Fault-tolerant control system and method for solid state transformer based on redundancy control of power units

Abstract

The application discloses a solid-state transformer fault-tolerant control system based on power unit redundancy control, comprising an input end and an output end, the input end is connected with an alternating current power grid in a star connection mode through a plurality of modular power units connected in series per phase, and the output end obtains a low-voltage direct-current bus through parallel connection of the power units. The application further discloses a solid-state transformer fault-tolerant control method based on power unit redundancy control, and solves the problems of large current impact, slow input of redundant backup units and low utilization rate of power unit redundancy in the process of switching of existing faulty power units and redundant backup power units.

Description

Technical Field

[0001] This invention belongs to the field of solid-state transformer fault-tolerant control technology, specifically relating to a solid-state transformer fault-tolerant control system based on power unit redundancy control, and also to a solid-state transformer fault-tolerant control method based on power unit redundancy control. Background Technology

[0002] With the increasing demands for power continuity and power quality in fields such as smart grids, rail transit, fast charging for electric vehicles, and data centers, solid-state transformers (SSTs) are gradually being adopted in engineering applications due to their advantages, such as fewer voltage transformation stages. SSTs are typically composed of multiple modular power units connected in series at the input and output (ISOP) stages. To address the risk of system downtime caused by the failure of a single power unit, SSTs generally employ a redundant design of N+X (X≥1) power units to enhance the system's fault tolerance. When any power unit fails, the faulty unit can be disconnected from the system, while the remaining power units continue operating, maintaining continuous power supply. The key to power unit disconnection is configuring bypass switches for the power units. These typically use semiconductor, mechanical, or a combination of both bypass switches, enabling rapid and reliable power unit disconnection.

[0003] Chinese patent "A Fault Redundancy Protection System and Fault Clearing Method for Power Electronic Transformers" (Application Date: 2017.03.23; Application No.: CN201710179578.1; Publication Date: 2019.04.05; Publication No.: CN107124096B) discloses that the redundant module is not put into operation when it is normal, and is put into operation when the fault module is deactivated. When switching between the fault module and the redundant module, the modulation wave of the H-bridge converter of the fault module is directly forwarded to the redundant module. However, in practice, the internal DC voltage of the fault module may be different from that of the redundant module. Directly replacing the modulation wave of the H-bridge converter of the fault module will cause the DC voltage of the redundant module to fluctuate and the system current to oscillate.

[0004] Chinese patent "An Optimized Fault-Tolerant Control Method Applicable to Cascaded Solid-State Transformers" (Application Date: 2024.11.19; Application No.: CN202411655384.0; Publication Date: 2025.02.18; Publication No.: CN119483226A) discloses a method for activating redundant modules when a faulty module is bypassed. However, the initial DC bus voltage of the redundant module is zero, requiring pre-charging before activation. Since the faulty module has been removed, the remaining modules will bear the power deficit, necessitating consideration of power overload in module design. Furthermore, the solution does not explain how the redundant module transitions from a disabled state to an activated state.

[0005] Chinese patent "A Seamless Fault-Tolerant Control Method for Solid-State Transformers Based on Cascaded H-Bridge Pre-Charging" (Application Date: 2025.05.12; Application No.: CN202510606601.5; Publication Date: 2025.08.05; Publication No.: CN120433595A) discloses a method of disconnecting the bypass switch and switching the H-bridge from control voltage mode to control current mode when pre-charging redundant power modules. However, it does not explain how the current command is given in current mode to balance the input power of normal modules and the pre-charging of redundant modules. During the intermittent charging of redundant modules, this method requires frequent switching of the bypass switch and changes in the modulation command of the H-bridge, which affects the service life of the bypass switch to some extent. At the same time, the switching logic is relatively complex, and the switching timing and logic between the bypass switch and the module pre-charging control are not explained.

