A flexible expansion method and system for a new energy transformer in a transformer area

Abstract

The present application relates to the technical field of flexible power distribution and new energy grid connection, and discloses a new energy transformer flexible expansion method and system for a transformer area, which adopts a system topology of parallel connection of a passive transformer and a flexible power electronic device based on series-parallel connection of a converter, can realize smooth expansion of system capacity through newly added flexible parallel branches without replacing and stopping operation of the original transformer, aggregates and reconstructs the grid side port voltage through the parallel converter, makes the grid side port voltage present virtual synchronous machine external characteristics, thereby enhances system inertia and damping, and suppresses weak grid oscillation, simultaneously, tracks and balances the parallel branch current in real time through the series converter, and combines with transient current feedforward compensation to supplement inertia support in the transient process of the system.

Description

Technical Field

[0001] This invention relates to the field of flexible power distribution and new energy grid connection technology, specifically to a method and system for flexible capacity expansion of transformers in new energy distribution areas. Background Technology

[0002] New energy power generation areas typically connect to the grid via power electronic converters, often employing a "grid-following" control strategy. This strategy relies on grid voltage for synchronization and lacks the inertia and damping characteristics of traditional synchronous generators, leading to a decrease in overall system inertia and disturbance rejection capability. Especially in weak grid areas with high grid impedance (low short-circuit ratio), this can easily trigger stability issues such as wideband oscillations, severely restricting the absorption of new energy and the reliable operation of the grid.

[0003] When addressing transformer capacity expansion demands due to load growth or renewable energy integration, traditional solutions typically involve directly adding transformers in parallel. However, this approach requires strict matching of parameters such as turns ratio and short-circuit impedance among the parallel-operated transformers. In practical engineering, manufacturing tolerances and aging processes can lead to parameter discrepancies, easily resulting in circulating currents and uneven load distribution, increasing losses, causing localized overheating, and impacting equipment lifespan and system safety. Other solutions propose using fully electronic "flexible power transfer devices" for capacity expansion or power regulation. While this avoids circulating currents, its power electronic components must withstand the entire transmission voltage, leading to high capacity requirements, high costs, and poor economic efficiency. Summary of the Invention

[0004] This invention provides a flexible capacity expansion method and system for new energy distribution transformers to solve the problem that existing technologies cannot simultaneously balance the economy of capacity expansion and renovation, equipment utilization rate and system operation stability.

[0005] In a first aspect, the present invention provides a method for flexible capacity expansion of transformers in new energy distribution areas, the method comprising: A circuit model of a transformer and a flexible parallel unit in a new energy distribution area is established. The flexible parallel unit includes a transformer branch, a DC converter on the energy storage side, a series converter, and a parallel converter. One end of the transformer branch is connected to the new energy distribution area, and the other end of the transformer branch is connected to the power grid. One end of the series converter is connected to the transformer branch, and the other end of the series converter is connected to one end of the parallel converter via a DC bus. The other end of the parallel converter is connected to the transformer branch, and the DC converter on the energy storage side is connected to the DC bus. Based on the energy storage-side DC converter, a dual closed-loop control strategy for voltage and current is adopted to stabilize the DC bus voltage. Based on the series converter, the steady-state current of the parallel transformer branch is distributed by current control, and transient inertia compensation is provided for the system by using transient current feedforward compensation. Based on parallel converters, a virtual synchronous network control strategy is adopted to aggregate and control the grid port voltage, thereby reshaping the grid port characteristics.

[0006] This invention provides a flexible capacity expansion method for transformers in new energy distribution areas. By employing a system topology that connects passive transformers in parallel with flexible power electronic devices based on series-parallel converters, the system capacity can be smoothly expanded by adding flexible parallel branches without replacing or interrupting the operation of the existing transformers. This fundamentally avoids the circulating current problem caused by parameter inconsistencies in traditional direct parallel connection of transformers. Furthermore, a series converter inertia compensation control method is proposed. By introducing a transient current feedforward mechanism, the remaining capacity of the series branches can be fully utilized to compensate for the inability of the parallel converters to provide sufficient power during system transients due to capacity limitations. The impact power effectively compensates for the shortcomings of small-capacity converters in transient inertia support capacity, significantly improving the system's dynamic response performance and operational stability. A port voltage aggregation control strategy based on a virtual synchronous generator (VSG) is adopted. By controlling the parallel converters, the grid-connected port, composed of the original transformer and the newly added flexible branch, exhibits the external characteristics of a synchronous generator. This provides adjustable virtual inertia and damping for the grid, effectively suppressing system oscillations caused by the large-scale integration of new energy distribution areas and grid-type converters in weak grids. This provides reliable technical support for distribution area expansion and stability control in scenarios with a high proportion of new energy integration.

[0007] In one optional implementation, the transformer branch includes: a first transformer and a second transformer, wherein, The primary winding of the first transformer is connected in series between the new energy power generation station and the secondary winding of the second transformer, and the secondary winding of the first transformer is connected in parallel to the series converter. The primary winding of the second transformer is connected to the power grid, and the secondary winding of the second transformer is connected in parallel to the parallel converter.

[0008] In one optional implementation, the step of stabilizing the DC bus voltage using a dual closed-loop control strategy based on the energy storage-side DC converter includes: Based on the deviation between the DC bus voltage and the DC bus voltage reference, a DC converter-side current reference is generated through DC bus voltage outer loop control. Based on the deviation between the DC converter side current and the DC converter side current reference, an intermediate control quantity is generated through DC current inner loop control. The supercapacitor voltage is then superimposed on the intermediate control quantity to perform feedforward compensation, thereby generating a DC converter modulation wave on the energy storage side. The modulation wave of the energy storage-side DC converter is sinusoidally pulse-width modulated to obtain the switching signal of the energy storage-side DC converter.

