JP3074749B2 - Power conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for converting a measured current into a voltage, which is applied to an input terminal of an operational amplifier via a switch, and the measured voltage is converted into a pulse width modulation signal proportional thereto. A power conversion circuit that opens and closes a switch and converts it into power proportional to the measurement current and measurement voltage, especially the power that has been improved to remove the noise of the fundamental wave component and lower frequency components of the input signal with a simple configuration The present invention relates to a conversion circuit.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a configuration of a conventional power conversion circuit of this kind. Reference numeral 10 denotes an input circuit, 11 denotes a switching circuit, 12 denotes a pulse width modulation circuit, and 13 denotes an output circuit.

[0003] The AC measurement current _Ii is supplied to input terminals T1 and T2.
And the measurement current I _i is applied to these input terminals T
1. The current flows through the primary winding of the current transformer CT1 connected to T2. The secondary winding of the current transformer CT1 voltage V1 which is proportional to the measured current I _i at both ends of the resistor R1 is connected the resistor R1 is generated. The voltage V1 is applied to the input terminal of the switch SW1 of the switching circuit 11 via the resistor R2.

A capacitor C connected to both ends of a resistor R1
Numeral 1 is for noise removal, and the resistor R2 and the common potential point COM
And diodes D1 and D connected to each other with opposite polarities.
2 is a diode for protection.

[0005] The measured voltage _{V i} of the AC input terminal T3, T4
And the measurement voltage V _i is passed through the primary winding of the current transformer CT2 via the resistor R3. The resistor R3 is a resistor for converting the measured voltage V _i to the current. The converted current is current-transformed by the current transformer CT2, and the secondary current flows through the operational amplifier Q1 to be converted into the voltage V2.

A protection diode D3, D is connected between the inverting input terminal (-) and the non-inverting input terminal (+) of the operational amplifier Q1.
4 is connected between the inverting input terminal (-) and the output terminal, a frequency characteristic compensating series circuit composed of a resistor R4 and a capacitor C2, and a resistor R5 connected in parallel with the series circuit.

The pulse width conversion circuit 12 converts the signal into a pulse width modulation signal PWM having a duty proportional to the voltage V2 to control the opening and closing of the switch SW1. When the voltage V2 is zero, the duty of the pulse width modulation signal PWM is 1/2, and the modulation is performed as the voltage V2 increases. However, the duty is 1/2 of the average of one cycle. .

Reference numeral 13 denotes an output circuit, which includes an operational amplifier Q2,
It is composed of a resistor R6, a capacitor C3 and the like. The inverting input terminal (-) of the operational amplifier Q2, whose inverting input terminal (+) is connected to the common potential point COM, is connected to the output terminal of the switch SW1 and is connected between the output terminal and the resistor R6 and the capacitor C3. Parallel circuits are connected to form an active filter. The measured power _PM1 is obtained at the output terminal T5.

With the above configuration, the measurement voltage V_iIs a pulse
It is converted into a pulse width modulation signal PWM by the width modulation circuit 12.
The switch SW1 is controlled by the duty of
Style I _iIs turned on / off, the output of the operational amplifier Q2
At the end is the measured voltage V_iAnd the measured current I_iDetermined by
Power P_M1Is obtained.

[0010] However, the power conversion circuit as described above, when noise is superimposed as a regular frequency components in the measured current I _i is removable by capacitor C3 for smoothing, ultra-low-frequency component If the noise is superimposed, since the reactance of the capacitor C3 is increased, its removal becomes insufficient state appears as a variation of the power P _M1. However, even in this case, even if noise of a different frequency component is included in one of the measurement voltage and the measurement current, it appears as a fluctuation in the output, but does not become effective power, so that no power error occurs.

Therefore, a power conversion circuit as shown in FIG. 4 is used. The voltage V1 is applied to the operational amplifier Q2 via the resistor R2 and the switch SW1, and the switch SW1 receives the pulse width signal PWM via the inverter Q3. Up to this point, it is basically similar to the corresponding circuit shown in FIG. In FIG. 4, the voltage V1 is further reduced by the inverting amplifier Q.
4. The voltage obtained via the resistor R7 and the switch SW2 is added to the input terminal of the operational amplifier Q2. In this case, the switch SW2 is controlled via the inverter Q5 so as to be turned on / off with a polarity opposite to that of the switch SW1.

