JP3478904B2 - Current transformer circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of current transformers which need a positive and a negative DC power supply, and to which a plurality of currents which are originally supposed to flow the same or similar currents. The present invention relates to a current transformer circuit for detecting a current in a current path of the present invention and performing control for maintaining the same or similar relationship, or detecting an abnormal state in which the relationship is broken. FIG. 6 shows an example of the configuration of a current transformer circuit using a current transformer generally known as a magnetic flux control type.
T is a current transformer, Ep and En are positive and negative DC power supplies, and R is a detection resistor. Here, the current transformer DCT is an AC current transformer ACT comprising an iron core T and its primary winding N1, secondary winding N2 and a magnetic sensor MS, an amplifier AMP and a transistor Trp.
, Transistor Trn, diode D1 and diode D2
Consists of [0006] That is, positive and negative DC power supplies Ep and En are connected to the current transformer DCT. AC current transformer ACT
A primary winding N1 and a secondary winding N2, which are generally through conductors, are wound around the iron core T, thereby forming a well-known AC current transformer ACT. The iron core T is provided with a magnetic sensor MS for detecting the magnetic flux. The output of the magnetic sensor MS is amplified by the amplifier AMP. The amplifier AMP controls the transistors Trp and Trn, and applies a voltage corresponding to the magnitude and polarity of the magnetic flux to the secondary winding N2 with the polarity to cancel the magnetic flux . , The magnetic flux of the iron core T is controlled to be substantially zero. As a result, the current in the primary winding N1 and the current in the secondary winding N2 are maintained in a high-precision equal-ampere-turn relationship where the magnetic flux is zero, so that high-precision current detection including DC can be performed. Here, K, L, and k indicate the input and output polarities of the well-known current transformer.
Polarity flowing out of FIG. 7 shows a conventional example to which the current transformer circuit shown in FIG. 6 is applied, wherein 1 is a main DC power supply, 2 is an inverter, 3 is a transformer, 41 and 42 are filter reactors and fire capacitors, 5 is a load, 61 and 62 are current transformers. Here, a black circle attached to the transformer 3 indicates the polarity of the winding, and indicates that the primary current I11 and the secondary current I12 have a polarity relationship as shown. Further, in a state in which no bias occurs in the transformer 3, the primary current I11 and the secondary current I12 have similar current waveforms regulated by the turns ratio. Furthermore, the current transformers 61 and 62, the DC power supplies 71, 82, 72 and 82, and the detection resistors 91 and 92 are the same components as those in FIG. [0005] Further, 10 is a voltage setting device, 11, 13, 16, and
18 and 19 are adders, 12 and 14 are control amplifiers, 15 is a triangular wave generator, 17 is a comparator, and 20 is an abnormality detector. In FIG. 7, the voltage setter 10 outputs a set voltage of, for example, a 50 Hz or 60 Hz sine wave, and an adder 11 outputs an error voltage between the output of the voltage setter 10 and the voltage V0 of the load 5 to control the voltage. The output current command Ir of the inverter 2 is amplified by the amplifier 12.
Get. Then, the primary current I11 detected by the current transformer 61 is fed back to the output current command Ir, and the error current obtained by the adder 13 is amplified by the control amplifier 14. The triangular wave generator 15, adder 16 and comparator 17 constitute a well-known pulse width control circuit. That is, the difference voltage between the output voltage of the control amplifier 14 and the output voltage of the triangular wave generator 15 is obtained by the adder 16, and the comparator 17
, A pulse train having a pulse width corresponding to the output of the control amplifier 14 is generated. Further, a switching element (not shown) of the inverter 2 performs an on / off operation using the output pulse train of the comparator 17 as a control signal, so that the inverter 2
Is converted into an alternating current having a pulse width controlled, and a filter reactor 41 and a filter capacitor are connected through the transformer 3.
By 42, the high frequency ripple component is removed to obtain the voltage V0, and the power is supplied to the load 5. As a result, the voltage V0
Is equal to the set voltage of the voltage setting device 10. On the other hand, the output voltage of the inverter 2 includes a DC component due to the voltage drop of the switching element of the inverter 2 or the variation of the switching time, so that the transformer 3 is demagnetized. Generally, the primary resistance of the transformer 3 is very small, so that even a small DC component generates a large bias current. The demagnetization distorts the waveform of the voltage V0, increases the noise of the transformer 3, and causes damage such as damage to the switching element due to an increase in switching loss. In order to prevent the occurrence of such a failure, FIG.
