Solid state transformer power cell voltage equalization method, system, and storage medium

Abstract

This invention provides a method, system, and storage medium for voltage equalization of power units in a solid-state transformer, belonging to the field of power electronic conversion technology. The method includes: acquiring the DC-side voltage and output power of each power unit; determining the unit voltage deviation based on the DC-side voltage; and determining the load variation range based on the output power. Within the load variation range, determining transient equalization requirements based on the unit voltage deviation; and adjusting the carrier phase of the corresponding power unit based on the transient equalization requirements. Based on the DC-side voltage after carrier phase adjustment, determining the remaining transient equalization requirements; and after the load variation range ends, determining the continuous equalization requirements based on the unit voltage deviation. Finally, adjusting the output active power command of the corresponding power unit based on the continuous equalization requirements and the remaining transient equalization requirements. This invention achieves rapid equalization and stable regulation of the DC-side voltage of power units during load changes.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, and more specifically to a method, system, and storage medium for voltage equalization of power units in a solid-state transformer. Background Technology

[0002] Solid-state transformers are a new type of power equipment that uses power electronic conversion technology to achieve voltage transformation and energy transfer. They are typically composed of multiple cascaded power units, each of which transmits power through a power electronic converter and maintains energy buffering and voltage stability through DC-side capacitors. In applications such as renewable energy integration, smart power distribution, and high-reliability power supply, solid-state transformers need to operate in environments with frequent load changes and large power fluctuations. Therefore, voltage coordination and control among the power units plays a crucial role in ensuring stable equipment operation.

[0003] During the operation of a solid-state transformer, due to differences in the parameters, switching states, and power transmission processes of power devices in different power units, the energy changes of the DC-side capacitors in each power unit may be inconsistent, resulting in DC-side voltage deviations. When the solid-state transformer is in a stable operating state, this type of voltage deviation can usually be regulated through existing equalization control methods. However, in actual operation, dynamic changes such as sudden load increases or rapid load decreases may occur on the load side. At this time, the energy exchange state between power units will change rapidly, causing transient fluctuations in the DC-side voltage of some power units.

[0004] Existing voltage balancing methods for solid-state transformer power units typically adjust power distribution based on detected voltage deviations to reduce voltage differences between different power units. However, during dynamic load changes, DC-side voltage deviations may be affected by both instantaneous power variations and long-term uneven power distribution. These two types of voltage deviations have different causes and regulation requirements. Using the same regulation method may result in insufficient or excessive regulation response during transient processes, and it is also difficult to simultaneously ensure rapid response during load changes and balancing effectiveness under stable operating conditions.

[0005] Therefore, existing solid-state transformer power unit voltage balancing technology still suffers from the problem of difficulty in distinguishing different types of voltage deviations during load changes and the lack of adaptive adjustment for different operating conditions, which limits the DC-side voltage balancing effect and dynamic operating stability of the power unit. Summary of the Invention

[0006] The purpose of this invention is to provide a method, system, and storage medium for voltage balancing of power units in a solid-state transformer, so as to at least solve the problem that it is difficult to adjust the DC-side voltage deviation of the power unit in a targeted manner during load changes.

[0007] To achieve the above objectives, a first aspect of the present invention provides a voltage equalization method for power units of a solid-state transformer. The method includes: acquiring the DC-side voltage and output power of each power unit; determining the unit voltage deviation based on the DC-side voltage; and determining a load variation range based on the output power. Within the load variation range, determining a transient equalization requirement based on the unit voltage deviation; and adjusting the carrier phase of the corresponding power unit based on the transient equalization requirement. The transient equalization requirement characterizes the direction and degree of deviation of the DC-side voltage deviation of the corresponding power unit relative to its stable state before the load change during the load variation process, thereby determining the carrier phase adjustment direction and adjustment amount for the corresponding power unit. The remaining transient equalization requirement is determined based on the DC-side voltage after carrier phase adjustment, and a continuous equalization requirement is determined based on the unit voltage deviation after the load variation range ends. The remaining transient equalization requirement characterizes the dynamic voltage deviation state still existing in the corresponding power unit after carrier phase adjustment; the continuous equalization requirement characterizes the steady-state voltage deviation state that continues to exist in the corresponding power unit after the load change ends; and adjusting the output active power command of the corresponding power unit based on the continuous equalization requirement and the remaining transient equalization requirement.

[0008] Optionally, determining the unit voltage deviation based on the DC-side voltage includes: determining the average voltage of the power unit based on the DC-side voltage corresponding to each power unit; calculating the difference between the DC-side voltage corresponding to each power unit and the average voltage of the power unit, and determining the difference as the unit voltage deviation of the corresponding power unit.

[0009] Optionally, determining the load change range based on the output power includes: determining the total output power of the solid-state transformer based on the output power of each power unit; obtaining the total output power within a continuous sampling period; determining the load change start time when the change in total output power between adjacent sampling periods is greater than a preset load change threshold; determining the load change end time when the change in total output power within a consecutive preset number of sampling periods is less than a preset stability threshold; and defining the time range corresponding to the load change start time to the load change end time as the load change range.

[0010] Optionally, within the load variation range, determining the transient equalization requirement based on the unit voltage deviation and adjusting the carrier phase of the corresponding power unit according to the transient equalization requirement includes: obtaining the unit voltage deviation of the corresponding power unit within the load variation range and determining the offset direction and offset amount of the unit voltage deviation relative to before the load change; determining the transient equalization requirement of the corresponding power unit based on the offset direction and the offset amount; and adjusting the carrier phase of the corresponding power unit according to the transient equalization requirement.

