Hybrid solid-state transformers for normal power optimization and their power allocation methods

Abstract

This invention provides a hybrid solid-state transformer and its power distribution method for normal power optimization, belonging to the field of power electronic transformer technology. It includes a power frequency transformer, a three-stage dual-parallel converter, a power sampling circuit, a hysteresis comparator circuit, and a combined controller. One end of the power frequency transformer is connected to the high-voltage grid, and the other end is connected to the AC load. The three-stage dual-parallel converter is connected in parallel with the power frequency transformer. The power sampling circuit acquires the voltage and current of the AC load and outputs an analog voltage signal. The hysteresis comparator circuit evaluates the operating conditions of the analog voltage signal and outputs a binary status signal. The combined controller acquires the binary status signal and the fault signal of the three-stage dual-parallel converter, and controls the operating state of the power frequency transformer and the three-stage dual-parallel converter. This invention solves the problems of low operating efficiency and uneven power distribution of existing transformers under light load, heavy load, and fault conditions.

Description

Technical Field

[0001] This invention belongs to the field of power electronic transformer technology, specifically relating to a hybrid solid-state transformer for normal power optimization and its power distribution method. Background Technology

[0002] With the increasing penetration of renewable energy and the growing number of DC and nonlinear loads, traditional AC distribution networks face challenges such as increased difficulty in power quality control and insufficient operational flexibility. As a key component of the distribution network, the evolution of transformer technology directly impacts the level of grid intelligence. Currently, transformer technologies applied to distribution networks mainly fall into three categories: Traditional power frequency transformers (LFTs) are technologically mature, low-cost, and highly reliable, but they have limited functionality, only capable of voltage transformation and electrical isolation, lacking active control capabilities. They require additional auxiliary devices such as dynamic voltage restorers and active power filters, leading to system complexity and increased investment.

[0003] Solid-state transformers (SSTs) convert electrical energy through high-frequency power electronic conversion, offering advantages such as high controllability and the ability to integrate various power quality regulation functions. However, as full-power conversion devices, they involve numerous switching devices, complex structures, high costs, and significant operating losses, which restricts their large-scale commercial application.

[0004] Hybrid solid-state transformers (HSSTs) combine small-capacity power electronic converters with traditional power frequency transformers, balancing high reliability with flexible controllability and reducing the capacity requirements of power electronic converters. HSSTs, with their high efficiency and flexibility, are particularly suitable for distributed power grid connection and have great application potential in solid oxide fuel cells, lithium batteries, and distributed photovoltaics. Existing HSST research based on isolated DC / DC converters largely focuses on single power quality management functions, lacking systematic research on power collaborative allocation under different load conditions. Especially under light load, heavy load, and fault conditions, it is difficult to utilize circuit structure characteristics to achieve dynamic optimization of power allocation, failing to achieve optimal synergy between efficiency, reliability, and economy. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, the present invention provides a hybrid solid-state transformer and its power distribution method for normal power optimization. By connecting a three-stage dual-parallel converter in parallel with the power frequency transformer on both sides, and combining it with a hysteresis comparator circuit for multi-condition dynamic distribution, the invention solves the problem of low operating efficiency and uneven power distribution of existing transformers under light load, heavy load, and fault conditions, which are caused by focusing only on power quality compensation or fault backup.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a hybrid solid-state transformer for normal power optimization, comprising: a power frequency transformer, a three-stage dual parallel converter connected in parallel with the power frequency transformer, and an externally connected power sampling circuit, a hysteresis comparison circuit, and a combined controller. One end of the power frequency transformer is connected to the high-voltage power grid to obtain the high-voltage power grid end, and the other end is connected to the AC load to obtain the AC load end; The input terminal of the three-stage dual-parallel converter is connected in parallel with the high-voltage grid terminal of the power frequency transformer, and the output terminal is connected in parallel with the AC load terminal of the power frequency transformer. The power sampling circuit is connected to the AC load, and the combined controller is connected to the three-stage dual parallel converter.

[0007] Furthermore: the power frequency transformer is used to bear the base power during normal operation and to independently supply power to the AC load when the three-stage double parallel converter is disconnected; The three-stage dual-parallel converter is used to dynamically connect to the power frequency transformer according to the load power, and to bear part of the power when connected; The power sampling circuit is used to acquire the voltage and current of the AC load and output an analog voltage signal; The hysteresis comparator circuit is used to evaluate the operating condition of the analog voltage signal against a preset threshold and output a binary status signal. The combined controller is used to acquire binary status signals and fault signals of the three-stage dual parallel converter, and output control signals to control the working status of the power frequency transformer and the three-stage dual parallel converter.