, A current transformer 62, adders 18, 19, and an abnormality detector 20 are provided. That is, the secondary current I
12 is detected, and the difference from the primary current I11, that is, the exciting current , is detected by the adder 18. And the detected excitation
The current is subtracted from the output of the voltage setting device 10 by the adder 19, the voltage of the polarity at which the demagnetization occurs decreases, and the demagnetization is prevented.
Further, when an excessively large magnetic current is generated despite such control, the abnormality detector 20 detects that a magnetic polarization exceeding a specified level has occurred, and stops the inverter 2 by means (not shown). Had become. [0009] In the conventional example of FIG. 7 shown by a single-phase inverter, originally, two current transformers for detecting a similar primary current and a secondary current are used as power supplies. Requires four DC power supplies. Similarly, in the case of a three-phase inverter, six current transformers are required, and therefore twelve DC power supplies. In addition, a system in which a plurality of three-phase inverters are generally connected in parallel for large-capacity output requires a large number of DC power supplies which is further multiplied by the number of units connected in parallel. Such a large number of DC power supplies makes the device expensive and large, and in addition, reduces the reliability of the device. [0010] In order to improve uneconomical, large-sized and low reliability, it is conceivable to simply use a pair of positive and negative DC power supplies for a plurality of current transformers. However, according to such a configuration, when either the positive or negative DC power supply fails, it becomes impossible to detect either the positive or negative current in all current transformers, and control becomes impossible. In addition, it becomes impossible to detect abnormalities. Therefore, the destruction of the switching element is widespread, and it takes a long time to recover the device. SUMMARY OF THE INVENTION In view of the above, the present invention uses a plurality of current transformers requiring positive and negative DC power supplies, and a current which should be the same or similar. A current transformer circuit for detecting a current in a path, wherein a common positive and negative DC power supply is provided for a plurality of current transformers,
The plurality of current transformers are divided into two groups, and a current transformer of one group and a current transformer of the other group have a configuration in which the current polarity of the primary current of the current transformer is reversed. . According to the above-mentioned solution, the number of DC power supplies can be reduced to a large extent, so that the apparatus can be reduced in cost, downsized and highly reliable, and the switching element can be destroyed by reliably detecting an abnormality. Without stopping, the inverter can be safely stopped. Hereinafter, the present invention will be described in detail with reference to the drawings. [0013] [Embodiment] FIG. 1 is a first of the present invention Ruishi 7 is applied
Shows the configuration of the principal part of the embodiment of, 611, 621 current transformer, 73 and 83 direct-current power source, 911, 921 sense resistor, 181 is an adder. That is, FIG. 7 in the circuit configuration of FIG.
The difference is that a pair of common positive and negative DC power supplies 73 and 83 are provided for the current transformers 611 and 621, and the primary winding current polarity of the current transformer 621 is different from the current transformer 611. And the result is that the polarity of the output of the current transformer 621 added to the adder 181 is inverted. Next, FIGS. 2 and 3 show waveforms at various points in the configuration of FIG. FIG. 2 shows an example of a normal waveform in FIG. 1, and (a) shows waveforms of the primary current I11 and the secondary current I12. Here, for simplicity, the winding ratio of the transformer 3 is set to (1:
1), and the same waveform is shown ignoring the exciting current that is only about several percent of the primary current I11. FIG.
(B) shows a waveform detected by the current transformer 611, and therefore, the same waveform as the primary current I11 is detected. FIG. 2 (c) shows a waveform detected by the current transformer 621, and is thus detected with a waveform having a polarity opposite to that of the secondary current I12. FIG. 2D shows the output waveform of the adder 181. The primary current detected by the current transformer 611 and the current transformer 621 are shown in FIG.
