Solid-state transformer efficiency testing device and testing method

Abstract

This invention discloses a solid-state transformer efficiency testing device and method, belonging to the fields of power electronics technology and power conversion testing technology. The device includes a 380V AC power supply. The output of the 380V AC power supply is connected to the input of an AC-DC module. The output of the AC-DC module is connected to a DC bus. The DC bus is connected to the power input of an inverter power supply unit array. The secondary side output of the inverter power supply unit array is connected to a high-voltage frequency converter module. The DC bus is also connected to the low-voltage DC output of the solid-state transformer under test via a feedback branch. The output of the high-voltage frequency converter module is connected to the high-voltage input of the solid-state transformer under test. An input-side energy metering device is installed between these components, and an output-side energy metering device is installed on the feedback branch. This invention eliminates the need for a high-voltage power supply and a high-power load, enabling continuous full-power operation and efficiency testing under different load rates. It offers advantages such as low cost, low power consumption, and grid friendliness.

Description

Technical Field

[0001] This invention relates to the fields of power electronics technology and power conversion testing technology, specifically to a solid-state transformer efficiency testing device and its testing method. Background Technology

[0002] Solid-state transformers (SSTs) are intelligent transformers that integrate power electronic conversion and high-frequency isolation technologies. They support 10kVAC to 35kVAC high-voltage AC input and output ±400V or 800V DC voltage, making them ideal for AI data centers, renewable energy grid connection, and next-generation power conversion systems. They are a key technology for future energy infrastructure. Efficiency and long-term operational reliability are core performance indicators for SSTs; therefore, accurate and efficient full-power operation and efficiency testing of SSTs is crucial.

[0003] Existing solid-state transformer testing methods typically employ the following approach: A high-voltage power supply (such as a 10kV or 35kV AC power supply) with the same rated voltage level as the solid-state transformer is configured, and a high-power electronic load is connected to the low-voltage DC output side of the solid-state transformer. Modern high-power electronic loads often use energy feedback topologies (such as four-quadrant converters), which can invert the test power and feed it back to the grid, thus reducing energy consumption to some extent.

[0004] However, such traditional solutions still have the following limitations:

[0005] 1. Reliance on high-voltage power supply and high equipment cost: The test system needs to be equipped with a high-voltage power supply that matches the voltage level of the solid-state transformer under test and its supporting protection and metering equipment. The investment is large and the area is large. In particular, for voltage levels of 35kV and above, high-voltage power distribution equipment is expensive and the installation conditions are harsh.

[0006] 2. Energy feedback has an impact on the high-voltage power grid: When electronic loads feed electrical energy back to the 10kV / 35kV power grid, although energy recovery can be achieved, the harmonics, reactive power and grid connection impact of the feedback current may cause pollution to the high-voltage power grid, requiring the addition of complex active filters and grid connection control devices, which further increases costs.

[0007] 3. Limited load regulation accuracy and dynamic response: It is still difficult for high-power electronic loads to achieve high-precision and fast-response power regulation across the entire power range, especially under small load or no-load conditions, where control performance degrades and affects the accuracy of efficiency testing.

[0008] 4. Long-term operation at full power is still uneconomical: Although energy can be fed back, the losses of the electronic load itself and the losses of the feedback circuit (usually 5% to 10% of the rated power) still need to be replenished from the grid, and the electricity cost of long-term operation at full power is still high.

[0009] 5. Insufficient testing flexibility: In traditional solutions, load adjustment relies on electronic loads, which makes it difficult to flexibly simulate different load characteristics (such as impact loads and nonlinear loads) and is not easy to integrate seamlessly with automated testing systems.

[0010] To address the aforementioned issues, there is an urgent need for a solid-state transformer efficiency testing device and its testing method to resolve the problems associated with traditional methods. Summary of the Invention

