JPH01152918A - Digital processing unit - Google Patents

Abstract

PURPOSE:To detect abnormality of a protective relay by changing a filter in its gain for trouble detecting calculation and by detecting that the output voltage of the filter is within a predetermined value. CONSTITUTION:Capacitor of switched capacitor filters 51-54, comprising an analog switch and a capacitor for a switched capacitor equivalent resistance, are represented as Cr1-Cr4. When switches 61, 62 of a gain control part 14 are turned off, the gains of output voltages Vout 1 and Vout 2 of the filter are given respectively by expressions I and II. And turning on the switches 61, 62 by a gain changing instruction, a gain changing capacitor 70(Crg) is connected in parallel with the capacitors Cr1-Cr4. Then, the gains of the output voltages Vout 1 and Vout 2 are changed as shown respectively by expressions III and IV. Next performing trouble detecting calculation about an overcurrent factor and an undercurrent factor, this arithmetic result is compared with a comparison value. When an absolute value of this difference is larger than a permissible value, a device is stopped and abnormality is indicated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a digital arithmetic processing device, and more particularly to an input circuit for a digital protection relay that inputs power-related voltage and current and converts them into digital quantities. .

[Conventional technology]

When inspecting the input section of a conventional digital protection relay, as shown in Patent No. 61-227628, the filter clock frequency is changed to change the filter characteristics, and the magnitude of the filter output relative to the input is determined. and detected filter abnormalities and protection relay abnormalities.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, when the clock signal is increased, the center frequency of the band-pass filter becomes higher, and the output relative to the input signal during inspection becomes smaller, making it possible to detect abnormalities. However, with regard to low-pass filters, even if the clock frequency is increased, the output in response to the input signal at the time of inspection does not decrease, and there is a problem that abnormality cannot be detected. Furthermore, the relay elements targeted for abnormality detection can only be overcurrent and undervoltage relay elements, and there is a problem that abnormality cannot be detected with respect to reactance relays.

An object of the present invention is to solve the above-mentioned problems.

[Means for solving problems]

The above object is a switched capacitor filter in which the gain of the input filter can be changed externally, and by changing the gain of the filter, it is possible to detect that the magnitude of the output voltage is within a permissible value.

This eliminates the need for an input filter for inspection, making the circuit smaller and lowering costs.
Moreover, consistent inspection of the protection relay including the input filter can be easily performed, and reliability can be improved.

[Effect]

A gain changing capacitor is provided so that it can be connected in parallel to the input equivalent resistance capacitor of the switched capacitor filter. At the time of inspection, the gain is changed by connecting the gain changing capacitor described above. The arithmetic processing unit of the protection relay uses the data after the gain change to perform calculations regarding overcurrent and undervoltage elements. This protection relay calculation processing section compares the calculation result with the above-mentioned calculation result. Thereby, the protection J? including the input filter? Relay abnormalities can be detected.

〔Example〕

An embodiment of the present invention will be described below.

First, the configuration of an embodiment of the present invention will be explained.

FIG. 1 shows a configuration when applied to a digital protection relay according to an embodiment of the present invention. In Figure 1, 1 and 2 are switched capacitor switches, 3 and 4 are sample and hold circuits, 5 is a multiplexer, 6 is an analog/digital converter (A/D converter), 7 is a setting section, and 8 is an input. The output section includes a microprocessor (CPU) 9, a random access memory (RAM) 10, a read only memory (ROM) 11, and a gain control section 12.

Next, the functions of each block shown in FIG. 1 will be explained.

In FIG. 1, switch l-capacitor filters 1 and 2 are used to remove harmonic components of the input signal and prevent aliasing errors in sampling. The sample and hold circuits 3 and 4 sample and hold the output of the previous stage filter every period T. The multiplexer 5 inputs the outputs of multiple S/H circuits,
One of them is sequentially switched and selected. A/D converter 6 converts analog data into digital data (eg, 12-bit resolution).

The setting section 7 sets a setting value of the protection relay. 8 Ilo is for inputting and outputting digital data. The CPU 9 performs processing according to an arithmetic algorithm. The RAM 10 stores input data and calculation data. The ROM 11 stores programs and data for operating the CPU shown in 9, and is read-only. A gain control section 12 changes the magnitude of the output voltage of the filters 1 and 2.

Next, the configuration and operation of the equivalent resistance using the switched capacitor circuit will be explained.

FIGS. 2(a) and 2(b) are for explaining in principle how equivalent resistance can be obtained by a switched capacitor. In Fig. 2, when the voltages at terminals ■ and ■ are Vl and V2, respectively, and switch S2 is turned on as shown in Fig. 2(a), capacitor C has a voltage of Q2.
This means that a charge Q2 represented by =CV2 is being charged. In this state, when switch S1 is turned on as shown in FIG. 2(b), the charge on capacitor C becomes Q1=C
V 1 , and the charge ΔQ, the difference between Qt and Q2, is applied to the terminal ■
This will lead to more inflow. That is, the charge ΔQ is as follows.

