JP2020176877A - Voltage detector - Google Patents

Abstract

To provide a novel technique for detecting high voltages.SOLUTION: A voltage detector 100 includes: a piezoelectric transformer PZT1, of which poles are divided to a measurement target side and a detection side; an oscillator 110 for driving the detection side of the piezoelectric transformer PZT1 in a frequency region where an input impedance is inductive; and a detector 120 for outputting a detection signal according to a measurement target voltage while a measurement target voltage is being applied to the measurement target side of the piezoelectric transformer PZT1.SELECTED DRAWING: Figure 1

Description

The present invention relates to a voltage detection device suitable for detecting a high voltage generated in, for example, a power generation facility.

Prior art for detecting a voltage to be detected by dividing the voltage to be detected by a voltage dividing resistor is conventionally known for this type of voltage detecting device (see, for example, Patent Document 1). In this prior art, the voltage to be detected applied between the voltage end and the ground end (GND) is divided by a large number of voltage dividing resistors, and this divided low voltage is sent to the subsequent control circuit. is there. In addition, while the grounding of the voltage detection device and the grounding of the control circuit are common, the voltage reduced by the voltage dividing resistor is sent to the control circuit via the insulation amplifier, so common mode noise is effectively suppressed. It is considered to be.

Japanese Unexamined Patent Publication No. 2012-117929

In the voltage detection device of the prior art, it is necessary to supply electric power to the input side of the detected voltage and the output side to the control circuit in the isolated amplifier. Of these, the output side can receive power from the power supply (Vcc) of the control circuit, but since there is no dedicated power supply on the input side of the detected voltage, in order to operate the insulation amplifier, It is necessary to supply power in a state of being insulated from the output side. For this reason, an isolated DC-DC converter is required between the input side of the detected voltage and the output side to the control circuit in addition to the isolated amplifier, which increases the size of the device and complicates the circuit configuration. There is a problem.

Further, in the voltage detection device of the prior art, the magnitude of the power loss generated in the voltage dividing resistor cannot be overlooked. That is, the power loss due to the voltage dividing resistor tends to increase with the square of the voltage value as the originally detected voltage becomes higher. Therefore, for example, if the voltage is as high as several hundred V or more. Further, the excessive temperature rise of the voltage dividing resistor due to the loss becomes a problem.

Therefore, the present invention provides a new technique for high voltage detection.

In order to solve the above problems, the present invention employs the following solutions. The parentheses in the following description are for reference only, and the present invention is not limited thereto.

The present invention provides a voltage detector. In the voltage detection device of the present invention, the piezoelectric transformer is placed at the center of voltage detection to perform the detection operation. For this purpose, the voltage detector includes piezoelectric transformers polarized on the primary and secondary sides. The primary side and the secondary side of the piezoelectric transformer are insulated by the piezoelectric body (piezoelectric element, piezoelectric ceramics) itself.

A drive signal is applied to one side (for example, the primary side) of the piezoelectric transformer in the vicinity of the resonance frequency at which the input impedance is inductive to cause resonance, and the other side (for example, the secondary side) is measured. Apply voltage. At this time, it is known that the resonance characteristics (for example, the sharpness of resonance) on one side of the piezoelectric transformer change depending on the magnitude of the voltage to be measured applied to the other side.

Based on the above findings, the inventors of the present invention predetermine the relationship between the magnitude (voltage value) of the voltage to be measured applied to the other side of the piezoelectric transformer and the resonance characteristic that appears on one side. By doing so, it has been found that the detection signal corresponding to the detected voltage can be output on one side of the piezoelectric transformer.

Therefore, if an oscillator is connected to one side of the piezoelectric transformer and its resonance characteristics are observed while driving in the frequency domain where the input impedance is inductive, the result can be output as a detection signal of the voltage to be measured. Become.

As described above, the voltage detection device of the present invention can detect the oscillator and the circuit portion constituting the detector in isolation from the detected voltage. At that time, there is no need to supply special power to the input side of the voltage to be measured (the other side of the piezoelectric transformer), and no voltage dividing resistor is required, so that the device can be downsized and the circuit configuration can be simplified. Can be achieved. In addition, the power consumption on the input side of the voltage to be measured is extremely small, and the power loss can be minimized.

According to the present invention, it is possible to provide a new technique for high voltage detection.

It is a block diagram which shows schematic structure of the voltage detection apparatus of one Embodiment. It is a figure which shows the frequency characteristic of the input impedance of a piezoelectric transformer. It is a figure which shows the equivalent circuit of a piezoelectric transformer. It is a figure which shows the equivalent circuit of the piezoelectric transformer seen from the detection side electrode pair in FIG. It is a figure which shows the equivalent circuit when the impedance of a piezoelectric transformer is driven in an inductive frequency domain. It is a figure which shows the change example of the Q value with respect to the applied voltage Vin. It is a circuit diagram which showed the detection method of Q appearing in the equivalent circuit of FIG. It is a figure which shows the specific circuit configuration example of the voltage detection apparatus of one Embodiment. It is a figure which showed the relationship between the output waveform of an oscillator OSC and the voltage waveform of the voltage Vca4 between terminals according to conditions (a) to (c). It is a figure which showed the relationship between the DC voltage Vdet and the applied voltage Vin. It is a figure which shows the relationship between the applied voltage Vin and the output signal Vout after processing. It is a block diagram which shows the structure of the voltage detection apparatus 200 of 2nd Embodiment. It is a figure which shows various modifications of the piezoelectric transformer used in 2nd Embodiment. It is a block diagram which shows the structure of the voltage detection apparatus 300 of 3rd Embodiment. It is a figure which shows the specific circuit structure example of 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram schematically showing the configuration of the voltage detection device 100 of one embodiment.
The voltage detection device 100 includes a piezoelectric transformer PZT1. The piezoelectric transformer PZT1 is, for example, a piezoelectric body (piezoelectric ceramics) polarized on the primary side and the secondary side, and has a primary side electrode pair (counter electrode P3, P4) and a secondary side electrode pair (counter electrode) on the outer surface. P1 and P2) are formed.

