JP2009049645A - Analog/digital conversion method, and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analog/digital conversion method and an apparatus which can achieve a necessary sampling speed by a simple configuration without adopting a high-speed A/D conversion circuit when measuring a part of analog input signals at high speed. <P>SOLUTION: In the analog/digital conversion method which selects a plurality of analog input signals 4 in order by switching control to an analog multiplexer 7 and carries out analog/digital conversion to obtains a series of sampling values, the method makes multiple selections for some of specific analog input signals in a period in which switching control to the multiplexer 7 takes a round and all analog input signals are selected, carries out analog/digital conversion to them and adds the result to the series of sampling values. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an analog / digital conversion method and apparatus for measuring some analog input signals at higher speed than other analog input signals in a substation control device, a protection device, a monitoring device, or the like.

  Conventionally, a method has been proposed in which the timing of opening and closing of a power circuit breaker is controlled so that a severe transient does not occur in a system or power equipment. Such a circuit breaker switching control device detects an opening command signal or a closing command in order to interrupt or turn on the circuit breaker at a desired current or voltage phase when an opening command signal or a closing command signal is detected. It has a function of delay-controlling the output timing of the signal to the circuit breaker.

  In a conventional device of such a circuit breaker switching control (hereinafter referred to as a synchronous switching control device), in order to self-verify whether the control has been correctly executed, the circuit breaker main contact stroke (stroke) or Some measure the switching timing of the main circuit breaker contact. Since this measurement is used for timing evaluation of the synchronous opening / closing control, it is required to be sufficiently faster than the control accuracy at the same timing.

  On the other hand, in a conventional digital substation control device, protection device or monitoring device including a synchronous switching control device, for example, as shown in FIG. 5, analog input signals of a plurality of channels CH1 to CH7 such as voltage and current are analogized. In general, a sampling value sequence of each input is obtained by sequentially switching by a multiplexer and performing analog / digital (A / D) conversion, and an arithmetic processing is performed by a CPU or the like to realize a device function. The analog multiplexer is a switch capable of a high-speed selection operation, and according to this configuration, an A / D conversion circuit can be saved, so that it is widely applied.

As an example, according to FIG. 2 of the following Patent Document 1, a plurality of analog input signals (1 to 5, T) are guided to the analog multiplexer 9 after signal processing and sequentially switched, and sampled by the A / D conversion circuit 10. It is converted into a value string and processed by the CPU 8.
Japanese Patent No. 3205451

In the method using the analog multiplexer as described above, there is an upper limit on the switching speed of the analog multiplexer because A / D conversion per analog input signal requires a certain time. Therefore, the number of analog input points and the sampling period in the conventional apparatus are in a mutually restrictive relationship. That is, if the A / D conversion time per analog input signal is Tc, the number of analog input points is N, and the sampling period is Ts, the constraint is expressed by the following equation, and the sampling period Ts is shorter (faster) than N · Tc. )Can not do it.
Ts ≧ N · Tc

  In order to increase the sampling period Ts while keeping the number N of analog inputs the same, it is necessary to shorten the A / D conversion time Tc, and a high-speed A / D conversion circuit is adopted, which complicates and consumes the apparatus. Increase in power and cost.

  In the invention described in Patent Document 1, in order to easily measure harmonic components of voltage and current, the sampling period is made variable, high-speed measurement is performed at a sampling period T1 over a predetermined period, and then further Low speed measurement is performed over a predetermined period at a sampling period T2 that is an integral multiple of the sampling period T1, and this is repeated. Accurate power is obtained by correcting the fundamental power calculated from the low-speed measurement result based on the high-speed measurement result.

  This method is effective for simply and accurately measuring power including harmonics, but cannot meet the need to measure only a part of analog input signals at high speed as in the case of a synchronous switching control device. In addition, the A / D conversion circuit used in this method needs to be sufficiently high speed to achieve the purpose of detecting harmonics, and the required speed of the A / D conversion circuit is different from the case of always performing high-speed measurement. Absent.

