Sampled current self-test circuit and zero current reference calibration method

Abstract

The application discloses a sampling current self-checking circuit and a zero-point current reference calibration method. The sampling current self-checking circuit comprises a mutual inductor, a control circuit, an integration circuit and a voltage reference circuit. The output end of the mutual inductor is connected with the integration circuit, the output end of the voltage reference circuit is connected with the integration circuit, and the output end of the integration circuit is connected with the control circuit. The control circuit comprises a microcontroller MCU. The microcontroller MCU performs a zero-point voltage calibration step. The zero-point voltage calibration step comprises obtaining a current sampling value collected by the mutual inductor, obtaining a voltage value output by the integration circuit when the current sampling value is zero, and calibrating a reference voltage based on the voltage value output by the integration circuit. The zero-point current reference calibration method is used for calibrating the reference voltage through self-checking of a split state, reference voltage checking, mutual inductor disconnection or rapid saturation mutual inductor power supply, and the like. The error of current sampling is reduced, so as to adapt to changes in different environments.

Description

Technical Field

[0001] This invention relates to the field of low-voltage electrical appliances, specifically to a sampling current self-test circuit and a zero-point current reference calibration method. Background Technology

[0002] Air-core instrument transformers are widely used in low-voltage power distribution systems due to their stable performance and ease of industrial production. Taking universal circuit breakers as an example, to achieve overload and short-circuit protection functions, most manufacturers use air-core instrument transformers to sample the current in the circuit. When using air-core instrument transformers, fast-saturation transformers are generally integrated to power the electronic trip unit. However, when using air-core instrument transformers for current acquisition, since the induced electromotive force (EMF) is proportional to the derivative of the measured current, to improve current sampling accuracy and reconstruct the current waveform, electronic circuitry is needed to integrate the induced EMF. In the integration circuit, a voltage reference is introduced to raise the induced EMF before outputting it to the microcontroller (MCU) for AD conversion to obtain a complete current waveform. Therefore, when the measured current is 0, the zero-point voltage acquired by the MCU is theoretically equal to the voltage reference. Due to individual differences in different components, the zero-point voltage will inevitably differ between the same products. Currently, the common practice is to manually set the zero-point voltage sampled by the MCU, specifying that the voltage acquired during factory testing is the zero-point voltage before shipment. However, after the product leaves the factory, due to changes in the environment, the parameters of the circuit components will undergo slight changes, resulting in a slight deviation between the zero-point voltage and the original factory value. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a sampling current self-test circuit and a zero-point current reference calibration method.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A sampling current self-test circuit includes a current transformer, a control circuit, an integrator circuit, and a voltage reference circuit. The output terminal of the current transformer is connected to the integrator circuit, the output terminal of the voltage reference circuit is connected to the integrator circuit, and the output terminal of the integrator circuit is connected to the control circuit. The control circuit includes a microcontroller (MCU). The MCU performs a zero-point voltage calibration step, which includes acquiring the current sampling value collected by the current transformer, acquiring the voltage value output by the integrator circuit when the current sampling value is zero, and calibrating the reference voltage based on the voltage value output by the integrator circuit.

[0006] Preferably, it further includes an amplifier circuit, a voltage reference circuit and an integrator circuit respectively connected to the amplifier circuit, and the amplifier circuit is connected to the control circuit; the microcontroller MCU calculates the current sampling value based on the integrator circuit and / or the amplifier circuit, and in the zero-point voltage calibration step, when the current sampling value is zero, the voltage value output by the integrator circuit and / or the amplifier circuit is obtained, and the reference voltage is calibrated based on the voltage value output by the integrator circuit and / or the amplifier circuit.

[0007] Preferably, it also includes a switch status detection circuit, which is connected to the control circuit and is used to transmit the switch opening / closing status signal to the control circuit.

[0008] Preferably, it further includes a reference detection circuit for detecting whether the reference voltage output by the voltage reference circuit is invalid. The voltage reference circuit and the reference detection circuit are respectively connected to the microcontroller (MCU), or the reference detection circuit is connected between the reference detection circuit and the microcontroller (MCU).

[0009] Preferably, it also includes a current transformer disconnection detection circuit, which is connected between the integrating circuit and the control circuit.