[Piezoelectric transformer]
The piezoelectric transformer PZT1 is formed by molding a piezoelectric material such as lead zirconate titanate into a plate shape and performing polarization treatment to form a primary side and a secondary side. In FIG. 1, one side view in the longitudinal direction is used. The outer shape is schematically shown. On the surface of the piezoelectric body, a thick film of primary side electrode pairs (counter electrode P3, P4) and secondary side electrode pairs (counter electrode P1, P2) is formed, for example, with silver paste or the like. The counter electrodes P3 and P4 and the counter electrodes P1 and P2 are each paired in the thickness direction of the piezoelectric body, and the space between the primary side electrode pair and the secondary side electrode pair is sufficient on the outer surface of the piezoelectric body. The insulation distance is secured. The piezoelectric transformer PZT1 may be composed of a laminated body in which a plurality of piezoelectric layers are laminated, or an electrode may be arranged in an inner layer.

Further, the voltage detection device 100 includes an oscillator 110 and a detector 120. The oscillator 110 and the detector 120 are connected to, for example, the primary side of the piezoelectric transformer PZT1. In the present embodiment, the circuit configuration is such that the oscillator 110 is connected to the primary side electrode pair (counter electrode P3, P4).

[Oscillator]
The oscillator 110 applies a drive signal between the primary side electrode pairs (opposed electrodes P3 and P4) of the piezoelectric transformer PZT1. At this time, the drive signal oscillates in the frequency region (near the resonance frequency) in which the impedance between the primary side electrode pairs (opposed electrodes P3 and P4) of the piezoelectric transformer PZT1 is inductive. The impedance-frequency characteristics of the piezoelectric transformer PZT1 will be described later.

〔Detector〕
The detector 120 detects a resonance characteristic (for example, resonance sharpness Q) appearing in the internal equivalent circuit of the piezoelectric transformer PZT1 in a driving state in which the impedance is inductive, performs a predetermined output process, and outputs a detection signal. The detection signal is output from, for example, the output terminals S3 and S4 of the voltage detection device 100.

[Voltage to be measured]
The secondary side of the piezoelectric transformer PZT1 is open in the voltage detection device 100. That is, the secondary side electrode pair (counter electrode P1 and P2) is connected to the input terminals S1 and S2, and the external DC high voltage power supply E is connected to the voltage detection device 100 through the input terminals S1 and S2. Can be done. Examples of the DC high-voltage power source E include various power generation facilities (for example, generators using wind power, hydraulic power, solar energy, etc.) and power supply facilities (for example, EDLC). The voltage to be measured from the DC high-voltage power supply E is applied between the secondary electrode pairs (opposed electrodes P1 and P2) of the piezoelectric transformer PZT1 via the resistor R1.

Here, in the present embodiment, the side to which the drive signal is applied to the piezoelectric transformer PZT1 is referred to as the "primary side" and the opposite side is referred to as the "secondary side", but the side where the applied voltage is relatively large is the "primary side". , And the opposite side may be considered as the "secondary side". In this case, it can be said that the input side of the detected voltage is the "primary side" and the input side of the drive signal is the "secondary side".

[Unification of names]
As described above, when the piezoelectric transformer PZT1 is referred to as "primary side / secondary side", it may not be unique due to differences due to the conditions of use on the spot, technical customs, and the like.
Therefore, in the present embodiment, in consideration of the relativity of the names such as "primary side / secondary side", the names are unified as follows.

[Measured side / Detection side]
That is, the side to which the voltage to be detected is applied to the piezoelectric transformer PZT1 is referred to as the "measured side", and the side to which the oscillator 110 and the detector 120 are connected is referred to as the "detection side". It should be noted that these names of "measured side / detection side" are for convenience of explanation, and that the piezoelectric transformer PZT1 has "primary side / secondary side" in the original meaning. Needless to say.

[Impedance frequency characteristics of piezoelectric transformer]
Here, FIG. 2 is a diagram showing the frequency characteristics of the input impedance of the piezoelectric transformer PZT1. Normally, the input impedance of the piezoelectric transformer PZT1 is inductive in a region where the phase is close to +90 degrees (region of resonance frequencies fr to frr), and is capacitive in other regions. In the region of resonance frequencies fr to frr, the absolute value of impedance increases as the frequency increases.