[0008] Furthermore: the three-stage dual-parallel converter includes a rectifier, an isolated DC / DC converter, and an inverter connected in sequence; The rectifier is used to convert high-voltage alternating current into high-voltage direct current; The isolated DC / DC converter is used for electrical isolation through a dual active bridge structure; The inverter is used to output AC current and AC voltage in different operating modes.

[0009] The input side of the rectifier is the input terminal of a three-stage dual-parallel converter, and the output side of the inverter is the output terminal of a three-stage dual-parallel converter.

[0010] The further beneficial effects mentioned above are as follows: Existing hybrid solid-state transformers require an additional coupling transformer for electrical isolation in their power electronic stage, resulting in low power density and a single inverter operating mode. This invention employs a dual active bridge structure for isolation, eliminating the need for a coupling transformer and improving power density. Furthermore, the inverter is equipped with both grid-connected and load modes, enabling seamless switching between collaborative operation and independent power supply.

[0011] Furthermore: the isolated DC / DC converter includes a primary-side full-bridge inverter circuit, a high-frequency transformer, and a secondary-side full-bridge rectifier circuit connected in sequence; The input terminal of the primary-side full-bridge inverter circuit is connected to the output terminal of the rectifier, the output terminal of the primary-side full-bridge inverter circuit is connected to the primary winding of the high-frequency transformer, the secondary winding of the high-frequency transformer is connected to the input terminal of the secondary-side full-bridge rectifier circuit, and the output terminal of the secondary-side full-bridge rectifier circuit is connected to the input terminal of the inverter.

[0012] The further beneficial effects mentioned above are as follows: Existing technologies using back-to-back converters require additional coupling transformers, resulting in low power density and large size. This invention employs a dual active bridge structure, achieving electrical isolation through a high-frequency transformer, eliminating the need for a power frequency coupling transformer, reducing system size, increasing power density, and simultaneously ensuring the flexible online switching capability of the power electronic converter.

[0013] This invention also provides a power allocation method for a hybrid solid-state transformer for normal power optimization, comprising the following steps: The load power is calculated by collecting the voltage and current of the AC load through the power sampling circuit. Based on the load power, the operating condition range is determined by the hysteresis comparator circuit to obtain the operating condition code that identifies different operating conditions; Based on the operating condition code and combined with the fault signal obtained by the combined controller from the three-stage dual parallel converter, the control signal is output. Based on the control signal, the combined controller outputs to the power frequency transformer and the three-stage dual parallel converter to complete the dynamic distribution of load power between the power frequency transformer and the three-stage dual parallel converter.

[0014] Furthermore: the operating conditions include no-load operating conditions, light-load operating conditions, normal-load operating conditions, heavy-load operating conditions, and fault operating conditions; The no-load condition is as follows: the fault signal is normal, and the load power is less than the first threshold; the corresponding control signal is that the power frequency transformer is working and the three-stage dual parallel converter is disconnected. The light load condition is as follows: the fault signal is normal, the load power is greater than the first threshold and less than the second threshold; the corresponding control signal is that the power frequency transformer is disconnected, the three-stage dual parallel converter is working, and the inverter is switched to load mode. The normal operating condition is as follows: the fault signal is normal, the load power is greater than the second threshold and less than the third threshold; the corresponding control signal is that both the power frequency transformer and the three-stage dual parallel converter are working, the inverter switches to grid-connected mode, and the amplitude of the inverter current command signal is a fixed compensation value divided by the effective value of the load rated voltage. The product; The heavy-load operating condition is as follows: the fault signal is normal, and the load power is greater than the third threshold; the corresponding control signal is that both the power frequency transformer and the three-stage dual parallel converter are working, the inverter switches to grid-connected mode, and the amplitude of the inverter current command signal is the load power minus the base power value divided by the effective value of the load rated voltage. The product; The fault condition is as follows: the fault signal indicates that the three-stage dual-parallel converter has failed; the corresponding control signal is: the power frequency transformer is working, and the three-stage dual-parallel converter is disconnected. The fixed compensation value is the power value undertaken by the three-stage dual-parallel converter under normal load conditions, and the base power value is the base power value undertaken by the power frequency transformer under heavy load conditions.

