Direct current sampling circuit and direct current circuit breaker

Abstract

The utility model discloses a direct current sampling circuit. One section of the main loop to be sampled is divided into N branches which are connected in parallel, one shunt is connected in series in each branch, and N is an integer greater than 1; the direct current sampling circuit comprises N differential amplification units which are in one-to-one correspondence with the shunts in the branches and are connected in the same direction, and an adder unit which is used for adding output signals of the N differential amplification units, and the AD conversion / digital isolation unit is used for performing AD conversion and digital isolation output on an output signal of the adder unit. The utility model also discloses a DC circuit breaker. Compared with the prior art, the technical scheme of the utility model has the advantages of simpler sampling circuit and lower cost.

Description

Technical Field

[0001] The utility model relates to a direct current sampling circuit. Background Art

[0002] In the new energy field dominated by photovoltaic power generation and wind power generation, DC systems are widely used, and DC current sampling is required to monitor and protect the DC system. At present, the commonly used DC current sampling methods include Hall sensors, shunts, etc. Among them, the advantages of Hall sensors are simple structure and high precision, and the disadvantages are that they are easily affected by magnetic fields, require shielding systems, and are costly. Therefore, the use of shunts for DC current signal sampling has become the preferred solution for various manufacturers. The advantages of shunts are simple structure, large measurement range, and no influence from external magnetic fields, but the disadvantage is that the shunt is directly connected to the main circuit and is not electrically isolated. At present, the isolation devices selected for DC current sampling using shunts are generally analog isolation amplifiers and digital isolators, but analog isolation amplifiers are expensive and have few options, while digital isolators are relatively low in cost, widely used, and have a richer selection. Generally, the sampling signal needs to be converted into a digital signal through an AD converter and then isolated and output through a digital isolator.

[0003] As the capacity of user DC systems continues to upgrade, the rated operating current of DC circuit breakers as circuit protection components is also increasing, and the performance indicators of short-circuit protection are increasingly required. In order to obtain a higher short-circuit protection breaking level, many DC circuit breakers with larger rated currents divide the internal main circuit into two, and the two branches are connected in parallel. Two sets of contacts are used to simultaneously break the short-circuit current, and the two branches are then connected in parallel at the two outlet ends. After the main circuit is divided into two, each branch needs to be installed with a shunt for current sampling to accurately sample the DC current signal, and each shunt only bears half of the load current, which reduces power consumption and improves the reliability of the shunt. The normal process of using shunt sampling and outputting through digital isolation is as follows: the shunt first samples the current signal, which is differentially amplified and conditioned, and input into the AD converter to convert it into a digital signal, which is then isolated and output to the serial communication port of the microprocessor through the digital isolator, and finally calculated and processed by the microprocessor. Obviously, if a DC circuit breaker with a larger rated current is used Figure 1 The current sampling circuit shown in the figure divides the internal main circuit into two (or more branches), which requires two (or more) sampling lines. The microprocessor needs to provide two (or more) serial communication ports to receive data and add the current values ​​calculated for each line. In addition, different DC system types have different wiring methods. Some wiring methods require shunts to be installed at both the power input and output ends of the circuit breaker to sample the input current and output current respectively. In this case, the power input and output ends of multiple branches of the DC circuit breaker with a larger rated current may need to be installed with at least 4 shunts to sample the current signal, which means that 4 lines are required. Figure 1The sampling circuit shown in the figure needs to have at least 4 serial communication ports to receive data, which greatly increases the cost. Utility Model Content

[0004] The technical problem to be solved by the utility model is to overcome the shortcomings of the current sampling technology of the existing DC circuit breaker with a larger rated current, and to provide a DC current sampling circuit with a simpler circuit structure and lower implementation cost.

[0005] The utility model specifically adopts the following technical solutions to solve the above technical problems:

[0006] A DC current sampling circuit, a section of a main loop to be sampled is divided into N parallel branches, each branch is serially connected with a shunt, wherein N is an integer greater than 1; the DC current sampling circuit comprises: N differential amplifier units corresponding to the shunts in each branch one by one and connected in the same direction, an adder unit for adding the output signals of the N differential amplifier units, and an AD conversion / digital isolation unit for performing AD conversion on the output signal of the adder unit and digitally isolating and outputting it.

