JPH0310169A - Digital type zero cross point detecting apparatus - Google Patents

Abstract

PURPOSE:To perform high speed detection and operation with high accuracy by changing over a plurality of digital type zero cross point detecting parts timewise to perform parallel processing. CONSTITUTION:An analogue filter 11 and an A/D conversion part 12 are provided to each of zero cross point detecting parts 1A, 1B and a high frequency component of a short cycle is removed to sample an AC waveform at a constant interval and said waveform is converted to instantaneous value digital data and a zero cross point is detected by a CPU 13. A change-over switch 2 is changed over in constant change-over timing and the detecting pats 1A, 1B subject data before and after the change of the code of the instantaneous value digital data to linear approximation when said code changes and two data of the same code continue to detect a zero cross point. Herein, when the detecting part 1A detects the presence of the zero cross point, a detection prohibiting signal SA is sent to the detecting part 1B from this point of time and released when two continuous data of the same code are detected after the elapse of a predetermined period. By this method, detection omission or double detection is prevented to make is possible to perform high speed operational processing.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a digital zero-crossing point detection device that digitally detects zero-crossing points of signal waveforms at high speed. The present invention relates to a zero-crossing point detection device that samples a value, converts it into digital data, and detects a zero-crossing point from a change in the sign of this digital data.

(Prior Art) In a PLL (phase locked loop) circuit used in an AC waveform measuring device, it is necessary to accurately detect the zero-crossing point of the AC waveform.

In this case, the zero-crossing point detection device needs to continuously sample the AC waveform at high speed so as not to overlook the zero-crossing point of the AC waveform, and if the sampling speed is lowered, the detection accuracy will decrease. Furthermore, when calculating the zero-crossing point, if the calculation time and calculation start timing are slow, a detection delay will occur, and the responsiveness of the PLL circuit will deteriorate.

For these reasons, it has traditionally been difficult to digitize zero-cross point detection devices, and analog detection devices have a simpler configuration than digital ones, requiring only one or two operational amplifiers. For this reason, analog zero-crossing point detection devices have traditionally been used exclusively.

(Problems to be Solved by the Invention) However, analog detection devices have the following problems.

That is, there is a deviation between the zero-crossing point detected by digital sampling data and the zero-crossing point detected by an analog detection device due to differences in detection method and circuit configuration. Even if it were attempted to match this deviation by adjustment, it would be difficult because one frequency characteristic would be different.

Furthermore, analog detection devices typically use a low-pass filter with a large time constant, resulting in slow response speed and a tendency for accuracy to deteriorate due to temperature changes.

The present invention was made to solve the above problems, and
The purpose of this is to enable the digitalization of zero-crossing point detection devices, which was considered difficult in the past, by using multiple zero-crossing point detection sections integrated with a digital sampling section, while also eliminating inconveniences such as missed detections and double detections. An object of the present invention is to provide a digital zero-crossing point detection device that can perform highly accurate and high-speed detection and calculation without any problems.

(Means for Solving the Problems) In order to achieve the above object, the present invention samples the instantaneous values of an AC waveform at regular intervals and converts them into digital data. In a digital zero-crossing point detection device that detects a zero-crossing point of the AC waveform existing between data, when the sign of the instantaneous value digital data changes and two pieces of data with the same sign occur in succession, A plurality of zero-crossing point detection units are provided in parallel to detect zero-crossing points by linear approximation of the data of The zero-crossing point is detected, and the zero-crossing point detection section detects the zero-crossing point after the detected zero-crossing point.

A detection prohibition signal as an interlock signal for prohibiting detection of a zero cross point to other zero cross point detection sections for a predetermined period is sent, and this detection prohibition signal can be reset, and each of the zero cross point detection sections is configured to be able to determine the presence or absence of a zero cross point near the switching timing.

Further, the zero crossing point detection section detects two consecutive data after the sign of the instantaneous value digital data changes,
Based on the two consecutive data before the sign changes, 3'/z3V1+'/a-V.

(Here, 'jam Vl is the value of the two consecutive data before the sign changes - yam Vs is the value of the two consecutive data after the sign changes, and xo is the sampling point of a certain data. It is desirable to find the ratio x0 using a linear approximation formula (ratio to the sampling interval) and detect the zero-crossing point.

(Operation) According to the present invention, the sampling cycles of the plurality of zero-crossing point detecting sections are switched at a constant switching timing, and each detecting section detects a zero-crossing point based on the data at four points before and after the sign change described above. Further, the presence or absence of a zero-crossing point near the switching timing is determined, and if there is a zero-crossing point, the detection function of the zero-crossing point detecting section that enters the next sampling cycle is stopped for a certain period of time.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of this embodiment.

IB is a zero-crossing point detecting section as a voltage detecting section having the same configuration, and these zero-crossing point detecting sections IA, 2
Sampling input (AC voltage waveform) is alternately inputted to B via the changeover switch 2 in a constant cycle. In addition, each zero cross point detection unit IA, 2B
Detection prohibition signals SA and SB are sent and received between them as interlock signals that stop the zero-crossing detection function of the other when each detects a zero-crossing point.

