Control method and device of solid-state transformer, controller, storage medium and solid-state transformer

Abstract

The application provides a control method and device of a solid-state transformer, a controller, a storage medium and the solid-state transformer. The method comprises the following steps: acquiring the AC side input power of each front-stage conversion module, and taking the average value of the AC side input power of each front-stage conversion module as an input power average value; generating a power ring output value based on the difference between the input power average value and the AC side input power of each front-stage conversion module; correcting the initial voltage modulation amount of each front-stage conversion module by using the power ring output value of the corresponding front-stage conversion module, so that each front-stage conversion module realizes power balance; and performing current balance control on each rear-stage conversion module based on the output current of each rear-stage conversion module. The above method can improve the balance of the DC bus voltage of the solid-state transformer by balancing the power of the front stage through the power ring and balancing the current of the rear stage.

Description

Technical Field

[0001] This invention relates to the field of solid-state transformer technology, and in particular to a control method, device, controller, storage medium, and solid-state transformer for a solid-state transformer. Background Technology

[0002] With the accelerated global energy transition, large-scale grid connection of new energy sources, construction of AC / DC hybrid power distribution systems, and improvement of industrial power efficiency have become core directions for power system development. Traditional power frequency transformers, due to their inherent limitations such as large size and weight, single function, and inability to proactively manage power quality, are no longer sufficient to meet the diversified needs of new power systems for power conversion and control. Solid-state transformers (SSTs), as a new generation of power conversion devices integrating power electronic conversion technology and high-frequency isolation technology, possess multiple functions including voltage transformation, electrical isolation, bidirectional power flow, power quality regulation, and AC / DC hybrid power supply. They have shown broad application prospects in areas such as new energy grid connection, smart grids, rail transit, and data center power supply, and have become a research hotspot and key technological equipment in the field of power electronics.

[0003] Currently, for solid-state transformers with a series-parallel front-end structure, existing technologies typically employ a dual closed-loop control strategy for voltage and current to control each conversion module individually. However, if the control characteristics of each module are not completely consistent due to differences in device parameters, drive delays, etc., independent control cannot guarantee a balanced distribution of active power absorbed from the grid by each module, inevitably leading to accumulated power deviations and severe imbalances in the DC bus voltages. Even with direct parallel connection on the output side, slight differences in the output voltage of each module or unequal line impedances can induce circulating currents and severely uneven output current distribution in the parallel circuit. Summary of the Invention

[0004] This invention provides a control method, device, controller, storage medium, and solid-state transformer for a solid-state transformer, in order to solve the problem of severe DC bus voltage imbalance in existing solid-state transformers with a series-parallel front structure.

[0005] In a first aspect, embodiments of the present invention provide a control method for a solid-state transformer, wherein the solid-state transformer includes multiple transformer units; and each transformer unit includes a front-stage conversion module and a back-stage conversion module; the input terminals of each front-stage conversion module are connected in series, the output terminals of each front-stage conversion module are respectively connected to the input terminal of the corresponding back-stage conversion module through their respective DC buses, and the output terminals of each back-stage conversion module are connected in parallel. The method includes: Obtain the AC input power of each pre-conversion module and take the average AC input power of each pre-conversion module as the average input power. The power loop output value is generated based on the difference between the average input power and the AC side input power of each pre-conversion module. The initial voltage modulation of the corresponding pre-conversion module is corrected by using the power loop output value of each pre-conversion module, so as to achieve power balance among the pre-conversion modules. Based on the output current of each subsequent conversion module, current sharing control is performed on the corresponding subsequent conversion module.

[0006] Secondly, embodiments of the present invention provide a control device for a solid-state transformer, wherein the solid-state transformer includes multiple transformer units; and each transformer unit includes a front-stage conversion module and a back-stage conversion module; the input terminals of each front-stage conversion module are connected in series, the output terminals of each front-stage conversion module are respectively connected to the input terminal of the corresponding back-stage conversion module through their respective DC buses, and the output terminals of each back-stage conversion module are connected in parallel. The device includes: The power average calculation module is used to obtain the AC side input power of each pre-conversion module and use the average value of the AC side input power of each pre-conversion module as the input power average. The power loop output value acquisition module is used to generate the power loop output value based on the difference between the average input power and the AC side input power of each pre-conversion module. The front-end power equalization module is used to correct the initial voltage modulation of the corresponding front-end conversion module by using the power loop output value of each front-end conversion module, so as to achieve power equalization among the front-end conversion modules. The current sharing module is used to perform current sharing control on the corresponding downstream conversion module based on the output current of each downstream conversion module.

