JP3083214B2 - Transformer excitation current detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exciting current detecting device for a transformer connected to an AC terminal of a power converter such as an inverter.

[0002]

2. Description of the Related Art In recent years, large-capacity self-extinguishing devices (for example, gate turn-off thyristors, etc.) have been actively developed, and have been used in power converters such as inverters. . Transformers are connected to the AC side terminals of power converters such as inverters for the purpose of insulation or for boosting or stepping down the AC voltage, and for the purpose of multiplexing multiple inverters. Will be installed.

In this transformer, a DC bias voltage is applied due to a variation in switching characteristics of elements constituting the power converter or an external factor, so that an exciting current increases, and eventually magnetic saturation (bias) occurs in one direction. (Magnetism). Such DC biasing of the transformer increases the element current of the power converter, and may destroy the element due to overcurrent. In addition, if the transformer is demagnetized, the required output voltage will not be output, and the function of the entire device will not be able to be exhibited. Therefore, the exciting current of the transformer is detected, and the AC side output voltage of the power converter is adjusted so that the exciting current does not become excessive. FIG. 9 is a configuration diagram showing a conventional exciting current detecting device for a transformer. In the figure, TR is a transformer, W1, W2
Is a primary and secondary winding of the transformer TR, CT1 and CT2 are current detectors, K is a proportional circuit, and A is an adder / subtractor. Transformer T
When the primary / secondary winding ratio of R is a1 to a2, an amplifier which is multiplied by (a2 / a1) by a proportional circuit K is prepared.

Each of the current detectors CT1 and CT2 causes one
The secondary current I1 and the secondary current I2 are detected. The secondary current detection value I2 is multiplied by (a2 / a1) by the proportional circuit K, and the difference I0 from the primary current detection value I1 is calculated by the adder / subtractor A.
1− (a2 / a1) · I2 is calculated. This calculated value I0 is the detected value of the exciting current of the transformer.

[0005]

However, such a conventional exciting current detecting device for a transformer has the following problems.

That is, the value of the exciting current I0 of the transformer is extremely small compared to the primary current I1 and the secondary current (primary conversion value) I2 ', and if the accuracy of the current detector is poor, However, the exciting current detected as described above has an unreliable value.

For example, in a large-capacity transformer, the exciting current I
0 is 2 to 3% of the primary current. Therefore, if the rating of the primary current I1 is 1,000 A, the rating of the exciting current I0 is 3%.
It is about 0A. Here, if the accuracy error of the current detectors CT1 and CT2 is 1%, a detection error of 10A appears,
If the excitation current I0 of the transformer is obtained by the conventional method, an error of about 30% is included even if it is simply considered. Actually, since the calculation of the exciting current I0 is the difference between the vectors of the primary current I1 and the secondary current I2 ', the detection error of the exciting current I0 is further increased.

[0008] The detection error of the exciting current causes a difference between the command value and the actual current when the exciting current is controlled, and it means that a necessary voltage cannot be obtained from the transformer. In addition, even when countermeasures against DC bias of the transformer are performed, accurate excitation current cannot be detected, so that there is a disadvantage that an appropriate compensation voltage cannot be generated from the power converter side.
The present invention has been made in view of the above problems,
An object of the present invention is to provide a transformer exciting current detection device capable of accurately detecting an exciting current of a transformer.

[0009]

In order to achieve the above object, an exciting current detecting device for a transformer according to the present invention comprises: a transformer;
A current detector for detecting primary and secondary currents of the transformer, a means for calculating an exciting current of the transformer from the primary current detection value and the secondary current detection value, and an excitation for the magnetic flux of the transformer Means for determining the phase angle of the current; and the one used for the exciting current calculating means so that the phase angle becomes zero.
Means for correcting one or both of the secondary current detection value and the secondary current detection value.