[0011] Optionally, determining the transient equalization requirement of the corresponding power unit based on the offset direction and the offset amount includes: determining the transient equalization direction of the corresponding power unit based on the offset direction; determining the transient equalization degree of the corresponding power unit based on the relationship between the offset amount and a preset offset threshold; and determining the transient equalization requirement of the corresponding power unit based on the transient equalization direction and the transient equalization degree.

[0012] Optionally, adjusting the carrier phase of the corresponding power unit according to the transient equalization requirement includes: determining the carrier phase adjustment direction and carrier phase adjustment amount of the corresponding power unit according to the transient equalization requirement of each power unit, wherein the carrier phase is the PWM carrier phase of the input stage of the corresponding power unit; and adjusting the carrier phase of the corresponding power unit within a preset carrier phase adjustment range according to the carrier phase adjustment direction and the carrier phase adjustment amount.

[0013] Optionally, determining the remaining transient equalization requirement based on the DC-side voltage after carrier phase adjustment includes: obtaining the DC-side voltage corresponding to each power unit after carrier phase adjustment, and determining the average voltage of the power unit based on each DC-side voltage; determining the difference between the DC-side voltage corresponding to each power unit and the average voltage of the power unit to obtain the adjusted unit voltage deviation; determining the offset of the adjusted unit voltage deviation relative to the load before the change, and determining the remaining transient equalization requirement of the corresponding power unit based on the direction and magnitude of the offset.

[0014] Optionally, adjusting the output active power command of the corresponding power unit according to the continuous balancing demand and the remaining transient balancing demand includes: when the directions of the continuous balancing demand and the remaining transient balancing demand of the corresponding power unit are the same, determining the power adjustment amount according to the sum of the magnitudes of the continuous balancing demand and the remaining transient balancing demand, and determining the corresponding balancing demand direction as the power adjustment direction; when the directions of the continuous balancing demand and the remaining transient balancing demand of the corresponding power unit are opposite, determining the power adjustment amount according to the difference between their magnitudes, and determining the power adjustment direction according to the larger of the two balancing demands; adjusting the output active power command of the corresponding power unit according to the power adjustment direction and the power adjustment amount, and keeping the sum of the adjusted output active power commands of each power unit unchanged.

[0015] A second aspect of the present invention provides a voltage balancing system for power units of a solid-state transformer. The system includes: an acquisition unit, configured to acquire the DC-side voltage and output power of each power unit, determine the unit voltage deviation based on the DC-side voltage, and determine the load variation range based on the output power; an adjustment unit, configured to determine transient balancing requirements based on the unit voltage deviation within the load variation range, and adjust the carrier phase of the corresponding power unit based on the transient balancing requirements; wherein the transient balancing requirements characterize the offset direction and degree of the DC-side voltage deviation of the corresponding power unit relative to the steady state before the load variation during the load variation process, so as to determine the carrier phase adjustment direction and adjustment amount of the corresponding power unit; a requirement determination unit, configured to determine the remaining transient balancing requirements based on the DC-side voltage after the carrier phase adjustment, and determine the continuous balancing requirements based on the unit voltage deviation after the load variation range ends; wherein the remaining transient balancing requirements characterize the dynamic voltage offset state still existing in the corresponding power unit after the carrier phase adjustment; the continuous balancing requirements characterize the steady-state voltage offset state that continues to exist in the corresponding power unit after the load variation ends; and an instruction generation unit, configured to adjust the output active power instruction of the corresponding power unit based on the continuous balancing requirements and the remaining transient balancing requirements.

[0016] On the other hand, the present invention provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described solid-state transformer power unit voltage equalization method.

[0017] Through the above technical solution, this invention acquires the DC-side voltage and output power of each power unit, and determines the voltage deviation change state of the power unit in conjunction with the load change process, thereby identifying voltage imbalance problems in different operating stages. By adjusting the carrier phase of the corresponding power unit according to the transient equalization requirements during load changes, the power unit can quickly respond to load disturbances, reducing the DC-side voltage fluctuation amplitude during dynamic processes. Simultaneously, by analyzing the voltage state after carrier phase adjustment, the remaining transient equalization requirements are further identified, and the output active power command is adjusted in conjunction with the continuous equalization requirements after load stabilization, thus compensating for long-term voltage deviations. Therefore, it avoids the problems of insufficient response or over-adjustment caused by the traditional single equalization control method using the same adjustment strategy for different types of voltage deviations, improving the voltage consistency and operational stability of the power units in the solid-state transformer during load changes.

[0018] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of the steps of a solid-state transformer power unit voltage equalization method provided in one embodiment of the present invention; Figure 2 This is a detailed flowchart of step S20 of the solid-state transformer power unit voltage equalization method provided in one embodiment of the present invention; Figure 3 This is a schematic diagram of the transient offset of the voltage deviation of a power unit provided in one embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the distinction between transient equilibrium demand and continuous equilibrium demand provided by one embodiment of the present invention; Figure 5 This is a system structure diagram of a solid-state transformer power unit voltage balancing system provided in one embodiment of the present invention. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] like Figure 1 As shown, this invention provides a voltage equalization method for power units of a solid-state transformer, the method comprising: Step S10: Obtain the DC-side voltage and output power of each power unit, determine the unit voltage deviation based on the DC-side voltage, and determine the load variation range based on the output power.

[0022] Specifically, determining the unit voltage deviation based on the DC-side voltage includes: determining the average voltage of the power unit based on the DC-side voltage corresponding to each power unit; calculating the difference between the DC-side voltage corresponding to each power unit and the average voltage of the power unit, and determining the difference as the unit voltage deviation of the corresponding power unit.