[0011] The purpose of this invention is to provide a solid-state transformer efficiency testing device and method, which does not require a high-voltage power supply and a high-power load, and can achieve continuous full-power operation and efficiency testing under different load rates. It has the advantages of low cost, low power consumption and grid-friendly design.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0013] A solid-state transformer efficiency testing device includes: a 380V AC power supply, an ACDC module, a DC bus, an inverter power supply unit array, a high-voltage frequency converter module, a solid-state transformer under test, and an energy metering unit. The output terminal of the 380V AC power supply is connected to the input terminal of the ACDC module, the output terminal of the ACDC module is connected to the DC bus, the DC bus is connected to the power input terminal of the inverter power supply unit array, the secondary output terminal of the inverter power supply unit array is connected to the high-voltage frequency converter module, the DC bus is also connected to the low-voltage DC output terminal of the solid-state transformer under test through a feedback branch, the output terminal of the high-voltage frequency converter module is connected to the high-voltage input terminal of the solid-state transformer under test, and the energy metering unit includes an input-side energy metering device and an output-side energy metering device. The input-side energy metering device is disposed between the output terminal of the high-voltage frequency converter module and the high-voltage input terminal of the solid-state transformer under test, and the output-side energy metering device is disposed at the low-voltage DC output terminal of the solid-state transformer under test.

[0014] Furthermore, the ACDC module includes a three-phase frequency converter, an intermediate frequency transformer, and a rectifier. The 380V AC power supply is connected to the three-phase frequency converter, which converts the 380V AC power into three-phase AC power with adjustable frequency and voltage. The output of the three-phase frequency converter is connected to the primary side of the intermediate frequency transformer, and the secondary side of the intermediate frequency transformer is connected to the rectifier. The secondary side of the intermediate frequency transformer provides multiple voltage outputs through taps. By adjusting the output voltage of the three-phase frequency converter and selecting and combining the turns ratio of the intermediate frequency transformer, a wide range of DC bus voltage adjustment can be achieved.

[0015] Furthermore, the inverter power supply unit array is composed of multiple inverter transformer sub-units. Each inverter transformer sub-unit includes an inverter and an isolation transformer. The DC bus is connected to the DC side of the inverter, the AC side of the inverter is connected to the primary side of the isolation transformer, and the secondary side of the isolation transformer is connected to the high-voltage frequency converter module for outputting a set of electrically isolated three-phase AC voltages.

[0016] Furthermore, the inverter is a three-phase full-bridge IGBT topology.

[0017] Furthermore, the high-voltage frequency converter module is composed of multiple power units connected in series, wherein the number of power units is the same as the number of inverter transformer sub-units, the secondary side of the isolation transformer is connected to the three-phase AC input terminal of the power unit, and the output side of the power unit is connected in series to the high-voltage input terminal of the solid-state transformer under test, in order to simulate the input power supply of the solid-state transformer under test when it is operating at rated speed.

[0018] Furthermore, the energy metering unit is a high-precision power analyzer or a digital energy meter.

[0019] The present invention also provides a testing method for a solid-state transformer efficiency testing device, applied to the aforementioned solid-state transformer efficiency testing device, comprising:

[0020] Step 1: Turn on the 380V AC power supply and adjust the ACDC module to stabilize the DC bus voltage at the rated DC voltage required by the solid-state transformer under test.

[0021] Step 2: Start each inverter in the inverter power supply unit array, output a three-phase AC voltage with a set frequency and amplitude, and supply power to each power unit of the high-voltage frequency converter module through their respective isolation transformers;

[0022] Step 3: Conduct a full-power continuous operation test or an efficiency test;

[0023] Step 4: During the test, the DC power output by the solid-state transformer under test returns to the DC bus through the feedback branch to achieve energy circulation. The 380V power supply only supplements the system losses.

[0024] Furthermore, in step 2, the output frequency of the high-voltage frequency converter module is fixed at 50Hz, and the amplitude is fixed at the AC current of the rated voltage of the solid-state transformer under test.

[0025] Furthermore, in step 3, a full-power continuous operation test is conducted, specifically as follows:

[0026] Adjust the output voltage of the ACDC module to make the output power of the solid-state transformer under test reach the rated power, maintain this state for a predetermined time, and monitor its operating parameters.

[0027] Furthermore, in step 3, an efficiency test is conducted, specifically as follows:

[0028] The output voltage of the ACDC module is gradually changed to make the solid-state transformer under test operate at different load rates. At each stable load point, the active power is recorded synchronously by the input-side power metering device and the output-side power metering device, and the efficiency at that load point is calculated.

