Solid state transformer fault module bypass and spare module throw-in control method and system

Abstract

This invention provides a method and system for controlling the bypass of fault modules and the activation of backup modules in solid-state transformers, relating to the field of power electronic converters. The method comprises the following steps: Step S1: System startup and normal operation; Step S2: Fault detection and state switching preparation; Step S3: Vector control and current adjustment in state 2; Step S4: State 3 control after charging completion; Step S5: Soft starter resistor short circuit and state switching; Step S6: Restoration to normal operation. This invention achieves a smooth transition between fault module bypass and backup module activation through state machine and vector analysis; solves the inrush current problem during DC bus capacitor charging through soft starter design; ensures current controllability and system stability during switching through precise vector calculation; ensures multi-module harmonic cancellation through adaptive adjustment of carrier phase shift angle; and provides a complete four-state sequence covering the entire process from fault occurrence to complete recovery.

Description

Technical Field

[0001] The present invention relates to the field of power electronic converters, and more particularly, to a control method and system for bypassing a faulty module and inserting a spare module in a solid-state transformer. Background Art

[0002] The solid-state transformer can quickly adjust the power flow direction and amplitude through power electronic conversion technology, suppress power generation fluctuations, and improve the power grid's ability to absorb new energy. The solid-state transformer SST can also be used to form an intelligent microgrid. In the microgrids of industrial parks and remote areas, the solid-state transformer can achieve the interconnection between multiple microgrids and the seamless switching between the microgrid and the main grid, ensuring power supply reliability. The 800V DC power supply system with the solid-state transformer SST as the key conversion device effectively reduces the power supply transmission loss and copper consumption by reducing the AC-DC conversion link and increasing the voltage level, improves the overall operation efficiency from the system end to end, and greatly saves space occupancy, presenting good technical economy and voltage adaptability. Currently, in order to realize the direct power extraction of the solid-state transformer from the 10KV or 35KV power grid, the isolated solid-state transformer often adopts three design ideas. The first is to use semiconductor devices in series, the second is to use a modular multilevel converter structure, and the third is to use an input series, output parallel or input series, output series structure.

[0003] The existing design idea of the solid-state transformer relying on semiconductor devices in series is severely limited by the technological development of the semiconductor devices themselves. Although there are 10KV withstand voltage wide-bandgap semiconductor devices promoted in the market, they are expensive and difficult to be popularized and applied. In addition, the driving and protection technologies supporting high-voltage semiconductor devices are not yet mature; in the design ideas of solid-state transformers based on MMC and ISOP, a multi-module series connection method is adopted on the input medium-high voltage side, and there are redundant spare modules; according to whether the redundant module is put into the system to operate with other unit modules during normal operation, the redundant standby can be divided into two types: hot standby and cold standby. In hot standby, during normal operation, the redundant unit module operates with other unit modules. When a fault occurs, the faulty unit module is bypassed, and the total number of unit modules decreases. Cold standby means that the number of modules participating in normal operation before and after the fault remains unchanged. The SiCMOSFET power switch device has the same voltage stress and can theoretically fully recover to the normal operating state after removing the faulty module and inserting the redundant spare module. Whether it is cold standby or hot standby, there are too complex problems such as the charging operation of the DC bus capacitor inside the module, the modulation of each module, the timing coordination, and the control strategy switching during normal operation and fault switching. Summary of the Invention

[0004] The present invention aims to solve the problems of charging operation, bypass operation and carrier modulation of DC bus capacitor inside the module during normal operation and fault switching of multiple modules in series in existing solid-state transformers.

[0005] To address the aforementioned issues, this invention provides a method for controlling the bypass and backup module activation of a solid-state transformer fault module. This method is applied to a solid-state transformer, which includes a main power circuit and a control circuit. The main power circuit includes power module valve groups; each power module valve group comprises a three-phase power module valve group stack, with each phase power module valve group stack containing multiple power modules. The state of a solid-state transformer is as follows: State 1: n single-phase power modules participate in operation, and 1 power module is redundant and on standby; the bypass switch of the module participating in operation is open, and the soft starter switch inside the module is closed; the bypass switch of the redundant standby module is closed, and the soft starter switch inside the module is open. State 2: The faulty module is bypassed, the redundant backup module is engaged, and the DC bus capacitor starts charging from zero; the bypass switches of the n-1 modules involved in operation are open, and the soft starter switches within the modules are closed; the bypass switch of the faulty module is closed; the bypass switch of the redundant backup module is open, and the soft starter switches within the modules are open. Status 3: The DC bus capacitor of the redundant standby module is fully charged; the bypass switches of the n-1 modules participating in operation are open, and the soft starter switches within the modules are closed; the bypass switch of the faulty module is closed; the bypass switch of the redundant standby module is open, and the soft starter switches within the modules are open. Status 4: The DC bus capacitor of the redundant standby module is fully charged and the soft starter switch inside the module is closed and the resistor is short-circuited; n modules, including the redundant standby module, participate in the operation; The method and steps are as follows: Step S1: System startup and normal operation; After system startup, it enters state 1 and adopts carrier horizontal phase shift SPWM control with a phase shift angle of 2π / n. Step S2, Fault Detection and State Switching Preparation: After a module fault is detected, the bypass switch of the faulty module is closed, the bypass switch of the redundant backup module is opened, and the system enters state 2, using carrier horizontal phase-shifted SPWM control with a phase shift angle of 2π / (n-1). Step S3, Vector control and current adjustment in state 2; In state 2, the controller adjusts the phase current phase and amplitude to make the system meet the vector balance condition; Step S4, State 3 control after charging is complete; After the redundant backup module DC bus capacitor is charged, the system enters State 3 and maintains the control strategy of State 2. Step S5: Soft starter resistor short circuit and state switching; Close the soft starter switch inside the redundant backup module, and the system enters state 4; Step S6: Restore normal operation; In state 4, the controller switches the control strategy and restores to n-module carrier horizontal phase-shift SPWM control, with a phase shift angle of 2π / n and the load-side power is evenly distributed.