[0010] Preferably, it also includes a fast saturation power supply detection circuit, which is connected between the fast saturation transformer and the control circuit, and is used to detect whether the current power supply is from the fast saturation transformer.

[0011] Preferably, the microcontroller (MCU) performs a circuit breaker state detection step before executing the zero-point voltage calibration step. The circuit breaker state detection step includes: obtaining the open / closed state of the switch through a switch state detection circuit, and performing the zero-point voltage calibration step only when the switch is in the open state.

[0012] Preferably, the microcontroller (MCU) performs a reference voltage failure detection step before performing the zero-point voltage calibration step, and the zero-point voltage calibration step is only performed when the reference voltage is normal.

[0013] The reference voltage failure detection step includes obtaining whether the reference voltage is failed through a reference detection circuit; or, the reference voltage failure detection step includes obtaining a reference voltage through a voltage reference circuit, obtaining a reference detection voltage through a reference detection circuit, comparing the reference detection voltage with the reference voltage, and if the reference detection voltage and the reference voltage are within a preset error range, the reference voltage is considered to be normal.

[0014] Preferably, before the microcontroller (MCU) performs the zero-point voltage calibration step, a transformer disconnection detection step is also performed. The transformer disconnection detection step includes: controlling the transformer disconnection detection circuit to turn on; after the transformer disconnection detection circuit is turned on, the voltage value output by the integrating circuit is obtained; if the voltage value output by the integrating circuit deviates from the reference voltage by more than a preset value, the transformer is considered to be disconnected; otherwise, the transformer is considered not to be disconnected. The zero-point voltage calibration step is performed only when the transformer is not disconnected.

[0015] Preferably, before the microcontroller (MCU) performs the zero-point voltage calibration step, it also performs a fast-saturation transformer power supply detection step. The fast-saturation transformer power supply detection step includes: determining whether the current power supply is supplied by the fast-saturation transformer through the fast-saturation power supply detection circuit, and performing the zero-point voltage calibration step only if the power supply is not supplied by the fast-saturation transformer.

[0016] Preferably, in the zero-point voltage calibration step, after obtaining the current sampling value collected by the current transformer, it is first determined whether the current sampling value exceeds a preset upper limit value. If the current sampling value exceeds the preset upper limit value, the process is exited.

[0017] The present invention also provides a zero-point current reference calibration method, including a zero-point voltage calibration step, and further including a tripping state detection step, a reference voltage failure detection step, a transformer disconnection detection step, and a fast-saturation transformer power supply detection step.

[0018] The zero-point voltage calibration step is only performed after the switch is detected to be in the open state through the open state detection step, the reference voltage is detected to be normal through the reference voltage failure detection step, the current transformer is detected to be not disconnected through the current transformer disconnection detection step, and the current transformer is detected to be not a fast-saturation current transformer through the fast-saturation current transformer power supply detection step.

[0019] The zero-point voltage calibration step includes acquiring the current sampling value collected by the current transformer, acquiring the voltage value output by the integrating circuit and the amplifying circuit when the current sampling value is zero, and calibrating the reference voltage based on the voltage value output by the integrating circuit and the amplifying circuit.

[0020] The sampling current self-test circuit of the present invention, by designing a sampling current self-test circuit, automatically resets the zero-point voltage after passing the self-test, reducing the error of current sampling and adapting to changes in different environments. It can be applied to a zero-point reference calibration in a current sampling circuit based on a hollow current transformer in a low-voltage power distribution system, which can improve the accuracy of current sampling and realize automatic detection of the current sampling circuit's current working status. When the sampling circuit meets the set conditions, it automatically calibrates its zero-point reference.

[0021] The zero-point current reference calibration method of the present invention can automatically calibrate the zero-point reference based on the self-test results, thereby improving the accuracy of current sampling. Attached Figure Description

[0022] Figure 1 This is the self-test circuit of the current sampling circuit in this embodiment of the invention;

[0023] Figure 2 This is the automatic zero-point voltage calibration process in this embodiment of the invention;

[0024] Figure 3 This is a circuit diagram of one embodiment of an integrating circuit, an amplifying circuit, and a current transformer open circuit detection circuit;

[0025] Figure 4 This is a circuit diagram of one embodiment of a fast saturation power supply detection circuit. Detailed Implementation

[0026] The following embodiments, in conjunction with the accompanying drawings, further illustrate the specific implementation of the sampling current self-test circuit and zero-point current reference calibration method of the present invention. The sampling current self-test circuit and zero-point current reference calibration method of the present invention are not limited to the descriptions in the following embodiments.

