JPH09308224A - Harmonic suppressing circuit for electric power system and communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress higher harmonics and prevent the production of overvoltage due to ground fault accident by series-connecting a bidirectional switching element with a coil having a required inductance, and exercising control so that the bidirectional switching element will has a constant switching voltage both in positive and in negative. SOLUTION: A coil L is series-connected with a diode anti-parallel circuit 1 having a certain positive and negative switching voltage. Another coil L1 and a capacitor C parallel circuit 5 are added as required to reduce the reactance of the entire circuit. A harmonic suppressing circuit 10a is thereby constituted, and it is connected with a sheath grounding conductor 9. The circuit allows fundamental waves to be passed and yet suppresses higher harmonics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic wave suppression circuit installed in a power system such as a power transmission line or a distribution line or a communication system.

[0002]

2. Description of the Related Art With the rapid spread of semiconductor applied equipment to household equipment, office automation equipment, and industrial equipment, harmonics generated during switching of semiconductor elements flow out to a distribution system and further propagate to a power system. As a result, the voltage / current waveform may be distorted, which may lead to malfunction, burnout, or deterioration of the device depending on the circuit conditions. For this reason, conventionally, a means has been generally used to remove harmonics by connecting a filter to a system to which semiconductor built-in devices such as an uninterruptible power supply and an AC / DC converter are connected.

[0003]

However, when a ground fault occurs in the current system, the filter resonates with a specific frequency in the ground current, resulting in an overvoltage, which is a secondary voltage. There was a risk of causing an accident.

On the other hand, conventional measures for suppressing harmonics were generally provided in the high voltage system of the power system, but according to the results of measurement and analysis by the present inventor, the harmonics also penetrate through the ground system. There was found. That is, the surge current generated when the semiconductor element is switched near the power line cable or the power transmission line flows as a stray circulating current in the ground based on the potential difference between the ground lines, and this flows to the transformer winding of the power system. It enters directly or by electromagnetic induction, or enters the core wire from the cable sheath by electromagnetic induction.

Further, for the same reason, there is a possibility that higher harmonics may enter the communication system (including the control system) and interfere with the control of communication and computers.

In view of the above, the present invention suppresses harmonics entering a power system or a communication system by using a simple circuit having a basic configuration of a combination of a semiconductor switching element and a coil without using a filter, and a ground fault accident. It is an object of the present invention to provide a harmonic suppression circuit that prevents the occurrence of overvoltage during operation and can be effectively applied to a ground system.

[0007]

In order to achieve the above object, the present invention is a harmonic suppression circuit connected to a power system, wherein the harmonic suppression circuit has a bidirectional semiconductor switching element and a required inductance. The bidirectional semiconductor switching element is configured by connecting a coil in series, and the bidirectional semiconductor switching element has a constant positive and negative switching voltage.

According to the above structure, when the voltage of the power system exceeds the switching voltage, the semiconductor switching element is selectively turned on according to the positive / negative of the voltage, and is turned off when the voltage is equal to or lower than the switching voltage. A back electromotive force is generated in the coil due to a rapid change in current due to on / off.
This counter electromotive force has a large effect on high-frequency harmonics and blocks its passage, but the counter electromotive force on low-frequency fundamental waves is small, so the fundamental waves are not blocked.

Further, it is possible to connect a capacitor to the above coil and select the circuit constants of such a magnitude as to resonate with the frequency of the fundamental wave of the power system. According to this configuration, the reactance of the circuit is reduced, and therefore it is effective in the ground system to ensure the operation of the system protection relay in the event of a ground fault.

As the bidirectional semiconductor switching element, it is possible to use a pair of diodes which have been subjected to a proton irradiation process and which are connected in parallel in mutually opposite polarities. The switching voltage of each semiconductor switching element can be changed by the proton irradiation process.

Further, as the bidirectional semiconductor switching element, a pair of thyristors connected in parallel with mutually opposite polarities, or a triac is used, and these control circuits are selected according to the positive / negative of the voltage of the power system. It is possible to control the gate current so that the gate current is made conductive at a voltage equal to or higher than the absolute value of the switching voltage and becomes non-conductive at a voltage lower than the absolute value.

