JPH0658384B2 - Electronic reactive energy meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an electronic reactive watt hour meter for measuring reactive power.

(Prior Art) If the instantaneous value and the effective value of the load voltage are represented by ev and V, the instantaneous value and the effective value of the consumption current are represented by ei and I, respectively, and the phase difference between the load voltage and the consumption current is φ, The instantaneous value ev of voltage and the instantaneous value ei of current are expressed by the following equations.

Therefore, the reactive power Q of this phase is as follows.

Q = VIsinψ Conventionally, in order to obtain this reactive power, the phase is shifted by π / 2 by the phase shifter of the voltage expressed by the above formula (1). Is obtained and is multiplied by the current represented by the above equation (2) to obtain the following equation.

ev ′ × ei = VIsin ψ−VIcos (2ωt−π / 2−ψ) Then, by integrating this formula, the reactive power Q = VI
I have got sin ψ.

Here, as the phase shifter for shifting the phase by π / 2, a filter, specifically, an integrator or the like is mainly used. However, when the phase is shifted by a filter or the like in this way, the amplitude may vary depending on the frequency component. For example, when the voltage ev is passed through an integrating circuit, the following equation is obtained.

As can be seen from this equation, the maximum amplitude of the voltage ev passing through the integrating circuit is restricted by 1 / ω,
Frequency characteristics are a problem.

FIG. 3 is a block diagram showing the configuration of a conventional electronic reactive energy meter. In the figure, 1 is an auxiliary transformer (PT) that converts a signal proportional to a load voltage, and 2 is an auxiliary current transformer (CT) that converts a signal proportional to a consumption current. The output signal of the secondary side of the auxiliary transformer 1 And the output signal of the secondary side of the auxiliary current transformer 2 is And Then, when the output signal ev of the auxiliary transformer 1 is passed through the phase shifter (PH) 3 and the phase is shifted by π / 2, the result is as follows.

In this equation, k is a constant of the phase shifter 3.

When the output signal ev ′ from the phase shifter 3 and the output signal ei from the auxiliary current transformer 2 are input to the multiplier (M) 4 and multiplied,
An output signal represented by the following equation is obtained from the multiplier 4.

ev′ei = (2kVI / ω) sin (ωt−π / 2) sin (ωt−ψ) The output signal of the multiplier 4 varies depending on ω.

On the other hand, the output signal ev of the auxiliary transformer 1 is supplied to the AC / pulse converter 5 that shapes the waveform of the AC signal and converts it into a pulse signal, and corresponds to the angular frequency ω of the signal ev from the AC / pulse converter 5. Signal is obtained. This angular frequency signal is supplied to the frequency / voltage converter (f / V) 6 and the output of ω = k′V is obtained from the frequency / voltage converter 6.

The output of the frequency / voltage converter 6 and the output of the multiplier 4 are supplied to a multiplier (M) 7 for multiplication, and an output shown by the following equation is obtained.

ev′eiω = 2kk′VI sin (ωt−π / 2) sin (ωt−ψ) As a result, as can be seen from this equation, the angular frequency ω, that is, the power not influenced by the frequency is obtained.

The above equation is transformed as follows.

ev'eiω = kk'VI {sin ψ-cos (2ωt-π / 2-ψ)} Therefore, by passing this through the integrator (I) 8, the reactive power shown by the following equation is obtained.

Q = kk′VIsin ψ In this way, it is possible to obtain reactive power with excellent frequency characteristics without being affected by the angular frequency ω.

FIG. 4 is a circuit diagram of a multiplier used in the electronic reactive energy meter of FIG.