[0027] like Figure 1 As shown, the sampling current self-test circuit of this embodiment includes a current transformer, a control circuit, an integrator circuit 3, a voltage reference circuit 4, and an amplifier circuit 6. The output terminal of the current transformer is connected to the integrator circuit 3, the output terminal of the voltage reference circuit 4 is connected to both the integrator circuit 3 and the amplifier circuit 6, the integrator circuit 3 is connected to the amplifier circuit 6, and the output terminals of the integrator circuit 3 and the amplifier circuit 6 are connected to the control circuit. The induced electromotive force of the current transformer is transmitted to the integrator circuit 3, which integrates the induced electromotive force. To obtain a complete current waveform, the integrator circuit uses the voltage reference of the voltage reference circuit 4 to raise the induced electromotive force before outputting it to the AD1 port of the microcontroller MCU. The amplifier circuit 6 amplifies the input signal and outputs it to the AD2 port of the microcontroller MCU. The control circuit calculates the current sampling value based on the signals input from the integrator circuit 3 and the amplifier circuit 6.

[0028] The improvement of this invention lies in the design of a sampling current self-test circuit. After passing the self-test, it automatically resets the zero-point voltage, reducing current sampling errors and adapting to changes in different environments. This sampling circuit self-test circuit can be widely applied in low-voltage power distribution systems, such as circuit breakers, contactors, and other switching devices. Figure 1 The preferred embodiment shown here uses a sampling circuit self-test circuit for a universal circuit breaker.

[0029] Figure 1The sampling circuit self-test circuit of the embodiment includes a current transformer, a control circuit, a current transformer open circuit detection circuit 2, an integrator circuit 3, a voltage reference circuit 4, a reference detection circuit 5, an amplifier circuit 6, a switch state detection circuit 7, and a fast saturation power supply detection circuit 1.

[0030] The control circuit includes a microcontroller (MCU), but can also be a single-chip microcomputer or other microcontrollers as needed.

[0031] The output terminal of the current transformer is connected to the integrator circuit 3, which is connected to the amplifier circuit 6. The output terminal of the voltage reference circuit 4 is connected to both the integrator circuit 3 and the amplifier circuit 6, providing a reference voltage for them. The integrator circuit 3 and the amplifier circuit are connected to the control circuit, specifically to the AD1 and AD2 ports of the microcontroller MCU in this embodiment. The current transformer is a hollow current transformer, a zero-sequence current transformer, or similar type. The amplifier circuit 6 amplifies the amplitude of the sinusoidal signal input to the integrator circuit 3. The control circuit periodically samples the signals input to the integrator circuit 3 and / or the amplifier circuit 6, converting the effective values ​​to obtain the current sample value. The calculation of the current sample value based on the current sample is existing technology and will not be elaborated further. When the current is small, the microcontroller MCU of the control circuit uses the signal from the amplifier circuit 6 to calculate the current sample value; when the current is large, it can directly use the signal from the integrator circuit 3 to calculate the current sample value. Therefore, the amplifier circuit 6 may not be necessary if needed. Theoretically, when the current detected by the current transformer is zero, the outputs of the integrator circuit and the amplifier circuit are equal to the reference voltage. When zero-point voltage calibration is required, such as during self-testing upon switch startup or manually initiated via a switch button, the microcontroller (MCU) performs a zero-point voltage calibration step. This step includes the MCU acquiring the current sampling value collected by the current transformer. When the acquired current sampling value is zero, the MCU acquires the voltage value output by the integrating circuit and / or amplifying circuit. Based on the voltage value output by the integrating circuit and / or amplifying circuit, the reference voltage is calibrated. That is, the zero-point reference voltage is reset based on the voltage value output by the integrating circuit and / or amplifying circuit, which can improve the accuracy of subsequent current sampling. For example, if the current sampling value acquired by the MCU is equal to 0, assuming the reference voltage is 2V and the output of the integrating circuit 3 is 1.99V, the MCU resets 1.99V as the zero-point reference voltage and calibrates the reference voltage.

