A fault-tolerant control method and system based on active and reactive synchronous regulation in a solid-state transformer

Abstract

The application discloses a fault-tolerant control method and system based on active and reactive synchronous regulation in a solid-state transformer, and belongs to the technical field of power electronic converters. The method comprises the following steps: judging the self-checking of a control system and the running state of a power module; when detecting a fault of a certain phase module, only removing the fault module, and all the non-fault phase modules are online running; obtaining normal state parameters and calculating the control target value after the fault, including the amplitude and phase of the voltage of each phase valve group stack; for the non-fault phase, increasing the active current and increasing the AC / DC voltage of each module; for the fault phase, reducing the active current, actively injecting the reactive current to assist the regulation, and synchronously increasing the voltage of each module; after the regulation is completed, the voltage and power of all the online modules are restored to be consistent. The application can effectively maintain the voltage balance and power balance of each phase module after the module fault, the control logic is clear, and the impact on the power grid is small.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, specifically to a fault-tolerant control method and system for solid-state transformers based on active and reactive power synchronous regulation. Background Technology

[0002] The new power distribution network architecture centered on solid-state transformers demonstrates significant advantages in enhancing the absorption capacity of new energy sources, constructing smart microgrids, and supporting efficient DC power supply for green data centers. To achieve direct power extraction from medium- and high-voltage grids, high-power solid-state transformers typically employ a structure with multiple power modules connected in series on the AC side, such as a topology combining H-bridge cascades with dual active bridge converters, or a modular multilevel converter topology. These solutions extensively utilize semiconductor devices such as SiC MOSFETs and associated drive, sensing, and control circuits, which introduce a certain probability of failure in actual operation.

[0003] When a power module fails, it must be quickly bypassed to prevent the fault from spreading and ensure continuous system operation. Current technologies primarily rely on cold standby or hot standby. Cold standby involves switching to a backup module after a fault, which introduces a charging delay and may impact the system. While hot standby eliminates the switching delay, the unequal number of online modules between the faulty and non-faulty phases can lead to inconsistencies in AC and DC bus voltages between the power modules, as well as differences in the power load borne by each module. This asymmetrical operation affects the long-term reliability of the system and the consistency of module lifespan, and complicates post-fault control strategies.

[0004] Therefore, how to effectively maintain the voltage and power balance of each phase of the online power module after a solid-state transformer module failure is an urgent problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a fault-tolerant control method and system based on active and reactive power synchronous regulation in solid-state transformers, which can effectively maintain voltage and power balance of each phase module after module failure, with clear control logic and minimal impact on the power grid.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A fault-tolerant control method based on active and reactive power synchronous regulation in a solid-state transformer includes: Step 1: Determine if the control system self-test is normal. If the self-test is abnormal, stop the machine for maintenance. Step 2: If the self-test is normal, determine whether the power module of the control system is operating normally; Step 3: If any one or more power modules in a phase power module valve group fail, disconnect the power module that failed. Step 4: Determine whether the faulty power module has been successfully isolated; if not, shut down the system for maintenance; Step 5: If the faulty power module is successfully isolated, determine the phase where the faulty power module is located; Step 6: Obtain system parameters under normal operating conditions, and estimate system parameters under fault conditions based on the system parameters under normal operating conditions; Step 7: For the valve group stack of non-faulty power modules, adjust the voltage of the power module valve group stack based on the system parameters under fault conditions, so as to increase the active current and the DC bus voltage of each power module; for the valve group stack comprising the faulty power module, adjust the voltage of the power module valve group stack based on the system parameters under fault conditions, so as to reduce the active current, adjust the reactive current, and increase the DC bus voltage of each power module; Step 8: After the adjustment is completed, repeat steps 3 to 7 to implement fault-tolerant control.