[0015] The further beneficial effects mentioned above are as follows: Existing technologies only use power electronic converters for power quality compensation or fault backup. Under light loads, the no-load loss of the power frequency transformer is large, and under heavy loads, it is prone to overload. This invention divides the load power into five operating conditions and dynamically allocates power: under light loads, the converter supplies power separately to reduce losses; under heavy loads, it undertakes excess power to avoid overload; and under faults, it automatically bypasses to ensure power supply reliability, thus achieving synergistic optimization of efficiency, reliability, and economy.

[0016] The beneficial effects of this invention are: In existing hybrid solid-state transformers, the power electronic stage is only used for power quality compensation or fault redundancy, while the power frequency transformer is always online. This results in high no-load losses under light loads and the risk of overload under heavy loads. This invention adopts a dual-side fully parallel structure of a power frequency transformer and a three-stage dual-parallel converter. It utilizes the electrical isolation characteristics of the dual active bridges to achieve flexible online switching of the converter. Combined with the dual-mode operation capability of the inverter, power is dynamically allocated according to the load power: under light loads, the converter supplies power alone, and under no-load conditions, the converter is disconnected, effectively reducing the system's no-load and light-load losses; under heavy loads, the converter bears the excess power, avoiding overload of the power frequency transformer and extending the equipment life.

[0017] Existing solid-state transformers operate at full power, resulting in numerous switching devices, high costs, and low reliability. This invention requires only a small-capacity power electronic converter, which optimizes normal power output to share part of the load of the power frequency transformer, reducing the capacity requirements and manufacturing costs of the power electronic components. At the same time, it avoids the need for grid capacity expansion due to short-term heavy loads, thus exhibiting excellent economic efficiency.

[0018] This invention automatically bypasses the power electronic converter when it fails, and supplies it independently by the power frequency transformer, thus achieving a redundant design and ensuring power supply reliability; moreover, the converter is easy to replace and has low maintenance costs.

[0019] This invention employs a dual active bridge structure to achieve electrical isolation, eliminating the need for a power frequency coupling transformer. The system is small in size and has high power density. The dual-mode design of the inverter enables seamless switching between grid-connected and off-grid modes, providing flexible control and making it suitable for various application scenarios. Attached Figure Description

[0020] Figure 1 A schematic diagram of a hybrid solid-state transformer used for normal power optimization; Figure 2 The current and voltage waveforms when the AC load changes from a heavy load of 110kW to a normal load of 50kW. Figure 3 The current and voltage waveforms when the load changes from a light load of 10kW to a constant load of 50kW; Figure 4 The voltage and current waveforms are those of a sudden SST fault under normal load of 50kW. Detailed Implementation

[0021] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0022] Example 1 like Figure 1 The diagram shows a hybrid solid-state transformer for normal power optimization, which includes: a power frequency transformer, a three-stage dual-parallel converter connected in parallel with the power frequency transformer, and externally connected power sampling circuit, hysteresis comparator circuit and combined controller. One end of the power frequency transformer is connected to the high-voltage power grid to obtain the high-voltage power grid end, and the other end is connected to the AC load to obtain the AC load end; The input terminal of the three-stage dual-parallel converter is connected in parallel with the high-voltage grid terminal of the power frequency transformer, and the output terminal is connected in parallel with the AC load terminal of the power frequency transformer. The power sampling circuit is connected to the AC load, and the combined controller is connected to the three-stage dual parallel converter.

[0023] The power frequency transformer is used to bear the basic power during normal operation and to independently supply AC load when the three-stage double parallel converter is disconnected; The three-stage dual-parallel converter is used to dynamically connect to the power frequency transformer according to the load power, and to bear part of the power when connected; The power sampling circuit is used to acquire the voltage and current of the AC load and output an analog voltage signal; The hysteresis comparator circuit is used to evaluate the operating condition of the analog voltage signal against a preset threshold and output a binary status signal. The combined controller is used to acquire binary status signals and fault signals of the three-stage dual parallel converter, and output control signals to control the working status of the power frequency transformer and the three-stage dual parallel converter.