[0010]

When the primary / secondary turns ratio of the transformer is a1 to a2, the exciting current I0 of the transformer is obtained from the primary current detection value I1 and the secondary current detection value I2 as follows: I0 = I1- (a2 / A1) · I2. On the other hand, the voltage V applied to the transformer
1 (fundamental wave of AC voltage) and the mutual inductance M of the transformer, the exciting current I0 ^*
Can be approximated by the following equation. I0 ^* = V1 / (jω · M) where ω is the angular frequency of the AC voltage V1. That is, the exciting current I0 ^* Has the same phase as the magnetic flux .PHI.0 of the transformer, and the phase is delayed by 90.degree. With respect to the applied voltage V1.

According to the present invention, the phase angle の of the exciting current detection value I0 with respect to the magnetic flux Φ0 is determined, and one of the primary current detection value I1 and the secondary current detection value I2 is determined so that the phase angle に な る becomes zero. Or correct both.

It is assumed that a1 = a2. 1
It is assumed that the secondary current I1 is detected to be 1% larger and the secondary current I2 is detected to be 1% smaller. Since the exciting current I0 is the vector difference between the primary current I1 and the secondary current I2, the phase angle に 対 す る with respect to the magnetic flux Φ0 (perpendicular to the applied voltage V1) is advanced, not to mention its magnitude. When the magnitude of the secondary current detection value I2 is corrected so that the phase angle に な る becomes zero, the result is 2
The secondary current I2 is also detected by 1% larger. When the primary and secondary currents both increase by 1%, the excitation current I0 is also detected by 1% from the similarity of the triangle.

When the magnitude of the primary current detection value I1 is corrected so that the phase angle に な る becomes zero, the primary current I1 is detected by 1% smaller as a result. Primary and 2
When the secondary currents are both reduced by 1%, the excitation current I0 is also detected to be smaller by 1% from the similarity of the triangle.
That is, the detection error of the exciting current is 1%, and a great improvement in accuracy can be achieved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a transformer exciting current detecting apparatus according to an embodiment of the present invention. In the figure, SUP is an AC voltage source, TR is a transformer, LOAD is an AC load, CT1,
CT2 is a current detector, K is a proportional circuit, H is a coefficient corrector,
A is an adder / subtractor and a CAL phase angle calculator.

The primary / secondary turns ratio of the transformer TR is a1 to a
2, an AC voltage source SUP is connected to the primary winding. When voltage V1 is applied to primary winding W1 of transformer TR, voltage V2 = (a2 / a1) .V is applied to secondary winding W2.
1 occurs, and the current I2 flows through the load LOAD. At this time, the angular frequency of the primary voltage V1 is ω = 2πf, and the transformer TR
Is M, the exciting current I0 of the transformer TR can be approximated as I0 = V1 / (j.omega.M). The primary current I1 of the transformer TR is equal to the secondary current I2.
And the vector sum of the excitation current I0 and I1 = (a2 / a1) .I2 + I0.

That is, if the primary and secondary currents of the transformer TR can be accurately detected, the exciting current I0 can be accurately detected. However, there is a detection error in the current detectors CT1 and CT2, and the problems as described in the conventional apparatus appear.

In the apparatus shown in FIG. 1, first, a current detector C
The primary current I1 and the secondary current I2 are detected by T1 and CT2. The secondary current detection value I2 is calculated by the proportional circuit K as (a
It is multiplied by 2 / a1 and converted to the primary amount. That is, the primary-side converted value I2 'of the secondary current I2 is I2' = (a2 / a1).
I2. The primary-side converted value I2 'of the secondary current I2 is corrected via a coefficient corrector H to I2 "= K.I2',
It is input to the adder / subtractor A. Further, the primary current detection value I1 is directly input to the adder / subtractor A, and the exciting current I0 becomes I0 =
It is output as I1 -I2 ''. Phase angle calculator CAL
Calculates the phase shift の of the excitation current detection value I0 with respect to the magnetic flux Φ0 of the transformer TR. The unit sine wave sinωt synchronized with the voltage V1 applied to the primary side of the transformer TR and the excitation current detection value I0 Is used to calculate the phase shift ψ.
The operation will be described later. The coefficient corrector H adjusts the correction coefficient K according to the phase angle ψ. If ψ is positive, K is increased, and if ψ is negative, K is decreased.

