An electronic dielectric loss factor standard and its control method

Abstract

The present invention relates to the field of measuring capacitance and dielectric loss factor of power equipment. It provides an electronic dielectric loss factor standard and a control method thereof. The technical problem to be solved is how to electronically adjust the dielectric loss factor and capacitance. The standard comprises a standard capacitor C0, a resistor R, a compensation capacitor C, four-quadrant multiplying D / A converters DA1 and DA2, operational amplifiers OPA1, OPA2, OPA3, and OPA4, and an amplifier circuit K. This standard electronically adjusts the dielectric loss factor and capacitance. Compared with traditional dielectric loss factor standards, it offers higher accuracy, simpler circuitry, and easier debugging.

Description

Technical Field

[0001] The present invention relates to the field of measuring capacitance and dielectric loss factor of electric power equipment, and in particular to an electronic dielectric loss factor standard and a control method thereof. Background Art

[0002] The statements in this section merely provide background art related to the present invention and do not necessarily constitute prior art.

[0003] Capacitance and dielectric loss factor (hereinafter referred to as dielectric loss) are important indicators of capacitors or power capacitive equipment. The dielectric loss factor meter (hereinafter referred to as dielectric loss meter) is a conventional instrument for measuring capacitance and dielectric loss. A dielectric loss factor standard is required to calibrate the dielectric loss meter.

[0004] The resistance r and the capacitance c are connected in series, and their equivalent dielectric loss is:

[0005] tgδ=ωcr

[0006] ω = 2πF, where F is the frequency. The current method is to keep the capacitance constant and obtain different dielectric loss factors by changing the resistance value. However, changing the resistance value requires switching between several resistors and several relays to obtain different total resistance values. The disadvantages of this method are: (1) it requires several high-precision resistors, (2) the relays are not reliable, and (3) the influence of stray capacitance requires that each dielectric loss standard value be calibrated separately, resulting in a large debugging workload.

[0007] In order to obtain different capacitances, the amplifier gain is generally modified. This also requires several resistors and several relays to switch and change the amplifier gain, and the circuit is also relatively complicated. Summary of the Invention

[0008] In order to address the deficiencies of the prior art, the present invention provides an electronic dielectric loss factor standard and a control method thereof, specifically an electronic dielectric loss factor standard that can electronically adjust dielectric loss and capacitance in a highly linear manner.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides an electronic dielectric loss factor standard.

[0011] An electronic dielectric loss factor standard device, comprising

[0012] a first capacitor, wherein the high-voltage end of the first capacitor is connected to an external voltage, the low-voltage end is connected to the negative input end of the first operational amplifier, the positive input end of the first operational amplifier is grounded, the output end of the first operational amplifier is respectively connected to one end of the first resistor, the input end of the first digitally controlled voltage proportional attenuator, and the input end of the second digitally controlled voltage proportional attenuator, and the other end of the first resistor is connected to the negative input end of the first operational amplifier; the output end of the first digitally controlled voltage proportional attenuator is connected to one end of the second capacitor via an inverting amplifier, and the other end of the second capacitor is connected to the negative input end of the first operational amplifier; and the output end of the second digitally controlled voltage proportional attenuator is connected to the current output end via an amplifying circuit;

[0013] The first digitally controlled voltage proportional attenuator and the second digitally controlled voltage proportional attenuator are both connected to a processor; the first digitally controlled voltage proportional attenuator is controlled by the processor to change the dielectric loss factor of the electronic dielectric loss factor standard, and the second digitally controlled voltage proportional attenuator is controlled by the processor to change the capacitance of the electronic dielectric loss factor standard.

[0014] Furthermore, the first digitally controlled voltage proportional attenuator includes a first D / A converter and a second operational amplifier, the reference voltage input terminal of the first D / A converter is connected to the output terminal of the first operational amplifier, the current output terminal of the first D / A converter is connected to the negative input terminal of the second operational amplifier, the positive input terminal of the second operational amplifier is grounded, and the output terminal of the second operational amplifier is connected to the negative feedback resistor lead terminal of the first D / A converter.

[0015] Furthermore, the first D / A converter is a four-quadrant multiplication type D / A converter.

[0016] Furthermore, the inverting amplifier includes a second resistor, a third resistor and a third operational amplifier, one end of the second resistor is connected to the output end of the first digitally controlled voltage proportional attenuator, that is, the output end of the second operational amplifier, and the other end is connected to the negative input end of the third operational amplifier. The positive input end of the third operational amplifier is grounded, and the output end of the third operational amplifier is respectively connected to one end of the third resistor and one end of the second capacitor, and the other end of the third resistor is connected to the negative input end of the third operational amplifier.

[0017] Furthermore, the second digitally controlled voltage proportional attenuator includes a second D / A converter and a fourth operational amplifier, the reference voltage input terminal of the second D / A converter is connected to the output terminal of the first operational amplifier, the current output terminal of the second D / A converter is connected to the negative input terminal of the fourth operational amplifier, the positive input terminal of the fourth operational amplifier is grounded, and the output terminal of the fourth operational amplifier is connected to the negative feedback resistor lead terminal of the second D / A converter.

[0018] Furthermore, the second D / A converter is a four-quadrant multiplication type D / A converter.

[0019] Furthermore, the output end of the fourth operational amplifier is also connected to the input end of the amplifier circuit, and the output end of the amplifier circuit is connected to the current output end.

[0020] Furthermore, the digital end of the first D / A converter in the first digitally controlled voltage proportional attenuator and the digital end of the second D / A converter in the second digitally controlled voltage proportional attenuator are both connected to the processor.

[0021] Furthermore, the voltage output by the first operational amplifier is digitally attenuated by the first digitally controlled voltage proportional attenuator and the inverting amplifier, and then forms negative feedback through the second capacitor.

[0022] In a second aspect, the present invention provides a control method for an electronic dielectric loss factor standard.

[0023] A control method for an electronic dielectric loss factor standard, comprising:

[0024] The electronic dielectric loss factor standard device described in the first aspect is connected to an external voltage, and an output current is obtained at the output end of the amplifier circuit, thereby obtaining a simulated impedance including capacitance and dielectric loss factor;

[0025] Adjusting the digital value of the first D / A converter in the first digitally controlled voltage proportional attenuator by the processor to change the dielectric loss factor;

[0026] The digitally changed capacitance of the second D / A converter in the second digitally controlled voltage proportional attenuator is adjusted by the processor.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention uses a processor to control the digital data written into the first D / A converter to adjust the dielectric loss factor of an electronic dielectric loss factor standard. This eliminates the need for numerous resistors and relays, significantly simplifies the circuit, and improves reliability. Because the first D / A converter has high linearity, calibration generally only requires the maximum dielectric loss value. Intermediate dielectric loss values only require linearly modifying the digital data written into the first D / A converter, significantly simplifying debugging.

[0029] 2. The present invention uses a processor to control the digital data written into the second D / A converter to adjust the capacitance of the electronic dielectric loss factor standard, thereby avoiding the use of resistors and relays for adjustment, greatly simplifying the circuit, and improving reliability. Calibration of capacitance only needs to be performed through software without changing the hardware. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0031] Figure 1 This is a circuit diagram of the electronic dielectric loss factor standard of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0034] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0035] It should be understood that, in the description of the embodiments of the present invention, words such as "first" and "second" are only used for the purpose of distinguishing the description, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order.

[0036] In the present invention, terms such as "connected" and "connected" should be interpreted broadly, meaning that they can be directly connected or indirectly connected through an intermediary. Relevant researchers or technicians in this field can determine the specific meanings of these terms in the present invention based on specific circumstances, and they should not be construed as limitations on the present invention.

[0037] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0038] Explanation of terms:

[0039] Virtual short means that under ideal conditions, the potentials of the two input terminals of the operational amplifier are equal, as if the two input terminals are shorted together, but in fact they are not shorted together, which is called "virtual short".

[0040] Virtual disconnect refers to the ideal situation where the current flowing into the op amp input is zero. This is because the input resistance of an ideal op amp is infinite, creating an open circuit between the two inputs. However, in reality, there is no open circuit, which is why it is called a virtual disconnect.

[0041] Example 1

[0042] like Figure 1 As shown, embodiment 1 of the present invention provides an electronic dielectric loss factor standard, comprising:

[0043] A first capacitor C0 has a high voltage terminal connected to an external test voltage U, a low voltage terminal connected to a negative input terminal of a first operational amplifier OPA1, and a positive input terminal of OPA1 connected to ground; the negative input terminal of OPA1 is connected to one end of a first resistor R, and the other end of the first resistor R is connected to the output terminal of OPA1; the output terminal of OPA1 is connected to a reference voltage input terminal Vref of a first D / A converter DA1, a current output terminal Iout of DA1 is connected to a negative input terminal of a second operational amplifier OPA2, an output terminal of OPA2 is connected to a negative feedback resistor lead-out terminal Rfb of DA1, and a positive input terminal of OPA2 is grounded;

[0044] The output end of OPA2 is connected to one end of the second resistor R1, the other end of R1 is connected to the negative input end of the third operational amplifier OPA3, and the positive input end of OPA3 is grounded; the negative input end of OPA3 is connected to one end of the third resistor R2, and the other end of R2 is connected to the output end of OPA3; the output end of OPA3 is connected to one end of the second capacitor C, and the other end of C is connected to the negative input end of OPA1; the output end of OPA1 is connected to the reference voltage input end Vref of the second D / A converter DA2, the current output end Iout of DA2 is connected to the negative input end of the fourth operational amplifier OPA4, the output end of OPA4 is connected to the negative feedback resistor lead end Rfb of DA2, and the positive input end of OPA4 is grounded; the output end of OPA4 is connected to the input end of the amplifier circuit, and the output end of the amplifier circuit outputs current I; the digital ends of the D / A converters DA1 and DA2 are both connected to the processor (CPU).

[0045] Among them, the first D / A converter DA1 is a four-quadrant multiplication type, and forms a first digitally controlled voltage proportional attenuator with OPA2; the second D / A converter DA2 is a four-quadrant multiplication type, and forms a second digitally controlled voltage proportional attenuator with OPA4; R1, OPA3 and R2 constitute an inverting amplifier.

[0046] After passing through DA1, OPA2 and OPA3, the output voltage of OPA1 is digitally attenuated and then forms negative feedback through capacitor C, which is equivalent to connecting a variable capacitor in parallel between the negative input and output terminals of OPA1.

[0047] The amplifier circuit converts the output voltage of OPA4 into an output current I, and its gain is K.

[0048] When voltage U is applied to the input terminal and current I is detected, the entire circuit behaves as a capacitor with adjustable dielectric loss factor and capacitance. The CPU changes the dielectric loss factor by adjusting the number of DA1 and changes the capacitance by adjusting the number of DA2.

[0049] The amplifier circuit can be implemented by using an existing amplifier circuit.

[0050] The working principle of the electronic dielectric loss factor standard is analyzed below:

[0051] The first D / A converter DA1 is a four-quadrant multiplication D / A converter. Unlike ordinary D / A converters, the reference voltage input Vref of the four-quadrant multiplication D / A converter, namely V1 in the figure, can be any voltage signal, including AC signals. In conjunction with the second operational amplifier OPA2, its output voltage V2 can be digitally linearly adjusted between 0 and V1:

[0052]

[0053] Where N1 is the number of bits of the first D / A converter, and D1 ranges from 0 to 2. N1 -1, the second resistor R1, the third resistor R2 and the third operational amplifier OPA3 form an inverting amplifier with a gain of -1, where R1 = R2, then V3 = -V2, V3 is the output voltage of the third operational amplifier, so the negative sign in equation (1) can be removed:

[0054]

[0055] When a voltage U with a frequency of F is applied, the following can be obtained from the virtual short and virtual break principle of OPA1:

[0056]

[0057] Where ω = 2πF, and formula (3) can be rearranged to obtain:

[0058]

[0059] The output voltage V1 of the first operational amplifier is attenuated by DA2 and OPA4 and amplified K times to become the output current I:

[0060]

[0061] Where N2 is the number of bits of the second D / A converter, and D2 ranges from 0 to 2. N2 -1.

[0062] Therefore, the entire circuit appears as an impedance:

[0063]

[0064] Z can be represented by a resistor r in series with a capacitor c:

[0065]

[0066] Comparing with equations (6) and (7), we can see that the series resistance r and series capacitance c of the entire circuit are:

[0067]

[0068]

[0069] Since the dielectric loss factor of the rc series circuit is ωrc, the dielectric loss factor is:

[0070]

[0071] Formulas (9) and (10) show that the capacitance of the overall circuit is determined by the number written into DA2 (i.e., D2, which ranges from 0 to 2 N2 -1) is controlled, and the dielectric loss factor of the overall circuit is determined by the number written into DA1 (i.e. D1, which ranges from 0 to 2 N1 -1) control; in particular, the dielectric loss factor has nothing to do with the standard capacitor capacitance C0, and the use of high-precision R and C can obtain a linear and high-precision dielectric loss factor.

