Device and method for electric heating aging test of high-voltage AC / DC cable and accessories thereof

Abstract

The invention discloses an electric heating aging test device and method for a high-voltage AC / DC cable and accessories thereof. The device comprises a power electronic transformer, an MMC main controller, a DAB main controller, a sampling plate, a protective resistor, a feed-through transformer and a cable accessory aging sample assembly. The power electronic transformer comprises a high-voltage alternating current port, a low-voltage alternating current port, a high-voltage direct current port and a low-voltage direct current port; the power electronic transformer comprises an MMC, a plurality of DAB converters and an inverter. Wherein the MMC and the DAB converter are respectively connected to the MMC main controller and the DAB main controller, so that the power electronic transformer generates alternating current voltage, direct current voltage or alternating current under the control of the MMC main controller and the DAB main controller; the alternating-current voltage comprises high-frequency, power-frequency or low-frequency alternating-current voltage; and the alternating current comprises high-frequency or power-frequency alternating current. According to the invention, the accuracy, reliability, safety and practicability of the aging test of the cable and accessories thereof can be improved from multiple aspects, and the cost is reduced.

Description

Technical Field

[0001] The invention relates to the field of power cables, and in particular to a device and method for electric and thermal aging testing of high-voltage AC and DC cables and accessories thereof. Background Art

[0002] Cables and their accessories are relatively weak links in the actual operation of the power transmission system because of the uneven distribution of internal electric and temperature fields and the difficulty in ensuring the construction process during on-site installation. Factors that usually cause insulation aging of cables and their accessories include: electrical aging under high-voltage electric fields, thermal aging caused by conductor resistance loss, mechanical damage during the production and assembly process, and environmental conditions such as moisture corrosion. Among them, electrical and thermal stresses and their synergistic effects are the main causes of insulation aging of cables and their accessories in actual operation. Research on the insulation reliability of cables and their accessories under the synergistic effects of electrical and thermal stresses is of great significance to ensure the stable operation of cables and their accessories.

[0003] There are few studies on the electrothermal aging devices of cables and their accessories under high voltage and high current. The more common aging method is to accelerate the thermal aging of the insulating material by using external heating and other means based on the application of high voltage. However, since the cable and its accessories are a complex insulation structure composed of multiple materials, their damage mechanism is affected by multiple factors. It is impossible to simulate the actual operating conditions of the cable and its accessories by heating only with an external heat source. On this basis, it is currently proposed to use a through-hole transformer to generate a large current in the experimental circuit to simulate the real working conditions as much as possible. However, the existing devices have relatively single functions, such as only being able to simulate large AC voltage and large current, and unable to accurately control voltage and current, resulting in the need to improve the accuracy of the test data; in addition, due to the use of a transformer, the test device is relatively large in size; and the existing test devices are all based on mechanical switch protection, resulting in the inability to quickly protect the test device in the event of a fault.

[0004] Therefore, if we can develop a high-power cable and accessory aging device that can test multiple working conditions such as high voltage AC and DC, can accurately control voltage and current, has high dynamic characteristics and can quickly protect, and occupies a small area, it will be able to improve the accuracy, reliability, safety and practicality of cable and accessory aging tests in many aspects, and at the same time reduce the cost of the system, which has important practical significance. Summary of the invention

[0005] In order to overcome the problems of the prior art, the purpose of the present invention is to provide a device and method that can be used for electrothermal aging testing of high-voltage AC and DC cables and their accessories, so as to solve the problems of the current aging devices for cables and their accessories, such as few test conditions, low test accuracy, large footprint, slow protection action, etc., thereby helping to improve the accuracy, reliability, safety and practicality of aging tests of cables and their accessories from many aspects, and reduce costs.

