JPS6039369A - Load current controlling method of delta-connection cycloconverter - Google Patents

Abstract

PURPOSE:To enable to accurately control a current by directly controlling a load current of a delta-connection cycloconverter. CONSTITUTION:The detected values of load currents IU, IV, IW are compared with the command values IU*, IV*, IW* to obtain deviations epsilonU=IU*-IU, epsilonV=IV* -IV, epsilonW=IW*-IW, the output of the first converter SS1 for forming a cycloconverter is controlled in response to the value of (epsilonU-epsilonV), the output voltage of the second converter SS2 is controlled in response to the value of (epsilonV-epsilonW), and the output voltage of the third converter SS3 is controlled in response to the value of (epsilonW-epsilonU). Thus, the load currents IU, IV, IW can be directly controlled, thereby performing an accurate current control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a load current control method for a triangularly connected cycloconverter.

[Technical background of the invention]

A cycloconverter is a frequency conversion device that directly converts AC power at one frequency into AC power at another frequency, and has recently been widely used as a drive power source for induction motors and synchronous motors.

The triangular connection cycloconverter has three AC/DC power converters (
A cycloconverter (a cycloconverter in which a positive group and a negative group converter are paired to form one phase of output) is commonly used in a device that supplies variable voltage, variable frequency AC power to a three-phase load by connecting converters). It has the advantage of requiring only half the number of converters, and has recently been attracting attention (Japanese Patent Application No. 56-158692).
).

Fig. 1 shows a configuration diagram of a conventional triangular connection cycloconverter device.
It is described in 2.

In the figure, BUS is a three-phase AC power line, C 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. The cycloconverter body CC has three AC/DC power converters (converters) ss, , ss2. It consists of ss3 and a DC reactor L1 + "21 La with an intermediate tap.The AC input side of the power converter ssl, ss2.ss3 is insulated by a power transformer T, and the DC side is unidirectional. They are Δ-connected via DC reactor L1 + "2 + L3 so that a circulating current flows. It constitutes a so-called triangular circulating current type cycloconverter.

DC reactor LL, L2. The center tap of L3 is connected to the three-phase winding of a three-phase AC motor M.

On the other hand, the control circuits include current transformers CTs that detect the three-phase AC current at the receiving end, and transformers PTs that detect the three-phase AC voltage.
, reactive power calculator VA)l, control compensation circuit H(SJ,
Reactive power setting device Va, comparator CQ + COrCl, C
2, C3, adder A, , A2. A3, operational amplifier KO
, to, , to 2. 3. Phase control circuits PH, PH2°PH3 and load current detectors CTU, CT■, CTw are used.

This cycloconverter uses a circuit that controls the current generators U, ■■, and Iw that are supplied to the three-phase AC electric TF4M, and the circulating current ■o of the triangularly connected cycloconverter in order to adjust the reactive power at the receiving end of the cycloconverter. Although a control circuit is included, the latter IIJ control operation will be omitted in order to clarify the purpose of the present invention.

The latter control operation is described in detail in Japanese Patent Application No. 56-158692, so please refer to that document.

The load current control operation of the conventional device will be explained below.

FIG. 2 shows an equivalent circuit of the cycloconverter CC and the electric motor M shown in FIG. 1, and it is assumed that the electric motor M is Δ-connected. V,,V,.

V3ij: I7/<-taSSt, SS2 and SS3 (D output 'fjl pressure can take positive and negative values. However, the output currents Il, I2 and I3 of each converter only flow in a fixed direction. .The electric motor M is connected in △, and its respective windings are Ma, Mb, and Mc.The currents flowing through each winding are Ia, Ib, and I.
Take c in the direction shown and gauze work U + work VI I
The relational expression with w becomes as follows.

Ia=(IU-Iv)/a-・(1)Ib=(
Iv - Iw )/'3...(2)ic -(
IW IU ) / 3 ・・・・・・(3) Furthermore, IU
, I'V, IW and Ia, Ib,
I c is handled as a balanced three-phase sinusoidal current.

FIG. 3 shows waveform diagrams of various parts of FIG. 2.

The line currents Itr, Iv, Iw (2) and the phase currents 1a, Ib, Ic are the above (1), (2),
Equation (3) is satisfied. Converter SS1. Since the output currents It, I2, and I3 ij of SS2 and ss3 cannot flow in the negative direction, they change as shown in the figure depending on the values of the line currents U, I, and W. This can be divided into the following three modes.

Mode I: Iv<O, Itv>.