[Explanation by equivalent circuit]
FIG. 3 is a diagram showing an equivalent circuit of the piezoelectric transformer PZT1.
When the DC high-voltage power supply E is connected to the input terminals S1 and S2 of the voltage detection device 100, in the equivalent circuit shown in FIG. 3, the measured voltage Vin, which is almost the same as the power supply voltage, is the measured side electrode pair (opposite electrode) of the piezoelectric transformer PZT1. Appears between P1-P2). The reason is that the resistance between the counter electrodes P1-P2 of the piezoelectric transformer PZT1 shows a very high value (for example, several hundred MΩ).

In the equivalent circuit shown in FIG. 3, the impedance pair of the impedance to be measured (opposite electrodes P1-P2) of the piezoelectric transformer PZT1 is shown to be short-circuited by the winding of the ideal transformer T1 in a direct current manner. Is only related to an AC signal in the vicinity of the resonance frequency, and the impedance between the counter electrodes P1 and P2 is very high for a DC signal or an AC signal in a frequency region sufficiently lower than the resonance frequency. Therefore, in a situation where a DC voltage to be measured Vin is applied, the counter electrodes P1 to P2 can be regarded as open in the equivalent circuit.

FIG. 4 is a diagram showing an equivalent circuit of the piezoelectric transformer PZT1 as seen from between the detection side electrode pairs (opposite electrodes P3-P4) in FIG. That is, in the equivalent circuit shown in FIG. 3, the equivalent circuit of the piezoelectric transformer PZT1 seen from the detection side electrode pair (opposing electrode P3-P4) when the counter electrode P1-P2 is open is shown in FIG. It becomes.

The conversion from the equivalent circuit of FIG. 3 to the equivalent circuit of FIG. 4 can be described by the following equation.
That is, the equivalent capacitance C1 in the equivalent circuit of FIG. 4 'is a series capacitance of phi ² × C02 and C1 in the equivalent circuit of FIG. 3, represented by the following equation (1).

FIG. 5 is a diagram showing an equivalent circuit when the impedance of the piezoelectric transformer PZT1 is driven in the inductive frequency region. That is, as already described, the impedance between the counter electrodes P3-P4 in FIG. 4 changes from capacitive to inductive to capacitive in the vicinity of the resonance frequency fr of the piezoelectric transformer PZT1 as shown in FIG. Is. Here, it is assumed that the piezoelectric transformer PZT1 is driven in the inductive region. That is, when a drive signal is applied to the piezoelectric transformer PZT1 from the oscillator 110, assuming that the drive frequency is limited to the frequency region in which the impedance is inductive, the counter electrodes P3-P4 are represented by the equivalent circuit shown in FIG. be able to.

The equivalent circuit of FIG. 5 is an equivalent circuit when the measurement side (between the counter electrodes P1 and P2) of the piezoelectric transformer is open. It is experimentally known that the Q value (= sharpness of resonance) of the input impedance Za of this equivalent circuit changes by applying a voltage between the open counter electrodes P1-P2. This means that when the voltage applied between the counter electrodes P1 to P2 changes, the Q value of the input impedance Za of the equivalent circuit also changes accordingly.

[Change in Q value with respect to applied voltage]
FIG. 6 is a diagram showing an example of a change in the Q value with respect to the applied voltage Vin. The sample used for the observation is, for example, a piezoelectric transformer having four terminals having a length of about 10 mm, a width of 3 mm, and a thickness of 1 mm. Further, the difference in the line type (solid line, broken line, alternate long and short dash line from the top) indicates that the value of the equivalent inductance La is selected into three different values (for example, 2 mH, 1 mH, 0.5 mH).

As is clear from the change example in FIG. 6, it is experimental that there is a unique correlation between the applied voltage Vin and the Q value, and the Q value decreases proportionally as the applied voltage Vin increases. Confirmed by. Such a relationship is not affected by the difference in equivalent inductance La. However, here, Q = ωr × La / Ra. Ωr in the left equation is the resonance angular frequency of the piezoelectric transformer. The value Vth on the horizontal axis is the applied voltage at which the Q value decreases in the piezoelectric transformer used in this experiment as the applied voltage increases.

[Q detection method]
FIG. 7 is a circuit diagram showing a method for detecting Q appearing in the equivalent circuit of FIG. That is, the counter electrodes P3-P4 are driven by a circuit in which the oscillator OSC and the capacitance Ca are connected in series. At this time, the oscillation frequency f of the oscillator OSC satisfies the following equation [Equation 2].

The absolute value Vca of the voltage between terminals of the capacitance Ca in the circuit of FIG. 7 is expressed by the following equation [Equation 3], where the output voltage of the oscillator OSC is 1V.

In this way, if the voltage Vca between the terminals of the capacitance Ca is measured, the Q of the impedance Za will be measured.

[Detection of measured voltage by measuring voltage between terminals]
On the other hand, as shown in FIG. 6, since the value of Q is related to the value of the applied voltage Vin, the inter-terminal voltage Vca of the capacitance Ca is also related to the value of the applied voltage Vin. From these relationships, the value of the voltage to be measured applied to the measured side of the piezoelectric transformer PZT1 is the voltage Vca between terminals of the capacitance Ca in series with the oscillator OSC in the circuit of FIG. 7, which is appropriate. It can be seen that it can be detected by processing.