FIG. 2 shows voltage and current waveforms of the apparatus of FIG. V1 is the primary voltage of the transformer TR, I0 ^* Represents an exciting current reference value, and I0 represents an exciting current detection value. Here, assuming that the primary voltage V1 is V1 = Vm · sin (ωt), the excitation current reference value I0 ^* Is I0 ^* = −Im ^* ・ Cos (ω
t). In addition, Im ^* = Vm / (ωM). That is, the excitation current reference value I0 ^* Is in phase with the magnetic flux .PHI.0 of the transformer TR and is delayed from the primary voltage V1 by a phase angle of .pi. / 2 radians. On the other hand, the exciting current detection value I0
Is the excitation current reference value I0 ^* (Magnetic flux Φ0) phase angle ψ
Only shows the case where it is advanced. That is, the exciting current detection value I0 is given by I0 = Im.cos (.omega.t + .SIGMA.) =-Im (cos.omega.t
· Cosψ-sinωt · sinψ). FIG. 3 shows a phase angle calculator C of the apparatus of FIG.
FIG. 9 is an operation block diagram illustrating a specific example of the AL.

In the figure, UN1 and UN2 are normalizing circuits for obtaining a unit sine wave, AD is an adder, ML is a multiplier, D is
V indicates a divider, ROM1 and ROM2 indicate table memory circuits, and SH indicates a sample hold circuit.

First, the primary voltage detection value V1 is input to the normalizing circuit UN1 and divided by the peak value Vm to obtain a unit sine wave sinωt synchronized with the voltage. By differentiating this, a unit cosine wave cosωt is obtained. Also, the excitation current detection value I0 is input to the normalization circuit UN2, and the peak value I
m divided by the unit sine wave synchronized with the current-cos
(Ωt + ψ) is obtained. The multiplier ML includes a normalization circuit UN1
And the output c of the sample hold circuit SH
osψ is multiplied to obtain cosωt · cosψ.
The adder AD outputs the output -cos (ωt +
ψ) and the output cos ωt · cosψ of the multiplier ML are added, and sinωt · sinψ = cosωt · cosψ−cos
(Ωt + ψ) is output. Further, the output sinωt · sinψ of the adder AD is output to the output si of the normalization circuit UN1 by the divider DV.
Divide by nωt to find sinψ.

The table memory ROM1 has an inverse sine function si.
The table stores n ⁻¹ x, and when x = sinψ is input to the address of the memory, the phase angle ψ can be obtained.
The table memory ROM 2 stores the cosine function cosx as a table. When x = ψ is input to a memory address, cosｃｏ is output. The siple hold circuit SH holds the output cos # of the table memory ROM 2 at every operation cycle and inputs it to the multiplier ML. That is, the multiplier ML multiplies using the operation value before the phase angle output ψ.

Thus, the phase angle calculator CAL is:
The primary voltage V1 of the transformer TR and the exciting current detection value I0 are input, and the exciting current reference value I0 ^* The phase angle の of the exciting current detection value I0 with respect to (magnetic flux Φ0) can be calculated.
The above calculation can be realized by a calculation program using a microcomputer. Excitation current detection value I
The phase angle 0 of 0 can be obtained by another method.

For example, with reference to the zero-cross point of the primary voltage V1, the time difference from the zero-cross point of the excitation current detection value I0 is obtained, converted to the phase angle θ, and calculated as ψ = (π / 2) −θ. be able to. FIG. 4 is a voltage and current vector diagram for explaining the operation of the apparatus of FIG. (A) is a vector diagram when there is no error in the primary and secondary current detectors, and (b) is a vector diagram when there is a detection error. First, a vector diagram when there is no detection error will be described.

In FIG. 4A, when the primary voltage V1 is applied to the transformer TR, the exciting current I0 = V1 / (jω.
M) flows, and a magnetic flux Φ0 is generated. As a result, a secondary voltage V2 = (a2 / a1) .V1 is generated, and the current I2
Flow. The primary current I1 of the transformer TR is one of the secondary current I2.
The vector sum of the secondary conversion value I2 '= (a2 / a1) .I2 and the exciting warm current I0 is obtained. That is, if the primary current I1 and the secondary current I2 can be accurately detected, the exciting current I0 = I
1-I2 'can be accurately detected. At this time, the exciting current I0 has the same phase as the magnetic flux Φ0 and is delayed by 90 ° with respect to the primary voltage V1.