[0007] Thirdly, embodiments of the present invention provide a controller, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the solid-state transformer control method as described in any possible implementation of the first aspect above.

[0008] Fourthly, embodiments of the present invention provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the solid-state transformer control method as described in any possible implementation of the first aspect above.

[0009] Fifthly, embodiments of the present invention provide a solid-state transformer, including the controller described in the third aspect.

[0010] This invention provides a control method, device, controller, storage medium, and solid-state transformer for a solid-state transformer. The method first acquires the AC input power of each front-stage converter module and calculates the average input power. Based on the difference between this average and the AC input power of each front-stage converter module, a power loop output value is generated. This power loop output value is used to correct the initial voltage modulation of the corresponding front-stage converter module, causing the input power of each front-stage converter module to automatically converge towards the average, thus solving the DC bus voltage imbalance problem. Simultaneously, current sharing control is implemented based on the output current of each rear-stage converter module, effectively suppressing circulating current in the parallel circuit and uneven distribution of output current. Furthermore, the coordinated control between the front and rear stages can improve the system's operational reliability and modular expansion capability under parameter perturbations. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of the solid-state transformer provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the implementation of the control method for a solid-state transformer provided in an embodiment of the present invention. Figure 3 This is the control loop diagram of the pre-conversion module provided in the embodiment of the present invention; Figure 4 This is the control loop diagram of the subsequent conversion module provided in the embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the control device for the solid-state transformer provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the controller provided in an embodiment of the present invention. Detailed Implementation

[0013] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0014] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0015] Figure 1 This is a schematic diagram of the structure of a solid-state transformer provided in an embodiment of the present invention. Figure 1 As shown, the solid-state transformer includes multiple transformer units; and each transformer unit includes a pre-stage conversion module and a post-stage conversion module; the input terminals of each pre-stage conversion module are connected in series, the output terminals of each pre-stage conversion module are connected to the input terminals of the corresponding post-stage conversion modules through their respective DC buses, and the output terminals of each post-stage conversion module are connected in parallel.

[0016] For solid-state transformers with series inputs and parallel outputs, in existing technologies, each front-end conversion module typically adopts independent voltage and current dual closed-loop control, meaning each module independently adjusts its own DC bus voltage; similarly, each rear-end conversion module also adopts independent voltage and current dual closed-loop control, with each module tracking the same output voltage setpoint.

[0017] However, in actual operation, the component parameters of each pre-conversion module are generally discrete and the switching characteristics are different. Under the control mode of independent adjustment of each pre-conversion module and lack of global coordination, the series structure determines that the input current of each pre-conversion module is equal everywhere, but the modulation quantities generated independently by each module are coupled with each other, which can easily lead to competitive adjustment between regulators. Ultimately, this will cause the DC bus voltage to deviate significantly from the equilibrium state: if the voltage is too high, it will directly compress the safe operating margin of the power devices and bring the risk of overvoltage damage; if the voltage is too low, it will limit the power transmission capability of a single module and restrict the power output capability of the whole machine. Meanwhile, due to differences in equivalent output impedance among the parallel-connected downstream converter modules, and with each module independently controlled and without a current sharing coordination mechanism, the voltage at the parallel output terminals is forcibly clamped to be consistent. Modules with lower equivalent output impedance will bear output current far exceeding the average level, while high-impedance modules will have insufficient output power. This will not only cause uneven distribution of output current and induce circulating current between modules, leading to some modules aging faster due to long-term overload heating, but also reduce the overall operational reliability and expected service life of the system. More importantly, the imbalance in the output power of the downstream stage will be reversed to the DC side of the upstream stage, further widening the output power difference between the upstream converter modules, continuously exacerbating the divergence trend of the DC bus voltages, and forming a vicious cycle of imbalance.