ΔQ=Qx Q2 =C(Vx −V2)=
・(1) Here, if the switch S2 is turned on again as shown in FIG. 2(c), the charge of the capacitor C becomes Q2=CV
z, and it is clear that the charge ΔQ shown in equation (1) and the wholesaler's charge flow from the capacitor C to the terminal ■.

Therefore, if the above operation is repeated at synchronization T,
At the synchronization T, the charge ΔQ moves through the capacitor C, and as a result, the current 1 shown by equation (2) flows on average from the terminal (2) to the terminal (2).

j=ΔQ/T=C(Vl-V2)/T-(2) On the other hand, when the voltages at both ends of the resistor R are Vl and V2, respectively, as shown in FIG. 2 (ci), the voltage flows through the resistor R. The current i1 is as follows.

in = (Vt - V2) /R - (3) where,
If 1=iR, then from equations (2) and (3) the following equation (
4) is obtained.゛R=T/C=engineering/
(fc) (4) where f is the switching frequency.

In other words, the equivalent resistance of a switched capacitor is determined by the ratio between the capacitance value (c) of capacitor C and the switching period T, and by changing the period T, the equivalent resistance can be freely changed without changing the capacitance value of capacitor C. It is something that can be changed.

The switched capacitor circuit described above is a basic circuit, but in reality it is a secondary circuit that is less susceptible to the effects of parasitic capacitance.
The circuits shown in Figures (e) and (f) are used. Figure 2(e).

φ in (f) indicates an inverted version of the clock φ.

Next, the switched capacitor filter will be explained.

In Fig. 3, 1 to 16 are analog switches, 21 to 16 are analog switches, and 21 to 16 are analog switches.
24 is a switched capacitor equivalent resistance capacitor;
31 and 32 are integrating capacitors, 41 and 42 are operational amplifiers (op amplifiers), and 51 to 54 are switched capacitor equivalent resistances consisting of the above-described analog switches and switched capacitor equivalent resistance capacitors.

FIG. 4 is an example of a taroch waveform for operating the switched capacitor filter of FIG.

In the switched capacitor filter shown in FIG. 3, l, 2, 5, 6, 9, 10.13 and 16 are ONL, ,'L when the clock φ shown in FIG. 4(a) is at the rr H++ level. ``Turn it off when the level is high.

Also, 3, 4, 7, 8, 11°12.14 and 15 are
When the clock φ shown in FIG. 4(b) is at the 7/H# level, it turns ONL, and when it is at the IIL'' level, it turns OFF. By repeating this series of operations every period TF, the Voutl and Vout2 can obtain an output expressed by the transfer function shown below (Voutl) Bad pass filter output (Vout2) Low pass filter output H: gain coefficient, Wo: angular frequency, Q: selectivity.
Assuming that the capacitors 21 to 24 and 31 to 32 shown in the figure are Cr 1 , Cr 21 Cr 3HCr 4 and C1, C2, the characteristic constant of the filter can be expressed by the following formula.

(Voutl) r x (Vout2) Cr number fo: center frequency, Q: selectivity, ■ (= gain coefficient 5th
The figure shows a block diagram of the filter and gain control section shown in FIG. 1. In FIG. 5, 61 and 62 are switches, and 70 is a capacitor. 14 in Figure 5
The part indicated by is the gain control section.

Next, the gain change of the filter shown in FIG. 5 will be explained. In FIG. 5, switches 61 and 62 are set to 0.
Make it FF. Therefore, Voutl and Vout of the filter
The gains of 2 are (9) and (12).

In FIG. 5, switches 61 and 62 are turned on by a gain control command. Here, 70 capacitors are Gr
g, this G r g connects the capacitor C ports in 51 in parallel. That is, the gain at this time is shown below.

(Voutl) (Vout2) Therefore, if the value of Crg is the same as Crt, (13
) and (19), it can be easily understood that vout 1 and Vout 2 are twice as large.

Next, the operation of the present invention shown in FIG. 1 will be explained in detail.

FIG. 6 is a flow diagram showing the operation of the present invention.

The following will explain the process according to this flowchart.

In the block shown at 1 in FIG. 6, the filter gain is changed by the gain control section shown at 14 in FIG. In detail, as explained earlier in FIG. 5, the gain change command signal changes the input equivalent resistance to the capacitor.
Gain changing capacitors are connected in parallel to change the gain.

Next, in block 2 shown in FIG. 6, accident detection calculations are performed. Calculations are mainly performed regarding overcurrent elements (OC) and undervoltage elements.