  The present invention has been made to solve the above-described problems, and is required for a simple configuration without employing a high-speed A / D conversion circuit when measuring some analog input signals at high speed. It is to provide an analog / digital conversion method and apparatus capable of achieving a sampling rate.

  In order to solve the above problems, an analog / digital conversion method according to the present invention is an analog / digital conversion method in which a plurality of analog input signals are sequentially selected by switching control of an analog multiplexer, and analog / digital conversion is performed to obtain a sampling value string. In the above-described analog multiplexer switching control cycle, all the analog input signals are selected and a part of specific analog input signals are selected a plurality of times, and each analog / digital conversion is performed to obtain a sampling value string. It is a method to add to.

  The analog / digital conversion device of the present invention includes an analog multiplexer that sequentially selects a plurality of analog input signals by switching control, an A / D conversion circuit that converts the analog input signals selected by the analog multiplexer into digital values, A control signal is output to the analog multiplexer, and the switching control of the analog multiplexer is completed to select all the analog input signals within a period in which all the analog input signals are selected, and the digital value is selected several times. And an input control unit that forms a sampling value sequence when input.

  According to the present invention, when some analog input signals are measured at high speed, analog / digital can achieve a required sampling speed with a simple configuration without employing a high-speed A / D conversion circuit. A conversion method and apparatus can be provided.

  Hereinafter, two embodiments of an analog / digital conversion method and apparatus according to the present invention will be described with reference to the drawings.

(First embodiment)
(Constitution)
FIG. 1 is a block diagram showing a configuration of a synchronous switching control device including an analog / digital conversion device according to an embodiment of the present invention. This figure mainly describes the portion related to the processing of the analog input signal, and details of the circuit breaker control circuit and the arithmetic circuit are omitted. That is, the synchronous opening / closing control device 1 includes a control unit 2 and an arithmetic processing unit 3. The control unit 2 includes a number of input converters 5 and analog low-pass filters (LPF) 6 corresponding to the number of analog input signals, An analog multiplexer (MPX) 7, an analog / digital conversion circuit (A / D conversion circuit) 8, an input control unit 9, a contact input circuit 13, an open / close command output control unit 15, and a semiconductor switch 16 are provided. . The arithmetic processing unit 3 includes a CPU 21, a RAM 22, a ROM 23, an external interface 24, and an I / O (input / output) bus 10. The MPX 7, the A / D conversion circuit 8, and the input control unit 9 constitute an analog / digital conversion device.

(Function)
The analog input signal 4 required for the synchronous switching control is first converted into a voltage signal of a level that can be easily processed by an electronic circuit by the input converter 5 of the control unit 2 and then included in the signal by the analog low-pass filter (LPF) 6. Components that exceed the Nyquist frequency are suppressed. The analog input signals indicated as CH1 to CH7 are all subjected to the same processing and sent to the analog multiplexer (MPX) 7. The MPX 7 sequentially switches and selects these signals and guides them to the A / D conversion circuit 8. The A / D conversion circuit 8 converts the selected signal into a digital value and passes it to the input control unit 9. The input control unit 9 instructs the MPX 7 to select an analog input signal to be selected by the analog multiplexer control signal 12, and uses the digital value conversion result of the A / D conversion circuit 8 as a sampling value string for each input. In a predetermined storage area (not shown).

  The CPU 21 of the arithmetic processing unit 3 reads a sampling value sequence of each analog input signal from the input control unit 9 of the control unit 2 via the I / O bus 10 and uses it for calculation and control. The input of the CH1 stroke sensor is used for verifying that the control is executed at the correct timing by measuring the stroke of the main circuit breaker contact. Each input of the CH2 instrument transformer, the CH3 instrument transformer, and the CH4 instrument current transformer is used to obtain a reference phase for switching control. Each input of the CH5 operation pressure sensor, the CH6 temperature sensor, and the CH7 circuit breaker control voltage is used for estimating an opening / closing operation time change amount according to the state of the circuit breaker and adjusting a delay amount of the opening / closing command signal.