Further, as a harmonic suppression circuit for suppressing harmonics flowing in from the ground system of the communication system, a bidirectional semiconductor switching element and an inductor are connected in series as in the above case, and the bidirectional It is possible to adopt a configuration in which the semiconductor switching element has a constant switching voltage in both positive and negative directions.

Also in this case, harmonics can be prevented from entering the communication system by the same operation as described above.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the circuit components of the harmonic suppression circuit will be described. As a specific example of the bidirectional semiconductor switching element used in the present invention, as shown in FIG. 1 (a), a pair of diodes are connected in parallel with opposite polarities (the positive and negative polarities are opposite), and FIG. As shown in (b), there is a triac shown in FIG. 1 (c), in which a pair of reverse blocking three-terminal thyristors are connected in parallel in mutually opposite polarities.

The type shown in FIG. 1A is abbreviated as a diode anti-parallel type, and its circuit is called a diode anti-parallel type circuit 1. Further, the form of FIG. 1B is abbreviated as a thyristor anti-parallel form, and its circuit is called a thyristor anti-parallel form 2. Further, the type of FIG. 1C is abbreviated as a triac type, and its circuit is simply called a triac 3. FIG.
Reference numeral 4 in (b) and (c) is a gate current control circuit.

FIG. 2A shows a VI characteristic diagram of each diode used in the diode anti-parallel type. This diode rapidly increases in current value at a constant value V ₁ (switching voltage) of a forward voltage of about several volts, and rapidly reverses at a constant value V ₂ of several tens of volts in the reverse direction (breakdown voltage). It has a characteristic that the directional current value increases. The characteristic indicated by the broken line in the figure shows the case where the switching voltage is increased to V ₁ 'and the breakdown voltage is increased to V ₂ ' by subjecting the diode to the proton irradiation treatment. For example by applying the proton treatment V ₁ = 2.5V diode, 'can be increased to = 4.0V, the control of the irradiation process, free V _1' V ₁ can be selected.

FIG. 2B shows V- of the diode parallel circuit 1.
This is the I characteristic, and the reverse characteristic is omitted.

A pure resistance R is added to the diode anti-parallel circuit 1 described above.
Is serially connected (see FIG. 3A), and the current i flowing through the pure resistance R when the commercial frequency AC voltage E is applied thereto is conceptually shown in FIG. 3B. AC voltage E
Current i flows only when the voltage exceeds the switching voltage V ₁ (or −V ₁ ), the current i becomes Δ every half cycle.
There is a quiescent period of T hours. The magnitude of this ΔT can be freely selected within the range of 20 ns to 500 μs by selecting the characteristics of the device itself and controlling the above-mentioned proton irradiation treatment.

FIG. 4 shows a diode antiparallel circuit 1 (having a resistance value of 0.139Ω in each of the positive and negative directions; the same applies hereinafter) to a resistor R (= 0).
AC voltage E (= 0.27)
When the current i flowing through the resistance R when V, the same applies below) is actually measured, the current i has a rest period ΔT (= 0.84 μ).
s) is present and the peak value of the current i is 1.14A. In addition, the fundamental wave (60
Hz) to the 5th harmonic (30%), and the 9th harmonic (30%)
%), The frequency analysis result of the current i is shown in FIG.
(C) and (d) show. As can be seen from this analysis result, it is understood that not only the fundamental wave but also the fifth and ninth harmonics are output without being blocked.

FIG. 5 shows the waveform of the current i when an AC voltage E is applied to an experimental circuit in which a coil L (self-inductance 20 mH, the same applies hereinafter) is connected in series to the diode antiparallel circuit 1 as shown in FIG. Is shown in FIG. Although the peak value (0.035A) of the current i is remarkably reduced, the rest period (Δ
T) disappears and becomes a positive flow wave as a whole. This is because the change in current is delayed by ΔT due to the self-induction action of the coil L, and as a result, the zero point of the positive half wave and the zero point of the next negative half wave coincide with each other. In other words, if the size of the self-inductance of the coil L is properly selected,
It can be said that a delay time of ΔT occurs in the change of the current and the current waveform becomes a forward current wave.

