JP2813155B2 - Filter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter device used as a measure for reducing harmonics in a secondary circuit of a single-phase three-wire transformer.

[0002]

2. Description of the Related Art In recent years, in addition to general industrial equipment, the use of semiconductor-applied equipment such as inverters has increased for various equipment such as home equipment and OA equipment. Etc.) are increasing. Therefore, the conventional distribution system (660)
0V) should of course be implemented, but further consideration of harmonic reduction measures in low-voltage circuits (210-105V) is more likely because the low-voltage circuit is closer to the source of harmonics. It is effective.

Conventionally, as shown in FIG. 2, when a single-phase (105 V) AC filter is installed on the secondary side of a single-phase three-wire type transformer (6600 V / 210 to 105 V) 1, The circuit requires single-phase AC filters F ₁ and F ₂ . In FIG. 2, 2a and 2b are resonance reactors, 3a and 3b are capacitors, and 4a and 4b are harmonic current sources of a load.

The terminal voltage on the secondary side of the transformer 1 is E, and the harmonic current from the harmonic current sources 4a and 4b of the load is J _n1.
And J _n2, resonant reactor 2a, 2b impedance X _L (= jωL) of a capacitor 3a, the impedance of _{3b X C (= -j / ωC} ), the impedance of the transformer side Z (harmonic at: Z _n ), The filters F ₁ ,
Current i _A1, i _B1 by the fundamental wave flowing in F _2, harmonic current source 4a, harmonic current i _An according 4b, i _Bn is as follows.

[0005]

(Equation 1) As described above, since the fundamental wave flows through the resonance reactors 2a and 2b, the fundamental wave current (i _A1 , i _B1 ) is reduced despite the fact that the fundamental wave is installed for the purpose of removing the harmonic currents J _n1 and J _n2 . In consideration of the tolerance, the resonance reactors 2a and 2b having specifications suitable for the harmonic current (i _An , i _Bn ) must be used.

[0006]

As described above, in the conventional harmonic filter device, there is a disadvantage that the filter in the low-voltage circuit is more expensive than the high-voltage circuit, including the filter of the voltage and capacity.

[0007] The problem to be solved by the present invention is to reduce the number and tolerance of expensive resonant reactors to reduce costs.

[0008]

In order to solve the above-mentioned problems, a filter device according to the present invention includes two single-phase AC filters provided in a secondary circuit of a transformer having a single-phase three-wire circuit. In the filter device, a resonance reactor shared by two circuits of a single-phase AC filter is installed on the neutral point side of the single-phase three-wire circuit, and the respective capacitors constituting the two single-phase AC filters are connected to the resonance reactor. It was done.

[0009]

The fundamental wave current of the capacitor of the single-phase AC filter is provided by sharing the resonance reactor of the single-phase AC filter on the secondary side of the single-phase three-wire circuit of the transformer with two circuits on the neutral point side. Are canceled, and only the harmonic current flowing into the two-circuit AC filter is applied to the resonance reactor. As a result, a reactor having a small resistance can be used.

[0010]

Embodiments of the present invention will be specifically described below.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, 1 is a single-phase three-wire transformer, 2 is a resonant reactor for an AC filter, 3a and 3b are capacitors,
4a and 4b are harmonic current sources of the load. A harmonic filter F is formed by the resonance reactor 2 and the capacitors 3a and 3b.

In this embodiment, two circuits of AC filter capacitors 3a and 3b have the same capacitance, and a two-circuit AC filter is constituted by the resonance reactor 2 on the neutral point side.

The terminal voltage on the secondary side of the transformer 1 is E, the currents from the harmonic current sources 4a and 4b of the load are J _n1 and J _n2 , respectively, and the impedance of the resonant reactor 2 with respect to the fundamental wave is X _L ( = JωL), the impedance for the nth harmonic is X _Ln (= jnωL), and the capacitor 3
The impedances for the fundamental waves a and 3b are all X
Assuming that the impedances for _C (= −j / ωC) and the nth harmonic are X _Cn (= −j / nωC), the currents i _A1 , i _B1 , and i _C1 due to the fundamental wave flowing through the filter F are as follows. Becomes

[0014]

(Equation 2) Here, since the sum of the currents flowing into the point P is 0, i _An + i _Bn + i _Cn = 0 (4) From the equations (1) to (4),

(Equation 3) Thus, V _P1 = 0. Incidentally, characteristics of the filter F with respect to the frequency (fundamental wave) of the commercial power supply is not always 2X _L
Since + X _C = 0 (f = １ ／ π√ (2LC)) is not set, V _P1 = 0. Since V _P1 = 0, the fundamental current does not flow through the reactor 2 and only the withstand amount of the harmonic current can be achieved.

[0015] For example, 105V to line voltage E, when the capacitor installed capacity Q and Q = 10Kvar (L = 4.2% ), in the conventional 2, current i _c1 flowing to the capacitor is represented by the following formula .

[0016]

(Equation 4) Assuming that the fifth harmonic is about 20% of the fundamental wave ( _ic5 = 20A),
The reactor capacity will be about 0.531 Kvar. This is 2
Total reactor capacity is 0.531 × 2 = 1.0
62 Kvar.

On the other hand, in FIG. 1 of the present invention,
Assuming a case where the fifth harmonic has an opposite phase, under the same conditions as in FIG.

(Equation 5) As compared with the conventional case, the withstand amount is only required to be about １ ／ of the capacity.

Even if the AC filter capacitors 3a and 3b of the two circuits do not have the same capacitance, the fundamental wave current flowing through the resonance reactor 2 is i _c1 = i _A1 -i _B1 , and the resonance of the capacitors 3a and 3b It becomes smaller than i _A1 + i _B1 of the fundamental wave current of the reactors 2a and 2b.

[0019]

As described above, according to the present invention, since the resonance filter of the harmonic filter is shared by two circuits, the fundamental wave component is not applied to the resonance reactor, and the amplitude of the harmonic wave is reduced. Therefore, it is possible to reduce the size of the device configuration and reduce the cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional configuration.

[Explanation of symbols]

1 transformer, 2 resonance reactor, 3a, 3b capacitor, 4a, 4b harmonic current source

Continuation of the front page (72) Inventor Hiroyuki Hiraishi 95-353 Kawazu, Iizuka-shi, Fukuoka Dentsu Management Co., Ltd. (56) References JP-A-54-75546 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02H 3/00-5/00

Claims (1)

(57) [Claims] 1. A filter device in which two single-phase AC filters are provided in a secondary circuit of a transformer having a single-phase three-wire circuit. A filter device comprising: a resonance reactor shared by two circuits of a phase AC filter; and respective capacitors forming two single-phase AC filters are connected to the resonance reactor.