JPH11162769A - Apparatus and method for evaluating dc polarization of transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely and easily evaluate the amount of DC polarization and its polarity of a transformer, by estimating condition of magnetic flux passing through an iron core by the exciting current of the transformer. SOLUTION: An apparatus for evaluating DC polarization which evaluates the amount of the DC polarization and its polarity of a converter transformer 2 consisting of an iron core with at least one gap cutting a magnetic path, a converter side winding 21 connected to a power converter 1, and an alternating current side winding 22 connected to a load or an electric power system 3 is provided with means 61 and 62 which detect current waveforms I1 and I2 flowing through converter side and alternating current side windings of the converter transformer 2, a means 41 which performs A/D conversion of a current waveform signal, a means which calculates an exciting current waveform I0 of the converter transformer 2 from an A/D converted current waveform signal, a means which calculates time intervals Δt1 and Δt2 of positive and negative sides of the exciting current waveform I0 , and a means which evaluates the amount of the DC polarization ϕdc and its polarity of the converter transformer 2 by the time intervals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for evaluating DC bias of a transformer, and more particularly to an apparatus and method for evaluating the DC bias of a conversion transformer connected between a power system and a power converter. The technology to evaluate.

[0002]

2. Description of the Related Art With the advance of power electronics technology, GTO (Gate Turn-Off Thy) has been developed.
The application of a self-excited power converter using a self-extinguishing semiconductor device such as a ristor to the power field has been advanced. Generally, a self-excited power converter is connected to a power system via a conversion transformer. In this transformer for conversion,
Since a DC component is generated in the applied voltage due to a variation in the firing angle of the semiconductor switch element of the power converter, a DC bias phenomenon in which the magnetic flux passing through the iron core is biased to one of the positive and negative polarities occurs. If the core of the transformer is DC-polarized, it causes loss and noise of the transformer. Further, depending on the degree of DC bias, the iron core is magnetically saturated and an excessive exciting current flows through the winding, which may cause damage to the semiconductor switch element of the power converter connected to the winding. Conventionally, to prevent magnetic saturation of the iron core due to this DC bias phenomenon,
DC bias suppression control is performed in which the amount of DC bias is detected and the output voltage of the power converter, that is, the voltage applied to the conversion transformer is adjusted so as to cancel the amount. As a method of detecting the amount of DC magnetization of the iron core, a method using an exciting current is practically used. For example, as described in Japanese Patent Application Laid-Open No. 1-5365, a DC bias is calculated from the average value of the exciting current. A method for determining the magnetic quantity and its polarity, or JP-A-2-142
As described in Japanese Patent Publication No. 358, a method has been proposed in which the amount of DC bias is obtained from the amplitude of the even-order harmonic contained in the exciting current, and the polarity is obtained from the average value. Also,
A method of directly monitoring the magnetic flux passing through the iron core and detecting the amount of DC bias has been considered.
As described in Japanese Patent Publication No. 1 (Kokai) No. 1, a method has been proposed in which a Hall element is buried in a gap provided in an iron core, a magnetic flux waveform in the iron core is measured, and a DC bias amount is obtained.

[0003]

The above prior art has the following problems. That is, in the method of detecting DC bias from the average value of the exciting current, the polarity of the DC bias can be easily detected, but since the magnetic characteristics of the iron core have nonlinearity, it passes through the average value of the exciting current and the inside of the iron core. It is very difficult to quantitatively relate the DC component of the magnetic flux, and the absolute value of the DC bias amount cannot be accurately obtained. Similarly, also in the method using the amplitude of the even-order harmonic contained in the exciting current, it is very difficult to quantitatively relate the amplitude of the even-order harmonic of the exciting current and the DC component of the magnetic flux. On the other hand, in the magnetic flux detection method, it is necessary to install a Hall element in a gap provided in an iron core of a transformer. Here, the vicinity of the void portion of the iron core is a portion that is exposed to severe conditions such as vibration due to magnetic attraction and a local temperature rise due to magnetic flux leaking from the iron core. Therefore, installing the Hall element in the gap and routing the output lead wire out of the tank of the transformer may cause damage to the element itself and impair the reliability of the transformer itself. There is also a problem that a DC power supply is separately required to operate the Hall element.

An object of the present invention is to overcome the above-mentioned problems by estimating the state of magnetic flux passing through an iron core from an exciting current of a transformer, and accurately determining the amount of DC bias of the transformer and its polarity.
And it is to evaluate easily.