[0023] Furthermore, determining the load change range based on the output power includes: determining the total output power of the solid-state transformer based on the output power of each power unit; acquiring the total output power within a continuous sampling period; determining the load change start time when the change in total output power between adjacent sampling periods is greater than a preset load change threshold; determining the load change end time when the change in total output power within a consecutive preset number of sampling periods is less than a preset stability threshold; and defining the time range corresponding to the load change start time to the load change end time as the load change range.

[0024] In this embodiment of the invention, the solid-state transformer includes multiple power units. Each power unit includes an input stage power electronic conversion section, a DC-side capacitor, and an output stage power electronic conversion section. The input stage of each power unit uses PWM modulation for power conversion, where the carrier phase is the position of the PWM carrier of the corresponding power unit's input stage relative to its reference carrier phase. The output stage of each power unit transfers energy through its corresponding DC side and adjusts the active power transferred to the load side according to the output active power command. The following example illustrates the positive operating state where energy is transferred from the input side to the load side. When the output active power of the corresponding power unit increases, its DC-side energy consumption increases; when the output active power decreases, its DC-side energy consumption decreases. The above power flow relationship is used to explain the subsequent voltage equalization adjustment process and does not constitute a limitation on the specific power conversion topology of the solid-state transformer.

[0025] In this embodiment of the invention, during the operation of the solid-state transformer, each power unit is equipped with a corresponding DC-side capacitor. By collecting the voltage information across the DC-side capacitor of each power unit, the DC-side voltage of each power unit is obtained. Simultaneously, the output power of each power unit under the current operating state is acquired to analyze the overall load changes of the solid-state transformer.

[0026] The step of determining the unit voltage deviation based on the DC-side voltage includes: determining the average voltage of the power unit based on the DC-side voltage corresponding to each power unit; calculating the difference between the DC-side voltage corresponding to each power unit and the average voltage of the power unit, and determining the difference as the unit voltage deviation of the corresponding power unit.

[0027] In practical implementation, for a solid-state transformer containing multiple power units, the DC-side voltage U corresponding to the i-th power unit in the current operating state is obtained. diThe average voltage of each power unit is determined based on the DC-side voltage of all operating power units. Taking a solid-state transformer containing N power units as an example, the DC-side voltages of the N power units are statistically analyzed to obtain the corresponding average voltage value. Then, the difference between the DC-side voltage of each power unit and the average voltage is calculated to obtain the unit voltage deviation for each power unit. The unit voltage deviation is used to characterize the degree of deviation of the DC-side voltage of the corresponding power unit from the overall average voltage of the power units, providing a data basis for subsequent judgment of the voltage imbalance state between different power units.

[0028] Further, determining the load change range based on the output power includes: determining the total output power of the solid-state transformer based on the output power of each power unit; acquiring the total output power within a continuous sampling period; determining the load change start time when the change in total output power between adjacent sampling periods is greater than a preset load change threshold; determining the load change end time when the change in total output power within a consecutive preset number of sampling periods is less than a preset stability threshold; and defining the time range corresponding to the load change start time to the load change end time as the load change range.

[0029] In practice, the output power of each power unit is acquired, and the output power of each power unit is accumulated to obtain the total output power P of the solid-state transformer at the current moment. During continuous sampling, the total output power of adjacent sampling periods is compared. When the change in total output power between two adjacent sampling periods exceeds a preset load change threshold, it is determined that the solid-state transformer has entered a load change process, and the corresponding moment is recorded as the start time of the load change. For example, the preset load change threshold is set to 5% of the rated output power. When the change in total output power between adjacent sampling periods exceeds this threshold, a load change is determined to have occurred.

[0030] During load changes, the total output power change status is continuously collected. When the total output power change is less than a preset stability threshold for a preset number of consecutive sampling periods, the load change process is considered to have ended, and the corresponding time is recorded as the load change end time. For example, the load is considered to have entered a stable state when the total output power change is less than 1% of the rated output power for 10 consecutive sampling periods. Therefore, the time range between the start time and the end time of the load change is defined as the load change interval.

[0031] It should be noted that the method for determining the average voltage of the power unit is not limited to the above average calculation method. Its essence lies in using the DC side voltage of multiple power units to construct a voltage reference for comparison. The load change threshold and stability threshold are set according to the rated capacity of the solid-state transformer, the sampling period and the actual operating requirements, as long as the load change process and the stable operation process can be distinguished.

[0032] Preferably, the sampling moment when the total output power first shows a continuous, same-direction change is used as the reference moment. Local change windows of five sampling periods are established before and after the reference moment to statistically analyze the consistency of the output power change direction for each power unit. When at least 80% of the power units show the same change direction within the same window, the corresponding total output power change is retained. When the consistency rate is less than 80%, the change is considered a transient fluctuation caused by local switching disturbance or sampling misalignment and is not used to determine the start time of the load change. This reduces misjudgments of the load change range caused by high-frequency switching ripple, communication delay, and sampling asynchrony.

[0033] Step S20: Within the load variation range, determine the transient equalization requirement based on the unit voltage deviation, and adjust the carrier phase of the corresponding power unit according to the transient equalization requirement.

[0034] Specifically, during load changes, the voltage deviation of each power unit is acquired, and the transient offset state of the DC-side voltage of the corresponding power unit is determined based on the trend of the voltage deviation relative to before the load change. The transient equalization requirement of the corresponding power unit is determined based on the transient offset state, whereby the transient equalization requirement characterizes the adjustment direction and degree of the DC-side voltage of the corresponding power unit deviating from the expected state during load changes.