[0032] The voltage reference circuit 4 and the reference detection circuit 5 are respectively connected to the microcontroller (MCU) and are used to detect whether the reference voltage output by the voltage reference circuit 4 is invalid. Before performing the zero-point voltage calibration step, the microcontroller (MCU) also performs a reference voltage failure detection step; the zero-point voltage calibration step is only performed if the reference voltage is normal. The reference detection circuit 5 establishes another reference detection voltage equal to the reference voltage through the power supply. The reference detection voltage is compared with the reference voltage. If the reference detection voltage and the reference voltage are within a preset error range, the reference voltage is considered normal; otherwise, the reference voltage is considered invalid. In this embodiment, the microcontroller (MCU) determines whether the reference voltage is invalid by comparing the reference detection voltage with the reference voltage difference. The microcontroller (MCU) obtains the reference voltage through the voltage reference circuit 4 and the reference detection voltage through the reference detection circuit 5. The reference detection voltage is compared with the reference voltage. If the reference detection voltage and the reference voltage are within a preset error range, the reference voltage is considered normal, preferably within 2%. Otherwise, the reference voltage is considered invalid, and the microcontroller (MCU) can control an alarm. Of course, as another embodiment, the reference detection voltage can also be compared with the reference voltage using a comparator in the reference detection circuit 5. The reference detection circuit 5 is connected between the reference detection circuit 5 and the microcontroller MCU, and the judgment result is transmitted to the microcontroller MCU. The microcontroller MCU directly obtains the result of whether the reference voltage is invalid through the reference detection circuit 5. The power supply is the power supply for the sampling current self-test circuit, such as the power supply from the sampled circuit, or the power supply for the fast-saturation transformer, or the power supply for the switch controller, such as the power supply inside the intelligent controller of the circuit breaker. In this embodiment, the sampling current self-test circuit is set in the intelligent controller of the circuit breaker, and the microcontroller MCU of the sampling current self-test circuit is the existing microcontroller MCU in the intelligent controller; in addition, the power supply can also be a hybrid power supply. The power supply in this embodiment is DC24V. The reference voltage and the reference detection circuit are powered by the power supply and output to the microcontroller MCU after being divided by a resistor and a voltage regulator; or they are powered by the power supply and output to the microcontroller MCU after passing through a reference voltage chip. The reference voltage and the reference detection circuit can be the same or different, preferably with different implementation circuits.

[0033] Preferably, the sampling circuit self-test circuit further includes a current transformer disconnection detection circuit 2. The current transformer disconnection detection circuit 2 is connected between the integrating circuit 3 and the control circuit. The microcontroller MCU controls whether the current transformer disconnection detection circuit 2 is activated via an I / O port. When the function is activated, the current transformer disconnection detection circuit 2 is connected to the integrating circuit 3. If the current transformer is disconnected, the AD1 port of the microcontroller MCU detects that the voltage output by the integrating circuit 3 deviates from the reference voltage by more than a preset amount, and thus considers the current transformer disconnected; otherwise, it is considered that the current transformer is not disconnected. Preferably, if the deviation between the voltage detected by the AD1 port of the microcontroller MCU and the reference voltage is greater than or equal to 3% of the reference voltage, it is determined that the current transformer is disconnected; if the deviation is less than 3% of the reference voltage, it is determined that the current transformer is not disconnected. Before the microcontroller MCU performs the zero-point voltage calibration step, it also performs a transformer disconnection detection step. The transformer disconnection detection step includes: controlling the transformer disconnection detection circuit 2 to turn on; after the transformer disconnection detection circuit 2 is turned on, it obtains the voltage value output by the integrating circuit 3; if the voltage value output by the integrating circuit 3 deviates from the reference voltage by more than a preset value, it is considered that the transformer is disconnected; otherwise, it is considered that the transformer is not disconnected. The zero-point voltage calibration step is performed only when the transformer is not disconnected.