[0006] To achieve the purpose of the present invention, the technical solution of the present invention is:

[0007] According to a first aspect of the present invention, a device for electrothermal aging testing of high-voltage AC and DC cables and their accessories is provided. The device comprises: a power electronic transformer, an MMC main controller, a DAB main controller, a sampling board, a protection resistor, a through-hole transformer and a cable accessory aging sample assembly;

[0008] The power electronic transformer comprises a high-voltage AC port, a low-voltage AC port, a high-voltage DC port and a low-voltage DC port; the power electronic transformer comprises an MMC, a plurality of DAB converters and an inverter; the MMC and the DAB are respectively connected to an MMC main controller and a DAB main controller, so that the power electronic transformer generates an AC voltage, a DC voltage or an AC current under the control of the MMC main controller and the DAB main controller; the AC voltage comprises a high-frequency, industrial frequency or low-frequency AC voltage; the AC current comprises a high-frequency or industrial frequency AC current; the MMC is a three-phase structure and each phase comprises an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm respectively comprise an inductor, a first half-bridge submodule and a second half-bridge submodule connected in sequence; wherein the first half-bridge submodule and the second half-bridge submodule are connected via a power switch unit;

[0009] One end of the protection resistor is connected to different ports according to the test requirements, and the other end of the protection resistor is connected to the cable accessory aging sample assembly;

[0010] The primary side of the through-hole transformer is used to connect to the cable accessory aging sample assembly when an aging test is required under AC current, and the secondary side of the through-hole transformer is used to connect to the power electronic transformer;

[0011] The sampling board is used to sample and obtain the voltage data and current data of each power switch and each port in the power electronic transformer and the voltage data and current data of the primary side and the secondary side of the through-core transformer, and send them to the MMC main controller and the DAB main controller.

[0012] Preferably, the power switch unit comprises a power switch tube and a diode anti-parallel connected to the power switch tube.

[0013] Preferably, the respective second half-bridge sub-modules in the upper and lower bridge arms of the MMC are respectively connected to the positive and negative electrodes of the high-voltage DC port; the respective inductors in the upper and lower bridge arms of the MMC are connected in series, and the connection point of the two inductors is led out and connected to the high-voltage AC port of the corresponding phase; the multiple DAB converters correspond one-to-one to all the half-bridge sub-modules in the MMC, and each DAB converter includes a front-stage part, a high-frequency transformation part and a rear-stage part connected in sequence; the front-stage part of each DAB converter is connected to the corresponding half-bridge sub-module in the MMC, and the rear-stage parts of all DAB converters are connected in parallel to the input end of the inverter; the input end of the inverter is a low-voltage DC port, and the output end of the inverter is a low-voltage AC port.

[0014] Preferably, the first half-bridge submodule and the second half-bridge submodule each include a first power switch unit, a second power switch unit and a DC capacitor; the first power switch unit and the second power switch unit are connected in series and in parallel with the DC capacitor.

[0015] Preferably, in the upper bridge arm of the MMC, the connection point of the first and second power switch units of the second half-bridge submodule is connected to the positive pole of the high-voltage DC port, the connection point of the first and second power switch units of the first half-bridge submodule is connected to the second power switch unit of the second half-bridge submodule, and the second power switch unit of the first half-bridge submodule is connected to the inductor in the upper bridge arm; in the lower bridge arm of the MMC, the second power switch unit of the second half-bridge submodule is connected to the negative pole of the high-voltage DC port, the connection point of the first and second power switch units of the second half-bridge submodule is connected to the second power switch unit of the first half-bridge submodule, and the connection point of the first and second power switch units of the first half-bridge submodule is connected to the inductor in the lower bridge arm.

[0016] Preferably, the DAB converter comprises an isolation transformer and two symmetrical voltage-fed full-bridge units located on both sides of the isolation transformer.

[0017] Preferably, the transformation ratio of the through-hole transformer is set to 20:1.

[0018] According to a second aspect of the present invention, a method for testing the electrothermal aging of high-voltage AC and DC cables is provided. The method uses the device described in the first aspect of the present invention, and comprises the following steps:

[0019] According to the test requirements, the cable accessory aging sample assembly and the protection resistor are connected in series and then connected to the corresponding port of the power electronic transformer; wherein, when the cable accessory aging sample assembly needs to be subjected to an aging test under an alternating current, the primary side of the through-hole transformer is connected to the cable accessory aging sample assembly, and the secondary side of the through-hole transformer is connected to the low-voltage AC port of the power electronic transformer via the protection resistor;

[0020] The voltage data and current data of each power element and each port in the power electronic transformer and the voltage data and current data of the primary side and the secondary side of the through-core transformer are obtained in real time through the sampling board;

[0021] Based on the data obtained by the sampling board, the MMC main controller and the DAB main controller are used to control the MMC and the DAB to generate the required AC voltage, DC voltage or AC current respectively;

[0022] An aging test is performed on the cable accessory aging sample assembly under a required AC voltage, DC voltage or AC current.