[Detection method]
The method for detecting the voltage to be measured will be described with reference to the circuit configuration of FIG.
The oscillator 110 of the voltage detection device 100 drives the piezoelectric transformer PZT1 via the detector 120 in the vicinity of the resonance frequency of the piezoelectric transformer PZT1 and at the oscillation frequency in the inductive region of impedance shown in FIG. At this time, the detector 120 has a circuit configuration in which the capacitance Ca shown in FIG. 7 is connected in series with the oscillator 110, measures the inter-terminal voltage Vca of the capacitance Ca in the circuit, and adds or subtracts the measured voltage. (Y-intercept), polarity and amplification factor are properly selected and output. The output obtained in this way can be used as it is as a detection signal according to the magnitude of the voltage to be measured.

As described above, the voltage detection device 100 of the present embodiment does not require a voltage divider or the like at all because the measurement current flowing from the voltage to be measured side is extremely small. Further, since no isolated DC-DC converter or the like is used and no voltage divider is required, there is a special advantage that the power consumption on the measured side is extremely low.

[Circuit configuration example]
FIG. 8 is a diagram showing a specific circuit configuration example of the voltage detection device 100 of one embodiment.

In the circuit of FIG. 8, the peripheral circuits of the differential amplifier IC1 (resistors R1 to R7, capacitors C1, C2, etc.) to the peripheral circuits of the transistors Q2 and Q3 (resistors R8 to R14) constitute the oscillator 110 in FIG. .. That is, the oscillator 110 is composed of a multivibrator including a differential amplifier IC1 and its peripheral circuits, and transistors Q1 and Q2 of an output circuit.

Further, in the circuit of FIG. 8, from the peripheral circuits of the capacitors C3 and C4 and the differential amplifier IC2 (resistors R24 to R29, diode D1, etc.) to the peripheral circuits of the differential amplifier IC3 (resistors R17 to R23, capacitor C5) , The detector 120 of FIG. 1 is configured. Here, capacitors C3 and C4 are arranged as corresponding to the capacitance Ca in FIG. 7. When the collectors of the transistors Q2 and Q3 operate as a current source, the capacitors C3 and C4 act as a capacitance Ca according to the relationship shown in the following [Equation 4].

On the other hand, when the collectors of the transistors Q2 and Q3 operate as a voltage source, the capacitor C4 becomes equal to the capacitance Ca, and the relationship is [Ca = C4].

Further, the resistors R15 and R16 connected to the electrode pair P1-P2 on the measured side of the piezoelectric transformer PZT1 correspond to the resistors R1 in FIG. These relationships are [R1 = R15 + R16]. Such a resistor represented by [R1] or [R15 + R16] is arranged for the purpose of avoiding a specific impedance being connected between the counter electrodes P1-P2 of the piezoelectric transformer PZT1 due to the impedance on the Vin side of the detected voltage. Is. The reason for this is that all the studies on the characteristics of the piezoelectric transformer PZT1 described so far have been carried out under the condition that the counter electrodes P1 to P2 of the piezoelectric transformer PZT1 are "open".

Therefore, the resistance value represented by [R1] or [R15 + R16] is a high resistance value (for example, several hundred kΩ) so as to give a condition of almost "opening" between the counter electrodes P1-P2 when viewed from the piezoelectric transformer PZT1. It is necessary. Further, since it is necessary to apply the voltage to be measured Vin as it is between the counter electrodes P1-P2 of the piezoelectric transformer PZT1, the value of [R1] or [R15 + R16] is the impedance between the counter electrodes P1-P2 of the piezoelectric transformer PZT1. It is required that the resistance value is sufficiently small.

[Oscillator operation]
The operation of the oscillator 110 is phase-controlled with the charge / discharge time constant at a target frequency with respect to the basic operation of the multivibrator. The phase control is a control that detects an error between the frequency and the target frequency due to the basic operation of the multivibrator as a phase difference, converts the phase difference into a voltage, and applies feedback. The target frequency here is the resonance frequency (1 / 2π√ (La × Ca)) in FIG.

In the circuit of FIG. 8, the differential amplifier IC1, the resistors R1 to R4, and the capacitor C2 constitute the basic circuit of the multivibrator. The impedance between the counter electrodes P4-P3 of the piezoelectric transformer PZ1, the capacitors C3 and C4, and the resistor R7 are circuits for phase-controlling the charge / discharge time constant to a target frequency. In the case of the circuit of FIG. 8, the target frequency is the resonance frequency of the resonance circuit composed of the capacitors C3 and C4 and the impedance between the counter electrodes P4-P3 of the piezoelectric transformer PZ1. However, the target frequency needs to be limited to the range in which the impedance between the counter electrodes P4-P3 of the piezoelectric transformer PZ1 is in the inductive region shown in FIG. By limiting the range of the target frequency in this way, it can be considered as an equivalent circuit between the counter electrodes P4-P3 of the piezoelectric transformer PZ1 shown in FIG.