[0007] Preferably, the differential amplification unit comprises a limiting circuit, a common-mode and differential-mode filtering circuit, and a differential operational amplifier circuit which are connected in sequence.

[0008] Furthermore, the differential amplification unit also includes a decoupling circuit.

[0009] Further preferably, the differential amplification unit includes a dual diode limiting circuit, first to third resistors, first to fifth capacitors, and a differential operational amplifier; one end of the first resistor is simultaneously connected to an output end of the shunt and one pole of the dual diode limiting circuit, one end of the second resistor is simultaneously connected to another output end of the shunt and the other pole of the dual diode limiting circuit, the other end of the first resistor is simultaneously connected to one end of the first capacitor, one end of the second capacitor, and an input end of the differential operational amplifier, the other end of the second resistor is simultaneously connected to the other end of the second capacitor, one end of the third capacitor, and another input end of the differential operational amplifier, the other end of the first capacitor and the other end of the third capacitor are both grounded, one end of the fourth capacitor is connected to the positive power input end of the differential operational amplifier, one end of the fifth capacitor is connected to the negative power input end of the differential operational amplifier, the other end of the fourth capacitor and the other end of the fifth capacitor are both grounded, and the third resistor is connected between the gain setting pins of the differential operational amplifier.

[0010] According to the same inventive concept, the following technical solutions can also be obtained:

[0011] A DC circuit breaker comprises at least one DC current sampling circuit, wherein the DC current sampling circuit is the DC current sampling circuit as described in any of the above technical solutions.

[0012] Further preferably, the DC circuit breaker comprises two DC current sampling circuits respectively used for sampling the main loop current at the power inlet terminal and the power outlet terminal.

[0013] Compared with the prior art, the utility model has the following beneficial effects:

[0014] In order to improve the short-circuit protection breaking level of a DC circuit breaker with a large rated current, the internal main circuit is divided into multiple parallel branches. The DC current signals sampled by the shunt of each branch are differentially amplified and conditioned, and the differential signals of each branch are added by the adder unit, and then the digital signal is output through AD conversion, and the digital isolator isolates the digital signal and outputs it to the serial communication port of the microprocessor. Finally, the microprocessor calculates and processes the data received by the serial communication port to obtain the primary side current amplitude. The technical solution of the utility model has the advantages of simple sampling circuit and low cost, and overcomes the disadvantages of the existing DC current sampling circuit that each branch is sampled, converted, isolated and output to the microprocessor for calculation and processing, resulting in high sampling circuit cost and complex circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the structural principle of an existing DC current sampling circuit;

[0016] Figure 2 This is a schematic diagram of the structure principle of the DC current sampling circuit of the utility model;

[0017] Figure 3 The utility model is a specific implementation circuit diagram of the DC current sampling circuit. DETAILED DESCRIPTION

[0018] In view of the situation that the internal main circuit of a DC circuit breaker with a large rated current is divided into multiple parallel branches in order to improve the short-circuit protection breaking level, the solution idea of ​​the utility model is to perform differential amplification and conditioning on the DC current signals sampled by the shunt in each branch, and the adder unit adds the differential signals of each branch, and then outputs a digital signal through AD conversion, and the digital isolator isolates the digital signal and outputs it to the serial communication port of the microprocessor. Finally, the microprocessor calculates and processes the data received by the serial communication port to obtain the primary side current amplitude, so as to simplify the circuit and reduce the cost.

[0019] The utility model specifically adopts the following technical solutions to solve the above technical problems:

[0020] A DC current sampling circuit, a section of a main loop to be sampled is divided into N parallel branches, each branch is serially connected with a shunt, wherein N is an integer greater than 1; the DC current sampling circuit comprises: N differential amplifier units corresponding to the shunts in each branch one by one and connected in the same direction, an adder unit for adding the output signals of the N differential amplifier units, and an AD conversion / digital isolation unit for performing AD conversion on the output signal of the adder unit and digitally isolating and outputting it.

[0021] Preferably, the differential amplification unit comprises a limiting circuit, a common-mode and differential-mode filtering circuit, and a differential operational amplifier circuit which are connected in sequence.

[0022] Furthermore, the differential amplification unit also includes a decoupling circuit.

