JPH01206874A - Control method for cyclo-converter - Google Patents

Abstract

PURPOSE:To operate a cyclo-converter efficiently, by performing control such that the sum of output currents from AC/DC power converters corresponds to the peak value of load current. CONSTITUTION:A triangle-connection current circulation cyclo-converter comprises a transformer Tr, a cycle-converter CC and an AC motor M, where the cycle-converter CC comprises three AC/DC power converters SS1-SS3 and DC reactors L1-L3. A sum current command is provided in proportion to the peak value command of load current in order to control the sum current to be constant. Since no fluctuation of reactive current exists at the input side, low order components of higher harmonic of input current can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for controlling a cycloconverter that supplies alternating current power of variable voltage and variable frequency to an alternating current motor or the like.

(Prior art) Conventional triangular connected linear circulating current type cycloconverters are disclosed in Japanese Patent Application Laid-Open No. 58-58621 and Japanese Patent Application Laid-open No. 58-60.
There are those described in JP-A No. 328, JP-A-60-39368, JP-A-60-39639, JP-A-60-39370, and JP-A-60-39371.

All of the systems described in these publications adjust the reactive power on the input side by controlling the circulating current flowing through the triangular connected linear cycloconverter and the reactive current on the input side. It attempts to maintain the input power factor at 1 together with the connected phase advancing capacitor.

The features of this cycloconverter are: (1) Compared to a three-phase output cycloconverter consisting of a forward/reverse converter, the number of elements is half, making it possible to provide an inexpensive device.

■ By adjusting the circulating current, the reactive power on the input side is controlled, and in combination with the constant leading reactive power of the phase advancing capacitor, operation with input power factor = 1 is possible, reducing the installed capacity of the power supply system. Can be done.

■ Compared to non-circulating current type cycloconverters, the waveform distortion of the output voltage is small and the upper limit of the output frequency can be set high.

■ Elements that make up the cycloconverter (cyrisk)
Because it performs natural commutation using the power supply voltage, it is highly reliable and easy to increase capacity.

etc.

Taking advantage of these features, triangular-connected linear circulating current type cycloconverters have recently come to be used as drive power sources for AC variable speed motors and the like.

(Problem to be Solved by the Invention) However, in the conventional triangular connected linear circulating current type cycloconverter, when trying to maintain the input power factor at 1 at all times, when the load of the cycloconverter is heavy,
The circulating current will be small, and if the load is light, the circulating current will be large.

As a result, compared to a non-circulating cycloconverter,
Losses at light loads increase, forcing inefficient operation.

This becomes a particular problem in applications where light load operation continues for a long time, and there is a tendency to desire more efficient operation than operation with an input power factor of 1.

However, non-circulating cycloconverters have a low upper limit value of the output frequency (generally speaking, the upper limit value is about 1/3 of the input frequency), so they are not often used.

Therefore, one method for increasing the operating efficiency during light loads is to control the circulating current of the cycloconverter to a minimum constant value. According to this method, the circulating current remains at a constant value regardless of the size of the load, and light load losses are reduced. However, when the circulating current is constant, not only can the input power factor not always be maintained at 1, but also reactive power fluctuations on the input side synchronized with the output frequency appear, and the input current has lower harmonics (sidebands around the fundamental wave). wave).

These low-order harmonics are difficult to remove with a filter or the like, and cause power supply voltage distortion, which has various adverse effects on electrical equipment connected to the same system.

Therefore, the present invention has been made in view of the above problems, and while maintaining the features of the circulating current type cycloconverter,
A cyclo converter that improves operating efficiency during light loads, eliminates reactive power fluctuations on the input side that depend on the cyclo converter's output frequency, and removes low-order harmonics (sidebands around the fundamental wave) contained in the input current. The purpose of this invention is to provide a method for controlling a converter.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a circulating current cycloconverter configured by connecting a plurality of AC-DC power converters in a triangular manner. Provided is a cycloconverter control method for controlling the sum of the output currents to a value corresponding to the peak value of the current supplied to the load.

(Function) In such a cycloconverter control method,
The circulating current of the cycloconverter changes in synchronization with the output frequency and works to suppress fluctuations in reactive power on the input side. Therefore, the reactive power fluctuation on the input side of the cycloconverter that depends on the output frequency is eliminated, and low-order harmonics (sideband waves around the fundamental wave) included in the input current are removed.

On the other hand, the average value of the circulating current of the cycloconverter does not increase even when the load is light, and efficient operation is possible.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are configuration diagrams showing a triangular connected linear circulating current type cycloconverter device which is an embodiment of the present invention.

In FIG. 1, BUS is a three-phase AC electric line, Tr is a transformer, CC is a cycloconverter, and M is an AC motor. The cycloconverter CC consists of three AC-DC power converters (hereinafter referred to as separately excited converters) SS□~SS,
and DC reactors L1 to L.