Next, a vector diagram in the case where there is an error in the primary current and the secondary current detector will be described. In FIG. 4B, i1 is a primary current detection value and is detected to be larger than I1 by .DELTA.I1. I2 'is a value obtained by converting the secondary current detection value to the primary side, and is detected to be smaller than I2' by .DELTA.I2.

From this detection value, the excitation current detection value i0 = i1
When -i2 'is obtained, the current vector shown is obtained. The exciting current i0 is a vector whose phase is advanced by ψ with respect to the magnetic flux Φ0. 1, the phase angle ψ is obtained by the phase angle calculator CAL, and the coefficient k of the coefficient corrector H is increased or decreased according to the phase angle ψ. That is, the phase angle 正 is positive (advance)
, The coefficient k is increased, and when the phase angle k is negative (lag), the coefficient k is decreased. In the case of FIG. 4B, since the phase angle 正 is positive (advanced), the coefficient k is increased and the secondary current detection value I2 ″ = k · i2 ′ is increased. Eventually, the coefficient k increases to the point where ψ = 0, and I 2 ″ in the figure
Calm down. At this time, the primary current detection value i1 is not corrected. As a result, the exciting current detection value I0 ″ becomes I0 ″.
″ = I1−I2 ″. From the similarity of triangles,
With respect to the true value I0, the error of the exciting current detection value I0 '' becomes equal to the detection error of the primary current. That is, the primary current I1
Is 1%, the detection error of the excitation current by the apparatus of FIG. 1 is 1%, and the detection accuracy can be greatly improved.

FIG. 5 is a block diagram showing another embodiment of the exciting current detecting device for a transformer according to the present invention. In the figure, SUP is an AC voltage source, TR is a transformer, LOAD is an AC load, CT
1 and CT2 are current detectors, k is a proportional circuit, H is a coefficient corrector, A is an adder / subtractor, and CAL is a phase angle calculator.

The primary / secondary turns ratio of the transformer TR is a1 to a
2, an AC voltage source SUP is connected to the primary winding. When voltage V1 is applied to primary winding W1 of transformer TR, voltage V2 = (a2 / a1) .V is applied to secondary winding W2.
1 occurs, and the current I2 flows through the load LOAD.

In the apparatus shown in FIG. 5, first, the current detector C
The primary current I1 and the secondary current I2 are detected by T1 and CT2. The secondary current detection value I2 is calculated by the proportional circuit K as (a
2 / a1) and converted to the primary amount. That is, the primary-side converted value of the secondary current I2 is I2 '= (a2 / a1) .I
2 is input to the adder / subtractor A. Further, the detected value of the primary current I1 is obtained through a coefficient correction circuit H to obtain I1 '= k
Is corrected to I1 and input to the adder / subtractor A. The adder / subtracter A calculates and outputs the exciting current I0 = I1−I2 ″. The phase angle calculator CAL outputs the exciting current detection value I
0 reference value I0 ^* Is calculated using the unit sine wave sinωt synchronized with the voltage V1 applied to the primary side of the transformer TR and the exciting current detection value I0. The coefficient corrector H adjusts the correction coefficient k in accordance with the phase angle ψ. When ψ is positive (leading), k is decreased, and when ψ is negative (lagging), k is increased. FIG. 6 is a voltage and current vector diagram for explaining the operation of the device of FIG.

In FIG. 6, i1 is a primary current detection value,
It is detected as large as ΔI1. Also, i2 'is a value obtained by converting the secondary current detection value to the primary side and is detected to be smaller by .DELTA.I2. From these detected values, the exciting current i0 = i
When 1-i2 'is obtained, the current vector shown is obtained. The exciting current i0 is a vector whose phase is advanced by ψ with respect to the magnetic flux Φ0.