[0005]

The object of the present invention is to provide an iron core provided with a gap at at least one location for breaking a magnetic path, a converter-side winding connected to a power converter using a semiconductor switching element, and A conversion transformer comprising an AC side winding connected to a load or an electric power system, wherein the amount of DC bias and its polarity are determined by the positive and negative time intervals of the exciting current waveform of the conversion transformer. It is solved by evaluating based on. Here, the exciting current waveform is obtained as a difference current between the currents flowing through the converter-side winding and the AC-side winding of the conversion transformer.

[0006] In the conversion transformer connected to the self-excited power converter, an air gap is provided in the iron core for the purpose of suppressing the inrush current of the excitation and improving the detection sensitivity of the excitation current. The properties are significantly worse. Therefore,
The residual magnetic flux (the magnetic flux remaining in the iron core when the exciting current is zero) is almost zero, and the time when the exciting current becomes zero and the time when the magnetic flux in the iron core becomes zero almost coincide. That is, in the present invention, knowing the time interval on the positive side and the negative side of the exciting current waveform is equivalent to indirectly knowing the time interval on the positive side and the negative side of the magnetic flux waveform in the iron core. The time intervals on the positive side and the negative side are focused on one-to-one correspondence with the DC component of the magnetic flux, so that the amount of DC bias and its polarity can be obtained accurately and easily. it can.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a DC bias evaluation apparatus for a transformer according to an embodiment of the present invention. The DC bias evaluation device 4 of the present embodiment includes an A / D converter 41 that converts the winding currents I ₁ and I ₂ of the conversion transformer 2 measured by the current detectors 61 and 62 into digital values, It comprises a waveform storage unit 42 for storing the waveforms of the / D-converted winding currents I ₁ and I ₂ , and a calculation unit 43 for calculating the amount of DC bias and its polarity. In FIG. 1, an AC side winding 22 of the conversion transformer 2 is connected to a load or the power system 3, and a converter side winding 21 is connected to the power converter 1 composed of a semiconductor switching element. The power converter 1 adjusts the firing timing of the semiconductor switch element in accordance with a command from the control device 5 while controlling the conversion transformer 2
To supply power. Current detectors 61 and 62 for detecting the respective winding currents I ₁ and I ₂ are provided on the converter side and the AC side of the conversion transformer 2. Current detector 61, 6
The output 2 is connected to be input to the DC bias evaluation device 4. The DC bias suppression device 4 is configured by a method described below.
The DC bias amount and its polarity are calculated, and the obtained DC bias amount and its polarity are output to the control device 5. The control device 5 controls the ignition timing of the semiconductor switch element of the power converter 1 based on the input DC polarization amount and its polarity, and eliminates the DC polarization of the conversion transformer 2. I do.

FIG. 2 shows an example of the structure of the iron core 23 of the conversion transformer 2. In the conversion transformer 2, in order to suppress the inrush current by setting the residual magnetic flux of the iron core 23 to substantially zero and to increase the detection sensitivity of the exciting current, for example, as illustrated, the windings 21 and 22 of the iron core 23 are A gap is provided in at least one location of the main leg to be wound. In the present invention, the position where the gap is provided is not particularly specified. Also, the structure of the iron core is not limited to the single-phase center core structure as shown.

Next, the DC bias evaluation method according to the present embodiment will be described. As shown in FIG. 1, the current detectors 61, 6
The analog signals of the winding currents I ₁ and I ₂ measured by
After being converted into a digital signal by the / D conversion unit 41, the digital signal is stored in the waveform storage unit 42, and the arithmetic unit 43 calculates the waveform of the exciting current Io from the winding currents I ₁ and I _{2 according} to the equation (1).

[Number 1] _{Io = I 1 -I 2 (A} ) (1) Next, Motoma' excitation current Io time interval of the positive side and the negative side as shown by the waveform in FIG. 1 .DELTA.t1, seeking .DELTA.t2. As a method for obtaining this, for example, of the waveform data of the excitation current Io for one cycle, the number of data points having positive and negative values is counted, and calculated by the equations (2) and (3).

Δt1 = T × (n1 / N) (sec.) (2)

Δt2 = T × (n2 / N) (sec.) (3) where T is one cycle time (sec.), N1 and n2
Is the number of positive and negative data points of the exciting current waveform, and N is A
The number of sampling points for one cycle determined by the / D conversion unit 41. Alternatively, Δt1 and Δt2 may be obtained by detecting the time when the polarity of the exciting current changes. From the time intervals Δt1 and Δt2 determined in this way, the DC bias amount φd
c is calculated by equation (4).

