JP3209807B2 - RMS detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an effective current value detecting device for a circuit breaker that performs a tripping operation of opening a contact of a main circuit when an accident current is detected.

[0002]

2. Description of the Related Art A control circuit configuration of a circuit breaker as disclosed in Japanese Patent Application Laid-Open No. Sho 60-32211 is conventionally known.

Further, in the above-mentioned Japanese Patent Application Laid-Open No. Sho 60-32211, as an example of solving the problem that a circuit for obtaining an effective value or an average value of a detected current is complicated and expensive.
JP-A-62-173929, JP-A-62-173
There is a technique disclosed in Japanese Patent Publication No. 930. JP-A-62-17
In the technique disclosed in Japanese Patent No. 3930, a maximum value discriminating circuit for each phase is provided, and only one effective value converting circuit can be used. In the technique disclosed in Japanese Patent Application Laid-Open No. 62-173929, the function of the signal conversion circuit is limited to the calculation of the mean square value.
The square root processing required for the effective value calculation is entrusted to the calculation function of the microcomputer. As a result, the square root circuit, which has been difficult in the related art, can be omitted. further,
As disclosed in Japanese Patent Application Laid-Open No. 2-101922, there is known an apparatus in which all effective value calculations are performed by a microcomputer.

[0004]

According to the prior art disclosed in Japanese Patent Application Laid-Open No. Sho 62-173930, one circuit breaker still requires an effective value detection circuit. There is a problem that is.

According to the technique disclosed in Japanese Patent Application Laid-Open No. 62-173930, in order to simplify the configuration of a signal conversion circuit,
Since the square root processing is performed by the microcomputer and is constituted only by the squaring circuit, there is a problem that the dynamic range (output range) is limited.

In the example disclosed in Japanese Patent Application Laid-Open No. Hei 2-101922, since the microcomputer performs all of the effective value calculation functions, a powerful processing capability is required for the microcomputer used. Therefore, there is a problem that it is difficult to adopt an inexpensive 4-bit microcomputer.

An object of the present invention is to provide a circuit configuration of an inexpensive effective value detecting device.

[0008]

According to the present invention, there is provided, in accordance with the present invention, an absolute value generating means for outputting an absolute value signal of a load current flowing in an AC circuit, and a triangular wave generating means for generating a triangular wave. Pulse width modulation means for comparing the triangular wave with the absolute value signal and performing pulse width modulation of the absolute value signal;
Averaging means for obtaining an average value of the modulated pulse, and inputting a signal indicating the average value obtained by the averaging means to the triangular wave generating means, and forming an effective value forming a feedback loop for determining the amplitude of the triangular wave A detection device is provided.

Further, an absolute value generating means for each phase for obtaining an absolute value signal of a load current flowing through a plurality of phases of AC power lines, a triangular wave generating means for generating a triangular wave, an absolute value of the triangular wave and the load current of each phase. Pulse width modulation means for comparing each signal with the pulse width modulation of the absolute value signal of the load current of each phase, and an average value for each phase pulse modulated by the plurality of pulse width modulation means. Averaging means for each phase and maximum value selecting means for selecting the maximum value among the average values of the pulses of each phase are provided. The maximum value is input to the triangular wave generating means to determine the amplitude of the triangular wave. An effective value detection device forming a feedback loop is provided.

Further, a trip contact arranged in the electric circuit, trip control means for controlling the trip operation of the contact based on the effective value detected by the effective value detecting device, and the contact by the trip control means And a driving means for performing a tripping operation.

[0011]

In the multiplication circuit configuration based on the pulse width modulation method, the output value as the multiplication result is fed back, and the pulse width is also modulated by the output value itself. As a result, a division function by an output value is easily added, and an effective value calculation circuit using a generally known indirect calculation method can be configured.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a block diagram of an effective value detecting device according to an embodiment of the present invention.