[0023] Further preferably, the differential amplification unit includes a dual diode limiting circuit, first to third resistors, first to fifth capacitors, and a differential operational amplifier; one end of the first resistor is simultaneously connected to an output end of the shunt and one pole of the dual diode limiting circuit, one end of the second resistor is simultaneously connected to another output end of the shunt and the other pole of the dual diode limiting circuit, the other end of the first resistor is simultaneously connected to one end of the first capacitor, one end of the second capacitor, and an input end of the differential operational amplifier, the other end of the second resistor is simultaneously connected to the other end of the second capacitor, one end of the third capacitor, and another input end of the differential operational amplifier, the other end of the first capacitor and the other end of the third capacitor are both grounded, one end of the fourth capacitor is connected to the positive power input end of the differential operational amplifier, one end of the fifth capacitor is connected to the negative power input end of the differential operational amplifier, the other end of the fourth capacitor and the other end of the fifth capacitor are both grounded, and the third resistor is connected between the gain setting pins of the differential operational amplifier.

[0024] In order to facilitate public understanding, the technical solution of the utility model is described in detail below with reference to the accompanying drawings:

[0025] For example, the main circuit of a DC circuit breaker is divided into two parallel branches, and each branch uses a shunt to perform current sampling. Figure 2 As shown, the utility model inputs the output signals of the two shunts into two differential amplifier units in the same direction for differential amplification respectively. The two differential amplified signals are added by the adder unit and then input into the AD conversion / digital isolation unit. The digital signal output by the AD conversion is isolated and output to a serial communication port of the microprocessor through the digital isolator. The microprocessor calculates and processes the data received by the serial communication port to obtain the DC current flowing through the entire main circuit. Figure 1The utility model directly adds the DC sampling signals of the two branches through the adder unit, eliminating the process of AD conversion and isolation output to the serial communication port of the microprocessor. The hardware circuit is simple and the cost is low.

[0026] Figure 3 for Figure 2 A specific implementation circuit of the DC sampling circuit shown in the figure includes a first differential amplifier unit, a second differential amplifier unit, an adder unit, an AD conversion / digital isolation unit, a microprocessor unit, and a power generation unit; the output signals of the two shunts are respectively input into the first differential amplifier unit and the second differential amplifier unit in the same direction, and differential amplification is performed respectively. After the two differential amplified signals are added by the adder unit, they are input into the AD conversion / digital isolation unit. The digital signal output by the AD conversion is isolated and output to a serial communication port of the microprocessor through a digital isolator. The microprocessor calculates and processes the data received by the serial communication port to obtain the DC current flowing through the entire main circuit.

[0027] like Figure 3 As shown, the first differential amplifier unit is connected to the shunt F1 inside the circuit breaker Q1 through the input connector X1, the 1st pin of the input connector X1 is connected to the 1st end of the shunt F1, and the 2nd pin of the input connector X1 is connected to the 2nd end of the shunt F1; the first differential amplifier unit includes a limiting circuit, a common mode and differential mode filtering circuit, and a differential operational amplifier circuit connected in sequence; specifically, the limiting circuit adopts a double diode limiting circuit D1 composed of two diodes connected in reverse parallel to limit the input signal amplitude; resistors R1, R2 and capacitors C1, C2, C3 form a common mode and differential mode filtering circuit; C4 and C5 are decoupling capacitors; R3 is a resistor for adjusting the gain of the amplifier circuit; Vref-ISO is a reference voltage used to raise the output signal level of the differential operational amplifier N1; the sampling signal amplified and conditioned by the first differential amplifier unit is input to the adder unit.

[0028] The second differential amplifier unit is connected to the shunt F2 inside the circuit breaker Q1 through the input connector X2, the pin 1 of the input connector X2 is connected to the end 1 of the shunt F2, and the pin 2 of the input connector X2 is connected to the end 2 of the shunt F2; the structure of the second differential amplifier unit is the same as that of the first differential amplifier unit, such as Figure 3 As shown; for the sake of saving space, it will not be repeated here. The sampling signal amplified and conditioned by the second differential amplifier unit is also input to the adder unit.

[0029] The adder unit receives the two current sampling signals amplified and conditioned by the first differential amplifier unit and the second differential amplifier unit, adds the two sampling signals, and outputs them to the AD conversion / digital isolation unit. The specific circuit of the adder unit is as follows: Figure 3 As shown, it is composed of operational amplifier N3A and resistors R7~R10.