[0006] Although existing patents have disclosed power unit redundancy control systems and methods, the existing methods still have the following significant shortcomings, which restrict the improvement of the reliability and intelligence level of solid-state transformers: (1) One-way power unit cut-off: Some existing technologies only support one-way cut-off operations after a power unit failure. Once a power unit is bypassed, the corresponding faulty power unit is permanently isolated and taken out of operation, and cannot be put back into operation after the fault is cleared, resulting in the one-time consumption of redundant resources and the irrecoverable fault tolerance of the system. (2) Deterioration of power quality after power unit cut-off: During and after the cut-off of the faulty power unit, the harmonic content of the grid current increases, the system current and power fluctuate, and thus affect the stability of the output voltage. (3) No support for online commissioning and hot-start: Whether it is a power unit that is cut off due to a temporary fault or a power unit that has been in a cold standby state for a long time, it is impossible to quickly and without disturbance be put back into operation without shutting down the system, resulting in low utilization of redundant resources and limiting the application depth of solid-state transformers in 24 / 7 high-availability scenarios such as data centers and rail transit. (4) The pre-charging strategy is complex when the power unit is put into operation: Before the power unit is put into operation, the internal bus capacitor needs to be pre-charged. Most existing strategies rely on the H-bridge part of the cascaded side of the power unit to pre-charge the internal bus of the redundant power unit to be put into operation by controlling the bypass switch and the modulation signal of the cascaded H-bridge. However, this strategy requires repeated adjustment of the modulation signal of the cascaded H-bridge and frequent switching on and off of the bypass switch, which is complex to implement. Moreover, due to the large internal bus capacitor, the pre-charging time is long and cannot achieve millisecond-level fast switching. Summary of the Invention

[0007] The purpose of this invention is to provide a fault-tolerant control system for solid-state transformers based on power unit redundancy control, which solves the problems of large current surges, slow activation of redundant backup units, and low utilization rate of power unit redundancy during the switching process of existing faulty power units and redundant backup power units.

[0008] The first technical solution adopted in this invention is a solid-state transformer fault-tolerant control system based on power unit redundancy control, including an input end and an output end. Each phase of the input end is connected in series with several modular power units and connected to the AC power grid in a star connection manner. The output end is connected in parallel with power units to obtain a low-voltage DC bus.

[0009] The invention is further characterized in that, Each power unit includes a set of H-bridge converters and isolated DC / DC converters. The inputs of the H-bridge converters are connected in series, and their outputs are connected to the inputs of the DC / DC converters, sharing an internal DC bus. The DC / DC converters use isolated converter circuits, and their outputs are connected in parallel to form the DC output bus of a solid-state transformer. Each H-bridge converter and DC / DC converter is controlled by a corresponding power unit controller, which is communicatively connected to the main controller. The input and output sides of the DC / DC converters are isolated by a high-frequency transformer. The input side of the DC / DC converter shares a power unit controller with the H-bridge converters, and the power unit controller is connected to an auxiliary power supply.

[0010] Each power unit includes a set of bypass switches, which consists of a semiconductor bypass switch and a mechanical bypass switch connected in parallel. The bypass switches are connected in parallel at the input of the H-bridge converter. The bypass switches of the power units are controlled by the power unit controller, and the power supply is also provided by the auxiliary power supply. The bypass switches short-circuit the input of the power unit, disconnecting the power unit from the solid-state transformer system. In addition, when the power unit is put into operation, the bypass switches are disconnected to put the power unit into the solid-state transformer system operation sequence.

[0011] Each power unit includes a power unit controller a and a power unit controller b; power unit controller a is powered by auxiliary power supply a, which is connected to the DC bus V. dc_H Power is supplied via auxiliary power supply a, which adapts to a wide range of voltage inputs to ensure reliable power supply to the power unit. The output side of the DC / DC converter of the power unit is controlled by the power unit controller b, and the auxiliary power supply b supplies power to the DC bus V. dc_LPower is drawn from the auxiliary power supply b, which can also adapt to a wide input voltage range; a bidirectional communication network is constructed between power unit controller a and power unit controller b, and each has a bidirectional communication network with the main controller. The communication data between power unit controller a and power unit controller b and the main controller is the same, ensuring that the main controller can control different parts of the power unit at any time to achieve control functions.

[0012] The bypass switch of the power unit is controlled by the power unit controller a, and the power supply is also provided by the auxiliary power supply a. The power unit controller a outputs control signals to the semiconductor bypass switch S1 and the mechanical bypass switch K1 respectively, so as to realize the opening and closing of the semiconductor bypass switch S1 and the mechanical bypass switch K1. The semiconductor bypass switch S1 and the mechanical bypass switch K1 respectively feed back their switching status to the power unit controller a, and the power unit controller a judges the result of the bypass execution based on the status of the bypass switch.

[0013] When the power unit is not in operation as a redundant backup unit, it exists in two states: cold standby and hot standby. In cold standby, the internal PWM of the power unit is completely locked, the power unit is not working, the bypass switch at the H-bridge input port is closed, and only the DC / DC output side of the power unit remains connected in parallel with the DC bus. In hot standby, the internal bus capacitor of the power unit does not require pre-charging and can be quickly put into operation within a very short time. In hot standby, the internal bus voltage V... dc_H It is controlled by a DC-DC converter, and the voltage command is equal to the voltage command of the power unit during normal operation.

