JPH0257374B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the removal of harmonic noise of commercial power frequencies.

[Prior art and its problems]

To give an example of conventional information transmission using a transmission line that has many harmonics of the commercial power frequency, when a signal is extracted from the transmission line, there are many harmonics of the commercial power frequency, so the signal-to-noise ratio (hereinafter referred to as S/ Because of the need to increase N (referred to as N), good information transmission was not possible unless a signal with a considerably higher level than the noise was transmitted.

Therefore, large transmission power was required. Also,
In some cases, the measurement equipment and other equipment had problems due to harmonic noise interference.

[Problem that the invention seeks to solve]

The present invention improves these conventional problems and
The purpose of this invention is to reduce the power consumption of information transmission equipment that uses a transmission line with many harmonics of the commercial power frequency, or to reduce harmonic noise interference to equipment such as measuring equipment.

[Means for solving problems]

In information transmission using a transmission line with many harmonics of the commercial power frequency, the present invention eliminates harmonics of the commercial power frequency by subtracting an input signal from a signal that is synchronized with the frequency of the commercial power and delayed by one cycle. This is a commercial power frequency harmonic removal filter characterized by a configuration that removes.

To explain more specifically, the present invention converts signals extracted from a number of transmission lines containing many harmonics of the commercial power frequency to one part of the commercial power frequency using a shift register or random access memory (hereinafter referred to as a delay element). This device removes harmonics of commercial power by subtracting a second-delayed signal and a non-delayed signal.

Harmonic noise of commercial power is periodic noise that repeats periodically at the commercial frequency. Let x(t) be the harmonic noise of the commercial frequency f ₀ . Also, from this n/
f ₀ =nτ ₀ The following relationship with delayed harmonic noise x(t+nτ ₀ ) is obtained.

x(t)=x(t+nτ ₀ )n=1, 2,...n
...Formula (1) If the delay time of the delay element is τ ₀ , the output of this filter can be expressed as follows.

Y(t)=y(t)−y(t+τ ₀ ) …(2) From equations (1) and (2), Y(t)=x(t)−x(t+τ ₀ )……(3 ) formula This shows that harmonic noise of commercial frequencies can be completely removed. However, commercial frequencies vary, and so do their harmonics. Therefore,
The device has a circuit that synchronizes the delay element with the commercial frequency.

Note that in the case of half-cycle addition, odd harmonics decrease, but even harmonics increase. However, there are many cases where the odd-order harmonics are much larger than the even-order harmonics, and in such cases, the half-cycle addition method is effective.

〔Example〕

Hereinafter, the present invention will be explained based on examples.

FIG. 1 shows one embodiment of the present invention. Explaining based on this example, 1 is a high pass filter, 2 is a delay element, 3 is a zero cross detector, 4 is a high pass filter, 2 is a delay element, 3 is a zero cross detector,
is a clock generator, and 5 is an adder.

In FIG. 1, when a commercial frequency as shown in FIG. 2a is input to point A, the zero-cross detector 3 obtains a rectangular wave (see FIG. 2b) synchronized with the commercial frequency. This square wave is passed to the clock generator 4.
The delay element 2 generates a clock f _c for obtaining a delay of the reciprocal of the commercial frequency. Due to this clock f _c , the delay element 2 obtains a delay characteristic synchronized with the commercial power frequency.

At point B, a signal S ₁ (see FIG. 2c) is obtained from which the commercial frequency has been removed by a high-pass filter.
At point C, the signal S ₁ obtained at point B is subtracted from the signal S ₂ delayed by the reciprocal of the commercial frequency by the delay element. As a result, at point D, a signal _S0 (see FIG. 2d) from which harmonic noise of commercial power has been removed is obtained.

FIG. 3 shows the frequency response of the device described above. Further, FIG. 4a shows the spectrum of harmonics of the commercial frequency, and FIG. 4b shows the output spectrum when this is input to the filter of this embodiment.

As shown in this spectrum, it has become possible to achieve an S/N improvement of 20 dB or more.

〔Effect of the invention〕

As described above, according to the present invention, efficient information transmission can be achieved by removing harmonics of the commercial power frequency.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention;
Figure 2 shows the waveform diagram of each part, Figure 3 shows its frequency response, Figure 4 a shows the harmonic spectrum of the commercial frequency, and b shows the output spectrum when it is input to the filter of the present invention. It shows. 1: High pass filter, 2: Delay element, 3: Zero cross detector, 4: Clock generator, 5: Adder.

Claims (1)

[Claims] 1. In a transmission line or equipment that is subject to interference by harmonics of the commercial power frequency, harmonics of the commercial power frequency are detected by subtracting or adding the input signal and a signal that is synchronized with the commercial power frequency and delayed by one cycle or half a cycle. A commercial power frequency harmonic removal filter characterized by a configuration that removes.