Accordingly, in the power conversion circuit shown in FIG. 4, the current i _A obtained by inverting the current i _A flowing through the switch SW2 hand and the current i _A flowing through the switch SW1
Since configured to apply to the input end of the addition to the operational amplifier Q2 bets, the power P _M2 obtained at the output terminal T5 of the operational amplifier Q2 is canceled noise ultra low frequency components from each other output Does not appear in

[0013]

However, such a power conversion circuit as described above requires two switch elements and a circuit related thereto in order to remove noise at an extremely low frequency, and therefore a high-density circuit is required. There is a problem in realizing the miniaturization by realizing the above, and it is an obstacle particularly for realizing a multi-transducer using many such power conversion circuits.

[0014]

According to the present invention, in order to solve the above problems, a measured current is converted to a first voltage and applied to an input terminal of an operational amplifier via a switch, and the measured voltage is proportional to the first voltage. The first voltage is input to the power conversion circuit which converts the current into a power proportional to the measured current and the measured voltage by opening and closing the switch by opening and closing the switch. And 1 of the first voltage
And a compensating means for calculating a compensation signal having a magnitude of / 2 and adding the compensation signal to the input terminal of the operational amplifier.

[0015]

The measuring current is converted to a first voltage and applied to the input terminal of an operational amplifier via a switch. The measuring voltage is converted to a pulse width modulation signal proportional to the first voltage, thereby opening and closing the previous switch. As a result, the power is converted into power proportional to the measured current and the measured voltage, and this power is output. In this case, the compensating means computes a compensation signal having a polarity opposite to that of the first voltage and half the magnitude of the first voltage, and adds this compensation signal to the input terminal of the operational amplifier. .

In this way, even if super-low frequency noise is superimposed on the measurement current, the noise can be removed by using only one switch, and its contribution to realizing miniaturization. Great effect. In particular, it is effective in realizing a multi-transducer using many such power conversion circuits.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of one embodiment of the present invention. Parts having the same functions as those of the conventional power conversion circuits shown in FIGS. 3 and 4 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

[0018] The voltage obtained by converting the measured current I _i to the voltage V1
Via the resistor R2 is applied to the input terminal of the switch SW1, while the voltage V2 appearing at the output terminal is applied to the input terminal of the operational amplifier Q2, the switch SW1 is the measured voltage V _i is the pulse width modulation the du is converted into a signal PWM - since it is opened and closed by Tei, thereby the product of the measured current I _i to its output and the measured voltage V _i, i.e. the voltage V2 corresponding to the measured power of this, and the resulting It will be.

The pulse width modulation signal PWM in this case, when the measured voltage V _i is zero is ON / OFF at Deyutei 50%, the measurement voltage V _i is changed with increasing, this Deyutei is It is about 50% on average of one cycle of the measured voltage V _i.

The inverting amplifier circuit INA is composed of the resistors R8 and R9 and the operational amplifier Q5. Then, the voltage V1 is inverted and amplified by the inverting amplifier circuit INA at an amplification degree of 1,
The output voltage-(V1) is added to the input terminal of the operational amplifier Q2 via the resistor R10.

The inverting amplifier circuit INA and the resistor R10
Constitutes the compensation circuit CM1, and the value of the resistor R10 in this case is selected to be twice as large as that of the resistor R2. Therefore, the voltage V1 is applied to the output terminal of the compensation circuit CM1.
A voltage Vc of − (V1) / 2 appears. The power conversion circuit shown in FIG. 1 has a simple configuration that does not require the switch SW2 in the compensation circuit CM1 as compared with the conventional power conversion circuit shown in FIG.

In the above configuration, when the measured voltage V _i is zero, the duty of the pulse width modulation signal PWM is 50%, so that the voltage V 1 proportional to the measured current I _i is a voltage at the output terminal of the switch SW 1. V2 = + (V1) / 2, while the voltage Vc output from the compensation circuit CM1 is-(V1) / 2, so that these voltages V2 and Vc are mutually different. The power P _{M3 that} is canceled and appears at the output terminal of the operational amplifier Q2 is zero. At the same time, the noise of the ultra-low frequency components included in the voltages V2 and Vc are also added in opposite polarities, and as a result, they do not appear as fluctuation components of the ultra-low frequency in the power _PM3 appearing at the output terminal of the operational amplifier Q2.