The oscillation frequency of the multivibrator configured by the oscillator 110 is determined by the charge / discharge time of the capacitor C2. The charge / discharge characteristics of the capacitor C2 are the total value of the current that enters from the output voltage of the differential amplifier IC1 via the resistor R3 and the current that is fed back from the voltage between the terminals of the capacitor C4 via the resistor R7. It is determined by the amount of charge stored in the capacitor C2. Here, let q be the amount of charge accumulated and discharged in the capacitor C2, let tc be the charge time of the capacitor C2, and let td be the discharge time. At this time, the charge / discharge times tc and td are expressed by the following equations.
tk = q / Ic
td = q / Id

Ic in the above equation is the average value of the total current of the current that enters from the output voltage of the differential amplifier IC1 via the resistor R3 and the current that enters from the voltage between the terminals of the capacitor C4 via the resistor R7 within the charging time. And.

Similarly, Id in the above is the average of the total current of the current flowing out to the output voltage of the differential amplifier IC1 via the resistor R3 and the current flowing out to the voltage between the terminals of the capacitor C4 via the resistor R7 within the discharge time. Use as a value.

Normally, the oscillation waveform of the oscillator 110 is made into a waveform having a duty of 1: 1 and oscillated. Therefore, in the following description, the condition of tk = td = ta is satisfied. Then, the current entering through the resistor R3 and the current flowing out become equal, and both can be set to the current Ir3. Further, the current entering through the resistor R7 and the current flowing out become equal, and both can be the current Ir7. With this definition, the charge / discharge time ta is given by the following equation, and the oscillation frequency f of the oscillator 110 is given by the following equation.
ta = q / Ic = q / (Ir3 + Ir7)
f = (Ir3 + Ir7) / (2q)

Assuming that the oscillation frequency f of the oscillator 110 is within the range in which the impedance between the counter electrodes P4-P3 of the piezoelectric transformer PZ1 is inductive, the operation can be represented by the equivalent circuit shown in FIG. At this time, the output of the oscillator OSC in the equivalent circuit of FIG. 7 corresponds to the collector of the transistors Q2 and Q3 in the circuit of FIG. Further, the resistance Ra and the inductance La in the equivalent circuit of FIG. 7 indicate the impedance between the counter electrodes P4-P3 of the piezoelectric transformer PZ1. The capacitance Ca in the equivalent circuit of FIG. 7 corresponds to the series capacitance of the capacitor C3 and the capacitor C4 in the circuit of FIG. However, the voltage between the terminals of the capacitor C4 in the circuit of FIG. 8 is actually a voltage obtained by dividing the voltage Vca between the terminals appearing in the equivalent circuit of FIG. 7 by the capacitors C3 and C4. Therefore, assuming that the output of the oscillator OSC is 1 in the equivalent circuit of FIG. 7, the capacitance Ca and the voltage Vca between the terminals are represented by the following equations [Equation 5], respectively. In the following equation [Equation 5], in order to distinguish between Vca shown in the equivalent circuit of FIG. 7 and the voltage between the terminals of the capacitor C4 in the circuit of FIG. 8, the voltage between the terminals of the capacitor C4 seen in FIG. 8 is referred to as Vca4. It shall be described.

From the above equation, it can be seen that the phase difference φ between the terminal voltage Vca4 of the capacitor C4 and the output voltage of the collectors of the transistors Q2 and Q3 in FIG. 8 is affected by the oscillation frequency. At this time, the phase difference φ is affected by the value of the oscillation frequency f (the following conditions (a), (b), and (c)) as shown in the following equation [Equation 6]. However, it is assumed that the oscillation frequency f is within the frequency range in which the impedance between the counter electrodes P4-P3 of the piezoelectric transformer PZ1 is inductive.

[Conditions (a) to (c) Different oscillation frequencies]
FIG. 9 is a diagram showing the relationship between the output waveform of the oscillator OSC and the voltage waveform of the inter-terminal voltage Vca4 according to the conditions (a) to (c). In FIG. 9, the voltage between terminals Vca4 is shown as a voltage waveform during the charging time of the capacitor C2. Therefore, the polarity of the voltage waveform at the discharge time of the capacitor C2 is opposite to that of FIG. Hereinafter, the conditions (a) to (c) will be described separately.

As seen in [Condition (b)] shown in the center of FIG. 9, when the oscillation frequency f matches the target frequency (f = 1 / 2π√ (La × Ca)), the output waveform of the oscillator OSC The phase difference φ of the inter-terminal voltage Vca4 with respect to the above is −90 °, and the inter-terminal voltage Vca4 becomes 0V at the midpoint of the charging time. In this case, the average value of the voltage waveform of the terminal voltage Vca4 within the charging time is 0, and the charging current Ir7 fed back via the resistor R7 in the circuit of FIG. 8 is also 0A. Therefore, the oscillation frequency f of the circuit constituting the multivibrator of FIG. 8 is a frequency determined purely by the charge / discharge time of the capacitor C2 by the current Ir3 via the resistor R3, and the oscillation is continued at the target frequency when there is no error. To do.

Next, as seen in [Condition (a)] shown on the left side of FIG. 9, when the oscillation frequency f is lower than the target frequency (f <1 / 2π√ (La × Ca)), the output of the oscillator OSC The phase difference φ of the terminal voltage Vca4 with respect to the waveform is larger than −90 ° but smaller than 0 °. In this case, since the average value of the voltage waveform of Vca4 within the charging time is positive, the current Ir7 that feeds back via the resistor R7 in the circuit of FIG. 8 is also positive, and this feedback current Ir7 charges the capacitor C2. Work in the direction. This means that the current Ir7 in addition to the current Ir3 via the resistor R3 charges the capacitor C2, shortening the charging time. Therefore, the oscillation frequency in this case is controlled to a higher frequency side than the frequency determined only by the resistor R3 and the capacitor C2. As a result, the oscillation frequency f, which was a low frequency, approaches the target frequency (1 / 2π√ (La × Ca)).

