JPH0711544B2 - Electronic phase shift circuit and electronic reactive energy meter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic phase shift circuit for shifting the phase of an input signal by a digital operation method, and an electronic phase shift circuit for measuring the reactive power of the input signal by applying the electronic phase shift circuit. The present invention relates to a reactive watt hour meter.

[0002]

2. Description of the Related Art Reactive watt-hour meters usually take the form of determining the amount of reactive power by taking the product of voltage and current signals that are 90 degrees out of phase with each other. Conventionally, a transformer is used as a phase shift circuit that is mainly used for 90-degree phase shift in this type of reactive energy meter (hereinafter, referred to as a transformer type phase shift circuit for convenience), There are known ones using an integrating circuit of an operational amplifier (hereinafter, referred to as an integral phase shift circuit for convenience), electronic ones using a digital operation method (hereinafter referred to as an electronic phase shift circuit for convenience), and the like. ing. These principles are as follows.

First, the transformer type phase shift circuit is used particularly in a three-phase three-wire type power feeding line. One voltage signal of one phase and another voltage signal of one phase are used. It is possible to realize the generation of a signal that is phase-shifted by 90 degrees by vector composition with a signal that is half the scalar of.

Further, the integral type phase shift circuit shifts the phase of the voltage signal by 90 degrees by utilizing the time constant of the integrating circuit provided as the feedback circuit of the operational amplifier.

Further, the electronic phase shift circuit is provided with a phase locked loop (PLL) circuit, and the sampling period of an analog-to-digital converter (hereinafter referred to as A / D converter) is determined by this PLL circuit. Of the load voltage and load current in proportion to the current signal, set the sampling period so that the phase difference of the sample interval is 90 degrees, and set the phase difference of 90 degrees. An analog signal whose phase is shifted by 90 degrees from the input signal is reproduced based on the sample value.

[0006]

However, the above-mentioned various phase shift circuits have their own problems, and it is difficult to say that all of them are sufficient.

That is, since the transformer type phase shift circuit utilizes the phase relation of the voltage signal of the power feeding line, the method of the power feeding line is limited to the three-phase three-wire type.

Further, it is necessary that each phase of the voltage is always in a balanced state. Actually, the amplitude, phase relationship, etc. change depending on the usage environment, and there are few stable power supply facilities so that these are always kept constant. Therefore, also from this point of view, it can be said that the transformer type phase shift circuit is poor in versatility.

Further, since this transformer type phase shift circuit uses a transformer, there is a problem that the characteristics change greatly due to the frequency change of the power feeding line and it is difficult to use in a wide band.

Next, although the integral type phase shift circuit is superior to the former in that it can be used regardless of the type of power feeding line, it has a frequency characteristic in which the ratio of the input voltage to the output voltage changes depending on the frequency. Therefore, it is necessary to compensate the frequency characteristic by some method, which causes a problem that the circuit becomes complicated.

In the electronic phase shift circuit, the sampling interval is frequency-synchronized with the load voltage and the load current of the power feeding line. Therefore, when the input signal is considered in units of one cycle, The A / D converter will always convert the same point of the input signal. Therefore, sufficient performance cannot be obtained unless the sample interval is made sufficiently smaller than the period of the input signal. This means that the higher the frequency of the object, the more difficult the performance will be.

[0012] Here, the problem in the transformer type or integral type phase shift circuit is not pointed out in the electronic type phase shift circuit, and if the above-mentioned sampling problem is solved, digital technology in recent years It is possible to realize a high-performance phase shift circuit that matches the orientation.

Therefore, the present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide an electronic phase shift circuit capable of improving the performance independently of the size of the sample interval. An object is to provide an electronic reactive watt-hour meter to which the same phase shift circuit is applied.

