A circuit module and a test platform for a power line carrier communication test platform

Abstract

The present invention relates to a circuit module for a power line carrier communication test platform and a corresponding test platform. The circuit module includes a power filter module (1) with one end connected to a power frequency power supply and the other end connected to a test machine (3) or a device under test (4), and a signal coupling module (2) connected between the power filter module (1) and the test machine (3) or the device under test (4). The signal coupling module (2) includes a high-pass filter (21) that can provide a low impedance within the frequency band of carrier communication, and a coupling transformer (22) connected to the high-pass filter (21) and capable of increasing the common-mode impedance between the first power line (31) between the test machine (3) and the power filter module (1) and the ground, and between the second power line (41) between the device under test (4) and the power filter module (1) and the ground through its own isolation characteristics to reduce the common-mode voltage on the ground wire. This application improves the test accuracy.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a circuit module for a power line carrier communication test platform and a corresponding test platform. Background Art

[0002] Power line carrier communication is a communication method using a power transmission line as the transmission medium of a carrier signal. Because there is no need to lay additional communication lines, it is economical and reliable, and has become the preferred communication means for all power departments in the world. In order to simulate power line carrier communication and simultaneously detect the receiving sensitivity of a device under test, establishing a power line carrier communication test platform is a commonly used means in laboratories.

[0003] The main structure of an existing power line carrier communication test platform is as Figure 1 shown. A test machine and a device under test are respectively connected to an artificial power network. The artificial power network separates a high-frequency carrier signal from the power frequency voltage and outputs it through a weak current port. Two artificial power networks are connected through an adjustable attenuator for adjusting the signal strength. At the same time, a shielded wire is used for interconnection between the artificial power network and the adjustable attenuator, and a power filter is placed at the front end of the power supply port of the artificial power network to weaken the influence of external power noise on the test result. Among them, the artificial power network is a standardized product, and its basic structure is as Figure 2 shown, that is, impedance isolation is achieved through L1 / L2 inductors and a pre-stage power supply, the power frequency signal is blocked through C1 / C2 capacitors, the high-frequency signal is separated through R1 / R2 resistors, and the R1 / R2 resistors are connected to the ground.

[0004] The receiving sensitivity of power line carrier communication products is very high (25 dBuV - 45 dBuV), which poses very high requirements for the test platform. However, since all devices in the existing test platform are not ideal, the two paths of L1 - C1 - R1 and L2 - C2 - R2 are not in an ideal balanced state. During the operation of an alternating current signal, that is, a high-frequency carrier signal, a common-mode current will be generated on the Figure 2 ground wire shown. At the same time, when the device under test and the test machine are working, a common-mode current consistent with the high-frequency carrier signal will also be generated and flow through the Figure 2 ground wire shown. And the common-mode noise caused by the common-mode current will be converted into a differential-mode signal and received by the test machine or the device under test, so that the true receiving sensitivity of the device cannot be measured. At the same time, the common-mode current will cause the carrier signal not to be transmitted along the established path, causing the carrier signal to skip the adjustable attenuator, resulting in the receiving sensitivity measured for the device being much better than the actual receiving sensitivity.

[0005] To solve this problem, the artificial power network needs to be connected to the ground with extremely low impedance to avoid the common-mode current flowing through a large grounding impedance and generating a common-mode signal consistent with the carrier signal. This requires that the office environment provide a grounding stake with low impedance, but the general office environment cannot meet this requirement.

[0006] Moreover, due to the presence of a large number of electrical devices such as computers and printers in the office environment, the power noise is relatively large, resulting in very large power noise in the power grid. The existing power filters can only meet the electromagnetic compatibility requirements of electrical equipment and cannot suppress the power grid noise to a level lower than the carrier communication sensitivity of the product. Summary of the Invention

[0007] In view of the above problems, the purpose of the present invention is to provide a circuit module for a power line carrier communication test platform that can reduce the common-mode voltage by reducing the common-mode current on the grounding wire and ensure the test accuracy.