[0029] In summary, the present invention has at least one of the following beneficial technical effects:

[0030] 1. Achieves energy recycling and extremely low power consumption: The DC power output of the solid-state transformer under test is directly fed back to the DC bus, and the system losses (switching losses, conduction losses, iron losses, etc.) are only supplemented from the 380V power grid. The test power consumption is reduced by more than 90%, making long-term full-power operation tests possible and significantly saving operating costs.

[0031] 2. No need for high-voltage power supply and high-power load: High-voltage test power supply is generated by low-voltage frequency conversion and multi-winding series superposition technology, eliminating the need for 10kV / 35kV high-voltage power distribution equipment, and eliminating external simulated loads. The equipment investment is small and the footprint is small.

[0032] 3. Grid friendly and shock-free: The test device draws power from the 380V low-voltage grid only, with smooth power supply, no sudden increase or decrease, and no high-voltage side harmonic pollution, so it has no adverse effects on the power grid.

[0033] 4. Flexible and adjustable DC voltage, compatible with various SSTs: The ACDC module can output a wide range of adjustable DC voltages (such as 200V, 400V, 800V, etc.), which can meet the testing needs of solid-state transformers with different DC voltage levels and has strong versatility.

[0034] 5. Continuously adjustable load rate and high test accuracy: By adjusting the output DC voltage of the ACDC module, the output power of the solid-state transformer can be changed precisely and continuously, covering no-load to full-load and even overload conditions, and the efficiency test data is comprehensive and accurate.

[0035] 6. Independent and flexible power supply topology: The parallel array scheme of multiple inverters and isolation transformers is adopted, and the power supply of each power unit is completely independent, with perfect electrical isolation, extremely high degree of control freedom, no need for phase shift control, and simplifies system complexity.

[0036] 7. Multi-functional and comprehensive testing capabilities: The same device can perform long-term full-power operation assessment of solid-state transformers and efficiency scanning tests under different load rates, meeting the needs of multiple scenarios such as R&D, production, and quality inspection.

[0037] 8. High degree of automation: Combined with the power metering and control system, it can realize fully automatic efficiency scanning test and long-term operation monitoring, improving test efficiency. Attached Figure Description

[0038] Figure 1 This is a block diagram of the device structure according to Embodiment 1 of the present invention;

[0039] Figure 2 This is a schematic diagram of the testing method of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0041] like Figure 1 As shown, this invention provides a solid-state transformer efficiency testing device, comprising: a 380V AC power supply, an ACDC module, a DC bus, an inverter power supply unit array, a high-voltage frequency converter module, a solid-state transformer under test, and an energy metering unit. The output terminal of the 380V AC power supply is connected to the input terminal of the ACDC module, the output terminal of the ACDC module is connected to the DC bus, the DC bus is connected to the power input terminal of the inverter power supply unit array, the secondary output terminal of the inverter power supply unit array is connected to the high-voltage frequency converter module, the DC bus is also connected to the low-voltage DC output terminal of the solid-state transformer under test through a feedback branch, the output terminal of the high-voltage frequency converter module is connected to the high-voltage input terminal of the solid-state transformer under test, and the energy metering unit includes an input-side energy metering device and an output-side energy metering device. The input-side energy metering device is disposed between the output terminal of the high-voltage frequency converter module and the high-voltage input terminal of the solid-state transformer under test, and the output-side energy metering device is disposed at the low-voltage DC output terminal of the solid-state transformer under test, i.e., on the feedback branch.

[0042] The ACDC module includes a three-phase frequency converter, an intermediate frequency transformer, and a rectifier. The 380V AC power supply is connected to the three-phase frequency converter, which converts the 380V AC power into three-phase AC power with adjustable frequency and voltage. The frequency can be adjusted within the range of 400Hz to 1kHz. The output of the three-phase frequency converter is connected to the primary side of the intermediate frequency transformer, and the secondary side of the intermediate frequency transformer is connected to the rectifier. The secondary side of the intermediate frequency transformer provides multiple voltage outputs through taps. By adjusting the output voltage of the three-phase frequency converter and selecting and combining the turns ratio of the intermediate frequency transformer, a wide range of DC bus voltage adjustment can be achieved. The typical output voltage is 800V, but it can also be set to 400V, 200V, or other voltage levels according to the rated DC voltage of the solid-state transformer under test to meet the testing requirements of solid-state transformers of different specifications.