[0018] Based on this, this application provides a control method for a solid-state transformer, see [link to relevant documentation]. Figure 2 The diagram illustrates the implementation flowchart of the control method for a solid-state transformer provided in this embodiment of the invention. The execution subject of this method can be the controller of the solid-state transformer, which may include an independent main controller, controllers corresponding to each front-stage conversion module, and controllers corresponding to each rear-stage conversion module; or it may include a comprehensive controller that integrates the main controller, controllers corresponding to each front-stage conversion module, and controllers corresponding to each rear-stage conversion module.

[0019] The following uses a comprehensive controller as an example to illustrate the method provided in this application in detail. The implementation process is described in detail below: S101: Obtain the AC input power of each pre-conversion module and use the average value of the AC input power of each pre-conversion module as the average input power.

[0020] In this embodiment, the controller synchronously samples the AC side phase voltage and phase current of each pre-conversion module. Based on the instantaneous values ​​of the AC side phase voltage and phase current at the same moment, the controller calculates the AC side input power of each pre-conversion module. The controller then takes the arithmetic mean of the AC side input power of all pre-conversion modules to obtain the average input power.

[0021] Specifically, the AC side input power can be defined as the AC side active power input. The controller acquires the instantaneous values ​​of the three-phase AC voltage. With the instantaneous value of three-phase current Then based on the formula Calculate the AC input active power. Finally, average the AC input active power of all preceding converter modules to obtain the average input power.

[0022] Since the series structure of the front-end converter determines that each front-end converter module shares the same input current, the difference in power transmission between modules is essentially due to the difference in the active component of the equivalent input voltage. The steady-state amplitude of the DC bus voltage is entirely determined by the balance of active power on the DC side. Reactive power only completes periodic energy exchange in the AC circuit and does not inject net energy into the DC bus, nor can it change the energy storage level of the bus capacitor. Therefore, only the imbalance of active power is the fundamental cause of the imbalance of DC bus voltage. Therefore, this embodiment selects the active power input on the AC side for power balancing control.

[0023] S102: Generate the power loop output value based on the difference between the average input power and the AC side input power of each pre-conversion module.

[0024] In this embodiment, the controller calculates the difference between the average input power and the AC input power of a single pre-converter module to obtain the power deviation value of that module. The power deviation value is then input into a linear proportional-integral controller, which performs proportional adjustment to achieve fast response and integral adjustment to eliminate steady-state error. Finally, the controller calculates and outputs the power loop output value corresponding to that pre-converter module.

[0025] S103: The initial voltage modulation amount of the corresponding pre-conversion module is corrected by using the power loop output value of each pre-conversion module, so as to achieve power balance among the pre-conversion modules.

[0026] In this embodiment, the controller can add the power loop output value of the front-end converter module to the initial voltage modulation amount of the corresponding front-end converter module to obtain the final voltage modulation amount of each front-end converter module.

[0027] As another embodiment, the controller can also convert the power loop output value of a single front-end converter module into a correction coefficient through normalization, multiply the correction coefficient by the initial voltage modulation amount of the front-end converter module, and use the multiplication result as the corrected voltage modulation amount; by scaling the modulation amount proportionally, the power transmission capability of the module is adjusted to achieve power balance among the modules.

[0028] S104: Based on the output current of each subsequent conversion module, perform current sharing control on the corresponding subsequent conversion module.

[0029] As can be seen from the above embodiments, this embodiment first obtains the AC side input power of each front-end conversion module and calculates the average input power. Based on the difference between the average value and the actual power of each module, a power loop output value is generated. The power loop output value is used to correct the initial voltage modulation amount of the corresponding front-end conversion module, so that the input power of each front-end conversion module automatically converges to the average value, thus solving the DC bus voltage imbalance problem. At the same time, current sharing control is implemented based on the output current of each back-end conversion module, which effectively suppresses the circulating current in the parallel circuit and the uneven distribution of output current, avoids device overload, and the coordinated control of front and back stages improves the system's operational reliability and modular expansion capability under parameter perturbation.

[0030] In one possible implementation, Figure 3 The control loop diagram of the pre-conversion module provided in this embodiment is shown. (Refer to...) Figure 3 The specific implementation process of S102 includes: Average the input power AC input power of each pre-conversion module The difference is input into the first controller to obtain the power loop output value of each front-end conversion module.

[0031] In this embodiment, the controller can average the input power. Subtract the AC input power of each pre-conversion module respectively The input power difference for each transformer unit is obtained. This input power difference is then input to the first controller to obtain the power loop output value of each front-end converter module. The first controller can be a PI, PID (Proportional-Integral-Derivative), or PR (Proportional-Resonant) controller, etc.