[0014] The second technical solution adopted in this invention is a fault-tolerant control method for solid-state transformers based on power unit redundancy control, which is implemented according to the following steps: First, power units are disconnected; then, the power unit online commissioning process is carried out; power units in redundant standby state have two states, namely cold standby state and hot standby state. A redundant power unit in cold standby state is commissioned, and the power unit first enters the hot standby state before being put into system operation.

[0015] The invention is further characterized by: Step 1, the specific steps for cutting off the power unit are: Step 1.1: The main controller issues a cut-off command to the two power unit controllers in the corresponding power unit. The power unit blocks the H-bridge and the DC / DC PWM signal. The main controller updates the modulation instructions of the remaining running power units. Step 1.2: Power unit controller a controls semiconductor bypass switch S1 to close and performs status detection and judgment. Step 1.3: After the semiconductor bypass switch S1 is correctly closed, the main controller issues a command to close the mechanical bypass switch K1 to perform status detection and judgment. Step 1.4: After the mechanical bypass switch K1 is correctly closed, disconnect the semiconductor bypass switch S1, leaving only the mechanical bypass switch K1 closed, and disconnect the corresponding power unit from the solid-state transformer system.

[0016] Step 2, online power unit activation specifically involves: When a power unit is not in operation as a redundant backup unit, it exists in two states: cold standby and hot standby; activating a power unit in cold standby state, when V... dc_H When the voltage reaches the rated voltage command of the power unit, the power unit enters hot standby mode and waits to be put into operation.

[0017] The specific process of activating power units that are in cold standby mode is as follows: Step 2.1: When a redundant power unit in cold standby state is put into operation, the main controller sends a state switching command to the power unit controller b of the power unit to be put into operation through the communication network. When the power unit is in cold standby mode, all internal PWMs are locked, mechanical bypass switch K1 is closed, and semiconductor bypass switch S1 is open; the power unit communicates normally with the main controller through power unit controller b, while communication between power unit controller a and the main controller and power unit controller b is interrupted.

[0018] Step 2.2: After receiving the command, the power unit controller b enters the pre-charge mode; Control the internal DC / DC converter of the power unit to achieve control over the internal V dc_H Voltage control, when V dc_H When the starting voltage of auxiliary power supply a is exceeded, auxiliary power supply a starts to work, supplies power to power unit controller a, and power unit controller a resumes communication with the main controller and power unit controller b; Step 2.3, DC / DC converter to V dc_H Perform closed-loop control; DC / DC converters complete internal V-phase control by adjusting switching frequency, duty cycle, or shift ratio, etc. dc_H Voltage control; where V dc_H The voltage command and the V of the solid-state transformer system currently operating power unit dc_H The voltage command is the same, thus completing V. dc_H The voltage is synchronized with the voltage of the solid-state transformer system; Step 2.4: In hot standby mode, the internal DC / DC PWM is unlocked, and the unit operates in hot standby voltage regulation mode. The input-side H-bridge PWM is locked, the mechanical bypass switch K1 is closed, and the semiconductor bypass switch S1 is open. The power unit is in hot standby level I state. At this time, the hot standby power unit cannot be put into operation quickly. When the power unit is put into operation, the mechanical bypass switch K1 needs to be opened, which has a certain delay. Step 2.5: Before the power unit in hot standby is put into operation, it enters the hot standby level II state. From hot standby level I to level II, the power unit controller a first closes the semiconductor bypass switch S1. After detecting the closed state of the semiconductor bypass switch S1, it then opens the mechanical bypass switch K1. After detecting the open state of the mechanical bypass switch K1, the power unit enters the hot standby level II state. Step 2.6: When the power unit in hot standby is in hot standby level II state, it can be put into operation at any time. When the main controller issues a further start command to the power unit in hot standby level II state, at the same time, the modulation instructions of all power units are updated. The modulation instructions of the input H-bridge converter include the modulation wave and the carrier phase shift angle. The modulation instructions of the DC / DC converter include the carrier frequency, duty cycle, and phase shift ratio. The DC / DC converter switches the operating mode from the internal bus voltage regulation mode to the normal output voltage control mode.

[0019] Step 2.7: Power unit controller a and power unit controller b simultaneously receive the activation command, the H-bridge, and the DC / DC modulation command. Then, power unit controller a disconnects the semiconductor bypass switch S1. After confirming the disconnection, the power unit to be activated unlocks the PWM of the H-bridge converter and is controlled by the modulation command issued by the main controller. The DC / DC converter switches its operating mode and is controlled by the modulation command issued by the main controller. The remaining operating power units continue to operate according to the adjusted modulation command issued by the main controller. At this point, the power unit completes the switch from hot standby Level II state to normal operation state and is put into operation.