[0024] In existing hybrid solid-state transformer (HSST) technologies, power electronic converters (SSTs) are mostly used for power quality management functions such as voltage dip compensation and harmonic suppression, or only as a backup path during faults. In these schemes, the power frequency transformer is always connected in parallel to the grid and is in operation regardless of the load. This results in a high proportion of no-load losses in the power frequency transformer when the load is light, leading to low overall system efficiency. When the load is heavy, the power frequency transformer may face overload risks, requiring the replacement with a larger capacity transformer or grid capacity expansion. At the same time, the capacity of the SST is usually only a small part of the rated power, but in conventional schemes it is only put into use under abnormal operating conditions, resulting in very low daily utilization and wasted resources.

[0025] This invention utilizes the flexible and controllable characteristics of SST (Single-Stage Transformer) to design a three-stage dual-parallel converter, i.e., a power electronic converter with a three-stage dual-parallel structure. During normal operation, the power distribution between the power frequency transformer and the three-stage dual-parallel converter is dynamically adjusted according to the load power: under light load, the three-stage dual-parallel converter supplies power solely to eliminate the no-load loss of the power frequency transformer; under heavy load, the three-stage dual-parallel converter shares the excess power to avoid overloading the power frequency transformer. This simultaneously solves the problems of efficiency, reliability, and economy. The three-stage dual-parallel converter designed in this invention enables safe connection or disconnection from the power grid while the power frequency transformer is operating normally, without causing impact or faults. Simultaneously, the real-time judgment of load power is fast and reliable, avoiding frequent oscillations in the control signal caused by load power fluctuations near threshold boundaries.

[0026] In one embodiment of the present invention, the three-stage dual-parallel converter includes a rectifier, an isolated DC / DC converter, and an inverter connected in sequence. The present invention employs a three-stage dual-parallel converter, while the prior art typically uses a back-to-back converter structure, which requires an additional power frequency coupling transformer to achieve electrical isolation, resulting in a large system size, low power density, and inverters that mostly operate in a single mode, unable to simultaneously support grid-connected coordination and off-grid independent power supply. The isolated DC / DC converter of the present invention achieves electrical isolation without a power frequency coupling transformer, improving power density. At the same time, the inverter has both grid-connected mode and load mode operating capabilities, which can automatically switch according to operating conditions, overcoming the single-function shortcomings of the prior art.

[0027] The rectifier is used to convert high-voltage alternating current into high-voltage direct current; The isolated DC / DC converter is used for electrical isolation through a dual active bridge structure; The inverter is used to output AC current and AC voltage in different operating modes.

[0028] The input side of the rectifier is the input terminal of a three-stage dual-parallel converter, and the output side of the inverter is the output terminal of a three-stage dual-parallel converter.

[0029] In one embodiment of the present invention, the isolated DC / DC converter includes a primary-side full-bridge inverter circuit, a high-frequency transformer, and a secondary-side full-bridge rectifier circuit connected in sequence. Existing isolated DC / DC converters mostly use resonant converters or forward / flyback structures, which require complex active clamping or resonant networks under high input-output voltage ratio conditions. They have a large number of components, complex control, narrow soft-switching range, and low efficiency under light load. The present invention adopts a dual active bridge DAB topology, which achieves zero-voltage turn-on of the switching transistors over a wide load range through phase-shift control of the primary and secondary full-bridge circuits. It does not require additional resonant components, simplifies the circuit structure, and improves efficiency and power density under light load.

[0030] The input terminal of the primary-side full-bridge inverter circuit is connected to the output terminal of the rectifier, and the output terminal of the primary-side full-bridge inverter circuit is connected to the primary winding of the high-frequency transformer. The secondary winding of the high-frequency transformer is connected to the input terminal of the secondary-side full-bridge rectifier circuit, and the output terminal of the secondary-side full-bridge rectifier circuit is connected to the input terminal of the inverter. This invention utilizes a high-frequency transformer to achieve electrical isolation and, in conjunction with phase-shift control, achieves bidirectional power flow. It overcomes the shortcomings of existing technologies, such as low efficiency under light loads, numerous components, and complex control, and achieves efficient and compact isolated power conversion.