FIGS. 5 (c) and 5 (d) show the results of frequency division of the current waveform when the fifth and ninth harmonics similar to those described above are added to the fundamental wave. From this analysis result, it is understood that the fundamental wave is sufficiently large, while the fifth and ninth harmonics are significantly suppressed.

This means that when a current change occurs when each diode of the diode parallel circuit 1 is turned on and off, only a small counter electromotive force acts on the fundamental wave, and therefore, it is necessary to pass this. On the other hand, a large counter electromotive force acts on high-frequency harmonics, and the energy is accumulated in the form of a magnetic field generated in the coil L.

Next, the experimental circuit shown in FIG. 6A is obtained by connecting the parallel circuit 5 of the coil L ₁ (20 mH) and the capacitor C (2 μF) to the circuit shown in FIG. 5A. By inserting the capacitor C, the reactance of the circuit is reduced. Desirably, the circuit constants of the coils L and L and the capacitor C are determined so that they resonate with respect to the fundamental frequency. This makes it easier for the fundamental wave to pass therethrough, and allows harmonics to be blocked by the counter electromotive force of the coil L, as in the case described above.

The waveform of the fundamental frequency in this case is shown in FIG. It can be seen that the crest value is slightly higher than in the case of FIG.

In addition to the above fundamental frequency, the fifth and ninth
The results of frequency analysis when harmonics are added are shown in Fig.
(D) Shown in the figure. It can be seen that the harmonics are significantly suppressed.

In FIG. 6, the parallel circuit 5 of the coil L ₁ and the capacitor C is added to reduce the reactance of the entire circuit. However, the coil L ₁ is omitted and the capacitor as shown in FIG. The same effect can be obtained by using a series circuit of C and the coil L.

From the above experiment, in the case of FIG. 4, there is no action of suppressing harmonics, but the circuits shown in FIGS. 5, 6 and 7 have the action of passing the fundamental wave and suppressing harmonics. I understand.

Although the diode anti-parallel type has been described above, in the case of the thyristor anti-parallel type as shown in FIG. 1B, the control circuit 4 causes the positive half-wave of the AC voltage to switch to the switching voltage V ₁ When the voltage exceeds V, the thyristor connected in the forward direction is turned on, and conversely its switching voltage V
_It controls the gate current to turn off when it goes below ₁ . Further, when a negative half wave is applied, the same control is performed for the thyristor connected in the negative direction.

Further, the control circuit 4 in the case of the triac type shown in FIG. 1 (c) also controls the gate current in the same manner as in the above thyristor antiparallel type.

The thyristor anti-parallel type and the triac type having the control circuit 4 as described above perform the same switching action as in the case of the diode anti-parallel type described above (see FIG. 3). Similar results can be obtained by using the thyristor anti-parallel circuit 2 or the triac 3 instead of the diode anti-parallel circuit 1 described with reference to FIG.

In both the thyristor anti-parallel type and the triac type, the current quiescent period ΔT (see FIG. 3).
(See (b)) can be arbitrarily changed by controlling the gate current.

[Embodiment] Next, as an embodiment applied to a ground system, an example applied to a ground wire of a cable sheath of a communication / control system will be described.

FIG. 8 shows an example in which the harmonic suppression circuit 10a is connected to the sheath ground wire 9 of the low voltage control cable 8. The harmonic suppression circuit 10 in this case is that shown in FIG. 6 (a). Reference numeral 11 in the drawing denotes a core wire of the cable 8.

FIG. 9 shows the above-mentioned hollow cylindrical body in which the existing grounding wire in which a hollow cylindrical body 12 made of Permalloy (high magnetic permeability material and high inductance) is connected to the same sheath grounding wire 9 is left as it is. 12 is connected in parallel with the harmonic suppression circuit 10a of FIG. The hollow cylindrical body 12 is installed to absorb a surge current flowing in at the time of a ground fault or the like.

