System for simultaneously measuring residual voltage and discharge capacitance of electric appliance plug

Abstract

The invention discloses a system for simultaneously measuring residual voltage and discharge capacitance of an electric appliance plug. The system comprises a phase detection unit, a measurement control unit, an electronic disconnection unit and a multi-input impedance measurement unit. According to the system, a conventional residual voltage test is carried out once, plug discharge voltage curves at different moments can be obtained by using the high-impedance measurement unit and the low-impedance measurement unit, discharge time constants during high-impedance measurement and low-impedance measurement are respectively calculated through curve fitting, the optimal estimated values of discharge capacitance and discharge resistance are obtained, and the test accuracy is improved. And reversely calculating whether the action of the electronic circuit participates in the discharge process after the peak value is switched off, thereby achieving a primary electric appliance plug discharge test and obtaining three measurement parameters. Therefore, the system disclosed by the invention can be used for conformity judgment on whether the charged capacitor on the plug pin of the electrical product can cause the electric shock danger, and has the characteristics of accurate test, simple operation and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of safety testing of electrical products, and in particular relates to a system for simultaneously measuring residual voltage and discharge capacity of an electrical plug. Background Art

[0002] The international standard for household appliances, IEC 60335-1:2020, states: "Appliances intended to be connected to the mains by means of a plug shall be constructed so that, in normal use, when the pins of the plug are touched, there is no risk of electric shock from charged capacitors; capacitors with a capacitance not exceeding 0.1 μF are not considered to cause a risk of electric shock". The test method for compliance is that the voltage between the plug pins does not exceed 34 V 1 second after the appliance is disconnected from the mains at the voltage peak. If compliance depends on the operation of the electronic circuit, additional testing is required. When making a residual voltage compliance determination, three parameters need to be measured: ① residual voltage value; ② capacitance; ③ whether it depends on the operation of the electronic circuit.

[0003] Traditional plug discharge test instruments, such as the Chinese patent application with publication number CN113064015A, provide a residual voltage and capacitor discharge automated test tool, including a computer, a control panel, an AC power input, a variable frequency power supply, a thyristor control circuit and a product to be tested, which combines plug discharge, capacitor discharge and electrical performance measurements in one machine, so that one machine can perform multiple tests, solves the problem that different tests need to switch to different test platforms, and improves test efficiency. Another example is the Chinese patent application with publication number CN109507547A, which provides a home appliance plug discharge test control device and a control method thereof, which monitors the zero-crossing trigger signal in real time and controls the relay drive circuit to cut off the power at the power peak through the set delay time, thereby cutting off the power output socket at the power peak, so that the oscilloscope can accurately measure the discharge curve of the home appliance plug at the power peak, ensuring the accuracy of the measurement. The above-mentioned prior art solutions can only measure the voltage value between the plug pins, and the capacitance and whether it depends on the action of the electronic circuit cannot be measured and determined. Since the discharge capacitance value is connected in parallel to the functional circuit of the device, for electronic and electrical products with more complex functions, general capacitance test instruments cannot accurately measure the capacitance of the complex circuit in parallel. Whether it depends on the electronic circuit can only be determined by monitoring the entire discharge process. Therefore, the compliance determination of such a standard becomes complicated due to too many measurement parameters, and a conclusion cannot be drawn through a single measurement.

[0004] Therefore, in combination with the need for standard determination, a method for simultaneously measuring the residual voltage and discharge capacitance of an electrical appliance plug is urgently needed. Summary of the invention

[0005] In view of the above, the present invention provides a system for simultaneously measuring the residual voltage and discharge capacity of an electrical appliance plug, which can simultaneously obtain the residual voltage value and discharge capacity of the electrical appliance plug under test by measuring a discharge process.