At this time, the output current 2 of SS2 becomes zero. Therefore L
= Iy, I3 ==work w flows.

Mode II: <o+ ■u > 0 At this time, the output current ■3 of SS3 becomes zero. Therefore L = ■U
+ Engineering 2-IW flows.

Mode In: IU<Or'v>0 At this time, the output current ■l of SSl becomes zero. Therefore I2 = Iv
, I4-IU flows.

As can be seen from the equivalent circuit of FIG. 2, when the output voltages of each converter are in a three-phase balanced state, the following voltage equation holds true. However, the windings Ma, Mb of the electric motor M
, 'Me resistance is FLa, R+b, Rc intitalance is La, Lb, Lc, and back electromotive force is Ea, E.
b, Ec. Also, p=d/dt (d differential operator).

Vl=(R+a+La fist p)sIa+Ea...-(4
)V2=(R,b+Lb-p)-Ib+Eb=-(5
)V3 = (Rc+Lc @p) *Ic+Ec
(6) Therefore, the current Ia can be controlled by changing V8, and the currents Ib and Ic can be controlled by changing V2 and v3. .

Returning to the apparatus shown in FIG. 1, the control operation of the phase currents Ia, Ib, and Ic will be explained.

Line current IU is detected by current detectors CTU, CTV, CTw.
Detect +■■, ■w, (1), (2), +
3) Phase current detection values Ia, I
b. Add Ic. These are input to comparators C1, C2, and C3 and compared with phase current command values I''a, I*b, and Pc.Each deviation *ε, = Ia - Ia * ε2 = Ib - Ib * ε3 = Ic -Ic into an amplifier!, 2. and 3, and phase control circuit PH
8, PH, and PH3 respectively.

*For example, Ia (in the case of Ia, ε, ·K1 increases, increasing the output voltage V1 of the converter SSI, increasing the phase current Ia shown by equation (4).Finally, Ia - * *Ia Conversely, in the case of Ia) Ia, ε1aK1 decreases, vl decreases, Ia decreases, and it is controlled so that pIa=I''a.

Similarly, Ib=? b.I. -Engineer *. It is controlled like this.

If Ia, Ib, and Ic are controlled as three-phase balanced sinusoidal currents as shown in FIG. As shown in the waveform, it becomes a three-phase balanced pressure sinusoidal current.

[Problems with background technology]

The conventional load current control method of the triangular connection cycloconverter has the following problems.

(a) First, in the conventional control method, the line current IU + ”
(1) ~ between Vr and phase currents Ia, Ib, and Ic
It is a prerequisite that the relationship shown in equation (3) holds; however, the windings Ma, M' of the electric motor M serving as the load
b, If a circulating current flows through Me, the above (1) to (
3) The relationship between the equations breaks down. Therefore, there is a possibility that the load flow force U + force V + IW to be actually supplied may not be accurately controlled.

(b) Load current to be actually supplied 'U + engineering V +
'W is not directly controlled, so it is unclear whether it is really accurately controlled. Therefore, torque control and speed control of the electric motor M tend to be unreliable.

In particular, when applying this cycloconverter to the vector control button of induction motors that have recently become popular, the load current I
Since it is necessary to accurately control the amplitude and phase of UIIV and IW, it is a fatal drawback that the value of the load current is unknown.

[Purpose of the invention]

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for directly controlling the load current of a triangularly connected cycloconverter.

[Summary of the invention]

The present invention relates to a triangular connection cycloconverter that supplies alternating current power to a three-phase load, in which the load current ■U + engineering v, Iw
The detected value is compared with its command value t, currency, IJ, and each deviation εU=IKi-■U +εV-Iv and *εw=:[w The output 4 voltage of converter SS1 of 1 is (εU-ε
V), and the second converter S82
The output voltage of the third converter SS3 is controlled according to the value of (ε■ - εW), and the output voltage of the third converter SS3 is controlled according to the value of (εW - εU).
By controlling according to the value of the load current IU,
This is a load current control method for a triangular-connected cycloconverter that directly controls ■v and ■w.

[Embodiments of the invention]

FIG. 4 is a configuration diagram showing an embodiment of the triangularly connected zychroconverter device of the present invention.