[0008] The purpose of the present invention is also to provide a circuit module for a power line carrier communication test platform that can ensure that the power grid noise is suppressed to an extremely low level.

[0009] The purpose of the present invention is also to provide a power line carrier communication test platform using the aforementioned circuit module.

[0010] In order to achieve the above purpose, the technical solution of the present invention is: a circuit module for a power line carrier communication test platform, the module includes a power filter module with one end connected to the industrial frequency power supply and the other end connected to the test machine or the device under test, and a signal coupling module connected between the power filter module and the test machine or the device under test. The characteristics are as follows:

[0011] The signal coupling module includes a high-pass filter that can provide low impedance within the frequency band of carrier communication, and a coupling transformer connected to the high-pass filter and capable of increasing the common-mode impedance between the first power line between the test machine and the power filter module and the ground, and the second power line between the device under test and the power filter module and the ground through its own isolation characteristics to reduce the common-mode voltage on the grounding wire.

[0012] Further, the high-pass filter is composed of a first capacitor.

[0013] Further, the capacitance value of the first capacitor is 1uF.

[0014] Further, the parasitic capacitance value of the coupling transformer is between 10pF - 30pF.

[0015] Further, the power filter module is a multi-stage filter.

[0016] Further, the power supply filtering module includes a first-stage filter composed of a first inductor, a second capacitor, a third capacitor, and a second inductor, and a second-stage filter formed by a third inductor, a fourth capacitor, a fifth capacitor, and a fourth inductor;

[0017] The third inductor is connected between the second capacitor and the fourth capacitor, and the fourth inductor is connected between the third capacitor and the fifth capacitor;

[0018] The power supply filtering module further includes a fifth inductor with one end connected to the fourth capacitor and the other end serving as the live wire output terminal and having an inductance equal to that of the first inductor, and a sixth inductor with one end connected to the fifth capacitor and the other end serving as the neutral wire output terminal and having an inductance equal to that of the second inductor.

[0019] Further, the inductances of the first inductor to the sixth inductor are > 0.5 mH, and the frequencies of the first-stage filter and the second-stage filter are ≤ 1 kHz.

[0020] Further, the secondary side of the coupling transformer is connected to a fixed attenuation module that can perform a first-stage attenuation on high-frequency signals, and the output terminal of the fixed attenuation module is connected to a splitter / combiner module.

[0021] A power line carrier communication test platform, characterized in that: the power line carrier communication test platform adopts the circuit module as described above.

[0022] Further, the test machine in the power line carrier communication test platform and the corresponding circuit module are arranged in a first shielding box, while the device under test and the corresponding circuit module are arranged in a second shielding box.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] The carrier signal is transmitted through the coupling transformer, and the isolation characteristic of the coupling transformer is used to increase the common-mode impedance formed between the power line between the test machine / the device under test and the power supply filtering module and the ground, thereby reducing the common-mode voltage on the grounding wire, that is, the common-mode voltage output to the backend circuit, through the voltage division method, ensuring the accuracy of the sensitivity test; the setting of multi-stage power supply filtering and the selection of larger inductance and capacitance values improve the attenuation effect and better reduce the influence of external noise on the test effect; the setting of the fixed attenuator ensures that the output amplitude of the signal is within the acceptance range of the test equipment, and the splitter / combiner module enhances the function of the test platform. The setting of this scheme reduces the requirements for the use environment, enables the entire test to be completed in an ordinary office environment, saves costs, and realizes the miniaturization of the test platform. Description of the Drawings

[0025] Figure 1 It is a structural block diagram of an existing power line carrier communication test platform.

[0026] Figure 2 It is the schematic diagram of the artificial power network in the existing power line carrier communication test platform.

[0027] Figure 3 It is the schematic diagram of the circuit module for the power line carrier communication test platform of this application.