[0020] The beneficial effects of the present invention are that the solid-state transformer fault-tolerant control system based on power unit redundancy control has the following advantages; (1) It breaks through the limitation that the power unit can only be cut off in one direction in the traditional technical solution. It can switch the power unit in both directions online, which can quickly isolate it in case of failure and quickly and without disturbance put it back into operation in the fault recovery or standby state.

[0021] (2) By introducing a power unit pre-charge control and H-bridge modulation command real-time compensation strategy, the voltage surge on the grid side is effectively suppressed at the moment of power unit switching, ensuring that the fluctuations of output voltage and current are within the range required for operation. This avoids the unreliability of using H-bridge for pre-charging and fundamentally solves the problems of slow power unit pre-charging speed, complex control strategy, and power quality deterioration caused by switching in the existing technology. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the solid-state transformer fault-tolerant control system based on power unit redundancy control of the present invention; Figure 2 This is a schematic diagram of the power unit connection architecture of the present invention; Figure 3 This is a flowchart of the power unit removal process of the present invention; Figure 4 This is a flowchart of the power unit input process of the present invention.

[0023] In the diagram, 1. Power unit controller a, 2. Auxiliary power supply a, 3. Power unit controller b, 4. Auxiliary power supply b. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0025] Example 1 The present invention relates to the structure of a solid-state transformer fault-tolerant control system based on power unit redundancy control, as follows: Figure 1 As shown, it includes an input terminal and an output terminal. Each phase of the input terminal is connected in series through several modular power units and connected to the AC power grid in a star connection manner. The output terminal is connected in parallel through power units to obtain a low-voltage DC bus.

[0026] Example 2 Based on Example 1, each power unit in this embodiment includes a set of H-bridge converters and isolated DC / DC converters. The input terminals of the H-bridge converters are connected in series, and the output terminals are connected to the input terminals of the DC / DC converters, sharing an internal DC bus. The DC / DC converters adopt isolated conversion circuits, and their output terminals are connected in parallel to form the DC output bus of the solid-state transformer. Each H-bridge converter and DC / DC converter is controlled by a corresponding power unit controller, which is communicatively connected to the main controller. The input and output sides of the DC / DC converters are isolated by a high-frequency transformer. The input side of the DC / DC converter shares a power unit controller with the H-bridge converter, and each power unit controller is connected to an auxiliary power supply.

[0027] Example 3 Based on Example 2, in this embodiment, each power unit includes a set of bypass switches. The set of bypass switches includes a semiconductor bypass switch and a mechanical bypass switch connected in parallel. The bypass switches are connected in parallel at the input of the H-bridge converter. The bypass switches of the power units are controlled by the power unit controller, and the power supply is also provided by the auxiliary power supply. The bypass switches short-circuit the input of the power unit, disconnecting the power unit from the solid-state transformer system. In addition, when the power unit is put into operation, the bypass switches are disconnected to put the power unit into the solid-state transformer system operation sequence.

[0028] Example 4 Based on Example 3, this embodiment is as follows: Figure 2 As shown, each power unit includes a power unit controller a1 and a power unit controller b3; the power unit controller a1 is powered by an auxiliary power supply a2, which is connected to the DC bus V. dc_H Power is supplied via auxiliary power supply a2, which adapts to a wide range of voltage inputs to ensure reliable power supply to the power unit. The output side of the power unit's DC / DC converter is controlled by the power unit controller b3, and the power is supplied via auxiliary power supply b4 to the DC bus V. dc_L Power is drawn from the auxiliary power supply b4, which can also adapt to a wide input voltage range. A two-way communication network is constructed between the power unit controller a1 and the power unit controller b3, and they also have a two-way communication network with the main controller. The communication data between the power unit controller a1 and the power unit controller b3 and the main controller is the same, ensuring that the main controller can control different parts of the power unit at any time to achieve control functions.

[0029] The bypass switch of the power unit is controlled by the power unit controller a1, and the power supply is provided by the auxiliary power supply a2. The power unit controller a1 outputs control signals to the semiconductor bypass switch S1 and the mechanical bypass switch K1 respectively, realizing the opening and closing of the semiconductor bypass switch S1 and the mechanical bypass switch K1. The semiconductor bypass switch S1 and the mechanical bypass switch K1 respectively feed back their switching status to the power unit controller a1, and the power unit controller a1 determines the result of the bypass execution based on the status of the bypass switches.

[0030] The semiconductor bypass switch S1 of the power unit has a short turn-on and turn-off delay time, but the circuit cannot maintain its original state when the auxiliary power supply a2 is lost. The mechanical bypass switch K1 has a larger switching delay, but it can maintain its original state after the auxiliary power supply a2 is lost.

