JP2004112882A - Inrush current suppressing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inrush current suppressing method of suppressing an inrush current with a simple structure in a single-phase circuit or a three-phase circuit. <P>SOLUTION: This inrush current suppressing method is used in a circuit for stepping down the voltage of a power supply 101. A power converter 131 is connected in series to the main transformer 102 through a matching transformer 134. The power converter 131 is operated as the braking resistance of the main transformer 102. In stopping the operation of the power converter 131, its output voltage is decreased in a prescribed time. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rush current suppression method for a transformer, and more particularly to a rush current suppression method using a voltage type inverter.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, power demanding facilities such as factories have a power receiving facility for drawing in power from a substation in a premises. In the power receiving equipment, in addition to a large-sized power receiving end transformer for lowering the voltage, protection equipment such as a circuit breaker that operates in the event of a ground fault or short circuit in a power line is installed. In addition, when the facility scale is large and there are a plurality of buildings in the premises, a plurality of medium-sized transformers and circuit breakers associated therewith are provided below the large-sized transformer at the power receiving end so as to be circuit independent. As a result, even if one building loses power, the other facilities can fully supply power.
[0003]
However, it is known that when a large-sized transformer or a medium-sized transformer is unnecessarily connected (turned on) to a power supply with no load, a current several tens of times the rated current, that is, an inrush current is generated. If an inrush current exceeding the rated current of the large transformer at the receiving end occurs, firstly, there is a problem that the circuit breaker provided immediately outside the premises circuit malfunctions and the whole premises is powered down. Was. This is a problem that can occur even if an inrush current occurs in the medium-sized transformer.
[0004]
Further, even when a power failure does not occur in the entire premises, the voltage waveform is greatly distorted, and in some cases, a malfunction may occur including devices in other buildings in the premises. For example, such a malfunction is not allowed in a facility such as a general hospital or a research institution of a university where a device that must not be stopped is operating.
[0005]
Conventionally, in order to solve these problems, a method of adjusting a power-on phase is used in a single-phase circuit. Also, in the three-phase circuit, a transformer having a built-in inrush current suppression resistor is known (Kazuhiro Mizuno et al., "Development of Transformer for Suppressing Exciting Excitation", Materials of the Institute of Electrical Engineers of Japan, SA-94-29, ( 1994)). A method is also known in which a PWM converter having a high-speed current response is connected in parallel with a transformer and an inrush current is supplied to suppress a momentary voltage drop or the like on the power supply side (Katsuji Fujiwara et al. Transformer Exciting Inrush Current Compensation Circuit Using Filter ", IEICE National Convention, 1998, No. 830).
[0006]
[Problems to be solved by the invention]
However, the conventional technique has the following problems.
That is, in the three-phase circuit, even if the power-on phase is adjusted in principle, there is a problem that the inrush current always occurs as a result of the phase difference of 120 °.
[0007]
In addition, the method of incorporating a suppression resistor in a transformer cannot prevent secondary rush, which is a problem when short-circuiting the suppression resistor, and it is necessary to limit the resistance value in order to prevent it. Was.
[0008]
Further, in the system using the parallel type PWM converter, it is necessary to increase the capacity (V × A) of the PWM converter itself, and there is a problem that it is not economical and is not practical.
[0009]
The present invention has been made in view of the above, and an object of the present invention is to provide an inrush current suppressing method for suppressing an inrush current with a simple configuration regardless of whether the circuit is a single-phase circuit or a three-phase circuit.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a method for suppressing inrush current according to claim 1 is a method for suppressing inrush current applied in a circuit for stepping down a power supply voltage using a transformer, and the method for suppressing inrush current via a matching transformer. A voltage source inverter is connected in series with the transformer, and the voltage source inverter is operated as a braking resistor of the transformer.
[0011]
According to a second aspect of the present invention, there is provided an inrush current suppressing method according to the first aspect, wherein the output voltage of the voltage type inverter is taken over a predetermined time when the operation of the voltage type inverter is stopped. Is reduced.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Embodiment 1]
FIG. 1 is a diagram showing a basic circuit configuration (single phase) to which the rush current suppressing method according to the first embodiment is applied. As shown, the circuit 100 includes a power supply 101, a main transformer 102, and an inrush current suppressor 103.