[0014]

SUMMARY OF THE INVENTION An electronic phase shift circuit according to the present invention comprises an analog-digital conversion means for sampling an analog input signal and converting it into a digital signal consisting of a plurality of sample values, and a plurality of the sample values. Time to specify this zero-cross point based on the sample values before and after the zero-cross point in the area that maintains the linearity within the allowable error range of the input signal and calculate the time interval between the specific zero-cross points Based on the interval calculation means and the ratio of the time interval between the specific zero-cross points and the phase shift amount, the phase shift amount is deviated from each of the predetermined number of sample points included in the plurality of sample points in the input signal. And a level calculating means for calculating a level value of the phase shift point from sample values before and after the time is calculated.

The electronic reactive watt hour meter of the present invention comprises an analog-digital conversion means for sampling an analog input voltage signal and the same current signal and converting them into a digital signal consisting of a plurality of sample values, and the input voltage signal and the above-mentioned input voltage signal. Based on the sample values before and after the zero crossing point of the area that maintains the linearity within the allowable error range of the one input signal among the plurality of sample values of the one input signal of the same current signal, A time interval calculating means for specifying a cross point and obtaining a time interval between the specific zero cross points, and the one input signal based on the ratio of the time interval between the specific zero cross points and the phase shift angle of 90 degrees. Of the sample points included in the plurality of sample points in FIG. Level calculation means for obtaining the level value of the phase shift point from the value, sample values of points corresponding to the predetermined number of sample points among the plurality of sample values of the other input signal, and output values of the level calculation means And multiplying means for converting into a power value by multiplying by.

[0016]

According to the present invention, since it is possible to obtain a level other than the sampling point by digital operation, it is not necessary to sample the same point in one cycle waveform of the analog input signal at all times, and the sampling point is synchronized with the analog input signal. Since the sampling can be performed asynchronously with the analog input signal and the sampling points can be shifted every cycle to trace the waveform evenly, it is possible to improve the performance separately from the size of the sampling interval by the filter effect.
Therefore, it is not essential to make the sample interval sufficiently smaller than the cycle of the input signal, and sufficient performance can be obtained even when the target has a high frequency.

Further, in the reactive energy meter of the present invention, if all the processes after the A / D conversion are realized by software such as a microprocessor, the same circuit as the active energy meter based on the digital operation formula is added without adding a special circuit. Can be achieved with.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

First, the principle of the present invention will be described with reference to FIGS.

FIG. 3 shows the sampling of only one phase of the three-phase AC voltage signal.

In this figure, is the voltage signal, t is its time axis, and T is the period. A broken line extending from the time axis t to the waveform indicates a sampling point, and T
s is the sample period.

Further, Sm-1, Sm, Sm + 1, ...
, Sn-1, Sn, Sn + 1 are digital voltage signals obtained by A / D converting the voltage signal proportional to the instantaneous value of the load voltage of the power feeding line.
m is a digital voltage signal consisting of sample values of the sampling point located immediately after one zero cross point O1 of the voltage signal, and Sn is also one of the plurality of sampling points, and one zero of the voltage signal A digital voltage signal composed of sample values at the sampling point located immediately before the cross point O3.

Further, referring to FIG. 4 and FIG. 5, the period T of the voltage signal is the sampling period Ts, the zero cross points O1 and O3 before and after one period, and the sampling points Sm,
When the time to Sn is Td1 and Td2 (see FIG. 4 for Td1 and FIG. 5 for Td2), the cycle T is T = Td1 + (n−m) Ts + Td2.
It can be expressed as (1).

Here, if the sampling period Ts is sufficiently small, the digital voltage signals Sm-1 and Sm and Sn and Sn are obtained.
The change in slope of the voltage signal during +1 is very small and can be regarded as a straight line. As a result, Td1 and Td2
Is Td1 = | Sm | .Ts from the condition of triangle similarity.
/ (| Sm-1 | + | Sm |) (2) Td
2 = | Sn | .Ts / (| Sn | + | Sn + 1 |)
It can be expressed as (3). Therefore, the period T of the voltage signal is T = (| Sm | / (| Sm-1 | + |
Sm |) + n-m + | Sn | / (| Sn | + | Sn + 1
|)) · Ts (4), and the sampling value Tm before and after the sampling period Ts and the zero-cross point Sm−1,
It can be obtained from Sm, Sn, Sn + 1. Here, | Sm-1 |, | Sm |, | Sn |, | Sn + 1 |
Is the absolute value of Sm-1, Sm, Sn, Sn + 1.