[0007] Further, in step 6, obtaining system parameters under normal operating conditions is specifically: Obtain grid voltages ea, eb and ec under normal operating conditions, active currents Ia, Ib and Ic of each phase, the voltage ∑Ua1 of A-phase power module valve group stack, the voltage ∑Ub1 of B-phase power module valve group stack, the voltage ∑Uc1 of C-phase power module valve group stack, the reactance value L of the reactor and the corresponding inductive reactance value L, voltage drop ULa1 across the reactor of the A-phase power module valve group stack, voltage drop ULb1 across the reactor of the B-phase power module valve group stack, and voltage drop ULc1 across the reactor of the C-phase power module valve group stack, where ea=∑Ua1+ULa1, eb=∑Ub1+ULb1, ec=∑Uc1+ULc1; Let ∑Ua2 be the voltage of the A-phase power module valve group stack under fault conditions, ∑Ub2 be the voltage of the B-phase power module valve group stack under fault conditions, and ∑Uc2 be the voltage of the C-phase power module valve group stack under fault conditions. Obtain active currents Ia2, Ib2 and Ic2 of each phase under fault conditions, and compare them with active currents Ia, Ib and Ic of each phase under normal operating conditions. Assuming that there is a faulty power module in the A-phase power module valve group stack, if Ia>Ia2, it means that the active current of the fault phase decreases; if Ib<Ib2, it means that the active current of a non-fault phase increases; if Ic<Ic2, it means that the active current of the other non-fault phase increases. The relationship between the active current of each phase under fault conditions and the active current of each phase under normal operating conditions is set as: Ia-Ia2=2*(Ib-Ib2)=2*(Ic-Ic2); Under normal operating conditions, the grid voltages ea, eb, and ec are numerically equal, denoted as the grid voltage value e. The active currents Ia, Ib, and Ic of each phase are numerically equal, denoted as the current value I. The voltage values ​​of the power module valve group in phase A (∑Ua1), phase B (∑Ub1), and phase C (∑Uc1) are numerically equal, denoted as the voltage value ∑U. The following exists: ; ; ; Substituting, we get: ; The AC side voltage of each power module is equal, denoted as ∑U / n; Furthermore, in step 6, the system parameters under fault conditions are calculated based on the system parameters under normal operating conditions, specifically as follows: Suppose there are faulty power modules in the power module valve group of phase A. When x power modules in phase A fail and are bypassed, the reduction in their active current is... I = (x / n) * I, the increase in active current values ​​for phase B and phase C is 0.5 * The voltage drop across the reactor caused by the active current in phases I and B is: ; ; Substituting, we get: ; Solving for: ; And the angle between ∑Ub2 and eb is: ; Similarly, the C-phase power module valve group stack voltage is: And the angle between ∑Uc2 and ec is: ; In summary: ; ; For the non-faulty phases, i.e., phases B and C, the AC side voltage increase values ​​for each power module are respectively ∑Ub / n, ∑Uc / n, the two values ​​are equal, denoted as ∑U / n; For the faulty phase, i.e., phase A, the AC voltage increase value for each power module is the same as that for each power module in phases B and C. ∑U / n, we get: ; And the angle between ∑Ua2 and ea is: ; Determine the amplitude and direction of the reactive current IaQ2 to be injected into the faulty phase, so that the voltage drop ULaQ2 generated by the reactive current IaQ2 on the reactor and the voltage drop ULa2 generated by the active current of the faulty phase are vectored together, and the sum of ∑Ua2 and the combined voltage drop is equal to the grid voltage ea.

[0008] The present invention also provides a fault-tolerant control system based on active and reactive power synchronous regulation in a solid-state transformer, which is applied to the above-mentioned fault-tolerant control method based on active and reactive power synchronous regulation in a solid-state transformer, including: a main power circuit and a three-level control system, wherein a medium- and high-voltage power grid is connected to the input terminal of the main power circuit, and the main power circuit is connected to the three-level control system; The main power circuit includes a first AC voltage sampling sensor group, a reactor, a grid-connected switch, a soft starter, a second AC voltage sampling sensor group, a fuse group, an AC current sampling sensor group, a power module valve group, a DC current sampling sensor group, and a DC voltage sampling sensor group. The medium- and high-voltage power grid is connected to the first AC voltage sampling sensor group. The first AC voltage sampling sensor group is connected to the reactor. The reactor is connected to the grid-connected switch. The grid-connected switch is connected to the second AC voltage sampling sensor group, and the soft starter is connected in parallel with the grid-connected switch. The second AC voltage sampling sensor group is connected to the fuse group. The fuse group is connected to the AC current sampling sensor group. The AC current sampling sensor group is connected to the power module valve group. The power module valve group is connected to the DC current sampling sensor group. The DC current sampling sensor group is connected to the DC voltage sampling sensor group. The first AC voltage sampling sensor group, the grid-connected switch, the soft starter, the second AC voltage sampling sensor group, the fuse group, the AC current sampling sensor group, the power module valve group, the DC current sampling sensor group, and the DC voltage sampling sensor group are connected to the three-level control system.

[0009] Furthermore, the power module valve group includes an A-phase power module valve group stack, a B-phase power module valve group stack, and a C-phase power module valve group stack, which are arranged in parallel, and each power module valve group stack includes multiple power modules.

[0010] Furthermore, the power module has a built-in static voltage equalization resistor and a bypass switch.

[0011] Furthermore, the three-level control system includes a main controller, three phase controllers, and multiple module controllers. The first AC voltage sampling sensor group, grid-connected switch, soft starter, second AC voltage sampling sensor group, fuse group, AC current sampling sensor group, DC current sampling sensor group, DC voltage sampling sensor group, and three phase controllers are connected to the main controller. The A-phase power module valve group, B-phase power module valve group, and C-phase power module valve group are respectively connected to the three corresponding phase controllers. Each power module is connected to one of the module controllers, and the module controller of the corresponding phase is connected to the phase controller of the corresponding phase.

[0012] In summary, the present invention has at least one of the following beneficial technical effects: First, by bypassing only the faulty module after a fault and utilizing the synchronous adjustment of active and reactive power, the DC bus voltage, AC side voltage, and operating power of all online modules in the faulty and non-faulty phases are restored to consistency under the new steady state, effectively improving the power balance of the multi-module series system during fault-tolerant operation.