In the figure, BUS is a three-phase AC power supply line, CAP is a phase advancing capacitor, TR is a power transformer, CC is a three-phase output cycloconverter body, and M is a three-phase AC 'B motor. Three AC/DC power converters (converters) SS, which constitute the cycloconverter body CC.

ss2. The AC input side of ss3 is insulated by a power transformer Tll, and the DC side is connected to a DC reactor: r'l + I'2, L so that a unidirectional circulating current flows.
Δ-connected via 3. It constitutes a so-called triangular circulating current type cycloconverter. DC reactors L, , L2. The middle tap of L3 is a 3-phase AC motor M
is connected to the three-phase winding of

In addition, as a control circuit, a current transformer c'rs1 that detects the three-phase alternating current at the power receiving end, and a transformer PT that detects the three-phase alternating current voltage.
s, reactive power calculator VAJ control compensation circuit H(S), reactive power setting device Va, comparators cQ, co.

cU, Cv, CW, adder Al, A2. A3. A
4. A5゜A6, Mm control compensation circuit G□, GU,
Gy, Gw, phase control circuits PH1, PH2, P
H3 and output current detectors CT, , CT, , CT3 are prepared.

The device of this embodiment includes a circuit that controls currents IU, IV, and IW supplied to a three-phase AC motor M, and a circuit that controls a circulating current IO of the cycloconverter CC to adjust the reactive power at the receiving end of the cycloconverter CC. Although it includes a control circuit, since the main purpose of the present invention is the former, it will be explained in detail.

First, the reactive power control operation at the power receiving end of the cycloconverter CC will be briefly described.

Power converters (converters) ssl, , ss, , ss3 constituting the cycloconverter CC perform commutation of each element (thyristor) using a power supply voltage.

This is the so-called natural commutation. For this reason, it is well known that the AC input current of the converter always has a delayed phase with respect to the power supply voltage, and that delayed reactive power is consumed when viewed from the power supply. The delayed reactive power is the current 'U supplied to the load.
It depends on the magnitude of the power supply voltage V r 'W and the value of the firing phase angle of each of the converters, and the reactive power fluctuations cause fluctuations in the power supply voltage, which has the disadvantage of having various adverse effects on the power supply system.

Therefore, a phase advancing capacitor CAP that consumes a certain amount of leading reactive power is installed at the power receiving end, and the cycloconverter CC is circulated so that the lagging reactive power of the cycloconverter CC is always equal to the leading reactive power of the phase advancing capacitor CAP. The current Io is controlled.

The circulating current o of the cycloconverter CC appears as delayed reactive power when viewed from the power supply side, but is not related to active power. On the other hand, the load current IU.

TV + "TV, when viewed from the power supply side, includes an active force component and a delayed reactive power component.

In other words, the value of the circulating current ■o is controlled so that the sum of the delayed reactive power due to the load current IU + TV + IW and the delayed reactive power due to the circulating current generator 0 is exactly equal to the value of the advanced reactive power of the phase advance capacitor CAP. Then, the reactive power component seen from the power supply becomes zero, and only the effective ridge component depends on the load current.

Specifically, in the device shown in Fig. 4, first, the voltage and current at the receiving end are detected by PTs and CTs, and the values are used to calculate the reactive power Q at the receiving end using the reactive power calculator VA. To detect. In addition, a reactive power setting device VR outputs a reactive power command value Q, and a comparator cQ calculates the deviation εQ=Q-Q. The deviation εQ becomes the circulating current command value IO via the control compensation circuit H(s).

Next, the comparator Co increases the phase control circuit circulating current command value expression of each converter through the compensation circuit of the cycloconverter CC. Therefore, it becomes IO, and the deviation εo
＞Depending on the value of O, the output voltage of the valley converter V+, Vz,
Vst” in the direction of the arrow.

Therefore, the sum V, +V2+V3)o of the output voltages is applied to the DC reactors L1 +L, +L3, increasing the circulating current Io of the cycloconverter CC, and settling as l0=to. Therefore, the delayed reactive power Q at the receiving end is controlled to be equal to the command value ζ of the increased cal.

Conversely, when η becomes Q less, the control is performed in the same way, and finally Q=Q and settles down.

Normally, the reactive power command value J is set to zero, and Q=Q=
o, so that the basic diagonal ratio at the power receiving end is always controlled to be 1.

For a more detailed explanation of the above reactive power control, please refer to Japanese Patent Application No. 56-158692.

Next, the operation of load current control, which is the object of the present invention, will be explained.

First, the current detector cT! , cT2 and CT3 converter ss1. ss2. Detect output current 11 + work 2 and ■3 of ss. The output current I of this converter,
, I, , I3 and the load currents IU, IV, and IW have the following relationships.