[0035] Furthermore, the carrier phase of the corresponding power unit is adjusted according to the determined transient equalization requirements, so that the power action timing of different power units is adjusted during the load change process, thereby changing the instantaneous energy exchange state between power units and realizing rapid adjustment of DC side voltage transient fluctuations caused by load disturbances.

[0036] By employing the above method, a rapid response is prioritized to voltage deviations caused by dynamic power changes during load variations. This avoids the lag in regulation response caused by directly adjusting power commands, providing a foundation for further eliminating incompletely eliminated transient deviations and persistent deviations under steady-state conditions. Specifically, such as... Figure 2 Step S20 includes the following steps: Step S201: Obtain the unit voltage deviation of the corresponding power unit within the load change range, and determine the offset direction and offset amount of the unit voltage deviation relative to the load change.

[0037] Specifically, the unit voltage deviation of the power unit at each sampling time within the load change range is obtained, and the unit voltage deviation under stable operating conditions before the load change is used as a comparison benchmark. Based on the difference between the unit voltage deviation within the load change range and the comparison benchmark, the offset direction and offset amount of the corresponding power unit are determined.

[0038] For example, such as Figure 3 As shown in the figure, three representative power units from multiple power units are selected to illustrate their voltage deviation changes; the remaining power units are not shown. Before the load change, the voltage deviation of one power unit is +5V. During the load change range, the voltage deviation of this power unit is sampled and found to be +18V. Therefore, the voltage deviation of this power unit is determined to be shifted in the positive direction, with an offset of 13V. When the voltage deviation before the load change is -4V, and the voltage deviation detected during the load change is -15V, the voltage deviation of this power unit is determined to be shifted in the negative direction, with an offset of 11V.

[0039] Furthermore, when the unit voltage deviation changes from positive to negative, or from negative to positive, during a load change, the current offset direction of the corresponding power unit is determined based on the direction of the deviation change, and the corresponding offset amount is determined based on the difference in deviation before and after the change. For example, if the unit voltage deviation is +8V before the load change and becomes -6V during the load change, then it is determined that the power unit has reversed its offset, and the offset amount is 14V.

[0040] By determining the direction and extent of voltage deviation changes in each power unit relative to the steady state during load changes, the dynamic voltage offset characteristics caused by load disturbances can be obtained, providing a basis for subsequently determining transient balancing requirements based on the offset direction and amount. The acquisition time range, sampling period, and offset calculation method of the comparison benchmark before load changes are set according to the actual operating state of the solid-state transformer, as long as they reflect the voltage deviation relationship before and after load changes.

[0041] Step S202: Determine the transient equalization requirement of the corresponding power unit based on the offset direction and the offset amount.

[0042] Specifically, the transient equalization direction of the corresponding power unit is determined based on the offset direction; the transient equalization degree of the corresponding power unit is determined based on the relationship between the offset amount and the preset offset threshold; and the transient equalization requirement of the corresponding power unit is determined based on the transient equalization direction and the transient equalization degree.

[0043] In this embodiment of the invention, the transient equalization direction of the corresponding power unit is determined according to the offset direction, the transient equalization degree of the corresponding power unit is determined according to the relationship between the offset amount and the preset offset threshold, and the transient equalization requirement of the corresponding power unit is generated according to the transient equalization direction and the transient equalization degree.

[0044] Specifically, the transient equalization requirement is determined based on the direction and degree of change of the unit voltage deviation relative to the steady state before the load change during the load change process. The unit voltage deviation of the corresponding power unit in the steady state before the load change is used as a reference deviation. The unit voltage deviation corresponding to the current sampling time within the load change interval is compared with the reference deviation to determine the offset direction and offset amount of the current unit voltage deviation. When the offset amount exceeds a preset offset threshold, the transient equalization direction is determined based on the offset direction, and the degree of transient equalization is determined based on the threshold interval in which the offset amount falls, thereby generating the transient equalization requirement.

[0045] For example, if a power unit's voltage deviation is +5V before a load change, and the detected voltage deviation is +18V during the load change, then the offset direction of this power unit is determined to be a positive offset, with an offset amount of 13V. When the preset first offset threshold is 10V and the second offset threshold is 20V, the corresponding transient equalization level is determined to be medium, and a transient equalization requirement to reduce the DC-side voltage is generated based on the buck adjustment direction corresponding to the positive offset.

[0046] The transient equilibrium direction is used to characterize the direction in which the corresponding power unit needs to regulate voltage during load changes. When the unit voltage deviation increases in the positive direction, it is determined that the corresponding power unit has an overvoltage trend, and reducing the DC side voltage is taken as the transient equilibrium direction; when the unit voltage deviation increases in the negative direction, it is determined that the corresponding power unit has an undervoltage trend, and increasing the DC side voltage is taken as the transient equilibrium direction.

[0047] Furthermore, the degree of transient equalization is determined based on the offset. In specific implementation, the preset offset threshold includes a first offset threshold and a second offset threshold. For example, the first offset threshold is set to 10V, and the second offset threshold is set to 20V. When the offset of the corresponding power unit is less than or equal to 10V, the transient equalization level is determined to be low; when the offset is greater than 10V and less than 20V, the transient equalization level is determined to be medium; and when the offset is greater than or equal to 20V, the transient equalization level is determined to be high. For example, if the unit voltage deviation of a power unit changes from +5V to +18V, with an offset of 13V, then the power unit is determined to have a transient equalization direction that reduces the DC-side voltage, and a medium-level transient equalization level is correspondingly determined.