[0023] Preferably, the method further comprises:

[0024] When the data acquired by the sampling board indicates that the voltage or current of any port exceeds the corresponding threshold, the voltage or current of any bridge arm exceeds the corresponding threshold, or the voltage or current of the primary side or the secondary side of the through-hole transformer exceeds the corresponding threshold, the driving of all power switches in the MMC and DAB is blocked through the MMC main controller and the DAB main controller.

[0025] Preferably, the method further comprises:

[0026] When the data acquired by the sampling board indicates that any of the following faults occurs more than a preset number of times within a preset time, the driving of all power switches in the MMC and DAB is blocked by the MMC main controller and the DAB main controller: the voltage or current of any port exceeds the corresponding threshold, the voltage or current of any bridge arm exceeds the corresponding threshold, or the voltage or current of the primary or secondary side of the through-core transformer exceeds the corresponding threshold; the preset number of times is an integer greater than 1.

[0027] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0028] (1) The device can be used to test the aging of high-voltage AC cables and their accessories, and can also be used to approximately simulate the aging test of high-voltage DC cables and their accessories;

[0029] (2) The AC voltage port and current port of the power electronic transformer can output high-frequency, industrial frequency and low-frequency voltage and current, and can simulate a variety of working conditions;

[0030] (3) The existing cable accessory aging device can only be tested under AC conditions, and the AC voltage is regulated by a mechanical transformer. The accuracy cannot be guaranteed due to manual voltage regulation. The device of the present invention uses power switching devices and is based on AC and DC voltage and current sensors, as well as closed-loop control through a sampling board, an MMC main controller and a DAB main controller. It can accurately control the voltage and current amplitudes, and the test results are more accurate.

[0031] (4) The present invention has a fast response characteristic and can act quickly when overvoltage or overcurrent occurs, which is beneficial to improving the safety of the system and can solve the problem of burning power devices and test circuits caused by DC short circuit.

[0032] (5) The prior art requires different aging test devices for different test conditions, while the present application has a power switch that can be quickly turned on and off by adjusting the control, and the power density is higher than that of the existing test device. Therefore, the required test interfaces can be integrated together, thereby reducing the footprint.

[0033] Therefore, the present invention can improve the accuracy, reliability, safety and practicality of the aging test of cables and their accessories from many aspects, and can also reduce the cost of the system, which has important practical significance. By adopting the MMC main controller and the DAB main controller including the high-speed digital processing chip, the cable accessory aging device can be improved based on the PET (Power Electronic Transformer), which can not only meet the demand of providing multiple test ports, but also fully consider the demand of short-circuit protection during DC test aging. By adding a power switch device between the two half-bridge submodules of the upper and lower bridge arms, when a short circuit occurs on the DC side, the switch tube can be quickly disconnected to realize the DC short-circuit protection function, which has important value. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a structural diagram of a device for performing electrothermal aging testing on high-voltage AC and DC cables and their accessories.

[0035] Figure 2 It is a schematic diagram of the structure of the power electronic transformer in the present invention.

[0036] Figures 3(a) to 3(c) They are schematic diagrams of the industrial frequency, high frequency and low frequency voltage waveforms output by the AC output port in the present invention respectively.

[0037] Figure 4 It is a schematic diagram of the output voltage waveform of the DC voltage port of the present invention.

[0038] Figures 5(a) to 5(c) They are the industrial frequency, high frequency and low frequency current waveforms connected to the secondary side of the through-hole transformer respectively.

[0039] Figures 6(a) to 6(c) They are the industrial frequency, high frequency and low frequency current waveforms generated on the primary side of the through-hole transformer respectively.

[0040] Figure 7 This is a schematic diagram of the software architecture adopted by the present invention.

[0041] Figure 8It is a schematic diagram of the protection action waveform of the present invention when the voltage is over-voltage.

[0042] Fig. 9 It is a schematic diagram of the protection action waveform of the present invention when the current is overcurrent.

[0043] Fig.10 This is a schematic diagram of the bridge arm current test waveform during protection when the DC side is short-circuited.