It consists of

Further, the control circuit includes a multiplier ML as shown in FIG.
Engineering~ML3. Proportional amplifier K, comparators C1 to C current control compensation circuits Gu'(s), Gv(s), Gw(s
), GT (9), adder/subtractor A, phase control circuits PH1 to PH , becomes the firing phase signal.

First, the load current supplied to the AC motor M. .

The control operation of IVt Iw will be explained.

The multiplier card ~ML3 is the peak value command of the load current.

Then, three-phase unit sine waves φυ, φV, and φυ are input.

When the output frequency of the cycloconverter CC is fo, the three-phase unit sine waves φU, φV, and φV are expressed as in the following equation. However, ω. =2πf0.

φυ=sin(ω.・t)...■
φヮ=sin(ω.・t −2π/3) ・・
・■φ1=sin (ω.・S+2π/3)
. . . ■Therefore, the output signals of the multipliers ML, ~ML, that is, the load current command values υ*, ν*, and knee are given as shown in the following equations.

Iu*=I, ・sin ((11°-t)
-(4) Iv*=1.・sin ((1).

・t −2π/3) −■Iw”=I,・5
in(c++.・t +27C/3) -(6) Comparators 01 to C1 calculate load current detected value υr IV+I
w and each of the above current command values IU*+ IV'+ I- are compared, and the deviation εU"IU*ILI+ εV=I
V” IVtεW ” 1w* − Current control compensation circuit Gu(s) IGv (S), Gv (
s).

The current control compensation circuit Gυ(S) for the U Japanese food load current compares and amplifies the deviation ευ (with a magnification of υ), and the adder/subtractor A
1 and A3.

Iu”) In the case of Iu, the deviation ευ becomes a positive value, increasing the input Vα of the one-phase control circuit PH1 and decreasing the input Vα of PH.Separately excited converters SS□ to SS3
The output voltages ■1 to V of the respective phase control circuits PR, to PH□ increase by phase control. 1 ~ V (proportional to the value of 13, so V increases and ■ 3 decreases. As a result, U Japanese food charge current = 11 ~ ■ increases, so that Iu'' = Iυky) controlled by.

■When the υ power is Iυ, the deviation εU becomes a negative value, increasing the output voltage v3 and decreasing . Therefore,
The current Iυ decreases and is again controlled to become a construction υHxυ tree.

If the command value engineering υ end is given as in equation (a), the U-phase current I
Following this, u is controlled sinusoidally.

The load currents IV+IW of the (2) phase and W phase are similarly controlled.

In addition, in steady state, three separately excited converters SS
The output voltages v1 to V of □ to SS are balanced and have the following relationship: ■□+V2+V3=O...■ Circulating current ■ flows in the triangular connection. will not be increased or decreased.

In this embodiment, the circulating current I1 of the cycloconverter CC
Instead of controlling one converter, three separately excited converters SS1 to SS
, the output current ■, the sum of the currents IT=11+I,
+ I, is controlled.

Next, the operation of the sum current control will be explained.

The sum current command value IT is given by proportionally amplifying the peak value command (2) of the load current. A proportional amplifier has
That's what it's for.

Engineering, wood = K・ Engineering,
... (c) Each converter SS, ~SS
1's output current, ~I3, is detected, their sum is taken, and the sum is input to the comparator C4. Comparator C4 outputs the sum current detection value I7
” Il + I2 + L and the sum current command value I7 quintillion are compared, and the deviation εT = IT*IT is input to the current control compensation circuit as GT(s).

The current control compensation circuit GT (!3) uses a comparison element or an integral element, but here, to simplify the explanation, a proportional element is used. Current control compensation circuit GT (S
) is input to the phase control circuit circle (, ~PH,) via adders A4 to A6. Therefore, PH0
The input signal Vα of ~PH, ~? 7o3 is expressed by the following equation. However, load current control compensation circuit Gu (
s), Gv(s), and Gy(s) are only comparison elements, and their magnification is assumed to be .

Z' C1x = K I-(ευ-εv)+KT reference
7... (9)? αz=KL(εso i 1
) +7・εT −(10)u a3= KL(
εV-εu)+KT'ET ・-(11) Note that 0
The first term on the right side of equation (11) is for controlling the load current. The second term on the right side relates to sum current control.

The sum current IT is controlled by the sum of output voltages v1 to v3 of the three separately excited converters SS1 to SS.

Taking the sum of equations (9) to (11), we get Vα, +yαz + '! ' a3 = 3 to 7・εT
...(12), three separately excited converters SS
The sum of the output voltages of 1 to SS, v = ■1 + v2 + v, is
It is proportional to the deviation E7.

If II wood > I wood, the deviation 6 wood will be a positive value.

Increase the sum voltage v d, circulating current. increase.

Therefore, the output currents □ to □3 of each converter also increase, resulting in an increase in the sum current II, which is controlled to become the IT valve IT'.

On the other hand, when IT45r is reached, the deviation εT becomes a negative value, reducing the sum current V and reducing the circulating current. decrease. Therefore, the sum current T is reduced, and the control is performed so that the sum current T is reduced and the current T is also controlled to become T bundle.