In the apparatus shown in FIG. 5, the phase angle ψ is obtained by the phase calculator CAL, and the coefficient k of the coefficient corrector H is increased or decreased according to the phase angle ψ. That is, when the phase angle ψ is positive (leading), the coefficient k is decreased, and when the phase angle ψ is negative (lagging),
The coefficient k is increased.

In the case of FIG. 6, since the phase angle 正 is positive (leading), the coefficient k is reduced, and the primary current detection value i 1 ′ = k · i
Decrease 1 Eventually, the coefficient k reaches the point where ψ = 0.
Is reduced and becomes i1 'in FIG. At this time,
The secondary current detection value i2 'is not corrected. As a result, the exciting current detection value Io 'becomes Io' = i1'-i2 '. From the similarity of the triangle, the exciting current I0 is compared with the true value I0.
Is equal to the detection error of the secondary current. That is, 2
If the detection accuracy error of the secondary current I2 is 1%, the excitation current detection error by the device of FIG. 5 becomes 1%, and the detection accuracy can be greatly improved.

In the apparatus shown in FIG. 1, the phase angle ψ of the exciting current I0
Is corrected to zero, whereas in the apparatus of FIG. 5, the primary current detection value is corrected so that the phase angle の of the exciting current I0 becomes zero.

Either method can improve the detection accuracy of the exciting current I0. However, when the detection accuracy of the primary and secondary current detectors is different, the one with the higher accuracy is used as it is and the one with the lower accuracy is used. When the detection value is corrected, the detection accuracy of the exciting current can be adjusted to a higher accuracy. Needless to say, even if both the primary current detection value and the secondary current detection value are corrected, the excitation current detection accuracy can be similarly improved. FIG. 7 is a configuration diagram showing still another embodiment of the present invention.

In the figure, Vd is a DC voltage source, INV is an inverter for converting DC to AC of variable voltage and variable frequency, TR
Is a transformer, CT1 and CT2 are current detectors, K is a proportional circuit, H is a coefficient correction circuit, CAL is a phase angle calculation circuit, A1
, A2 denotes an adder / subtractor, C1 denotes a comparator, G0 (s) denotes a control correction circuit, and PWM denotes a pulse width modulation circuit.

The inverter INV is a self-turn-off device (eg, a gate turn-off thyristor, hereinafter referred to as GTO) S
1 to S4 and feedback diodes D1 to D4. The inverter INV is subjected to pulse width modulation control, and its output voltage VINV is a value proportional to the input signal (voltage command value) ei of the PWM control circuit PWM. Voltage command value e
If i is changed sinusoidally, the output voltage VINV also changes sinusoidally, and by changing its amplitude and frequency,
An AC voltage having a variable voltage and a variable frequency can be generated.

When the voltage VINV is applied to the primary winding of the transformer TR to generate a magnetic flux Φ0 and the primary / secondary turns ratio of the transformer TR is (a1 / a2), the secondary winding And V2 =
A voltage of (a2 / a1) .V1 is generated. Load LOA
This secondary voltage V2 is applied to D, and a load current (secondary current) I2 flows.

The current detectors CT1 and CT2 detect the primary current I1 and the secondary current I2 of the transformer TR, respectively. The proportional circuit K converts the secondary current detection value I2 to the primary side. When the primary / secondary turns ratio of the transformer TR is (a1 / a2), the primary side conversion value is I2 '. = (A2 / a1) ・
I2.

The phase angle calculator CAL calculates the phase angle ψ of the exciting current I0 of the transformer TR with respect to the magnetic flux Φ0. The details have been described above, and thus are omitted. The coefficient correction circuit H corrects the correction coefficient k of the secondary current detection value according to the phase angle ψ.
The primary current detection value I1 and the above-mentioned 2
The difference between the next current detection value and the correction value I2 "= k.I2" is obtained, and the exciting current I0 = I1-I2 "is output. The coefficient k is corrected so that the phase angle に 対 す る of the exciting current I0 with respect to the magnetic flux Φ0 becomes zero, and the detection accuracy of the exciting current I0 at that time is improved to the detection accuracy of the primary current I1. In the device shown in FIG. 7, the transformer T
The countermeasures against R magnetization are taken. V1 ^* Is the inverter INV
Is a command value of the output voltage VINV to be generated, and is usually given from an output signal of load current control or the like.