[0044] Marking Description:

[0045] 1- High voltage AC port, 2- Power electronic transformer, 3- Low voltage AC port, 4- High voltage DC port, 5- Grounding protection terminal, 6- Protection resistor, 7- Cable accessory aging sample assembly, 8- Through-core transformer, 9- Low voltage DC port. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment discloses an electrothermal aging test device that can be used for high-voltage AC and DC cables and their accessories. Figure 1-2 The device includes a power electronic transformer 2, an MMC main controller (not shown), a DAB main controller (not shown), a sampling board (not shown), a protection resistor 6, a through-hole transformer 8 and a cable accessory aging sample assembly 7.

[0049] The power electronic transformer 2 includes a high-voltage AC port 1, a low-voltage AC port 3, a high-voltage DC port 4 and a low-voltage DC port 9. The power electronic transformer 1 includes an MMC, a plurality of DAB converters and an inverter. The MMC and the DAB converter are respectively connected to the MMC main controller and the DAB main controller to generate an AC voltage, a DC voltage or an AC current under the control of the MMC main controller and the DAB main controller. The AC voltage includes a high-frequency, industrial frequency or low-frequency AC voltage. The AC current includes a high-frequency or industrial frequency AC current.

[0050] The MMC is a three-phase structure, and each phase includes an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm respectively include an inductor, a first half-bridge submodule and a second half-bridge submodule connected in sequence. The first half-bridge submodule and the second half-bridge submodule are connected via a power switch unit.

[0051] One end of the protection resistor 6 is connected to different ports according to test requirements, and the other end of the protection resistor 6 is connected to the cable accessory aging sample assembly 7 .

[0052] The primary side of the through-hole transformer 8 is used to connect to the cable accessory aging sample assembly 7 when an aging test is required under AC current, and the secondary side of the through-hole transformer 8 is used to connect to the power electronic transformer 1 .

[0053] The sampling board is used to sample and obtain the voltage data and current data of each port and each bridge arm in the power electronic transformer 1 and the primary side and the secondary side of the through-core transformer 8, and send them to the MMC main controller and the DAB main controller.

[0054] Through the above settings, the aging test device of this embodiment can not only be used for aging tests of high-voltage AC cables and their accessories, but also can be used to approximately simulate aging tests of high-voltage DC cables and their accessories; at the same time, this embodiment adopts power switching devices, and based on AC and DC voltage and current sensors, and realizes closed-loop control through sampling boards, MMC main controllers and DAB main controllers, it is possible to accurately control the voltage and current amplitudes, and the test results are more accurate; further, by arranging power switching devices between the two sub-modules of the upper and lower bridge arms, it can be ensured that when a DC short circuit fault is detected, all power switching device drives are blocked, and the bridge arms cannot form a loop, so the problem of power devices and test loops being burned out due to DC short circuits can be solved; in addition, the device can act quickly when overvoltage and overcurrent occur, which is beneficial to improving the safety of the system and can solve the problem of power devices and test loops being burned out due to DC short circuits.

[0055] More specifically, the sampling board may be integrated with a voltage sensor and a current sensor, so as to realize the sampling of the voltage data and current data of each port and each bridge arm in the power electronic transformer and the primary and secondary sides of the through-core transformer. The cable accessory aging sample assembly 7 includes a cable and its accessories. The MMC main controller and the DAB main controller may include a high-speed digital processing chip to improve processing efficiency.

[0056] In order to further improve circuit safety, the device that can be used for high-voltage AC and DC cable electrothermal aging testing also includes a grounding protection terminal to provide grounding protection.

[0057] Furthermore, the power switch unit connected between the first half-bridge submodule and the second half-bridge submodule includes a power switch tube and a diode connected in anti-parallel with the power switch tube, wherein the anti-parallel diode can protect the circuit and increase the switching speed.

[0058] Furthermore, the second half-bridge submodules in the upper and lower bridge arms of the MMC are respectively connected to the positive and negative electrodes of the high-voltage DC port; the inductors in the upper and lower bridge arms of the MMC are connected in series, and the connection point of the two inductors is led out and connected to the high-voltage AC port of the corresponding phase. Multiple DAB converters correspond to all half-bridge submodules in the MMC one by one, and each DAB converter includes a front-stage part, a high-frequency transformer part and a rear-stage part connected in sequence; the front-stage part of each DAB converter is connected to the corresponding half-bridge submodule in the MMC, and the rear-stage parts of all DAB converters are connected in parallel to the input end of the inverter; the input end of the inverter is a low-voltage DC port, and the output end of the inverter is a low-voltage AC port.