Next, the pulse width modulation signal PWM in accordance with the measured voltage V _i is applied to change Deyutei, since the voltage V1 is off this Deyutei, the voltage V2 of the output terminal of the switch SW1 is changed A difference is generated between the voltage Vc and the power P _M3 corresponding to the difference.
2 appears at the output end.

Further, even when the ultra-low frequency noise in the voltage V1 is superimposed, by the operation of the circuit of the
This effect is eliminated and the power P _m3 is affected by output fluctuation.
Does not affect. That formula power P is a voltage V _m s
in (ωt), current _{I m sin (ωt + θ)} , the period
If T

(Equation 1) This V _m sin (ωt) and I _m sin (ωt +
θ) is ω = 2πf, the frequency must be the same
I have to. If the current and voltage frequencies are different at this time,
In this case, the power P becomes zero. Therefore, the above equation (1)
Applied to the circuit of the invention, the measured voltage is Visin (ω
₁ t), the voltage corresponding to the measured current Ii is V1 sin (ω ₁
t + θ), the voltage V1 sin (ω ₁ t + θ)
The very low frequency ILsin (ω _Two t) measuring the measured current and
The power P _m3 And ask for

(Equation 2) Becomes Therefore, from equation (2), Visi having the same frequency is obtained.
n (ω ₁ t) and V1 sin (ω ₁ t + θ) components only
It appears at the output of operational amplifier Q2 as P _m3, different frequencies
Where IL sin (ω ₂ t) is the output terminal of the operational amplifier Q2.
Does not appear in It also, measured with respect to ω ₂ of the ultra-low frequency
From it or we ω ₁ is the relationship ω ₁ of the current is ω ₂ «ω ₁ ω ₂
When you look at it, you can instantly think that it is DC,
DC component rises and falls due to the operation of the operational amplifier Q5.
To consider that the output does not fluctuate to the canceled power P _m3
Can also. Therefore, by these actions, the very low frequency I
Lsin (ω ₂ t) does not affect power P _m3 as output fluctuation.

FIG. 2 is a circuit diagram showing a configuration of another embodiment of the present invention. In this case, the measured current I _i is
A resistor R input through T3 and connected to its secondary winding
11, R12, a voltage + V with respect to these middle points COM.
3. Generate -V3. The voltage + V3 is equal to the resistance R
2, and is output to the input terminal of the operational amplifier Q2 via SW1 controlled by the pulse width modulation signal PWM. on the other hand,
The voltage -V3 is output to the input terminal of the operational amplifier Q2 via the resistor R10. The compensation circuit CM2 is composed of the resistors R10 and R12.

Here, R11 = R12, R10 = 2 · R
Since the resistance value is selected as 2, the operation is performed in the same manner as in the case shown in FIG. 1, and the ultra-low frequency noise can be removed. In this case, the resistors R2, R10, R11, R12
Can be used and a module resistor can be used in such a configuration, so that downsizing and characteristics can be balanced.

[0027]

As described above, according to the present invention, as described in detail with reference to the embodiment, the ultra-low frequency noise superimposed on the measurement current is removed by the compensation circuit without using the switch. The downsizing is possible, and the advantage of the downsizing is particularly great when applied to a multi-transducer using a large number of such power conversion circuits. Further, such a power conversion circuit is effective when measuring the power of a load having a complicated waveform such as an inverter.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of one embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of another embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional first power conversion circuit.

FIG. 4 is a circuit diagram showing a configuration of a conventional second power conversion circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Input circuit 11 Switching circuit 12 Pulse width modulation circuit 13 Output circuit CM1, CM2 Compensation circuit PWM Pulse width modulation signal CT1, CT2, CT3 Current transformer

Claims (1)

(57) [Claims] The measured current is converted to a first voltage and applied to the input of an operational amplifier via a switch, and the measured voltage is converted to a proportional pulse width modulated signal to open and close the switch. In the power conversion circuit for converting the measured current and the measured voltage into electric power proportional to the measured voltage, the first voltage is input, and a compensation signal having a polarity opposite to that of the first voltage and a magnitude of １ ／ of the first voltage is supplied. A power conversion circuit comprising a compensating means for performing a calculation and adding the compensation signal to an input terminal of the operational amplifier.