Next, in the block shown in 3 of Fig. 6, the calculation results of the OC and UV relay elements calculated in the block shown in 2 are compared with the comparison value A, and the absolute value of this difference is determined to be larger than the allowable value. judge whether

If it is larger than the allowable value, the process moves to block 4 in FIG. 6, displays an abnormality, and stops.

If it is smaller than the allowable value, the arithmetic processing of the relay including the filter is being performed normally.

Inspection is performed using the above operations.

With the method described above, even without switching to the inspection input signal,
Can be inspected. That is, as described above, the input signal from the power system is gain controlled, and the OC and UV relay elements are calculated and inspected. In this way, a special oscillator for inspection input can be made unnecessary, so that the circuit can be made more compact.

FIG. 7 shows examples of gain-frequency characteristics of the filters shown in 1 and 2 of FIG. 1, where (a) is an example of a low-pass filter, and (b) is an example of a band-pass filter. (a)-1
The characteristic curve shown in 3 and (b) is the gain-frequency characteristic before the gain is changed. In addition, (a) 2 and (b)
) The characteristic curve shown in 4 is an example of the gain-frequency characteristic after the gain is changed (at the time of inspection). That is, the gain before the gain change is H, and after the change, it becomes H multiplied by .

From FIG. 7, the gains of the low-pass filter and band-pass filter during inspection are multiplied by , regardless of the frequency of the input signal (inspection signal).

FIG. 8 is an example of the waveform of each block in FIG. 1 (an example in which the gain is changed to a large value) for explaining the inspection operation.

In FIG. 8, (a) is an inspection input switching command signal.

This signal is applied from the CPU side via the I10 section every certain period TN.

(c) of FIG. 8 shows the inspection input signal switched according to (a). FIG. 8(d) shows the output signal of the filter. Here, as shown in FIG. 8(b), a gain switching signal is output. This signal doubles the gain of the filter. As a result, if the filter and relay arithmetic processing section are normal, the relay output (OC element) shown in FIG. 8(e) becomes "operational".

FIG. 9 is an example of waveforms of each part shown in FIG. 1 when the gain of the filter is changed to a small value.

When changing the gain to a small value, it can be realized by performing the reverse operation of connecting the gain changing capacitors in parallel as described above. That is, normally, a capacitor for changing the gain can be connected in parallel, and this capacitor can be disconnected at the time of inspection.

In FIG. 9, (a) is an inspection input switching command signal. (b) is the gain switching signal, (C) is the inspection input signal, (
d) is the filter output signal.

Here, it can be seen that the gain of the filter is multiplied by 1/2 by the gain switching signal. (e) is a relay output. This relay output is an undervoltage element. In this way, if the filter and arithmetic processing unit are normal, "operation"
'.

A filter was included by performing the above-described point/power verification method for each period TN under the control of the CPU. Automatic inspection of relays can be easily performed.

Further, as filters that can be applied in the present invention.

Not only bandpass and lowpass filters, but also bypass,
It goes without saying that a notch filter or the like can also be easily realized.

(Effects of the Invention) According to the present invention: (1) Since the gain of the input filter is changed and the abnormality of the protection relay can be easily detected based on this data, the reliability of the protection relay can be improved. .

(2) It is possible to eliminate the input filter and inspection input circuit provided for inspection, which has the effect of making the circuit more compact, lower in cost, and more reliable.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a block diagram of a switch and capacitor equivalent resistance, Fig. 3 is a circuit diagram of a switch and capacitor filter, and Fig. 4 is a diagram of a switch and capacitor filter. A clock waveform side diagram, FIG. 5 is a circuit configuration diagram of the switch and capacitor filter of the present invention, FIG. 6 is a flow diagram showing the operation of the present invention, and FIG. 7 is a gain-frequency characteristic diagram of the switch and capacitor filter.
Figure 8 is an example of waveforms of each part (OC element) showing the operation of the present invention.
Figure 9 shows waveform examples of various parts showing the operation of the present invention (
FIG. 1.2...Switch and capacitor switch, 3,4.
...Sample hold circuit, 5...Multiplexer. 6... Analog/digital converter, 7... Rectifier,
8... Input/output unit, 9... Microprocessor, 10
. . . Random access memory, 11 . . . Read only memory, 12 . . . Gain control unit. Figure 1 Figure 2 Figure 6 Figure 7

Claims (1)

[Claims] 1. A switched capacitor filter using a plurality of switched capacitor circuits each consisting of an analog switch and a capacitor driven by a clock signal of a predetermined frequency as a resistance element of the filter circuit is used for filtering an input signal from an electric power system, A digital processing unit that processes data obtained by converting the output signal of the filter into a digital quantity according to a calculation algorithm changes the gain of the filter, performs an accident detection calculation, and changes the output voltage of the filter. A digital arithmetic processing device characterized in that it is equipped with an inspection means for detecting that the size is within a predetermined value.