[0048] The above method converts the direction and degree of change in unit voltage deviation during load changes into transient equalization requirements, enabling subsequent carrier phase adjustment to be differentiated according to the voltage change states of different power units. The preset offset threshold and transient equalization level classification are determined based on the rated voltage level and allowable voltage fluctuation range of the solid-state transformer, without limiting specific values, as long as they reflect the adjustment requirements corresponding to the unit voltage deviation.

[0049] Step S203: Adjust the carrier phase of the corresponding power unit according to the transient equalization requirement. Specifically, the carrier phase adjustment direction and carrier phase adjustment amount of the corresponding power unit are determined according to the transient equalization requirements of each power unit, wherein the carrier phase is the PWM carrier phase of the input stage of the corresponding power unit; the carrier phase of the corresponding power unit is adjusted within a preset carrier phase adjustment range according to the carrier phase adjustment direction and the carrier phase adjustment amount.

[0050] In this embodiment of the invention, the carrier phase adjustment direction and carrier phase adjustment amount of each power unit are determined according to the transient equalization requirements of each power unit, wherein the carrier phase is the PWM carrier phase of the input stage of the corresponding power unit. The carrier phase adjustment direction is determined according to the transient equalization direction in the transient equalization requirements, and the carrier phase adjustment amount is determined according to the degree of transient equalization, so that the power action timing of different power units changes accordingly during load changes.

[0051] In practice, each power unit has a corresponding reference carrier phase under normal operating conditions. The carrier phase adjustment is a phase correction applied based on the reference carrier phase. The correspondence between the carrier phase change direction and the DC-side voltage change direction is predetermined for each power unit. Specifically, small positive and negative carrier phase disturbances are applied to the corresponding power unit during stable operation, and the DC-side voltage change direction is recorded within a preset observation period. This determines the DC-side voltage response direction corresponding to the positive and negative carrier phase adjustments, respectively. For example, after applying a +2° carrier phase disturbance to the i-th power unit, its DC-side voltage drops by 0.8V within a 2ms observation period. If the transient equilibrium direction of this power unit is to decrease the DC-side voltage, the positive direction is determined as the carrier phase adjustment direction; if the transient equilibrium direction is to increase the DC-side voltage, the negative direction is determined as the carrier phase adjustment direction. If the corresponding power units have opposite phase response relationships, the carrier phase adjustment direction is determined in reverse.

[0052] Furthermore, the carrier phase of the corresponding power unit is adjusted within a preset carrier phase adjustment range. Specifically, the carrier phase adjustment range is limited to -30° to 30°. When it is determined that a power unit needs to increase its carrier phase by 10°, the current carrier phase of that power unit is shifted 10° in the positive direction; when it is determined that it needs to decrease its carrier phase by 10°, the current carrier phase of that power unit is shifted 10° in the negative direction. By limiting the carrier phase adjustment range, excessive changes in the carrier phase shift relationship between power units are avoided.

[0053] By employing the above method, the carrier phase is adjusted differently based on the transient equalization requirements of different power units. This regulates the instantaneous power distribution of each power unit during load changes, providing a basis for subsequently determining the remaining transient equalization requirements after carrier phase adjustment. The carrier phase adjustment range, adjustment level, and corresponding adjustment amount are set based on the number of power units, the PWM modulation frequency, and the allowable voltage fluctuation range.

[0054] Step S30: Determine the remaining transient equalization requirement based on the DC-side voltage after carrier phase adjustment, and determine the continuous equalization requirement based on the unit voltage deviation after the load change interval ends.

[0055] Specifically, determining the remaining transient equalization requirement based on the DC-side voltage after carrier phase adjustment includes: obtaining the DC-side voltage corresponding to each power unit after carrier phase adjustment, and determining the average voltage of the power unit based on each DC-side voltage; determining the difference between the DC-side voltage corresponding to each power unit and the average voltage of the power unit to obtain the adjusted unit voltage deviation; determining the offset of the adjusted unit voltage deviation relative to the load before the change, and determining the remaining transient equalization requirement of the corresponding power unit based on the direction and magnitude of the offset.

[0056] In this embodiment of the invention, after carrier phase adjustment is completed, the DC-side voltage corresponding to each power unit is reacquired, and the average voltage of the power unit under the current operating state is determined based on the adjusted DC-side voltage of each power unit. The difference between the DC-side voltage corresponding to each power unit and the average voltage of the power unit is calculated to obtain the unit voltage deviation after carrier phase adjustment. By comparing the unit voltage deviation before and after carrier phase adjustment, the degree to which carrier phase adjustment eliminates voltage offset caused by load changes is determined.

[0057] In practice, after completing carrier phase adjustment, the solid-state transformer containing N power units obtains the DC-side voltage U corresponding to the i-th power unit. diThe adjusted average voltage of the power units is calculated based on the DC-side voltages of all power units. In another specific embodiment, the unit voltage deviation of the power unit is 0V before the load change, increases to +18V before carrier phase adjustment, and decreases to +6V after carrier phase adjustment. Therefore, there is still a positive offset of 6V relative to the state before the load change, and the corresponding remaining transient equalization requirement is determined accordingly. The remaining transient equalization requirement of the corresponding power unit is determined based on the offset direction and offset amount of the adjusted unit voltage deviation relative to the state before the load change.

[0058] Specifically, the remaining transient equalization requirement is determined based on the remaining offset of the unit voltage deviation after carrier phase adjustment relative to the stable state before the load change. The unit voltage deviation after carrier phase adjustment is obtained and compared with the reference deviation corresponding to the stable state before the load change. If the adjusted unit voltage deviation still has an offset, the remaining transient equalization direction is determined based on the remaining offset direction, and the remaining transient equalization degree is determined based on the remaining offset amount, thus generating the remaining transient equalization requirement.