The voltage signal ev supplied to this multiplier is supplied to the inverting input of the operational amplifier A ₁ forming an integrator via the resistor R ₁ . Between the input and output of the operational amplifier A ₁ integrating capacitor C ₁ is connected, also the non-inverting input of the operational amplifier A ₁ is connected to ground. The integrated output from the operational amplifier A ₁ is supplied to the non-inverting input of the comparator A ₂ ,
It is compared with the comparison voltage eh supplied to the other inverting input. The output of the comparator A ₂ is connected to the inverting input of the operational amplifier A ₁ via the resistor R ₁ , and the switches S ₁ and S ₂ are connected via the inverter IV having an amplification factor of 1.
Is connected to the control input of. The output of the inverter IV is connected to the ground via two resistors R ₁ and R ₁ connected in series. The connection point of the two resistors R ₁ connected in series is connected to the inverting input of the comparator A ₂ . The output of comparator A ₂ is connected to the control inputs of switches S ₃ and S ₄ . The four switches S _{1 to} S ₄ are connected to the bridge, and the switches S ₁ and S ₃ are connected.
The current signal ei is supplied to the connection point with and the switches S ₂ and S
_A current signal -ei is supplied to the connection point with ₄ . Also,
From a connection point between the switches S ₁ and S ₄ signal eop is output via the resistor R _2, a signal eon through another resistor R ₂ is output from a connection point between the switches S ₂ and S ₃ There is.
A pair of capacitors C ₂ connected in series is connected between the output terminals that output these signals. The circuit composed of the resistor R ₂ and the capacitor C ₂ connected to the output end constitutes a low pass filter.

In the multiplier thus configured, first consider the case where the input voltage signal ev = 0. Further, at this time, if the output of the comparator A ₂ is set to logic “1” and the output of the inverter IV that is the inverse of this is set to −er, this output er is divided by the resistor R ₁ connected in series and the comparator A 2 is divided. _The comparison voltage supplied to the inverting input of 2 is -er / 2. Since the output er of the comparator A ₂ is supplied to the inverting input of the operational amplifier A ₁ via the resistor R ₁ ,
The integrated output of the operational amplifier A ₁ exhibits an integration slope in the negative direction, and when this integrated value reaches the comparison voltage eh = −er / 2, the comparator A ₂ is inverted and becomes a logic “0”.

As a result, the output of the inverter IV becomes + er, so the comparison voltage eh supplied to the inverting input of the comparator A ₂ becomes er.
/ 2. And, to the inverting input of the operational amplifier A ₁ , −
Since er is supplied, the integrated output of the operational amplifier A ₁ exhibits an integration slope in the positive direction. When the integrated value of the operational amplifier A ₁ reaches the comparison voltage eh = er / 2, the comparator A ₂ is inverted and becomes the logic “1”.

As described above, when the input voltage signal er = 0, self-excited oscillation is performed and a pulse having a duty of 1: 1 is formed.

Next, consider the case where the input voltage signal ev is supplied. The output of the comparator A ₂ indicates the time division of logic "1".
Let ta be the time interval of logic "0" and tb, and the output of the integrator composed of operational amplifiers in each interval is as follows.

From the above, when the ratio of change in ta and tb due to er and the duty cycle are examined, the results are as follows.

D = ta / (ta + tb ) = (er-ev) / 2er ... (7) = tb / (ta + tb) = (er + ev) / 2er ... (8) switches _S 1 to S ₄ is driven by the output, the switch A current signal ei is output via a resistor R ₂
By integrating through a low-pass filter composed of the capacitor C ₂ and the capacitor C _2, an output proportional to the product of the voltage signal ev and the current signal ei can be obtained as shown in the following equation.

eop = ei () + (− ei) D = ev ei / er ... (9) eon = ei (D) + (− ei) = ev ei / er ... (10) Driving the multiplier configured in this way Power supply voltage is Vdd, V
If ss, Vdd is almost + er (Vdd≈ + er), and Vdd
Since ss is almost −er (Vss≈−er), the input signal ev
Is | Vdd |, | Vss |> | ev | and | Vdd |, | V
Since ss |> | −ev |, that is, the input signal must be smaller than the power supply voltage, the outputs eop and eon are smaller than ev ei from the above equations (9) and (10).