[0034] like Figure 3 As shown, this embodiment includes an integrating circuit 3, an amplifying circuit 6, and a current transformer disconnection detection circuit 2. The integrating circuit 3 includes an operational amplifier U106A, resistors R119, R120, R121, R122, R123, R124, and capacitors C116 and C120. The output terminal IC1 of the current transformer is connected to the negative input terminal of the operational amplifier U106A via resistor R119, and the output terminal IC2 of the current transformer is connected to the positive input terminal of the operational amplifier U106A via resistor R122. One end of the series connection of resistors R119 and R120 is connected between the output terminal IC1 of the current transformer and resistor R119. The other end is connected between the output terminal IC2 of the current transformer and the resistor R122. The capacitor C116 and the resistor R123 are connected in parallel between the output terminal and the negative input terminal of the operational amplifier U106A, feeding back the output of the operational amplifier U106A to the negative input terminal. The reference voltage 2.5Vref output by the voltage reference circuit 4 is connected to the positive input terminal of the operational amplifier U106A through the capacitor C120. The output terminal of the operational amplifier U106A is connected to the control circuit through the resistor R124. One end of the resistor R124 serves as the output terminal ADC_IC of the integrator circuit 3, and the output terminal of the operational amplifier U106A is connected to the amplifier circuit 6. Preferably, the integrating circuit 3 further includes capacitors C108 and C112. Capacitor C108 is connected in parallel with the two ends of the series resistors R119 and R120. Capacitor C112 is connected in parallel between the negative input terminal and the positive input terminal of the operational amplifier U106A. One end of capacitor C124 is connected between resistor R124 and the output terminal ADC_IC of the integrating circuit 3, and the other end is grounded.

[0035] The amplifier circuit 6 in this embodiment includes operational amplifier U107A. The output terminal IC2 of the current transformer is connected to the positive input terminal of operational amplifier U107A through resistors R122, R125, and R127 connected in series. Obviously, the resistance value and number between the output terminal IC2 of the current transformer and the positive input terminal of operational amplifier U107A can be set as needed, or it can be without resistor R122. The negative input terminal of operational amplifier U107A is connected to integrator circuit 3, that is, the output terminal of operational amplifier U106A of integrator circuit 3 is connected to the negative input terminal of operational amplifier U107A through resistor R126. The reference voltage 2.5Vref output by voltage reference circuit 4 is connected to one end of resistor R125. The output terminal of operational amplifier U107A is connected to the control circuit through resistor R129, that is, the other output terminal ADC_IC in the figure, and the output terminal of operational amplifier U107A is connected to the negative input terminal of U107A through resistor R126. Preferably, the amplifier circuit 6 further includes a capacitor C128, one end of which is connected between the resistor R129 and the output terminal ADC_IC of the amplifier circuit 6, and the other end is grounded.

[0036] The transformer disconnection detection circuit 2 in this embodiment includes a detection resistor R210. One end of the detection resistor R210 is connected to the integrator circuit, i.e., connected to the positive input terminal of the operational amplifier U106A. The other end of the detection resistor R210 is connected to the microcontroller MCU of the control circuit. The microcontroller MCU controls the circuit by pulling R210 low, outputting a low level. Then, the microcontroller MCU detects the output of the integrator circuit 3. If the transformer is disconnected, the output of the integrator circuit 3 will deviate from the reference voltage by more than a preset value. Preferably, the sampling circuit self-test circuit also includes a switch state detection circuit 7, which is connected to the control circuit and is used to transmit the switch's open / closed state signal to the control circuit. Before performing the zero-point voltage calibration step, the microcontroller MCU also performs a switch-opening state detection step. The switch-opening state detection step includes: obtaining the switch's open / closed state through the switch state detection circuit 7; the zero-point voltage calibration step is only performed when the switch is in the open state. One embodiment of the switch state detection circuit 7 includes a microswitch corresponding to the operating mechanism or contact mechanism of the circuit breaker. When the operating mechanism or contact mechanism moves to the closed position during closing, it triggers the corresponding microswitch; or when the operating mechanism or contact mechanism moves to the open position during opening, it triggers the corresponding microswitch. The microswitch transmits the circuit breaker's opening / closing signal to the microcontroller (MCU). Another embodiment of the switch state detection circuit 7 detects the voltage of the main circuit of the switch. When the switch is closed, the main circuit is conducting and outputs a high level; when the switch is open, the main circuit is disconnected and outputs a low level. For example, a comparator operational amplifier is used, and the level of the non-inverting and inverting input terminals of the operational amplifier is compared to determine the voltage level. When the switch is closed, the operational amplifier outputs a high level; when the switch is open, it outputs a low level.