On the other hand, in the case shown in [Condition (c)] shown on the right side of FIG. 9, it is as follows. In this case, the oscillation frequency f is higher than the target frequency (1 / 2π√ (La × Ca) <f), and the phase difference φ of the terminal voltage Vca4 with respect to the output waveform of the oscillator OSC is smaller than −90 °. In this case, since the average value of the voltage waveform of Vca4 within the charging time is negative, the current Ir7 that feeds back via the resistor R7 in the circuit of FIG. 8 also becomes negative, and this feedback current Ir7 charges the capacitor C2. Since it acts on the polarity of discharging, it has the effect of extending the charging time of the capacitor C2 by the current Ir3. Therefore, the oscillation frequency in this case is controlled to be lower than the frequency determined only by the resistor R3 and the capacitor C2. As a result, the oscillation frequency f, which was a high frequency, also approaches the target frequency (1 / 2π√ (La × Ca)).

In this way, the oscillator 110 detects the error between the target frequency (resonance frequency between the piezoelectric transformer PZT1 and the capacitance composed of the capacitors C3 and C4) as the phase difference, and converts the phase difference into a voltage for net charging. The discharge current can be increased or decreased to control the oscillation frequency f near the target frequency.

[Detector operation]
In the voltage detection device 100 of FIG. 8, when a constant voltage Vcc is applied between the power supply terminals S5-S3 (GND), a constant voltage (or current) is generated from the collectors of the transistors Q2 and Q3, which are the output circuits of the oscillator 110. An AC waveform with is output. From the operation of the oscillator 110 described above, the frequency of the AC waveform is in the vicinity of the resonance frequency of the piezoelectric transformer PZT1 and the impedance between the counter electrodes P1-P2 of the piezoelectric transformer PZT1 is inductive.

At this time, since the inter-terminal voltage Vca of the capacitor C4 has a relationship with the measured voltage Vin as shown in FIG. 6, measuring the inter-terminal voltage Vca is the same as measuring the measured voltage Vin. However, since the voltage between terminals Vca itself is not in a simple proportional relationship with the voltage to be measured Vin, in the present embodiment, the following processing is appropriately performed to obtain a detection signal.

That is, the operation of the oscillator 110 is adjusted, and a condition is set in which the output waveform of the inter-terminal voltage Vca becomes a sine wave centered on Vcc / 2. Under such conditions, the differential amplifier IC2 and its peripheral circuits amplify the output waveform [Vcc / 2-Vca] with an amplification factor Aic2 and rectify it with a diode D1 and a capacitor C5 to obtain an inter-terminal voltage Vca. The AC component is converted to a DC voltage Vdet.

[Example of setting each value]
Here, it is assumed that the capacitors C3 and C4 having the equivalent inductance La of the piezoelectric transformer PZT1 having a predetermined value (for example, 1 mH) are selected. In this case, the change in the Q value with respect to the applied voltage Vin has the relationship shown by the broken line in FIG. 6, Q≈q0 (for example, 8.5) when the applied voltage Vin is 0V, and the applied voltage Vin is the predetermined value Vth (for example, 800V). When Q≈qth (for example, 6.5).

[Primary output]
FIG. 10 is a diagram showing the relationship between the DC voltage Vdet output from the differential amplifier IC2 and the applied voltage Vin.
For example, if the amplification factor Aic2 of the differential amplifier IC2 is adjusted and [Vdet = VH (for example, 3.00V)] is set to be output under the condition of [Vin = 0V], [Vin = Vth (for example, 3.00V)] is set. Under the condition of [800V)], [Vdet = 3.0 × (6.5 / 8.5) = VL (for example, 2.29V)].
The DC voltage Vdet, which has a relationship with the applied voltage Vin in FIG. 10, is processed, and finally an output signal proportional to the applied voltage Vin is obtained.

[Output after processing]
FIG. 11 is a diagram showing the relationship between the applied voltage Vin and the output signal Vout after processing.
In the detector 120, the output voltage Vout of the differential amplifier IC3 becomes a value represented by the following equation due to the differential amplifier IC3 and its peripheral circuits.
Vout = (Vref-Vdet) x Aic3

Here, if the value of Vref is taken in the Y-intercept in FIG. 10 and selected as Vref = VH (3.0 in the example) and Aic3 = 4.225, the output voltage Vout will be expressed by the following equation. ..
Vout = (VH-Vdet) x 4.225

[At Vin = 0V]
Then, when Vin = 0V, Vdet = VH (3V in the example), so Vout = 0 from the above equation.

[At Vin = Vth (V)]
Further, when Vin = Vth (800V in the example), Vdet = VL (2.29V in the example), so Vout = 3.0V from the above equation.

In this way, by taking out the output voltage Vout processed by the detector 120 from between the output terminals S3-S4, the output voltage Vout becomes a detection signal corresponding to the value of the voltage to be measured Vin, and the voltage detection device 100 serves as a detection signal. The function can be realized.