[0059] For example, if a power unit's voltage deviation is 0V before a load change, and then changes to +18V due to load disturbance during the load change, and then decreases to +6V after carrier phase adjustment, it indicates that the carrier phase adjustment has eliminated some of the dynamic offset, but there is still a residual offset of +6V relative to the steady state. Therefore, it is determined that this power unit has a residual transient equalization requirement to reduce the DC-side voltage, and the subsequent active power adjustment amount is determined based on the offset degree corresponding to 6V.

[0060] Furthermore, after the load change interval ends, the unit voltage deviation of each power unit under the load stabilization state is obtained, and it is determined whether the unit voltage deviation persists within a preset stabilization time. When the unit voltage deviation of a power unit continuously exceeds a preset balancing threshold within the preset stabilization time, it is determined that the power unit has a continuous balancing requirement. For example, if the preset stabilization time is set to 10 sampling periods and the preset balancing threshold is 5V, when the unit voltage deviation of a power unit remains at 8V for 10 consecutive sampling periods after the load stabilizes, it is determined that the power unit has a continuous balancing requirement, and the corresponding continuous balancing requirement is determined based on the offset direction and offset amount (the offset direction and offset amount can also be called the direction and magnitude of the offset amount) of the unit voltage deviation relative to the load change. To enable the remaining transient balancing requirement and the continuous balancing requirement to be used for subsequent output active power command adjustment, the magnitudes of the two types of balancing requirements are uniformly converted into equivalent active power adjustment amounts.

[0061] In practice, a mapping relationship between voltage deviation and active power adjustment is established in advance based on the rated power and allowable voltage deviation of the corresponding power unit. For example, the equivalent active power adjustment corresponding to a unit voltage deviation absolute value greater than 5V but not exceeding 10V is set to 3kW, the equivalent active power adjustment corresponding to a deviation greater than 10V but not exceeding 20V is set to 5kW, and the equivalent active power adjustment corresponding to a deviation greater than 20V is set to 8kW. Thus, both the remaining transient equilibrium demand and the continuous equilibrium demand are characterized by the adjustment direction and the corresponding equivalent active power adjustment.

[0062] The continuous balancing requirement is determined based on the persistent unit voltage deviation under stable operating conditions after the load change ends. After the load change interval ends, the unit voltage deviation of each power unit is continuously acquired; it is determined whether the unit voltage deviation continuously exceeds a preset balancing threshold within a preset stable time; when the above condition is met, it is determined that the corresponding power unit has a continuous balancing requirement, and the continuous balancing direction and balancing degree are determined based on the persistent voltage offset direction and offset amount.

[0063] For example, a preset settling time of 10 sampling periods and a preset equalization threshold of 5V are set. If the unit voltage deviation of a certain power unit remains at 8V for 10 consecutive sampling periods after the load change ends, it is determined that the power unit has a continuous equalization requirement, and the continuous equalization requirement in the direction of reducing the DC side voltage is determined based on this positive voltage offset state.

[0064] In forward power transmission mode, when the unit voltage deviation is positive and the DC side voltage needs to be reduced, the direction of increasing the output active power command is determined as the corresponding balancing demand direction; when the unit voltage deviation is negative and the DC side voltage needs to be increased, the direction of decreasing the output active power command is determined as the corresponding balancing demand direction. In reverse power transmission mode, the direction is switched according to the actual power direction.

[0065] like Figure 4 As shown, within the load change range, the unit voltage deviation increases rapidly and forms a transient equalization demand. After carrier phase adjustment, there is still a residual transient equalization demand. When the load change ends, if the unit voltage deviation continues to exceed the preset equalization threshold within a preset stable time, it is determined that the corresponding power unit has a continuous equalization demand.

[0066] The above method distinguishes between dynamic voltage deviations that persist after carrier phase adjustment and voltage deviations that remain under stable load conditions, providing a basis for subsequent targeted balancing using output active power commands. The calculation method for the average voltage of the power units, the preset stabilization time, and the preset balancing threshold are set based on the number of power units in the solid-state transformer, the voltage level, and the allowable operating deviation range, without limiting specific values.

[0067] Preferably, the adjusted cell voltage deviation is recorded within eight consecutive sampling periods after carrier phase adjustment. If the deviation direction is consistent with the direction before carrier phase adjustment for at least six sampling periods, the current remaining transient equalization demand direction is maintained. If the deviation direction is opposite for three consecutive sampling periods and the absolute value of the deviation exceeds 3V, the remaining transient equalization demand direction is updated to the current deviation direction. If the deviation alternates within ±3V, it is considered a swing interval caused by carrier switching, and no direction reversal is performed. By suppressing short-term reverse fluctuations, frequent changes in the direction of the remaining transient equalization demand are avoided.

[0068] Step S40: Adjust the output active power command of the corresponding power unit according to the continuous balancing demand and the remaining transient balancing demand.

[0069] Specifically, when the directions of the continuous balancing demand and the remaining transient balancing demand of the corresponding power unit are the same, the power adjustment amount is determined based on the sum of the magnitudes of the continuous balancing demand and the remaining transient balancing demand, and the corresponding balancing demand direction is determined as the power adjustment direction; when the directions of the continuous balancing demand and the remaining transient balancing demand of the corresponding power unit are opposite, the power adjustment amount is determined based on the difference between their magnitudes, and the power adjustment direction is determined based on the larger of the two balancing demands; the output active power command of the corresponding power unit is adjusted according to the power adjustment direction and the power adjustment amount, and the sum of the output active power commands of each power unit after adjustment remains unchanged.