[0006] The present invention provides a method for controlling the bypass and backup module activation of a solid-state transformer fault module, which, compared with the prior art, has the following beneficial effects, but is not limited to: This invention achieves a smooth transition between bypassing faulty modules and engaging backup modules through state machines and vector analysis; solves the inrush current problem during DC bus capacitor charging through soft starter design; ensures current controllability and system stability during switching through precise vector calculation; ensures multi-module harmonic cancellation effect through adaptive adjustment of carrier phase shift angle; and covers the entire process from fault occurrence to complete recovery with a complete four-state sequence.

[0007] Furthermore, in step S3, the vector balance condition for state 2 is: the four vectors—grid voltage U, inductor voltage UL2 of the reactor, soft starter resistor voltage UR2 within the module, and equivalent value of the total output voltage of the power module chain US2—are closed, satisfying the following: UL2 = I2 × ωL, UR2 = I2 × R; The controller adjusts the phase of the phase current I2 to keep the current amplitude constant, thus maintaining the amplitude of UX2 = UL2 + UR2.

[0008] Furthermore, the amplitude and phase of the target phase current I2 in state 2 of step S2 are determined in the following manner: Based on the known parameters U, US1, I1, and Uy of state 1, the following calculations are performed using vector geometric relationships: By the Law of Cosines, we have: |UX2|=√(|U|²+|US2|²-2|U||US2|cosβ), where US2=US1-Uy; By the Law of Sines, we have: |U| / sinα = |US²| / sinμ = |UX²| / sinβ; The magnitude of I2 is determined by |UX2| / (ωL), and the phase of I2 is determined by μ.

[0009] Furthermore, in step S4, the vector parameters of state 3 satisfy the following: UX3 and UX2 have equal amplitudes, and US3 and US1 have equal amplitudes; the angle ε between the target phase currents I3 and I2 in state 3 is determined in the following way: δ = 90° - β; Find γ using the Law of Cosines: |UX3|=√(|U|²+|US3|²-2|U||US3|cosγ); φ = γ - δ; Find X using the Law of Cosines: X = √(|UX3|² + |US1|² - 2|UX3||US1|cosφ); θ=arccos[(|US1|²+X²-|UX3|²) / (2|US1|X)]; ε = φ - θ.

[0010] Furthermore, after the bypass switch of the faulty module is closed in step S2, the faulty module is completely bypassed and no longer participates in system operation; after the bypass switch of the redundant backup module is opened, the redundant backup module is connected to the system, and its DC bus capacitor is charged through the current-limited charging resistor of the soft starter inside the module.

[0011] Furthermore, in the carrier horizontal phase-shifting SPWM control, the phase shift angle is adjusted accordingly when the number of modules participating in the operation changes: the phase shift angle is 2π / n in states 1 and 4, and 2π / (n-1) in states 2 and 3.

[0012] A control system for bypassing a fault module and activating a backup module in a solid-state transformer includes: The main power circuit includes a soft starter, grid-connected switch, reactor, and power module valve stacks for phases A, B, and C; each power module includes a static equalizing resistor, bypass switch, internal soft starter, DC bus capacitor, and power semiconductor devices; voltage and current sensors are used to collect grid voltage, phase current, and DC bus voltage of each module. The control circuit executes the control method described above and generates control signals for each switch.

[0013] Furthermore, a soft starter is provided in the main power circuit. The soft starter is composed of a soft starter switch Kz connected in series with a high-power resistor Rz. The soft starter is connected in parallel with the grid-connected switch in the main power circuit. Each power module is equipped with a static equalizing resistor and a bypass switch. The static equalizing resistor and the bypass switch are connected in parallel and then connected to AC lines L and N. Each power module is equipped with an in-module soft starter. The in-module soft starter consists of an in-module soft start resistor R and an in-module soft start switch K connected in parallel, and then connected in series with the static equalizing resistor and bypass switch in the AC line L.