The effective value detecting apparatus 100 shown in FIG. 1 is applied to three-phase currents (R-phase, S-phase, and T-phase), and includes voltage signal generation circuits 29 to 31, pulse width modulation units 1 to 3, Averaging units 4 to 6 are provided for each phase, and the averaging units 4 to 6 are connected to the maximum value selecting unit 7. The maximum value selector 7 is an amplifier 8
, And the amplifier 8 is connected to the triangular wave generator 9. The triangular wave generator 9 is connected to the pulse width modulators 1 to 3 so as to feed back its output.

In the effective value detecting device 100, portions other than the triangular wave generator 9 (pulse width modulators 1 to 3, averaging unit 4
FIG. 2 shows an example of a specific circuit configuration of the maximum value selector 6, the maximum value selector 7, and the amplifier 8). 2, the same reference numerals as those in FIG. 1 denote the same names.

Hereinafter, a specific configuration and operation of the effective value detecting device 100 will be described.

The voltage signal generating circuits 29, 30 and 31 receive the R-phase, S-phase and T-phase currents respectively, convert them into rectified voltage signals, and output them to the effective value detector 100.

In FIG. 2, the pulse width modulator 1 comprises a resistor R11 and a comparator CP1. The pulse width modulator 2 includes a resistor R21 and a comparator (comparator) CP2. Pulse width modulator 3
Is composed of a resistor R31 and a comparator (comparator) CP3.

The pulse width modulation section 1 takes in the R-phase current ER as an input signal and performs pulse width modulation by comparing with the triangular wave generated by the triangular wave generation section 9. The pulse width modulator 2 takes in the S-phase current ES, and the pulse width modulator 3 takes in the T-phase current ET, and performs pulse width modulation, respectively.

The pulse width modulation section 1 is connected to the averaging section 4, the pulse width modulation section 2 is connected to the averaging section 5, and the pulse width modulation section 3 is connected to the averaging section 6.

The averaging units 4 to 6 are low-pass filters for averaging the input current. The averaging unit 4
Operational amplifier (hereinafter referred to as operational amplifier) O
P11, resistors R12, R13, capacitors C11, C
12 is comprised. The averaging unit 5 includes an operational amplifier OP2
1, resistors R22, R23, capacitors C21, C22
Consists of The averaging unit 6 includes an operational amplifier OP31,
It is composed of resistors R32 and R33 and capacitors C31 and C32.

The signal ER that has been pulse width modulated by the pulse width modulation unit 1 is input to an averaging unit 4 and averaged, and the signal ES that has been pulse width modulated by the pulse width modulation unit 2 is
The signal is input to the averaging unit 5 and averaged.
Is input to the averaging unit 6 and averaged.

The signal ER averaged by the averaging unit 4, the signal ES averaged by the averaging unit 5, and the signal ET averaged by the averaging unit 6 are input to the maximum value selection unit 7.

The maximum value selecting section 7 constitutes an ideal diode circuit corresponding to the R phase by the operational amplifier OP12 and the diode D1. The operational amplifier OP22 and the diode D2 are in the S phase, and the operational amplifier OP32 and the diode D2 are in the S phase.
Reference numeral 3 denotes an ideal diode circuit corresponding to the T phase. These three ideal diode circuits are connected in parallel to form an OR circuit capable of selecting the maximum value Erms of the average value of the three phases.
A maximum average value Erms among R, signal ES, and signal ET is selected.

The maximum average value Erms selected by the maximum value selection section 7 is determined by the operational amplifier OP1, the resistors R1 and R2.
Are amplified by K times (this value is described as an effective value K · Erms). Effective value K
Erms is input to the triangular wave generator 9 and the amplitude is K ·
A triangular wave of Erms is generated.

The triangular wave generated by the triangular wave generator 9 is input to the pulse width modulators 1, 2, 3 and used for the above-described pulse width modulation.

In FIG. 2, the triangular wave generating circuit is constituted by a simple analog circuit as generally known.