[0006] A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug comprises a phase detection unit, a measurement control unit, an electronic disconnection unit and a multi-input impedance measurement unit, wherein:

[0007] The phase detection unit is used to detect the phase of the power supply; the electronic disconnect unit is arranged on the power supply line between the power supply and the electrical appliance to be tested; the measurement control unit determines the disconnection time of the electronic disconnect unit through calculation according to the phase and provides a shutdown signal to it; after the electronic disconnect unit performs the disconnection operation, the measurement control unit controls the multi-input impedance measurement unit to connect to the plug pin of the electrical appliance to be tested, starts to monitor the whole process of the plug capacitance discharge, and timely switches the input impedance of the multi-input impedance measurement unit according to the test needs, and measures the residual voltage value, discharge capacitance and whether there is an electronic circuit action involved in the discharge process of the plug of the electrical appliance to be tested at one time.

[0008] Furthermore, the multi-input impedance measurement unit includes a high input impedance measurement unit and a low input impedance measurement unit, both of which are connected between the plug pins of the electrical appliance to be tested after the electronic disconnection unit is disconnected and 1s after disconnection, respectively. The measurement resistance of the high input impedance measurement unit is greater than 100MΩ (calibrable), and the measurement resistance of the low input impedance measurement unit is between 1 and 10MΩ (calibrable).

[0009] Furthermore, the measurement control unit is also used to measure the power quality of the power supply, including the voltage effective value, THD (total harmonic distortion) and peak factor, and to determine whether the current power quality meets the residual voltage test requirements.

[0010] Furthermore, after the multi-input impedance measurement unit is connected to the plug pins of the electrical appliance to be tested, the measurement control unit uses a high-speed sampling circuit to perform high-speed sampling and recording of the voltage between the pins, obtains a curve of voltage change over time, and calculates the residual voltage value of the plug of the electrical appliance to be tested after denoising and filtering.

[0011] Furthermore, the measurement control unit timely switches the input impedance of the multi-input impedance measurement unit according to the test needs, measures the voltage variation curve obtained by different impedances participating in the capacitor discharge, and fits and compares it with the theoretical RC discharge curve, and calculates the discharge time constant during high impedance and low impedance measurement in combination with the calibrated impedance value, thereby calculating the discharge capacitance and discharge resistance value of the electrical plug to be tested.

[0012] Furthermore, when the measurement control unit fits the measured voltage-time curve with the theoretical RC discharge curve, if convergence or expected results cannot be obtained, it is determined that the electronic circuit is involved in the discharge process after the plug of the tested electrical appliance is disconnected from the voltage peak.

[0013] Furthermore, the measurement control unit calculates the residual voltage value of the electrical appliance plug to be tested by the following formula;

[0014]

[0015] Among them: U 1 is the residual voltage value of the electrical plug to be tested, U 0 is the initial value of the residual voltage in the equivalent circuit of the tested electrical plug at the peak disconnection moment, C X and R X are the capacitance and resistance values ​​in the equivalent circuit of the electrical plug to be tested (consisting of a capacitor and a resistor in parallel), R dis1 is the high impedance equivalent discharge resistance of the electrical plug to be tested, R G is the measurement resistance of the high input impedance measurement unit, and e is a natural constant.

[0016] Furthermore, the expression of the theoretical RC discharge curve is as follows:

[0017]

[0018] τ 2 =C X ·R dis2

[0019]

[0020] Where: U(t) is the voltage value at time t in the theoretical RC discharge curve, U 1 is the residual voltage value of the electrical plug to be tested, R dis2 is the low impedance equivalent discharge resistance of the electrical plug to be tested, R L is the measurement resistance of the low input impedance measurement unit, C X and R X are the capacitance and resistance values ​​in the equivalent circuit of the electrical plug to be tested, τ 2 is the discharge time constant during low impedance measurement, and e is a natural constant.

[0021] Furthermore, the measurement control unit calculates the discharge capacity and discharge resistance of the electrical plug to be tested by combining the following equations:

[0022]

[0023]

[0024] C X ·R dis2 =T 2

[0025] Where: R dis1 is the high impedance equivalent discharge resistance of the electrical plug to be tested, C X and R X are the capacitance and resistance values ​​in the equivalent circuit of the electrical plug to be tested, R dis2 is the low impedance equivalent discharge resistance of the electrical plug to be tested, U 1 is the residual voltage value of the electrical plug to be tested, U 0 is the initial value of the residual voltage in the equivalent circuit of the tested electrical plug at the peak disconnection moment, T 2 The measured voltage variation curve with time is fitted with the theoretical RC discharge curve and converges with τ 2 The estimated value of τ 2 is the discharge time constant for low impedance measurement; by solving the above equations, we can get X and R X The positive real number solution of is the discharge capacitance and discharge resistance of the electrical plug to be tested.