[0009] In one alternative implementation, based on a series converter, the steady-state current of the parallel transformer branch is distributed by current control, and transient inertia compensation is provided to the system using transient current feedforward compensation, including: Based on the turns ratio and power distribution coefficient of the first transformer and the current of the new energy distribution transformer, the series-side tracking current reference is calculated. The series-side tracking current reference is transformed to obtain the current reference vector in the stationary coordinate system. Based on the capacity limitation of the parallel converter, the transient current feedforward coefficient on the series side is calculated; During system transients, when the impulse power demand exceeds the capacity of the parallel converter, the transient current feedforward coefficient is superimposed to perform feedforward compensation on the current reference vector to generate the output current reference on the series side in the stationary coordinate system. Based on the output current reference, a proportional resonant controller is used to perform closed-loop calculations to generate a series converter modulation wave. The modulation wave of the series converter is pulse-width modulated to output the switching drive signal of the series converter.

[0010] In one optional implementation, based on a parallel converter, a virtual synchronous grid control strategy is used to aggregate and control the grid port voltage, thereby reshaping the grid port characteristics, including: Collect the grid-side current and filter capacitor voltage, and calculate the first active power and the first reactive power output from the grid port; Based on the deviation between the supercapacitor voltage and the supercapacitor voltage reference, a second active power reference for the virtual synchronous machine is generated through the active power controller, and based on the deviation between the first reactive power and the reactive power reference at the grid port, a second reactive power reference for the virtual synchronous machine is generated through the reactive power controller. Based on the second active power reference, the second reactive power reference, the first active power, and the first reactive power, the voltage frequency deviation and amplitude deviation of the grid port are calculated by virtual synchronous mechanism network control, combined with virtual inertia and damping coefficient. Based on the voltage frequency deviation and the amplitude deviation, the port voltage reference in the rotating coordinate system is calculated; The port voltage reference is transformed to obtain the port voltage reference vector in the stationary coordinate system; Based on the port voltage reference vector, the grid port voltage is aggregated and controlled through the voltage and current dual closed-loop control of the parallel converter.

[0011] In one optional implementation, based on the port voltage reference vector, the grid port voltage is aggregated and controlled through the voltage and current dual closed-loop control of the parallel converter, including: Based on the deviation between the port voltage reference vector and the filter capacitor voltage, a port current reference is generated through voltage loop control; Based on the deviation between the port current reference and the port current, a modulated wave for the parallel converter is generated through current loop control. The modulation wave of the parallel converter is sinusoidally pulse-width modulated to generate the switching drive signal of the parallel converter.

[0012] In one alternative implementation, the second active power reference of the virtual synchronous machine is limited based on the capacity of the parallel converter.

[0013] Secondly, the present invention provides a flexible capacity expansion device for new energy distribution transformers, the device comprising: The model building module is used to establish the circuit model of the transformer and flexible parallel unit in the new energy distribution area. The flexible parallel unit includes a transformer branch, an energy storage-side DC converter, a series converter, and a parallel converter. One end of the transformer branch is connected to the new energy distribution area, and the other end of the transformer branch is connected to the power grid. One end of the series converter is connected to the transformer branch, and the other end of the series converter is connected to one end of the parallel converter through a DC bus. The other end of the parallel converter is connected to the transformer branch, and the energy storage-side DC converter is connected to the DC bus. The energy storage side control module is used to stabilize the DC bus voltage based on the energy storage side DC converter using a dual closed-loop control strategy of voltage and current. The series-side control module is used to distribute the steady-state current of the parallel transformer branch through current control based on the series converter, and to provide transient inertia compensation for the system by using transient current feedforward compensation. The parallel-side control module is used to aggregate and control the grid port voltage based on the parallel converter and adopt a virtual synchronous network control strategy, thereby reshaping the grid port characteristics.

[0014] This invention provides a flexible capacity expansion device for transformers in new energy distribution areas. By employing a system topology that connects a passive transformer in parallel with a flexible power electronic device based on series-parallel converters, the system capacity can be smoothly expanded by adding flexible parallel branches without replacing or interrupting the operation of the existing transformers. This fundamentally avoids the circulating current problem caused by parameter inconsistencies in traditional direct parallel connection of transformers. Furthermore, a series converter inertia compensation control method is proposed. By introducing a transient current feedforward mechanism, the remaining capacity of the series branches can be fully utilized to compensate for the capacity limitations of the parallel converters during system transients. The impact power effectively compensates for the shortcomings of small-capacity converters in transient inertia support capacity, significantly improving the system's dynamic response performance and operational stability. A port voltage aggregation control strategy based on a virtual synchronous generator (VSG) is adopted. By controlling the parallel converters, the grid-connected port, composed of the original transformer and the newly added flexible branch, exhibits the external characteristics of a synchronous generator. This provides adjustable virtual inertia and damping for the grid, effectively suppressing system oscillations caused by the large-scale integration of new energy distribution areas and grid-type converters in weak grids. This provides reliable technical support for distribution area expansion and stability control in scenarios with a high proportion of new energy integration.

[0015] Thirdly, the present invention provides an electronic device, comprising: a memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the flexible capacity expansion method for new energy distribution transformers in the first aspect or any corresponding embodiment described above.