The pulse width modulator 1 converts an input signal ER (absolute value output) corresponding to the load current and a triangular wave having an amplitude of K · Erms (effective value output value) output from the triangular wave generator 9. The pulse width modulation of the input signal ER is performed by comparison with the comparator CP1.

The pulse width modulator 2 converts the input signal ES (absolute value output) corresponding to the load current and the triangular wave having the amplitude of K · Erms (effective value output value) output from the triangular wave generator 9. The pulse width modulation of the input signal ES is performed by comparison with the comparator CP2.

The pulse width modulation section 3 converts the input signal ET (absolute value output) corresponding to the load current and the triangular wave having the amplitude of K · Erms (effective value output value) output from the triangular wave generation section 9. The pulse width modulation of the input signal ET is performed by comparison with the comparator CP3.

FIG. 3 is a diagram for explaining that the output value K · Erms of the amplifier 8 in FIGS. 1 and 2 is a value corresponding to the maximum effective value of the load current flowing through each phase.

For the sake of explanation, the effective value of the R-phase signal is different from that of the other phase (S
Phase, T phase). The oscillation cycle of the triangular wave (comparative triangular wave) in the triangular wave generator 9 is set to be sufficiently smaller than the frequency of the input signal (signal ER, signal ES, signal ET).

FIG. 3A is a diagram showing a comparison situation between the input signal ER and a triangular wave for comparison (the amplitude of the triangular wave is controlled to have the same value as K · Erms). FIG.
(B) is a diagram showing a pulse train 11 obtained as a result of comparison between the input signal ER and a comparison triangular wave. At this time,
The duty ratio T ₁ / T of the loose train 11 is

(Equation 1) Becomes

If the average value of the pulse train shown in FIG.

(Equation 2) So, together with the previous formula,

(Equation 3) And the average value Erms becomes the effective value of the input signal ER.
It can be seen that the value is according to. Therefore, the output value Er
The value K · Erms obtained by amplifying ms by K times is also a value corresponding to the effective value of the input signal ER.

Assuming that the average value of the pulse train shown in FIG. 3B is Erms, this value is a value corresponding to the effective value of the input signal ER from the relational expression shown in FIG. it is obvious. Therefore, the value K · Erms obtained by amplifying the output value Erms by K times is also a value corresponding to the effective value of the input signal ER.

FIG. 4 is a block diagram showing an embodiment of a circuit configuration of a control device of a circuit breaker incorporating an effective value detecting device. In FIG. 4, the output of the effective value detection device 100 is input to the microcomputer 24 via the A / D converter 22, and the microcomputer 24 responds to the magnitude and the duration of the output of the effective value detection device 100. , The alarm output circuit 25 or the trigger circuit 26.

The control device for the circuit breaker shown in FIG.
1, A / D converter 22, microcomputer 24, alarm output circuit 25, trigger circuit 26, trip device 27,
Instantaneous value detection circuit 28, voltage signal generation circuits 29, 30, 3
1. It is composed of an effective value detecting device 100.

The power supply 21 receives the currents of the three phases R, S and T, and outputs the current to the trip device 27.

The voltage signal generation circuits 29, 30, and 31 receive the R-phase, S-phase, and T-phase currents, respectively, convert the currents into voltage signals, and send the signals to the effective value detection device 100 and the instantaneous value detection circuit 28. Output. The instantaneous value detection circuit 28 sets the signal voltage output from the voltage signal generation circuits 29, 30, and 31 to a voltage value corresponding to a current (instantaneous tripping current) that is much larger (usually 10 times or more) than the rated current. When it reaches, the trigger circuit 2 is activated without waiting for the operation of the effective value detection circuit 100.
6 to give a signal.

On the other hand, the effective value K · Erms output from the effective value detecting device 100 is transmitted through the A / D converter 22 to
It is input to the microcomputer 24.