[0013] Second, the control logic is clear and reliable. This method does not rely on complex negative-sequence and zero-sequence component control. By obtaining the normal operating state parameters, the control target values ​​after a fault can be derived. The main controller and phase controllers work in a hierarchical manner, which is easy to implement in engineering practice.

[0014] Third, the impact on the power grid is relatively small. The entire fault transition process is achieved by smoothly adjusting the voltage and reactive current of each module, which reduces the voltage and current fluctuations perceived by the grid side, helps to achieve a more friendly fault ride-through, and reduces disturbances to the external power grid and load equipment.

[0015] Fourth, the system module utilization rate is high. This method is based on a hot standby mode, which eliminates the need to bypass healthy modules of non-faulty phases after a fault. All remaining healthy modules can continue to participate in power transmission, which helps maintain the overall operating efficiency and power supply capacity of the system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the control flow of the method of the present invention; Figure 2 For normal operation, the vector diagram is in state 1. Figure 3 The system is operating under fault conditions; State 2 vector diagram. Figure 4 This is a vector comparison diagram before and after the fault; Figure 5 A schematic diagram of the main power circuit; Figure 6 Diagram of the main controller interface; Figure 7 This is a schematic diagram of the phase controller interface; Figure 8 This is a schematic diagram showing the connection of the module controller interface, driver adapter circuit, and module power circuit. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0018] like Figures 5-8 As shown, the present invention provides a fault-tolerant control system based on active and reactive power synchronous regulation in a solid-state transformer, including a main power circuit and a three-level control system. The medium- and high-voltage power grid is connected to the input terminal of the main power circuit, and the main power circuit is connected to the three-level control system.

[0019] like Figure 5 As shown, the main power circuit includes a first AC voltage sampling sensor group (PT group 1), a reactor, a grid-connected switch, a soft starter, a second AC voltage sampling sensor group (PT group 2), a fuse group, an AC current sampling sensor group (CT group), a power module valve group, a DC current sampling sensor group, and a DC voltage sampling sensor group. The specific connections are as follows: the medium- and high-voltage power grid is connected to the first AC voltage sampling sensor group; the first AC voltage sampling sensor group is connected to the reactor; the reactor is connected to the grid-connected switch; the grid-connected switch is connected to the second AC voltage sampling sensor group, and the soft starter is connected in parallel with the grid-connected switch; the second AC voltage sampling sensor group is connected to the fuse group; the fuse group is connected to the AC current sampling sensor group; the AC current sampling sensor group is connected to the power module valve group; the power module valve group is connected to the DC current sampling sensor group; and the DC current sampling sensor group is connected to the DC voltage sampling sensor group. The aforementioned first AC voltage sampling sensor group, grid-connected switch, soft starter, second AC voltage sampling sensor group, fuse group, AC current sampling sensor group, power module valve group, DC current sampling sensor group, and DC voltage sampling sensor group are all connected to the three-level control system to provide sampling signals or receive control commands.

[0020] The power module valve group includes an A-phase power module valve group stack, a B-phase power module valve group stack, and a C-phase power module valve group stack, which are arranged in parallel. Each phase power module valve group stack includes multiple power modules with identical structures. These power modules are connected in series on the AC side to form a cascaded H-bridge structure for each phase. Each power module has a built-in static equalizing resistor and a bypass switch, which are connected in parallel across the L and N terminals of the module's AC line. This is used to reliably bypass the module in the event of a fault, allowing the module to exit the main power circuit operation.

[0021] In this invention, the internal main circuit of each power module consists of three H-bridge circuits, all employing SiC MOSFET power devices. One H-bridge circuit is used for AC / DC conversion on the rectification side, rectifying the AC input into a stable internal DC bus voltage. The internal DC buses of each module are independent of each other, forming a DC link. The other two H-bridge circuits, together with an isolation transformer, form an isolated DC / DC converter on the load side, located on the primary and secondary sides of the transformer respectively, achieving isolated power transmission. A voltage sampling sensor is installed at each internal DC bus for real-time monitoring of the bus voltage.

[0022] The three-level control system adopts a hierarchical control architecture, including one main controller, three phase controllers, and multiple module controllers. The number of module controllers is equal to the total number of power modules in the system, and each power module is connected to one of these module controllers, achieving one-to-one local control.

[0023] The main controller, as the core decision-making unit of the system, has the following interface configuration: Figure 6 As shown, it connects the first AC voltage sampling sensor group, the grid-connected switch, the soft starter, the second AC voltage sampling sensor group, the fuse group, the AC current sampling sensor group, the DC current sampling sensor group, the DC voltage sampling sensor group, and the three phase controllers. The main controller acquires the signals from these sensors to monitor the grid voltage, grid-connected point voltage, various currents, DC side voltage and current, and switch status in real time. Based on system-level scheduling requirements, it issues opening and closing commands to the grid-connected switch and the soft starter, and issues operating mode, power commands, and fault handling commands to the three phase controllers.