[0037] Preferably, the sampling circuit self-test circuit further includes a fast-saturation power supply detection circuit 1. This circuit is connected between the fast-saturation transformer and the control circuit to detect whether the circuit is currently powered by the fast-saturation transformer. The fast-saturation transformer provides power to the sampling circuit self-test circuit, including the microcontroller (MCU) of the control circuit, and can also power the electronic trip unit of the circuit breaker. The fast-saturation power supply detection circuit 1 detects the power supply circuit powered by the fast-saturation transformer, converts the current signal into a voltage signal, and connects it to the MCU. The MCU then calculates and determines whether the circuit is currently powered by the fast-saturation transformer. An embodiment of a fast-saturation power supply detection circuit 1 includes a power-taking resistor and a power-taking resistor voltage detection and monitoring circuit that monitors the voltage across the resistor. The power-taking resistor is connected in series in the power supply circuit of the fast-saturation transformer. The power-taking resistor voltage detection and monitoring circuit is connected across the power-taking resistor. After amplifying and filtering the voltage across the resistor, it is input to a microcontroller (MCU) to monitor and determine whether the current power supply is from the fast-saturation transformer. If the detected voltage across the power-taking resistor is less than or equal to a preset power-taking voltage value, it is considered that the current power supply is not from the fast-saturation transformer; otherwise, it is considered that the current power supply is from the fast-saturation transformer. In this embodiment, the MCU performs a fast-saturation transformer power supply detection step before executing the zero-point voltage calibration step. The fast-saturation transformer power supply detection step includes: determining whether the current power supply is from the fast-saturation transformer through the fast-saturation power supply detection circuit 1; only when the current power supply is not from the fast-saturation transformer is the zero-point voltage calibration step performed.

[0038] like Figure 4 In the embodiment of the fast saturation power supply detection circuit 1 shown, the two input terminals of the fast saturation transformer power supply are connected to the load. The power-taking resistors are resistors R202-1, R202-2, and R203, which are connected to the power supply circuit of the fast saturation transformer power supply. Of course, only one, two, or more resistors can be set as needed. The power-taking resistor voltage detection and monitoring circuit is connected across the two ends of the power-taking resistor. The output terminal SBH_AD2 is connected to the microcontroller MCU of the control circuit. The power-taking resistor voltage detection and monitoring circuit includes a comparator U113A. The negative input terminal of the comparator U113A is connected to one end of the power-taking resistor via resistor R204. The positive input terminal of the comparator U113A is grounded via resistor R206. The output terminal of the comparator U113A is connected to the negative input terminal via resistor R205. The output terminal of the comparator U113A is connected to the control circuit via resistor R207. The end of resistor R207 connected to the control circuit is connected to the other end of the power-taking resistor and grounded.

[0039] The present invention also provides an automatic zero-point current calibration method, based on the sampling circuit self-test circuit of the present invention, the automatic zero-point current calibration method comprising the following steps:

[0040] Zero-point voltage calibration steps: Obtain the current sampling value of the current transformer. When the current sampling value is zero, obtain the voltage value output by the integrating circuit and the amplifying circuit. Based on the voltage value, calibrate the reference voltage.

[0041] One specific embodiment, such as Figure 2 As shown, the automatic zero-point current calibration method of this embodiment further includes a circuit breaker state detection step, a reference voltage failure detection step, a transformer disconnection detection step, and a fast-saturation transformer power supply step before the zero-point voltage calibration step. The zero-point voltage calibration step is only performed after the circuit breaker state detection step detects that the switch is in the open state, the reference voltage failure detection step detects that the reference voltage is normal, the transformer disconnection detection step detects that the transformer is not disconnected, and the fast-saturation transformer power supply detection step detects that it is not a fast-saturation transformer. It should be noted that the circuit breaker state detection step, the reference voltage failure detection step, the transformer disconnection detection step, and the fast-saturation transformer power supply step in this embodiment can be performed in any order, and one or more of them can be selected for detection as needed.