The A / D converter 22 and the microcomputer 24 can be constituted by an inexpensive 4-bit general-purpose microcomputer having a built-in A / D converter. The microcomputer 24 compares K · Erms with a predetermined threshold value, and when it exceeds the threshold value, sends a signal to the alarm output circuit 25 and the trigger circuit 26.

When a signal from the microcomputer 24 or the instantaneous value detection circuit 28 is input to the trigger circuit 26, the circuit is cut off by the trip device 27.

A second embodiment of the present invention will be described with reference to FIGS.
This will be described below.

The present embodiment is an example in which a microcomputer 24 generates a triangular wave.

FIG. 5 shows an effective value detecting device 10 shown in FIG.
FIG. 3 is a diagram illustrating a circuit configuration of a triangular wave generation unit 32 of FIG. In this embodiment, the A / D converter 23 and the microcomputer 24 are used to generate a triangular wave.

The control device for the circuit breaker shown in FIG.
1, A / D converters 22, 23, microcomputer 2
4. Alarm output circuit 25, trigger circuit 26, trip device 27, instantaneous value detection circuit 28, voltage signal generation circuits 29 and 3.
0, 31 and an effective value detecting device 100.

The power supply 21 receives the currents of the three phases R, S, and T and outputs the current to the trip device 27.

The voltage signal generation circuits 29, 30, and 31 receive the R-phase, S-phase, and T-phase currents, respectively, rectify and convert them into voltage signals, and output the effective value detection device 100 and the instantaneous value detection. Output to the circuit 28.

The effective value detecting device 100 receives the voltage signals from the voltage signal generating circuits 29, 30, 31 and the triangular wave for comparison fed back from the microcomputer 24. The effective value detection device 100 outputs an effective value K · Erms and a comparison triangular wave. This K
The Erms and the triangular wave are input to the microcomputer 24 via the A / D converters 22 and 23.

The A / D converters 22 and 23 and the microcomputer 24 can be constituted by an inexpensive 4-bit general-purpose microcomputer with a built-in A / D converter. The microcomputer 24 compares K · Erms with a predetermined threshold value, and when it exceeds the threshold value, sends a signal to the alarm output circuit 25 and the trigger circuit 26.

The configuration and operation of the instantaneous value detection circuit 28 are as follows.
This is the same as the embodiment.

For this reason, the triangular wave generator 32 shown in FIG.
Can be configured with a simpler circuit than the triangular wave generator 9 in FIG.

In FIG. 5, the operational amplifier OP2 constitutes a well-known integrator together with the resistors R3 and R4 and the capacitor C1. The microcomputer 24 controls the charge / discharge operation of the integrator by comparing the detected effective value K · Erms with the triangular wave output value.

FIG. 7A shows the triangular wave generator 32 of FIG.
4 is a flowchart showing an operation for generating a triangular wave in the A / D converters 22 and 23 and the microcomputer 24. FIG. 7B is an auxiliary explanatory diagram for explaining the operation of FIG. 7A.

Here, the operation of generating a triangular wave in the triangular wave generator 32, the A / D converters 22 and 23, and the microcomputer 24 will be described with reference to FIGS.

The effective value K · Erms detected by the effective value detecting device 100 and the triangular wave signal waveform generated by the triangular wave generator 32 are read into the microcomputer 24 via the A / D converters 22 and 23. .

In the signal processing in the microcomputer 24, first, the output signal _VCP4 is set to "1" (step S201). Descriptive, the output voltage value when the output is set to '1' V _H, also be representative of the output voltage value when the output is set to '0' and V _L.

The comparison voltage V _REF is set in the range of V _L <V _REF <V _H.

When the output signal _VCP4 becomes _VH , the output stage of the comparator CP4 is opened. Therefore, the effective value signal K · Erms is input to a general integrator including the resistors R ₃ and R ₄ , the capacitor C ₁ , and the operational amplifier OP ₂ .

Here, the frequency of the triangular wave to be generated needs to be sufficiently higher than the frequencies of the input signals E _R , E _S and E _T in order to increase the accuracy of the effective value detection. From this, it can be considered that the effective value output value K · Erms is relatively constant as compared with the change in the output value of the integrator.

