JP3293277B2 - Active 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 an active filter device for compensating a zero-phase harmonic component flowing through a neutral line of a three-phase four-wire system.

[0002]

For powering the Related Art load, sometimes three-phase four-wire distribution line such as shown in FIG. 4 is employed. In this case, the load is a personal computer, television, OA
(Office Automation) If the harmonics of equipment are easily generated, even if the load of each phase is balanced, the zero-phase harmonic component current generated from the load will be generated in the three-phase four-wire supply transformer. A large amount of current flows over the sex wire N beyond the rating of the wire.

Conventionally, in order to compensate for harmonic components flowing through the neutral line N, an active filter is connected to each of the lines A, B, C
And the neutral line N. In this active filter, as shown in FIG. 5, the primary side of a three-phase insulating transformer is connected to each line A, B, C and the neutral line N, and the secondary side of the transformer is connected to a single-phase inverter. it intended, harmonic current i _lA flowing through the load, i _lB, by high-speed current control single-phase inverter are detected by i _lC a current transformer CT and a band-pass filter BPF, the system current i _SA, i _SB ,
Compensation currents i _Af , i having magnitude equal to i _SC and opposite phase
_Bf, generates a i _Cf, is to suppress harmonic current i _lA, i _lB, the i _lC.

[0004]

According to the configuration of the active filter, since three single-phase inverters are required, the configuration becomes large. In addition, since the fundamental wave voltage is applied to the transformer and the single-phase inverter, their capacities must be made larger than those required for compensation, and the operating loss increases.

Therefore, even if there is a demand to reduce the cable capacity of the neutral wire N and to distribute the active filters near the load, the demand cannot be met because the active filter itself cannot be made compact and lightweight. There is a problem. Therefore, an object of the present invention is to solve the above-mentioned technical problems, and to provide a compact and lightweight active filter device which requires a smaller number of single-phase inverters and a smaller capacity of a transformer.

[0006]

According to a first aspect of the present invention, there is provided an active filter device comprising a three-phase four-wire system having a Δ connection on a secondary side and a Y connection with a neutral point on a primary side. A transformer is prepared, the primary Y-connection of the transformer is connected to each of the three phases, and a single-phase inverter is connected to the zero-phase circuit of the transformer to detect the zero-phase component of the load current. Times to do
Path and a predetermined harmonic current from the detected zero-sequence component.
Outflow circuit, and flows from the neutral point on the primary side of the transformer to the neutral line
A circuit for extracting a predetermined harmonic current;
The harmonic current flowing from the primary neutral point of the
The harmonic current extracted from the zero-phase component of the load current is opposite
A control signal is supplied to the single-phase inverter so as to be in a phase, and a compensation current flows from the single-phase inverter to a three-phase four-wire circuit.

[0007]

According to the active filter device, a predetermined harmonic component of the load current is detected, and the harmonic component is supplied to the single-phase inverter as a control current. And
A compensation current can be injected from the single-phase inverter through the zero-phase circuit of the transformer.

In the active filter device, since a single-phase inverter is connected to the zero-phase circuit of the transformer, no fundamental wave voltage is applied to the single-phase inverter. Therefore, the capacity of the single-phase inverter can be reduced to the minimum necessary for compensation, and the size of the single-phase inverter and the transformer can be reduced.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 shows an active filter device according to the present invention.
1 is a diagram showing a configuration applied to a phase four-wire distribution line, in which an active filter device 1 has a three-phase four-wire filter transformer having a Δ connection on a secondary side and a Y connection with a neutral point on a primary side. T _rh
The provided is connected with its primary neutral point N _F, the single-phase inverter 11 between the neutral line N. The active filter device 1 further includes a pulse circuit 12 for controlling the single-phase inverter 11 and a band-pass filter 13 for extracting the third harmonic component of the current flowing from the single-phase inverter 11 to the neutral line N.

On the other hand, each phase current flowing to the load is
T is detected by T, mixed by the mixing circuit 2 and passed through the band-pass filter 3, so that only the third-order zero-phase harmonic component is input to the active filter device 1 as the command current i _0ref . With the active filter device 1 described above, when the third harmonic component of the load current is detected,
The pulse circuit 12 outputs a control PWM pulse signal to the single-phase inverter 11 so that the current flowing from the single-phase inverter 11 to the neutral _conductor N and the command current i _0ref have exactly opposite phases. Therefore, harmonic components flowing through the neutral line N can be compensated.