[Other Embodiments]
FIG. 12 is a block diagram showing the configuration of the voltage detection device 200 of the second embodiment. The voltage detection device 200 of the second embodiment is different from that of the previous embodiment in that a 3-terminal piezoelectric transformer PZT1 is used.

That is, the piezoelectric transformer PZT1 has counter electrodes P4 and P3 formed on the detection side, but a single electrode P1 is formed on the measurement side. In this case, since it is necessary to connect the detection side counter electrode P3 of the piezoelectric transformer PZT1 to the measurement side, the measurement side / detection side is not insulated. However, by using the same oscillator 110 and detector 120 as in the previous embodiment, it is possible to output the detection signal Vout according to the value of the voltage to be measured Vin.

FIG. 13 is a diagram showing various modifications of the piezoelectric transformer PZT1 used in the second embodiment. The piezoelectric transformer PZT1 of the modified example has a four-terminal structure in which counter electrodes P1 and P2 are formed on the side to be measured, and FIG. 13 (A) shows an example in which one of the counter electrodes P1 is connected to the input terminal S1. is there. Further, FIG. 13B is an example in which the other counter electrode P2 is connected to the input terminal S1, and FIG. 13C is an example in which both counter electrodes P1 and P2 are connected to the input terminal S1. The point at which the detection side counter electrode P3 is connected to the measurement side is the same as in FIG. Also in such various modifications, the detection signal Vout corresponding to the value of the voltage to be measured Vin can be output as in the second embodiment.

[Correction function]
FIG. 14 is a block diagram showing the configuration of the voltage detection device 300 of the third embodiment. Further, FIG. 15 is a diagram showing a specific circuit configuration example of the third embodiment. The voltage detection device 300 of the third embodiment is different from that of the first embodiment in that the first piezoelectric transformer PZT1 and the second piezoelectric transformer PZT2 are used.

Generally, depending on the material properties of a piezoelectric transformer, the Q of its impedance may be affected by a change in ambient temperature as an external factor. In such a case, the configuration of the third embodiment can be used.

First, the piezoelectric transformers PZT1 and PZT2 used are individuals having pair characteristics. That is, these piezoelectric transformers PZT1 and PZT2 are manufactured of the same piezoelectric material.

A voltage to be measured is applied to the first piezoelectric transformer PZT1. On the other hand, it is assumed that 0 V is applied to the second piezoelectric transformer PZT2 (no voltage is applied). At this time, the resistor R1 is a high resistance for ensuring that the impedance of the voltage source to be measured (DC high-voltage power supply E in FIG. 1) does not affect the characteristics of the piezoelectric transformer PZT1. Further, the resistor R2 is a high resistance for applying 0V to the piezoelectric transformer PZT2.

The oscillator 110 has basically the same configuration as that described in the first embodiment, and the piezoelectric transformer PZT1 and the piezoelectric transformer PZT2 are placed in the vicinity of their resonance frequencies and at frequencies in the region where the impedance shown in FIG. 2 is inductive. Drive. The oscillation frequency of the drive signal by the oscillator 110 can be applied at the same frequency for both the two piezoelectric transformers PZT1 and PZT2, or can be applied at individually set frequencies.

The detector 320 monitors the impedance between the counter electrodes P3-P4 of the piezoelectric transformers PZT1 and PZT2, and converts the Q value into a voltage. The operation mechanism at this time is the same as the circuit shown in FIG.

Here, the value obtained by voltage-converting the Q value between the counter electrodes P3-P4 for the piezoelectric transformer PZT1 in FIG. 14 is defined as Vdet. Vdet is a voltage-converted Q value corresponding to Vin in FIG. Similarly, for the piezoelectric transformer PZT2, the value obtained by voltage-converting the Q value between the counter electrodes P3-P4 is defined as Vref. Vref is a voltage-converted Q value corresponding to Vin = 0V in FIG.

In the third embodiment, the detector 320 is provided with a unique configuration. That is, a differential amplifier for detecting the difference voltage between the two DC voltages Vdet and Vref is provided.
Such a differential amplifier can be composed of, for example, the IC3 shown in FIG. 14 and its peripheral resistors R21, R22, R17, and R19. The output of this differential amplifier (terminal 1 output of IC3) represents the difference between the case where the voltage to be measured is Vin and the case where the voltage to be measured is 0V. Therefore, the output of the differential amplifier eventually becomes a voltage corresponding to the value of the voltage to be detected, and becomes the detection signal Vout of the voltage detector 300 as it is. The detection signal Vout is represented by the following equation.
Vout = (Vdet-vdet) x Adef
Here, Adef is the amplification factor of the differential amplifier.

When the above conditions are applied to drive the piezoelectric transformers PZT1 and PZT2, the voltage between the counter electrodes P1 to P2 of the piezoelectric transformer PZT2 is always 0V. Therefore, regardless of the voltage to be measured Vin, Vref = VH (eg) for the piezoelectric transformer PZT2. 3.0V).

On the other hand, the Vdet of the piezoelectric transformer PZT1 is Vdet = VH (for example, 3V) when Vin = 0V, and Vdet = VL (for example, 2.29V) when Vin = Vth (for example, 800V).