[0030] The AD conversion / digital isolation unit includes a functional device N4, which integrates AD conversion and digital isolation functions, receives the sampling signal transmitted by the adder unit, converts it into a digital signal, and then isolates and outputs it to the serial communication port of the microprocessor unit through the digital isolator.

[0031] like Figure 3 As shown, the power generation unit generates isolated VCC-ISO+ from VCC via the isolated power module P1, and VCC-ISO+ is used as the positive power supply of the first differential amplifier unit operational amplifier N1, the second differential amplifier unit N2, the adder unit operational amplifier N3A, and the AD conversion / digital isolation unit; VCC-ISO+ generates VCC-ISO- through the DC / DC chip N6, and VCC-ISO- is used as the negative power supply of the differential operational amplifier N1 and the differential operational amplifier N2; VCC-ISO+ generates a reference voltage Vref-ISO through the resistor R11 and the voltage regulator D3, which is respectively provided to the differential operational amplifier N1 in the first differential amplifier unit, the differential operational amplifier N2 in the second differential amplifier unit, and the operational amplifier N3A in the adder unit, all of which are used to raise the level of the input signal.

[0032] The microprocessor unit receives the isolated digital signal output from the AD conversion / digital isolation unit through the serial communication port, and calculates and processes these data to obtain the amplitude of the corresponding primary-side DC large current.

[0033] Figure 3 The differential amplifier unit, adder unit, AD conversion / digital isolation unit, microprocessor unit, and power generation unit are used as examples, and each functional unit can be implemented by other equivalent circuits in the prior art.

[0034] For a DC circuit breaker that requires shunts to be installed at both the power input and output ends to sample the input current and output current respectively, two (or more) shunts at two (or more) branch input ends can be used as one group, and two (or more) shunts at two (or more) branch output ends can be used as another group. Each group of shunts uses the above-mentioned DC sampling circuit to sample the current. The microprocessor unit receives the current sampling signals of the two groups of shunts through two serial communication ports and calculates them respectively, so as to obtain the current amplitudes at the power input and output ends of the DC circuit breaker.

Claims

1. A DC current sampling circuit, a section of the main circuit to be sampled is divided into N parallel branches, each branch is connected in series with a shunt, wherein: N is an integer greater than 1; it is characterized in that the DC current sampling circuit includes: N differential amplifier units corresponding to the shunts in each branch and connected in the same direction, an adder unit for adding the output signals of the N differential amplifier units, and an AD conversion / digital isolation unit for performing AD conversion on the output signal of the adder unit and digitally isolating the output.

2. The DC current sampling circuit according to claim 1, characterized in that: The differential amplifier unit includes a limiting circuit, a common mode and differential mode filtering circuit, and a differential operational amplifier circuit which are connected in sequence.

3. The DC current sampling circuit as claimed in claim 2, characterized in that: The differential amplification unit further includes a decoupling circuit.

4. The DC current sampling circuit as claimed in claim 3, characterized in that: The differential amplification unit includes a dual-diode limiter circuit, first to third resistors, first to fifth capacitors, and a differential operational amplifier; one end of the first resistor is simultaneously connected to an output end of the shunt and one pole of the dual-diode limiter circuit, one end of the second resistor is simultaneously connected to another output end of the shunt and another pole of the dual-diode limiter circuit, the other end of the first resistor is simultaneously connected to one end of the first capacitor, one end of the second capacitor, and an input end of the differential operational amplifier, the other end of the second resistor is simultaneously connected to the other end of the second capacitor, one end of the third capacitor, and another input end of the differential operational amplifier, the other end of the first capacitor and the other end of the third capacitor are both grounded, one end of the fourth capacitor is connected to the positive power input end of the differential operational amplifier, one end of the fifth capacitor is connected to the negative power input end of the differential operational amplifier, the other end of the fourth capacitor and the other end of the fifth capacitor are both grounded, and the third resistor is connected between the gain setting pins of the differential operational amplifier.

5. A DC circuit breaker, comprising at least one DC current sampling circuit, characterized in that: The DC current sampling circuit is the DC current sampling circuit as claimed in any one of claims 1 to 4.

6. The DC circuit breaker according to claim 5, characterized in that: It comprises two DC current sampling circuits which are respectively used for sampling the main loop current of the power supply input terminal and the power supply output terminal.

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