Also, I0 ^* Is an exciting current command value of the transformer TR, the voltage command value V1 ^* And the mutual inductance M of the transformer TR and the output angular frequency ω are given as follows. I0 ^* = V1 ^* / (Jω · M)

This exciting current command value I0 ^* And the exciting current detection value I0 are input to a comparator C1, and a deviation .epsilon.0 = I0 ^* −
I0 is obtained, amplified by the control compensation circuit G0 (s), and input to the adder A2. Therefore, the input signal ei of the PWM control circuit PWM is ei = V1 ^* + G0 (s) · ε0. Next, the excitation current control will be described.

I 0 ^* If> I0, the deviation .epsilon.0 becomes positive, the PWM control input signal ei increases, the output voltage VINV of the inverter INV increases, and the exciting current I0 of the transformer TR increases. Conversely, I0 ^* If <I0,
The deviation .epsilon.0 becomes negative, decreasing the PWM control input signal ei, decreasing the output voltage VINV of the inverter INV, and decreasing the exciting current I0 of the transformer TR.

Thus, the exciting current I of the transformer TR
0 is the command value I0 ^* Is controlled to match. I
0 = I0 ^* , The DC bias of the transformer TR does not occur, and the primary current I1 can be prevented from becoming excessive.
In addition, the voltage V2 required for the load LOAD can be supplied. FIG. 8 is a block diagram showing still another embodiment of the present invention, showing an embodiment in which a PWM inverter is operated in a multiplex manner.

In the figure, Vd is a DC voltage source, INV1, INV
V2 is an inverter for converting DC into AC of variable voltage and variable frequency; TR1 and TR2 are transformers; LOAD is an AC load; CT1 to CT3 are current detectors; K is a proportional circuit;
, H2 are coefficient correction circuits, CAL1 and CAL2 are phase angle calculation circuits, CAL0 is an excitation current command value calculator, A1 to A
5 is an adder / subtracter, c1 to C3 are comparators, G01 (s), G02
(S), GL (s) are current control correction circuits, PWM1, P
WM2 indicates a pulse width modulation control circuit.

In this apparatus, two inverters INV
1. INV2 is multiplexed via transformers TR1 and TR2. That is, the carrier signals X1, Y1 (inversion of X1) applied to the first PWM control circuit PWM1 and the second PWM
The carrier signals X2, Y2 (X2
The PWM control is performed by shifting the phase by 90 °. Here, assuming that the primary / secondary turns ratio of the transformer TR1 is 1: 1, the secondary voltage V12 of the transformer TR1 matches the output voltage V11 of the inverter INV1. Similarly,
The output voltage V22 of the transformer TR2 also matches V21.

The load LOAD is equal to two of the transformers TR1 and TR2.
The sum of the next voltages V12 and V22 is applied. Load voltage VL = V
The equivalent carrier frequency of 12 + V22 has a value four times the PWM control carrier frequency due to the effect of the multiplex operation.
Therefore, the pulsation of the current supplied to the load LOAD has an extremely small value. The load current IL is two inverters INV
The control is performed by simultaneously adjusting the output voltages of INV2 and INV2.

That is, the load current IL is detected by the current detector CT3, and the load current command value IL ^* is detected by the comparator C3 ^. Deviation from εL = IL ^* -Find IL. The deviation .epsilon.L is amplified by a current control compensation circuit GL (s), and is amplified via an adder A3.
The input signal ei1 of WM1 is used as the input signal ei1, and the PWM
2 input signal ei2.

IL ^* > IL, the deviation εL becomes a positive value, the input signals ei1 and ei2 are increased, and the load voltage V
L = V12 + V22 is increased. Therefore, the load current IL increases, and IL becomes IL ^* Is controlled. Conversely, IL ^* <IL
, The deviation εL becomes a negative value and the input signal ei
1, ei2 is reduced, and the load voltage VL = V12 + V22 is reduced. Therefore, the load current IL decreases, and again, IL becomes I
L ^* Is controlled. Here, the signal VL ^* applied to the adder A5 / 2 is for improving the response of the load current control, and compensates the voltage on the load side forward. This V
L ^* Is given by the following equation. VL ^* = (Vc ^* + JωLL · IL ^* + RL · IL ^* However, Vc ^* Is the back electromotive force of the load, ω is the output angular frequency,
LL and RL are the inductance and resistance of the load.