[0031] The operation process of the hybrid solid-state transformer for normal power optimization of the present invention is as follows: After power-on, the power frequency transformer and the three-stage dual parallel converter are put into operation simultaneously. At this time, the power sampling circuit collects the voltage and current at the AC load end in real time, calculates the load power and converts it into an analog voltage signal; the analog signal is sent to the hysteresis comparison circuit and compared with the preset first, second and third thresholds. The hysteresis characteristic is used to eliminate the oscillation of power at the threshold boundary and outputs a stable binary operating condition code to the combined controller; the combined controller reads the fault signal of the three-stage dual parallel converter at the same time, and generates a control signal according to the operating condition code and the fault signal according to the preset mapping rule; when the load power is less than the first threshold (no load) or a fault signal is received, the combined controller issues a command to disconnect the three-stage dual parallel converter, and only the power frequency transformer is powered independently. At this time, due to the electrical isolation characteristics of the dual active bridge, the disconnection of the converter will not cause any impact on the power frequency transformer; when the load power rises to between the first and second thresholds (light load) and there is no fault, the combined controller disconnects the power frequency transformer and the power frequency transformer is connected to the AC load. When the inverter switches to load mode, the three-stage dual parallel converter provides a stable AC voltage to the load independently, thus eliminating the no-load loss of the power frequency transformer. When the load power falls between the second and third thresholds (normal load), the power frequency transformer and the three-stage dual parallel converter operate simultaneously, and the inverter switches to grid-connected mode, outputting a stable AC current according to a fixed compensation value to achieve coordinated power distribution. When the load power exceeds the third threshold (heavy load), the two continue to operate in parallel, and the amplitude of the inverter output current increases linearly with the excess power. The three-stage dual parallel converter bears the portion exceeding the base power, avoiding overload of the power frequency transformer. Under any operating condition, if the three-stage dual parallel converter fails, the combined controller immediately disconnects it, and the system returns to the independent operation mode of the power frequency transformer, ensuring uninterrupted power supply. Throughout the entire process, all operating condition switching is based on the hardware output of the hysteresis comparator circuit, and with the help of the electrical isolation of the dual active bridges and the dual-mode capability of the inverter, online flexible switching and efficient power distribution between the power frequency transformer and the three-stage dual parallel converter are achieved.

[0032] Example 2 Based on the hybrid solid-state transformer for normal power optimization provided in Embodiment 1, the present invention also provides a power allocation method for the hybrid solid-state transformer for normal power optimization, comprising the following steps: The load power is calculated by collecting the voltage and current of the AC load through the power sampling circuit. Based on the load power, the operating condition range is determined by the hysteresis comparator circuit to obtain the operating condition code that identifies different operating conditions; Based on the operating condition code and combined with the fault signal obtained by the combined controller from the three-stage dual parallel converter, the control signal is output. Based on the control signal, the combined controller outputs to the power frequency transformer and the three-stage dual parallel converter to complete the dynamic distribution of load power between the power frequency transformer and the three-stage dual parallel converter.

[0033] In one embodiment of the present invention, the operating conditions include no-load, light-load, normal-load, heavy-load, and fault conditions. Existing power allocation strategies typically only set one or two operating conditions, and the judgment method uses software threshold comparison, lacking hardware hysteresis characteristics. This leads to frequent oscillations of the control signal when power fluctuates at threshold boundaries, reducing the lifespan of switching devices. The present invention uses a hysteresis comparison circuit to determine load power and outputs operating condition codes in hardware, avoiding critical oscillation problems. Simultaneously, it integrates fault and normal operating conditions into the allocation logic, achieving smooth switching of operating condition coverage.

[0034] The no-load condition is as follows: the fault signal is normal, and the load power is less than the first threshold; the corresponding control signal is that the power frequency transformer is working and the three-stage dual parallel converter is disconnected. The light load condition is as follows: the fault signal is normal, the load power is greater than the first threshold and less than the second threshold; the corresponding control signal is that the power frequency transformer is disconnected, the three-stage dual parallel converter is working, and the inverter is switched to load mode. The normal operating condition is as follows: the fault signal is normal, the load power is greater than the second threshold and less than the third threshold; the corresponding control signal is that both the power frequency transformer and the three-stage dual parallel converter are working, the inverter switches to grid-connected mode, and the amplitude of the inverter current command signal is a fixed compensation value divided by the effective value of the load rated voltage. The product; The heavy-load operating condition is as follows: the fault signal is normal, and the load power is greater than the third threshold; the corresponding control signal is that both the power frequency transformer and the three-stage dual parallel converter are working, the inverter switches to grid-connected mode, and the amplitude of the inverter current command signal is the load power minus the base power value divided by the effective value of the load rated voltage. The product; The fault condition is as follows: the fault signal indicates that the three-stage dual-parallel converter has failed; the corresponding control signal is: the power frequency transformer is working, and the three-stage dual-parallel converter is disconnected. The fixed compensation value is the power value undertaken by the three-stage dual-parallel converter under normal load conditions, and the base power value is the base power value undertaken by the power frequency transformer under heavy load conditions.