[0013]
The inrush current suppressor 103 includes a power converter 131 that is a PWM converter, a DC power supply 132 that drives the power converter 131, and a switching ripple suppression filter (LC filter) 133 provided on the output side of the power converter 131. And a matching transformer 134. The matching transformer is a transformer used to match the voltage and current ratings of each other when the voltage type inverter is connected to the power system. As shown, in the present invention, the rush current suppressor 103 is connected in series with the power supply 101 via the matching transformer 134.
[0014]
Although not shown, the DC power supply 132 is provided with a capacitor in the immediate vicinity thereof and is charged in advance and used. Further, a regenerative converter is connected to the DC capacitor (not shown), and energy generated when the main transformer 102 is turned on is regenerated to the power supply 101. Here, a PWM converter is used as the power converter 131, but the present invention is not limited to this, and any voltage-type inverter can be used.
[0015]
In the first embodiment, verification is mainly performed by computer experiments. First, a system (single-phase circuit) for generating an inrush current is constructed, and then, experimental results in a case where the present invention is applied will be described.
[0016]
As the main transformer 102, a single-phase transformer having a rated voltage V ₀ = 200 [V], a rated current of 30 [A], and a capacity of 6000 [VA] is used. FIG. 2 is a chart showing the characteristics of the main transformer 102. FIG. 3 is a table showing converter constants that can be derived from the main transformer 102 shown in FIG. In the experiments, PSCAD / EMTC (manitoba HVDC Research Center, Canada), which is the world standard software for simulating electromagnetic transients in power systems, was used. In the experiment, the winding resistance was assumed to be equal on the primary side and the secondary side, and the values shown in FIG. 4 were used for the inrush current decay time, the saturation voltage, the magnetizing current, and the air-core reactance. For simplicity, the experiment did not consider hysteresis and residual magnetic flux.
[0017]
The power source 101, 200 [V] the voltage effective value _{V s,} the frequency was 60 [Hz], was based on 6000 [VA]. The power supply side impedance _{L s} was 5%.
[0018]
First, in FIG. 1, the inrush current suppressor 103 was removed from the circuit 100, and the power supply voltage and the current waveform when the main transformer 102 was turned on at a power supply voltage phase of 0 ° (when the switch SW1 was turned on) were measured. FIG. 5 shows the result. As shown, the current _{i s} of circuit 100 at most has recorded about 330 [A], the main transformer 102 8 times the rated current 30 [A], that is, the inrush current is generated The system was confirmed. When the main transformer 102 is turned on at a power supply voltage phase of 90 ° in the circuit 100, although not shown, only the no-load current flows as theoretically confirmed, and no inrush current occurs. Was confirmed.
[0019]
Next, the configuration and operation of the inrush current suppressor 103 will be described in detail. FIG. 6 is a diagram illustrating a configuration example of the power converter 131, and FIG. 7 is a table illustrating circuit constants used in a computer experiment. The power converter 131 obtains the output voltage _vab using a triangular wave comparison method PWM (Pulse Width Modulation) as shown in FIG. The power converter 131 detects the current i _s flowing into the main transformer 102 is compared with the triangular wave v _t is multiplied by the gain of K times. This makes it possible to the average value of the output voltage _{v ab} of the power converter 131 (see FIG. 6) to K _· i s [VA]. This means that the inrush current suppressor 103 operates as a resistance of K [Ω]. Actually, in the circuit 100, components caused by switching are removed by using the LC filter 133.
[0020]
_G 1 to g ₄ of the blocks shown in FIG. 8 is connected to _g 1 to g ₄ shown in FIG. Since the main transformer 102 is in a no-load state, when the iron core is saturated, the control gain K is set so as to output the output voltage v _out of the power converter 131 so as not to exceed the no-load current I ₀ (see FIG. 2). To determine. Incidentally, S ₁ inputs a signal for controlling the operation stop of the power converter 131 of FIG.
[0021]
In the first embodiment, since the gain is determined so as not to exceed the no-load current I ₀ , the rated current of the modeled main transformer 102 is set to 0.3 [A], and the transformer constant is determined. A transformer 134 is used. FIG. 9 shows the constants of the matching transformer.
[0022]
A computer experiment was performed as described above. Supply voltage _{v s} closed is 0 [V] and becomes t = 0.0167 [s] at SW1, was charged with the main transformer 102 to the power source 101. The results are shown in FIG. As is clear from the comparison with FIG. 5, it can be confirmed that an inrush current has not occurred immediately after being turned on and is in a steady state. However, it was found that when the operation of the power converter 131 was suddenly stopped, a secondary rush occurred and a current of about 2 [A] was flowing.