[0043] The inverter power supply unit array consists of multiple inverter transformer sub-units. Each inverter transformer sub-unit includes an inverter and an isolation transformer. The DC bus is connected to the DC side of the inverter, the AC side of the inverter is connected to the primary side of the isolation transformer, and the secondary side of the isolation transformer is connected to the high-voltage frequency converter module to output a set of electrically isolated three-phase AC voltages.

[0044] The inverter is a three-phase full-bridge IGBT topology, and the output frequency can be adjusted within the range of 400Hz to 1kHz to reduce the size and weight of the isolation transformer.

[0045] The turns ratio of the isolation transformer is designed according to the input voltage level of the power unit, with a typical secondary line voltage of 690V or 1700V.

[0046] The high-voltage frequency converter module is composed of multiple power units connected in series. The number of power units is the same as the number of inverter transformer sub-units. Each inverter transformer sub-unit independently supplies power to one power unit. The secondary side of the isolation transformer is connected to the three-phase AC input terminal of the power unit. The output side of the power unit is connected in series to the high-voltage input terminal of the solid-state transformer under test. The output sides of each power unit are connected in series to form a 10kV or 35kV high-voltage AC power with a fixed frequency of 50Hz, which is used to simulate the input power supply of the solid-state transformer under test when it is operating at its rated speed.

[0047] This invention provides an embodiment in which the number of inverter power supply unit arrays is configured as follows:

[0048] For a 10kV output voltage level, the high-voltage frequency converter module consists of 24 power units connected in series (8 per phase), corresponding to 24 sets of inverter transformer sub-units;

[0049] For the 35kV output voltage level, the high-voltage frequency converter module consists of 36 power units connected in series (12 per phase), corresponding to 36 sets of inverter transformer sub-units.

[0050] The high-voltage frequency converter module forms a high-voltage AC power by superimposing the output sides of each power unit in series. By adjusting the modulation wave of each power unit, the output voltage amplitude and frequency can be continuously adjusted. However, in this invention, the output frequency of the high-voltage frequency converter module is fixed at 50Hz, and the output voltage amplitude is fixed at the rated voltage (10kV or 35kV) of the solid-state transformer under test, so as to simulate the power supply of a real power grid.

[0051] The power metering unit is a high-precision power analyzer or a digital power meter, which synchronously collects the active power on the input side and the output side, and calculates the efficiency of the solid-state transformer under test at the corresponding load point by the ratio.

[0052] The solid-state transformer efficiency testing device provided by this invention can realize the following two solid-state transformer testing modes:

[0053] 1. Full-power continuous operation test

[0054] The output voltage of the ACDC module is adjusted to stabilize the DC bus voltage at a certain value. At this point, the 10kV / 35kV 50Hz AC power output from the high-voltage frequency converter drives the solid-state transformer. The DC power output from the solid-state transformer returns to the DC bus via the feedback branch, forming an energy cycle. By adjusting the output voltage of the ACDC module to change the load rate of the solid-state transformer, and maintaining this state continuously when the load rate reaches 100% of the rated power, the thermal stability, insulation performance, and long-term operational reliability of the solid-state transformer are evaluated. Due to the energy cycle, losses are only replenished from the 380V grid, allowing for long-term, low-cost operation.

[0055] 2. Efficiency testing under different load rates

[0056] Maintaining the high-voltage inverter module output at its rated voltage (10kV or 35kV) and rated frequency (50Hz), the voltage difference between the solid-state transformer output side and the DC bus is changed by continuously adjusting the output DC voltage of the ACDC module, thereby altering the output power of the solid-state transformer and achieving a wide-range load rate adjustment from no-load to full-load (even short-term overload). Input and output power are simultaneously measured at each stable load point, efficiency is calculated, and efficiency curves are plotted.

[0057] like Figure 2 As shown, the present invention also provides a testing method for a solid-state transformer efficiency testing device, applied to the aforementioned solid-state transformer efficiency testing device, comprising:

[0058] Step 1: Turn on the 380V AC power supply and adjust the ACDC module to stabilize the DC bus voltage at the rated DC voltage required by the solid-state transformer under test (such as 800V, 400V, 200V, etc.).

[0059] Step 2: Start each inverter in the inverter power supply unit array, output a three-phase AC voltage with a set frequency and amplitude, and supply power to each power unit of the high-voltage frequency converter module through their respective isolation transformers;

[0060] Step 3: Conduct a full-power continuous operation test or an efficiency test;

[0061] Step 4: During the test, the DC power output by the solid-state transformer under test returns to the DC bus through the feedback branch to achieve energy circulation. The 380V power supply only supplements the system losses.