[0035] In a specific embodiment of the present invention, the first threshold can be set to 10W, the second threshold to 20kW, and the third threshold to 100kW, resulting in the power allocation strategy of the present invention as shown in Table 1:

[0036] Based on the operating conditions in Table 1, apply them to practical transformer applications, such as... Figure 2 The figure shows the current and voltage waveforms when the AC load changes from a heavy load of 110kW to a constant load of 50kW. Before the sudden change, the LFT current is approximately 214.96A, the SST output current is approximately 76.59A, and the load voltage is approximately 379.02V. The calculated power handled by the LFT is approximately 81.44kW, and the power handled by the SST is approximately 29.06kW. After the sudden change, the LFT current is approximately 83.47A, the SST output current is approximately 51.20A, and the load voltage is approximately 387.58V. The calculated power handled by the LFT is approximately 32.59kW, and the power handled by the SST is approximately 19.61kW.

[0037] like Figure 3 The figure shows the current and voltage waveforms when the load changes from a light load of 10kW to a constant load of 50kW. Before the sudden change, the LFT is disconnected with no output, the SST output current is approximately 27.74A, and the load voltage is approximately 385.44V, calculating that the SST handles approximately 10.69kW. After the sudden change, the LFT current is approximately 82.23A, the SST output current is approximately 52.48A, and the load voltage is approximately 387.58V, calculating that the LFT handles approximately 31.87kW and the SST handles approximately 20.34kW.

[0038] like Figure 4 The figure shows the voltage and current waveforms during a sudden SST failure under a normal load of 50kW. Before the failure, the LFT current was approximately 214.96A, the SST output current was approximately 76.585A, and the load voltage was approximately 379.02V. The calculated power handled by the LFT was approximately 81.44kW, and the power handled by the SST was approximately 29.06kW. After the failure, the LFT current was approximately 134.20A, the SST was disconnected with no output, and the load voltage was approximately 387.58V. The calculated power handled by the LFT was approximately 52.01kW.

[0039] The beneficial effects of this invention are: In existing hybrid solid-state transformers, the power electronic stage is only used for power quality compensation or fault redundancy, while the power frequency transformer is always online. This results in high no-load losses under light loads and the risk of overload under heavy loads. This invention adopts a dual-side fully parallel structure of a power frequency transformer and a three-stage dual-parallel converter. It utilizes the electrical isolation characteristics of the dual active bridges to achieve flexible online switching of the converter. Combined with the dual-mode operation capability of the inverter, power is dynamically allocated according to the load power: under light loads, the converter supplies power alone, and under no-load conditions, the converter is disconnected, effectively reducing the system's no-load and light-load losses; under heavy loads, the converter bears the excess power, avoiding overload of the power frequency transformer and extending the equipment life.

[0040] Existing solid-state transformers operate at full power, resulting in numerous switching devices, high costs, and low reliability. This invention requires only a small-capacity power electronic converter, which optimizes normal power output to share part of the load of the power frequency transformer, reducing the capacity requirements and manufacturing costs of the power electronic components. At the same time, it avoids the need for grid capacity expansion due to short-term heavy loads, thus exhibiting excellent economic efficiency.

[0041] This invention automatically bypasses the power electronic converter when it fails, and supplies it independently by the power frequency transformer, thus achieving a redundant design and ensuring power supply reliability; moreover, the converter is easy to replace and has low maintenance costs.

[0042] This invention employs a dual active bridge structure to achieve electrical isolation, eliminating the need for a power frequency coupling transformer. The system is small in size and has high power density. The dual-mode design of the inverter enables seamless switching between grid-connected and off-grid modes, providing flexible control and making it suitable for various application scenarios.

Claims

1. A hybrid solid-state transformer for optimizing normal power output, characterized in that, include: The system includes a power frequency transformer, a three-stage dual-parallel converter connected in parallel with the power frequency transformer, and an externally connected power sampling circuit, hysteresis comparator circuit, and combined controller. One end of the power frequency transformer is connected to the high-voltage power grid to obtain the high-voltage power grid end, and the other end is connected to the AC load to obtain the AC load end; The input terminal of the three-stage dual-parallel converter is connected in parallel with the high-voltage grid terminal of the power frequency transformer, and the output terminal is connected in parallel with the AC load terminal of the power frequency transformer. The power sampling circuit is connected to the AC load, and the combined controller is connected to the three-stage dual parallel converter.