[0024] The three phase controllers correspond to phases A, B, and C respectively, and their interface configurations are as follows: Figure 7As shown, each phase controller has a bidirectional communication connection with the main controller and also has a cross-phase communication link, enabling bidirectional data exchange with the phase controllers of the other two phases. More importantly, each phase controller is connected to all module controllers in its respective phase via multiple pairs of fiber optic or electrical interfaces, thus forming a three-level bidirectional communication network of main controller—phase controller—module controller. The correspondence is as follows: the A-phase power module valve group is connected to the A-phase controller, the B-phase power module valve group is connected to the B-phase controller, the C-phase power module valve group is connected to the C-phase controller, and each module controller within each phase is connected to the corresponding phase controller.

[0025] As the lowest-level execution unit, the module controller's interfaces and connections are as follows: Figure 8 As shown in the diagram, each module controller contains a bypass control unit, an AC / DC control unit, and a DC / DC control unit. The bypass control unit is connected to the bypass switch drive adapter circuit within the power module, and is used to trigger thyristors or switching devices upon receiving a command to achieve module bypass. The AC / DC control unit is connected to the rectifier-side AC / DC H-bridge circuit and its drive adapter circuit, and is responsible for executing carrier horizontal phase-shifting SPWM control. The DC / DC control unit is simultaneously connected to the primary-side H-bridge circuit and its drive adapter circuit, as well as the secondary-side H-bridge circuit and its drive adapter circuit of the load-side DC / DC isolation transformer, to complete load-side power transmission and distribution control.

[0026] like Figure 1 As shown, the present invention also provides a fault-tolerant control method based on active and reactive power synchronous regulation in a solid-state transformer, applied to the above-mentioned system, including: Step 1: Determine if the control system self-test is normal. If the self-test is abnormal, stop the machine for maintenance. Step 2: If the self-test is normal, determine whether the power module of the control system is operating normally; Step 3: If any one or more power modules in a phase power module valve group fail, disconnect the power module that failed. Step 4: Determine whether the faulty power module has been successfully disconnected. If not, shut down the machine for maintenance. Step 5: If the faulty power module is successfully disconnected, determine the phase in which the faulty power module is located; Step 6: Obtain system parameters under normal operating conditions, and deduce system parameters under fault conditions based on the system parameters under normal operating conditions; Step 7: For power module valve groups that have not experienced a fault, adjust their voltage based on the system parameters under fault conditions, increase the active current and the DC bus voltage of each power module; for power module valve groups that have experienced a fault, adjust their voltage based on the system parameters under fault conditions, decrease the active current, adjust the reactive current, and increase the DC bus voltage of each power module. Step 8: After adjustment, repeat steps 3-7 to achieve fault-tolerant control.

[0027] Next, each step will be explained in detail: In step 1, it is determined whether the control system self-test is normal. If the self-test is abnormal, the system is stopped for maintenance. Specifically: After the system is powered on, the main controller first initiates a system-wide self-test process to check whether the communication links between the three controllers are normal, whether the feedback signals from each sensor are within the normal range, and whether there are any abnormalities in the initial state of each power module. If the self-test fails, the system determines that there is a fault that cannot be recovered by itself, immediately enters a shutdown maintenance state, and reports the fault information to the higher-level management system.

[0028] In step 2, if the self-test is normal, then determine whether the power module of the control system is operating normally, specifically: After a normal self-test, the system closes the soft starter and pre-charges the internal DC bus of all power modules through the current-limiting resistor. Once the voltage of each module is established, the grid-connected switch is closed, the soft starter disengages, and the solid-state transformer enters normal operation; this is state 1. In state 1, n power modules on each of the three phases of 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 by 2π / n. The DC / DC average of the 3n power modules on the load side distributes the active power of the load. The active power of a single power module is P1, the input power factor is 1 (cosφ=1), and the total active power of the three phases is P=3n*P1. The control system continuously judges whether each power module is operating normally, specifically through a comprehensive judgment based on the status words reported by the module controller, the internal DC bus voltage deviation, and SiC MOSFET overcurrent or drive fault signals.

[0029] In step 3, if any one or more power modules in a phase power module valve group fail, the faulty power module will be disconnected, specifically as follows: When the control system detects a fault in a power module, it immediately sends a closing command to the bypass switch in the faulty module through the module controller and phase controller in the three-level control system, thereby bypassing and disconnecting the faulty power module from the main power circuit and taking it out of operation.

[0030] In step 4, it is determined whether the faulty power module has been successfully disconnected. If it fails, the system is shut down for maintenance, specifically as follows: The control system determines whether the bypass operation was successfully executed by monitoring the terminal voltage and current feedback of the bypassed module and the status feedback signal of the bypass switch. If the bypass fails, it indicates that the fault may have spread or that the bypass mechanism itself has failed, and the system immediately executes a shutdown maintenance procedure to ensure safety.