IU = I, -I3 ... (force IV = I2-
11... (8) Iw=I3-I2...
・ (9) This relationship holds true whether or not the circulating current Io flows in the cycloconverter CC, and the above (
Using equations 7) to (9), calculate the output current of the converter 1゜I
,, I3 to load electric construction U + construction V 11. "W can be measured. Of course, the load currents (U), (V), and (W) may be directly detected.

The comparator CU r CV r "W is the load current detection value U, U, ■, W and its command value IW + f + I
By comparing W, the deviations εU, εV, and εW are determined.

εg=Ikichi-IU...αQ εV=Iji-Iv...-u's εw=Kokichi-Iw...@The above deviations εU, εV and εW are determined by each current control compensation circuit Via GU, Gv and Gw, adder A1. A3゜A5
The control signals eαl, eail and e expressed by the following equations are
(Converted to 13.

eal=GUaε, -Gv@εv...Q3ea
z ==Qv11 εy−GWa gy −・−(14
) e (13=GW ' e W Gl, U * i
ty, 4% where each current control compensation circuit GU, GV, G
By matching the control constants of w, it can be replaced with GIJ = Gv = Gw = G(s) m++ m, and equations (c) to (c) become as follows.

eat = (iu −g v) −(3(S) ・・−
・αηeα2−(eV−εW)・G(s) ・・・・
・・Scream eα3−(εW −εU) Fist G(s) ・・・・
... q9 These control signals...,..., 2 and...
Next loan adder A2. A4. A6 adds the signal eaQ=εo#Go from the circulating current control circuit described above and inputs the signal to the phase control circuits PH1, PH2, and PH3.

To simplify the explanation here, the reactive power Q at the power receiving end matches its command value q, and the circulating current IO is in a steady state (
Io −Io ), the deviation εo=i Io
is explained as zero or extremely small. Therefore,
Consider the above signal eα0ki0.

For 3-phase 3-wire loads, IU +IV +IW =
0 is satisfied. Therefore, the command value of the load current is also given so as to satisfy the following equation. As a result, the sum of the current deviations ευ, εV, and εW for each phase is εσ+εV+εW=
It becomes O.

If we look at it as a specific value, for example, εU=2゜gv
=t, εw=-3. Therefore Konkunuta SSl
The output voltage vl of SS increases by an amount proportional to (εU-εv)-1, and the output voltage V2 of SS2 increases as (ε■-εw)=4
However, the output voltage V3 of SS3 decreases in proportion to the value of (εW-εo)−5.

The equivalent circuit of the main circuit of the device in FIG. 4 can be expressed in the same way as in FIG.

Therefore, the current Ia increases in proportion to the increase in vl (11m), the current Ib also increases in proportion to the increase in v2 (m4w), and the current I decreases in proportion to the decrease in V. -5. do. Here, the following relational expression holds between the load currents (line currents) IU, IV, and IW and the phase currents Ia, Ib, and Ic.

Work υ = Ia - Ic ... (a) Iv = I b - I a - H Iy = I c - I b ” ... (a) This relational expression circulates to the load connected by △ This holds true regardless of whether current is flowing. Therefore, IU increases by w6m, and I
v increases by w31 and 1w decreases by 1-91. These increases and decreases △■U.

△Iv, 61w are each △IU==”5'ocευ=-so△Iy=”3″oc tv=-”l ”△■w
= l 9 # cl:'vr' l 31, and it can be seen that it is proportional to each deviation.

The load current control method of the present invention is largely different from conventional load current control methods in that it is a control method using equations (e) to (a). In other words, equations (1) to (3) do not hold if a circulating current flows through the △ wired load represented by the equivalent circuit, whereas the relationship between equations (a) to (a) depends on the presence or absence of the circulating current. This holds true regardless of the current, so it is possible to always accurately control the load current.

In the above embodiments of the present invention, a circulating current type cycloconverter has been described, but it goes without saying that a non-circulating current type cycloconverter can be similarly applied.

In addition, the power converter (converter) is 3 pulse, 6 pulse,
Needless to say, this method can be applied regardless of the number of control pulses, such as 12 pulses, etc.

FIG. 5 is a control circuit configuration diagram showing another embodiment of the device of the present invention.

A back electromotive force is generated in the motor load as the motor rotates, and acts as a disturbance on the load current control system. Therefore, for the current command value Iff, the actual current value 1g,
There was a problem that Ly and Iw did not track well and the expected characteristics could not be obtained.