[0028] Figure 4 It is the structural block diagram of the power line carrier communication test platform of this application. Specific embodiments

[0029] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0030] As Figure 3 described, the circuit module for the power line carrier communication test platform of this application includes a power filter module 1 with one end connected to the power frequency power supply and the other end connected to the test machine or the device under test, and a signal coupling module 2 connected between the power filter module 1 and the test machine or the device under test. The power frequency power supply is input through the L-IN and N-IN ports, and the test machine or the device under test is connected through the L-OUT and N-OUT ports.

[0031] As described above, due to the non-ideal state of the devices and the working environment of the device under test and the test machine, common-mode current will be generated during the operation of the test platform, which will in turn affect the test accuracy of the receiving sensitivity of the device under test. The common-mode current is mainly output to the backend circuit through the ground wire. Obviously, when the ground impedance corresponding to the ground wire is smaller, the generated common-mode signal is smaller, and the influence on the test result is weaker. Therefore, reducing the ground impedance as much as possible can solve the common-mode signal problem to a certain extent, but this requires extremely high requirements for the test site, which is unlikely to be achieved in the actual test environment.

[0032] This application effectively reduces the influence of the common-mode signal without changing the ground impedance by improving the artificial power network. Specifically, this application replaces the artificial power network with the signal coupling module 2. The signal coupling module 2 includes a high-pass filter 21 that can provide a low impedance within the frequency band of carrier communication, and a coupling transformer that is connected to the high-pass filter 21 and can increase the common-mode impedance between the first power line 31 between the test machine 3 and the power filter module 1 and the ground, and between the second power line 41 between the device under test 4 and the power filter module 1 and the ground through its isolation characteristics to reduce the common-mode voltage on the ground wire.

[0033] That is, the parasitic capacitance of the coupling transformer can increase the common-mode impedance between the first power line 31 and the ground, and between the second power line 41 and the ground. This common-mode impedance and the grounding impedance on the ground wire share the voltage. Since this common-mode impedance is very large, the larger the common-mode impedance, the smaller the common-mode voltage applied to the ground wire, and thus the smaller the common-mode signal output to the subsequent circuit, and the test accuracy is greatly improved.

[0034] This improvement can effectively weaken the influence of the common-mode signal without changing the grounding impedance. In other words, the improvement of this application can reduce the requirements for the use environment, enabling the experiment to be completed even in ordinary office places, and obtaining accurate test results at the same time, greatly improving the applicability of the device.

[0035] In this embodiment, the high-pass filter 21 is composed of a first capacitor C1 with a capacitance value of 1 uF. Of course, this capacitance value can also be other values, as long as it can provide low impedance and high-pass filtering effects within the frequency band range of carrier communication.

[0036] The device forming the coupling transformer T1 is simple, avoiding the drawback that the original artificial power network requires multiple devices, and each device is not ideal, resulting in a large common-mode current. That is to say, due to the simple structure of the coupling transformer, the common-mode current caused by the imbalance of the devices in the original artificial power network no longer exists.

[0037] At the same time, when the coupling transformer T1 is used in this application, although there is a parasitic capacitance, usually between 10 pF and 30 pF, which will cause the common-mode impedance to be affected and become smaller, even if the common-mode impedance becomes smaller, its value is still much larger than the common-mode impedance of 25 Ω of the artificial power network. Therefore, through the voltage division effect, it shares more of the common-mode voltage originally applied to the ground wire that is consistent with the high-frequency carrier signal generated by the device under test and the test machine during operation, greatly reducing the common-mode voltage on the ground wire, and effectively ensuring the measurement accuracy.

[0038] The impedance calculation formula of the capacitor is Zc = 1 / 2πfC, where f is the carrier frequency and C is the capacitance value of the parasitic capacitance. In the original artificial power network, the common-mode impedance of 25 Ω of the artificial power network is formed by the parallel connection of R1 and R2. In addition, it should be mentioned that the coupling transformer T1 can isolate strong electricity while transmitting the carrier signal.