By thus obtaining the period T of the voltage signal, the time corresponding to an arbitrary phase shift angle can be obtained.

Here, let us consider the time corresponding to 90 degrees which is important for the reactive energy meter as the phase shift angle. 1 cycle is 3
Since it is 60 degrees, the time T90 corresponding to 90 degrees
Is T90 = T / 4 = k · Ts + Tx
It can be expressed as (5). Here, k is the number of sample periods included in the time corresponding to the phase shift angle (90 degrees in this case), and Tx is the difference between T90 and k sample periods.

Similar to the method for obtaining the period, if the sampling period Ts is sufficiently small, the digital voltage signals Sy-k, Sy-k-1 and Sy before and after the time corresponding to 90 degrees are obtained.
The change in slope of the voltage signal between + k and Sy + k + 1 is very small and can be regarded as a straight line. This allows
Sx is Sx = S from the conditions of similarity of triangles.
y−k− (Tx / Ts) · (Sy−k −Sy−k−
1) (6) Sx = Sy + k- (Tx / Ts)
(Sy + k-Sy + k + 1) (7),
The instantaneous reactive power can be obtained by multiplying the current signal sampled at the same time as Sy by the voltage signal Sx obtained by the calculation, and the reactive power is integrated by accumulating the instantaneous power obtained by sequentially repeating these processes. The amount of electric power can be obtained.

Although a phase shift of 90 degrees is considered here as an example, the phase shift is not limited to this, and phase shifts of various arbitrary angles can be realized according to the above principle.

Therefore, generalizing the equation (5), the time T _ω corresponding to the phase shift angle ω [degree (deg)] is
Tω = T · (ω / 360) = k · Ts + Tx
(5) '.

Next, FIG. 1 shows the configuration of an electronic phase shift circuit utilizing the phase shift principle according to the present invention.

In this figure, 1 is a sample period controller and 2 is an A / D converter, which constitute means for sampling an analog input signal and converting it into a digital signal consisting of a plurality of sample values. It is a thing. The sample period controller 1 outputs a timing clock that determines the sample period Ts. The A / D converter 2 is triggered by this timing clock and holds the level of the analog input voltage signal at that time as a sample value.

Reference numeral 3 is a zero-cross detector, 4 is a period calculator, and these are allowable error ranges in the input voltage signal among a plurality of sample values (that is, the allowable error range in the calculation using the above-mentioned similarity relation). ), The zero cross points are specified based on sample values before and after the zero cross points in the region where the linearity is maintained, and a calculation means for obtaining the time interval between the specific zero cross points is configured. That is,
The zero-crossing detector 3 captures the presence of a zero-crossing point by changing the sign of the output value of the A / D converter 2, and further,
The time corresponding to Td1 and Td2 is expressed by the above equation (2),
It is obtained by performing the calculation of (3) and given to the period calculator 4. When the period calculator 4 receives the Td1 and Td2, the period calculator 4 calculates the above formula () based on the sample period data Ts provided from the sample period controller 1 in parallel and the number of samples included between the zero cross points. The period T is obtained by performing the calculation represented by 1).

Reference numeral 5 is a data memory, 6 is an arbitrary phase data calculator, and these are a plurality of samples in the input voltage signal based on the ratio when the time interval between specific zero-cross points and the phase shift amount are compared. A level calculating means for obtaining a level value of a point deviated by the phase shift amount from each of a predetermined number of sample points included in the point is configured. A / D converter 2
The output data of 1 are all stored in the data memory 5. The arbitrary phase data calculator 6 first solves the above equation (5) ′ for Tx based on the data of the period T from the period calculator 4 and the data of ω given in advance, and then the equation (6) Alternatively, Sx is obtained by performing the operation represented by (7).