If there is an existing hollow cylindrical body 12, the transformer 2 of the transformer 13 is connected to the ground wire 9 as shown in FIG.
The harmonic suppression circuit 10b is connected between the secondary side and the ground.
The function of the coil of the harmonic suppression circuit 10b in this case is substituted by the inductance of the transformer 13. Also, two anti-parallel circuits of diode 1 are connected in series,
The circuit is the same as that of FIG.

FIG. 11 shows a case where a surge absorbing coil 14 (40 to 400 mH) is connected to the sheath ground wire 9 and an existing circuit is used. A transformer 15 is connected in series with the coil 14 and The harmonic suppression circuit 10c is connected between the secondary side of the transformer 15 and the ground. In this case, the secondary coil of the transformer 15 is connected in series to the diode anti-parallel circuit 1, and the circuit shown in FIG.
Same as (a).

As the harmonic suppression circuit 10d of FIG. 12, another diode antiparallel circuit is connected in series to the circuit of FIG.

The harmonic suppression circuit 10e shown in FIG.
The capacitor C is connected in series to the circuit of FIG. 7 and is basically the same as the circuit of FIG.

FIG. 14 is applied to the sheath ground wire 17 of the power line cable 16. In this case, Phase A, B
A so-called cross-bonding method is adopted in which the potential difference between the sheaths is eliminated by connecting the sheaths of the C-phase and the C-phase to each other in a cross, and the three phases are collectively grounded. The harmonic suppression circuit 10f is connected to the sheath ground wire 17.

The harmonic suppression circuit 10f in this case is shown in FIG.
(A) is shown, but other circuits (Fig. 5 (a),
Figure 7) can also be used. Also in the following embodiments, FIG.
Although (a) is shown, those shown in FIGS. 5 (a) and 7 can be used.

FIG. 15 is applied to the ground wire 19 of the distribution line 18, FIG. 16 is applied to the capacitor ground wire 22 of the power transmission line 21, and FIG. 17 is a neutral point ground wire of the transformer 23 of the power transmission line 21. 24 is applied. 18 is applied to the ground line 27 of the communication device 26 of the communication line 25.

Although each of the above embodiments has been applied to the grounding system, FIG. 19 shows the harmonic suppression circuit 10g connected to the high voltage side of the transmission line 21. In this case, the function as the inductor is substituted by the coil of the transformer 23 connected to the terminal end of the power transmission line 21 or the stray inductance existing in the system of the power transmission line. In the figure, 27 is a circuit breaker.

The above embodiments show that the power system and the communication system have a function of suppressing the harmonics by allowing the fundamental wave to pass therethrough. It also means that it has the function of suppressing the surge current flowing into the system due to a ground fault.

[0044]

As described above, according to the present invention, a counter electromotive force is generated in the coil by the action of the bidirectional semiconductor switching element having a constant positive and negative switching voltage, and harmonic intrusion is caused by the counter electromotive force. This has the effect of suppressing the surge current that flows into the system due to a ground fault or the like, and preventing the occurrence of overvoltage.

Further, since the passage of the fundamental wave is allowed, when applied to the ground system, for example, it does not adversely affect the system protection relay connected to the ground system.

[Brief description of drawings]

FIG. 1A is a circuit diagram of a diode anti-parallel type, and FIG. 1B is a circuit diagram of a thyristor anti-parallel type.

FIG. 2A is a V-I characteristic diagram of a diode. FIG. 2B is a V-I characteristic diagram of a diode anti-parallel type.

FIG. 3A is a circuit diagram of a diode anti-parallel type, and FIG. 3B is a characteristic explanatory diagram of the above.