[0059] The first half-bridge submodule and the second half-bridge submodule in the upper and lower bridge arms of the MMC each include a power switch unit K1, a power switch unit K2 and a DC capacitor. The power switch unit K1 and the power switch unit K2 are connected in series and then connected in parallel with the DC capacitor. The power switch units K1 and K2 each include a power switch tube and a diode connected in anti-parallel with the power switch tube.

[0060] More specifically, in the upper bridge arm of the MMC, the connection point of the power switch units K1 and K2 of the second half-bridge submodule is connected to the positive pole of the high-voltage DC port, the connection point of the power switch units K1 and K2 of the first half-bridge submodule is connected to the power switch unit K2 of the second half-bridge submodule, and the power switch unit K2 of the first half-bridge submodule is connected to the inductor in the upper bridge arm. In the lower bridge arm of the MMC, the power switch unit K2 of the second half-bridge submodule is connected to the negative pole of the high-voltage DC port, the connection point of the power switch units K1 and K2 of the second half-bridge submodule is connected to the power switch unit K2 of the first half-bridge submodule, and the connection point of the power switch units K1 and K2 of the first half-bridge submodule is connected to the inductor in the lower bridge arm.

[0061] The DAB converter includes an isolation transformer and first and second voltage-fed full-bridge units located at the primary side and the secondary side of the isolation transformer, respectively. The first voltage-fed full-bridge unit located at the primary side corresponds to the front-stage part of the DAB converter, the isolation transformer corresponds to the high-frequency transformer part of the DAB converter, and the second voltage-fed full-bridge unit located at the secondary side corresponds to the rear-stage part of the DAB converter.

[0062] More specifically, the first and second voltage-fed full-bridge units each include four power switch units K3 to K6. Among them, the power switch unit K3 and the power switch unit K4 are connected in series to form a first branch, the power switch unit K5 and the power switch unit K6 are connected in series to form a second branch, and the first branch and the second branch are connected in parallel. The connection points of the power switch units K3 and K4 in the first voltage-fed full-bridge unit and the connection points of the power switch units K5 and K6 are respectively led out and connected to the positive and negative pole ports of the primary side of the isolation transformer. The connection points of the power switch units K3 and K4 in the second voltage-fed full-bridge unit and the connection points of the power switch units K5 and K6 are respectively led out and connected to the positive and negative pole ports of the primary side of the isolation transformer. The power switch units K3 to K6 each include a power switch tube and a diode anti-parallel to the power switch tube.

[0063] Furthermore, the rear stage of each DAB converter is connected to the low voltage DC port via a parallel filter capacitor.

[0064] Furthermore, the inverter in the power electronic transformer adopts a three-phase three-bridge-arm inverter. Specifically, the three-phase three-bridge-arm inverter includes three parallel bridge arm branches, each bridge arm branch includes two power switch units connected in series, and the connection points of the two power switch units connected in series are respectively led out to form a low-voltage AC port. Similarly, each power switch unit in the inverter also includes a power switch and a diode connected in reverse parallel to the power switch. The two ends of each bridge arm branch of the inverter are respectively connected to the positive and negative poles of the low-voltage DC port.

[0065] Figure 3 shows the high-frequency, industrial frequency, and low-frequency AC voltage waveforms output by the high-voltage AC port of the power electronic transformer of the present invention. It can be seen that the amplitude of the AC voltage is 10kV, and the frequencies are 500Hz, 50Hz, and 10Hz, respectively, proving that the power electronic transformer can generate high-frequency, industrial frequency, and low-frequency AC high voltages.

[0066] Figure 4 The DC voltage output by the power electronic inverter of the present invention is given, and the amplitude is 10 kV, which proves that the power electronic transformer can also generate a DC voltage.

[0067] FIG5 shows the AC current generated by the power electronic transformer of the present invention, with frequencies of 500 Hz, 50 Hz, and 10 Hz, respectively, and an effective value of 20 A. The current is connected to the secondary side of the through-hole transformer, and the transformation ratio of the through-hole transformer 8 in this embodiment is set to 20:1. Correspondingly, FIG6 shows the current of the loop composed of the cable accessory aging sample assembly and the through-hole transformer. It can be seen that the current amplitude has increased by 20 times, and the effective value has become 400 A, which can prove that the aging test device of the present invention can accurately generate the desired large current. It should be noted that in other embodiments, the transformation ratio of the through-hole transformer 8 can also be set to other values ​​according to actual needs.