[0062] In step 2, the output frequency of the high-voltage frequency converter module is fixed at 50Hz, and the amplitude is fixed at the AC voltage of the rated voltage of the solid-state transformer under test (10kV or 35kV).

[0063] Step 3 involves conducting a full-power continuous operation test, specifically as follows:

[0064] Adjust the output voltage of the ACDC module to make the output power of the solid-state transformer under test reach the rated power (100% load rate), maintain this state for a predetermined time, and monitor its operating parameters.

[0065] In step 3, an efficiency test is conducted, specifically as follows:

[0066] By gradually changing the output voltage of the ACDC module (e.g., from high to low or from low to high), the solid-state transformer under test is operated at different load rates. At each stable load point, the active power is recorded synchronously by the input-side power metering device and the output-side power metering device, and the efficiency at that load point is calculated.

[0067] In step 1, the DC bus voltage can be adjusted over a wide range by adjusting the output voltage of the three-phase frequency converter and the tap selection of the intermediate frequency transformer.

[0068] In step 3, during efficiency testing, the output current of the solid-state transformer is increased by reducing the output voltage of the ACDC module (i.e., reducing the DC bus voltage), thus increasing the load rate; conversely, the load rate is reduced by increasing the output voltage of the ACDC module.

[0069] In step 2, the output frequency of the inverter is set to a fixed value between 400Hz and 1kHz to optimize the power density of the transformer.

[0070] The present invention will now provide several embodiments to further illustrate the above-described apparatus and method:

[0071] Example 1: 10kV level efficiency test, DC 800V;

[0072] like Figure 1 As shown, this embodiment provides a solid-state transformer efficiency testing device, which is suitable for efficiency testing of solid-state transformers used in data centers with a rated input voltage of 10kV and an output voltage of 800V DC.

[0073] The specific components of the device are as follows:

[0074] (1) 380V AC power supply

[0075] The system uses three-phase 380V / 50Hz industrial mains power to provide energy input for the entire test system.

[0076] (2) ACDC module

[0077] It includes a three-phase frequency converter, an intermediate frequency transformer, and a rectifier.

[0078] The three-phase frequency converter converts 380V / 50Hz AC power into three-phase AC power with adjustable frequency and voltage. In this embodiment, the output frequency is set to 500Hz, and the output voltage is adjusted according to the target DC voltage.

[0079] The primary side of the intermediate frequency transformer is connected to the output of the frequency converter, and the secondary side has multiple taps that can be selected as needed. In this embodiment, the secondary winding outputs a stable 800V DC bus after passing through a rectifier (three-phase bridge rectifier) ​​and a filter capacitor.

[0080] By adjusting the output voltage of the inverter power supply and the turns ratio of the intermediate frequency transformer, this ACDC module can also output DC voltages such as 400V and 200V to meet the testing requirements of solid-state transformers of different specifications.

[0081] (3) Inverter power supply unit array

[0082] It consists of 24 identical inverter transformer sub-units connected in parallel.

[0083] Each subunit includes:

[0084] Inverter: Three-phase full-bridge IGBT inverter, DC side connected to 800V DC bus, AC side output 500Hz three-phase AC power, voltage amplitude adjustable;

[0085] Isolation transformer: The primary side is connected to the inverter output, and the secondary side outputs three-phase AC power with a line voltage of 690V, providing electrical isolation for the power unit.

[0086] (4) High-voltage frequency converter module

[0087] Each phase consists of 8 low-voltage power units connected in series.

[0088] Each power unit is an AC-DC-AC converter circuit with three-phase AC input and single-phase AC output.

[0089] There are a total of 24 power units in three phases. The 24 power units are connected in series with 8 units per phase. The three phases are connected in a Y-shape. The output terminals are connected in series and superimposed to form a 10kV / 50Hz three-phase AC high voltage, simulating the input power supply of a solid-state transformer under rated operation.

[0090] (5) The solid-state transformer under test

[0091] Its high-voltage input terminal is connected to 10kV / 50Hz AC power, and its low-voltage DC output terminal outputs 800V DC power.

