JPS628152B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC power measuring device that outputs a DC voltage proportional to AC power to be measured, using an arithmetic circuit known as a feedback sum-difference-square AC signal multiplier. be.

The circuit configuration of a conventionally known AC power measuring device of this type is shown in FIG. This device is provided with two sets of addition/subtraction arithmetic units 2 and 3. From the reference DC signal V _R from the reference DC signal generator 1, the voltage signal V _AC and current signal I _AC related to the AC power to be measured, and the feedback DC signal V _F fed back from the final output, both addition and subtraction calculation units 2, 3 performs the following calculation to obtain outputs V ₂ and V ₃ .

V ₂ =V _AC +I _AC +V _R -V _F …………(1) V ₃ =V _AC +I _AC +V _R +V _F …………(2) Both outputs V ₂ and V ₃ are connected to the next stage, respectively. DC voltage V _A corresponding to the effective value is generated by the thermoelectric elements 4 and 5,
It is converted to _VB . Here, if the specific conversion constants of both thermoelectric elements 4 and 5 are K ₂ and K ₃ and one period of the AC voltage or AC current signal is T, then the output DC voltage V
_A and _VB are as follows.

V _A = 1/T∫ ^T _O K ₂ V ₂ ² dt …………(3) V _B = 1/T∫ ^T _O K ₃ V ₃ ² dt …………(4) These two output signals are the difference The signal is input to a dynamic amplifier 6.
Here, if the amplification factor of the differential amplifier 6 is sufficiently large and both constants K ₂ and K ₃ can always be made equal to each other regardless of the magnitude of the measured power, then from equations (1) to (4), K ₂ , Eliminate K ₃ and get 1/T∫ ^T _O (V _AC + I _AC + V _R - V _F ) ² dt=1/T∫ ^T _O (V _AC - I _AC + V _R + V _F ) ² dt ……(5 ) is obtained. Considering that the integral value over one cycle of the product of the AC signal and the DC signal is zero, the following equation is derived from equation (5).

1/T∫ ^T _O V _R・V _F dt=1/T∫ ^T _O V _AC・I _AC dt V _R・V _F =1/T∫ ^T _O V _AC・I _AC dt V _F =1/V _R・1/T∫ ^T _O V _AC・I _AC dt ...(6) Equation (6) means that the output signal V _F of the differential amplifier 6 is determined from the voltage signal V _AC and the current signal I _AC . This means that it is proportional to the amount of power that is generated. Thus, power can be measured using the circuit configuration shown in FIG.

However, although the constants K ₂ and K ₃ inherent to thermoelectric elements used as effective value calculators can generally be considered constants with respect to time, they change nonlinearly with respect to temperature, and therefore are not required. It is extremely difficult to match the constants K ₂ and K ₃ with high precision over the entire range of multiplication levels.

Therefore, in order to solve this problem, the circuit configuration shown in FIG. 2 was proposed. The device shown in FIG. 2 is a partial improvement of the device shown in FIG. An amplifier 8 having an amplification degree C that closely matches the amplification degree of the amplifier 7 is provided between the entire output terminal. The amplification degree C of both amplifiers 7 and 8 is adjusted in conjunction with the swing of a DC galvanometer 11, which will be described later. Further, a differential amplifier 10 is provided to which the output signal V _B of the thermoelectric element 5 and the reference DC voltage V _C generated by the reference DC voltage generator 9 are input, and a DC galvanometer is connected to the output side of the differential amplifier 10 . 1
1 is provided.

In the apparatus shown in FIG. 2, when the magnitude of the measured power changes, the amplification degree C of the amplifiers 7 and 8 is adjusted so that the deflection of the DC galvanometer 11 becomes zero. By doing this, for both inputs of the differential amplifier 6, 1/ ^{T∫ TOK} _{2 (} V _AC +I _AC +CV _R −V _F ) ² dt=1/ _{T∫ TO} ^K ₃ (V _AC − I _AC +CV _R +V _F ) ² dt ...(7) holds true, and regarding the differential amplifier 10, V _C =1/T∫ ^T _O K ₃ (V _AC -I _AC +CV _R +V _F ) ² dt ...(8) holds true. Equation (8) shows that the amplification degree C of the amplifier 7 is adjusted so that the magnitude of the output DC voltage of the thermoelectric element 5 is always maintained at a constant value V _C even if the magnitude of the measured power changes. It shows that there is. If we make sure that the constants K ₂ and K _{3 of both thermoelectric elements 4 and 5} match at least at this voltage V _C , equation (7) can be expanded and rearranged as follows, similar to equation (5). can do.