[0070] In this embodiment of the invention, after obtaining the continuous equalization demand and the remaining transient equalization demand corresponding to each power unit, the direction and magnitude of the two types of equalization demands are comprehensively analyzed to determine the final power adjustment direction and power adjustment amount of the corresponding power unit. The continuous equalization demand characterizes the long-term DC-side voltage deviation adjustment demand under stable load conditions, while the remaining transient equalization demand characterizes the dynamic voltage deviation adjustment demand that has not been eliminated after carrier phase adjustment.

[0071] In practice, when the direction of the continuous balancing demand of a corresponding power unit is the same as the direction of the remaining transient balancing demand, it indicates that both types of balancing demands require the corresponding power unit to adjust its energy in the same direction. In this case, the magnitude of the continuous balancing demand and the magnitude of the remaining transient balancing demand are combined to determine the final power adjustment amount, and the corresponding balancing demand direction is taken as the power adjustment direction. For example, if a power unit has a continuous balancing demand to reduce the DC-side voltage, with a demand of 5kW, and simultaneously has a remaining transient balancing demand to reduce the DC-side voltage, with a demand of 3kW, then the final power adjustment direction for this power unit is determined to be the direction of reducing the DC-side voltage, and the corresponding power adjustment amount is 8kW.

[0072] When the direction of the continuous equalization demand of a corresponding power unit is opposite to the direction of the remaining transient equalization demand, it indicates that the energy adjustment directions corresponding to the two types of equalization demands are different. In this case, the two types of equalization demands are canceled out according to their magnitudes, and the direction corresponding to the larger equalization demand is taken as the final power adjustment direction. For example, if a power unit has a continuous equalization demand to increase the DC-side voltage with a demand of 10kW, and at the same time has a remaining transient equalization demand to decrease the DC-side voltage with a demand of 4kW, then the final power adjustment direction is determined to be the direction of increasing the DC-side voltage, and the corresponding power adjustment amount is 6kW.

[0073] Furthermore, the output active power command of the corresponding power unit is adjusted according to the determined power adjustment direction and amount. During the adjustment process, the output active power commands of each power unit are coordinated and allocated so that the sum of the output active power commands of each power unit after adjustment remains consistent with that before adjustment. Thus, the energy redistribution among the power units is achieved without changing the overall output power of the solid-state transformer.

[0074] For example, a solid-state transformer contains four power units. Before adjustment, the active power commands of each power unit are 25kW, 25kW, 25kW, and 25kW, respectively, with a total active power command of 100kW. When the DC-side voltage of the first power unit is too high, and it is determined that its active power command needs to be increased by 5kW, the active power command of the first power unit is adjusted from 25kW to 30kW, and the total active power commands of the remaining power units are reduced by 5kW, for example, to 23.33kW, 23.33kW, and 23.34kW, respectively, so that the sum of the active power commands of the adjusted power units remains at 100kW. When the corresponding power unit needs to increase its DC-side voltage, its active power command is reduced, and the corresponding power adjustment is allocated to other power units with power regulation margins.

[0075] By employing the above method, the residual transient equalization requirement after carrier phase adjustment is coordinated with the continuous equalization requirement after load stabilization. This avoids the problem that a single adjustment method cannot simultaneously address dynamic response and long-term equalization, thereby improving the voltage consistency and operational stability of the solid-state transformer power unit during load changes. The calculation method for the power adjustment amount, the power allocation ratio, and the adjustment range of the output active power command are determined based on the rated capacity of the power unit and operating constraints.

[0076] like Figure 5As shown, this invention provides a solid-state transformer power unit voltage balancing system. The system includes: an acquisition unit, configured to acquire the DC-side voltage and output power of each power unit, determine the unit voltage deviation based on the DC-side voltage, and determine the load variation range based on the output power; an adjustment unit, configured to determine transient balancing requirements based on the unit voltage deviation within the load variation range, and adjust the carrier phase of the corresponding power unit based on the transient balancing requirements; a demand determination unit, configured to determine the remaining transient balancing requirements based on the DC-side voltage after carrier phase adjustment, and determine the continuous balancing requirements based on the unit voltage deviation after the load variation range ends; and an instruction generation unit, configured to adjust the output active power instructions of the corresponding power unit based on the continuous balancing requirements and the remaining transient balancing requirements.

[0077] The present invention also provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described solid-state transformer power unit voltage equalization method.

[0078] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe the various possible combinations.

[0079] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the embodiments of the present invention, they should also be regarded as the content disclosed by the embodiments of the present invention.

Claims

1. A method for voltage equalization of power units in a solid-state transformer, characterized in that, The method includes: Obtain the DC-side voltage and output power of each power unit, determine the unit voltage deviation based on the DC-side voltage, and determine the load variation range based on the output power; Within the load variation range, transient equalization requirements are determined based on the unit voltage deviation, and the carrier phase of the corresponding power unit is adjusted according to these transient equalization requirements; wherein, The transient equalization requirement is used to characterize the direction and degree of deviation of the DC side voltage deviation of the corresponding power unit relative to the steady state before the load change during the load change process, so as to determine the carrier phase adjustment direction and adjustment amount of the corresponding power unit. The remaining transient equalization requirement is determined based on the DC-side voltage after carrier phase adjustment, and the continuous equalization requirement is determined based on the unit voltage deviation after the load change interval ends; wherein... The remaining transient equalization requirement is used to characterize the dynamic voltage offset state that still exists in the corresponding power unit after carrier phase adjustment. The continuous balancing requirement is used to characterize the steady-state voltage offset state that continues to exist in the corresponding power unit after the load change ends. Adjust the output active power command of the corresponding power unit according to the continuous balancing demand and the remaining transient balancing demand.