[0031] When a power unit fails and cannot continue to operate, or when the main controller needs to disconnect a power unit (rotation operation, disconnecting one group of power units and putting on another group of power units), the main controller sends a disconnect command to the corresponding power unit. The power unit controller then locks all PWM of the corresponding power unit and closes the bypass switch to disconnect the power unit.

[0032] The disconnected power unit will lose its ability to control the internal bus voltage, and the internal capacitor voltage V of the power unit will decrease. dc_H The power supply will drop to 0, the auxiliary power supply a2 will be unable to provide a stable power supply to the power unit controller a1, the power unit controller a1 will stop working, and the communication between the power unit controller a1, the power unit controller b3 and the main controller will be interrupted.

[0033] Since the auxiliary power supply b4 draws power from the output DC bus and operates normally, it ensures the normal operation of the power unit controller b3. Even after the power unit is disconnected from the solid-state transformer system, the power unit controller b3 continues to communicate with the main controller. The main controller uses the power unit controller b3 to enable the output of the DC-DC converter to perform soft-start charging on the DC bus inside the power unit.

[0034] When the power unit is not in operation as a redundant backup unit, it exists in two states: cold standby and hot standby. In cold standby, the internal PWM of the power unit is completely locked, the power unit is not working, the bypass switch at the H-bridge input port is closed, and only the DC / DC output side of the power unit remains connected in parallel with the DC bus. In hot standby, the internal bus capacitor of the power unit does not require pre-charging and can be quickly put into operation within a very short time. In hot standby, the internal bus voltage V... dc_H It is controlled by a DC-DC converter, and the voltage command is equal to the voltage command of the power unit during normal operation.

[0035] This invention relates to a solid-state transformer fault-tolerant control system based on power unit redundancy control. Several modular power units are cascaded and connected in parallel. Each modular power unit receives a medium-voltage AC power grid as input and outputs a low-voltage DC power. When a power unit fails, all PWM drive pulses of the failed power unit are first blocked, then the failed power unit is bypassed, and a redundant backup power unit is activated. The redundant backup power unit is pre-charged before activation, and its internal bus capacitor voltage remains at its rated value. The internal controller of the power unit draws power from the internal bus capacitor via an auxiliary power supply. When a power unit fails and stops operating, the internal bus capacitor voltage drops, losing its power supply capability to the internal controller. The power unit will then be unable to receive any external communication commands or perform any operations. The front-end H-bridge and DC / DC input stage of the power unit use the same controller, while the DC / DC output stage uses a separate controller. The two controllers within the power unit have a communication connection and also communicate externally. Based on the internal self-powering mode and solid-state transformer fault-tolerant control technology, the power unit can be switched on and off quickly, bidirectionally and without disturbance, thereby improving the fault-tolerant operation capability of the solid-state transformer. It has significant improvements in the process of disturbanceless disconnection of faulty power units, pre-charging of redundant power units, and smooth switching between faulty power units and redundant power units.

[0036] Example 5 This invention relates to a fault-tolerant control method for solid-state transformers based on power unit redundancy control. First, power units are disconnected; then, an online power unit activation process is performed. Power units in redundant standby state have two states: cold standby state and hot standby state. When a redundant power unit in cold standby state is activated, the power unit enters the hot standby state and is then put into system operation.

[0037] Example 6 The present invention relates to a fault-tolerant control method for solid-state transformers based on power unit redundancy control, which is implemented according to the following steps; Step 1, the power unit removal process is as follows: Figure 3 As shown, specifically; Step 1.1: The main controller issues a cut-off command to the two power unit controllers in the corresponding power unit, blocking the PWM drive signals of the H-bridge and DC / DC converter. The main controller then updates the modulation instructions of the remaining operating power units. Step 1.2: The power unit controller controls the semiconductor bypass switch S1 to close and performs status detection and judgment. After the semiconductor bypass switch S1 is correctly closed, the next operation is performed; if the semiconductor bypass switch S1 is not detected to be closed after the delay, the semiconductor bypass switch S1 is faulty and the bypass operation cannot be performed. The power unit controller a1 generates a fault signal and sends it to the main controller through the communication network. The main controller generates a stop operation command and all power units stop operating. Step 1.3: After the semiconductor bypass switch S1 is correctly closed, the main controller issues a command to close the mechanical bypass switch K1 to perform status detection and judgment. If the mechanical bypass switch K1 is detected to be closed, proceed to the next step; otherwise, it indicates that the mechanical bypass switch K1 is faulty and the bypass operation cannot be performed. The power unit controller a1 generates a fault signal and sends it to the main controller through the communication network. The main controller generates a stop operation command, and all power units stop operating. Step 1.4: After the mechanical bypass switch K1 is correctly closed, disconnect the semiconductor bypass switch S1, leaving only the mechanical bypass switch K1 closed, and disconnect the corresponding power unit from the solid-state transformer system.

