to the three-phase load. , consisting of a sum current control circuit that controls the sum of the output currents of the respective converters, and a phase control circuit that controls the firing phase of each converter according to the output signals from the load current control circuit and the sum current control circuit. Circulating current type cycloconverter device. (2) The three-phase load is a motor load, and the sum current command value of the sum current control circuit is adjusted according to the rotational speed of the motor so that the reactive power at the receiving end of the cycloconverter is constant. The circulating current type cycloconverter device according to claim 1, characterized in that: