An active zero-flux sampling device

Abstract

The present invention discloses an active zero-flux sampling device, comprising: a current transformer, a conversion sampling circuit, a compensation circuit, a low-pass filter circuit and an ADC sampling chip. The current transformer is used to receive the current input from the external primary side and convert it into a current signal to be measured. The conversion sampling circuit is used to receive the current signal to be measured, convert it into a voltage signal to be measured and transmit it to the low-pass filter circuit. The compensation circuit is used to receive the current signal to be measured, convert it into a compensation voltage signal and input it into the conversion sampling circuit for output compensation of the current signal to be measured. The low-pass filter circuit is used to receive the voltage signal to be measured and filter out the high-frequency component. The ADC sampling chip is used to receive the voltage to be measured after filtering out the high-frequency component for sampling and calculation. By compensating the excitation current, the current transmission error is eliminated, the current transformer is placed in a zero-flux state, and the input and output magnetic fluxes of the current transformer are offset against each other to achieve a balanced state, thereby achieving a high-precision measurement.

Description

Technical Field

[0001] The invention belongs to the field of electrical measurement, and in particular relates to an active zero-flux sampling device. Background Art

[0002] Power equipment such as online power quality monitoring terminals and instruments such as high-precision multi-function meters need to measure, calculate, and analyze the AC current. To obtain data such as the current amplitude, phase, harmonics, etc., it is necessary to sample and analyze the current.

[0003] The traditional monitoring solutions for distribution terminal batteries are as follows:

[0004] Sampling resistor solution. Sampling is performed using a high-power sampling resistor at the milliohm level, and the current I = U / R is finally calculated. This solution has two main problems. First, when a large current flows through the resistor, it will generate heat, and the resistance value will drift with temperature, resulting in inaccurate accuracy. Second, this solution is not isolated, and an isolation transmission circuit needs to be added, which makes it difficult to achieve high accuracy in the synchronization of multi-channel sampling, ultimately resulting in poor phase accuracy.

[0005] Ordinary current transformer sampling scheme. Ordinary current transformers are passive devices, so it is difficult to achieve magnetic balance. The excitation current will affect the measurement accuracy of the transformer, and the amplitude accuracy and phase will have large errors, making it difficult to achieve a high-precision measurement solution within 0.02%. Summary of the invention

[0006] The technical purpose of the present invention is to provide an active zero-flux sampling device to solve the technical problems of low measurement accuracy and easy generation of measurement errors.

[0007] To solve the above problems, the technical solution of the present invention is:

[0008] An active zero-flux sampling device comprises: a current transformer, a conversion sampling circuit, a compensation circuit, a low-pass filtering circuit and an ADC sampling chip.

[0009] The current transformer is used to receive the current from the external primary input and convert it into a current signal to be measured.

[0010] The conversion sampling circuit is used to receive the current signal to be measured, convert it into the voltage signal to be measured and transmit it to the low-pass filtering circuit.

[0011] The compensation circuit is used to receive the current signal to be measured and convert it into a compensation voltage signal, which is then input into the conversion sampling circuit for output compensation of the current signal to be measured.

[0012] The low-pass filter circuit is used to receive the voltage signal to be measured and filter out the high-frequency component.

[0013] The ADC sampling chip is used to receive the voltage to be measured after filtering out the high-frequency component for sampling and calculation to obtain the information of the current input by the external primary side. Specifically, the conversion sampling circuit includes a first operational amplifier, a common emitter amplifier subcircuit and a ring subcircuit.

[0014] The first operational amplifier is used to receive the current signal to be measured and convert it into the voltage signal to be measured through the ring sub-circuit.

[0015] The common emitter amplifier sub-circuit is used to expand the output current of the first operational amplifier to increase the driving current of the ring sub-circuit.

[0016] The ring subcircuit is used for receiving the amplified current signal to be measured outputted by the common emitter amplifier subcircuit and converting it into a voltage signal to be measured.

[0017] Specifically, the common emitter amplifier subcircuit includes a first triode, a second triode, a first resistor, a second resistor, a third resistor and a fourth resistor.

[0018] The base of the first transistor is electrically connected to one end of the first resistor and one end of the second resistor respectively, the collector of the first transistor is electrically connected to the other end of the first resistor and the compensation circuit respectively, and the emitter of the first transistor is electrically connected to one end of the third resistor.

[0019] The base of the second triode is electrically connected to the output end of the first operational amplifier and the other end of the second resistor respectively, the collector of the second triode is electrically connected to the compensation circuit, the emitter of the second triode is electrically connected to one end of the fourth resistor, and the other end of the third resistor is electrically connected to the other end of the fourth resistor.

[0020] Specifically, the ring sub-circuit includes a first capacitor and a fifth resistor.

[0021] One end of the fifth resistor is electrically connected to the inverting input terminal of the first operational amplifier and one end of the first capacitor respectively, and the other end of the fifth resistor is electrically connected to the other end of the third resistor, the other end of the fourth resistor and the other end of the first capacitor respectively.

[0022] Specifically, the compensation circuit includes a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a second operational amplifier, a third transistor and a fourth transistor.

[0023] The base of the third triode is electrically connected to one end of the eighth resistor and one end of the ninth resistor respectively, the collector of the third triode is electrically connected to the other end of the eighth resistor and the conversion sampling circuit respectively, and the emitter of the third triode is electrically connected to one end of the tenth resistor.

[0024] The base of the fourth triode is electrically connected to the other end of the ninth resistor and the output end of the second operational amplifier respectively, the collector of the fourth triode is electrically connected to the conversion sampling circuit, the emitter of the fourth triode is electrically connected to one end of the eleventh resistor, and the other end of the eleventh resistor is electrically connected to the other end of the tenth resistor.

[0025] One end of the sixth resistor is electrically connected to the other end of the tenth resistor and the other end of the eleventh resistor respectively, and the other end of the sixth resistor is electrically connected to one end of the seventh resistor and the inverting input terminal of the second operational amplifier respectively, and the non-inverting input terminal of the second operational amplifier is grounded.

[0026] Specifically, the low-pass filter circuit includes a twelfth resistor, a thirteenth resistor and a second capacitor.

[0027] One end of the twelfth resistor is electrically connected to the compensation circuit, the other end of the twelfth resistor is electrically connected to one end of the second capacitor and the ADC sampling chip respectively, the other end of the second capacitor is electrically connected to one end of the thirteenth resistor, and the other end of the thirteenth resistor is grounded.

[0028] More preferably, a protection circuit is further included, and the protection circuit includes a first protection sub-circuit and a second protection sub-circuit.

[0029] The first protection subcircuit is used for receiving the current signal to be measured and inputting it into the conversion sampling circuit for voltage reduction protection.

[0030] The second protection subcircuit is used to receive the current signal to be measured and input it to the compensation circuit for voltage reduction protection.

[0031] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0032] 1) The conversion sampling circuit adopted in the present invention has higher accuracy and linearity than the traditional transformer output parallel sampling resistor.

[0033] 2) The compensation circuit of the present invention can improve the accuracy of the mutual inductor from the order of 0.2% to the order of 0.2%, thereby designing a high-precision instrument or performing a higher-precision monitoring of the power quality.

[0034] 3) The present invention can dynamically compensate for the excitation current, with low requirements on parameters such as the magnetic permeability and magnetic path length of the electromagnetic transformer core. It does not require complex process materials to adjust the transformer to a near-zero magnetic flux, but instead enables the transformer to achieve zero magnetic flux, has strong versatility and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the following detailed description of the preferred embodiment.The drawings are only for the purpose of illustrating the preferred embodiments and are not to be construed as limiting the invention.

[0036] Figure 1 This is a block diagram of the overall architecture of an active zero-flux sampling device proposed in an embodiment of the present invention;

[0037] Figure 2 A circuit diagram of a protection circuit proposed in an embodiment of the present invention;

[0038] Figure 3 A circuit diagram of a conversion sampling circuit and a compensation circuit proposed in an embodiment of the present invention;

[0039] Figure 4 A circuit diagram of a low-pass filter circuit proposed in an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of an overall circuit of an active zero-flux sampling device proposed in an embodiment of the present invention.

[0041] Description of Reference Numerals

[0042] R1: first resistor; R2: second resistor; R3: third resistor; R4: fourth resistor; R5: fifth resistor; R6: sixth resistor; R7: seventh resistor; R8: eighth resistor; R9: ninth resistor; R10: tenth resistor; R11: eleventh resistor; R12: twelfth resistor; R13: thirteenth resistor; C1: first capacitor; C2: second capacitor; Q1: first transistor; Q2: second transistor; Q3: third transistor; Q4: fourth transistor; U1: first operational amplifier; U2: second operational amplifier. DETAILED DESCRIPTION

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work.

[0044] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0045] The following is a further detailed description of an active zero-flux sampling device proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims.

[0046] Example

[0047] See also Figure 1 , this embodiment provides an active zero-flux sampling device, including a current transformer, a protection circuit, a conversion sampling circuit, a compensation circuit, a low-pass filter circuit and an ADC sampling chip. Among them, the current transformer is used to receive the AC signal input from the external primary side and convert it into a current signal to be measured. The protection circuit is arranged between the current transformer and the conversion sampling circuit, and the voltage of the current signal to be measured is reduced to limit the transient electromotive force generated by the secondary coil of the electromagnetic current transformer, which causes damage to the operational amplifier sampling of the subsequent sampling circuit. The conversion sampling circuit, which can also be called the main loop IV conversion sampling circuit, is used to receive the current signal to be measured, convert it into a voltage signal to be measured, and transmit it to the low-pass filter circuit. At the same time, the compensation circuit, which can also be called the winding zero-flux compensation circuit, is used to receive the current signal to be measured and convert it into a compensation voltage signal and input it to the conversion sampling circuit for output compensation of the current signal to be measured. Then, the low-pass filter circuit is used to receive the voltage signal to be measured and filter out the high-frequency component. Finally, the ADC sampling chip receives the voltage to be measured after filtering out the high-frequency component, and obtains the external power distribution terminal battery.

[0048] Now let's explain the overall signal transmission process. Figure 1 , Figure 2 and Figure 3 First, the external device to be tested is connected to the current transformer so that its current passes through the coil on one side of the current transformer, and the induction coil on the other side generates a mutual induction current, that is, the current signal to be measured. Among them, since the subsequent conversion sampling circuit and the compensation circuit are independent of each other and electrically connected, there are two induction coils, and correspondingly, there are also two protection circuits, which are divided into a first protection subcircuit and a second protection subcircuit. The induction coil in the first protection subcircuit induces the current signal to be measured, and the current at one end of the induction coil will be input to the conversion sampling circuit for step-down protection, and the current at the other end will be input to the compensation circuit. Similarly, the induction coil in the second protection subcircuit obtains the current signal to be measured, and the current at both ends of the induction coil will be input to the compensation circuit for step-down protection. The first protection subcircuit and the second protection subcircuit both limit the secondary coil (induction coil) of the electromagnetic current transformer to generate an excessively high electromotive force due to the transient induction, causing damage to the subsequent conversion sampling circuit and compensation circuit.

[0049] See also Figure 3As mentioned above, the current signal to be measured of the first protection subcircuit will enter the conversion sampling circuit. Specifically, the conversion sampling circuit can be divided into the first operational amplifier U1, the common emitter amplifier subcircuit and the ring subcircuit. First, the current signal to be measured will enter the inverting input terminal of the first operational amplifier U1 and the ring subcircuit respectively, the non-inverting input terminal of the first operational amplifier U1 is grounded, and the first operational amplifier U1 amplifies the current signal to be measured and then inputs it into the common emitter amplifier subcircuit.

[0050] Specifically, the common emitter amplifier subcircuit includes a first transistor Q1, a second transistor Q2, a first resistor R1, a second resistor R2, a third resistor R3 and a fourth resistor R4. After the current signal to be measured is output from the first operational amplifier U1, it is divided into two branches through the second resistor R2, one of which enters the base of the first transistor Q1, thereby expanding the current signal to be measured. The other branch passes through the first resistor R1 and the current output of the compensation circuit and enters the collector of the first diode, wherein the first resistor R1 and the second resistor R2 provide base bias for the first transistor Q1 and the second transistor Q2 respectively. Then, a part of the output from the emitter of the first diode enters the ring subcircuit after passing through the third resistor R3, and a part enters the emitter of the second transistor Q2 through the fourth resistor R4. The third resistor R3 and the fourth resistor R4 are negative feedback resistors of the first transistor Q1 and the second transistor Q2 respectively. The first transistor Q1 and the second transistor Q2 will form a common emitter amplifier subcircuit. When the voltage of the current signal to be measured output by the first operational amplifier U1 increases, the base current of the first transistor Q1 or the second transistor Q2 increases, causing the emitter current of the first transistor Q1 or the second transistor Q2 to increase, and the voltage drop of the current flowing through the third resistor R3 or the fourth resistor R4 increases, thereby increasing the corresponding emitter signal voltage drop, thereby causing the corresponding transistor forward bias voltage to decrease, forming a negative feedback process. After the current signal to be measured is output from the first operational amplifier U1, it will also enter the base of the second transistor Q2, and its collector is electrically connected to the compensation circuit.

[0051] Specifically, the ring subcircuit includes a first capacitor C1 and a fifth resistor R5. The fifth resistor R5 is a sampling resistor, and the first capacitor C1 is a feedback loop capacitor. The current signal to be measured entering the conversion sampling circuit can directly enter the fifth resistor R5 and the first capacitor C1, and after passing through the fifth resistor R5 and merging with the signal output by the common emitter amplifier subcircuit, it is converted into a voltage signal to be measured and enters the low-pass filter circuit. In addition, the signal output by the common emitter amplifier subcircuit will also enter the first capacitor C1, and the first capacitor C1 can prevent oscillation caused by loop delay feedback.

[0052] See also Figure 3, now the compensation circuit is explained. From left to right, the compensation circuit can be divided into two parts. Among them, the left half circuit includes the second operational amplifier U2, the sixth resistor R6 and the seventh resistor R7, and a bidirectional diode. The second protection subcircuit outputs two signals (ACTA+, ACTA-) that enter the left half circuit. The current signal to be measured that ACTA+ enters the seventh resistor R7 and enters the inverting input terminal of the second operational amplifier U2, and the current signal to be measured that ACTA- enters is grounded and electrically connected to the non-inverting input terminal of the second operational amplifier U2. The two branches are electrically connected through a bidirectional diode. One end of the sixth resistor R6 is also electrically connected to the inverting input terminal of the second operational amplifier U2, and the other end is electrically connected to ACTB+ of the first protection subcircuit. The output terminal of the second operational amplifier U2 is electrically connected to the right half circuit, and the signal of the induced voltage is negatively feedback amplified. The amplified signal is provided to the right half circuit for compensation.

[0053] The right half circuit includes the third transistor Q3, the fourth transistor Q4, the eighth resistor R8, the ninth resistor R9, the tenth resistor R10 and the eleventh resistor R11. The electrical signal enters the right half circuit after being amplified by the second operational amplifier U2, and is divided into two branches after passing through the ninth resistor R9, one of which enters the base of the third transistor Q3, thereby expanding the current signal to be measured. The other enters the collector of the third diode and the conversion sampling circuit after being combined with the 15V positive source input through the eighth resistor R8, wherein the eighth resistor R8 and the ninth resistor R9 provide base bias for the third transistor Q3 and the fourth transistor Q4 respectively. Then, a part of the output from the emitter of the third diode after passing through the tenth resistor R10 is electrically connected to ACTB+, so its output electrical signal enters the emitter of the fourth transistor Q4 through the eleventh resistor R11, and enters the inverting input terminal of the second operational amplifier U2 through the sixth resistor R6. The tenth resistor R10 and the eleventh resistor R11 are respectively negative feedback resistors of the third transistor Q3 and the fourth transistor Q4. The third transistor Q3 and the fourth transistor Q4 will form a common emitter amplifier subcircuit. When the voltage of the electrical signal output by the second operational amplifier U2 increases, the base current of the third transistor Q3 or the fourth transistor Q4 increases, causing the emitter current of the third transistor Q3 or the fourth transistor Q4 to increase, and the voltage drop of the current flowing through the tenth resistor R10 or the eleventh resistor R11 increases, thereby increasing the corresponding emitter signal voltage drop, thereby causing the corresponding transistor forward bias voltage to decrease, forming a negative feedback process. After the electrical signal is output from the second operational amplifier U2, it will also enter the base of the second transistor Q2, and its collector is electrically connected to the collector of the second transistor Q2. When the electromagnetic current transformer is not in a zero flux state, the compensation circuit will induce a voltage. The induced voltage is amplified and current compensated, so that the input and output fluxes of the transformer cancel each other out until a zero flux equilibrium state is reached.

[0054] See also Figure 4Specifically, the low-pass filter circuit includes a twelfth resistor R12, a thirteenth resistor R13 and a second capacitor C2. The twelfth resistor R12, the thirteenth resistor R13 and the second capacitor C2 form a first-order passive low-pass RC filter, which filters out the high-frequency components of the signal and sends it to the ADC sampling chip for sampling calculation, thereby obtaining the current amplitude, phase, harmonics and other data of the device under test.

[0055] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the protection scope of the present invention.

Claims

1. An active zero-flux sampling device, characterized in that: include: Current transformer, conversion sampling circuit, compensation circuit, low-pass filter circuit and ADC sampling chip; The current transformer is used to receive the current input from the external primary side and convert it into a current signal to be measured; The conversion sampling circuit is used to receive the current signal to be measured, convert it into a voltage signal to be measured and transmit it to the low-pass filter circuit; The compensation circuit is used to receive the current signal to be measured and convert it into a compensation voltage signal and input it into the conversion sampling circuit for outputting compensation for the current signal to be measured; The low-pass filter circuit is used to receive the voltage signal to be measured and filter out high-frequency components; The ADC sampling chip is used to receive the voltage to be measured after filtering out the high-frequency component, perform sampling calculation, and obtain the information of the current input by the external primary side; Wherein, the compensation circuit includes a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a second operational amplifier, a third transistor and a fourth transistor; The base of the third triode is electrically connected to one end of the eighth resistor and one end of the ninth resistor respectively, the collector of the third triode is electrically connected to the other end of the eighth resistor and the conversion sampling circuit respectively, and the emitter of the third triode is electrically connected to one end of the tenth resistor; The base of the fourth triode is electrically connected to the other end of the ninth resistor and the output end of the second operational amplifier respectively, the collector of the fourth triode is electrically connected to the conversion sampling circuit, the emitter of the fourth triode is electrically connected to one end of the eleventh resistor, and the other end of the eleventh resistor is electrically connected to the other end of the tenth resistor; One end of the sixth resistor is electrically connected to the other end of the tenth resistor and the other end of the eleventh resistor respectively, the other end of the sixth resistor is electrically connected to one end of the seventh resistor and the inverting input terminal of the second operational amplifier respectively, and the non-inverting input terminal of the second operational amplifier is grounded.

2. The active zero-flux sampling device according to claim 1, characterized in that: The conversion sampling circuit includes a first operational amplifier, a common emitter amplifier sub-circuit and a ring sub-circuit; The first operational amplifier is used to receive the current signal to be measured and convert it into the voltage signal to be measured through amplification by the ring sub-circuit; The common emitter amplifier sub-circuit is used to expand the output current of the first operational amplifier to increase the driving current of the ring sub-circuit; The ring sub-circuit is used for receiving the amplified current signal to be measured outputted by the common emitter amplifier sub-circuit and converting the amplified current signal to be measured into the voltage signal to be measured.

3. The active zero-flux sampling device according to claim 2, characterized in that: The common emitter amplifier subcircuit comprises a first triode, a second triode, a first resistor, a second resistor, a third resistor and a fourth resistor; The base of the first transistor is electrically connected to one end of the first resistor and one end of the second resistor respectively, the collector of the first transistor is electrically connected to the other end of the first resistor and the compensation circuit respectively, and the emitter of the first transistor is electrically connected to one end of the third resistor; The base of the second transistor is electrically connected to the output end of the first operational amplifier and the other end of the second resistor respectively, the collector of the second transistor is electrically connected to the compensation circuit, the emitter of the second transistor is electrically connected to one end of the fourth resistor, and the other end of the third resistor is electrically connected to the other end of the fourth resistor.

4. The active zero-flux sampling device according to claim 3, characterized in that: The ring subcircuit includes a first capacitor and a fifth resistor; One end of the fifth resistor is electrically connected to the inverting input terminal of the first operational amplifier and one end of the first capacitor, and the other end of the fifth resistor is electrically connected to the other end of the third resistor, the other end of the fourth resistor and the other end of the first capacitor.

5. The active zero-flux sampling device according to claim 1, characterized in that: The low-pass filter circuit includes a twelfth resistor, a thirteenth resistor and a second capacitor; One end of the twelfth resistor is electrically connected to the compensation circuit, the other end of the twelfth resistor is electrically connected to one end of the second capacitor and the ADC sampling chip respectively, the other end of the second capacitor is electrically connected to one end of the thirteenth resistor, and the other end of the thirteenth resistor is grounded.

6. The active zero-flux sampling device according to claim 1, characterized in that: Also included is a protection circuit, the protection circuit including a first protection subcircuit and a second protection subcircuit; The first protection subcircuit is used to receive the current signal to be measured and input it to the conversion sampling circuit for voltage reduction protection; The second protection subcircuit is used to receive the current signal to be measured and input it to the compensation circuit for voltage reduction protection.

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