[0031] In step 5, if the faulty power module is successfully disconnected, the phase in which the faulty power module is located is determined, specifically: After confirming that the faulty module has been successfully disconnected, the main controller, based on the source of the received fault signal, determines which phase (A, B, or C) the fault occurred in, and determines the number x of faulty modules disconnected in that phase. At this point, the number of online operating modules in the faulty phase becomes nx, while the non-faulty phases maintain n modules online. The system is about to transition from state 1 to state 2.

[0032] In step 6, the system parameters under normal operating conditions are obtained, and the system parameters under fault conditions are calculated based on the system parameters under normal operating conditions. Specifically: In state 1, the control system acquires the grid voltages ea, eb, and ec through the first AC voltage sampling sensor group (PT group 1) of the main power circuit; acquires the outlet voltages ∑Ua1, ∑Ub1, and ∑Uc1 of each phase power module valve group through the second AC voltage sampling sensor group (PT group 2); and acquires the active currents Ia, Ib, and Ic of each phase through the AC current sampling sensor group (CT group). Simultaneously, it acquires the input-side reactance value L and its corresponding inductive reactance value. L.

[0033] Assume that under normal operating condition 1, the grid voltages ea, eb, and ec are numerically equal, denoted as grid voltage e; the active currents Ia, Ib, and Ic of each phase are numerically equal, denoted as current I; and the output voltages ∑Ua1, ∑Ub1, and ∑Uc1 of each phase power module valve group are numerically equal, denoted as voltage ∑U. Therefore, the voltage drop ULa1 = Ia on the input side reactor of each phase can be obtained. L、ULb1=Ib L、ULc1=Ic* L. The vector relationships of each phase satisfy: the sum of ∑Ua1 and ULa1 equals the grid voltage vector ea; the sum of ∑Ub1 and ULb1 equals the grid voltage vector eb; the sum of ∑Uc1 and ULc1 equals the grid voltage vector ec.

[0034] After x modules in one phase fail and are bypassed, the active currents of each phase in state 2 are defined as Ia2, Ib2, and Ic2. Taking the faulty phase as phase A for calculation, compared with the active currents of each phase in state 1: Ia>Ia2, that is, the active current of the faulty phase decreases; Ib<Ib2, that is, the active current of the non-faulty phase increases; Ic<Ic2, that is, the active current of the non-faulty phase increases. In order to achieve consistent active power of all online power modules, the relationship between the magnitudes of variations of active currents of each phase in state 2 and active currents of each phase in state 1 is set as: Ia-Ia2=2*(Ib-Ib2)=2*(Ic-Ic2).

[0035] In state 1, grid voltages ea, eb, ec are equal in magnitude, which are denoted as grid voltage magnitude e, the active currents Ia, Ib, Ic of each phase are equal in magnitude, which are denoted as current magnitude I, the voltages of the power module valve stack of phase A ∑Ua1, the voltage of the power module valve stack of phase B ∑Ub1, and the voltage of the power module valve stack of phase C ∑Uc1 are equal in magnitude, which are denoted as voltage magnitude ∑U, and the following holds: ; ; ; By substitution we obtain: ; The AC-side voltage magnitude of each power module is equal, denoted as ∑U / n; The system parameters of state 2 are calculated based on the system parameters of state 1, specifically: It is assumed that there are faulty power modules in the power module valve stack of phase A. When x power modules in phase A fail and are bypassed, the reduction in active current magnitude is I=(x / n)*I, the increase in active current magnitude of phase B and phase C is 0.5* I, and the voltage drop formed by the active current of phase B on the reactor is: ; ; By substitution we obtain: ; By solving we obtain: ; and the included angle between ∑Ub2 and eb is: ; Similarly, the voltage of the power module valve stack of phase C is: and the included angle between ∑Uc2 and ec is: ; In conclusion, we obtain: ; ; For the non-faulty phases, i.e., phases B and C, the AC side voltage increase values ​​for each power module are respectively ∑Ub / n, ∑Uc / n, the two values ​​are equal, denoted as ∑U / n; For the faulty phase, i.e., phase A, the AC voltage increase value for each power module is the same as that for each power module in phases B and C. ∑U / n, we get: ; And the angle between ∑Ua2 and ea is: .

[0036] Determine the amplitude and direction of the reactive current IaQ2 to be injected into the faulty phase, so that the voltage drop ULaQ2 generated by the reactive current IaQ2 on the reactor and the voltage drop ULa2 generated by the active current of the faulty phase are vectored together, and the sum of ∑Ua2 and the combined voltage drop is equal to the grid voltage ea.

[0037] In step 7, for power module valve groups that have not experienced a fault, the voltage of the power module valve group is adjusted based on the system parameters under fault conditions, increasing the active current and the DC bus voltage of each power module; for power module valve groups that have experienced a fault, the voltage of the power module valve group is adjusted based on the system parameters under fault conditions, decreasing the active current, adjusting the reactive current, and increasing the DC bus voltage of each power module, specifically as follows: During the transition from state 1 to state 2, the control system uses the voltages ∑Ua1, ∑Ub1, and ∑Uc1 of each phase power module valve group as initial values, and ∑Ua2, ∑Ub2, and ∑Uc2 derived in step 6 as target values. The main controller is responsible for coordination between the three phases and synchronously sends the calculated target voltage values ​​of each phase and active / reactive current commands to the three phase controllers. The three phase controllers control their respective phases to adjust parameters.