FIG. 3 shows an example of the current waveforms of each part of this embodiment, where υ* IVy IW is the three-phase load current +11'? I
2'TI3' is the output current of each converter that depends on the load current (the output current of each converter when the circulating current is zero), and IT' is the sum of the output currents (IT' = engineering □' + I2'+I3'), 1. Town sum current command value, ■. represents each waveform of the circulating current.

Circulating current■. When is set to zero, it is divided into three modes,
Waveforms can be analyzed.

In mode ■ (Iu≧O, Iw<O), L' = ■,
, I2'=-I, I,'=O.

In mode ■ (Iv≧O, Iu<O), ■, = Ot
I2'''Iv, Is'=-Iu.

In mode ■ (Iw≧O, IV<O), ■1'=-engine v.

L' = O# I3' = II.

As a result, the circulating current works. = 0, the sum of the output currents of the three separately excited converters SS ~ SS, IT' = I□' + I
2'+work,' has the same waveform in the above three modes.

That is, the maximum value J31. (I is the load current peak value),
Minimum value (J3/2) 1. bawl.

Here, the sum of the output currents of the three separately excited converters ss1 to ss is IT=E,+L+Ii, J3-I, and when the total output current is controlled, the circulating current is E. =-(J3 ・I, -I d')
...(13), and the waveform becomes as shown in the bottom row of FIG. That is, minimum value=0. Maximum value = (J'
J/6)r.

The reactive power QCC on the input side of the cycloconverter CC is
It is expressed as the following formula.

Qcc=Kg(I,・sin α1+I,・sin α,+
I,・sinα,)...(14) Here, KQ is a proportional constant, α, ~α3 is the firing phase angle of each separately excited converter SS~SS, and I~~ is each separately excited converter This is the output current of SS engineering to SS3.

The ignition phase angles α1 to α3 also change moment by moment and influence the reactive power on the input side, but the one that has the greatest influence is:

The current value is I~I□. In other words, the cycloconverter CC performs natural commutation using the power supply voltage, but in order to take the commutation margin angle, it is often controlled within the range of 30°≦α≦150''.Therefore, as sin α is 0
．． It varies in the range of 5 to 1. Moreover, α□ to α3 do not have the same value at the same time, and their influence on the input side reactive power is averaged. Therefore, equation (14) can be approximated as equation (15).

Qcc=@' (I, +I, +I,)
''' In (15), Q' is a proportional constant.If the circulating current is controlled to be constant as in the conventional control method, the sum current IT is IT=I +1.+1.=3. 1'+I2'÷
1.1 ...(16), and I-cho' = I,'
+I,' The variation in +I,' directly appears as a variation in the input side reactive power Qcc, increasing the low-order harmonics of the input current.

Therefore, according to the control method of this embodiment, the sum current command value T
Since * is given constant in proportion to the peak value command ■ of the load current, the sum current ■↑ is also controlled to be constant accordingly. Therefore, fluctuations in the reactive current Qcc on the input side are eliminated, and low-order harmonic components of the input current can be removed.

Also, circulating current work for cycloconverter CC. varies as shown in FIG. 3, and its average value is roughly proportional to the peak value of the load current. Therefore, circulating current work during light loads. becomes smaller, and almost no loss occurs.

When the load becomes heavy, circulating electric current works. The average value of is increasing and the loss is also increasing, but since the operation is performed where the output of the cycloconverter CC is large, the increase in loss can be ignored. Rather, when the load becomes heavy, suppressing reactive power fluctuations on the input side and removing low-order harmonic components of the input current has a great effect in eliminating negative effects on the power supply system.

〔Effect of the invention〕

As described above, according to the present invention, the operating efficiency at light loads can be improved without impairing the features of the triangular connected linear circulating current type cycloconverter, and the input current that depends on the output frequency can be improved. It becomes possible to remove low-order harmonic components, and various adverse effects on the power supply system can be removed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the main circuit of one embodiment of the present invention;
FIG. 3 is a control block diagram showing a control circuit according to an embodiment of the present invention, and FIG. 3 is a time chart showing the operation of the embodiment of the present invention. BUS...Electric line Tr of three-phase AC power supply...Transformer CC...Cycloconverter SS□~SS3...Separately excited converter (AC/DC power converter) L1~L3...DC reactor M...・AC motor ML1 to ML,... Multiplier K... Proportional amplifier 01 to C2... Comparator Gu(s), Gv(s), Gw(s), GT(s
l...Current control compensation circuit A□~A6...Adder/subtractor PH1~PH,...Phase control circuit agent Patent attorney Noriyuki Chika Yudo Ken Daikomaru

Claims (1)

[Claims] In a circulating current type cycloconverter configured by triangularly connecting multiple AC-DC power converters, the sum of the output currents of each AC-DC power converter is a value corresponding to the peak value of the current supplied to the load. A method for controlling a cycloconverter, characterized by controlling the cycloconverter so that