  Further, the CPU 21 generates a timing signal 11 for instructing the input control unit 9 to start the MPX 7 switching control. The input control unit 9 starts the switching control with reference to the rising or falling edge of the timing signal 11.

  The RAM 22 mainly stores data temporarily, the ROM 23 mainly stores programs, and the external interface 24 performs apparatus setting, status display, history display, and the like, but it is not always necessary to include all of them.

  The contact input circuit 13 detects an open / close command signal from the host system, and detects the open / close state of the breaker main contact by the a contact input and the b contact input of the breaker. The opening / closing command output control unit 15 controls the semiconductor switch 16 based on the delay time instructed by the CPU 21 and energizes the circuit breaker operation coil 18.

An analog signal sampling method of the synchronous switching control apparatus 1 in the present embodiment will be described with reference to FIG.
Since the input signal of the stroke sensor of CH1 needs to be measured at a higher speed than other signals, the selection is performed twice within a period in which the MPX7 switching control makes a round.

  With reference to the rising edge of the timing signal 11, the CH1 input signal is first selected by the MPX control signal 12 from the input control unit 9. After a predetermined A / D conversion time has elapsed, the input control unit 9 stores the conversion result, and one sample of A / D conversion is completed. Next, the CH2 input signal is selected by the MPX control signal 12. Similarly, A / D conversion proceeds in the order of CH3 and CH4.

  Thereafter, the timing signal 11 falls, and when the CH1 input signal is selected again based on this timing and A / D conversion is completed, CH5, CH6, and CH7 are selected in this order to complete A / D conversion. The switching control is completed as described above, and then the same control is repeated when the timing signal 11 rises.

  Here, the time from the rising edge to the falling edge of the timing signal 11 and the time from the falling edge to the rising edge become the sampling period necessary for CH1, and the time from the rising edge of the timing signal 11 to the next rising edge is all Are controlled so as to have a sampling period required for the input signal. Such generation of the timing signal 11 can be realized by, for example, a built-in timer of the CPU 21. The control of the input signal selection order can be realized by a logic circuit of the input control unit 9 or a program executed by the CPU 21.

(effect)
As described above, according to the analog / digital conversion method and apparatus of the present embodiment, the input signal selection order is devised, and the CH1 input signal that requires high-speed measurement is selected twice within one round cycle of MPX7. As for the input signal, a sampling value string having a speed twice that of the other input signals is obtained.

  Compared to the conventional method shown in FIG. 5, it is allowed to extend the A / D conversion time of one sample to 7/4 times while achieving the sampling rate required for each input. Therefore, it is not necessary to employ a high-speed A / D conversion circuit, and a simple, low power consumption, low-cost transformer control device, protection device, monitoring device, or the like can be realized.

  In the present embodiment, when the input signals of CH1 and CH2 are measured faster than the other signals, the input signal selection order shown in FIG. 3 may be used. When this is compared with FIG. 5, the A / D conversion time of one sample can be extended to 7/5 times, and the same effect as described above can be obtained.

  As another modification, a configuration in which a sample hold circuit is provided after the LPF 6 may be adopted, or an A / D converter incorporating a peripheral circuit may be adopted. Further, it goes without saying that the same method can be applied even if the input signal shown in this embodiment is a different type of signal or the number of points of the input signal is increased or decreased.

(Second Embodiment)
The configuration of the analog / digital conversion apparatus according to the second embodiment of the present invention is the same as that of FIG. 1 in the first embodiment.

An analog / digital conversion method in this embodiment will be described with reference to FIG. In the present embodiment, since the input signals of CH5 to CH7 are signals that vary more slowly than other signals, they may be measured at low speed, and within the period in which the signals of CH1 to CH4 are selected three times, It is assumed that the input signals of CH5 to CH7 are selected once each. for that reason,
(A) With reference to the rising edge of the timing signal 11, the CH1 input signal is first selected in the MPX 7 by the MPX control signal 12 from the input control unit 9. After a predetermined A / D conversion time has elapsed, the input control unit 9 stores the conversion result and the conversion of one sample is completed. Subsequently, conversion proceeds in the order of CH2, CH3, CH4, and CH5.