[0023]
The output voltage of the power converter 131 was reduced over a period of 50 [ms] in order to prevent a secondary inrush and a rapid change in the voltage phase. Specifically, the output voltage v _out was reduced by taking 50 [ms] after elapse of t = 0.1 [s], and the operation of the power converter 131 was stopped at t = 0.15 [s]. FIG. 11 shows the results. At the moment when the main transformer 102 is turned on to the power supply 101, a maximum current of about 0.17 [A] flows, but after one cycle, the current becomes about 0.12 [A], and a steady state is maintained, which also affects the power supply voltage. Is not affected. In addition, since the output voltage v _out of the power converter 131 was reduced over 50 [ms], it was confirmed that the secondary inrush did not occur. When the operation of the rush current suppressor 103 was completely stopped, a current of 0.28 [A] flowed to the circuit 100 as a no-load current, and it was confirmed that the rush current was suppressed in both the primary and the secondary.
[0024]
Next, the capacity of the inrush current suppressor 103 is determined from the computer experiment results. In the result shown in FIG. 10, the maximum value of the output voltage v _out of the power converter 131 was 170 [V]. The maximum value of the current _{i s} was 0.17 [A]. Therefore, the peak value capacity P _peak of the power converter 131 is
P _peak = 170 × 0.17 = 28.9 [VA]
It becomes. Therefore, the effective value capacity of the inrush current suppressor 102 is about 15 [VA]. Accordingly, the inrush current can be suppressed by the inrush current suppressor 102 having a capacity of 1/400 with respect to the capacity of the main transformer 102 of 6000 [VA].
[0025]
As described above, according to the rush current suppressing method of the first embodiment, it has been clarified that the rush current of the single-phase circuit can be suppressed with a simple configuration.
[0026]
[Embodiment 2]
In a second embodiment, a description will be given of a rush current suppressing method for a three-phase circuit. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted unless otherwise specified.
[0027]
FIG. 12 is a diagram illustrating a basic circuit configuration (three-phase) to which the inrush current suppressing method according to the second embodiment is applied. As shown, the circuit 200 has a configuration in which the circuit 100 is combined for three phases, and the primary side is connected to the power supply 101 with a Δ connection. In the second embodiment, the line voltage effective value of the three-phase power supply voltage is set to 200 [V] and the frequency is set to 60 [Hz], and is based on 10,000 [VA]. Similarly to the single-phase circuit 100, and the power supply side impedance _{L s} is 5%.
[0028]
First, in order to confirm occurrence of an inrush current, in FIG. 12, the inrush current suppressor 103 is removed from the circuit 200, and the main transformers 102 ( _Tra , _Trb , and _Trc ) are set at 0 ° in the a-phase voltage phase. The power supply 101 (v _sa , _vsb , v _sc ) was turned on, and the power supply voltage and the current waveform were measured. FIG. 13 shows the result. As shown, a current of about 330 [A] at maximum flows in the a phase, and a current of -330 [A] flows in the b phase in order to satisfy Kirchhoff's law. It was confirmed that the system was a system in which an inrush current of 10 times or more than that of the above system flowed. Since the circuit 100 is symmetrical, the same result is obtained regardless of the phase in which the main transformer 102 is turned on to the power supply 101. Further, as described above, since the phases are shifted from each other by 120 °, an inrush current always occurs in one of the phases.
[0029]
Computer experiments were performed with the circuit constants for a three-phase circuit as the values shown in FIG. In the experiment, the circuit configuration was three-phase, and the circuit configuration was the same as that of the first embodiment except for the circuit constants shown in FIG. 14. When the voltage phase of the a-phase was 0 °, the three-phase main transformer 102 was connected to the power supply 101 at the same time. I put it in. The result is shown in FIG. As is clear from comparison with FIG. 13, it can be confirmed that no rush current is generated immediately after the injection and a steady state is obtained. However, it was found that when the operation of the power converter 131 was suddenly stopped, a secondary rush occurred and a current of about 3 [A] was flowing.