That is, the signal level is lowered in the multiplier. Considering this with the reactive energy meter of FIG. 3, since the multipliers 4 and 7 are connected in series, the output signal level of the multiplier 7 is reduced accordingly, and as a result, the integrator is obtained. 8 deteriorates, and adjustment becomes difficult.

(Problem to be Solved by the Invention) In a conventional electronic reactive watt hour meter, there is a problem that the characteristics are deteriorated because the signal level is lowered in the multiplier.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electronic reactive watt-hour meter that has improved characteristics and can measure reactive power with high accuracy.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, in the electronic reactive watt hour meter for calculating the reactive power due to the load voltage and the consumption current flowing through the load, the present invention provides: The phase shift means for shifting the phase of the voltage signal proportional to the voltage, and the pulse width modulation signal obtained by pulse width modulating the voltage signal output from the phase shift means so as to have a duty cycle corresponding to the level of the signal. Multiplier means for obtaining reactive power by taking out a current signal proportional to current consumption, frequency-voltage converter means for outputting a voltage proportional to the frequency of the voltage signal, and output voltage of the converter means for multiplying means. The gist is to have a power supply voltage control means for variably controlling the drive power supply voltage.

(Operation) In the electronic reactive energy meter of the present invention, the power supply voltage of the multiplication means for obtaining the reactive power by extracting the current signal by the pulse width modulation signal obtained by pulse width modulating the phase-shifted voltage signal is used as the frequency of the voltage signal. It is variably controlled by a voltage proportional to.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an electronic reactive watt hour meter according to an embodiment of the present invention. In the electronic reactive energy meter of the present embodiment, reference numerals 1 to 6 and 8 are the same as the constituent elements indicated by the same reference numerals in FIG. 3, and the auxiliary transformer 1, the auxiliary current transformer 2 and the phase shifter are used. 3, a multiplier 4, an AC / pulse converter 5, and an integrator 8.

Output signal from auxiliary transformer 1 Is shifted in phase by π / 2 by the phase shifter 3 and is given by the following equation, and is supplied to the multiplier 4.

Also, the output signal from the auxiliary current transformer 2 Is directly supplied to the multiplier 4 and is multiplied by the output signal ev 'of the phase shifter 3 shown in the above equation to obtain the product of both.

On the other hand, the output signal ev of the auxiliary transformer 1 is supplied to the AC / pulse converter 5, and a signal corresponding to the angular frequency ω of the signal ev is obtained from the AC / pulse converter 5. This angular frequency signal is supplied to the frequency / voltage converter 6, and a voltage proportional to the frequency is obtained from the frequency / voltage converter 6.

The output voltage from the frequency / voltage converter 6 is supplied to the power supply voltage conversion circuit 9. The power supply voltage conversion circuit 9 is supplied with power supply voltages Vdd and Vss for supplying to the multiplier 4 as inputs. These power supply voltages Vdd and V
ss is variably controlled by the output voltage of the frequency / voltage converter 6. Specifically, since the output voltage of the frequency / voltage converter 6 is proportional to the frequency, the power supply voltages Vdd and Vss are variably controlled in proportion to the frequency. After being variably controlled in this way, the power supply voltage conversion circuit 9 supplies the power supply voltage to the multiplier 4.
Then, the output signal of the multiplier 4 whose power supply voltage is controlled in this way is integrated by the integrator 8 and reactive power is obtained.