[0068] Example 2

[0069] This embodiment provides a method for testing the electrothermal aging of high-voltage AC and DC cables, and adopts the electrothermal aging test device for high-voltage AC and DC cables of the present invention.

[0070] This method is based on Figure 7 The PET software architecture shown in the figure. Among them, the voltage and current information of each power element and each port in the MMC and DAB converters can be sent to the MMC main controller and the DAB main controller respectively through the sampling board. The information of the MMC main controller and the DAB main controller can be sent to the upper computer management system for decision-making and control. The control instructions of the upper and management systems can be sent to the MMC main controller and the DAB main controller respectively, so that the MMC main controller and the DAB main controller generate corresponding drive signals respectively, and are transmitted to the MMC submodule control board and the DAB submodule control board respectively via the MMC optical fiber board and the DAB optical fiber board, so as to control the power switches in each power submodule in the MMC and DAB converters to change and adjust their switch states and obtain the required voltage and current output.

[0071] Specifically, the electrothermal aging test method for high-voltage AC and DC cables of this embodiment includes the following steps:

[0072] Step 1. According to the test requirements, the cable accessory aging sample assembly and the protection resistor are connected in series and then connected to the corresponding port of the power electronic transformer; when the cable accessory aging sample assembly needs to be subjected to an aging test under an AC current, the primary side of the through-hole transformer is connected to the cable accessory aging sample assembly, and the secondary side of the through-hole transformer is connected to the low-voltage AC port of the power electronic transformer via the protection resistor.

[0073] Step 2: The voltage data and current data of each port and each bridge arm in the power electronic transformer and the primary side and the secondary side of the through-hole transformer are obtained in real time through the sampling board.

[0074] Step 3: Based on the voltage data and current data of each power element and each port in the power electronic transformer obtained by the sampling board, the MMC main controller and the DAB main controller are used to control the MMC and the DAB to generate the required AC voltage, DC voltage or AC current.

[0075] Step 4: Perform an aging test on the cable accessory aging sample assembly under the required AC voltage, DC voltage or AC current.

[0076] Preferably, the method further comprises:

[0077] Step 5: When the data acquired by the sampling board indicates that the voltage or current of any port exceeds the corresponding threshold, the voltage or current of any bridge arm exceeds the corresponding threshold, or the voltage or current of the primary side or the secondary side of the through-hole transformer exceeds the corresponding threshold, the driving of all power switches in the MMC and the DAB is blocked through the MMC main controller and the DAB main controller.

[0078] Figure 8 The waveform of the rapid action of the aging test device is given when the AC voltage at the high-voltage AC port of the power electronic transformer is overvoltage. Since the sampling board can collect voltage data of each port in the power electronic transformer, when the AC voltage gradually increases, once the instantaneous value of the AC voltage at the high-voltage AC port exceeds the set AC voltage threshold, the drive of all power switches in the power electronic transformer can be quickly blocked, so that the AC voltage output of the high-voltage AC port becomes zero.

[0079] Fig. 9 The waveform of the rapid action of the aging test device when the AC current generated on the secondary side of the through-hole transformer is overcurrent is given. It can be seen that the aging test device of the present invention can also achieve rapid protection when an overcurrent fault occurs.

[0080] It should be noted that, since the two half-bridge submodules in the upper and lower bridge arms of the MMC in the present invention are connected via a power switch unit, when a DC short circuit fault occurs, the power switch in the power switch unit between the two half-bridge submodules can be quickly blocked, so that the bridge arm cannot form a loop. In this way, the problem of burning power devices and test loops caused by DC short circuits can be more effectively solved.

[0081] Fig.10 The current waveform of the bridge arm in the MMC when the DC port is short-circuited is given. It can be seen that after a fault occurs, the current in the bridge arm can quickly become zero.