(Equation 4) Here, φac is the amplitude of the AC component of the magnetic flux in the iron core,
It can be theoretically obtained from the amplitude of the output voltage of the power converter 1 and the degree of modulation. Formula (4) is a calculation formula when the magnetic flux waveform in the iron core is a sine wave or close to a sine wave, that is, when the power converter 1 is under sine wave PWM control. In addition, when the magnetic flux passing through the iron core is close to a non-sinusoidal wave, for example, a triangular wave or a trapezoidal wave, the DC magnetic flux φdc is calculated by the equation (5).

(Equation 5) Here, φmax (Δt1) and φmin (Δt2) are the maximum value and the minimum value of the magnetic flux waveform in the iron core, respectively, and need to be defined in advance as functions of the time intervals Δt1 and Δt2.

Next, the reason why the DC bias amount φdc is obtained from the positive and negative time intervals Δt1 and Δt2 of the exciting current waveform by using equation (4) or (5) will be described. FIG. 3 shows the excitation characteristics of the transformer. FIG. 3A shows the case where the core of the transformer is not DC-polarized, and FIG. 3B shows the case where the core is DC-polarized. A broken line in the figure is a core without a gap, and a solid line in the figure. Indicates a voided iron core. The excitation characteristics of a normal transformer using a gapless core draws a history as shown by a broken line in the figure. That is, even when the exciting current Io is zero, the magnetic flux φ passing through the iron core does not become zero, and the residual magnetic flux φr remains in the iron core. Therefore, in this case, the zero point of the magnetic flux waveform in the iron core does not match the zero point of the exciting current waveform. This phenomenon is the same when the iron core is DC-polarized as shown by the broken line in FIG. On the other hand, in the case of the iron core with a gap, as shown by the solid line in the figure, the gradient of the excitation characteristic is extremely small as compared with the iron core without the gap, so that the residual magnetic flux φr ′ is almost zero. Therefore, in this case, the zero point of the magnetic flux waveform and the zero point of the exciting current waveform substantially match. This phenomenon is the same when the iron core is DC-polarized, as indicated by the solid line in FIG. The present invention has focused on this point.

FIG. 4 shows waveforms of the magnetic flux φ and the exciting current Io in the iron core of the transformer using the iron core with the air gap. As described above, since the zero point of the magnetic flux waveform matches the zero point of the exciting current waveform, the time intervals Δt1 and Δt2 on the positive and negative sides of the exciting current Io naturally match the time intervals of the magnetic flux φ. FIG. 5 shows waveforms of the magnetic flux φ and the exciting current Io in the iron core with the gap when the iron core of the transformer is DC-magnetized to the positive side by the DC magnetic flux φdc. Also in this case, similarly, the time intervals Δt1 and Δt2 on the positive and negative sides of the exciting current Io coincide with the time interval of the magnetic flux φ. Therefore, in the transformer for conversion using the iron core with the air gap, the time interval on the positive side and the negative side of the magnetic flux waveform can be obtained indirectly from the time interval on the positive side and the negative side of the exciting current waveform. Since the time intervals on the positive and negative sides of the magnetic flux waveform correspond one-to-one with the value of the DC component magnetic flux φdc passing through the iron core, the DC interval from this time interval is calculated using equations (4) and (5). The amount of magnetic deflection can be obtained. Further, as is clear from FIG. 5, the polarity of the DC bias is obtained by comparing the time intervals Δt1 and Δt2, and when the time interval Δt1 is larger than Δt2, the polarity becomes positive.
When the time interval Δt2 is larger than Δt1, it can be determined as negative polarity.

As described above, the present embodiment is a transformer for converting a core with a gap, and knows the time intervals on the positive side and the negative side of the exciting current waveform to indirectly change the magnetic flux waveform in the core. The time intervals on the positive and negative sides of the magnetic flux can be known.On the other hand, the time intervals on the positive and negative sides of this magnetic flux waveform correspond one-to-one with the DC component of the magnetic flux. Can be asked well. Further, the present embodiment does not use the magnetic characteristics of the non-linearity of the iron core as in the related art,
Since the state of the magnetic flux passing through the iron core is estimated using the time intervals on the positive and negative sides of the exciting current waveform of the transformer, the DC bias amount and its polarity can be easily obtained.