2. The hybrid solid-state transformer for normal power optimization according to claim 1, characterized in that, The power frequency transformer is used to bear the basic power during normal operation and to independently supply AC load when the three-stage double parallel converter is disconnected; The three-stage dual-parallel converter is used to dynamically connect to the power frequency transformer according to the load power, and to bear part of the power when connected; The power sampling circuit is used to acquire the voltage and current of the AC load and output an analog voltage signal; The hysteresis comparator circuit is used to evaluate the operating condition of the analog voltage signal against a preset threshold and output a binary status signal. The combined controller is used to acquire binary status signals and fault signals of the three-stage dual parallel converter, and output control signals to control the working status of the power frequency transformer and the three-stage dual parallel converter.

3. The hybrid solid-state transformer for normal power optimization according to claim 2, characterized in that, The three-stage dual-parallel converter includes a rectifier, an isolated DC / DC converter, and an inverter connected in sequence. The rectifier is used to convert high-voltage alternating current into high-voltage direct current; The isolated DC / DC converter is used for electrical isolation through a dual active bridge structure; The inverter is used to output AC current and AC voltage in different operating modes. The input side of the rectifier is the input terminal of a three-stage dual-parallel converter, and the output side of the inverter is the output terminal of a three-stage dual-parallel converter.

4. The hybrid solid-state transformer for normal power optimization according to claim 3, characterized in that, The isolated DC / DC converter includes a primary-side full-bridge inverter circuit, a high-frequency transformer, and a secondary-side full-bridge rectifier circuit connected in sequence. The input terminal of the primary-side full-bridge inverter circuit is connected to the output terminal of the rectifier, the output terminal of the primary-side full-bridge inverter circuit is connected to the primary winding of the high-frequency transformer, the secondary winding of the high-frequency transformer is connected to the input terminal of the secondary-side full-bridge rectifier circuit, and the output terminal of the secondary-side full-bridge rectifier circuit is connected to the input terminal of the inverter.

5. A power allocation method for a hybrid solid-state transformer for normal power optimization according to any one of claims 1-4, characterized in that, Includes the following steps: The load power is calculated by collecting the voltage and current of the AC load through the power sampling circuit. Based on the load power, the operating condition range is determined by the hysteresis comparator circuit to obtain the operating condition code that identifies different operating conditions; Based on the operating condition code and combined with the fault signal obtained by the combined controller from the three-stage dual parallel converter, the control signal is output. Based on the control signal, the combined controller outputs to the power frequency transformer and the three-stage dual parallel converter to complete the dynamic distribution of load power between the power frequency transformer and the three-stage dual parallel converter.

6. The power allocation method for a hybrid solid-state transformer for normal power optimization according to claim 5, characterized in that, The operating conditions include no-load operating conditions, light-load operating conditions, normal-load operating conditions, heavy-load operating conditions, and fault operating conditions; The no-load condition is as follows: the fault signal is normal, and the load power is less than the first threshold; the corresponding control signal is that the power frequency transformer is working and the three-stage dual parallel converter is disconnected. The light load condition is as follows: the fault signal is normal, the load power is greater than the first threshold and less than the second threshold; the corresponding control signal is that the power frequency transformer is disconnected, the three-stage dual parallel converter is working, and the inverter is switched to load mode. The normal operating condition is as follows: the fault signal is normal, the load power is greater than the second threshold and less than the third threshold; the corresponding control signal is that both the power frequency transformer and the three-stage dual parallel converter are working, the inverter switches to grid-connected mode, and the amplitude of the inverter current command signal is a fixed compensation value divided by the effective value of the load rated voltage. The product; The heavy-load operating condition is as follows: the fault signal is normal, and the load power is greater than the third threshold; the corresponding control signal is that both the power frequency transformer and the three-stage dual parallel converter are working, the inverter switches to grid-connected mode, and the amplitude of the inverter current command signal is the load power minus the base power value divided by the effective value of the load rated voltage. The product; The fault condition is as follows: the fault signal indicates that the three-stage dual-parallel converter has failed; the corresponding control signal is: the power frequency transformer is working, and the three-stage dual-parallel converter is disconnected. The fixed compensation value is the power value undertaken by the three-stage dual-parallel converter under normal load conditions, and the base power value is the base power value undertaken by the power frequency transformer under heavy load conditions.

Images