[0038] The specific adjustment process is as follows: The AC side voltage and DC bus voltage of all online power modules in each phase power module valve group are uniformly increased, so that the AC side voltage increase value of each power module is the same. ∑U / n. For non-faulty phases, increase their active current to Ib2 and Ic2; for faulty phases, decrease their active current to Ia2, and simultaneously actively inject the reactive current IaQ2 determined in step 6. The voltage drop formed by this reactive current IaQ2 on the reactor on the input side of the faulty phase is ULaQ2, which is vectorially synthesized with the voltage drop ULa2 generated by the active current of the faulty phase to form a total voltage drop ULa, so that the vector sum of ∑Ua2 and ULa equals the vector voltage ea of ​​the grid, thereby achieving precise control of the outlet voltage of the faulty phase valve group. After the adjustment is completed, the system reaches a fault operation steady state, i.e., state 2, where the AC side voltage of all online power modules is consistent, the DC bus voltage is consistent, and the active power value P2 is consistent.

[0039] In state 2, nx single-phase power modules on the rectifier side of the faulty phase participate in operation, using carrier horizontal phase-shift SPWM control. The carrier horizontal phase shift angle of the power modules is adjusted sequentially by 2π / (nx). On the rectifier side of the non-faulty phase, n single-phase power modules participate in operation, and the carrier horizontal phase shift angle remains at 2π / n. The DC / DC converters in the 3n-x power modules operating online on the load side share the load active power equally, the input power factor recovers to 1, i.e., cosφ=1, and the total three-phase active power P=(3*nx)*P2.

[0040] In step 8, after the adjustment is completed, repeat steps 3-7 to achieve fault-tolerant control, specifically as follows: The system continues to operate in state 2 and continuously monitors the operating status of each power module. If a power module failure is detected again, the above-mentioned fault clearing, parameter derivation, and synchronization adjustment process is executed repeatedly, so that the system can continuously reconfigure to a new symmetrical operating point even when module failures continue to occur, until the module redundancy is exhausted.

[0041] It should be noted that the above method is also applicable to the case where the solid-state transformer feeds back active power to the grid. Under this condition, the grid voltages ea, eb, and ec remain constant. Simply rotate all current vector directions by 180°; the parameter derivation process in step 6 is exactly the same as the control logic. Furthermore, the parameter derivation process based on phase A as the fault phase is also applicable to the case where the fault phase is phase B or phase C. The derivation process is consistent and will not be repeated here.

[0042] The embodiments of the present invention will be further described in detail below with reference to specific examples.

[0043] In this embodiment, the solid-state transformer uses a 10KV AC voltage input, with 12 single-phase modules connected in series, i.e., n=12. The H-bridge circuit in the power module is composed of 1200V withstand voltage SiC MOSFETs. The rectifier-side AC / DC H-bridge circuit adopts a carrier horizontal phase-shift SPWM modulation strategy with a modulation frequency of 50Hz and a period of 20ms.

[0044] like Figure 2 As shown, under normal operating conditions (State 1): 12 power modules in each of the three phases A, B, and C are connected in series online. The 12 triangular carrier waves are sequentially phase-shifted, with a phase shift angle θ = 2π / 12, a carrier frequency of 400Hz, and a period of 2.5ms. The control system obtains the grid voltages ea, eb, and ec through the first AC voltage sampling sensor group (PT group 1) of the main power circuit; obtains the outlet voltages ∑Ua1, ∑Ub1, and ∑Uc1 of each phase power module valve group through the second AC voltage sampling sensor group (PT group 2); and obtains the active currents Ia, Ib, and Ic of each phase through the AC current sampling sensor group (CT group). The active power of a single power module is P1, and the input-side power factor is 1, i.e., cosφ = 1. The total active power of the three phases is P = 312P1 = 36P1.

[0045] like Figure 3 As shown, when a power module in phase A fails, the control system executes a fault-tolerant control procedure. First, the fault is identified and the faulty module is successfully disconnected (x=1). Then, the phase where the fault occurs is determined to be phase A. Next, the system parameters under state 1 are obtained: grid voltages ea, eb, ec; active currents Ia, Ib, Ic for each phase; and input-side reactance value L (corresponding to inductive reactance value). L), the voltage values ​​of the power module valve group ∑Ua1, ∑Ub1, ∑Uc1. Based on the known parameters of state 1, calculate the target values ​​of the control parameters ∑Ua2, ∑Ub2, ∑Uc2 for state 2.

[0046] Vector comparison diagram before and after the fault is as follows Figure 4 As shown.