[0042] like Figure 2 As shown, the tripping state detection step includes: the microcontroller MCU obtains the tripping state of the switch through the switch state detection circuit 7. If it is in the tripping state, it returns and exits. If it is in the tripping state, it proceeds to the next step of reference voltage failure detection.

[0043] The reference voltage failure detection step includes: the microcontroller MCU determines whether the reference voltage is failed through the reference detection circuit 5; the microcontroller MCU obtains the reference voltage through the voltage reference circuit 4 and the reference detection circuit 5; the reference detection voltage is compared with the reference voltage; if the reference detection voltage and the reference voltage are within the preset error range, the reference voltage is considered normal; otherwise, the reference voltage is considered failed. If the reference voltage is failed, the process returns and exits; otherwise, the next step of the current transformer disconnection detection step is performed.

[0044] The current transformer disconnection detection step includes: the microcontroller MCU determines whether the current transformer disconnection detection circuit 2 is turned on. If it is not turned on, the current transformer disconnection detection circuit 2 is turned on or the next step of fast saturation current transformer power supply detection is directly performed. If the current transformer disconnection detection circuit 2 is turned on, it determines whether the current transformer is disconnected. The microcontroller MCU obtains the voltage value output by the integrating circuit 3. If the voltage value output by the integrating circuit 3 deviates from the reference voltage by more than a preset value, the current transformer is considered to be disconnected. If the current transformer is disconnected, the process returns and exits. Otherwise, the current transformer is considered not disconnected, that is, the wiring is normal, and the next step of saturation current transformer power supply detection is performed.

[0045] The fast saturation transformer power supply detection steps include: the microcontroller MCU determines whether the fast saturation transformer is currently supplying power through the fast saturation power supply detection circuit 1. If the fast saturation transformer is supplying power, it returns and exits; otherwise, if the fast saturation transformer is not supplying power, it proceeds to the next zero-point voltage calibration step.

[0046] Zero-point voltage calibration steps include:

[0047] Obtain the current sampling value of the current transformer.

[0048] First, it is determined whether the current sampling value exceeds the preset upper limit. The microcontroller (MCU) calculates and obtains the current sampling value of the current transformer. If the current sampling value exceeds the preset upper limit, it returns and exits. For example, if the current sampling value exceeds 6%Inm, it returns and exits. If it is less than or equal to 6%Inm (rated current), it performs automatic zero-point voltage calibration.

[0049] When the current sampling value is zero, the voltage value output by the integrating circuit and the amplifying circuit is obtained, and the reference voltage is calibrated based on the voltage value. Preferably, the number of calibrations for each automatic zero-point voltage calibration is counted. Before performing automatic zero-point voltage calibration, it is first determined whether the number of calibrations is less than a preset threshold. If it is greater than the threshold, the feedback is exited; if it is less than or equal to the threshold, the automatic zero-point voltage calibration is performed again. For example, the threshold can be set to 3. When the number of calibrations is less than or equal to 3, the automatic zero-point voltage calibration is performed; when it exceeds 3, the process exits and returns.

[0050] The sampling current self-test circuit in this embodiment is used to self-test whether the sampling circuit is working properly. The microcontroller (MCU) combines the self-test results to automatically perform zero-point voltage calibration.

[0051] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A sampling current self-test circuit, comprising a current transformer, a control circuit, an integrating circuit (3), and a voltage reference circuit (4), wherein the output terminal of the current transformer is connected to the integrating circuit (3), the output terminal of the voltage reference circuit (4) is connected to the integrating circuit (3), the output terminal of the integrating circuit (3) is connected to the control circuit, and the control circuit comprises a microcontroller (MCU), characterized in that: It also includes an amplifier circuit (6), a voltage reference circuit (4) and an integrator circuit (3) connected to the amplifier circuit (6) respectively, and the amplifier circuit (6) connected to the control circuit; the microcontroller MCU performs a zero-point voltage calibration step, the zero-point voltage calibration step includes acquiring the current sampling value collected by the current transformer, the microcontroller MCU calculates the current sampling value based on the integrator circuit (3) and / or the amplifier circuit (6), when the current sampling value is zero, acquires the voltage value output by the integrator circuit (3) and / or the amplifier circuit (6), and calibrates the reference voltage based on the voltage value output by the integrator circuit (3) and / or the amplifier circuit (6).