  (B) With the next rising edge of the timing signal 11 as a reference, they are selected in the order of CH1, CH2, CH3, CH4, and CH6. That is, CH1 to CH4 are in the same order, but CH6 is finally selected.

(C) CH1, CH2, CH3, CH4, and CH7 are selected in order of the next rising edge of the timing signal 11 as a reference. That is, finally CH7 is selected.
Thereafter, the process returns to (a) and the same control as above is repeated.

  Here, the time T from the rise of the timing signal 11 to the next rise is a sampling period necessary for the input signals of CH1 to CH4, and an integral multiple of the time T is necessary for the input signals of CH5 to CH7. Each sampling period is controlled.

  According to the present embodiment, the input signals of CH5 to CH7, which may be low-speed measurement, are selected only once every three switching cycles of MPX7, so that it is not necessary to perform high-speed measurement more than necessary. Therefore, the speed of the A / D conversion circuit 8 can be optimized, and a simple, low power consumption, low price transformer control device, protection device, monitoring device, or the like can be realized.

The block diagram which shows the structure of the synchronous opening / closing control apparatus provided with the analog / digital conversion apparatus of embodiment of this invention. 2 is a time chart for explaining the analog / digital conversion method according to the first embodiment of the present invention. The time chart explaining the analog / digital conversion method of the modification of the 1st Embodiment of this invention. The time chart explaining the analog / digital conversion method of the 2nd Embodiment of this invention. The time chart explaining the conventional analog / digital conversion method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Synchronous switching control apparatus, 2 ... Control part, 3 ... Operation processing part, 4 ... Analog input signal, 5 ... Input converter, 6 ... Analog low pass filter (LPF), 7 ... Analog multiplexer (MPX), 8 ... Analog / Digital conversion circuit (A / D conversion circuit), 9 ... input control unit, 10 ... I / O bus, 11 ... timing signal, 12 ... analog multiplexer control signal (MPX control signal), 13 ... contact input circuit, 15 ... Open / close command output control unit, 16 ... semiconductor switch, 18 ... breaker operation coil, 21 ... CPU, 22 ... RAM, 23 ... ROM, 24 ... external interface.

Claims (5)

  In the analog / digital conversion method in which a plurality of analog input signals are sequentially selected by switching control of the analog multiplexer and analog / digital conversion is performed to obtain a sampling value sequence, the switching control of the analog multiplexer completes and all the analog input signals are processed. A certain analog input signal is selected a plurality of times within a period in which is selected, and each analog / digital conversion is performed and added to the sampling value sequence, and the analog / digital conversion method is characterized.   A timing signal instructing start of switching control is input to the analog multiplexer, a series of switching control is started at either the rising edge or falling edge of the timing signal, and the identification is performed at both the rising edge and falling edge of the timing signal. 2. The analog / digital conversion method according to claim 1, wherein an analog input signal is selected.   Assuming that a period until the original analog input signal is selected again after a complete cycle of the switching control of the analog multiplexer is T, for analog input signals other than the specific analog input signal, every time the period T passes a plurality of times 2. The analog / digital conversion method according to claim 1, wherein the analog / digital conversion is performed once, and analog / digital conversion is performed and added to the sampling value sequence.   A timing signal instructing start of switching control is input to the analog multiplexer, a series of switching control is started at either the rising edge or falling edge of the timing signal, and for the analog input signal other than the specific one, the timing signal 4. The analog / digital conversion method according to claim 3, wherein a selection is made once for a plurality of rising or falling times.   An analog multiplexer that sequentially selects a plurality of analog input signals by switching control, an A / D conversion circuit that converts the analog input signals selected by the analog multiplexer into digital values, and a control signal that is output to the analog multiplexer An input for selecting a specific analog input signal a plurality of times and inputting the digital value to form a sampling value sequence within a period in which the switching control of the analog multiplexer is completed and all analog input signals are selected. An analog / digital conversion device comprising a control unit.

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