[0039] In order to meet the noise suppression effect within the carrier communication frequency band range (at least considering within 30 kHz in the low-frequency part), reduce the influence of external noise on the test, and at the same time, increase the common-mode impedance between the first power line 31 and the second power line 41 and the ground as much as possible to prevent the carrier product at the opposite end from receiving the common-mode voltage signal, and increase the common-mode impedance between the first power line 31 and the second power line 41 and the input power supply 220VAC as much as possible to prevent the carrier signal from entering the carrier product at the opposite end from the external "220VAC" power supply in the form of a common-mode voltage, the power filter module 1 of the present application adopts a multi-stage filter in the design.

[0040] Specifically, the power filter module 1 includes a first-stage filter formed by a first inductor L1, a second capacitor C2, a third capacitor C3, and a second inductor L2, and a second-stage filter formed by a third inductor L3, a fourth capacitor C4, a fifth capacitor C5, and a fourth inductor L4. The third inductor L3 is connected between the second capacitor C2 and the fourth capacitor C4, and the fourth inductor L4 is connected between the third capacitor C3 and the fifth capacitor C5.

[0041] Since the common-mode impedance between the first power line 31 and the second power line 41 and the ground, and the common-mode impedance between the first power line 31 and the second power line 41 and the input power supply 220VAC are both determined by the inductance of the inductor, the larger the inductance, the larger the impedance. Therefore, in order to further weaken the influence of the common-mode signal, the inductance of the first to fourth inductors is above 0.5 mH.

[0042] Since the product of the inductor and the capacitor determines the noise suppression ability for the external input power supply 220VAC, the larger the product, the stronger the noise suppression ability, and the product determines the cut-off frequency of the filter. Therefore, in order to achieve a better filtering effect, the cut-off frequency formed by the product between the inductor and the capacitor is within 1 kHz.

[0043] Moreover, in order to better implement filtering, the power filter module 1 further includes a fifth inductor L5 with one end connected to the fourth capacitor C4 and the other end serving as the live wire output terminal LOUT and having an inductance equal to that of the first inductor L1, and a sixth inductor L6 with one end connected to the fifth capacitor C5 and the other end serving as the neutral wire output terminal NOUT and having an inductance equal to that of the second inductor L2. In this way, whether the signal is input from the left end side or the right end side of the power filter, it can play a filtering role and effectively suppress the grid noise to a level lower than the carrier communication sensitivity of the product.

[0044] The present application also provides a splitter / combiner module 5 at the rear end of the signal coupling module 2, which is used to expand the external interface of the signal, facilitate access to a spectrum analyzer and an oscilloscope to observe the carrier signal amplitude at each interface, and also facilitate access to a signal generator to inject a noise signal for evaluating the receiving performance of the product in a noisy environment.

[0045] At the same time, in order to avoid excessive amplitude of the device input signal, causing signal overflow or damage to the device, and to protect external devices such as spectrum analyzers, signal generators, oscilloscopes, etc., the present application also connects a fixed attenuation module 6 that can perform a first-level attenuation on the high-frequency signal to the secondary side of the coupling transformer T1, and the splitter / combiner module 5 is connected to the output end of the fixed attenuation module 6.

[0046] The fixed attenuator module 6 is composed of a first resistor R1, a second resistor R2 and a third resistor R3. Since the input and output impedances of the fixed attenuator 6 are both 50Ω, the values of R1 and R3 are the same, and the resistance values of R1 and R3 determine the attenuation.

[0047] The splitter / combiner module 5 is composed of a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10 and an eleventh resistor R11. The input and output impedances of the four ports of the module are all 50Ω. In order to achieve interchangeability of the ports, that is, the ports have the same insertion loss, it is required that the fourth resistor R4, the fifth resistor R5, the eighth resistor R8 and the tenth resistor R10 have the same resistance value, and the sixth resistor R6, the seventh resistor R7, the ninth resistor R9 and the eleventh resistor R11 have the same resistance value.