[0072] Generally, DA2 and DA1 use the same type of four-quadrant multiplication D / A converter, and N1 = N2 = N. Equations (9) and (10) can be rewritten as:

[0073]

[0074]

[0075] The innovation of the present invention is that the negative feedback voltage of OPA1 is attenuated and then fed back through capacitor C, which is equivalent to converting the fixed capacitor C into a digitally controlled variable capacitor adjustable from 0 to C. The use of this method is not limited to the present invention and has reference value for any application requiring high-precision digitally controlled variable capacitors.

[0076] Example 2:

[0077] This embodiment provides an electronic dielectric loss factor standard, such as Figure 1As shown, the standard capacitor C0 uses a 50pF three-terminal SF6 gas-filled structure standard capacitor with a rated working voltage of 10kV. The resistors R, R1 and R2 all use 20kΩ low-temperature drift metal foil resistors. The capacitor C uses a 2200pF mica capacitor. DA1 uses a 16-bit four-quadrant multiplication type D / A converter AD5543. The operational amplifiers OPA1, OPA2 and OPA3 use AD8512. According to formula (12), the maximum dielectric loss factor that can be obtained at 50Hz is 13.8%. The error of AD5543 is only 2LSB. The main error source of formula (12) is the product of RC. Therefore, D1 is adjusted at the maximum set value of 10% of the dielectric loss factor. The high-precision bridge test is used to make the measured value consistent with the set value, that is, the digital D 1(10％) If 10% dielectric loss is obtained, the remaining dielectric loss can be directly output as follows without point-by-point calibration:

[0078]

[0079] The standard values (%) commonly used for general dielectric loss factor standards are: 0.000, 0.005, 0.010, 0.020, 0.030, 0.040, 0.050, 0.060, 0.070, 0.080

[0080] 0.090, 0.100, 0.200, 0.300, 0.400, 0.500, 0.600, 0.700, 0.800, 0.900

[0081] 1.000, 2.000, 3.000, 4.000, 5.000, 6.000, 7.000, 8.000, 9.000, 10.000

[0082] It can be seen that Equation (12) or Equation (13) can arbitrarily modify the dielectric loss factor value or increase or decrease the number of standard value points through software without changing the hardware.

[0083] Example 3:

[0084] This embodiment provides an electronic dielectric loss factor standard, such as Figure 1 As shown, the standard capacitor C0 uses a 50pF three-terminal SF6 gas-filled structure standard capacitor with a rated working voltage of 10kV. The resistors R, R1, and R2 all use 20kΩ low-temperature drift metal foil resistors. The capacitor C uses a 2200pF mica capacitor. DA1 and DA2 both use 16-bit four-quadrant multiplication type D / A converter AD5543. The operational amplifiers OPA1, OPA2, OPA3, and OPA4 use AD8512. According to formula (11), When D2 = 52429, an equivalent capacitance of 100pF can be obtained. Generally, C0, R, and K are all allowed to have large errors. Therefore, the specific capacitance requires a high-precision bridge and a high-precision standard capacitor for actual measurement and calibration. Since the calibration is implemented through software, no hardware changes are required.

[0085] The setting value and gain K of the capacitance of a general dielectric loss factor standard are shown in Table 1:

[0086] Table 1. Common capacitance settings and required amplifier gains

[0087] Capacitance C 100pF 500pF 1nF 5nF 10nF 50nF 100nF 500nF Gain K (mS) 0.125 0.625 1.25 6.25 12.5 62.5 125 625

[0088] Example 4

[0089] An embodiment of the present invention provides a control method for an electronic dielectric loss factor standard.

[0090] A control method for an electronic dielectric loss factor standard, comprising:

[0091] The electronic dielectric loss factor standard device described in the first aspect is connected to an external voltage, and a current is output from the output end of the amplifier circuit, thereby obtaining a simulated impedance including capacitance and dielectric loss factor;

[0092] Adjusting the digital value of the first D / A converter in the first digitally controlled voltage proportional attenuator by the processor to change the dielectric loss factor;

[0093] The digitally changed capacitance of the second D / A converter in the second digitally controlled voltage proportional attenuator is adjusted by the processor.

[0094] The above disclosure only describes the basic structure and implemented functions of the present invention. Any person skilled in the art can easily conceive of changes or modifications based on the technology disclosed in the present invention, such as: adding input and output protection and filtering circuits, compensating for circuit delay to achieve a zero-value dielectric loss factor, what kind of amplification circuit to use, what kind of resistors and capacitors to use, how to make the operational amplifier work more stably, using other D / A converters and operational amplifier models with similar functions, how to power supply, what kind of mechanical structure to use, which leads need to be shielded, what type of CPU to use, how to compile software, etc. As long as the basic structure and implemented functions remain unchanged, they are all within the scope of protection of the present invention.

[0095] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. An electronic dielectric loss factor standard, characterized in that: include: A first capacitor, a high-voltage end of the first capacitor is connected to an external voltage, a low-voltage end is connected to the negative input end of the first operational amplifier, the positive input end of the first operational amplifier is grounded, the output end of the first operational amplifier is respectively connected to one end of the first resistor, the input end of the first digitally controlled voltage proportional attenuator and the input end of the second digitally controlled voltage proportional attenuator, the other end of the first resistor is connected to the negative input end of the first operational amplifier; the output end of the first digitally controlled voltage proportional attenuator is connected to one end of the second capacitor through an inverting amplifier, and the other end of the second capacitor is connected to the negative input end of the first operational amplifier; the output end of the second digitally controlled voltage proportional attenuator is connected to the current output end through an amplifying circuit.

2. The electronic dielectric loss factor standard according to claim 1, characterized in that: The first digitally controlled voltage proportional attenuator includes a first D / A converter and a second operational amplifier, wherein the reference voltage input terminal of the first D / A converter is connected to the output terminal of the first operational amplifier, the current output terminal of the first D / A converter is connected to the negative input terminal of the second operational amplifier, the positive input terminal of the second operational amplifier is grounded, and the output terminal of the second operational amplifier is connected to the negative feedback resistor lead terminal of the first D / A converter.

3. The electronic dielectric loss factor standard according to claim 2, characterized in that: The first D / A converter is a four-quadrant multiplication type D / A converter.

4. The electronic dielectric loss factor standard according to claim 1, characterized in that: The inverting amplifier includes a second resistor, a third resistor and a third operational amplifier, one end of the second resistor is connected to the output end of the first digitally controlled voltage proportional attenuator, and the other end is connected to the negative input end of the third operational amplifier, the positive input end of the third operational amplifier is grounded, the output end of the third operational amplifier is respectively connected to one end of the third resistor and one end of the second capacitor, and the other end of the third resistor is connected to the negative input end of the third operational amplifier.

5. The electronic dielectric loss factor standard according to claim 1, characterized in that: The second digitally controlled voltage proportional attenuator includes a second D / A converter and a fourth operational amplifier, the reference voltage input terminal of the second D / A converter is connected to the output terminal of the first operational amplifier, the current output terminal of the second D / A converter is connected to the negative input terminal of the fourth operational amplifier, the positive input terminal of the fourth operational amplifier is grounded, and the output terminal of the fourth operational amplifier is connected to the negative feedback resistor lead terminal of the second D / A converter.

6. The electronic dielectric loss factor standard according to claim 5, characterized in that: The second D / A converter is a four-quadrant multiplication type D / A converter.

7. The electronic dielectric loss factor standard according to claim 6, characterized in that: The output end of the fourth operational amplifier is also connected to the input end of the amplifier circuit, and the output end of the amplifier circuit is connected to the current output end.

8. The electronic dielectric loss factor standard according to any one of claims 1 to 7, characterized in that: The digital end of the first D / A converter in the first digitally controlled voltage proportional attenuator and the digital end of the second D / A converter in the second digitally controlled voltage proportional attenuator are both connected to the processor.

9. The electronic dielectric loss factor standard according to claim 1, characterized in that: The voltage output by the first operational amplifier is digitally attenuated by the first digitally controlled voltage proportional attenuator and the inverting amplifier, and then forms negative feedback through the second capacitor.

10. A control method for an electronic dielectric loss factor standard, characterized in that: include: The electronic dielectric loss factor standard according to any one of claims 1 to 9 is connected to an external voltage, and a current is output from the output end of the amplifier circuit to obtain a simulated impedance including capacitance and dielectric loss factor; Adjusting the digital value of the first D / A converter in the first digitally controlled voltage proportional attenuator by the processor to change the dielectric loss factor; The digitally changed capacitance of the second D / A converter in the second digitally controlled voltage proportional attenuator is adjusted by the processor.

Images