More specifically, the voltage of the phase shifter 3 is shifted by n / 2 and the voltage signal ev of the auxiliary transformer 1 is multiplied by the current signal ei from the auxiliary AC 2, and the result is output from the multiplier 4. The electric power is eop = ev ei / er from the above equation (7), but the voltage signal ev in this equation is π / 2 in the phase shifter 3, that is, 90 °.
As a result of the phase shift, ev ′ = ko ev / ω, which is affected by the frequency. Therefore, it is necessary to compensate for the influence of this frequency, but for that reason, the voltage er that constitutes the denominator of the power eop defined by equation (7) should be similarly varied in proportion to the frequency. become. Since this voltage er is substantially equal to the power supply voltage Vdd as described above (Vdd≈er), Vdd and Vss are variably controlled in the power supply voltage conversion circuit 9 in proportion to the frequency instead of this er. To do. Thus, the power supply voltage variably controlled by the frequency, that is, the voltage er 'is er'
= K ₁ er / ω. Therefore, the electric power eop is eop = ev ei / e
In r, ev as ev ′ = ko ev / ω and er as er ′
By substituting = k ₁ er / ω, the following is obtained.

eop = (ko ev / ω) ei / (k ₁ er / ω) = Koev ei / (k ₁ er) As can be seen from this equation, the power eop is not affected by the frequency.

In order to perform such variable control in the power supply voltage conversion circuit 9, the auxiliary transformer 1 in the AC / pulse converter 5 is used.
The frequency of the voltage signal ev is converted into a pulse, the frequency is detected, this is converted into a voltage in the frequency / voltage converter 6, that is, a voltage proportional to the frequency, and the power supply voltage is converted based on the voltage proportional to this frequency. By controlling the power supply voltages Vdd and Vss in the circuit 9 and operating the multiplier 4 by the variable-controlled power supply voltages Vdd 'and Vss', the fluctuation due to the influence of the frequency can be eliminated as described above. . With such a configuration, the multiplier 7 is also unnecessary as compared with the conventional electronic reactive energy meter shown in FIG.

FIG. 2 is a block diagram showing another embodiment of the present invention. The embodiment shown in the figure is different only in that the power supply voltage of the integrator 8 is controlled instead of controlling the power supply voltage of the multiplier 4 in the embodiment of FIG. The output voltage of 9 is supplied to the integrator 8. In addition,
Other configurations and operations in this embodiment are the same as those in FIG.

[Effects of the Invention] As described above, according to the present invention, the power supply voltage of the multiplication means for obtaining the reactive power by extracting the current signal by the pulse width modulation signal obtained by pulse width modulating the phase-shifted voltage signal is used as the voltage signal. Since it is variably controlled by the voltage proportional to the frequency of, the influence of the frequency due to the phase shift of the voltage signal is removed by variably controlling the power supply voltage of the multiplying means in accordance with the frequency. In addition, the characteristic is not deteriorated due to the decrease in the signal level of the multiplier, and the frequency variation due to the phase shifter is not present, so that the reactive power can be measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an electronic reactive energy meter according to an embodiment of the present invention, FIG. 2 is a block diagram of another embodiment of the present invention, and FIG. 3 is a conventional electronic reactive power. FIG. 4 is a block diagram showing the configuration of the quantity meter, and FIG. 4 is a circuit diagram of the multiplier. 1 ... Auxiliary transformer, 2 ... Auxiliary current transformer, 3 ... Phase shifter, 4 ... Multiplier, 5 ... AC / pulse converter, 6 ... Frequency / voltage converter, 8 ... Integrator, 9 ... Power supply voltage conversion Circuit, A ₁ ... Operational amplifier, A ₂ ... Comparator, C ₁ ... Integrating capacitor,
S _{1 to} S ₄ ... Switches.

Claims (1)

[Claims] 1. An electronic reactive watt hour meter for calculating a reactive power due to a load voltage and a consumption current flowing through the load, and a phase shift means for shifting a phase of a voltage signal proportional to the load voltage, and the phase shift means. Multiplier means for obtaining reactive power by extracting a signal proportional to the consumed current by a pulse width modulation signal obtained by pulse width modulating the output voltage signal so as to have a duty cycle corresponding to the level of the signal, and the voltage signal. Of the frequency-voltage conversion means for outputting a voltage proportional to the frequency and a power supply voltage control means for variably controlling the drive power supply voltage of the multiplication means by the output voltage from the conversion means. Electricity meter.