[0016] Fourthly, the present invention provides a computer-readable storage medium storing computer instructions for causing a computer to execute the flexible capacity expansion method for new energy distribution transformers as described in the first aspect or any corresponding embodiment. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the first process of the flexible capacity expansion method for new energy distribution transformers according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a flexible capacity expansion system for new energy distribution transformers according to an embodiment of the present invention; Figure 3 This is the circuit topology of a passive transformer and flexible parallel system according to an embodiment of the present invention; Figure 4 This is a control block diagram of the energy storage-side DC converter according to an embodiment of the present invention; Figure 5 This is a control block diagram of a series converter according to an embodiment of the present invention; Figure 6 This is a control block diagram of a parallel converter according to an embodiment of the present invention; Figure 7 This is a flowchart of the operation of the control algorithm for a flexible parallel system according to an embodiment of the present invention; Figures 8(a)-8(d) This is a schematic diagram of the primary frequency regulation characteristics of the system when a load is supplied to the grid side according to an embodiment of the present invention; Figure 9 This is a schematic diagram of the reactive power output characteristics of a power grid port according to an embodiment of the present invention; Figures 10(a)-10(b) This is a schematic diagram of the current tracking characteristics of a transformer by a flexible parallel unit according to an embodiment of the present invention; Figure 11 This is a structural block diagram of a flexible capacity expansion device for new energy distribution transformers according to an embodiment of the present invention; Figure 12 This is a schematic diagram of the hardware structure of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.

[0021] Traditional transformer capacity expansion often employs a method of directly paralleling new transformers. This method requires strict matching of key parameters such as turns ratio, connection group, and short-circuit impedance between the parallel-operating transformers to avoid problems with uneven parallel circulating current and load distribution. However, in actual engineering renovations, the parameters of new and old transformers are difficult to be completely identical due to factors such as manufacturing tolerances and long-term aging. Moreover, these parameter differences can be further amplified during operation, leading to long-term additional circulating current losses in the system, as well as safety hazards such as equipment overheating and shortened lifespan.

[0022] Currently, most renewable energy power generation areas use grid-connected converters. These converters lack the inherent inertia and damping support capabilities of traditional synchronous generators. When a power generation area is connected to a weak grid with low short-circuit ratios, the overall system inertia is insufficient, and the disturbance rejection capability is significantly reduced. This easily induces stability problems such as wideband oscillations, severely restricting the safe consumption of high-proportion renewable energy and the reliable operation of the power grid.

[0023] Therefore, this invention provides a method for flexible capacity expansion of transformers in new energy distribution areas. For example... Figure 1 As shown, the process includes the following: Step S1: Establish the circuit model of the new energy distribution transformer and the flexible parallel unit. For example... Figure 2 As shown, the flexible parallel unit includes a transformer branch, an energy storage-side DC converter, a series converter, and a parallel converter. One end of the transformer branch is connected to the new energy distribution area, and the other end of the transformer branch is connected to the power grid. One end of the series converter is connected to the transformer branch, and the other end of the series converter is connected to one end of the parallel converter via a DC bus. The other end of the parallel converter is connected to the transformer branch, and the energy storage-side DC converter is connected to the DC bus.

[0024] It should be noted that a new energy distribution transformer refers to a power transformer installed between a new energy power generation area (such as the access point of distributed photovoltaic, decentralized wind power, etc.) and the distribution network for voltage level transformation and energy transmission. In this embodiment of the invention, the new energy distribution transformer specifically refers to... Figure 2 The passive transformer T1 in the diagram has its primary winding connected to the medium-voltage power grid and its secondary winding connected to the low-voltage busbar. Its turns ratio is set to... N :1.

[0025] A flexible parallel unit is a modular device with active regulation capabilities, composed of a transformer branch, an energy storage-side DC converter, a series converter, and a parallel converter. This unit operates in parallel with the existing passive transformer T1, enabling flexible expansion of system capacity and active support for grid characteristics. Specifically, the series and parallel converters exchange energy through a shared DC bus. The series converter converts transient power from the AC side into DC power and injects it into the bus, while the parallel converter draws power from the bus to control the port voltage. The energy storage-side DC converter stabilizes the DC bus voltage through the charging and discharging of supercapacitors, providing power support for the entire flexible parallel unit.

[0026] Specifically, a circuit topology for the transformer and flexible parallel unit in the new energy distribution area is established, and the output current on the series converter side of this circuit topology is measured. i s1 Output current on the parallel converter side i p1 Filter capacitor voltage vp DC converter side current i b Supercapacitor voltage v sc DC bus voltage v dc Grid-side current i g Transformer T1 current i T1 A circuit model is established for a passive transformer and a flexible parallel system with supercapacitor energy storage. This circuit model refers to the transformation of the electrical structure, component parameters and connection relationships of the actual physical system into an identifiable and computable mathematical description.

[0027] In this embodiment of the invention, a topology architecture in which the original passive transformer in the distribution area is connected in parallel with the newly added flexible parallel unit is adopted. There is no need to replace or shut down the original transformer. The system capacity can be smoothly expanded by simply adding a flexible parallel branch. This fundamentally avoids the problem of parallel circulating current caused by inconsistent equipment parameters in the traditional direct parallel connection mode of transformers.

[0028] Step S2: Based on the DC converter on the energy storage side, a dual closed-loop control strategy of voltage and current is adopted to stabilize the DC bus voltage.

[0029] Specifically, when the series or parallel converters are affected by power fluctuations, causing the DC bus voltage to rise or fall, the energy storage-side DC converter will instantly absorb or release energy through supercapacitors, quickly pulling the DC bus voltage back to a stable value. Thanks to the rapid response characteristics of the inner current loop, the system can instantly provide or absorb power, effectively suppressing DC bus voltage fluctuations and ensuring a stable and constant DC bus voltage. This provides a stable operating voltage platform for both the series and parallel converters, ensuring that they can independently and accurately perform their respective power control tasks.