At this time, the reference voltage K · Er is supplied to the integrator.
This means that a positive voltage has been input for ms / 2. For this reason, the integrator output voltage V _OS decreases almost linearly. The microcomputer within 24, at the time of repeating a comparison between V _G value is initialized to a value with any V _OS to be read (step S202), the condition of V _OS ≦ V _G is satisfied, the output value V _{CP4 VL} is set (step S203).

As a result, the output of the comparator CP4 is inverted to zero potential. In this state, the resistor R _4, a capacitor C _1, the integrator is constituted by an operational amplifier OP _2, so that the negative voltage is input to the reference voltage K · Erms / 2 in the integrator. For this reason, the output voltage of the integrator turns in a direction that increases almost linearly.

In the microcomputer 24, as the next procedure, the comparison between the read V _OS and the value of K · Erms is repeated (step S204), and V _OS ≧ K · Erms
When the condition is satisfied, the output value V _CP4 is set to V _H (step S201). By repeating such a procedure, a triangular wave as shown in FIG. 7B is obtained as an integrator output value.

A third embodiment of the present invention will be described with reference to FIGS.

FIG. 8 uses a microcomputer having four A / D converters, calculates a triangular waveform virtually inside the microcomputer, compares this value with the input signal value, and performs pulse modulation. FIG.

In FIG. 8, in the effective value detection circuit 100, the pulse width modulation units 33, 34 and 35, the averaging / maximum value selection / amplification unit 40 (the averaging unit 4, the maximum value selection unit 7 and the A circuit having the configuration of the amplification unit 8). The voltages of the three phases R, S, and T are
3, 34 and 35. At the same time, the voltages of the three phases R, S, and T are input to the microcomputer 24 via the A / D converters 36 to 39. In the microcomputer 24, a triangular waveform is virtually calculated. The calculated triangular waveform is output to the pulse width modulation units 33, 34, and 35.
, Respectively.

FIG. 9 is a flowchart showing the operation of the circuit shown in FIG.

With reference to FIGS. 8 and 9, an operation in the case where pulse width modulation is performed using an A / D converter and a microcomputer will be described.

The voltage signals E _R , E _S , E _{T of} each phase, and
The effective value K · Erms is read into the microcomputer 24 via the A / D converters 36 to 39.

The microcomputer 24 controls the control signals V _CP1 , V _CP2 ,
Set V _CP3 to _VL . At the same time, the triangular wave signal V virtually calculated in the microcomputer 24
_{The OS} is set to 0 (step S210).

Steps S 211 to S 216 correspond to the triangular wave V virtually generated in the microcomputer 24.
_This section compares the _OS with the input signals E _R , E _S , and E _T. The control signal V _CP1 determined by the result,
By using V _CP2 and V _CP3 , comparators CP1, CP2, C
The output of P3 has the input signals E _R , E _S , E as in FIG.
A pulse train resulting from pulse width modulation of _T is generated.

[0071] After lapse of time required to process the step S211～S216, a virtual triangular wave output value V _OS, the value is set to an arbitrary n, the effective value K · that are loaded separately
The value determined by Erms is added (step S2).
17).

In step S218, the value of the virtual triangular wave V _OS is compared with K · Erms. As a result of this comparison, if the value of the virtual triangular wave V _OS is larger than K · Erms, the process returns to step S210, and V _OS is reset to 0. If the value of the virtual triangular wave V _OS is equal to or smaller than K · Erms, the process returns to step S211.

As a result, V _OS has a peak value of K · Erm.
s sawtooth waveform, the microcomputer 2
4 will virtually exist.

A fourth embodiment of the present invention will be described with reference to FIGS.

FIG. 10 shows an example in which the triangular wave generator is composed of only analog circuits (for example, the triangular wave generator 9 shown in FIG. 2).
Is the case).