CV _F =1/V _R・1/T∫ ^T _O V _AC・I _AC dt……(9) Therefore, the DC output signal of the differential amplifier 6 V _F
By multiplying by C by the amplifier 8, the output V _W =CV _F can be made to correspond to the measured power according to equation (9).

However, in the circuit system shown in FIG. 2, as is clear from equation (9), the feedback DC signal V _F depends on the amplification degree C of the variable amplification amplifier 7, and the output DC voltage V of the thermoelectric element 5 Between the operating system (auxiliary control system) for matching _B with the reference voltage V _C and the operating system (main control system) for matching the output DC voltages V _A and V _B of both thermoelectric elements 4 and 5. There is mutual interference. As a result, it is difficult to realize an automatic control system that balances the two operating systems at the same time, and one has to do so automatically and the other manually to satisfy equations (7) and (8), respectively. The power was calculated from the output V _W of the amplifier 8. In this way, the circuit device shown in Fig. 2 saves the trouble of aligning the characteristics of the two sets of thermoelectric elements by adding one set of variable amplification amplifiers, but on the other hand, due to the operating principle as a measuring device, It has become difficult to perform automatic measurements.

An object of the present invention is to provide an AC power measuring device that can eliminate the trouble of aligning the characteristics of both effective value calculators, ie, both thermoelectric elements, and at the same time can perform highly accurate automatic measurement.

In order to achieve this object, the present invention simultaneously controls the effective value signal of a composite value signal of one of the AC voltage and the AC current to be multiplied and one of the reference DC signal and the feedback DC signal. This will be described in detail below based on examples.

FIG. 3 shows an embodiment in which an alternating current voltage and a reference direct current signal are used as elements for obtaining the above-mentioned composite value. In this circuit device, 2
A set of addition/subtraction operators 2, 3 and two sets of thermoelectric elements 4, 5
, a differential amplifier 6, and a feedback circuit 12 constitute a main control system L _M , which includes an addition/subtraction operator 3, a thermoelectric element 5, a differential amplifier 10, and an A/D converter 13.
and a variable amplification amplifier 7.
_S is configured.

Addition/subtraction calculators 2 and 3 calculate the following from the voltage signal V _AC and current signal I _AC related to the AC power to be measured, the feedback DC signal V _F , and the reference DC signal _VR generated by the reference DC signal generator 1, respectively. These calculations are performed to form output signals V ₂₀ and V ₃₀ .

V ₂₀ = C (V _AC + V _R ) + I _AC - V _F ...... (10) V ₃₀ = C (V _AC + V _R ) - I _AC + V _F ... (11) Here, V _AC + V _R is the signal V _AC and _VR are obtained by adder 14, and the addition result is passed through amplifier 7 with amplification degree C to obtain C(V _AC +V
_R ) is formed and used as an input signal to the addition/subtraction calculators 2 and 3. The amplification degree C of the amplifier 7 is adjusted by the output signal of the AD converter 13 as described later.

Thermoelectric elements 4 and 5 receive signals V ₂₀ and V ₃₀ according to equations (10) and (11).
are converted into DC signals V _A and V _B corresponding to the effective values according to conversion constants K ₂ and K ₃ , respectively.

V _A = 1/T∫ ^T _O K ₂ V ₂₀ ² dt ……(12) V _B = 1/T∫ ^T _O K ₃ V ₃₀ ² dt …………(13) Both signals V _A , V _B is input to the differential amplifier 6, and eventually a control operation is performed in the main control system L _M such that V _A =V _B.