2. The solid-state transformer power unit voltage equalization method according to claim 1, characterized in that, Determining the unit voltage deviation based on the DC-side voltage includes: The average voltage of the power unit is determined based on the DC-side voltage of each power unit. Calculate the difference between the DC side voltage of each power unit and the average voltage of the power unit, and determine the difference as the unit voltage deviation of the corresponding power unit.

3. The solid-state transformer power unit voltage equalization method according to claim 1, characterized in that, Determining the load variation range based on the output power includes: The total output power of the solid-state transformer is determined based on the output power of each power unit. The total output power within a continuous sampling period is obtained, and the load change start time is determined when the change in total output power between adjacent sampling periods is greater than a preset load change threshold. When the change in the total output power is less than a preset stability threshold within a consecutive preset number of sampling periods, the end time of the load change is determined, and the time range corresponding to the start time of the load change and the end time of the load change is determined as the load change interval.

4. The solid-state transformer power unit voltage equalization method according to claim 1, characterized in that, Within the load variation range, the transient equalization requirement is determined based on the unit voltage deviation, and the carrier phase of the corresponding power unit is adjusted according to the transient equalization requirement, including: Obtain the unit voltage deviation of the corresponding power unit within the load change range, and determine the offset direction and offset amount of the unit voltage deviation relative to the load before the change; The transient equalization requirement of the corresponding power unit is determined based on the offset direction and the offset amount; Adjust the carrier phase of the corresponding power unit according to the transient equalization requirements.

5. The solid-state transformer power unit voltage equalization method according to claim 4, characterized in that, Determining the transient equalization requirement of the corresponding power unit based on the offset direction and the offset amount includes: The transient equalization direction of the corresponding power unit is determined based on the offset direction; The transient equalization degree of the corresponding power unit is determined based on the relationship between the offset and the preset offset threshold. The transient balance requirement of the corresponding power unit is determined based on the transient balance direction and the transient balance degree.

6. The solid-state transformer power unit voltage equalization method according to claim 5, characterized in that, Adjusting the carrier phase of the corresponding power unit according to the transient equalization requirements includes: The carrier phase adjustment direction and carrier phase adjustment amount of the corresponding power unit are determined according to the transient equalization requirements of each power unit, wherein the carrier phase is the PWM carrier phase of the input stage of the corresponding power unit. Based on the carrier phase adjustment direction and the carrier phase adjustment amount, the carrier phase of the corresponding power unit is adjusted within a preset carrier phase adjustment range.

7. The solid-state transformer power unit voltage equalization method according to claim 6, characterized in that, The determination of the remaining transient equalization requirement based on the DC-side voltage after carrier phase adjustment includes: Obtain the DC-side voltage of each power unit after carrier phase adjustment, and determine the average voltage of the power unit based on the DC-side voltage of each power unit; The difference between the DC-side voltage of each power unit and the average voltage of the power unit is determined to obtain the adjusted unit voltage deviation. Determine the offset of the adjusted unit voltage deviation relative to the load before the change, and determine the remaining transient equalization requirement of the corresponding power unit based on the direction and magnitude of the offset.

8. The solid-state transformer power unit voltage equalization method according to claim 7, characterized in that, The step of adjusting the output active power command of the corresponding power unit according to the continuous balancing demand and the remaining transient balancing demand includes: When the directions of the continuous balancing demand and the remaining transient balancing demand of the corresponding power unit are the same, the power adjustment amount is determined according to the sum of the magnitudes of the continuous balancing demand and the remaining transient balancing demand, and the corresponding balancing demand direction is determined as the power adjustment direction. When the continuous balancing demand and the remaining transient balancing demand of the corresponding power unit are in opposite directions, the power adjustment amount is determined according to the difference between the two, and the power adjustment direction is determined according to the larger of the two balancing demands. Adjust the output active power command of the corresponding power unit according to the power adjustment direction and the power adjustment amount, and keep the sum of the output active power commands of each power unit unchanged after adjustment.

9. A voltage balancing system for a solid-state transformer power unit, characterized in that, The system includes: The acquisition unit is used to acquire the DC-side voltage and output power of each power unit, determine the unit voltage deviation based on the DC-side voltage, and determine the load variation range based on the output power. An adjustment unit is configured to determine transient equalization requirements based on the unit voltage deviation within the load variation range, and adjust the carrier phase of the corresponding power unit according to the transient equalization requirements; wherein, The transient equalization requirement is used to characterize the direction and degree of deviation of the DC side voltage deviation of the corresponding power unit relative to the steady state before the load change during the load change process, so as to determine the carrier phase adjustment direction and adjustment amount of the corresponding power unit. The demand determination unit is used to determine the remaining transient equalization demand based on the DC-side voltage after carrier phase adjustment, and to determine the continuous equalization demand based on the unit voltage deviation after the load change interval ends; wherein... The remaining transient equalization requirement is used to characterize the dynamic voltage offset state that still exists in the corresponding power unit after carrier phase adjustment. The continuous balancing requirement is used to characterize the steady-state voltage offset state that continues to exist in the corresponding power unit after the load change ends. The instruction generation unit is used to adjust the output active power instruction of the corresponding power unit according to the continuous balancing requirement and the remaining transient balancing requirement.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions that, when executed on a computer, cause the computer to perform the solid-state transformer power unit voltage equalization method according to any one of claims 1-8.

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