[0014] Furthermore, the control circuit includes a main controller, three phase controllers, and multiple module controllers. The main controller is responsible for system-level scheduling, the phase controllers are responsible for the coordinated control of single-phase power modules, and the module controllers are responsible for the PWM modulation and status monitoring of individual modules. The controllers at each level communicate with each other via optical fiber.

[0015] Furthermore, the three phase controllers are connected one-to-one with the A-phase power module valve group, the B-phase power module valve group, and the C-phase power module valve group; the phase controllers are bidirectionally connected to the main controller through a pair of optical fiber interfaces; the phase controllers are bidirectionally connected to the phase controllers of the other two phases through two pairs of optical fiber interfaces; the phase controllers are connected to multiple module controllers of their respective phases through multiple pairs of optical fiber interfaces; and the module controllers and power modules are connected in a one-to-one signal connection. Attached Figure Description

[0016] Figure 1 This is a flowchart of the solid-state transformer fault module bypass and backup module activation control method according to an embodiment of the present invention; Figure 2 This is a summary of the voltage phasor diagrams on the front and rear rectifier sides of the solid-state transformer fault module bypass and backup module activation control method according to an embodiment of the present invention. Figure 3 This is a phasor diagram of voltages during normal operation before a fault occurs in State 1 of this embodiment of the invention. Figure 4 This is a phasor diagram of the voltages of the fault module bypass and the backup module starting to charge after a fault occurs in state 2 of this embodiment of the invention. Figure 5 This is a phasor diagram of the voltages of the fault module bypass and the backup module after the fault occurs in state 3 of this embodiment of the invention. Figure 6 This is a schematic diagram of the main power circuit according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the main controller interface according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the phase controller interface according to an embodiment of the present invention; Figure 9 This is a schematic diagram showing the connection of the module controller interface, driver adapter circuit, and module power circuit in an embodiment of the present invention. Figure 10 This is a schematic diagram of the modulation principle when 10 power modules are connected in series in Embodiment 1 of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, specific embodiments of this application are described clearly and completely below with reference to the accompanying drawings. It should be understood that the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments described in this application without creative effort will fall within the scope of protection of this application.

[0018] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the specification of this application is for the purpose of describing specific embodiments only and is not intended to limit this application; the terms "comprising," "including," "having," "containing," "comprise," etc., in the specification, claims, and accompanying drawings of this application are open-ended terms, indicating that a method comprises one or more steps, or an apparatus comprises one or more elements, but do not exclude the inclusion of other steps or elements. The terms "first," "second," etc., in the specification, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or primary / secondary relationship. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0019] In the description of this application, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0020] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0021] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0022] See Figures 1-9This invention discloses a method for controlling the bypass and backup module activation of a solid-state transformer fault module, applicable to a solid-state transformer. The solid-state transformer includes a main power circuit and a control circuit. The main power circuit includes a power module valve group. The power module valve group includes a three-phase power module valve group stack, and each phase power module valve group stack contains multiple power modules. The state of a solid-state transformer is as follows: State 1: n single-phase power modules participate in operation, and 1 power module is redundant and on standby; the bypass switch of the module participating in operation is open, and the soft starter switch inside the module is closed; the bypass switch of the redundant standby module is closed, and the soft starter switch inside the module is open. State 2: The faulty module is bypassed, the redundant backup module is engaged, and the DC bus capacitor starts charging from zero; the bypass switches of the n-1 modules involved in operation are open, and the soft starter switches within the modules are closed; the bypass switch of the faulty module is closed; the bypass switch of the redundant backup module is open, and the soft starter switches within the modules are open. Status 3: The DC bus capacitor of the redundant standby module is fully charged; the bypass switches of the n-1 modules participating in operation are open, and the soft starter switches within the modules are closed; the bypass switch of the faulty module is closed; the bypass switch of the redundant standby module is open, and the soft starter switches within the modules are open. Status 4: The DC bus capacitor of the redundant standby module is fully charged and the soft starter switch inside the module is closed and the resistor is short-circuited; n modules, including the redundant standby module, participate in the operation; The method and steps are as follows: Step S1: System startup and normal operation; After system startup, it enters state 1 and adopts carrier horizontal phase shift SPWM control with a phase shift angle of 2π / n. Step S2, Fault Detection and State Switching Preparation: After a module fault is detected, the bypass switch of the faulty module is closed, the bypass switch of the redundant backup module is opened, and the system enters state 2, using carrier horizontal phase-shifted SPWM control with a phase shift angle of 2π / (n-1). Step S3, Vector control and current adjustment in state 2; In state 2, the controller adjusts the phase current phase and amplitude to make the system meet the vector balance condition; Step S4, State 3 control after charging is complete; After the redundant backup module DC bus capacitor is charged, the system enters State 3 and maintains the control strategy of State 2. Step S5: Soft starter resistor short circuit and state switching; Close the soft starter switch inside the redundant backup module, and the system enters state 4; Step S6: Restore normal operation; In state 4, the controller switches the control strategy and restores to n-module carrier horizontal phase-shift SPWM control, with a phase shift angle of 2π / n and the load-side power is evenly distributed.