[0026] The measuring system of the present invention can obtain the plug discharge voltage curve at different times by performing a conventional residual voltage test, using two measuring units of high impedance and low impedance, respectively calculating the discharge time constants during high impedance and low impedance measurements by fitting the curves, obtaining the best estimated values ​​of the discharge capacitance and the discharge resistance, and then reversely calculating whether the action of the electronic circuit participates in the discharge process after the peak value is disconnected, thereby achieving a discharge test of the electrical plug and obtaining three measurement parameters. Therefore, the measuring system of the present invention can be used for compliance determination of whether the charged capacitor on the plug pin of an electrical product will cause an electric shock hazard, and has the characteristics of accurate testing and simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a structural block diagram of a system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug.

[0028] Figure 2 This is a schematic diagram of the principle of a multi-input impedance measurement unit.

[0029] Figure 3 This is the schematic diagram of the equivalent circuit for measuring the residual voltage after the plug is powered off.

[0030] Figure 4 This is the equivalent circuit diagram when the high input impedance measurement unit is connected.

[0031] Figure 5This is the equivalent circuit diagram when the low input impedance measurement unit is connected. DETAILED DESCRIPTION

[0032] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0033] The system for simultaneously measuring the residual voltage and discharge capacity of an electrical appliance plug of the present invention can simultaneously measure the residual voltage value and discharge capacity of the plug pin through the discharge process of the electrical appliance plug; Figure 1 As shown, the system includes a power phase detection unit, an isolating switch, an electronic disconnect unit, a multi-input impedance measurement unit and a measurement control unit, wherein the multi-input impedance measurement unit includes a high input impedance measurement unit and a low input impedance measurement unit, which are respectively connected between the plug pins during residual voltage measurement (after disconnection) and after measurement (such as 1 second after disconnection).

[0034] During a normal household electrical product plug discharge process, the power phase detection unit detects the phase of the power supply and disconnects the peak position of the power supply voltage phase of the appliance through the precise delay of the measurement control unit and the electronic disconnection unit. Figure 2 As shown, after the disconnection, the multi-input impedance measurement unit is immediately connected to the two poles of the plug pin, and the high-impedance measurement unit is immediately connected after the power is disconnected. After a delay of 1 second, it switches to the low-impedance measurement unit, and obtains the voltage change curve between the plug pins after the disconnection through the high-speed sampling circuit. After the voltage change curve is obtained and denoised and filtered, the measurement control unit gives the best estimate of the residual voltage of this measurement. At the same time, the voltage change curve obtained by the capacitor discharge is obtained by measuring different impedances, and is fitted and compared with the theoretical RC discharge curve. Combined with the calibrated impedance value, the best estimate of the time constant discharge of high-impedance discharge and low-impedance discharge is given, and the discharge capacitance and inherent discharge resistance value and uncertainty are calculated.

[0035] According to the electrical theory, when the power is off for an electrical product, from the perspective of residual voltage measurement, the electrical product is equivalent to C X and R X A parallel circuit such as Figure 3 As shown, if the discharge of the residual voltage does not depend on the electronic circuit, C in the equivalent circuit X and R X is a fixed value, which belongs to a linear circuit; when the residual voltage discharge depends on the action of the electronic circuit, C X The equivalent capacitance value for storing the residual electricity is a constant, and R X It becomes a variable value due to the operation of the electronic circuit.

[0036] When measuring the residual voltage, the initial voltage value U of the residual voltage in the equivalent circuit is obtained by measuring the peak disconnection moment of the control unit. 0 , and connected to the high input impedance measurement unit at the same time, its equivalent circuit is as follows Figure 4 As shown, R G The measuring resistance of the high input impedance measuring unit. When the high input impedance measuring unit is connected for 1 second, the residual voltage value U is measured. 1 .