[0038] During bypass operation, the power unit H-bridge and DC / DC section require no further operation; after the power unit is disconnected, its internal capacitor voltage V dc_H The power supply will gradually decrease to 0, the auxiliary power supply a2 will stop working, the communication between the power unit controller a1 and the main controller and the power unit controller b3 will be interrupted, but the power unit controller b3 will still maintain normal communication with the main controller.

[0039] Step 2, the online power unit commissioning process is as follows: Figure 4 As shown, specifically, when a power unit is not in operation as a redundant backup unit, it has two states: cold standby and hot standby. First, the power unit in the cold standby state is activated, and when V... dc_H When the voltage of the power unit is synchronized with the system voltage, the power unit enters a hot standby state.

[0040] The specific process of activating power units that are in cold standby mode is as follows: Step 2.1: When a redundant power unit in cold standby state is put into operation, the main controller sends a state switching command to the power unit controller b3 of the power unit to be put into operation through the communication network. When the power unit is in cold standby mode, all internal PWMs are locked, mechanical bypass switch K1 is closed, and semiconductor bypass switch S1 is open; the power unit communicates normally with the main controller through power unit controller b3, while communication between power unit controller a1 and the main controller and power unit controller b3 is interrupted.

[0041] Step 2.2: After receiving the command, the power unit controller b3 enters the pre-charge mode; Control the internal DC / DC converter of the power unit to achieve control over the internal V dc_H Voltage control, when V dc_H When the starting voltage of auxiliary power supply a2 is exceeded, auxiliary power supply a2 starts to work and supplies power to power unit controller a1. Power unit controller a1 then resumes communication with the main controller and power unit controller b3.

[0042] Step 2.3, DC / DC converter to V dc_H Perform closed-loop control; DC / DC converters complete internal V-phase control by adjusting switching frequency, duty cycle, or shift ratio, etc. dc_H Voltage control; where V dc_H The voltage command and the V of the solid-state transformer system currently operating power unit dc_H The voltage command is the same, thus completing V. dc_H The voltage is synchronized with the solid-state transformer system voltage. At this time, the power unit enters hot standby mode.

[0043] Step 2.4: In the hot standby state, the internal DC / DC PWM is unlocked and the power unit operates in the hot standby voltage regulation mode. The input H-bridge PWM is locked, the mechanical bypass switch K1 is closed, and the semiconductor bypass switch S1 is open. The power unit is in the hot standby level I state. At this time, the hot standby power unit cannot be put into operation quickly. Before the power unit is put into operation, the mechanical bypass switch K1 needs to be opened, which has a certain delay. Step 2.5: When the redundant standby power unit is put into operation, it needs to enter the hot standby level II state. From the hot standby level I state to the level II state, the power unit controller a1 first closes the semiconductor bypass switch S1. After detecting the closed state of the semiconductor bypass switch S1, it then opens the mechanical bypass switch K1. After detecting the open state of the mechanical bypass switch K1, the power unit enters the hot standby level II state. Step 2.6: When the redundant standby power unit is in the hot standby level II state, it can be put into operation at any time. When the main controller issues a further start command to the power unit in the hot standby level II state, at the same time, the modulation instructions of all power units are updated. The modulation instructions of the input H-bridge converter include the modulation wave and the carrier phase shift angle. The modulation instructions of the DC / DC converter include the carrier frequency, duty cycle, and phase shift ratio. The DC / DC converter switches the operating mode from the internal bus voltage regulation mode to the normal output side voltage control mode.

[0044] Step 2.7: Power unit controllers a1 and b3 simultaneously receive the activation command, the H-bridge, and the DC / DC modulation command. Then, power unit controller a1 disconnects the semiconductor bypass switch S1. After confirming the disconnection (with a slight delay representing the power device's turn-off time), the power unit to be activated unlocks the PWM drive signal of the H-bridge converter and is controlled by the modulation command issued by the main controller. The DC / DC converter switches its operating mode and is controlled by the modulation command issued by the main controller. The remaining operating power units continue to operate according to the adjusted modulation command issued by the main controller. At this point, the power unit completes the switch from hot standby Level II state to normal operation state and is put into operation.

[0045] This invention presents a fault-tolerant control method for solid-state transformers based on power unit redundancy control. This method enables online disconnection and connection of power units in solid-state transformers, meeting diverse switching requirements. During online disconnection, power deficits can be quickly compensated by adjusting control commands, minimizing the impact of power unit disconnection on the system. During online connection, no additional hardware is required; the power unit itself performs pre-charging control of its internal capacitors. In hot standby mode, only a microsecond-level delay is needed to seamlessly connect the standby power unit to the system, improving the system stability of the solid-state transformer.