FIGS. 6 to 8 show configuration diagrams when the DC bias evaluation apparatus according to the present invention is applied as DC bias detection means for various power conversion systems. FIG. 6 is a configuration diagram when applied to a DC power transmission system. 6, AC / DC converters 71 and 72 are power converters for converting alternating current to direct current or direct current to alternating current, are connected to each other via a DC transmission line 73, and are respectively connected to conversion transformers 7 and 7.
4 and 75 are connected to the AC system. The DC transformer evaluation units 76 and 77 are connected to the conversion transformers 74 and 75, respectively. The above-described embodiment is applied to the DC bias evaluation devices 76 and 77, and the DC bias amounts φdc of the conversion transformers 74 and 75 are obtained and output to the control devices 78 and 79, respectively. The control devices 78 and 79 control the AC-DC converters 71 and 79 so as to cancel the input DC bias amount φdc.
The ignition timing of the semiconductor switch element constituting 72 is corrected, and a command is sent to AC / DC converters 71 and 72. Thereby, DC bias of the conversion transformers 74 and 75 is eliminated,
It is possible to prevent inconvenience due to DC bias.

FIG. 7 is a configuration diagram when applied to a reactive power compensation system. The power converter 81 is a conversion transformer 8
2 to the power system 83. Further, the power converter 81 is connected to a starting power supply 84 such as a capacitor. The converter 82 includes a DC bias evaluation device 85.
Connect. The above-described embodiment is applied to the DC bias evaluation device 85, which obtains the DC bias amount φdc of the conversion transformer 82 and outputs the DC bias amount φdc to the control device 86. The control device 86 controls the power converter 5 so as to cancel the input DC bias amount φdc.
Correction control of the ignition timing of the semiconductor switch element constituting 1 is performed. As a result, the DC bias of the conversion transformer 82 is eliminated, the inconvenience associated with the DC bias is prevented, and the desired reactive power compensation can be stably performed. Note that, in the configuration of FIG.
If a power storage device such as an ES (power storage system using superconductivity) is used, it can be used as a power storage system and can be used for load leveling.

FIG. 8 is a configuration diagram when applied to a phase adjustment system. In FIG. 8, a power converter 91 has a function of forward conversion and reverse conversion, and is connected to an AC system 93 via a transformer 92 for adjustment, and a series transformer 94 connected in series to the AC system 93. Connected to. Then, a DC bias evaluation device 95 is connected to the series transformer 94. The above-described embodiment is applied to the DC bias evaluation device 95, and the DC bias amount φdc of the series transformer 94 is obtained by the control device 96.
Output to In the control device 96, the input amount of demagnetization φd
The ignition timing of the semiconductor switch element included in the power converter 91 is corrected and controlled so as to cancel out c. According to the phase adjustment system configured as described above, the power converter 9
1, a voltage Vs having an arbitrary phase difference with respect to the ground voltages V11 and V12 at both ends of the power system 93 is applied to the power system 93 via the series transformer 94, and the phase difference between V11 and V12 is arbitrarily adjusted. be able to. The DC bias evaluation device 95 and the control device 96 eliminate the DC bias of the series transformer 94, thereby preventing the inconvenience associated with the DC bias and stably performing the desired phase adjustment. it can.

[0016]

As described above, according to the present invention,
By using the time intervals on the positive and negative sides of the exciting current waveform of the conversion transformer, the exciting current waveform and the DC component of the magnetic flux passing through the iron core can be quantitatively related. Can be obtained with high accuracy. Further, according to the present invention, the state of the magnetic flux passing through the core is determined by using the positive and negative time intervals of the exciting current waveform of the transformer without using the magnetic characteristics of the nonlinearity of the core as in the related art. , The amount of DC bias and its polarity can be easily obtained. Further, if the DC bias evaluation device of the present invention is applied as a bias detection means for DC bias suppression control of a power conversion system, the reliability of the entire system is enhanced in addition to the improvement of control reliability. Also, since it is not necessary to put sensors in the transformer tank as in the method of directly detecting magnetic flux,
There is no fear that the long-term reliability of the transformer body will be impaired.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a DC bias evaluation apparatus for a transformer according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a conversion transformer.

FIG. 3 is an excitation characteristic diagram when a transformer is polarized and when it is not polarized.

FIG. 4 is a waveform diagram of a magnetic flux and an exciting current in an iron core when the conversion transformer is not polarized.