[0032] Specifically, after the first controller outputs the power loop output value, the power loop output value can be limited to prevent excessive compensation from causing modulation saturation.

[0033] In one possible implementation, refer to Figure 3 Before S103, the method provided in this embodiment further includes: S201: Obtain the actual values ​​of the bus voltage of each DC bus of the solid-state transformer; S202: The average value of the actual bus voltage of each DC bus is taken as the average bus voltage. ; S203: Based on bus voltage reference value and the average bus voltage The difference is used to generate the initial voltage modulation amount.

[0034] In this embodiment, the voltage sensor of each transformer unit samples the actual value of the bus voltage of the corresponding DC bus in real time, and sends it to the controller of the solid-state transformer after analog-to-digital conversion. The controller sums all the actual values ​​of the bus voltage and divides them by the number of units to obtain the average value of the bus voltage. .

[0035] Specifically, the controller can also use a recursive filtering averaging algorithm, which updates the average bus voltage based on the average bus voltage of the previous control cycle and the actual values ​​of each bus voltage in the current cycle, using a first-order recursive filtering formula to achieve a smooth filtering effect.

[0036] In one possible implementation, refer to Figure 3 The specific implementation process of S203 includes: Based on the bus voltage reference value With the average bus voltage The difference is used to generate the current command value; The input current of each pre-conversion module is obtained, and an initial voltage modulation amount is generated based on the difference between the input current of each pre-conversion module and the current command value.

[0037] In this embodiment, the controller will use the bus voltage reference value Subtract the average bus voltage The controller obtains the bus voltage difference and then controls it to generate a current command value. This current command value is the target value of the desired input current to the preceding conversion modules, generated by the outer voltage loop. The controller then subtracts the input current of each preceding conversion module from the current command value to obtain the input current difference, and generates the initial voltage modulation amount based on this difference.

[0038] As can be seen from the above embodiments, this embodiment generates a current command value by the difference between the average bus voltage and the reference bus voltage value, and generates an initial voltage modulation amount by combining the difference between the input current of each front-end conversion module and the current command value, forming a double closed-loop structure of voltage outer loop and current inner loop. This structure balances voltage stability and fast current tracking, has excellent dynamic response performance, strong anti-disturbance capability, ensures that the DC bus voltage accurately follows the given value, and improves power transmission quality.

[0039] In one possible implementation, the current command value includes a d-axis current command value. and q-axis current command value ;refer to Figure 3 The specific implementation process of generating the current command value based on the difference between the bus voltage reference value and the average bus voltage in S203 above includes: The bus voltage difference is input into the second controller to generate the d-axis current command value. ; Obtain the actual value of reactive power of the power grid Q The actual value of the reactive power of the power grid Q With the power grid reactive power setpoint Q By subtracting the values, we obtain the reactive power difference. The reactive power difference is input into the third controller to generate the q-axis current command value. .

[0040] In this embodiment, the current command value is further refined by decomposing it into active d-axis current command values ​​based on a synchronous rotating coordinate system. With reactive q-axis current command value Two independent components. The d-axis current command value... Generated by the bus voltage closed loop, it represents the target current value of the active axis in the synchronous rotating coordinate system, corresponding to active power transmission, and is used to maintain the stability of the DC bus voltage; q-axis current command value. Generated from the closed-loop reactive power of the power grid, corresponding to reactive power regulation, it is used to achieve power factor control and reactive power compensation of the power grid. This embodiment is used to achieve independent decoupled control of active and reactive power, which can simultaneously meet the requirements of bus voltage stabilization and power quality management of the power grid.

[0041] Specifically, the second and third controllers operate independently and in parallel; the second controller only receives the bus voltage difference and outputs the d-axis command value, while the third controller only receives the reactive power deviation and outputs the q-axis command value; the parameters of the two controllers are independently tuned, and the active and reactive power control are completely decoupled and do not interfere with each other.

[0042] The second and third controllers can be PI, PID, or PR controllers. The controller can dynamically adjust the gain coefficient in the third controller according to the bus voltage difference. The larger the bus voltage difference, the smaller the gain coefficient, thus prioritizing active power regulation and restoring reactive power regulation capability after the voltage recovers.