The control circuit shown in FIG. 5 compensates for the disturbance caused by the counter electromotive force.

In the figure, PS is the rotor position detector of the motor (considering the case of a synchronous motor), PTG is the three-phase unit sine wave generator, and ML
U, MLy, MLW, MLN are multiplication circuits G
N is a speed control compensation circuit, CN is a comparator, A, .A8.A is an adder, and the other symbols are the same as those for the circuit in FIG.

The speed command value ♂ and the actual speed are compared by the comparator CN, and the deviation εN=N*-N is calculated. The deviation ε provides a peak value Im of the armature current (load current) of the motor via the speed control compensation circuit GN.

On the other hand, the motor rotor position detector PS outputs three rectangular wave signals synchronized with the back electromotive force of the motor.
3-phase unit sine wave s via 3-phase unit sine wave generator PTG
It is converted into jnθU, Stnθy, and SjnθW.

The following calculation is performed by the multipliers ML, MLv, MLw, and the command value of the load current, 1↓, is rounded.

a=Im fist sinθU...Kan n=Im*sinθv −・e241 1jH=Im@sinθw −・・@ Control of the load current is as described above.

In addition, the multiplier M[JN represents three parts together, and the rotational speed N of the electric motor and the unit sine wave sinθυ
, sinθy, and sinθW to obtain the following value.

However, k is a proportionality constant.

eNU: k N 'S jnou song °eAeNy
= k N e s jnou ... 翰e kN
*sin θw−1°+2 @W− The above value eNU+eNV 1 eNW is the amount of compensation added to cancel the disturbance caused by the back electromotive force of the electric motor.

That is, the current control deviations εU, ε of the U, V, and W phases
After passing V and IIW through the control compensation circuit GU + ov and GW, the adder A7. A8. The above compensation amount is added to A9. After that, the phase control circuit P of each converter
Input signals H1, PH2, and PH3 are provided as explained in FIG.

In this way, even when there is a disturbance such as a back electromotive force of the motor, load current control compensation can be performed for each phase, and a control circuit that is extremely easy to understand when designing a control system can be provided.

〔Effect of the invention〕

As described above, according to the load current control method for a cycloconverter of the present invention, the load current can be directly controlled and accurate current control can be performed. Furthermore, various types of compensation for the current control system can be performed for each phase, thereby providing a system that is easy to design.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional triangular-connected cycloconverter device, Figure 2 is an equivalent circuit diagram of the main circuit of the device in Figure 1, Figure 3 is a waveform diagram of each part of Figure 2, and Figure 4 is the main circuit diagram of the main circuit of the device in Figure 1. FIG. 5 is a block diagram showing an embodiment of the triangularly connected cycloconverter device of the invention, and FIG. 5 is a control circuit diagram showing another embodiment of the device of the present invention. BUS... 3-phase AC power supply line CAP... Phase advancing capacitor TR... Power transformer CC... 3-phase output cycloconverter body M...
... 3-phase AC motor (load) S Sl, 882
, S S3... AC/DC power converter L1 r "2
r”3...DC reactor CTs, CT1
, CT2, CT3---・Current transformer PTs...
...Transformer VAR...Reactive power calculator H(S) r GOr GU + GV + "W +
GN ""' Control compensation circuit CQ + CO+ CU
r CV ) CW l “N”・Comparator Al, A2
, A3 , A4 , A5 , A, , A, , A8 , A
9... Adders PH1, PH2, PH3... Phase control circuit MLU,
MLy, MLw, MLN-= Multiplier 1) S.
...Rotor position detector PTG...Unit sine wave generator (7317) Agent Patent attorney Noriyuki Chika (and one other person) Fig. 2 V Fig. 3

Claims (1)

[Scope of Claims] The first . In the cycloconverter which is triangularly connected by the second and third AC/DC power converters (converters), the first. For the output currents Ir, Iz and I3 of the second and third converters, the three-phase load current U y "V +1w is I, = I, , -I3 Iv = I2-I. IW = 43-I. Connect the load so that it has a relationship, and the load current
Compare the detected values of , Iw, and Iw with their command values, and calculate each deviation ευ==I'IU*ε■=WorkV−■v*εweIw IW. The output voltage of the converter is (εU−εV
), the output voltage of the second converter is controlled according to the value of (εV-εW), and the output voltage of the third converter is controlled according to the value of (εv-6U). A load current control method for a triangular-connected cycloconverter, characterized in that the load current is controlled.