2. The sampling current self-test circuit according to claim 1, characterized in that: It also includes a switch status detection circuit (7), which is connected to the control circuit and is used to transmit the switch opening and closing status signal to the control circuit.

3. The sampling current self-test circuit according to claim 1, characterized in that: It also includes a reference detection circuit (5) for detecting whether the reference voltage output by the voltage reference circuit (4) is invalid. The voltage reference circuit (4) and the reference detection circuit (5) are respectively connected to the microcontroller MCU, or the reference detection circuit (5) is connected between the reference detection circuit (5) and the microcontroller MCU.

4. The sampling current self-test circuit according to claim 1, characterized in that: It also includes a current transformer open circuit detection circuit (2), which is connected between the integrator circuit (3) and the control circuit.

5. The sampling current self-test circuit according to claim 1, characterized in that: It also includes a fast saturation power supply detection circuit (1), which is connected between the fast saturation transformer and the control circuit to detect whether the current power supply is from the fast saturation transformer.

6. The sampling current self-test circuit according to claim 2, characterized in that: Before performing the zero-point voltage calibration step, the microcontroller MCU also performs a circuit breaker status detection step. The circuit breaker status detection step includes: obtaining the open / closed status of the switch through the switch status detection circuit (7), and performing the zero-point voltage calibration step only when the switch is in the open state.

7. The sampling current self-test circuit according to claim 3, characterized in that: Before performing the zero-point voltage calibration step, the microcontroller (MCU) also performs a reference voltage failure detection step. The zero-point voltage calibration step is only performed when the reference voltage is normal. The reference voltage failure detection step includes obtaining whether the reference voltage is failed through the reference detection circuit (5); or, the reference voltage failure detection step includes obtaining the reference voltage through the voltage reference circuit (4), obtaining the reference detection voltage through the reference detection circuit (5), comparing the reference detection voltage with the reference voltage, and if the reference detection voltage and the reference voltage are within the preset error range, then the reference voltage is considered to be normal.

8. The sampling current self-test circuit according to claim 4, characterized in that: Before the microcontroller MCU performs the zero-point voltage calibration step, it also performs the current transformer disconnection detection step. The current transformer disconnection detection step includes: controlling the current transformer disconnection detection circuit (2) to turn on. After the current transformer disconnection detection circuit (2) is turned on, it obtains the voltage value output by the integration circuit (3). If the voltage value output by the integration circuit (3) deviates from the reference voltage by more than a preset amount, it is considered that the current transformer is disconnected. Otherwise, it is considered that the current transformer is not disconnected. The zero-point voltage calibration step is performed only when the current transformer is not disconnected.

9. The sampling current self-test circuit according to claim 5, characterized in that: Before the microcontroller MCU performs the zero-point voltage calibration step, it also performs the fast saturation transformer power supply detection step. The fast saturation transformer power supply detection step includes: determining whether the current power supply is supplied by the fast saturation transformer through the fast saturation power supply detection circuit (1), and performing the zero-point voltage calibration step only when the power supply is not supplied by the fast saturation transformer.

10. The sampling current self-test circuit according to claim 1, characterized in that: In the zero-point voltage calibration step, after obtaining the current sampling value collected by the current transformer, it is first determined whether the current sampling value exceeds the preset upper limit value. If the current sampling value exceeds the preset upper limit value, the process is exited.

11. A zero-point current reference calibration method based on the sampling current self-test circuit according to any one of claims 1-10, characterized in that: It includes a zero-point voltage calibration step, as well as a tripping status detection step, a reference voltage failure detection step, a transformer disconnection detection step, and a fast-saturation transformer power supply detection step. The zero-point voltage calibration step is only performed after the switch is detected to be in the open state through the open state detection step, the reference voltage is detected to be normal through the reference voltage failure detection step, the current transformer is detected to be not disconnected through the current transformer disconnection detection step, and the current transformer is detected to be not a fast-saturation current transformer through the fast-saturation current transformer power supply detection step. The zero-point voltage calibration step includes acquiring the current sampling value collected by the current transformer, acquiring the voltage value output by the integrating circuit and the amplifying circuit when the current sampling value is zero, and calibrating the reference voltage based on the voltage value output by the integrating circuit and the amplifying circuit.

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