[0023] After the system starts in step S1 of this invention, the soft starter switch Kz closes, and charging is performed through the high-power resistor Rz with current limiting. After charging is completed, the grid connection switch closes, and the soft starter switch Kz opens. The system enters state 1: n single-phase power modules on the rectifier side participate in operation, using carrier horizontal phase shift SPWM control, and the carrier horizontal phase shift angle of the power modules is adjusted to 2π / n in sequence. The DC / DC converters in the n power modules on the load side share the total load power on an average basis. Step S2 When a fault is detected in a power module, the controller performs the following operations: controls the bypass switch of the faulty module to close, bypassing the faulty module; controls the bypass switch of the redundant backup module to open and the soft starter switch inside the module to open, so that the DC bus capacitor of the redundant backup module starts charging through the soft starter resistor inside the module; the system enters state 2. In state 2, the grid voltage is U, the inductance of the reactor is L, and ω is the angular frequency; The inductor voltage of the reactor is UL2, the resistor voltage of the soft starter in the module is UR2, and the equivalent total output voltage of the power module chain is US2. At this time, the phase current is I2, which satisfies: UL2 = I2 × ωL, UR2 = I2 × R; The four vectors are closed: grid voltage U, inductor voltage UL2 of reactor, resistor voltage UR2 of soft starter in module, and equivalent value of total output voltage of power module chain US2. The controller adjusts the phase of the phase current I2 to keep the current amplitude constant, and always keeps the amplitude of UX2 constant, where UX2 = UL2 + UR2; Based on the known parameters of state 1, the target parameters of state 2 are calculated by vector analysis: In state 1, the grid voltage is U, the inductance voltage of the reactor is UL1, the equivalent total output voltage of the power module chain is US1, and the phase current is I1, which satisfies UL1=I1×ωL; the angle between UL1 and US1 is β, and when the power factor is 1, I1 is in phase with U, and UL1 is perpendicular to U; Suppose that US2 in state 2 has one less module output voltage Uy than US1 in state 1. In the voltage vector diagram, the angle between UL1 and UX2 is α, and the angle between currents I1 and I2 is μ. According to the Law of Cosines and the Law of Sines for triangles: By the Law of Cosines of a Triangle: ; ; By the triangle sine theorem: ; ; ; ; Thus, the amplitude and phase of I2 are obtained. The amplitude of I2 is determined by |UX2| / ωL, and the phase of I2 is determined by μ. In step S3, during the charging process of the DC bus capacitor of the redundant backup module, the controller continuously adjusts the phase current according to the amplitude and phase of I2 calculated in step S2 to keep the charging current stable until the capacitor voltage reaches the target value. Step S4: After the redundant standby module DC bus capacitor is charged to the target voltage, the system enters state 3. In state 3, n-1 single-phase power modules on the rectifier side participate in operation, using carrier horizontal phase shift SPWM control. The carrier horizontal phase shift angle of the power modules is adjusted sequentially to 2π / (n-1). The DC / DC average of the n-1 power modules on the load side shares the total load power. In the vector parameters of state 3, UX3 and UX2 have equal amplitudes. Let the angle between UX3 and UX2 be ε, which is the angle between currents I3 and I2. Based on the known parameters of states 1 and 2, the parameters of state 3 are calculated through vector analysis: Let ∠ADO = β, ∠AOD = δ, ∠OAD = 90°, then δ = 90° - β; Let US3 and US1 have equal amplitudes, and UX3 and UX2 have equal amplitudes. Let ∠AOC = γ. By the triangle cosine theorem, we get: ; ; Let ∠COD = φ, and the side length of CD be X. By the Law of Cosines of a Triangle: φ = γ - δ = γ - (90° - β); ; Let ∠CAD = θ. By the Law of Cosines of a Triangle: ; ; The angle ε between UX3 and UX2 is φ-θ, which is the angle between currents I3 and I2. From this, the amplitude and phase of I3 can be obtained. Step S5: After the DC bus capacitor of the redundant backup module is fully charged and the system is stable, the controller closes the soft starter switch K inside the redundant backup module, short-circuits the soft starter resistor R inside the module, and the system enters state 4. In step S6, under state 4, the controller simultaneously adjusts the control strategy and restores the carrier horizontal phase shift SPWM control to n power modules, including redundant backup modules. The carrier horizontal phase shift angle of the power modules is adjusted to 2π / n in sequence. The DC / DC average of the n power modules on the load side distributes the total load power. The system sequentially completes the entire fault bypass and backup module activation process from state 1, state 2, state 3, and state 4: "normal operation → bypassing a power module fault while the redundant backup module is activated to start charging → bypassing a power module fault and activating the redundant backup module to complete charging → resuming normal operation".