[0030] Step S3: Based on the series converter, the steady-state current of the parallel transformer branch is distributed by current control, and transient inertia compensation is provided for the system by using transient current feedforward compensation.

[0031] Specifically, by introducing a transient current feedforward control mechanism, the remaining capacity of the series branch can be fully utilized to compensate for the impact power that the parallel converter cannot output due to capacity limitations during transient processes. This effectively makes up for the shortcomings of small-capacity converters in transient inertia support capabilities and significantly improves the dynamic response speed and operational stability of the system.

[0032] Step S4: Based on the parallel converter, a virtual synchronous network control strategy is adopted to aggregate and control the grid port voltage, thereby reshaping the grid port characteristics.

[0033] Specifically, a port voltage aggregation control strategy based on virtual synchronous generator (VSG) is adopted. Through precise regulation of the parallel converter, the grid-connected port composed of the original transformer and the newly added flexible parallel unit exhibits the external characteristics of a synchronous generator. This provides adjustable virtual inertia and damping support for the power grid, effectively suppressing the system oscillation problem caused by the large-scale access of new energy distribution areas and grid-type converters in weak grid scenarios.

[0034] In one alternative implementation, such as Figure 3 As shown, the transformer branch includes a first transformer T11 and a second transformer T12. The primary winding of the first transformer T11 is connected in series between the new energy power generation station and the secondary winding of the second transformer T12. The secondary winding of the first transformer T11 is connected in parallel to a series converter. The primary winding of the second transformer T12 is connected to the power grid, and the secondary winding of the second transformer T12 is connected in parallel to a parallel converter.

[0035] Specifically, the primary winding of the first transformer T11 is connected in series between the renewable energy power generation area and the secondary winding of the second transformer T12, serving as a power transmission bridge between the renewable energy power generation area and the second transformer T12. The primary winding of the second transformer T12 is directly connected to the power grid, realizing the grid connection of the flexible parallel unit with the power grid.

[0036] The series converter connects the secondary winding of the second transformer T12 to the new energy power generation area through the first transformer T11. By regulating the secondary current of the first transformer T11, the series converter indirectly changes the power transmission characteristics of the primary winding of the first transformer T11, thereby achieving precise control of the current between the new energy power generation area and T12, and completing steady-state current distribution and transient inertia compensation.

[0037] The parallel converter is connected in parallel to the secondary winding of the second transformer T12, forming a direct voltage interaction link with the grid side. It can directly collect the voltage and current signals from the secondary winding of the second transformer T12, and achieve aggregated control of the grid port voltage using a virtual synchronous generator (VSG) control strategy, thus reshaping the grid-connected port characteristics. In this embodiment, the first transformer T11 is an isolation transformer with a turns ratio of 1: N s The turns ratio of the second transformer T12 is... N :1.

[0038] The energy storage-side DC converter connects the supercapacitor module to the DC bus of the series-parallel converters. The series and parallel converters share the same DC bus. The energy storage-side DC converter stabilizes the DC bus voltage, enabling bidirectional energy flow between the two converters. The series converter converts transient surge power into DC power and injects it into the bus, while the parallel converter draws power from the bus to control the port voltage. The supercapacitor acts as an energy buffer, absorbing or releasing energy in real time to ensure bus stability.

[0039] In one optional implementation, step S2 includes the following steps: Step S21, based on the DC bus voltage v dc and DC bus voltage reference v dc_ref The deviation is controlled by the outer loop of the DC bus voltage to generate a reference current for the DC converter side. i b_ref .

[0040] Specifically, the system controller acquires the DC bus voltage in real time through a voltage sensor. v dc Simultaneously, the DC bus voltage reference stored in the controller is retrieved. v dc_ref (This reference is a preset rated operating voltage, which is the stable value that the DC bus needs to maintain, and is adapted to the rated operating voltage requirements of series and parallel converters.)

[0041] The system controller will collect the DC bus voltage. v dc DC bus voltage reference v dc_ref The difference is calculated to obtain the DC bus voltage deviation value, which directly reflects the fluctuation state of the DC bus voltage. This voltage deviation value is then input into the DC bus voltage controller (using a PI proportional-integral controller). Through the controller's proportional and integral adjustment calculations, a DC converter-side current reference is generated. i b_ref For the control process of the DC converter on the energy storage side, please refer to [link / reference]. Figure 4 .

[0042] DC converter side current reference i b_ref The expression is:

[0043] In the formula, G vd (s) is the DC bus voltage controller. v dc_ref For DC bus voltage reference, kpvd and k ivd These are the proportional and integral coefficients of the DC bus voltage controller. s For the Laplace operator.

[0044] Step S22, based on the DC converter side current i b and DC converter side current reference i b_ref The deviation is addressed by using DC current inner loop control to generate an intermediate control quantity. This intermediate control quantity is then fed forward and compensated by superimposing the supercapacitor voltage, generating a modulation wave for the energy storage-side DC converter. v out_dc .

[0045] Specifically, the system controller collects the current on the DC converter side in real time. i b And compare it with the DC converter-side current reference output from the outer voltage loop in step S21. i b_ref The current deviation signal is obtained by comparison. This signal is then sent to the DC current controller for adjustment calculations. The DC current controller outputs a corresponding intermediate control quantity based on the magnitude of the deviation. This intermediate control quantity reflects the duty cycle adjustment command required to track the current reference, and is used to quickly smooth out current fluctuations, ensure accurate tracking of the given reference current on the DC converter side, and improve the system's dynamic response speed.