Sx obtained by the arbitrary phase data calculator 6 is sequentially digital-analog converted (hereinafter referred to as D /
It is called A conversion. ) Is given to device 7. The D / A converter 7 reproduces an analog signal having a level (that is, Sx) at a point shifted from the input signal by a predetermined phase angle ω in synchronization with the timing clock supplied from the sample period controller 1. . As a result, an analog signal obtained by phase-shifting the input signal by the angle ω is obtained from the D / A converter 7.

Since the sample value utilization method as described above is used, it is not necessary to always sample the same point in one cycle waveform of the analog input signal, and it is not necessary to synchronize the sample point with the analog input signal. Since it is possible to perform sampling in which the waveform is evenly traced by making the sampling point asynchronous with the signal in every cycle, the filter effect can improve the performance separately from the size of the sampling interval. Therefore, it is not necessary to take the sample interval sufficiently smaller than the cycle of the input signal,
Sufficient performance can be obtained even when the target has a high frequency.

FIG. 2 shows an embodiment of the reactive energy meter of the present invention which is an application example of the phase shift circuit shown in FIG. 1. The elements corresponding to the constituent elements of the phase shift circuit shown in FIG. It is attached with a code.

In this figure, an instrument transformer 8 is for converting the load voltage e of the power feed line into a voltage signal proportional thereto, and a current transformer 9 is a current proportional to the load current i of the power feed line. It is converted into a signal. This current signal remains in the current mode or is converted into the voltage mode.

Reference numerals 2a and 2b are A / D converters. A / D
The converter 2a samples the voltage signal output from the transformer 8 in synchronization with the clock from the sample period controller 1 and digitizes it. The A / D converter 2b is the current transformer 2b
The current signal output from is sampled in synchronization with the clock from the sample period controller 1 and digitized.

The output of the A / D converter 2a is supplied to the zero cross detector 3 and the data memory 5. In the zero-cross detector 3, the zero-cross point is captured based on the sample value from the A / D converter 2a, and the time corresponding to Td1 and Td2 is calculated by the equation (2),
It is obtained by performing the calculation of (3) and given to the period calculator 4. Also in the period calculator 4, the period T is obtained by similarly performing the calculation represented by the equation (1). The data memory 5 stores the output data of the A / D converter 2a for a half cycle or one cycle, and the arbitrary phase data calculator 6 calculates the above based on the given data T, ω (= 90 degrees). The equation (5) is solved for Tx, and then the operation represented by the equation (6) or (7) is performed to obtain Sx.

The multiplier 10 is given the Sx obtained by the arbitrary phase data calculator 6 and the output data of the A / D converter 2b, where they are multiplied and the result is given to the integrator 11. Sent. The integrator 11 integrates the calculation results of the multiplier 10 and gives a pulse generation signal to the pulse generator 12 when the integrated value exceeds a certain value and subtracts a value corresponding to the generated pulse from the integrated value. The pulse generator 12 outputs a pulse proportional to the load power based on the output of the integrator 11. The display 13 displays the amount of electric power based on the output of the pulse generator 12.

Therefore, in this reactive watt-hour meter, if all the processes after the A / D converters 2a and 2b are realized by software such as a microprocessor, it becomes an active watt-hour meter based on a digital arithmetic operation without adding a special circuit. It can be realized with the same circuit.

Although the illustrated embodiment of the present invention has been described above, this does not provide a limiting interpretation of the present invention.

For example, in the above embodiment, the phase shift data of the sample value of the voltage signal is obtained, but this may be the current signal.