The sum of the detected waveforms of the secondary current with the opposite polarity,
That is, it is a detection waveform of the exciting current of the transformer 3. This waveform is applied to the adder 19 and subtracts from the output voltage of the voltage setting device 10. As a result, the exciting current, which is a DC component in the exciting current, is controlled to almost zero. The excitation current detection waveform shown in FIG. 2D is sufficiently small as described above, and therefore, the abnormality detector 20 does not detect an abnormality. FIG. 3 shows a typical waveform example of the operation when the negative DC power supply in FIG. 1 fails and its output becomes zero. Now, when the output of the negative DC power supply 83 is zero, accurate detection is possible for the current flowing through the primary winding in the positive direction, that is, from K to L, because the ability to control the magnetic flux to zero is maintained. However, for the negative direction, that is, the current flowing through the primary winding from L to K, the ability to control the magnetic flux to zero is lacking, so that the core is saturated and the output becomes zero. As a result, feedback in the negative direction with respect to the output current command Ir of the inverter 2 by the control amplifier 12 is lost, so that the output current with this polarity becomes enormous and the switching element is destroyed.
However, in FIG. 3, for convenience of explanation, the inverter output current, that is, the primary current I11 is shown as having positive and negative symmetry. FIG. 3A shows the waveforms of the primary current I11 and the secondary current I12. FIG. 3B shows a current transformer 611.
The same waveform as the primary current I11 is detected for the positive side current of the primary current I11, that is, the polarity current flowing through the primary winding from K to L of the current transformer 611. No current is detected and goes to zero. FIG. 3C shows a detected waveform of the current transformer 621. The primary winding conduction polarity of the current transformer 621 is configured opposite to that of the current transformer 611, so that the secondary current I
The same waveform as the secondary current I12 is detected for the 12 negative currents, that is, the currents flowing through the primary winding from the current transformer K to L, but the positive current is not detected and becomes zero. . FIG. 3 (d)
Shows the output waveform of the adder 181. That is, the positive side is the same as the primary current I11, and the negative side is the same as the secondary current I12, and is detected as a negative waveform. An extremely large output is detected as compared with the output. Therefore, the abnormality detector 20 obtains an excessive output of the adder 181 exceeding the specified value, and stops the inverter 2. The positive DC power supply 73
In the case of a failure, only the detection polarity changes, and the same is true. In the description of FIG. 3, for convenience, it is assumed that the current shown in FIG. 3A continues. However, in practice, zero control of the current transformer core is performed due to failure or deterioration of any power supply. It is clear that as a result of disabling, the core is saturated, the output of the current transformer is reduced, and the above-mentioned situation occurs instantaneously. Therefore, the abnormality can be detected in a safe state at a high speed and long before the inverter output current abnormally grows, and the inverter can be safely stopped. FIG. 4 shows the configuration of a main part of a second embodiment of the present invention applied to the control of the magnetism of a transformer and the detection of an abnormality in a three-phase inverter. In FIG. 4, 31 is a three-phase transformer, 411, 412, 413 are filter reactors, 421, 42
2, 423 are filter capacitors, and 51, 52, 53 are loads. Here, the primary current I of the transformer 31 when there is no magnetic bias
11, I21, and I31 and the secondary currents I21, I22, and I23 have similar current waveforms regulated by the turns ratio, respectively. Further, current transformers 612 , 613, 614 for detecting primary currents I11, I21, I31 of each phase and current transformers 622, 623, 624 for detecting secondary currents I21, I22, I23 of each phase are provided. The current transformers are provided with a pair of positive and negative DC power supplies 74 and 84 in common. 912, 913, 914,
922, 923, and 924 are detection resistors. Where the current transformer 6
12 to Current Transformer 614 Current Transformer for Primary Winding Polarity 622
-The polarity of the current flowing through the primary winding of the current transformer 624 is reversed as shown in the figure, and as a result, the current transformer 62 is added to the adders 182, 183 and 184.
The output polarity of 2, 623, 624 is reversed. In FIG. 4, for example, 111
~ 113, 131 ~ 133, 161 ~ 163, 191 ~ 193 are adders, 1
21 to 123, 141 to 143 are control amplifiers, 171 to 173 are
, 201 to 203 are abnormality detectors, 101 is a voltage setting device, and 151 is a triangular wave generator. With such a configuration, the present embodiment operates exactly the same as in FIG. 1 except for the difference between the three phases and the single phase. In particular, the bias current of the transformer 31 is suppressed to almost zero, and the adders 181 and 182 are provided. , 183 detect an excitation current of several%. And a positive or negative DC power supply
When a failure occurs in any of 74 and 84, the operation is performed in exactly the same manner as in FIG. 1, and extremely large outputs are obtained in the adders 181, 182, and 183, and the abnormality detectors 201, 202, and 203 similarly operate Can work. FIG. 5 shows a main part of a third embodiment of the present invention applied to the parallel control of the single-phase inverter shown in FIG. 1. 201 and 202 are inverters and 321 and 322.