[0046] Based on this, in order to further offset the impact of the supercapacitor's own voltage fluctuations on the control effect and avoid bus voltage disturbances caused by supercapacitor voltage fluctuations, the controller will collect the supercapacitor voltage in real time. v sc As a feedforward compensation quantity, it is directly superimposed on the aforementioned intermediate control quantity to pre-compensate and correct the control command. The compensated signal ultimately generates the modulation wave of the DC converter on the energy storage side. v out_dc .

[0047] The expression for the modulation wave of the DC converter on the energy storage side is:

[0048] In the formula, G id (s) is a DC current controller. k pd and k id These are the proportional and integral coefficients of the DC current controller.

[0049] By introducing supercapacitor voltage feedforward, control deviations caused by changes in energy storage voltage can be compensated in advance based on current closed-loop regulation. This allows the DC bus to maintain high stability under conditions such as power surges and transient impacts, providing a stable and reliable DC operating voltage platform for series and parallel converters, and ensuring the reliable execution of subsequent power control and inertia compensation functions.

[0050] Step S23: Perform sinusoidal pulse width modulation on the modulation wave of the energy storage side DC converter to obtain the switching signal of the energy storage side DC converter.

[0051] Specifically, the modulated waveform of the DC converter on the energy storage side... v out_dc Input a sinusoidal pulse width modulator to perform sinusoidal pulse width modulation, and obtain the switching signal of the DC converter on the energy storage side.

[0052] In one optional implementation, step S3 includes the following steps: Step S31: Based on the turns ratio and power distribution factor of the first transformer and the current of the new energy distribution transformer... i T1 The series-side tracking current reference was calculated. i T2_ref(abc) .

[0053] Specifically, the system controller collects the current of transformer T1 in the new energy distribution area in real time. i T1 At the same time, the preset power distribution coefficient (set according to engineering requirements, used to determine the load distribution ratio between the original transformer and the newly added flexible parallel unit, such as 1:1 or capacity ratio) and the turns ratio of the first transformer T11 are retrieved.

[0054] Through a preset control algorithm, the current of the transformer in the new energy distribution area is controlled. i T1 The turns ratio of the first transformer is 1: N s The power allocation coefficient is used for collaborative calculation to finally obtain the series-side tracking current reference. i T2_ref(abc) Its expression is:

[0055] In the formula, D is the power distribution coefficient.

[0056] Step S32, set the series-side tracking current reference. i T2_ref(abc) Perform a coordinate system transformation to obtain the current reference vector in the stationary coordinate system. i T2_ref(ab) .

[0057] Specifically, the system controller will use the three-phase series-side tracking current reference obtained in step S31. i T2_ref(abc) The three-phase current signal is converted into a current reference vector in a two-phase stationary coordinate system through Clark transformation. i T2_ref(ab) .

[0058] The above operations simplify the computational complexity of the system controller, reduce control latency, and improve response speed. Simultaneously, they provide a suitable signal format for subsequent implementation of zero-steady-state-error current control using a PR controller, ensuring that the output current of the series converter accurately tracks the reference command and avoids current distortion. Current reference vector. i T2_ref(ab) The expression is: .

[0059] Step S33: Calculate the transient current feedforward coefficient on the series side based on the capacity limitation of the parallel converter.

[0060] Specifically, the system controller retrieves the rated capacity and maximum output power limit of the parallel converter (the inherent hardware parameters of the parallel converter determine its maximum output impulse power), and, in conjunction with the current system operating status (such as renewable energy output and load size), calculates the transient current feedforward coefficient on the series side online. c This coefficient is a quantitative value that reflects how much current the series converter needs to supplement to compensate for the impact power that the parallel converter cannot provide due to capacity limitations. The larger the transient current feedforward coefficient, the more current the series converter needs to supplement, and the stronger the transient inertia support it provides. When the coefficient is 0, it means that the parallel converter can meet the current impact power demand, and the series converter does not need to perform transient compensation, but only needs to maintain steady-state current tracking.

[0061] Since the system output active power is usually much greater than reactive power during transient processes, neglecting the reactive power allows us to obtain the transient current feedforward coefficient. c Simplified expression:

[0062] In the formula, i ref It is the output current reference of the parallel converter. E ref It is a port voltage reference. S p0 It is the rated power of the parallel converter.

[0063] Step S34: During the system transient process, when the impulse power demand exceeds the capacity of the parallel converter, the transient current feedforward coefficient is superimposed on the current reference vector. iT2_ref(ab) Perform feedforward compensation to generate the output current reference on the series side in the stationary coordinate system. i s_ref .

[0064] Specifically, the system controller monitors the system's operating status in real time to determine whether it is in a transient process (such as sudden changes in new energy output, sudden increases / decreases in load, grid voltage fluctuations, etc.). Simultaneously, it detects the magnitude of the current system's required surge power and compares it with the maximum capacity of the parallel converters. When the system's required surge power exceeds the capacity limit of the parallel converters, it indicates that the parallel converters alone cannot provide sufficient transient inertia support. In this case, the transient current feedforward coefficient calculated in step S33 is superimposed onto the current reference vector in the stationary coordinate system generated in step S32. i T2_ref(ab) Above, the current reference command is corrected through feedforward compensation.

[0065] After superposition compensation, the output current reference of the series side in the stationary coordinate system is obtained. i s_ref This reference instruction retains the goal of balanced current distribution in steady state while adding an inertia compensation component in transient state. This ensures that the series converter can quickly output additional current in transient state to compensate for the capacity shortfall of the parallel converter, provide sufficient transient inertia support for the system, and suppress system fluctuations.