In the above embodiment, one cycle is obtained as the time interval between the zero cross points, but this is a half cycle,
Alternatively, it may be an integral multiple of one cycle. For example, in the case of obtaining the half cycle, in the case of the voltage signal shown in FIG. 3, the half cycle starting from the zero cross O1 uses not the zero cross O3 but the sampling points before and after the zero cross O2.

[0045]

As described above, according to the present invention, it is not necessary to always sample the same point in one cycle waveform of an analog input signal, so it is not necessary to synchronize the sampling point with the analog input signal, and the analog input Since it is possible to perform sampling in which the waveform is evenly traced by making the sampling point asynchronous with the signal in every cycle, the filter effect can improve the performance separately from the size of the sampling interval. Therefore, it is not essential to make the sample interval sufficiently smaller than the cycle of the input signal, and sufficient performance can be obtained even when the target has a high frequency.

Further, in the reactive energy meter of the present invention, if all the processes after the A / D conversion are realized by software such as a microprocessor, the same circuit as the active energy meter based on the digital operation formula can be used without adding a special circuit. Can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an electronic phase shift circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an electronic reactive energy meter according to an embodiment of the present invention.

FIG. 3 is a waveform diagram showing a relationship between a sampling interval of a voltage or current signal and a cycle.

FIG. 4 is a waveform diagram showing the relationship between zero-cross points and sample values before and after the zero-cross points.

FIG. 5 is a waveform chart showing another example of the relationship between the zero cross point and sample values before and after the zero cross point.

FIG. 6 is a waveform diagram showing a time relationship between an arbitrary sample signal and a signal whose phase is shifted by 90 degrees.

FIG. 7 is a waveform diagram showing a time relationship necessary for calculating the 90 ° phase-shifted signal shown in FIG. 6.

FIG. 8 is a waveform diagram showing another example of the time relationship between an arbitrary sample signal and a signal whose phase is shifted by 90 degrees.

9 is a waveform diagram showing a time relationship necessary for calculating the 90-degree phase-shifted signal shown in FIG.

[Explanation of symbols]

 1 Sample period controller 2, 2a, 2b Analog-digital converter 3 Zero cross detector 4 Period calculator 5 Data storage 6 Phase data calculator 7 Digital-analog calculator 8 Transformer 9 Current transformer 10 Multiplier 11 integrator 12 pulse generator 13 indicator

Claims (2)

[Claims] 1. An analog-to-digital conversion means for sampling an analog input signal and converting it into a digital signal composed of a plurality of sample values, and maintaining linearity within an allowable error range of the input signal among the plurality of sample values. A time interval calculating means for specifying the zero cross points based on sample values before and after the zero cross points of the area and for obtaining a time interval between the specific zero cross points; and a time interval between the specific zero cross points. Based on the ratio with the phase shift amount, the time shifted by the phase shift amount from each of the predetermined number of sample points included in the plurality of sample points in the input signal is calculated, and the sample values before and after the time are calculated from the phase shift point. An electronic phase shift circuit comprising a level calculating means for obtaining a level value. 2. An analog-to-digital conversion means for sampling an analog input voltage signal and the same current signal and converting them into a digital signal composed of a plurality of sample values respectively; and one of the input voltage signal and the same current signal. The zero-cross point is specified based on the sample values before and after the zero-cross point in the region that maintains the linearity within the allowable error range of the one input signal among the plurality of sample values related to the input signal, and the specified zero A time interval calculation means for determining a time interval between cross points, and a time interval calculation means included in the plurality of sample points in the one input signal based on a ratio of the specific zero / cross point time interval and a phase shift angle of 90 degrees. The time shifted by 90 degrees from each of the predetermined number of sample points is calculated, and the level value of the phase shift point is calculated from the sample values before and after that. Converting the power value by multiplying the output value of the level calculation means and the sample value of the point corresponding to the predetermined number of sample points among the plurality of sample values related to the other input signal. And an electronic reactive watt-hour meter provided with a multiplying unit.