Now, in the apparatus shown in FIG.
A slight DC bias is applied to the transformers TR1 and TR1 due to variations in switching characteristics of the elements constituting the NV1 and INV2.
It is applied to TR2 and may cause DC bias. Thus, in the apparatus shown in FIG. 8, two transformers TR1, T
The exciting current of R2 is detected, and the exciting current is controlled by each inverter.

First, the transformer T is detected by the current detector CT1.
The primary current I11 of R1 is detected, multiplied by k1 through a coefficient corrector H1, and input to an adder / subtractor A1. Also, the current detector C
The load current IL is detected by T3 and input to the adder / subtractor A1 via the proportional circuit K. The proportional circuit K is the transformer 2
The primary current is converted to the primary current, and two transformers TR
1 and TR2 are the same, and if the primary / secondary turns ratio is a1 to a2, k = (a2 / a1). The output of the adder / subtractor A1 is the exciting current Io1 of the transformer TR1, and I01 = k1.I11- (a2 / a1) .IL. The phase angle calculator CAL1 calculates the magnetic flux Φ of the transformer TR1.
Calculates the phase angle 検 出 1 of the exciting current detection value I01 with respect to 01. More specifically, the output voltage detection value V11 of the inverter INV1 and the excitation current detection value I01 are calculated in the same manner as described with reference to FIG. Can be calculated using Here, the output voltage command value V11 ^{* of the} inverter INV1 is used instead of the voltage detection value V11 ^. = VL ^* / 2 is used. The coefficient corrector H1 controls the coefficient k1 so that the phase angle ψ1 becomes zero.
And the detection accuracy of the exciting current detection value I01 can be improved as described above. Exciting current I of transformer TR2
02 also has a proportional circuit K, a coefficient corrector H2, and an adder / subtractor A
2 and the phase angle calculator CAL2 enable accurate detection. CAL0 is the excitation current command value I0 ^* Is a computing unit that calculates the mutual inductance M of the two transformers
Are the same, I0 ^* = VL ^* / (Jω · 2 · M). The exciting current of the transformer TR1 is controlled as follows.

That is, the exciting current command value I0 ^* And the exciting current detection value I01 are input to a comparator C1, and the deviation ε01 = I
0 ^* -Find Io1. The deviation .epsilon.01 is amplified by a current control compensation circuit G01 (s) and input to a PWM control circuit PWM1 via an adder / subtracter A3.

I01 ^* If> I01, the deviation .epsilon.01 becomes a positive value, and the input signal ei1 of the PWM control circuit PWM1 is increased. Therefore, the output voltage V11 of the inverter INV1
Increases to increase the exciting current I01 of the transformer TR1.

Conversely, I01 ^* If <I01, the deviation ε
01 becomes a negative value and decreases the input signal ei1 of the PWM control circuit PWM1. Therefore, the output voltage V11 of the inverter INV1 decreases, and the exciting current I01 of the transformer TR1 decreases. Therefore, Io1 is I01 ^* It is controlled so that The exciting current I02 of the transformer TR2 is similarly controlled. In this way, the exciting current of each of the transformers TR1 and TR2 is controlled, and DC bias of the transformers can be prevented.

Although the excitation current control has some influence on the load current control, it is usually possible to lower the gain of the excitation current control and increase the gain of the load current control to mitigate the interference. Similarly, even in the multiplex operation of three or more inverters, the load current can be controlled while controlling the exciting current of each output transformer. Although the above description has been made with respect to an inverter having a single-phase output, it goes without saying that the present invention can be similarly implemented with a PWM inverter having two or more phases.