[0011] The primary side neutral point N _F, because only occur zero-phase component, the fundamental wave positive phase voltage of the single-phase inverter 1
Do not participate in 1. Therefore, the single-phase inverter 11 needs to generate only the harmonic voltage, and thereby the capacity of the single-phase inverter 11 can be significantly reduced.
Further, since only the harmonic component of a predetermined order of the transformer T _rh needs to flow, the transformer T _rh can be reduced.

From the above, it is possible to realize a small and efficient active filter device which can sufficiently compensate for harmonics generated from a load. The present invention is not limited to the above embodiments, for example, as shown in FIG. 2, the primary-side neutral point N _F of the transformer T _rh and connected to the neutral line N, 2 primary Δ A part of the connection may be opened, and the single-phase inverter 11a may be arranged there. Even in this case, since only the zero-phase component is added to the single-phase inverter 11a, the active filter device 1a that compensates for the zero-phase harmonic component can be realized.

Further, when there are a plurality of harmonic orders to be compensated, as shown in FIG. 3, the number of filters 3a-3c for limiting the band of the zero-phase current flowing through the load is changed to the harmonic order (3rd order, 3rd order). Nineth and fifteenth orders) may be provided. Thereby, each harmonic component generated from the load becomes 3
It is possible to simultaneously prevent a large amount of current from flowing into the neutral line N of the phase 4 wire supply transformer.

[0014]

As described above, according to the active filter device of the present invention, the single-phase inverter can be arranged in the circuit to which the fundamental wave voltage is not applied, so that the capacity of the single-phase inverter can be greatly reduced. Can be. Further, since only the harmonic component of a predetermined order of the transformer needs to flow, the transformer can be reduced in size.

Therefore, it is possible to realize an active filter device capable of sufficiently compensating for the harmonic components even if the capacitance is small in a wiring in which the harmonic components are significantly increased in the neutral line. Also, only one single-phase inverter is required,
Since the whole can be made compact, the overload of the neutral cable can be economically implemented by distributing the active filter devices close to the load.

[Brief description of the drawings]

FIG. 1 is a circuit diagram in which an active filter device is applied to a three-phase four-wire type distribution line.

[2] The primary neutral point N _F of the transformer T _rh and connected to the neutral line N, a circuit diagram showing a modification example in which the single-phase inverters on the secondary side Δ connection.

FIG. 3 is a diagram showing a modified example in which, when there are a plurality of harmonic orders to be compensated, a plurality of filters for limiting the band of the zero-phase current flowing through the load are provided in accordance with the harmonic order.

FIG. 4 is a circuit diagram of a three-phase four-wire distribution line to which a load is connected.

FIG. 5 shows a diagram for compensating harmonic components flowing through the neutral line N.
FIG. 9 is a circuit diagram showing a conventional countermeasure in which a single-phase inverter is arranged between each of the lines A, B, C and the neutral line N.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 active filter device 2 mixing circuit 3 band-pass filter 11 single-phase inverter 12 pulse circuit 13 band-pass filter CT current transformer N neutral line N _F primary-side neutral point _Thr filter transformer

Claims (3)

(57) [Claims] 1. An active filter device for compensating a zero-phase harmonic component flowing through a neutral line of a three-phase four-wire circuit, comprising a Δ connection on the secondary side and a neutral point Y on the primary side. 3 with connections
Providing a phase 4-wire transformer with connecting the primary side Y connection of the transformer to each phase of the three-phase, connect the single-phase inverter in zero-phase circuit of the transformer, the zero-phase load current A circuit for detecting the component and the detected zero phase
A circuit for extracting a predetermined harmonic current from the components and a transformer
The specified harmonic current flowing from the primary neutral point to the neutral
And a harmonic circuit that flows from the neutral point on the primary side of the transformer to the neutral line.
Current and harmonics extracted from the zero-phase component of the load current
An active filter device , wherein a control signal is supplied to the single-phase inverter so that the current has a reverse phase, and a compensation current flows from the single-phase inverter to a three-phase four-wire circuit. 2. The active filter device according to claim 1, wherein the zero-phase circuit of the transformer to which the single-phase inverter is connected is between a neutral point on the primary side of the transformer and the neutral line. 3. The active filter device according to claim 1, wherein the zero-phase circuit of the transformer to which the single-phase inverter is connected is an open end when a part of the secondary Δ connection of the transformer is opened.