[0092] (6) Electricity metering unit

[0093] Input-side power metering device: Located between the output end of the high-voltage frequency converter module and the high-voltage input end of the solid-state transformer, it uses a high-precision power analyzer to measure the active power Pin of the input solid-state transformer.

[0094] Output-side power metering device: installed at the low-voltage DC output end of the solid-state transformer, also using a high-precision power analyzer to measure the active power Pout output by the solid-state transformer.

[0095] (7) Energy feedback branch

[0096] The 800V DC output from the solid-state transformer under test is directly connected to the DC bus to achieve power circulation.

[0097] The following is a description of the work process (efficiency test):

[0098] First, close the 380V power supply and adjust the ACDC module to stabilize the DC bus voltage at 800V (rated value).

[0099] Start the 24 inverters in the inverter power supply unit array, set the output frequency to 500Hz, and adjust the output voltage amplitude to output 690V three-phase AC power from the secondary side of the isolation transformer. The 24 channels of 690V AC power are then fed into the 24 power units respectively.

[0100] Each power unit converts AC to DC through PWM rectification, and then inverts it back to single-phase AC. Its fundamental amplitude is controlled, and finally the AC is superimposed in series to form a 10kV / 50Hz three-phase AC, which is applied to the high-voltage side of the solid-state transformer.

[0101] After the solid-state transformer under test is operational, it outputs 800V DC power from its low-voltage side. This 800V DC output is connected to a power analyzer to measure the output power; and it is also connected to the DC bus via a feedback branch to supplement the DC bus's energy. At this time, the 380V power supply only needs to provide the power loss of the entire test system (including the losses of the ACDC module, inverter, transformer, power unit, and the solid-state transformer itself).

[0102] The following section will elaborate on load rate adjustment and efficiency testing:

[0103] Keeping the high-voltage inverter module output constant at 10kV / 50Hz, gradually decrease the output voltage of the ACDC module, i.e., decrease the DC bus voltage. Since the solid-state transformer output voltage (800V) is higher than the DC bus voltage, the output current increases, the solid-state transformer output power increases accordingly, and the load rate increases. Conversely, increasing the ACDC module output voltage decreases the load rate.

[0104] At each stable load point (e.g., 10%, 20%, ..., 100% load rate), the input power Pin and output power Pout are read synchronously, and the efficiency η = Pout / Pin × 100% is calculated. By repeating the adjustment, a complete efficiency curve from no load to full load (or even short-term overload) can be obtained.

[0105] Phase control explanation in this embodiment:

[0106] The three-phase AC voltage output from the 24 inverters requires no phase shift control. Each inverter can operate at the same phase or with an arbitrary phase difference. Since each power unit contains an independent rectifier circuit, the phase relationship of the inverter output voltage does not affect the DC bus power quality, nor does it perform harmonic suppression. System harmonic suppression is ensured by the PWM rectification of the power units and the multi-level output characteristics of the high-voltage frequency converter module.

[0107] Example 2: Efficiency test at 35kV level, DC 800V;

[0108] This embodiment is basically the same as Embodiment 1, except that the rated input voltage of the solid-state transformer under test is 35kV.

[0109] (1) Inverter power supply unit array

[0110] It consists of 36 sets of inverter transformer sub-units connected in parallel, with each set outputting one 1700V three-phase AC power.

[0111] (2) High-voltage frequency converter module

[0112] It consists of 36 power units connected in series, with 12 units per phase. The output sides of each unit are connected in series and superimposed to form a 35kV / 50Hz three-phase AC high-voltage power supply.

[0113] (3) Work process

[0114] Completely consistent with Example 1. 36 inverters were started to power 36 power units, with the high-voltage frequency converter output fixed at 35kV / 50Hz. The load rate was changed by adjusting the output voltage of the ACDC module to achieve full-range efficiency testing.

[0115] Example 3: Testing at different DC voltage levels;

[0116] In this embodiment, the low-voltage DC rated voltage of the solid-state transformer under test is 400V (e.g., in some industrial DC power distribution network applications). In this case, the ACDC module needs to output a 400V DC bus.

[0117] Specific adjustment methods:

[0118] The output frequency of the three-phase frequency converter is still set to 500Hz, but the output voltage amplitude is reduced.