Claims

1. A fault-tolerant control system for solid-state transformers based on power unit redundancy control, characterized in that, It includes an input end and an output end. Each phase of the input end is connected in series through several modular power units and connected to the AC power grid in a star connection. The output end is connected in parallel through power units to obtain a low-voltage DC bus.

2. The solid-state transformer fault-tolerant control system based on power unit redundancy control according to claim 1, characterized in that, Each power unit includes a set of H-bridge converters and isolated DC / DC converters. The inputs of the H-bridge converters are connected in series, and their outputs are connected to the inputs of the DC / DC converters, sharing an internal DC bus. The DC / DC converters use isolated converter circuits, and their outputs are connected in parallel to form the DC output bus of a solid-state transformer. Each H-bridge converter and DC / DC converter is controlled by a corresponding power unit controller, which is communicatively connected to the main controller. The input and output sides of the DC / DC converters are isolated by a high-frequency transformer. The input side of the DC / DC converter shares a power unit controller with the H-bridge converters, and the power unit controller is connected to an auxiliary power supply.

3. The solid-state transformer fault-tolerant control system based on power unit redundancy control according to claim 2, characterized in that, Each power unit includes a set of bypass switches, which consists of a semiconductor bypass switch and a mechanical bypass switch connected in parallel. The bypass switches are connected in parallel at the input of the H-bridge converter. The bypass switches of the power units are controlled by the power unit controller, and the power supply is also provided by the auxiliary power supply. The bypass switches short-circuit the input of the power unit, disconnecting the power unit from the solid-state transformer system. In addition, when the power unit is put into operation, the bypass switches are disconnected to put the power unit into the solid-state transformer system operation sequence.

4. The solid-state transformer fault-tolerant control system based on power unit redundancy control according to claim 3, characterized in that, Each power unit includes a power unit controller a (1) and a power unit controller b (3); the power unit controller a (1) is powered by an auxiliary power supply a (2), which is connected to the DC bus V. dc_H Power is supplied by auxiliary power supply a(2), which adapts to a wide range of voltage inputs to ensure reliable power supply to the power unit; the output side of the DC / DC converter of the power unit is controlled by the power unit controller b(3), and the auxiliary power supply b(4) supplies power to the DC bus V. dc_L Power is drawn from the auxiliary power supply b(4), which can also adapt to a wide input voltage range. A two-way communication network is constructed between the power unit controller a(1) and the power unit controller b(3), and they also have a two-way communication network with the main controller. The communication data between the power unit controller a(1) and the power unit controller b(3) and the main controller is the same, ensuring that the main controller can control different parts of the power unit at any time to achieve the control function.

5. The solid-state transformer fault-tolerant control system based on power unit redundancy control according to claim 4, characterized in that, The bypass switch of the power unit is controlled by the power unit controller a(1), and the power supply is also provided by the auxiliary power supply a(2); the power unit controller a(1) outputs control signals to the semiconductor bypass switch S1 and the mechanical bypass switch K1 respectively, so as to realize the opening and closing of the semiconductor bypass switch S1 and the mechanical bypass switch K1. Semiconductor bypass switch S1 and mechanical bypass switch K1 respectively feed back their switching status to power unit controller a(1), and power unit controller a(1) determines the result of bypass execution based on the status of the bypass switches.

6. The solid-state transformer fault-tolerant control system based on power unit redundancy control according to claim 5, characterized in that, When the power unit is not in operation as a redundant backup unit, it exists in two states: cold standby and hot standby. In cold standby, the internal PWM of the power unit is completely locked, the power unit is not working, the bypass switch at the H-bridge input port is closed, and only the DC / DC output side of the power unit remains connected in parallel with the DC bus. In hot standby, the internal bus capacitor of the power unit does not require pre-charging and is rapidly put into operation within a very short time. The internal bus voltage V of the power unit in hot standby is... dc_H It is controlled by a DC-DC converter, and the voltage command is equal to the voltage command of the power unit during normal operation.

7. A fault-tolerant control method for solid-state transformers based on power unit redundancy control, characterized in that, The specific implementation is carried out according to the following steps: First, the power unit is disconnected; then the power unit online commissioning process is carried out; there are two states for power units in redundant standby state, namely cold standby state and hot standby state. When a redundant power unit in cold standby state is commissioned, the power unit enters hot standby state and is then put into system operation.