[0066] If the system is in steady state and the impact power demand does not exceed the capacity of the parallel converter, the transient current feedforward coefficient is 0. At this time, the output current reference on the series side is consistent with the current reference vector in step S32, and only steady-state current tracking and distribution are realized.

[0067] Output current reference on the series side in stationary coordinate system i s_ref expression: .

[0068] Step S35, based on the output current reference i s_ref A proportional resonant controller is used for closed-loop calculation to generate the modulation wave of the series converter. .

[0069] Specifically, the system controller collects the output current from the series converter side in real time. i s1 Compare it with the output current reference generated in step S34 i s_refThe difference is calculated to obtain the current deviation signal. This signal is then input to a proportional-resonant (PR) controller for closed-loop regulation. Based on the magnitude and direction of the current deviation, the PR controller, through the synergistic action of the proportional and resonant elements, outputs a corresponding control signal to correct the current deviation, ensuring that the actual current quickly and accurately tracks the reference command.

[0070] After further processing, the output signal of the PR controller is finally used to generate the series converter modulation wave. This modulated wave is the core reference signal for controlling the operation of the power switch tubes in the series converter. Its amplitude and phase directly determine the magnitude and phase of the output voltage and current of the series converter, and serve as the direct basis for generating the subsequent switch drive signal and realizing current control.

[0071] Series converter modulation wave The expression is:

[0072] In the formula, G is (s) is the current loop controller for the series converter, where ω b Characterizing the bandwidth at the center frequency, ω 0 represents the fundamental angular frequency. k pis It is a proportionality coefficient. k ris It is the resonance coefficient.

[0073] Step S36: Perform pulse width modulation processing on the modulation wave of the series converter and output the switching drive signal of the series converter.

[0074] Specifically, the series converter modulation wave generated in step S35 The input sinusoidal pulse width modulator performs pulse width modulation processing to obtain the switching signal for the series converter. See [link to series converter control process] for details. Figure 5 .

[0075] In one optional implementation, step S4 includes the following steps: Step S41: Collect grid-side current i g and filter capacitor voltage v p Calculate the first active power output at the grid port. P g With the first reactive power Q g .

[0076] Specifically, the system controller collects grid-side current in real time through voltage and current sensors. ig With filter capacitor voltage v p Based on the collected electrical quantities, ignoring the power losses on transformer T1 and the second transformer T12 in the new energy distribution area, the first active power currently actually output at the grid port is calculated using an instantaneous power algorithm. P g and first reactive power Q g The above power reflects the actual power level currently transmitted from the renewable energy distribution area to the grid, and serves as the basis for subsequent virtual synchronous machine control and power regulation. The first active power currently actually output from the grid port. P g and first reactive power Q g The expression is:

[0077] Step S42, based on supercapacitor voltage v sc With supercapacitor voltage reference v sc_ref The deviation is used to generate a second active power reference for the virtual synchronizer through the active power controller. P 0, and based on the first reactive power Q g Reactive power reference at grid port Q ref The deviation is used to generate a second reactive power reference for the virtual synchronous machine through the reactive power controller. Q 0.

[0078] Specifically, power commands for the VSG are generated through a two-stage closed loop to achieve energy storage voltage stability and reactive power support for the grid. On one hand, the system controller will collect the supercapacitor voltage in real time... v sc Compared with the preset supercapacitor voltage reference v sc_ref The voltage deviation is obtained by comparison. After adjustment by the active power controller, this voltage deviation is output as the second active power reference of the virtual synchronizer. P 0, used to maintain the supercapacitor voltage stability while providing active power commands to the VSG. On the other hand, the first reactive power output from the grid port... Q g Reactive power reference at grid port Q ref The reactive power deviation is obtained through comparison. After adjustment by the reactive power controller, this reactive power deviation is output as the second reactive power reference of the virtual synchronizer. Q 0 is used to achieve reactive power compensation and voltage support at the power grid port.

[0079] A second power reference with a virtual synchronizer P 0. Second reactive power reference of the virtual synchronous machine Q The expression for 0 is:

[0080] In the formula, G sc (s) is an active power controller. v sc_ref For supercapacitor voltage reference, k psc and k isc These are the proportional and integral coefficients of the active power controller; G q (s) is a reactive power controller. Q ref For the reactive power reference at the grid port, k pq and k iq These are the proportional and integral coefficients of the reactive power controller.

[0081] Step S43, based on the second active power reference P 0. Second reactive power reference Q 0. First active power P g and the first reactive power Q g By controlling the virtual synchronous network and combining virtual inertia and damping coefficient, the voltage frequency deviation at the grid port is calculated. Amplitude deviation E .

[0082] Specifically, after obtaining the power reference of the virtual synchronizer, the first active power is used. P g With the second active power reference P The deviation of 0, and the first reactive power Q g With the second reactive power reference Q A deviation of 0 is taken as input, and the virtual synchronous machine control algorithm is executed. The algorithm simulates the rotor motion equation and excitation regulation characteristics of a traditional synchronous generator, combined with the set active virtual inertia J and reactive virtual inertia. 、 Active control damping coefficient D p Reactive power control damping coefficient D qThe voltage frequency deviation at the grid port was calculated. Amplitude deviation E Among them, virtual inertia is used to simulate rotor inertia and suppress frequency abrupt changes; damping coefficient is used to suppress power oscillations, thereby improving system stability under weak power grid conditions.