[0082] Further preferably, in order to avoid frequent shutdown and startup of PET (power electronic transformer) caused by false detection and triggering protection, it can be set that when multiple port voltage overvoltages, multiple port current overcurrents or multiple DC short circuit faults are detected continuously, the MMC main controller and the DAB main controller block the drive of all power switch devices and shut down. In other words, step 5 can be replaced by: when the data obtained by the sampling board indicates that any of the following faults occurs more than a preset number of times within a preset time, the MMC main controller and the DAB main controller block the drive of all power switches in the MMC and DAB: the voltage or current of any port exceeds the corresponding threshold, the voltage or current of any bridge arm exceeds the corresponding threshold, or the voltage or current of the primary or secondary side of the through-core transformer exceeds the corresponding threshold; the preset number of times is an integer greater than 1.

[0083] In summary, compared with the prior art, the present invention can achieve the following beneficial effects:

[0084] (1) The device can be used to test the aging of high-voltage AC cables and their accessories, and can also be used to approximately simulate the aging test of high-voltage DC cables and their accessories;

[0085] (2) The AC voltage port and current port of the power electronic transformer can output high-frequency, industrial frequency and low-frequency voltage and current, and can simulate a variety of working conditions;

[0086] (3) The existing cable accessory aging device can only be tested under AC conditions, and the AC voltage is regulated by a mechanical transformer. The accuracy cannot be guaranteed due to manual voltage regulation. The device of the present invention uses power switching devices and is based on AC and DC voltage and current sensors, as well as closed-loop control through a sampling board, an MMC main controller and a DAB main controller. It can accurately control the voltage and current amplitudes, and the test results are more accurate.

[0087] (4) The present invention has a fast response characteristic and can act quickly when overvoltage or overcurrent occurs, which is beneficial to improving the safety of the system and can solve the problem of burning power devices and test circuits caused by DC short circuit.

[0088] (5) The prior art requires different aging test devices for different test conditions, while the present application has a power switch that can be quickly turned on and off by adjusting the control, and the power density is higher than that of the existing test device. Therefore, the required test interfaces can be integrated together, thereby reducing the footprint.

[0089] Therefore, the present invention can improve the accuracy, reliability, safety and practicality of the aging test of cables and their accessories from many aspects, and can also reduce the cost of the system, which has important practical significance. By adopting the MMC main controller and the DAB main controller including the high-speed digital processing chip, the cable accessory aging device can be improved based on the PET (Power Electronic Transformer), which can not only meet the demand of providing multiple test ports, but also fully consider the demand of short-circuit protection during DC test aging. By adding a power switch device between the two half-bridge submodules of the upper and lower bridge arms, when a short circuit occurs on the DC side, the switch tube can be quickly disconnected to realize the DC short-circuit protection function, which has important value.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A device for electrothermal aging testing of high voltage AC and DC cables and their accessories, characterized in that , including: power electronic transformer, MMC main controller, DAB main controller, sampling board, protection resistor, through-hole transformer and cable accessories aging sample assembly; The power electronic transformer comprises a high-voltage AC port, a low-voltage AC port, a high-voltage DC port and a low-voltage DC port; the power electronic transformer comprises an MMC, a plurality of DAB converters and an inverter; wherein the MMC and the DAB converter are respectively connected to the MMC main controller and the DAB main controller, so that the power electronic transformer generates an AC voltage, a DC voltage or an AC current under the control of the MMC main controller and the DAB main controller; the AC voltage comprises a high-frequency, industrial frequency or low-frequency AC voltage; the AC current comprises a high-frequency or industrial frequency AC current; the MMC is a three-phase structure and each phase comprises an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm respectively comprise an inductor, a first half-bridge submodule and a second half-bridge submodule connected in sequence; wherein the first half-bridge submodule and the second half-bridge submodule are connected via a power switch unit; One end of the protection resistor is connected to different ports according to the test requirements, and the other end of the protection resistor is connected to the cable accessory aging sample assembly; The primary side of the through-hole transformer is used to connect to the cable accessory aging sample assembly when an aging test is required under AC current, and the secondary side of the through-hole transformer is used to connect to the power electronic transformer; The sampling board is used to sample and obtain the voltage data and current data of each port and each bridge arm in the power electronic transformer and the primary side and the secondary side of the through-core transformer, and send them to the MMC main controller and the DAB main controller.

2. The device for electrothermal aging test of high voltage AC and DC cables and their accessories according to claim 1, characterized in that: The power switch unit includes a power switch tube and a diode anti-parallel connected to the power switch tube.