[0119] Intermediate frequency transformers can be selected with combinations of smaller turns ratios, which can be adjusted via winding taps;

[0120] After rectification and filtering, a stable 400V DC bus is obtained.

[0121] The remaining parts (inverter power supply unit array, high-voltage frequency converter module, etc.) are the same as in Example 1, but it should be noted that the input voltage of the power unit may need to be adjusted accordingly (e.g., by adjusting the inverter output or transformer turns ratio matching). Since the power unit is usually designed with a wide input range, this example can also be directly applied.

[0122] In a similar manner, the ACDC module can also output other DC voltages such as 200V to meet the testing requirements of various solid-state transformers.

[0123] Example 4: Power frequency test, inverter output 50Hz;

[0124] In this embodiment, the three-phase frequency converter output of the ACDC module is fixed at 50Hz (power frequency). The inverter output frequency in the inverter power supply unit array is also set to 50Hz, and the isolation transformer is designed according to the power frequency. The high-voltage frequency converter module synthesizes 50Hz high-voltage AC power, which is completely consistent with the power frequency design of the solid-state transformer. Other structures and testing methods remain unchanged.

[0125] Example 5: Full-power continuous operation test;

[0126] This embodiment is based on the device of Embodiment 1 or Embodiment 2, and performs a full-power continuous operation test of a solid-state transformer.

[0127] Test objective: To assess the thermal stability, insulation performance, and reliability of solid-state transformers under long-term operation at rated power.

[0128] Test steps:

[0129] (1) Complete the device startup and parameter setting according to Example 1 (10kV level) or Example 2 (35kV level).

[0130] (2) Adjust the output voltage of the ACDC module to make the output power of the solid-state transformer reach the rated power (100% load rate). Specifically, gradually reduce the DC bus voltage until the output current of the solid-state transformer reaches the rated value.

[0131] (3) Set the continuous running time (e.g., 2 hours, 8 hours, 24 hours or longer), during which the ACDC module output voltage is kept stable by the control system, thereby maintaining a constant load rate.

[0132] (4) During operation, monitor the following parameters in real time:

[0133] Temperature of key points inside the solid-state transformer under test (such as power modules and magnetic components);

[0134] Input and output voltage, current, and power;

[0135] DC bus voltage fluctuation;

[0136] System loss changes (indirectly reflected by the 380V power input power).

[0137] (5) If any abnormality occurs (such as over-temperature, over-current, or voltage drop), the system will automatically protect itself and record the fault data.

[0138] (6) After the operation is completed, analyze the data and evaluate whether the solid-state transformer meets the requirements for long-term full-power operation.

[0139] Energy cycling advantage: Since energy circulates through the feedback branch, the 380V power supply only needs to replenish system losses (usually 5% to 10% of the rated power). Therefore, the electricity cost for long-term full-power operation is extremely low, making long-term full-power testing, which was originally difficult to implement due to huge energy consumption, economically feasible.

[0140] Example 6: Comprehensive Testing Process;

[0141] This embodiment describes a comprehensive test process that combines full-power operation testing with efficiency testing, applicable to factory testing or type testing of solid-state transformers.

[0142] Test process:

[0143] (1) No-load test: Adjust the output voltage of the ACDC module to the rated value (so that the solid-state transformer under test is unloaded) and measure the no-load loss.

[0144] (2) Efficiency curve test: According to the method of Example 1 or 2, gradually change the output voltage of the ACDC module to make the solid-state transformer operate at different load rates (such as 25%, 50%, 75%, 100%), record the efficiency at each point, and draw the efficiency curve.

[0145] (3) Full power operation test: Adjust the output voltage of the ACDC module to achieve a load rate of 100%, run continuously for a specified time (e.g., 2 hours), and monitor various parameters.

[0146] (4) Overload capacity test: For a short period of time (e.g., 1 minute), further reduce the output voltage of the ACDC module to increase the load rate to 110% or 120% to test the overload capacity.

[0147] (5) Data summary and analysis: Generate a complete test report.

[0148] Throughout the test, energy circulates through the feedback branch, replenishing losses only from the 380V power supply. This results in low test costs and no impact on the power grid.