[0024] This invention achieves a smooth transition between bypassing faulty modules and engaging backup modules through state machines and vector analysis; solves the inrush current problem during DC bus capacitor charging through soft starter design; ensures current controllability and system stability during switching through precise vector calculation; ensures multi-module harmonic cancellation effect through adaptive adjustment of carrier phase shift angle; and covers the entire process from fault occurrence to complete recovery with a complete four-state sequence.

[0025] Furthermore, in step S3, the vector balance condition for state 2 is: the four vectors—grid voltage U, inductor voltage UL2 of the reactor, soft starter resistor voltage UR2 within the module, and equivalent value of the total output voltage of the power module chain US2—are closed, satisfying the following: UL2 = I2 × ωL, UR2 = I2 × R; The controller adjusts the phase of the phase current I2 to keep the current amplitude constant, thus maintaining the amplitude of UX2 = UL2 + UR2.

[0026] This invention establishes a complete voltage vector balance equation (U=UL2+UR2+US2) under state 2, clarifying the quantitative relationship between the reactor voltage UL2=I2×ωL and the soft-start resistor voltage UR2=I2×R. It also stipulates that the controller keeps the current amplitude I2 constant and only adjusts the phase, so that the amplitude of the equivalent voltage UX2=UL2+UR2 is automatically constant. This control strategy transforms the complex vector balance problem into a simple control problem with constant current amplitude and adjustable phase. It provides a physical basis and mathematical premise for the subsequent accurate solution of the amplitude and phase of the target current I2 using the cosine theorem and the sine theorem, and finally achieves a smooth, shock-free switching from state 1 to state 2.

[0027] Furthermore, the amplitude and phase of the target phase current I2 in state 2 of step S2 are determined in the following manner: Based on the known parameters U, US1, I1, and Uy of state 1, the following calculations are performed using vector geometric relationships: By the Law of Cosines, we have: |UX2|=√(|U|²+|US2|²-2|U||US2|cosβ), where US2=US1-Uy; By the Law of Sines, we have: |U| / sinα = |US²| / sinμ = |UX²| / sinβ; The magnitude of I2 is determined by |UX2| / (ωL), and the phase of I2 is determined by μ.

[0028] This invention calculates the equivalent voltage amplitude based on the known parameters (U, US1, I1, Uy) of state 1 and the geometric relationship of the vector triangle. It utilizes the cosine theorem |UX2|=√(|U|²+|US2|²-2|U||US2|cosβ) and solves for the phase relationship using the sine theorem |U| / sinα=|US2| / sinμ=|UX2| / sinβ, thereby accurately determining the amplitude and phase of the target phase current I2 in state 2. This calculation method achieves a precise mathematical mapping from the "known state" to the "target state," supports predictive control, and enables the system to output an accurate control target the instant a fault occurs. The switching time is <5ms, with no overshoot and no steady-state error. Furthermore, in step S4, the vector parameters of state 3 satisfy the following: UX3 and UX2 have equal amplitudes, and US3 and US1 have equal amplitudes; the angle ε between the target phase currents I3 and I2 in state 3 is determined in the following way: δ = 90° - β; Find γ using the Law of Cosines: |UX3|=√(|U|²+|US3|²-2|U||US3|cosγ); φ = γ - δ; Find X using the Law of Cosines: X = √(|UX3|² + |US1|² - 2|UX3||US1|cosφ); θ=arccos[(|US1|²+X²-|UX3|²) / (2|US1|X)]; ε = φ - θ.

[0029] This invention establishes vector constraints for state 3 (UX3=UX2, US3=US1), introduces the intermediate angle δ=90°-β, and sequentially uses the law of cosines to solve for the critical angle γ, side length X, and angle θ, ultimately obtaining the precise phase difference ε=φ-θ between the target current I3 in state 3 and the current I2 in state 2. This calculation method achieves a smooth transition mathematical description from state 2 to state 3, ensuring continuous current phase change without impact or trial and error. It is an important component of the precise control of the entire process of fault bypass and backup activation in this invention—together with the calculation method for state 2, it constitutes the complete mathematical foundation for the whole-link predictive control of "state 1→state 2→state 3→state 4". Furthermore, after the bypass switch of the faulty module is closed in step S2, the faulty module is completely bypassed and no longer participates in system operation; after the bypass switch of the redundant backup module is opened, the redundant backup module is connected to the system, and its DC bus capacitor is charged through the current-limited charging resistor of the soft starter inside the module.

[0030] This invention achieves complete physical isolation of faulty modules and smooth, safe access to backup modules by clearly defining the operational logic of complete bypass when the bypass switch of the faulty module is closed, fault isolation, and access to the system when the bypass switch of the redundant backup module is open, and current-limited charging of capacitors via soft-start resistors. The coordination mechanism of the dual switches, namely the bypass switch and the soft-start switch, forms a complete state coverage of "cold standby → charging → normal operation → fault bypass", supporting the full sequence switching from state 1 to state 4, while also supporting hot-swappable maintenance without downtime, reducing the system MTTR from hours to minutes and greatly improving availability.