8. The solid-state transformer fault-tolerant control method based on power unit redundancy control according to claim 7, characterized in that, Step 1, the specific steps for cutting off the power unit are: Step 1.1: The main controller issues a cut-off command to the two power unit controllers in the corresponding power unit, blocking the PWM signal of the H-bridge and DC / DC converter. The main controller then updates the modulation instructions of the remaining operating power units. Step 1.2: The power unit controller controls the semiconductor bypass switch S1 to close for detection and judgment. Step 1.3: After the semiconductor bypass switch S1 is correctly closed, the main controller issues a command to close the mechanical bypass switch K1 to perform status detection and judgment. Step 1.4: After the mechanical bypass switch K1 is correctly closed, disconnect the semiconductor bypass switch S1, leaving only the mechanical bypass switch K1 closed, and disconnect the corresponding power unit from the solid-state transformer system.

9. The solid-state transformer fault-tolerant control method based on power unit redundancy control according to claim 8, characterized in that, Step 2, online power unit activation specifically involves: When a power unit is not in operation as a redundant backup unit, it exists in two states: cold standby and hot standby. First, the power unit in the cold standby state is activated. When V... dc_H When the voltage of the power unit is synchronized with the system voltage, the power unit enters a hot standby state.

10. The solid-state transformer fault-tolerant control method based on power unit redundancy control according to claim 9, characterized in that, The specific process of activating power units that are in cold standby mode is as follows: Step 2.1 When a redundant power unit in a cold standby state is put into operation, the main controller sends a state switching command to the power unit controller b(3) of the power unit to be put into operation through the communication network; When the power unit is in cold standby mode, all internal PWMs are locked, mechanical bypass switch K1 is closed, and semiconductor bypass switch S1 is open; the power unit communicates normally with the main controller through the power unit controller b (3), and the communication between the power unit controller a (1) and the main controller and the power unit controller b (3) is interrupted; Step 2.2, after receiving the command, the power unit controller b (3) enters the pre-charge mode; Control the internal DC / DC converter of the power unit to achieve control over the internal V dc_H Voltage control, when V dc_H When the starting voltage of the auxiliary power supply a(2) is exceeded, the auxiliary power supply a(2) starts to work and supplies power to the power unit controller a(1). The power unit controller a(1) resumes communication with the main controller and the power unit controller b(3). Step 2.3, DC / DC converter to V dc_H Perform closed-loop control; DC / DC converters complete internal V-phase control by adjusting switching frequency, duty cycle, or shift ratio, etc. dc_H Voltage control; where V dc_H The voltage command and the V of the solid-state transformer system currently operating power unit dc_H The voltage command is the same, thus completing V. dc_H The voltage is synchronized with the solid-state transformer system voltage; at this time, the power unit enters hot standby mode. Step 2.4: When the power unit is in hot standby mode, the internal DC / DC PWM is unlocked and the hot standby voltage regulation mode is adopted. The input H-bridge PWM is locked, the mechanical bypass switch K1 is closed, the semiconductor bypass switch S1 is open, and the power unit is in hot standby level I state. At this time, the hot standby power unit cannot be put into operation quickly. When the power unit is put into operation, the mechanical bypass switch K1 needs to be opened. Step 2.5 When the redundant standby power unit is put into operation, it needs to enter the hot standby level II state; from hot standby level I to level II state, the power unit controller a (1) first closes the semiconductor bypass switch S1. After detecting the closed state of the semiconductor bypass switch S1, it then opens the mechanical bypass switch K1. After detecting the open state of the mechanical bypass switch K1, the power unit enters the hot standby level II state. Step 2.6: When the redundant standby power unit is in the hot standby level II state, it can be put into operation at any time. When the main controller issues a further start command to the power unit in the hot standby level II state, at the same time, the modulation instructions of all power units are updated. The modulation instructions of the input H-bridge converter include the modulation wave and the carrier phase shift angle. The modulation instructions of the DC / DC converter include the carrier frequency, duty cycle, and phase shift ratio. The DC / DC converter switches the operating mode from the internal bus voltage regulation mode to the normal output side voltage control mode. Step 2.7: Power unit controller a (1) and power unit controller b (3) simultaneously receive the power-on command, the H-bridge, and the DC / DC modulation command. Then, power unit controller a (1) disconnects the semiconductor bypass switch S1, confirms that the power unit to be put into operation unlocks the PWM drive signal of the H-bridge converter after disconnection, and uses the modulation command issued by the main controller for control. The DC / DC converter switches its operating mode and is controlled by the modulation command issued by the main controller. The remaining power units in operation continue to operate according to the adjusted modulation command issued by the main controller. Thus, the power unit completes the switch from the hot standby level II state to the normal operating state and is put into operation.

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