JPH10136639A - Filter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter circuit whose input voltage frequency gain is hardly changed by a frequency by a method, wherein a parallel circuit consisting of a low-pass filter and a band-pass filter which are connected in parallel to each other is provided in the filter circuit. SOLUTION: A parallel circuit 3, consisting of a low-pass filter 1 and a band-pass filter 2 which are connected in parallel to each other, is provided in a filter circuit, and an attenuation circuit 4 is connected to the input part of the band-pass filter 2 of the parallel circuit 3. If the frequency of a voltage inputted to the filter circuit is larger than 60Hz which is a reference frequency, the voltage is outputted with an advanced phase and, if the frequency of the input voltage is smaller than 60Hz which is a reference frequency, the voltage is outputted with a delayed phase. With this constitution, even if the frequency of the input voltage is around the reference frequency, the gain of the input voltage frequency is hardly change by the frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter circuit in which an input AC voltage signal is output with its phase changed.

[0002]

2. Description of the Related Art Conventionally, as this kind of filter circuit, there is one disclosed in Japanese Patent Application Laid-Open No. Hei 7-131937.
In this filter, as shown in FIG. 7, two bandpass filters A and B are connected in parallel, and the phase of an input AC voltage signal can be delayed when its frequency is higher than the fundamental frequency. When the frequency is smaller than the fundamental frequency, the phase is advanced and output.

[0003]

In the above-mentioned conventional filter circuit, as shown in FIG. 8, the gain of the input voltage frequency largely changes depending on the frequency around 50 Hz which is the reference frequency. There was a problem.

The present invention has been made in view of the above points, and an object of the present invention is to provide a filter circuit in which the gain of the input voltage frequency is hard to change with frequency.

[0005]

According to a first aspect of the present invention, when an input AC voltage signal has a frequency greater than a fundamental frequency, the AC voltage signal is output with its phase advanced. When the frequency is lower than the fundamental frequency, the filter circuit that outputs a signal with a delayed phase has a parallel circuit in which a low-pass filter and a band-pass filter are connected in parallel.

According to a second aspect of the present invention, in the first aspect, an amplifier circuit is connected in series to an input section of the low-pass filter.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 2, the filter circuit 10 is connected to a power transmission system 40 having a connection point 40a capable of transmitting power from the first and second AC power supplies 20 and 30.
By comparing the frequency of the voltage at 40a with the reference frequency, it is detected that power transmission from the first AC power supply 20 has stopped and only the second AC power supply 30 is operating alone,
This is used for an islanding prevention device 50 that stops power transmission from the second AC power supply 30. The power transmission system 40 and the islanding prevention device 50 will be described later in detail.

As shown in FIG. 1, the filter circuit 10 comprises a parallel circuit 3 in which a low-pass filter 1 and a band-pass filter 2 are connected in parallel, and an attenuator 4 connected in series to an input section of the band-pass filter 2. .

As shown in FIG. 3, when the frequency of the input voltage to the filter circuit 10 is higher than the reference frequency of 60 Hz, the filter circuit 10 outputs a signal with an advanced phase, and the frequency of the input voltage is When the frequency is lower than the reference frequency of 60 Hz, the phase is delayed and output. Further, in the filter circuit 10, the gain of the input voltage frequency, which is one of the frequency characteristics, does not vary so much with frequency as in the conventional example, as shown in FIG.

Next, the power transmission system 40 will be described.
The power transmission system 40 includes a first AC power supply which is a commercial power supply.
20 and a second AC power supply 30 comprising a solar cell 30a and an inverter circuit 30b. This second AC power supply 30
Indicates that the direct current generated by the solar cell 30a is an inverter circuit.
It is converted to AC via 30b and fed later.

Next, the islanding prevention device 50 will be described. The isolated operation prevention device 50 includes a filter circuit 10, a system interconnection protection unit 50a, and an inverter control unit 50b. When the frequency of the input voltage to the filter circuit 10 deviates from the reference frequency of 60 Hz due to only the second AC power supply 30 operating alone, the phase is changed by passing through the filter circuit 10. be changed. The input voltage whose phase has been changed is passed through the inverter control unit 50b so that the AC voltage is supplied from the inverter circuit 30b with the phase changed by passing through the filter circuit 10. Will be returned to

Thus, the input voltage whose phase has been changed is
With the feedback to the inverter circuit 30b via the inverter control unit 50b, the frequency shifts toward either plus or minus and diverges as shown in FIG. Can be detected.
When the isolated operation is detected in this way, the grid connection protection unit 50a stops the power supply from the second AC power supply 30.

In such a filter circuit 10, since the low-pass filter 1 and the band-pass filter 2 are composed of the parallel circuit 3 connected in parallel, the gain of the input voltage frequency becomes larger before and after the reference frequency as in the conventional example. No longer changes with frequency.

Further, since the low-pass filter 1 and the band-pass filter 2 comprise a parallel circuit 3 connected in parallel,
DC signals can also be passed.

Next, a second embodiment of the present invention will be described with reference to FIG. The components having substantially the same functions as those of the first embodiment are denoted by the same reference numerals, and only the differences from the first embodiment will be described. In the first embodiment, the attenuator 4 connected in series to the input of the bandpass filter 2 is provided, whereas in the present embodiment, the amplifier 5 connected in series to the input of the lowpass filter 1 The configuration is provided.

In such a filter circuit, in addition to the effects of the first embodiment, the amplifier circuit 5 can be configured more easily than the attenuation circuit 4 by a combination of an operational amplifier and a resistor. The manufacturing is easier than in the first embodiment in which the attenuation circuit 4 connected in series to the input unit 2 is provided.

[0018]

Since the low-pass filter 1 and the band-pass filter 2 comprise the parallel circuit 3 in which the low-pass filter 1 and the band-pass filter 2 are connected in parallel, the gain of the input voltage frequency is higher or lower than the reference frequency. Does not change with frequency.

According to a second aspect of the present invention, in addition to the effect of the first aspect, the amplifier circuit can be configured more easily than the attenuation circuit by the combination of the operational amplifier and the resistor. It is easier to manufacture than the one having a damping circuit connected in series to the input section.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a power transmission system using the above.

FIG. 3 is an explanatory diagram of a relationship between an input voltage frequency and a phase of the above.

FIG. 4 is an explanatory diagram of a relationship between an input voltage frequency and a gain of the above.

FIG. 5 is an explanatory diagram showing a change in frequency of a voltage when the power transmission system using the above device is operated independently.

FIG. 6 is a configuration diagram of a second embodiment of the present invention.

FIG. 7 is a configuration diagram of a power transmission system using a conventional example.

FIG. 8 is an explanatory diagram of a relationship between an input voltage frequency and a gain of the above.

[Explanation of symbols]

 1 Low pass filter 2 Band pass filter 3 Parallel circuit 4 Attenuation circuit 5 Amplification circuit

Claims (2)

[Claims] 1. A filter circuit for outputting an input AC voltage signal with an advanced phase when its frequency is higher than a fundamental frequency, and a delayed output when the frequency is lower than the fundamental frequency, A filter circuit comprising a parallel circuit in which a low-pass filter and a band-pass filter are connected in parallel. 2. The filter circuit according to claim 1, wherein an amplifier circuit is connected in series to an input section of said low-pass filter.