[0083] Voltage frequency deviation Amplitude deviation E The expression is:

[0084] Step S44, based on voltage frequency deviation Amplitude deviation E The port voltage reference in the rotating coordinate system is calculated. v ref .

[0085] Specifically, based on the voltage frequency deviation obtained in step S43 Amplitude deviation E The controller corrects the rated voltage phase angle and amplitude to generate a port voltage reference in a rotating coordinate system. v ref This voltage reference already incorporates virtual inertia and damping adjustment effects, making the grid-connected port exhibit the external characteristics of a synchronous generator, providing frequency support and voltage regulation capabilities.

[0086] Port voltage reference v ref The expression is:

[0087] In the formula, It is the port voltage reference phase angle. Reference voltage amplitude output from the virtual synchronous machine excitation control circuit.

[0088] Step S45, refer to the port voltage v ref Perform a coordinate transformation to obtain the port voltage reference vector in the stationary coordinate system. v ref ( ) .

[0089] Specifically, to facilitate AC voltage control in the controller, the port voltage reference in the rotating coordinate system is...v ref The port voltage reference vector is converted into a two-phase stationary coordinate system through the inverse Park transform. v ref ( ) This transformation simplifies the subsequent dual-loop control algorithm, making it easier to achieve zero steady-state error tracking of power frequency AC quantities using a proportional resonant (PR) controller.

[0090] Port voltage reference vector v ref ( ) The expression is:

[0091] Step S46: Based on the port voltage reference vector, the grid port voltage is aggregated and controlled through the voltage and current dual closed-loop control of the parallel converter.

[0092] In this embodiment of the invention, step S46 includes the following steps: Step S461, based on port voltage reference vector v ref ( ) With filter capacitor voltage v p The deviation is controlled by a voltage loop to generate a port current reference. i ref .

[0093] Specifically, the system controller will use the port voltage reference vector in the stationary coordinate system. v ref ( ) The actual collected filter capacitor voltage v p The voltage deviation signal is obtained by comparison. This deviation signal is sent to the voltage loop controller for adjustment calculation, and the output is the port current reference. i ref .

[0094] Port current reference i ref The expression is:

[0095] In the formula, G vp (s) is the voltage loop controller for the parallel converter, where kpvp It is a proportionality coefficient. k rvp It is the resonance coefficient.

[0096] Step S462, based on port current reference i ref The current references to different branches are distributed to control the output current of the parallel converter. i p1 The modulation wave of the parallel converter is obtained through current loop control calculation. v out_p .

[0097] Specifically, the system controller first uses the port current as a reference. i ref As the master command, based on the system topology and control objectives, it is rationally allocated to the corresponding branches, forming a current control target for the parallel converter branches. Subsequently, the controller collects the output current of the parallel converter side in real time. i p1 This current deviation signal is compared with the allocated branch current reference to obtain the current deviation signal. After adjustment and calculation by the current loop controller, the modulated wave of the parallel converter is finally calculated. v out_p This provides a basis for subsequently generating switch drive signals and achieving accurate current tracking.

[0098] Parallel converter modulated wave v out_p The expression is:

[0099] In the formula, G ip (s) is the current loop controller for the parallel converter, where k pip It is a proportionality coefficient. k rip It is the resonance coefficient.

[0100] Step S463, modulate the waveform of the parallel converter. v out_p Sinusoidal pulse width modulation is performed to generate the switching drive signal for the parallel converter.

[0101] Specifically, the controller will generate a modulated wave from the parallel converter. v out_pThe signal is compared with an internal high-frequency triangular carrier wave and subjected to sinusoidal pulse width modulation (SPWM) to obtain a series of pulse signals with duty cycles varying according to the modulating wave. This signal is amplified and electrically isolated by the drive circuit to form the switching drive signal for the parallel converter, directly controlling the on / off state of the internal IGBTs / MOSFETs. Through this drive signal, the parallel converter outputs the required voltage and current, achieving aggregated control of the grid port voltage. This ultimately completes the physical realization of VSG virtual inertia and damping support, effectively improving the operational stability of new energy distribution areas under weak grid conditions. For the parallel converter control process, please refer to [link to relevant documentation]. Figure 6 .

[0102] In one alternative implementation, the second active power reference of the virtual synchronous machine is limited based on the capacity of the parallel converter.

[0103] Specifically, after receiving the second active power reference output by the virtual synchronous machine, the system controller does not directly send it to the subsequent control loop. Instead, it first compares the second active power reference with the rated capacity and maximum allowable output power of the parallel converter itself. When the second active power reference exceeds the maximum output limit that the parallel converter can withstand, the controller automatically limits it to within the allowable range of the converter capacity. If it does not exceed the limit, the original command remains unchanged.

[0104] This limiting process avoids excessive active power commands caused by transient impacts, power surges, and other operating conditions, ensuring that the parallel converter operates within a safe operating range and preventing overcurrent, overheating, or even damage to power devices. At the same time, it ensures that the entire flexible capacity expansion system can reliably achieve virtual inertia support and grid voltage aggregation control under the capacity constraints of the parallel converter.