Furthermore, 3A and 3B are path buffers, and 4 is a system bus, through which zero-crossing point data detected by zero-crossing point detecting units IA and IB is sent to a host CPU, etc. (not shown).

Next, the internal configuration of the zero-crossing point detection units IA and IB will be explained with reference to FIG. 2. In other words, the zero-cross point detection units IA and IB include an analog filter 11 to which a sampling input (AC voltage waveform) is input, and this analog filter 11 has a cycle shorter than the cycle of four samples of instantaneous value digital data. This removes high frequency components.

An A/D converter 12 that samples an AC waveform at regular intervals and converts it into instantaneous value digital data is connected to the downstream of the analog filter 11.
A CPU 13 is connected downstream of the D converter 12 and performs calculations for detecting zero-crossing points using a method described later.

The zero-crossing point detection operation in the CPU 13 will be described below with reference to FIG.

Now, as shown in Figure 3, when the AC voltage waveform is sampled at regular intervals, the digital data is Di, D.
,,D,,D,, and the value of each data is Vow
'/□*'/z+y3. At this time, since the value y1 of the data D2 is negative and the value y2 of the data D is positive, it is clear that the zero crossing point Px exists between these two data.

The CPU 13 sequentially takes in the data D, D, , D, and also takes in the second data after the sign of the data changes from negative to positive, that is, D4, and detects a linear approximation equation. Here, xo has the meaning of - as a ratio to the sampling interval ts based on the sampling point of certain data.

The process of deriving the above equation (1) will be explained below. first.

As shown in FIG. 3, a straight line is assumed to be a linear approximation of each data, and this straight line is expressed as Y(x)=ax+b. Here, X is expressed as a ratio to the sampling interval ti, and its reference (X=O) is the sampling point of data D.

Now, the value of Y at point PX' where x=1.5 on the straight line Y(x) is: Y (1-5) = (y o + y + y z +
y a)/4.

On the other hand, the slope a of the straight line Y(x)=ax+b is determined by each data D
The average value of the slope of the straight line connecting 1 to D4 and point Px' is determined as follows.

(hereinafter referred to as the margin), find X, and from this, the zero-crossing point Px Also, at the zero-crossing point Px, Y (xo) = a x0 + b = 0, so x, = −・・・・・・(1 )-■, and Y(x) at point Px' is Y(1,5)
= 1.5a, + b, so b = Y (1,5) -1,5a.

If you organize the above.

Y (1-5)= (ya + y 1+ y2+ y
3) / 4 ... (1) - ■ ... (1) - ■ b = Y (1, 5) - a x - ... (1) -
■ It becomes. Therefore, according to the above formulas (1)-■ to (1)-0,
b 3 Y(1,5) 2 (2(y 2- y t) + (y 3- y
n)2/3)2(3(ya-y 工)"y3-yo) =(3yz-6yi-3yo)/(3yz-3yi"y
3-yo), and the zero-crossing point can be found using the above equation (1).

Next, the operation of the entire zero-crossing point detection device shown in FIG. 1 will be explained with reference to FIG. 4. First, assuming that the AC voltage waveform input to the device is as shown in FIG. Sample the alternating voltage waveform over Ts.

If one zero-crossing point detection section IA detects a zero-crossing point at time t□, for example, by the method described above, from this point on, a detection prohibition signal SA is sent to the other zero-crossing point detection section IB, and the AC voltage waveform is When two consecutive negative data are detected after half a cycle has elapsed, the detection inhibit signal SA is released at time t2.

After that, when the sampling switching timing tc comes,
End check EC is performed to determine the position of the next zero cross point using the above zero cross point detection method. In other words, there is no sign change in the data at this switching timing tc,
If it is determined that there is no zero-crossing point near the switching timing tc, the selector switch 2 is switched to switch the sampling to the other zero-crossing point detection section IB.

Even if a zero-crossing point is detected at time t immediately before this timing, as shown in the switching timing tc' in the figure, a detection prohibition signal S is sent to one zero-crossing point detection section IA.
Send B. Upon receiving this detection prohibition signal SB, the zero-crossing point detecting section IA temporarily stops the zero-crossing and loss detecting functions even when sampling starts to prevent double detection. That is, during the period indicated by hatching in the figure, the sampled data is masked and no detection is performed.

However, during this period, the other zero-crossing point detector IB, which previously sent the detection prohibition signal SB, is not sampling, so it cannot make a decision to release the detection prohibition signal SB as at time t2. The determination is carried over until entering the next sampling cycle T's, causing a detection delay.

Therefore, at time t4, when 172 cycles of the maximum response period have elapsed from time t, the detection prohibition signal SB is reset (
R3T), and a timer reset function is provided so as not to unnecessarily disturb the zero-crossing point detection function of one zero-crossing point detection section IA that is in the sampling cycle Ts.