[0043] As can be seen from the above embodiments, this embodiment decomposes the current command value into d-axis active power command value and q-axis reactive power command value, which are generated independently through voltage loop and reactive power loop respectively, realizing decoupled control of active power and reactive power. This scheme can flexibly adjust the reactive power of the power grid, support unity power factor operation or dynamic reactive power compensation, and improve the adaptability of solid-state transformers to the power grid and the power quality management capability.

[0044] After obtaining the d-axis current command value and the q-axis current command value, as follows: Figure 3 As shown, the specific implementation process of obtaining the input current of each pre-conversion module and generating the initial voltage modulation amount based on the difference between the input current of each pre-conversion module and the current command value includes: The input current from the pre-stage transformation module is transformed from the abc coordinate system to the synchronous rotating coordinate system to obtain the d-axis input current. and q-axis input current ; d-axis current command value Subtract d-axis input current The d-axis current difference is obtained, and then the d-axis current difference is input into the d-axis current loop controller to obtain the initial control quantity of the d-axis. ; q-axis current command value Subtract q-axis input current The q-axis current difference is obtained, and then the q-axis current difference is input into the q-axis current loop controller to obtain the initial control quantity for the q-axis. ; Initial control value of the d-axis and q-axis initial control value The initial voltage modulation of the three phases is obtained by transforming from the synchronous rotating coordinate system to the abc coordinate system. , , ).

[0045] In one possible implementation, the specific implementation process of S103 includes: The initial voltage modulation values ​​of each pre-conversion module are superimposed with the power loop output value to obtain the final voltage modulation value of the pre-conversion module.

[0046] In this embodiment, the controller can directly add the initial voltage modulation amount of each front-end conversion module to the corresponding power loop output value to obtain the final voltage modulation amount of the front-end conversion module.

[0047] As another specific embodiment, the controller can also perform a weighted summation of the initial voltage modulation of each front-end conversion module with the corresponding power loop output value to obtain the final voltage modulation of the corresponding front-end conversion module.

[0048] Specifically, the difference between the average bus voltage and the actual bus voltage of a single DC bus is obtained and used as the bus deviation. When the bus deviation is less than or equal to a first preset threshold, the weighting coefficient of the initial voltage modulation of the corresponding front-end conversion module is the first value, and the weighting coefficient of the power loop output value is the second value. If the bus deviation of a front-end conversion module is greater than the first preset threshold, the first and second values ​​are adjusted according to the bus deviation, with the first value being negatively correlated with the bus deviation and the second value being positively correlated with the bus deviation. Simultaneously, the sum of the first and second values ​​is always 1.

[0049] Since the initial voltage modulation is crucial for maintaining the overall DC bus voltage tracking reference value, if the first value remains too low for an extended period, the power loop output will dominate the modulation. In this case, the power loops of each upstream converter module will adjust based solely on power deviation rather than absolute values, potentially causing the modulation of each upstream converter module to deviate from the system's required baseline value, and the average bus voltage will fail to effectively track the given value. Therefore, the first value must be no less than 0.5, and correspondingly, the second value must be no greater than 0.5 to ensure that the overall regulation capability of the main control loop is not undermined.

[0050] The above method can address situations where the bus deviation of a certain pre-conversion module is large, indicating a severely unbalanced system. By reducing the weighting coefficient of the initial voltage modulation and increasing the weighting coefficient of the power loop output value, the power loop compensation signal becomes dominant, strongly driving the module's voltage back to the equilibrium range. When the bus deviation is small, the system approaches equilibrium. In this case, the weighting coefficient of the initial voltage modulation is increased, while the weighting coefficient of the power loop output value is decreased. This allows the global commands of the main control dual closed loop to regain dominance, with the voltage equalization loop only playing a fine-tuning role, thus avoiding compensation noise interference with steady-state accuracy.

[0051] Furthermore, the specific implementation process of S103 includes: The initial voltage modulation of each front-end conversion module is weighted and summed with the corresponding power loop output value; If the initial voltage modulation is within the linear range, the weighting coefficients of the initial voltage modulation and the power loop output value are kept constant; the linear range includes the upper limit of the linear region. When the initial voltage modulation is detected to be greater than the upper limit of the linear region, the weighting coefficient of the initial voltage modulation is reduced and the weighting coefficient of the power loop output value is increased.