In FIG. 10, an integrating circuit composed of an operational amplifier OP ₂ and a comparator C for controlling the integrating circuit are shown.
The operation of P4 is the same as the example of FIG. That is, the output value of the hysteresis comparator using positive feedback, which is configured by the operational amplifier OP21 and the comparator CP21, has only two levels of '0' or K · Erms. Then, this output value and the triangular wave output value are compared with the comparator CP4.
, The input voltage to the integrator is inverted. In this case, if the initial K · Erms value is 0, subsequent oscillation becomes impossible, so it is necessary to provide a limiter so that the minimum value does not become 0.

FIG. 11 shows an example of an ideal diode which is OR-connected as the above-described limiter.
In this example, when the input signal K · Erms is smaller than the bias voltage V _B , the value of K · Erms as the output signal is V _B.

[0078]

As described above, according to the present invention, the maximum effective value of the load current flowing through the multi-phase electric circuit can be simply constituted by an inexpensive general-purpose operational amplifier and comparator, so that the production cost can be suppressed. Can be planned.

[Brief description of the drawings]

FIG. 1 is a block diagram of an effective value detecting device according to a first embodiment of the present invention.

FIG. 2 is a specific circuit configuration diagram (excluding a triangular wave generation unit) of the first embodiment of the present invention.

FIG. 3 is a diagram illustrating the principle of effective value conversion.

FIG. 4 is a block diagram of a control device of the circuit breaker according to the first embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of a triangular wave generator of an effective value detection device according to a second embodiment of the present invention.

FIG. 6 is a block diagram of a control device for a circuit breaker according to a second embodiment of the present invention.

FIG. 7 is a flowchart showing an operation for generating a triangular wave according to a second embodiment of the present invention, and an explanatory diagram.

FIG. 8 is a circuit configuration diagram for generating a triangular wave by a microcomputer according to a third embodiment of the present invention.

FIG. 9 is a flowchart showing an operation of generating a triangular wave by a microcomputer according to a third embodiment of the present invention.

FIG. 10 is a circuit diagram for generating a triangular wave by a triangular wave generator (analog circuit) according to a fourth embodiment of the present invention.

FIG. 11 is a circuit diagram of a limiter according to a fourth embodiment of the present invention.

[Explanation of symbols]

1,2,3 ... pulse width modulation section, 4,5,6 ... averaging section,
7: maximum value selector, 8: amplifier, 9: triangular wave generator, 2
9, 30, 31: voltage signal generation circuit, 100: effective value detection device.

Claims (3)

(57) [Claims] 1. An absolute value generating means for outputting an absolute value signal of a load current flowing in an AC circuit, a triangular wave generating means for generating a triangular wave, and comparing the triangular wave with the absolute value signal to obtain the absolute value signal. Pulse width modulation means for performing pulse width modulation, and averaging means for obtaining the average value of the modulated pulse, comprising: a signal indicating the average value obtained by the averaging means,
An effective value detecting device, comprising a feedback loop that is input to the triangular wave generating means and determines the amplitude of the triangular wave. 2. An absolute value generating means for each phase for obtaining an absolute value signal of a load current flowing through a plurality of phases of AC power lines, a triangular wave generating means for generating a triangular wave, the triangular wave, and a load current of each phase. Pulse width modulation means for comparing the absolute value signal of the absolute value signal of the load current of each phase, and pulse width modulation means for each phase modulated by the plurality of pulse width modulation means, Averaging means for each phase for calculating an average value, and maximum value selecting means for selecting a maximum value among the average values of the pulses of each phase, and the maximum value is input to the triangular wave generating means. And forming a feedback loop for determining the amplitude of the triangular wave. 3. An effective value detecting device according to claim 2, further comprising: a trip contact disposed in an electric circuit; and a trip operation of said contact based on an effective value detected by said effective value detecting device. A circuit breaker comprising: a trip control unit that controls the contact; and a driving unit that performs an operation of tripping the contact point by the trip control unit.