As a result, one zero-crossing point detection section IA becomes capable of detecting a zero-crossing point again, and when the zero-crossing point is detected at t6 via time t5, the other zero-crossing point detection section IA
A detection prohibition signal SA is sent to B. Then, the detection function of the other zero-crossing point detection section IB is stopped by the same end check EC at the switching timing tc', and thereafter, its own detection prohibition signal SA is reset (R
8T).

Next, as shown in FIG. 5, if a zero-crossing point Px exists within one sampling interval ts sandwiching the switching timing tc, the zero-crossing point detection units IA and IB are switched at the switching timing tc. Therefore, zero cross detection based on the above-mentioned principle becomes impossible within either sampling cycle Ts. Therefore, detection accuracy may decrease due to detection failure or double detection.

Therefore, with the end check function described above, even if it is impossible to detect the zero-crossing point, the zero-crossing point is estimated from the data of the four points before the switching timing tc, and whether the zero-crossing point is before or after the switching timing ta. Check. Then, the zero-crossing point detection section 1A or IB which has the closer side calculates the zero-crossing point.

As described above, according to this embodiment, the switching timing t
By providing an end check function that determines the presence or absence of a zero cross point near c and an interlock signal transmission/reception function that temporarily stops the zero cross point detection function of each zero cross point detection section IA, IB, switching timing tc It is possible to prevent failure to detect or double detect nearby zero-crossing points, and to perform high-speed and highly accurate zero-crossing point detection.

(Effects of the Invention) As described above, according to the present invention, high-speed and continuous data sampling can be performed by temporally switching a plurality of digital zero-crossing point detection units and performing parallel processing.

Furthermore, by transmitting and receiving a detection prohibition signal as an end check function and an interlock signal, it is possible to prevent failure to detect a zero cross point or double detection near the switching timing. Furthermore, the end check function and the transmission and reception of the detection prohibition signal can eliminate delays in calculation time and calculation start timing, eliminating detection delays and enabling high-speed calculation processing.

In addition, by using a DSP (digital signal processor) in the zero-crossing point detection section, it is possible to achieve a smaller size compared to conventional analog or digital detection devices. In addition, since there is no need to use a powerful analog filter as long as it can remove a predetermined high frequency as the analog filter in the zero-crossing point detection section, the effects of delays, temperature drift, etc. are also small. Furthermore, since equation (1) for linear approximation requires only one division, five constant multiplications, and addition and subtraction, the calculation process in the CPU is simpler than Fourier transform or least squares method.

By digitally integrating the data sampling and zero-crossing point detection sections, there is no data deviation between sampling and calculation processing compared to analog methods, improving detection accuracy. It is possible to directly control the PLL circuit at the zero-crossing point of .

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a configuration diagram of this embodiment, FIG. 2 is a configuration diagram of a zero-crossing point detection section, and FIG. 3 is an explanatory diagram showing a method of detecting a zero-crossing point. FIG. 4 is an explanatory diagram of the operation of the zero-crossing point detection section, and FIG. 5 is an enlarged diagram of the vicinity of the switching timing. IA, IB... Zero cross point detection section 2... Changeover switch 3A, 3B... Path buffer 4... System bus

Claims (2)

[Claims] (1) A digital method that samples the instantaneous value of an AC waveform at regular intervals and converts it into digital data, and detects the zero-crossing point of the AC waveform that exists between these data from a change in the sign of this instantaneous value digital data. The zero-crossing point detection device includes a zero-crossing point detecting section that detects a zero-crossing point by linearly approximating the data before and after the change in sign when the sign of the instantaneous value digital data changes and two pieces of data with the same sign occur in succession. A plurality of zero-crossing point detectors are provided in parallel, and each of the zero-crossing point detectors detects the zero-crossing point by switching and inputting the AC waveform over a sampling cycle between fixed switching timings, and the zero-crossing point detector detects the zero-crossing point by switching and inputting the AC waveform over a sampling cycle between fixed switching timings. Thereafter, a detection prohibition signal as an interlock signal for prohibiting the detection of zero cross points is transmitted to other zero cross point detection sections for a predetermined period of time, and this detection prohibition signal can be reset, and each of the zero cross point detection sections A digital zero-cross point detection device, characterized in that the section is configured to be capable of determining the presence or absence of a zero-cross point near the switching timing. (2) The zero-crossing point detection unit calculates x_0=3y_2-6y_1-3y_0 based on two consecutive data after the sign of the instantaneous value digital data changes and two consecutive data before the sign changes. /3y_2-3
y_1+y_3-y_0 (here, y_0, y_1 are the values of two consecutive data before the sign changes, y_
2. y_3 is the value of two consecutive data after the sign has changed, x_0 is the ratio to the sampling interval based on the sampling point of a certain data) Find the ratio x_0 using the linear approximation formula and detect the zero-crossing point. A digital zero-crossing point detection device according to claim (1).