[0047] The calculation process is as follows: Reduction in active current of the faulted phase I = (1 / 12)I, the increase in active current of the non-faulty phase is 0.5. I. Substituting into the vector relationship equation and solving, we obtain the target value of the outlet voltage ∑Ub2 of the valve group in the non-faulty phase B and its angle with eb, and the target value of the outlet voltage ∑Uc2 of the valve group in the non-faulty phase C and its angle with ec. The AC side voltage increase value for each power module in the non-faulty phase is... ∑Ub / 12 and ∑Uc / 12, the two values ​​are equal, denoted as ∑U / 12. The AC side voltage increase value of each power module in the faulty phase A is consistent with that of the power modules in the non-faulty phases, and is also ∑U / 12. ∑U / 12. From this, we can obtain the target value of the A-phase valve group outlet voltage ∑Ua2 and its angle with ea in state 2.

[0048] The control system uses ∑Ua1, ∑Ub1, and ∑Uc1 as initial values ​​and the derived ∑Ua2, ∑Ub2, and ∑Uc2 as target values ​​to perform transient regulation. The main controller is responsible for three-phase coordination, and the three phase controllers control their respective phases to adjust parameters: uniformly increasing the AC side voltage and DC bus voltage of all online power modules, with the increase value being... ∑U / 12; The active current of the non-faulty phase is increased, the active current of the faulty phase is reduced and the calculated reactive current IaQ2 is injected, so that the outlet voltage of the faulty phase valve group reaches the target value with the help of the reactive voltage drop.

[0049] After adjustment, the system enters fault operation state (state 2). At this time, the rectifier side of the faulty phase A is operated by 11 power modules, using carrier horizontal phase shift SPWM control, with the carrier horizontal phase shift angle of the power modules adjusted sequentially to 2π / 11; the DC / DC converters of the 11 power modules on the load side share the load power equally. The rectifier sides of the non-faulty phases B and C are still operated by 12 power modules, with the carrier horizontal phase shift angle maintained at 2π / 12; the DC / DC converters of the 12 power modules on the load side share the load active power equally. The active power of a single power module is P2, and the input power factor is restored to 1, i.e., cosφ=1. The total active power of the three phases is P=(3*12-1)P2=35P2. All 35 power modules operating online reach a new steady state with consistent AC side voltage, consistent DC bus voltage, and consistent operating power.

[0050] After that, the system continues to perform status monitoring. If another module fails, the above steps are repeated for fault tolerance control until the operating conditions can no longer be met.

[0051] Embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0052] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0053] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0054] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0055] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A fault-tolerant control method based on active and reactive power synchronous regulation in a solid-state transformer, characterized in that, Comprising: Step 1: determine whether the control system passes the self-check normally; if the self-check is abnormal, perform shutdown maintenance; Step 2: if the self-check is normal, determine whether the power module of the control system operates normally; Step 3: if any one or more power modules in the power module valve stack of a certain phase fail, remove the faulty power module; Step 4: determine whether the faulty power module is removed successfully; if not, perform shutdown maintenance; Step 5: if the faulty power module is removed successfully, determine the phase where the faulty power module is located; Step 6: acquire system parameters under normal operating conditions, and calculate system parameters under the fault condition based on the system parameters under normal operating conditions; Step 7: for the power module valve stack without faults, adjust the voltage of the power module valve stack based on the system parameters under the fault condition, increase the active current and the DC bus voltage of each power module; for the power module valve stack with faults, adjust the voltage of the power module valve stack based on the system parameters under the fault condition, decrease the active current, adjust the reactive current, and increase the DC bus voltage of each power module; Step 8: after the adjustment is completed, repeat steps 3 to 7 to implement fault-tolerant control.

2. The fault-tolerant control method based on active and reactive power synchronous regulation in a solid-state transformer according to claim 1, characterized in that, In step 6, acquiring the system parameters under normal operating conditions is specifically: Obtain the grid voltages ea, eb, and ec under normal operating conditions; the active currents Ia, Ib, and Ic of each phase; the A-phase power module valve group voltage ∑Ua1; the B-phase power module valve group voltage ∑Ub1; the C-phase power module valve group voltage ∑Uc1; and the reactance value L of the reactor and its corresponding inductive reactance value. L, the voltage drop ULa1 on the reactor of the A-phase power module valve group, the voltage drop ULb1 on the reactor of the B-phase power module valve group, and the voltage drop ULc1 on the reactor of the C-phase power module valve group, where ea=∑Ua1+ULa1, eb=∑Ub1+ULb1, and ec=∑Uc1+ULc1. let the voltage of A-phase power module valve stack under the fault condition be ∑Ua2, the voltage of B-phase power module valve stack be ∑Ub2, and the voltage of C-phase power module valve stack be ∑Uc2; acquire the active currents Ia2, Ib2 and Ic2 of each phase under the fault condition, and compare them with the active currents Ia, Ib and Ic of each phase under the normal operating condition. Assuming that there is a faulty power module in the A-phase power module valve stack, if Ia>Ia2, it indicates that the active current of the fault phase decreases; if Ib<Ib2, it indicates that the active current of the non-fault phase increases; if Ic<Ic2, it indicates that the active current of the non-fault phase increases. The relationship between the active current of each phase under the fault condition and the active current of each phase under the normal operating condition is set as: Ia-Ia2=2*(Ib-Ib2)=2*(Ic-Ic2); under the normal operating condition, the grid voltages ea, eb and ec are equal in value, denoted as grid voltage value e; the active currents Ia, Ib and Ic of each phase are equal in value, denoted as current value I; the voltages ∑Ua1 of the A-phase power module valve stack, ∑Ub1 of the B-phase power module valve stack and ∑Uc1 of the C-phase power module valve stack are equal in value, denoted as voltage value ∑U, and the following relation holds: ； ； ； by substitution, we obtain: ； the AC-side voltage of each power module is equal in value, denoted as ∑U / n.