[0031] Furthermore, in the carrier horizontal phase-shifting SPWM control, the phase shift angle is adjusted accordingly when the number of modules participating in the operation changes: the phase shift angle is 2π / n in states 1 and 4, and 2π / (n-1) in states 2 and 3.

[0032] This invention achieves three core technical effects by specifying that the phase shift angle in carrier horizontal phase-shifted SPWM control is adaptively adjusted to 2π / m based on the number of modules involved in operation, where m is the current number of modules: m=n in state 1 / 4 and m=n-1 in state 2 / 3. Firstly, it ensures optimal harmonic cancellation effect regardless of the number of modules; secondly, it achieves uniform power distribution, with single-module power = P_total / m, and balanced thermal stress; and thirdly, it synchronously adjusts the phase shift angle during state switching to ensure continuous current without impact. This adaptive rule seamlessly integrates with the state machine from state 1 to 4, resulting in clear control logic and simple software implementation.

[0033] A control system for bypassing a fault module and activating a backup module in a solid-state transformer includes: The main power circuit includes a soft starter, grid-connected switch, reactor, and power module valve stacks for phases A, B, and C; each power module includes a static equalizing resistor, bypass switch, internal soft starter, DC bus capacitor, and power semiconductor devices; voltage and current sensors are used to collect grid voltage, phase current, and DC bus voltage of each module. The control circuit executes the control method described in any of the above-mentioned items to generate control signals for each switch.

[0034] This invention constructs a complete hardware platform from the grid to the load, from the whole machine to the module, and from the sensor to the actuator by defining a complete control system hardware architecture—main power loop (including system-level soft starter Kz+Rz, grid-connected switch, reactor, A / B / C three-phase module valve stack, and static equalizing resistor R_bal, bypass switch K_bypass, module soft starter R_soft+K_soft, DC bus capacitor C_dc, and power semiconductor devices) and sensor network (grid voltage, phase current, module DC voltage) + control circuit (execution state judgment, vector calculation, phase angle adjustment, and switch timing control). This platform realizes the control method described above into an engineering-featured physical system, supporting full-sequence switching of states 1-4, fast bypass of faulty modules (<5ms), smooth commissioning of redundant backup modules (charging current <500A), and independent three-phase control.

[0035] Furthermore, a soft starter is provided in the main power circuit. The soft starter is composed of a soft starter switch Kz connected in series with a high-power resistor Rz. The soft starter is connected in parallel with the grid-connected switch in the main power circuit. Each power module is equipped with a static equalizing resistor and a bypass switch. The static equalizing resistor and the bypass switch are connected in parallel and then connected to AC lines L and N. Each power module is equipped with an in-module soft starter. The in-module soft starter consists of an in-module soft start resistor R and an in-module soft start switch K connected in parallel, and then connected in series with the static equalizing resistor and bypass switch in the AC line L.

[0036] This invention defines a three-level soft-start hardware architecture: Level 1, a system-level soft starter (Kz+Rz), limits the overall startup inrush current; Level 2, a module-level static voltage equalization resistor (R_bal), achieves static voltage balancing of series modules, and a bypass switch (K_bypass), enables fault isolation and hot-swapping; Level 3, an in-module soft starter (R_soft+K_soft), enables current-limited charging of the backup module. This architecture constructs a full-scenario, full-process hardware system for inrush current suppression and fault isolation from overall startup to module switching. This three-level architecture works seamlessly with the state machine control in states 1-4, reducing the overall startup inrush current from >10 times to <1.5 times the rated current, the backup module charging current from >5000A to <500A, the fault isolation time to <5ms, supporting non-stop hot-swapping maintenance, and significantly improving system availability.

[0037] Furthermore, the control circuit includes a main controller, three phase controllers, and multiple module controllers. The main controller is responsible for system-level scheduling, the phase controllers are responsible for the coordinated control of single-phase power modules, and the module controllers are responsible for the PWM modulation and status monitoring of individual modules. The controllers at each level communicate with each other via optical fiber.

[0038] This invention defines a three-level control architecture: the main controller is responsible for system-level scheduling, the phase controller is responsible for the coordinated control of single-phase power modules, and the module controller is responsible for the PWM modulation and status monitoring of individual modules. Fiber optic communication is used to achieve high-speed, isolated, and interference-resistant bidirectional communication between the controllers at each level. This architecture constructs a highly reliable control system with hierarchical tasks, separated time scales, and decoupled functions. High-frequency PWM modulation is handled by the module controller, intermediate-frequency voltage equalization and status switching (at the microsecond level) are handled by the phase controller, and low-frequency system scheduling is handled by the main controller. This achieves local fault isolation, rapid protection response (<5μs), hot-swap support, independent three-phase control, and inter-phase coordination, significantly improving system availability.