FIG. 4 (a) Experimental circuit diagram of diode anti-parallel type (b) Same current waveform diagram (c) Same frequency spectrum diagram (d) Same frequency analysis result diagram

FIG. 5 (a) Experimental circuit diagram of diode anti-parallel type (b) Same current waveform diagram (c) Same frequency spectrum diagram (d) Same frequency analysis result diagram

FIG. 6A is an experimental circuit diagram of a diode anti-parallel type. FIG. 6B is a current waveform diagram of the above. FIG. 6C is a frequency spectrum diagram of the above.

FIG. 7: Experimental circuit diagram of diode anti-parallel type

FIG. 8 is a circuit diagram of an embodiment.

FIG. 9 is a circuit diagram of an embodiment.

FIG. 10 is a circuit diagram of an embodiment.

FIG. 11 is a circuit diagram of an example.

FIG. 12 is a circuit diagram of an example.

FIG. 13 is a circuit diagram of an example.

FIG. 14 is a circuit diagram of an example.

FIG. 15 is a circuit diagram of an example.

FIG. 16 is a circuit diagram of an example.

FIG. 17 is a circuit diagram of an example.

FIG. 18 is a circuit diagram of an example.

FIG. 19 is a circuit diagram of an example.

[Explanation of symbols]

 1 diode anti-parallel circuit 2 thyristor anti-parallel circuit 3 triac 4 control circuit 5 parallel circuit of coil and capacitor 8 low-voltage control cable 9 sheath ground wire 10a-10g harmonic suppression circuit 11 core wire 12 hollow cylindrical body 13 transformer 14 coil 15 transformer 16 Power line cable 17 Sheath ground line 18 Distribution line 19 Ground line 21 Power line 22 Capacitor ground line 23 Transformer 24 Neutral point ground line 25 Communication line 26 Communication equipment

Claims (9)

[Claims] 1. A harmonic suppression circuit connected to a power system, wherein the harmonic suppression circuit is configured by connecting a bidirectional semiconductor switching element and a coil having a required inductance in series, and the bidirectional semiconductor. A harmonic suppression circuit in a power system, wherein a switching element has a constant positive and negative switching voltage. 2. A parallel circuit of another coil and a capacitor is connected in series with the coil, and the circuit constants of these coils are selected to have a size that resonates with the fundamental frequency of the power system. A harmonic suppression circuit in the power system according to 1. 3. The power system according to claim 1, wherein a capacitor is connected in series with the coil and the circuit constants of these are selected to have a size that resonates with a fundamental frequency of the power system. Harmonic suppression circuit. 4. The electric power according to claim 1, wherein the bidirectional semiconductor switching element is formed by connecting a pair of diodes, which have been subjected to a proton irradiation process, in parallel in mutually opposite polarities. Harmonic suppression circuit in the system. 5. The bidirectional semiconductor switching element comprises a pair of thyristors connected in parallel with mutually opposite polarities, and the control circuit of each thyristor is selectively turned on or off depending on whether the voltage of the power system is positive or negative. 2. The gate current is controlled so that it conducts at a voltage equal to or higher than the absolute value of the switching voltage and becomes non-conductive at a voltage lower than the absolute value.
A harmonic suppression circuit in the electric power system according to any one of 1 to 3. 6. The bidirectional semiconductor switching element is a triac, and a control circuit of the triac is configured to selectively operate at a voltage equal to or higher than an absolute value of the switching voltage depending on whether the voltage of a power system is positive or negative. The harmonic suppression circuit in a power system according to any one of claims 1 to 3, wherein the gate current is controlled so that it conducts and becomes non-conductive at a voltage lower than that. 7. The harmonic suppression circuit in a power system according to claim 1, wherein the coil is replaced by a winding of a transformer connected to the power system. 8. The harmonic suppression circuit in a power system according to claim 1, wherein the coil is replaced by a stray inductance existing in the power system. 9. A harmonic suppression circuit connected to a ground system of a communication system, wherein the harmonic suppression circuit is configured by connecting a bidirectional semiconductor switching element and a coil having a required self-inductance in series. A harmonic suppression circuit in a communication system, wherein the bidirectional semiconductor switching element has a constant switching voltage in both positive and negative directions.