3. The fault-tolerant control method based on active and reactive power synchronous regulation in a solid-state transformer according to claim 2, characterized in that, In step 6, calculating the system parameters under the fault condition based on the system parameters under the normal operating condition is specifically: Suppose there are faulty power modules in the power module valve group of phase A. When x power modules in phase A fail and are bypassed, the reduction in their active current is... I = (x / n) * I, the increase in active current values ​​for phase B and phase C is 0.5 * The voltage drop across the reactor caused by the active current in phases I and B is: ； ； by substitution, we obtain: ； after solving, we obtain: ； and the included angle between ∑Ub2 and eb is: ； similarly, the voltage of the C-phase power module valve stack is: and the included angle between ∑Uc2 and ec is: ； in conclusion, we obtain: ； ； For the non-faulty phases, i.e., phases B and C, the AC side voltage increase values ​​for each power module are respectively ∑Ub / n, ∑Uc / n, the two values ​​are equal, denoted as ∑U / n; For the faulty phase, i.e., phase A, the AC voltage increase value for each power module is the same as that for each power module in phases B and C. ∑U / n, we get: ； and the included angle between ∑Ua2 and ea is: ； Determine the amplitude and direction of the reactive current IaQ2 to be injected into the faulty phase, so that the voltage drop ULaQ2 generated by the reactive current IaQ2 on the reactor and the voltage drop ULa2 generated by the active current of the faulty phase are vectored together, and the sum of ∑Ua2 and the combined voltage drop is equal to the grid voltage ea.

4. A fault-tolerant control system based on active and reactive power synchronous regulation in a solid-state transformer, applied to the fault-tolerant control method based on active and reactive power synchronous regulation in any one of claims 1-3, characterized in that, include: The main power circuit and the three-level control system are connected to the input terminal of the main power circuit via a medium- and high-voltage power grid, and the main power circuit is connected to the three-level control system. The main power circuit includes a first AC voltage sampling sensor group, a reactor, a grid-connected switch, a soft starter, a second AC voltage sampling sensor group, a fuse group, an AC current sampling sensor group, a power module valve group, a DC current sampling sensor group, and a DC voltage sampling sensor group. The medium- and high-voltage power grid is connected to the first AC voltage sampling sensor group. The first AC voltage sampling sensor group is connected to the reactor. The reactor is connected to the grid-connected switch. The grid-connected switch is connected to the second AC voltage sampling sensor group, and the soft starter is connected in parallel with the grid-connected switch. The second AC voltage sampling sensor group is connected to the fuse group. The fuse group is connected to the AC current sampling sensor group. The AC current sampling sensor group is connected to the power module valve group. The power module valve group is connected to the DC current sampling sensor group. The DC current sampling sensor group is connected to the DC voltage sampling sensor group. The first AC voltage sampling sensor group, the grid-connected switch, the soft starter, the second AC voltage sampling sensor group, the fuse group, the AC current sampling sensor group, the power module valve group, the DC current sampling sensor group, and the DC voltage sampling sensor group are connected to the three-level control system.

5. A fault-tolerant control system based on active and reactive power synchronous regulation in a solid-state transformer according to claim 4, characterized in that, The power module valve group includes an A-phase power module valve group stack, a B-phase power module valve group stack, and a C-phase power module valve group stack. The A-phase power module valve group stack, the B-phase power module valve group stack, and the C-phase power module valve group stack are arranged in parallel, and each power module valve group stack includes multiple power modules.

6. A fault-tolerant control system based on active and reactive power synchronous regulation in a solid-state transformer according to claim 5, characterized in that, The power module has a built-in static voltage equalization resistor and a bypass switch.

7. A fault-tolerant control system based on active and reactive power synchronous regulation in a solid-state transformer according to claim 6, characterized in that, The three-level control system includes a main controller, three phase controllers, and multiple module controllers. The first AC voltage sampling sensor group, grid-connected switch, soft starter, second AC voltage sampling sensor group, fuse group, AC current sampling sensor group, DC current sampling sensor group, DC voltage sampling sensor group, and three phase controllers are connected to the main controller. The A-phase power module valve group, B-phase power module valve group, and C-phase power module valve group are respectively connected to the three corresponding phase controllers. Each power module is connected to one of the module controllers, and the module controller of the corresponding phase is connected to the phase controller of the corresponding phase.

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