[0052] The above method avoids the situation where assigning a large weight to an initially large voltage modulation amount could lead to overmodulation even with a small compensation amount. By dynamically adjusting the weighting coefficients of the two parameters, the directionality of the power loop output value can be used to guide the final voltage modulation amount to remain within a safe range without changing the overall effective control amplitude. Similarly, during the adjustment process, the weighting coefficient of the initial voltage modulation amount must be ensured to be no less than 0.5.

[0053] In one possible implementation, Figure 4 The control loop diagram of the subsequent conversion module provided in this embodiment is shown. (Refer to...) Figure 4 The specific implementation process of S104 includes: Calculate the output current of each subsequent conversion module. I o The average value, and used as the average current value. ; Based on the average current The output current of each subsequent conversion module I o The difference is used to calculate the flow control quantity; Actual output voltage values ​​of each subsequent conversion module U o With the output voltage setpoint The difference between the output voltages of each subsequent conversion module is obtained by subtracting the output voltages. The current sharing control quantity is added to the output voltage difference of each subsequent conversion module to obtain the compensated output voltage difference. The output voltage difference after compensation of each subsequent conversion module is input into the fourth controller to obtain the voltage modulation amount of the corresponding subsequent conversion module.

[0054] In this embodiment, a current sharing control strategy is adopted for the subsequent conversion module.

[0055] Specifically, the controller first calculates the output current of each subsequent conversion module. I o The average value is used as the average current value. Then average the current. Subtract the output current of each subsequent conversion module respectively I o The output current difference is obtained; this difference is then input to the fifth controller to obtain the current sharing control quantity; on the other hand, the controller is also used to set the output voltage setpoint of each subsequent conversion module. Subtract the corresponding actual output voltage value U o The output voltage difference is obtained, and then the current sharing control quantity is added to the output voltage difference of each subsequent conversion module to obtain the compensated output voltage difference. Finally, the compensated output voltage difference is input to the fourth controller to obtain the voltage modulation quantity of the corresponding subsequent conversion module.

[0056] The subsequent conversion module can be a dual active bridge (DAB) converter. After obtaining the final voltage modulation amount, it converts the voltage modulation amount into a phase shift angle, and then uses the phase shift angle to generate a phase-shifted PWM (Pulse Width Modulation) signal to control the DAB.

[0057] The subsequent conversion module can also be an LLC resonant converter. After obtaining the final voltage modulation amount, the controller converts the voltage modulation amount into a switching frequency, and then uses the switching frequency to generate a PFM (Pulse Frequency Modulation) signal to control the LLC resonant converter.

[0058] As can be seen from the above embodiments, the control of the subsequent conversion module adopts a control structure of voltage outer loop + current sharing inner loop. This ensures both the stability and accuracy of the output voltage and the uniform distribution of the output current. The two are organically integrated through superposition and do not conflict with each other. The direct effect of current sharing control is that the output current stress of each parallel subsequent conversion module tends to be consistent, preventing individual subsequent conversion modules from overheating and aging due to excessive current. It also suppresses circulating current phenomena caused by voltage differences or impedance inequalities in the parallel loop, reducing unnecessary circulating current losses and improving overall conversion efficiency. Simultaneously, the uniform current distribution makes the operating state of each subsequent conversion module more balanced, which helps extend the service life of the entire device, improves the reliability and redundancy of the system, and ensures continuous system operation.

[0059] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0060] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0061] Figure 5 A schematic diagram of the control device for a solid-state transformer provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 5As shown, the control device 100 for the solid-state transformer includes: The power average calculation module 110 is used to obtain the AC side input power of each pre-conversion module and use the average value of the AC side input power of each pre-conversion module as the input power average. The power loop output value acquisition module 120 is used to generate a power loop output value based on the difference between the average input power and the AC side input power of each pre-conversion module. The front-end power equalization module 130 is used to correct the initial voltage modulation amount of the corresponding front-end conversion module by using the power loop output value of each front-end conversion module, so as to achieve power equalization of each front-end conversion module. The current sharing module 140 is used to perform current sharing control on the corresponding downstream conversion module based on the output current of each downstream conversion module.