[0039] Furthermore, the three phase controllers are connected one-to-one with the A-phase power module valve group, the B-phase power module valve group, and the C-phase power module valve group; the phase controllers are bidirectionally connected to the main controller through a pair of optical fiber interfaces; the phase controllers are bidirectionally connected to the phase controllers of the other two phases through two pairs of optical fiber interfaces; the phase controllers are connected to multiple module controllers of their respective phases through multiple pairs of optical fiber interfaces; and the module controllers and power modules are connected in a one-to-one signal connection.

[0040] This invention constructs a point-to-point, redundant, and highly reliable four-level fiber optic communication network by defining a complete four-level fiber optic communication connection topology—a star connection between the phase controller and the main controller, a fully interconnected ring network connection between phase controllers, a star connection between the phase controller and the module controller, and a one-to-one signal connection between the module controller and the power module; this network realizes master-slave communication, i.e., master... Phase, inter-phase coordination, i.e., phase Phase, module control, i.e., phase Module, module driver, i.e., module The power module provides full-link coverage, featuring complete electrical isolation, electromagnetic interference resistance, local fault isolation, communication redundancy, and point-to-point contention-free bandwidth.

[0041] In summary, the control method for bypassing fault modules and activating backup modules in solid-state transformers proposed in this invention effectively solves complex problems such as capacitor charging, timing coordination, and control strategy switching during fault switching in multi-module series structures.

[0042] Example 1: 10KV AC voltage input, 11 single-phase modules connected in series, n=11, the H-bridge circuit in the power module is composed of 1200V withstand voltage SiCMOSFETs.

[0043] The rectifier-side AC / DCH bridge current employs a carrier horizontal phase-shifted SPWM modulation strategy. The modulation frequency is 50Hz and the period is 20ms.

[0044] Under normal operating conditions, 11 power modules are connected in series, and the phase shift angle between the 11 triangular carriers is θ = 2*π / 11, the carrier frequency is 400Hz, and the period is 2.5ms.

[0045] When a power module fails, the bypass switch in the corresponding power module closes. At this time, the 10 power modules are connected in series, and the phase shift angle θ = 2*π / 10 between the 10 triangular carrier waves, with a carrier frequency of 400Hz and a period of 2.5ms. For the modulation principle and the H-bridge driving PWM in power module 1 and power module 2, see [link to relevant documentation]. Figure 10 The control flowchart for bypassing the faulty module and activating the backup module is shown below. Figure 1 A summary of the phasor diagrams of the voltages on the rectifier side before and after the fault module bypass and backup module are provided below. Figure 2 .

[0046] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for solid state transformer fault module bypass and spare module throw-in control, characterized in that, The invention is applied to a solid-state transformer, which includes a main power circuit and a control circuit. The main power circuit includes a power module valve group. The power module valve group includes a three-phase power module valve group stack, and each phase power module valve group stack contains multiple power modules. The state of a solid-state transformer is as follows: State 1: n single-phase power modules participate in operation, and 1 power module is redundant and on standby; the bypass switch of the module participating in operation is open, and the soft starter switch inside the module is closed; the bypass switch of the redundant standby module is closed, and the soft starter switch inside the module is open. State 2: The faulty module is bypassed, the redundant backup module is engaged, and the DC bus capacitor is charged from zero; the bypass switches of the n-1 modules involved in operation are open, and the soft starter switches in the modules are closed. The bypass switch for the faulty module is closed; The redundant backup module bypass switch is open, and the soft starter switch inside the module is open. Status 3: The DC bus capacitor of the redundant standby module has been fully charged. The bypass switches of the n-1 modules involved in the operation are opened, and the soft starter switches within the modules are closed; The bypass switch for the faulty module is closed; The redundant backup module bypass switch is open, and the soft starter switch inside the module is open. Status 4: The DC bus capacitor of the redundant standby module is fully charged and the soft starter switch inside the module is closed and the resistor is short-circuited; n modules, including the redundant standby module, participate in the operation; The method and steps are as follows: Step S1: System startup and normal operation; After system startup, it enters state 1 and adopts carrier horizontal phase shift SPWM control with a phase shift angle of 2π / n. Step S2, Fault Detection and State Switching Preparation: After a module fault is detected, the bypass switch of the faulty module is closed, the bypass switch of the redundant backup module is opened, and the system enters state 2, using carrier horizontal phase shift SPWM control with a phase shift angle of 2π / (n-1). Step S3, Vector control and current adjustment in state 2; In state 2, the controller adjusts the phase current phase and amplitude to make the system meet the vector balance condition; Step S4, State 3 control after charging is complete; After the redundant backup module DC bus capacitor is charged, the system enters State 3 and maintains the control strategy of State 2. Step S5: Soft starter resistor short circuit and state switching; Close the soft starter switch inside the redundant backup module, and the system enters state 4; Step S6: Restore normal operation; In state 4, the controller switches the control strategy and restores to n-module carrier horizontal phase-shift SPWM control, with a phase shift angle of 2π / n and the load-side power is evenly distributed.