[0149] Embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0150] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0151] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0152] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0153] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A solid-state transformer efficiency testing device, characterized in that, include: The system comprises a 380V AC power supply, an ACDC module, a DC bus, an inverter power supply unit array, a high-voltage frequency converter module, a solid-state transformer under test, and an energy metering unit. The output of the 380V AC power supply is connected to the input of the ACDC module, the output of the ACDC module is connected to the DC bus, the DC bus is connected to the power input of the inverter power supply unit array, the secondary output of the inverter power supply unit array is connected to the high-voltage frequency converter module, the DC bus is also connected to the low-voltage DC output of the solid-state transformer under test via a feedback branch, the output of the high-voltage frequency converter module is connected to the high-voltage input of the solid-state transformer under test, and the energy metering unit includes an input-side energy metering device and an output-side energy metering device. The input-side energy metering device is located between the output of the high-voltage frequency converter module and the high-voltage input of the solid-state transformer under test, and the output-side energy metering device is located at the low-voltage DC output of the solid-state transformer under test. The ACDC module includes a three-phase frequency converter, an intermediate frequency transformer, and a rectifier. The 380V AC power supply is connected to the three-phase frequency converter, which converts the 380V AC power into three-phase AC power with adjustable frequency and voltage. The output of the three-phase frequency converter is connected to the primary side of the intermediate frequency transformer, and the secondary side of the intermediate frequency transformer is connected to the rectifier. The secondary side of the intermediate frequency transformer provides multiple voltage outputs through taps. By adjusting the output voltage of the three-phase frequency converter and the selection and combination of the turns ratio of the intermediate frequency transformer, a wide range of DC bus voltage adjustment can be achieved. The load rate of the solid-state transformer can be changed by adjusting the output voltage of the ACDC module. The inverter power supply unit array consists of multiple inverter transformer sub-units. Each inverter transformer sub-unit includes an inverter and an isolation transformer. The DC bus is connected to the DC side of the inverter, the AC side of the inverter is connected to the primary side of the isolation transformer, and the secondary side of the isolation transformer is connected to the high-voltage frequency converter module to output a set of electrically isolated three-phase AC voltages. The high-voltage frequency converter module is composed of multiple power units connected in series. The number of power units is the same as the number of inverter transformer sub-units. The secondary side of the isolation transformer is connected to the three-phase AC input terminal of the power unit. The output side of the power unit is connected in series to the high-voltage input terminal of the solid-state transformer under test to simulate the input power supply of the solid-state transformer under test when it is operating at rated speed.

2. The solid-state transformer efficiency testing device according to claim 1, characterized in that, The inverter is a three-phase full-bridge IGBT topology.

3. The solid-state transformer efficiency testing device according to claim 1, characterized in that, The energy metering unit is a high-precision power analyzer or a digital energy meter.

4. A test method for a solid-state transformer efficiency testing device, applied to the solid-state transformer efficiency testing device according to any one of claims 1-3, characterized in that, include: Step 1: Turn on the 380V AC power supply and adjust the ACDC module to stabilize the DC bus voltage at the rated DC voltage required by the solid-state transformer under test. Step 2: Start each inverter in the inverter power supply unit array, output a three-phase AC voltage with a set frequency and amplitude, and supply power to each power unit of the high-voltage frequency converter module through their respective isolation transformers; Step 3: Conduct a full-power continuous operation test or an efficiency test; Step 4: During the test, the DC power output by the solid-state transformer under test returns to the DC bus through the feedback branch to achieve energy circulation. The 380V power supply only supplements the system losses.

5. The testing method of the solid-state transformer efficiency testing device according to claim 4, characterized in that, In step 2, the output frequency of the high-voltage frequency converter module is fixed at 50Hz, and the amplitude is fixed at the AC current of the rated voltage of the solid-state transformer under test.

6. The testing method of the solid-state transformer efficiency testing device according to claim 4, characterized in that, Step 3 involves conducting a full-power continuous operation test, specifically as follows: Adjust the output voltage of the ACDC module to make the output power of the solid-state transformer under test reach the rated power, maintain this state for a predetermined time, and monitor its operating parameters.

7. The testing method of the solid-state transformer efficiency testing device according to claim 4, characterized in that, In step 3, an efficiency test is conducted, specifically as follows: The output voltage of the ACDC module is gradually changed to make the solid-state transformer under test operate at different load rates. At each stable load point, the active power is recorded synchronously by the input-side power metering device and the output-side power metering device, and the efficiency at that load point is calculated.

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