In the above-described detection of the exciting current, the primary or secondary current detection value is corrected online, but the coefficient may be corrected offline. That is, the above correction may be performed near the rated voltage, the rated current, and the rated frequency of the transformer, and the excitation current may be detected using the correction coefficient. When the correction coefficient k is determined offline, the set value does not need to be changed during operation. Therefore, it is not necessary to calculate each phase of the excitation current detection value based on the current detection value that changes every moment, and there is an advantage that the calculation time during operation can be shortened.

When performing coefficient correction online,
Instead of correcting in all areas, for example, rated voltage,
It goes without saying that the correction can be made only near the rated current.

[0058]

As described above, according to the exciting current detecting device for a transformer of the present invention, the exciting current of the transformer can be detected with high accuracy, and the exciting current can be controlled accurately. DC bias of the transformer can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a transformer exciting current detection device of the present invention.

FIG. 2 is a voltage-current waveform diagram for explaining the operation of the transformer excitation current detecting device of FIG. 1;

FIG. 3 is a configuration diagram showing a specific embodiment of a phase calculator constituting the excitation current detection device for the transformer of FIG. 1;

FIG. 4 is a voltage and current vector diagram for explaining the operation of the exciting current detecting device for the transformer of FIG. 1;

FIG. 5 is a configuration diagram of a transformer excitation current detection device according to another embodiment of the present invention.

FIG. 6 is a voltage and current vector diagram for explaining the operation of the transformer exciting current detection device shown in FIG. 5;

FIG. 7 is a configuration diagram of a transformer exciting current detection device according to another embodiment of the present invention.

FIG. 8 is a configuration diagram of a transformer exciting current detection device according to another embodiment of the present invention.

FIG. 9 is a configuration diagram of a conventional exciting current detecting device for a transformer.

[Explanation of symbols]

SUP: AC voltage source, TR, TR1, TR2: Anode reactor, LOAD: AC load, CT1 to CT3: Current detector, K: Proportional circuit, H: Coefficient corrector, CAL, CAL1 , CAL2... Phase angle calculator, A, A1 to A5... Adder / subtractor, Vd... DC voltage source, PWM, PWM1, PWM2 ... pulse width modulation control circuit, C1 to C3 ... comparator, G0 (s ), G01 (s), G02 (s) ... exciting current control compensation circuit, GL (s) ... load current control compensation circuit, INV, INV1, INV2 ... inverter, CAL0 ... exciting current command calculator .

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01R 19/00-19/32 G05F 1/00-1/70 H01F 5/00-7/20 H01F 27 / 00-29/14 H01F 39/00-40/14 H02M 1/00-7/98 G01R 15/00-17/22

Claims (6)

(57) [Claims] 1. A transformer and the primary and secondary of the transformer.
A current detector for detecting a secondary current, means for calculating an exciting current of the transformer from the detected primary current value and the detected secondary current value, and means for calculating a phase angle of the exciting current with respect to the magnetic flux of the transformer. Means for correcting the primary current detection value used in the excitation current calculation means so that the phase angle becomes zero. 2. The exciting current detecting device for a transformer according to claim 1, wherein the primary current detected value used in the exciting current calculating means is corrected off-line. 3. A transformer and the primary and secondary of the transformer.
A current detector for detecting a secondary current, means for calculating an exciting current of the transformer from the detected primary current value and the detected secondary current value, and means for calculating a phase angle of the exciting current with respect to the magnetic flux of the transformer. Means for correcting the secondary current detection value used in the exciting current calculating means so that the phase angle becomes zero. 4. The exciting current detecting device for a transformer according to claim 3, wherein the correction of the secondary current detected value used in the exciting current calculating means is performed off-line. 5. A transformer and the primary and secondary of the transformer.
A current detector for detecting a secondary current, means for calculating an exciting current of the transformer from the detected primary current value and the detected secondary current value, and means for calculating a phase angle of the exciting current with respect to the magnetic flux of the transformer. Means for correcting the primary current detection value and the secondary current detection value used in the excitation current calculation means so that the phase angle becomes zero. apparatus. 6. The exciting current of a transformer according to claim 5, wherein the correction of the primary current detection value and the secondary current detection value used in the excitation current calculating means is performed off-line. Detection device.