Is a transformer, 615 and 616 are current transformers, 74 and 84 are DC power supplies, 9
3, 94 are detection resistors, 134 , 135, 164, 165 are adders , 14
4, 145 is a control amplifier, 152 is a triangular wave generator, 174, 17
5 is a comparator. It is desirable that the output current I11 of the inverter 201 and the output current I41 of the inverter 202 are balanced and have the same value, but a difference occurs due to the voltage drop of the switching element in each inverter and the variation of the switching time. , A control for balancing is required. FIG.
In the above, a current transformer 615 for detecting the output current I11 and a current transformer 616 for detecting the output current I41 are commonly provided with a pair of positive and negative DC power supplies 75 and 85.
The current transformer 616 for the primary winding conduction polarity of the current transformer 615
The polarity of the primary winding current is reversed, and as a result, the adder 1
35 and 18 are obtained by reversing the output polarity of the current transformer 616. With the configuration shown in FIG. 5, the output current I11 and the output current I41 are controlled so as to match the output current command Ir, and the output currents I11 and I41 have the same balanced value.
Only a small error current is output to the adder 18, and the abnormality detector 20 does not detect an abnormality. When a failure occurs in either the positive or negative DC power supply 75 or 85, a large output is generated in the adder 18 and the abnormality detector 20 can operate just like in FIGS. Of course. As described above, according to the present invention, a common DC power supply can be used for a plurality of current transformers, so that the apparatus can be reduced in cost, miniaturized, and highly reliable. Can be planned. Further, even if one of the common DC power supplies fails, the inverter can be safely stopped by reliably detecting the failure, so that the switching element can be prevented from being damaged, and the device can be restored in a short time. In this description, control of the demagnetizing current of the transformer of the inverter, abnormality detection, and balance control and abnormality detection in parallel operation have been described, but the present invention is not limited to these application examples. It is clear from the description.

[Brief description of the drawings] FIG. 1 is an example to which a first embodiment of the present invention is applied;
FIG. FIG. 2 is a diagram showing an example of a normal waveform in FIG. 1;
is there. FIG. 3 is a diagram showing an example of a waveform at the time of abnormality in FIG. 1;
is there. FIG. 4 is an example to which the second embodiment of the present invention is applied;
FIG. FIG. 5 shows an example to which the third embodiment of the present invention is applied.
FIG. FIG. 6 is a circuit diagram showing a configuration example of a current transformer circuit.
You. FIG. 7 is a diagram showing a conventional example to which a current transformer circuit is applied.
It is a diagram. [Explanation of symbols] DCT current transformer ACT AC current transformer AMP amplifier Trp transistor Trn transistor Ep DC power supply En DC power supply R detection resistor 1 Main DC power supply 2, 201,202        Inverter 3, 31        Transformer 41, 411-413        Filter reactor 42, 421-423        Filter capacitor 5, 51〜53        load 61, 611-616        Current transformer 62, 621-624        Current transformer 71DC power supply 72 DC power supply 73 DC power supply 74 DC power supply 75 DC power supply 81 DC power supply 82 DC power supply 83 DC power supply 84 DC power supply 85 DC power supply 91, 911-914        Detection resistor 92, 921〜924        Detection resistor 93 Detection resistance 94 Detection resistor Ten, 101        Voltage setting device 12, 121〜123        Control amplifier 14, 141〜143        Control amplifier Fifteen, 151        Triangular wave generator 17, 171-175        comparator 20, 201-203        Anomaly detector

Claims (1)

(57) [Claims 1] A plurality of current transformers for detecting currents of current paths that should be the same or similar, the current transformers are a positive / negative DC power supply , a detection resistor, and the detection resistor. configure the current transformer circuit comprising using <br/> and adder for calculating the output, by dividing the plurality of current transformer DC power supply of the positive and negative were commonly provided two groups, and whereas A current transformer circuit characterized in that the current polarity of the primary current of the current transformer is reversed between the group of the current group and the other group.