JP3582260B2 - Filter circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a filter circuit that outputs an input AC voltage signal with its phase changed.
[0002]
[Prior art]
Conventionally, as this type of filter circuit, there is one disclosed in Japanese Patent Application Laid-Open No. 7-131937. In this device, as shown in FIG. 7, two band-pass 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 lower than the fundamental frequency, the output is advanced in phase.
[0003]
[Problems to be solved by the invention]
In the above-described conventional filter circuit, as shown in FIG. 8, there is a problem that the gain of the input voltage frequency largely changes depending on the frequency around 50 Hz which is the reference frequency.
[0004]
SUMMARY OF THE INVENTION 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]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 outputs an input AC voltage signal by advancing the phase when the frequency is higher than the fundamental frequency, and outputs the AC voltage signal when the frequency is lower than the fundamental frequency. In a filter circuit that outputs a signal with a delayed phase, the filter circuit has a parallel circuit in which a low-pass filter and a band-pass filter are connected in parallel, and the parallel circuit converts an input AC voltage signal based on the frequency. When the frequency is higher than the frequency, the phase is advanced and output.When the frequency is lower than the fundamental frequency, the phase is delayed and output, and the gain of the input voltage frequency around the fundamental frequency is not largely changed by the frequency. It is characterized by.
[0006]
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]
BEST MODE FOR CARRYING OUT THE INVENTION
A first embodiment of the present invention will be described below with reference to FIGS.
[0008]
As shown in FIG. 2, the filter circuit 10 includes a power transmission system 40 having a connection point 40a that can be transmitted from the first and second AC power supplies 20 and 30. Based on the comparison with the reference frequency, it is detected that the power transmission from the first AC power supply 20 is stopped and only the second AC power supply 30 is operating alone, and the power transmission from the second AC power supply 30 is stopped. This is used for the islanding prevention device 50 to be operated. The power transmission system 40 and the islanding prevention device 50 will be described later in detail.
[0009]
As shown in FIG. 1, the filter circuit 10 includes a parallel circuit 3 in which a low-pass filter 1 and a band-pass filter 2 are connected in parallel, and an attenuation circuit 4 in series with an input section of the band-pass filter 2.
[0010]
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 advances the phase and outputs the same. When it is lower than a certain 60 Hz, the phase is delayed and output. Further, in the filter circuit 10, as shown in FIG. 4, the gain of the input voltage frequency, which is one of the frequency characteristics, does not greatly change depending on the frequency as in the conventional example.
[0011]
Next, the power transmission system 40 will be described. The power transmission system 40 has a first AC power supply 20 which is a commercial power supply, and a second AC power supply 30 including a solar cell 30a and an inverter circuit 30b. The second AC power supply 30 is supplied with power after the DC generated by the solar cell 30a is converted into AC via the inverter circuit 30b.
[0012]
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 because only the second AC power supply 30 operates alone, the phase of the input voltage is reduced by passing the filter circuit 10. be changed. The input voltage whose phase has been changed is supplied to the inverter circuit 30b via 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.
[0013]
The frequency of the input voltage whose phase has been changed is shifted toward either plus or minus as shown in FIG. 5 as the input voltage is fed back to the inverter circuit 30b via the inverter control unit 50b. Then, the vehicle diverges and islanding can be detected. Then, when the isolated operation is detected in this way, the system interconnection protection unit 50a stops the power supply from the second AC power supply 30.
[0014]
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 changes before and after the reference frequency as in the conventional example. No longer.
[0015]
Further, since the low-pass filter 1 and the band-pass filter 2 are composed of the parallel circuit 3 connected in parallel, a DC signal can be passed.
[0016]
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 band-pass filter 2 is provided, whereas in the present embodiment, the amplifier 5 connected in series to the input of the low-pass filter 1 is provided. The configuration is provided.
[0017]
In such a filter circuit, in addition to the effect 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 damping circuit 4 connected in series to the section is provided.
[0018]
【The invention's effect】
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 varies depending on the frequency even before and after the reference frequency. Disappears.
[0019]
According to the invention of claim 2, in addition to the effect of the invention of claim 1, 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 one having an attenuation circuit connected in series to
[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 system.
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 a 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]
DESCRIPTION OF SYMBOLS 1 Low-pass filter 2 Band-pass filter 3 Parallel circuit 4 Attenuation circuit 5 Amplification circuit

Claims (2)

A filter circuit that outputs an input AC voltage signal with its phase advanced when its frequency is larger than the fundamental frequency and with its phase delayed when the frequency is smaller than the fundamental frequency,
The filter circuit has a parallel circuit in which a low-pass filter and a band-pass filter are connected in parallel,
When the frequency is higher than the basic frequency, the parallel circuit outputs the input AC voltage signal with the phase advanced, and when the frequency is lower than the basic frequency, the phase is delayed and output. Wherein the gain of the input voltage frequency does not change significantly with frequency . 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.

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