[0030]
As in the first embodiment, the output voltage of the power converter 131 is reduced over 50 [ms] to prevent the secondary rush and to prevent a sudden change in the voltage phase. Tried prevention. FIG. 16 shows the results. At the moment when the power supply 101 is turned on, a maximum current of about 0.12 [A] flows, but in a steady state, a current of about 0.08 [A]. When the operation of the power converter 131 is completely stopped, a current of 0.28 [A] flows as a no-load current, and it can be seen that the rush current is suppressed by the power converter 131 in both the primary and secondary powers.
[0031]
Next, the capacity of the inrush current suppressor 103 in the case of the three-phase circuit is obtained from the calculation experiment results. The maximum output voltage of the power converter 131 is about 120 [V] per phase. The maximum value of the current _{i s} is 0.12 [A]. Therefore, the peak value capacity P _peak of the power converter 131 is
P _peak = 120 × 0.12 = 14.4 [VA]
It becomes. Therefore, the effective value capacity per one power converter 131 is about 7.2 [VA], and becomes 22 [VA] when all three phases are combined. Accordingly, the inrush current can be suppressed by the inrush current suppressor 102 having a capacity of 1/454 with respect to the capacity of the main transformer 102 of 10,000 [VA].
[0032]
As described above, according to the rush current suppressing method of the second embodiment, it has been clarified that the rush current can be suppressed with a simple configuration even with a three-phase circuit.
[0033]
【The invention's effect】
As described above, according to the inrush current suppressing method of the present invention, it is possible to provide an inrush current suppressing method for suppressing an inrush current with a simple configuration regardless of whether the circuit is a single-phase circuit or a three-phase circuit. Was. Further, the inrush current can be suppressed with a capacity of several hundredths of the capacity of the main converter. That is, the capacity of the matching transformer can be reduced to several hundredths of the capacity of the main transformer, and it can be said that an economical rush current suppression method can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a basic circuit configuration (single phase) to which an inrush current suppressing method according to a first embodiment is applied.
FIG. 2 is a table showing characteristics of a main transformer according to the first embodiment.
FIG. 3 is a table showing converter constants that can be derived from the main converter shown in FIG. 2;
FIG. 4 is a table showing inrush current decay time, saturation voltage, magnetizing current, and air-core reactance.
FIG. 5 is a diagram for confirming how an inrush current occurs in a numerical experiment using a constructed single-phase circuit model.
FIG. 6 is a diagram illustrating a configuration example of a power converter according to the first embodiment.
FIG. 7 is a table showing circuit constants used in a computer experiment of the first embodiment.
FIG. 8 is a diagram showing signal generation configuration blocks of the power converter according to the first embodiment.
FIG. 9 is a table showing constants of the matching transformer according to the first embodiment;
FIG. 10 is a diagram showing a state of a change in a current voltage when the main converter is turned on using the inrush current suppressing method according to the first embodiment.
FIG. 11 is a diagram showing a state of a change in a current voltage when the inrush current suppressor is gradually attenuated after the main converter is turned on and a steady state is applied, using the inrush current suppression method according to the first embodiment. It is.
FIG. 12 is a diagram showing a basic circuit configuration (three-phase) to which the inrush current suppressing method according to the second embodiment is applied.
FIG. 13 is a diagram for confirming how an inrush current occurs in a numerical experiment using a constructed three-phase circuit model.
FIG. 14 is a table showing circuit constants in the case of a three-phase circuit.
FIG. 15 is a diagram showing a state of a change in a current voltage when the main converter is turned on using a rush current suppressing method according to the second embodiment.
FIG. 16 is a diagram showing a state of a change in a current voltage when the inrush current suppressor is gradually attenuated after the main converter is turned on and a steady state is applied, using the inrush current suppression method according to the second embodiment. It is.
[Explanation of symbols]
101 power supply 102 main transformer 103 inrush current suppressor 131 power converter (power type PWM converter)
132 Drive power supply 133 LC filter 134 Matching transformer

Claims (2)

A rush current suppression method applied in a circuit for stepping down a power supply voltage using a transformer, wherein a voltage-type inverter is connected in series with the transformer via a matching transformer, and the voltage-type inverter is connected to the transformer. A rush current suppression method characterized by operating as a braking resistor. 2. The rush current suppressing method according to claim 1, wherein when the operation of the voltage source inverter is stopped, the output voltage of the voltage source inverter is reduced for a predetermined time.

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