3. The device for electrothermal aging test of high voltage AC and DC cables and their accessories according to claim 1, characterized in that: The second half-bridge submodules in the upper and lower bridge arms of the MMC are respectively connected to the positive and negative electrodes of the high-voltage DC port; the inductors in the upper and lower bridge arms of the MMC are respectively connected in series, and the connection point of the two inductors is led out and connected to the high-voltage AC port of the corresponding phase; The multiple DAB converters correspond one-to-one to all the half-bridge sub-modules in the MMC, and each DAB converter includes a front-stage part, a high-frequency transformer part and a rear-stage part which are connected in sequence; the front-stage part of each DAB converter is connected to the corresponding half-bridge sub-module in the MMC, and the rear-stage parts of all the DAB converters are connected in parallel to the input end of the inverter; the input end of the inverter is a low-voltage DC port, and the output end of the inverter is a low-voltage AC port.

4. The device for electrothermal aging test of high voltage AC and DC cables and their accessories according to claim 3 is characterized in that: The first half-bridge submodule and the second half-bridge submodule each include a first power switch unit, a second power switch unit and a DC capacitor; the first power switch unit and the second power switch unit are connected in series and then connected in parallel with the DC capacitor.

5. The device for electrothermal aging test of high voltage AC and DC cables and their accessories according to claim 4, characterized in that: In the upper bridge arm of the MMC, a connection point of the first and second power switch units of the second half-bridge submodule is connected to the positive electrode of the high-voltage DC port, a connection point of the first and second power switch units of the first half-bridge submodule is connected to the second power switch unit of the second half-bridge submodule, and the second power switch unit of the first half-bridge submodule is connected to the inductor in the upper bridge arm; In the lower bridge arm of the MMC, the second power switch unit of the second half-bridge submodule is connected to the negative pole of the high-voltage DC port, the connection point of the first and second power switch units of the second half-bridge submodule is connected to the second power switch unit of the first half-bridge submodule, and the connection point of the first and second power switch units of the first half-bridge submodule is connected to the inductor in the lower bridge arm.

6. The device for electrothermal aging test of high voltage AC and DC cables and their accessories according to claim 3 is characterized in that: The DAB converter comprises an isolation transformer and two symmetrical voltage-fed full-bridge units located on both sides of the isolation transformer.

7. The device for electrothermal aging test of high voltage AC and DC cables and their accessories according to claim 1, characterized in that: The transformation ratio of the through-core transformer is set to 20:

1.

8. A method for testing the electrothermal aging of high-voltage AC and DC cables, using the device as described in any one of claims 1 to 7, characterized in that: The steps include: According to the test requirements, the cable accessory aging sample assembly and the protection resistor are connected in series and then connected to the corresponding port of the power electronic transformer; wherein, when the cable accessory aging sample assembly needs to be subjected to an aging test under an alternating current, the primary side of the through-hole transformer is connected to the cable accessory aging sample assembly, and the secondary side of the through-hole transformer is connected to the low-voltage AC port of the power electronic transformer via the protection resistor; The voltage data and current data of each port and each bridge arm in the power electronic transformer and the primary side and the secondary side of the through-core transformer are obtained in real time through the sampling board; Based on the data obtained by the sampling board, the MMC main controller and the DAB main controller are used to control the MMC and the DAB to generate the required AC voltage, DC voltage or AC current respectively; An aging test is performed on the cable accessory aging sample assembly under a required AC voltage, DC voltage or AC current.

9. The method for testing the electrothermal aging of high-voltage AC and DC cables according to claim 8, characterized in that: The method further comprises: When the data acquired by the sampling board indicates that the voltage or current of any port exceeds the corresponding threshold, the voltage or current of any bridge arm exceeds the corresponding threshold, or the voltage or current of the primary side or the secondary side of the through-hole transformer exceeds the corresponding threshold, the driving of all power switches in the MMC and DAB is blocked through the MMC main controller and the DAB main controller.

10. The method for testing the electrothermal aging of high-voltage AC and DC cables according to claim 8, characterized in that: The method further includes: When the data acquired by the sampling board indicates that any of the following faults occurs more than a preset number of times within a preset time, the driving of all power switches in the MMC and DAB is blocked by the MMC main controller and the DAB main controller: the voltage or current of any port exceeds the corresponding threshold, the voltage or current of any bridge arm exceeds the corresponding threshold, or the voltage or current of the primary or secondary side of the through-core transformer exceeds the corresponding threshold; the preset number of times is an integer greater than 1.

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