[0037] We first assume that R X is a fixed value, the entire discharge circuit is a linear circuit, during this discharge period, the high impedance equivalent discharge resistance of the circuit is R X and R G The parallel connection is:

[0038]

[0039] According to the principles of electrical theory, the equivalent discharge time constant is:

[0040] τ 1 =C X ·R dis1 (2)

[0041] According to the capacitor discharge formula, we have:

[0042]

[0043] When t = 1s, we have:

[0044]

[0045] Can be obtained:

[0046]

[0047] When measuring U 1 After that, the high input impedance measurement unit immediately exits the circuit and the low input impedance measurement unit enters. The equivalent measurement circuit is as follows: Figure 5 As shown, R L The measured resistance of the low input impedance measurement unit; at this time, the low impedance equivalent discharge resistance of the circuit is:

[0048]

[0049] According to the principles of electrical theory, the equivalent discharge time constant is:

[0050] τ 2 =C X ·R dis2 (7)

[0051] According to the capacitor discharge formula, we have:

[0052]

[0053] Can be obtained:

[0054]

[0055] The voltage between the pins is sampled and recorded at high speed through a high-speed sampling circuit. 1 Start recording continuously for 1 second and draw a discharge curve of voltage changing with time. If the actual measured curve has a poor fit with the theoretical curve shown in formula (8) and cannot converge, it can be determined that the discharge of the residual voltage depends on the action of the electronic circuit. The measurement can be ended and the measurement conclusion can be obtained: the residual voltage value is U 1 , the residual voltage discharge depends on the action of the electronic circuit.

[0056] If the actual measured curve fits and converges with the theoretical curve shown in equation (8), the equivalent discharge time constant τ of low impedance discharge can be given: 2 The best estimate of T 2 .

[0057] According to the above conditions, R G and R L is the instrument calibration value, which is a known parameter, U 0 and U 1 is the measured value, T 2 is the estimated value of the curve fitting, and solving the equation can obtain C X , R X , R dis1 , R dis2 Four parameters. If R X and C X The result is a negative number or other obviously unreasonable value. It can be concluded that during the measurement period when the high impedance measurement unit is connected, the discharge of the residual voltage depends on the electronic circuit. The measurement conclusion can be drawn: the residual voltage value is U 1 , the residual voltage discharge depends on the action of the electronic circuit.

[0058] If R X , C X There are solutions R and C on positive real numbers, so we can conclude that the residual voltage value is U 1 , the residual voltage discharge does not depend on the action of the electronic circuit, the equivalent discharge capacitance is C, and the equivalent discharge resistance is R.

[0059] The sampling circuit samples the voltage between the pins continuously at high speed for 1 second. The voltage U 2 , substituting into formula (9), we can get:

[0060]

[0061] Set a value range δ for Tx, then τ 2 The best estimate of T X -δ to T X +δ value range, The theoretical curve of formula (8) is substituted into the measured curve using the latest square method to fit the calculated result. If the result can converge, then the closest result is τ 2 The best estimate of T 2 If it cannot converge to a certain point, it is considered that the discharge of the residual voltage causes the electronic circuit to operate. The value range of δ should be comprehensively considered based on the test accuracy of the measurement system.

[0062] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug, characterized in that: The invention comprises a phase detection unit, a measurement control unit, an electronic disconnection unit and a multi-input impedance measurement unit, wherein: The phase detection unit is used to detect the phase of the power supply; the electronic disconnect unit is arranged on the power supply line between the power supply and the electrical appliance to be tested; the measurement control unit determines the disconnection time of the electronic disconnect unit through calculation according to the phase and provides a shutdown signal to it; after the electronic disconnect unit performs the disconnection operation, the measurement control unit controls the multi-input impedance measurement unit to connect to the plug pin of the electrical appliance to be tested, starts to monitor the whole process of the plug capacitance discharge, and timely switches the input impedance of the multi-input impedance measurement unit according to the test needs, and measures the residual voltage value, discharge capacitance and whether there is an electronic circuit action involved in the discharge process of the plug of the electrical appliance to be tested at one time.

2. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug according to claim 1, characterized in that: The multi-input impedance measurement unit includes a high input impedance measurement unit and a low input impedance measurement unit, which are respectively connected between the plug pins of the electrical appliance to be tested after the electronic disconnection unit is disconnected and 1 second after the disconnection. The measurement resistance of the high input impedance measurement unit is greater than 100MΩ, and the measurement resistance of the low input impedance measurement unit is between 1 and 10MΩ.

3. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug according to claim 1, characterized in that: The measurement control unit is also used to measure the power quality of the power supply, including the voltage effective value, THD and peak factor, and to determine whether the current power quality meets the residual voltage test requirements.

4. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug according to claim 2, characterized in that: After the multi-input impedance measurement unit is connected to the plug pins of the electrical appliance to be tested, the measurement control unit uses a high-speed sampling circuit to perform high-speed sampling and recording of the voltage between the pins, obtains a curve of voltage change over time, and calculates the residual voltage value of the plug of the electrical appliance to be tested after denoising and filtering.

5. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug according to claim 2, characterized in that: The measurement control unit timely switches the input impedance of the multi-input impedance measurement unit according to the test needs, measures the voltage variation curve obtained by different impedances participating in the capacitor discharge, and compares it with the theoretical resistor-capacitor discharge curve, and calculates the discharge time constant during high impedance and low impedance measurement in combination with the calibrated impedance value, thereby calculating the discharge capacitance and discharge resistance value of the electrical plug to be tested.

6. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug according to claim 5, characterized in that: When the measurement control unit fits the measured voltage variation curve over time with the theoretical RC discharge curve, if convergence or expected results cannot be obtained, it is determined that the electronic circuit is involved in the discharge process after the plug of the tested electrical appliance is disconnected from the voltage peak.

7. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug according to claim 4, characterized in that: The measurement control unit calculates the residual voltage value of the plug of the electrical appliance to be tested by the following formula; Among them: U1 is the residual voltage value of the plug of the electrical appliance to be tested, U0 is the initial value of the residual voltage in the equivalent circuit of the plug of the electrical appliance to be tested at the peak disconnection moment, C X and R X are the capacitance and resistance values ​​in the equivalent circuit of the electrical plug to be tested, R dis1 is the high impedance equivalent discharge resistance of the electrical plug to be tested, R G is the measurement resistance of the high input impedance measurement unit, and e is a natural constant.

8. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug according to claim 5 or 6, characterized in that: The expression of the theoretical RC discharge curve is as follows: τ2=C X ·R dis2 Where: U(t) is the voltage value at time t in the theoretical RC discharge curve, U1 is the residual voltage value of the plug of the appliance to be tested, R dis2 is the low impedance equivalent discharge resistance of the electrical plug to be tested, R L is the measurement resistance of the low input impedance measurement unit, C X and R X are the capacitance and resistance values ​​in the equivalent circuit of the electrical plug to be tested, τ2 is the discharge time constant during low impedance measurement, and e is a natural constant.

9. A system for simultaneously measuring residual voltage and discharge capacity of an electrical appliance plug according to claim 5, characterized in that: The measurement control unit calculates the discharge capacity and discharge resistance of the electrical plug to be tested by combining the following equations: C X ·R dis2 =T2 Where: R dis1 is the high impedance equivalent discharge resistance of the electrical plug to be tested, C X and R X are the capacitance and resistance values ​​in the equivalent circuit of the electrical plug to be tested, R dis2 is the low impedance equivalent discharge resistance of the electrical plug to be tested, U1 is the residual voltage value of the electrical plug to be tested, U0 is the initial value of the residual voltage in the equivalent circuit of the electrical plug to be tested at the peak disconnection moment, T2 is the estimated value of τ2 when the measured voltage variation curve with time is fitted with the theoretical RC discharge curve and converges, τ2 is the discharge time constant in low impedance measurement; by solving the above equations, we can get the value of C X and R X The positive real number solution of is the discharge capacitance and discharge resistance of the electrical plug to be tested.

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