On the other hand, the output signal V _B of the thermoelectric element 5 and the reference DC voltage signal V _C generated by the reference DC voltage generator 9 are input to the differential amplifier 10 , and the output signal is sent to the AB converter 13 . The signal is then converted into a digital signal. This output digital signal adjusts the amplification degree C of the amplifier 7, and as a result, the auxiliary control system L _S performs a control operation such that both input signals of the differential amplifier 10 match, that is, V _B =V _C. It will be done.

As in the case of Fig. 2, the value of the reference DC voltage V _C is set to both constants at least at this voltage V _C.
If K ₂ and K ₃ are selected to match, as long as both control systems L _M and L _S are in steady state, 1/T∫ ^T _O V ₂₀ ² dt=1/T∫ ^T _O V ₃₀ ² dt……(14). Substituting equations (10) and (11) into this, we get 1/T∫ ^T _O {C(V _AC +V _R )+I _AC −V _F } ² dt=1/T∫ ^T _O {C(V _AC + V _R ) - I _AC + V _F } ² dt (15) is obtained. Expand this and further alternating current signal (V
Considering that the integral value over one period of the product of _AC or I _AC ) and the DC signal (V _R or V _F ) is zero, the following equation is derived.

1/T∫ ^T _O CV _R V _F dt=1/T∫ ^T _O CV _AC I _AC dt V _R V _F =1/T∫ ^T _O V _AC I _AC dt V _F =1/V _R・1/T ∫ ^T _O V _AC I _AC dt ………(16) This equation (16) is exactly the same as the above equation (6),
The power to be measured can be determined from the DC output signal _VF . What is important here is that both sides of equation (16) include the multiplication factor C set by the variable amplification amplifier 7.
This means that it does not appear. In other words, the operation of the auxiliary control system, which maintains the operating level of the thermoelectric element constant regardless of the value of the measured power, does not affect the operation of the main control system, so both control systems This means that automatic control operations can be performed at the same time, allowing completely automatic measurement of AC power.

As is clear from the conversion process from equation (15) to equation (16), even if the signal V _AC and signal I _AC are converted or the signal _VR and feedback DC signal V _F are exchanged,
Furthermore, even if the combination of signs of each signal is changed in equations (10) and (11), the same measurement results can be obtained.

As described above, according to the present invention, it is not necessary to uniform the constants of the effective value calculator such as a thermoelectric element over a wide range, and the amplification of the variable amplification amplifier used to fix the operating level is eliminated. Since the degree value does not appear in the measured value, there is no need to install a variable amplification amplifier in the output stage, simplifying the circuit configuration, and providing excellent AC power measurement with improved conversion accuracy from AC power to DC voltage. equipment can be provided.

[Brief explanation of the drawing]

1 and 2 are block diagrams of different known feedback type sum-difference-square-difference AC power measuring devices, and FIG. 3 is a block diagram showing an embodiment of the AC power measuring device according to the present invention. 1... Reference DC signal generator, 2, 3... Addition/subtraction operator, 4, 5... Thermoelectric element, 6, 10... Differential amplifier,
7...Variable gain amplifier, 13...A-D converter, 1
4... Adder.

Claims (1)

[Claims] 1 A pair of addition/subtraction calculators that receive as input an AC voltage signal and an AC current signal related to the AC power to be measured, a reference DC signal, and a feedback DC signal, and output a signal corresponding to the effective value of the output of each addition/subtraction calculator. AC comprising a main control system including a pair of effective value calculators and a differential amplifier that receives the output signals of both effective value calculators as input and outputs the feedback DC signal as a DC signal corresponding to the AC power. In the power measuring device, both addition and subtraction operation units are connected to input sides of the addition/subtraction calculation unit for both input signals, one of the AC voltage signal and the AC current signal, and one of the reference DC signal and the feedback DC signal. An adder that calculates the sum of input signals, and a variable amplification amplifier that amplifies the output signal of the adder and inputs it as a composite signal of both input signals to the adder/subtractor, and the variable amplification amplifier An alternating current power measuring device comprising an auxiliary control system that controls the operating level of the effective value calculator to a constant value by adjusting the amplification degree of the AC power measuring device.