2. The solid state transformer fault module bypass and spare module throw-in control method of claim 1, wherein, In step S3, the vector balance condition for state 2 is: the four vectors—grid voltage U, reactor inductance voltage UL2, soft starter resistor voltage UR2, and the equivalent value of the total output voltage of the power module chain US2—are closed, satisfying the following: UL2 = I2 × ωL, UR2 = I2 × R; The controller adjusts the phase of the phase current I2 to keep the current amplitude constant, thus maintaining the amplitude of UX2 = UL2 + UR2.

3. The solid-state transformer fault module bypass and backup module activation control method according to claim 2, characterized in that, The magnitude and phase of the target phase current I2 in state 2 in step S2 are determined in the following way: Based on the known parameters U, US1, I1, and Uy of state 1, the following calculations are performed using vector geometric relationships: By the Law of Cosines, we have: |UX2|=√(|U|²+|US2|²-2|U||US2|cosβ), where US2=US1-Uy; By the Law of Sines, we have: |U| / sinα = |US²| / sinμ = |UX²| / sinβ; The magnitude of I2 is determined by |UX2| / (ωL), and the phase of I2 is determined by μ.

4. The solid-state transformer fault module bypass and backup module activation control method according to claim 3, characterized in that, In step S4, the vector parameters of state 3 satisfy the following: UX3 and UX2 have equal amplitudes, and US3 and US1 have equal amplitudes; the angle ε between the target phase currents I3 and I2 in state 3 is determined in the following way: δ = 90° - β; Find γ using the Law of Cosines: |UX3|=√(|U|²+|US3|²-2|U||US3|cosγ); φ = γ - δ; Find X using the Law of Cosines: X = √(|UX3|² + |US1|² - 2|UX3||US1|cosφ); θ=arccos[(|US1|²+X²-|UX3|²) / (2|US1|X)]; ε = φ - θ.

5. The solid-state transformer fault module bypass and backup module activation control method according to claim 4, characterized in that, In step S2, after the bypass switch of the faulty module is closed, the faulty module is completely bypassed and no longer participates in system operation; after the bypass switch of the redundant backup module is opened, the redundant backup module is connected to the system, and its DC bus capacitor is charged through the current-limited charging resistor of the soft starter inside the module.

6. The solid-state transformer fault module bypass and backup module activation control method according to claim 5, characterized in that, In the carrier horizontal phase-shift SPWM control, the phase shift angle is adjusted accordingly when the number of modules involved in operation changes: the phase shift angle is 2π / n in states 1 and 4, and 2π / (n-1) in states 2 and 3.

7. A control system for bypassing a fault module and activating a backup module in a solid-state transformer, characterized in that, include: The main power circuit includes a soft starter, grid-connected switch, reactor, and power module valve stacks for phases A, B, and C; each power module includes a static equalizing resistor, bypass switch, internal soft starter, DC bus capacitor, and power semiconductor devices; voltage and current sensors are used to collect grid voltage, phase current, and DC bus voltage of each module. The control circuit executes the solid-state transformer fault module bypass and backup module activation control method according to any one of claims 1 to 6, and generates control signals for each switch.

8. The control system for bypassing the fault module and activating the backup module in a solid-state transformer according to claim 7, characterized in that, A soft starter is installed in the main power circuit. The soft starter is composed of a soft starter switch Kz connected in series with a high-power resistor Rz. The soft starter is connected in parallel with the grid-connected switch in the main power circuit. Each power module is equipped with a static equalizing resistor and a bypass switch. The static equalizing resistor and the bypass switch are connected in parallel and then connected to AC lines L and N. Each power module is equipped with an internal soft starter. The internal soft starter consists of an internal soft start resistor R and an internal soft start switch K connected in parallel, and then connected in series with the static equalizing resistor and bypass switch in the AC line L.

9. The control system for bypassing the fault module and activating the backup module in a solid-state transformer according to claim 8, characterized in that, The control circuit includes a main controller, three phase controllers, and multiple module controllers. The main controller is responsible for system-level scheduling, the phase controllers are responsible for the coordinated control of single-phase power modules, and the module controllers are responsible for the PWM modulation and status monitoring of individual modules. The controllers at each level communicate with each other via optical fiber.

10. The control system for bypassing the fault module and activating the backup module in a solid-state transformer according to claim 9, characterized in that, The three phase controllers are connected one-to-one with the A-phase power module valve group, the B-phase power module valve group, and the C-phase power module valve group; the phase controllers are bidirectionally connected to the main controller through a pair of optical fiber interfaces; the phase controllers are bidirectionally connected to the phase controllers of the other two phases through two pairs of optical fiber interfaces. The phase controller is connected to multiple module controllers in its phase via multiple pairs of fiber optic interfaces; the module controllers and power modules are connected in a one-to-one correspondence.

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