[0048] In order to make the structure concise and easy to operate and manage, the various modules of the present application are integrated on a circuit board, which is convenient for carrying and assembling when assembling the test platform. At the same time, the integrated design also makes the assembled test platform miniaturized and saves space.

[0049] When the frequency of the common-mode signal is very high, the common-mode signal may affect the test result through radiation, so that the carrier signal is not transmitted along the predetermined path, but skips the adjustable attenuator, making the measured receiving sensitivity far better than the actual receiving sensitivity. In order to solve this problem, a test platform composed of the circuit modules of the present application is adopted, which arranges the test machine 3 and the corresponding circuit module in a first shielding box 7, and the device under test 4 and the corresponding circuit module in a second shielding box 8.

[0050] The solution of the present application reduces the requirements for the use environment, so that the entire test can be completed in an ordinary office environment, eliminating the trouble of building an expensive test laboratory and achieving the miniaturization of the test platform.

[0051] Although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A circuit module for a power line carrier communication test platform, the module comprising a power filter module (1) with one end connected to the industrial frequency power supply and the other end connected to a test machine (3) or a device under test (4), and a signal coupling module (2) connected between the power filter module (1) and the test machine (3) or the device under test (4), characterized in that: The signal coupling module (2) includes a high-pass filter (21) that can provide a low impedance within the frequency band of carrier communication, and a coupling transformer (22) connected to the high-pass filter (21) and capable of increasing the common-mode impedance between the first power line (31) between the test machine (3) and the power filter module (1) and the ground, and between the second power line (41) between the device under test (4) and the power filter module (1) and the ground through its own isolation characteristics to reduce the common-mode voltage on the ground wire; The power filter module (1) is a multi-stage filter; The power filter module (1) includes a first-stage filter formed by a first inductor (L1), a second capacitor (C2), a third capacitor (C3), and a second inductor (L2), and a second-stage filter formed by a third inductor (L3), a fourth capacitor (C4), a fifth capacitor (C5), and a fourth inductor (L4); The third inductor (L3) is connected between the second capacitor (C2) and the fourth capacitor (C4), and the fourth inductor (L4) is connected between the third capacitor (C3) and the fifth capacitor (C5); The power filter module (1) further includes a fifth inductor (L5) with one end connected to the fourth capacitor (C4) and the other end serving as the live wire output terminal (LOUT) and having an inductance equal to that of the first inductor (L1), and a sixth inductor (L6) with one end connected to the fifth capacitor (C5) and the other end serving as the neutral wire output terminal (NOUT) and having an inductance equal to that of the second inductor (L2).

2. The circuit module for a power line carrier communication test platform according to claim 1, characterized in that: The high-pass filter (21) is constituted by a first capacitor (C1).

3. The circuit module for a power line carrier communication test platform according to claim 2, characterized in that: The capacitance value of the first capacitor (C1) is 1 uF.

4. The circuit module for a power line carrier communication test platform according to claim 1, characterized in that: The parasitic capacitance value of the coupling transformer (22) is between 10 pF and 30 pF.

5. The circuit module for a power line carrier communication test platform according to claim 1, characterized in that: The inductance of the first inductor to the sixth inductor > 0.5 mH, and the frequency of the first-stage filter and the second-stage filter ≤ 1 kHz.

6. The circuit module for a power line carrier communication test platform according to claim 1, characterized in that: The secondary side of the coupling transformer is connected to a fixed attenuation module (6) that can perform a first-stage attenuation on high-frequency signals, and the output terminal of the fixed attenuation module (6) is connected to a splitter / combiner module (5).

7. A power line carrier communication test platform, characterized in that: The power line carrier communication test platform adopts the circuit module according to any one of claims 1 to 6 above.

8. The power line carrier communication test platform according to claim 7, characterized in that: The testing machine (3) in the power line carrier communication test platform and the corresponding circuit modules are arranged in the first shielding box (7), while the device under test (4) and the corresponding circuit modules are arranged in the second shielding box (8).

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