[0062] In one possible implementation, the power loop output value acquisition module 120 includes: The difference between the average input power and the AC side input power of each pre-conversion module is input to the first controller to obtain the power loop output value of each pre-conversion module.

[0063] In one possible implementation, the control device 100 for the solid-state transformer further includes an initial voltage modulation generation module, comprising: The bus voltage actual value acquisition unit is used to acquire the actual bus voltage value of each DC bus of the solid-state transformer before correcting the initial voltage modulation amount of the corresponding front-stage conversion module by using the power loop output value of each front-stage conversion module. The bus voltage average value calculation unit is used to take the average value of the actual bus voltage of each DC bus as the bus voltage average value. An initial voltage modulation generation unit is used to generate an initial voltage modulation amount based on the difference between the bus voltage reference value and the average value of the bus voltage.

[0064] In one possible implementation, the initial voltage modulation amount generation unit includes: A current command generation subunit is used to generate a current command value based on the difference between the bus voltage reference value and the average bus voltage. An initial voltage modulation generation subunit is used to obtain the input current of each pre-conversion module and generate the initial voltage modulation based on the difference between the input current of each pre-conversion module and the current command value.

[0065] In one possible implementation, the current command value includes a d-axis current command value and a q-axis current command value; the current command generation subunit includes: The bus voltage difference is obtained by subtracting the average bus voltage from the reference bus voltage value. The bus voltage difference is input into the second controller to generate the d-axis current command value; Obtain the actual value of reactive power in the power grid, and subtract the actual value of reactive power in the power grid from the given value of reactive power in the power grid to obtain the reactive power difference value; The reactive power difference is input into the third controller to generate the q-axis current command value.

[0066] In one possible implementation, the downstream current sharing module 140 includes: Calculate the average value of the output current of each subsequent conversion module and use it as the average current value; The current sharing control quantity is calculated based on the difference between the average current and the output current of each subsequent conversion module. The difference between the actual output voltage value and the given output voltage value of each subsequent conversion module is obtained by subtracting the actual output voltage value from the given output voltage value of each subsequent conversion module. The current sharing control value is added to the output voltage difference of each subsequent conversion module to obtain the compensated output voltage difference. The output voltage difference after compensation of each subsequent conversion module is input into the fourth controller to obtain the voltage modulation amount of the corresponding subsequent conversion module.

[0067] Figure 6 This is a schematic diagram of the controller provided in an embodiment of the present invention. Figure 6 As shown, the controller 6 in this embodiment includes a processor 60, a memory 61, and a computer program 62 stored in the memory 61 and executable on the processor 60. When the processor 60 executes the computer program 62, it implements the steps in the various solid-state transformer control method embodiments described above, for example... Figure 2 Steps S101 to S104 are shown. Alternatively, when the processor 60 executes the computer program 62, it implements the functions of each module / unit in the above-described device embodiments, for example... Figure 5 The functions of modules 110 to 140 are shown.

[0068] For example, the computer program 62 can be divided into one or more modules / units, which are stored in the memory 61 and executed by the processor 60 to complete the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program 62 in the controller 6.

[0069] The controller 6 may include, but is not limited to, a processor 60 and a memory 61. Those skilled in the art will understand that... Figure 6 This is merely an example of controller 6 and does not constitute a limitation on controller 6. It may include more or fewer components than shown, or combine certain components, or different components. For example, the controller may also include input / output devices, network access devices, buses, etc.

[0070] The processor 60 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0071] The memory 61 can be an internal storage unit of the controller 6, such as a hard disk or memory of the controller 6. The memory 61 can also be an external storage device of the controller 6, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the controller 6. Furthermore, the memory 61 can include both internal storage units and external storage devices of the controller 6. The memory 61 is used to store the computer program and other programs and data required by the controller. The memory 61 can also be used to temporarily store data that has been output or will be output.