Therefore, assuming that the amplification factor is Adef = 4.225, when the actual voltage to be measured is Vin = 0V, Vout = 0V, and when Vin = Vth (800V in the example), Vout = 3.0V. That is, it can be seen that this realizes the same characteristics as in FIG.

[Correction principle]
Further, when the resonance characteristics (Q value) of the piezoelectric transformers PZT1 and PZT2 change due to the influence of the ambient temperature or the like, the following correction function operates.
That is, the piezoelectric transformers PZT1 and PZT2 are molded from the same material. Therefore, even if the temperature of each Vdet (PZT1) and Vref (PZT2) fluctuates due to the influence of the ambient temperature, the change of each value is in the same direction with respect to the temperature change. Therefore, it is possible to compensate for the fluctuation due to the influence of temperature inside the circuit of the detector 320 and reduce the width of the temperature fluctuation given to the detection signal.

According to the above embodiment, the following advantages can be obtained.
(1) The voltage detection devices 100, 200, and 300 of all the embodiments do not require voltage division by a voltage dividing resistor, and can detect the voltage to be measured (so-called high voltage of 500 V or more) with a simple circuit configuration. And. It is also advantageous in that almost no power loss occurs on the measured side.
(2) Since the voltage detection devices 100, 200, and 300 of all the embodiments do not require power supply to the measured side, it is not necessary to bother to provide a DC-DC converter.
(3) As for the voltage detection devices 100 and 300, since the measurement side and the detection side are insulated by a piezoelectric transformer, it is not necessary to take measures against the influence of noise in the detector 120.
(4) The voltage detection devices 100, 200, and 300 of all the embodiments realize a novel circuit configuration as a whole by applying a material called "piezoelectric transformer" to "voltage detection". On top of that, since the reliability of the "piezoelectric transformer" itself has already been established, it is not necessary to consider safety and reliability when putting the voltage detection device into practical use, and it is highly industrially applicable.

The present invention can be implemented by transforming it into a species without being restricted by the above-described embodiment.
The voltage detection devices 100, 200, and 300 can be implemented by being modified into a configuration capable of exhibiting the same function as well as the configuration shown in each figure.

Further, in the embodiment, the shapes and sizes of the piezoelectric transformers PZT1 and PZT2, the impedance frequency characteristics, and the resonance characteristics are given as examples, and different shapes, sizes, and characteristics may be adopted.

The various values shown in the operation of the oscillator and detector are merely examples, and it is natural that circuit elements and the like are selected and prepared according to various different conditions at the time of implementation.

It goes without saying that the structures shown in the drawings in each embodiment are merely preferable examples, and the present invention can be preferably carried out even if various elements are added to the basic structure or a part thereof is replaced. Absent.

100,200,300 Voltage detector 110 Oscillator 120 Detector PZT1, PZT2 Piezoelectric transformer

Claims (7)

Piezoelectric transformers polarized to the primary and secondary sides,
An oscillator that drives one side of the piezoelectric transformer in a region near the resonance frequency at which the input impedance is inductive,
A voltage detection device including a detector that outputs a detection signal corresponding to the voltage to be measured on one side of the piezoelectric transformer in a state where a voltage to be measured is applied to the other side of the piezoelectric transformer. In the voltage detection device according to claim 1,
The detector
A voltage detection device characterized in that the detection signal is output based on a change in the sharpness Q of resonance appearing on one side of the piezoelectric transformer according to a change in the voltage to be measured applied to the other side. In the voltage detection device according to claim 1 or 2.
The piezoelectric transformer is
The oscillator and the detector are provided with electrode pairs on the primary side and the secondary side, respectively, driven by the oscillator through the electrode pair on one side, and a voltage to be measured is applied through the electrode pair on the other side. A voltage detector characterized by being insulated from the voltage to be measured. In the voltage detection device according to claim 1 or 2.
The piezoelectric transformer is
It has an electrode pair on one side of the primary side and the secondary side and a single electrode on the other side, and is driven by the oscillator through the electrode pair on one side while being driven by the single electrode on the other side and one side. A voltage detection device characterized in that a voltage to be measured is applied through one of a pair of electrodes. In the voltage detection device according to claim 1 or 2.
The piezoelectric transformer is
It has electrode pairs on the primary side and the secondary side, respectively, and is driven by the oscillator through the electrode pair on one side, and is measured through at least one of the electrode pairs on the other side and one of the electrode pairs on the one side. A voltage detection device characterized in that a voltage is applied. In the voltage detection device according to any one of claims 1 to 3.
A voltage detection device further provided with a correction means for correcting fluctuations in the resonance characteristics of the piezoelectric transformer due to external factors and causing the detector to output a detection signal. A first piezoelectric transformer polarized to the primary and secondary sides,
A second piezoelectric transformer that is polarized to the primary and secondary sides and has the same characteristics as the first piezoelectric transformer.
An oscillator that drives one side of each of the first and second piezoelectric transformers in a region near the resonance frequency at which the input impedance is inductive.
A resistor that sets the voltage applied to the other side of the second piezoelectric transformer to 0, and
With the voltage to be measured applied to the other side of the first piezoelectric transformer, the difference in resonance characteristics that appears on one side of the first and second piezoelectric transformers is output as a detection signal according to the voltage to be measured. A voltage detector equipped with a detector.

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