FIG. 5 is a waveform diagram of a magnetic flux and an exciting current in an iron core when a conversion transformer is magnetized.

FIG. 6 is a configuration diagram of a DC power transmission system to which the DC bias evaluation apparatus of the present invention is applied.

FIG. 7 is a configuration diagram of a reactive power compensation system to which the DC bias evaluation apparatus of the present invention is applied.

FIG. 8 is a configuration diagram of a phase adjustment system to which the DC bias evaluation apparatus of the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Power converter, 2 ... Conversion transformer, 21 ... Converter side winding, 22 ... AC side winding, 23 ... Iron core, 3 ... Load or power system, 4 ... DC bias evaluation apparatus, 41 ... A / D conversion unit, 42: waveform storage unit, 43: arithmetic unit, 5: control device,
61, 62 ... current detector

Claims (8)

[Claims] 1. An iron core provided with a gap at least at one position where a magnetic path is cut off, a converter-side winding connected to a power converter using a semiconductor switching element, and connected to a load or a power system. In a DC bias evaluation apparatus for evaluating a DC bias amount and a polarity of a conversion transformer including an AC winding, the conversion based on a positive-side and a negative-side time interval of an exciting current waveform of the conversion transformer. A DC bias evaluation device for a transformer, wherein the DC bias amount and polarity of the transformer are evaluated. 2. An iron core provided with a gap at least at one position where a magnetic path is cut off, a converter-side winding connected to a power converter using a semiconductor switching element, and connected to a load or a power system. In a DC bias evaluation apparatus for evaluating the DC bias amount and its polarity of a conversion transformer comprising an AC side winding, an indirect measurement is performed on the positive and negative time intervals of the exciting current waveform of the conversion transformer. Estimating the positive and negative time intervals of the exciting magnetic flux waveform passing through the iron core of the conversion transformer, and evaluating the DC bias amount of the conversion transformer and its polarity based on the time intervals. DC bias evaluation device for transformers. 3. The transformer according to claim 1, wherein the exciting current waveform is obtained as a difference current between currents respectively flowing through a converter-side winding and an AC-side winding of the conversion transformer. DC bias evaluation device 4. An iron core provided with an air gap at least at one position where a magnetic path is cut off, a converter-side winding connected to a power converter using a semiconductor switching element, and connected to a load or a power system. In a DC bias evaluation apparatus for evaluating the DC bias amount and its polarity of a conversion transformer including an AC winding, a current waveform flowing in the converter side and the AC winding of the conversion transformer is detected. Means and the current waveform signal
Means for D-converting, means for calculating an exciting current waveform of the converting transformer from the A / D-converted current waveform signal, and means for calculating time intervals on the positive and negative sides of the exciting current waveform And a means for evaluating the amount of DC bias of the conversion transformer and its polarity from the time interval. 5. The transformer according to claim 1, wherein the DC bias evaluation device for the transformer is applied to a DC transmission system, a reactive power compensation system, or a phase adjustment system. DC bias evaluation device. 6. An iron core provided with an air gap at least at one position where a magnetic path is cut off, a converter-side winding connected to a power converter using a semiconductor switching element, and connected to a load or a power system. In a DC bias evaluation method for evaluating a DC bias amount and its polarity of a conversion transformer including an AC winding, the conversion is performed based on a positive-side and a negative-side time interval of an exciting current waveform of the conversion transformer. A DC bias evaluation method for a transformer, comprising: evaluating a DC bias amount and a polarity of the transformer for use. 7. An iron core provided with a gap at least at one position where a magnetic path is cut off, a converter-side winding connected to a power converter using a semiconductor switching element, and connected to a load or a power system. In a DC bias evaluation method for evaluating the DC bias amount and its polarity of a conversion transformer comprising an AC winding, a current waveform flowing in the converter side and the AC winding of the conversion transformer is detected. A / D-converting the current waveform signal, calculating an exciting current waveform of the conversion transformer from the A / D-converted current waveform signal, and determining a time interval on the positive side and the negative side of the exciting current waveform. A DC bias evaluation method for a transformer, comprising calculating and evaluating a DC bias amount and a polarity of the conversion transformer from the time interval. 8. The method according to claim 6, wherein the calculation of the exciting current waveform is performed by converting a current flowing in the converter-side winding of the A / D-converted conversion transformer into a current flowing in the AC-side winding thereof. A DC bias evaluation method for a transformer, characterized by subtracting