[0072] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0073] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0074] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0075] In the embodiments provided by this invention, it should be understood that the disclosed devices / controllers and methods can be implemented in other ways. For example, the device / controller embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0076] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0077] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0078] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the control method embodiments of the various solid-state transformers described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0079] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A control method for a solid-state transformer, characterized in that, The solid-state transformer includes multiple transformer units; and each transformer unit includes a front-stage conversion module and a back-stage conversion module; the input terminals of each front-stage conversion module are connected in series, the output terminals of each front-stage conversion module are connected to the input terminals of the corresponding back-stage conversion modules through their respective DC buses, and the output terminals of each back-stage conversion module are connected in parallel. The method includes: Obtain the AC input power of each pre-conversion module and take the average AC input power of each pre-conversion module as the average input power. The power loop output value is generated based on the difference between the average input power and the AC side input power of each pre-conversion module. The initial voltage modulation of the corresponding pre-conversion module is corrected by using the power loop output value of each pre-conversion module, so as to achieve power balance among the pre-conversion modules. Based on the output current of each subsequent conversion module, current sharing control is performed on the corresponding subsequent conversion module.

2. The control method for a solid-state transformer according to claim 1, characterized in that, The generation of the power loop output value based on the difference between the average input power and the AC side input power of each preceding conversion module includes: The difference between the average input power and the AC side input power of each pre-conversion module is input to the first controller to obtain the power loop output value of each pre-conversion module.

3. The control method for a solid-state transformer according to claim 1, characterized in that, Before correcting the initial voltage modulation amount of the corresponding pre-conversion module using the power loop output value of each pre-conversion module, the method further includes: Obtain the actual values ​​of the bus voltage of each DC bus of the solid-state transformer; The average value of the actual bus voltage of each DC bus is taken as the average bus voltage. An initial voltage modulation amount is generated based on the difference between the bus voltage reference value and the average bus voltage.

4. The control method for a solid-state transformer according to claim 3, characterized in that, The generation of the initial voltage modulation amount based on the difference between the bus voltage reference value and the average bus voltage includes: A current command value is generated based on the difference between the bus voltage reference value and the average bus voltage. The input current of each pre-conversion module is obtained, and the initial voltage modulation amount is generated based on the difference between the input current of each pre-conversion module and the current command value.

5. The control method for a solid-state transformer according to claim 4, characterized in that, The current command value includes a d-axis current command value and a q-axis current command value; the generation of the current command value based on the difference between the bus voltage reference value and the average bus voltage includes: The bus voltage difference is obtained by subtracting the average bus voltage from the reference bus voltage value. The bus voltage difference is input into the second controller to generate the d-axis current command value; Obtain the actual value of reactive power in the power grid, and subtract the actual value of reactive power in the power grid from the given value of reactive power in the power grid to obtain the reactive power difference value; The reactive power difference is input into the third controller to generate the q-axis current command value.

6. The control method for a solid-state transformer according to claim 1, characterized in that, The current sharing control of the corresponding subsequent conversion modules based on the output current of each subsequent conversion module includes: Calculate the average value of the output current of each subsequent conversion module and use it as the average current value; The current sharing control quantity is calculated based on the difference between the average current and the output current of each subsequent conversion module. The difference between the actual output voltage value and the given output voltage value of each subsequent conversion module is obtained by subtracting the actual output voltage value from the given output voltage value of each subsequent conversion module. The current sharing control value is added to the output voltage difference of each subsequent conversion module to obtain the compensated output voltage difference. The output voltage difference after compensation of each subsequent conversion module is input into the fourth controller to obtain the voltage modulation amount of the corresponding subsequent conversion module.

7. A control device for a solid-state transformer, characterized in that, The solid-state transformer includes multiple transformer units; and each transformer unit includes a front-stage conversion module and a back-stage conversion module; the input terminals of each front-stage conversion module are connected in series, the output terminals of each front-stage conversion module are connected to the input terminals of the corresponding back-stage conversion modules through their respective DC buses, and the output terminals of each back-stage conversion module are connected in parallel. The device includes: The power average calculation module is used to obtain the AC side input power of each pre-conversion module and use the average value of the AC side input power of each pre-conversion module as the input power average. The power loop output value acquisition module is used to generate the power loop output value based on the difference between the average input power and the AC side input power of each pre-conversion module. The front-end power equalization module is used to correct the initial voltage modulation of the corresponding front-end conversion module by using the power loop output value of each front-end conversion module, so as to achieve power equalization among the front-end conversion modules. The current sharing module is used to perform current sharing control on the corresponding downstream conversion module based on the output current of each downstream conversion module.

8. A controller comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the control method for the solid-state transformer as described in any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the control method for the solid-state transformer as described in any one of claims 1 to 6.

10. A solid-state transformer, characterized in that, Includes the controller as described in claim 8.

Images