[0105] This invention proposes a system topology that connects a passive transformer in parallel with a flexible power electronic device based on a series-parallel converter. This architecture allows for smooth expansion of system capacity by adding a flexible parallel branch without replacing or interrupting the existing transformer, avoiding the circulating current problem caused by inconsistent parameters in traditional direct parallel transformer connections. The proposed series converter inertia compensation control method, by introducing a transient current feedforward mechanism, can effectively utilize the remaining capacity of the series branch to compensate for the impact power that the parallel converter cannot provide due to capacity limitations during system transients. This overcomes the insufficient transient inertia support capability of smaller capacity converters, enhancing the dynamic response and stability of the system. A port voltage aggregation control strategy based on a virtual synchronous machine (VSG) is adopted. This method controls the parallel converter so that the grid-connected port, composed of the original transformer and the newly added flexible branch, exhibits the external characteristics of a synchronous machine. This provides adjustable virtual inertia and damping to the grid, effectively suppressing system oscillations caused by the large-scale connection of new energy distribution areas and grid-type converters in weak grid conditions. Figure 7This is a flowchart of the control algorithm for a flexible parallel system.

[0106] Simulation experiments were conducted on embodiments of the present invention, and the experimental results are as follows: Figures 8(a)-8(d) , Figure 9 , Figures 10(a)-10(b) As shown.

[0107] Figures 8(a)-8(d) Figure 8(a) shows the primary frequency regulation characteristics of the system when a load is connected to the grid side. At 2 seconds, a load is connected to the grid side. Before 2 seconds, the grid voltage remains at 50Hz. After 2 seconds, the grid voltage enters a new steady-state equilibrium point after a brief transient process. Subsequently, as the flexible parallel device gradually transitions to the charging state of the supercapacitor on the energy storage side, the frequency begins to slowly decrease until the system's active power reference stabilizes. Figure 8(b) shows the output power of the flexible parallel system. Before 2 seconds, the output power remains stable. After 2 seconds, with the load connected, the system outputs transient impulse power through series and parallel converters to provide inertia to the grid. After the transient process, the output power of the flexible parallel system gradually decreases and returns to steady state. Figure 8(c) shows the DC bus voltage waveform of the flexible parallel system. Before 2 seconds, the DC bus voltage remains unchanged. After 2 seconds, due to the transient impulse power output by the system, the DC bus voltage experiences a small disturbance, but it quickly returns to a stable state through the voltage control of the DC converter. Figure 8(d) shows the voltage waveform of the supercapacitor in the flexible parallel system. Before 2s, the voltage remains stable. After 2s, the voltage of the supercapacitor drops rapidly due to the rapid energy supply to the AC side. After the transient process, the system begins to adjust the power reference, and the supercapacitor voltage begins to stabilize and slowly recover.

[0108] Figure 9 To determine the reactive power output characteristics of the grid port, before 2 seconds, both the reactive power reference and reactive power output of the grid port are 6kVar; after 2 seconds, the reactive power reference switches to 10kVar according to the controller command. At this time, through the port aggregation control of the flexible parallel device, the reactive power output of the grid port is also smoothly adjusted to 10kVar, realizing the tracking of the reactive power reference.

[0109] Figures 10(a)-10(b) To demonstrate the current tracking characteristics of the flexible parallel section for transformer T1, a power distribution factor of 1 was selected in the experiment. Figure 10(a) shows the current in transformer T1. After 1 second, the current in transformer T1 increases due to the change in power output from the new energy distribution area. Figure 10(b) shows the output current of the flexible parallel section. Before and after 1 second, rapid tracking of the current in transformer T1 was achieved.

[0110] This embodiment also provides a flexible capacity expansion device for new energy distribution transformers. This device is used to implement the above embodiments and preferred embodiments, and details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that performs a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0111] This embodiment provides a flexible capacity expansion device for transformers in new energy distribution areas, such as... Figure 11 As shown, it includes: Model building module 1101 is used to establish the circuit model of the transformer and flexible parallel unit of the new energy distribution area. The flexible parallel unit includes a transformer branch, a DC converter on the energy storage side, a series converter and a parallel converter. One end of the transformer branch is connected to the new energy distribution area, and the other end of the transformer branch is connected to the power grid. One end of the series converter is connected to the transformer branch, and the other end of the series converter is connected to one end of the parallel converter through the DC bus. The other end of the parallel converter is connected to the transformer branch, and the DC converter on the energy storage side is connected to the DC bus.

[0112] The energy storage side control module 1102 is used to stabilize the DC bus voltage based on the energy storage side DC converter using a dual closed-loop control strategy of voltage and current.

[0113] The series-side control module 1103 is used to distribute the steady-state current of the parallel transformer branch through current control based on the series converter, and to provide transient inertia compensation for the system by using transient current feedforward compensation.

[0114] The parallel-side control module 1104 is used to aggregate and control the grid port voltage based on the parallel converter and adopt a virtual synchronous network control strategy to reshape the grid port characteristics.

[0115] The flexible capacity expansion device for new energy transformer substations provided in this embodiment of the invention can execute the flexible capacity expansion method for new energy transformer substations provided in any embodiment of the invention, and has the corresponding functional modules and beneficial effects for executing the method. Further functional descriptions of the above modules and units are the same as those in the corresponding embodiments above, and will not be repeated here.

[0116] Figure 12 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention.

[0117] The following is a detailed reference. Figure 12The diagram illustrates a structural schematic suitable for implementing an electronic device according to embodiments of the present invention. The electronic device may include a processor (e.g., a central processing unit, graphics processor, etc.) 1201, which can perform various appropriate actions and processes according to a program stored in read-only memory (ROM) 1202 or a program loaded from memory 1208 into random access memory (RAM) 1203. The RAM 1203 also stores various programs and data required for the operation of the electronic device. The processor 1201, ROM 1202, and RAM 1203 are interconnected via a bus 1204. An input / output (I / O) interface 1205 is also connected to the bus 1204.

[0118] Typically, the following devices can be connected to I / O interface 1205: input devices 1206 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 1207 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; memory devices 1208 including, for example, magnetic tapes, hard disks, etc.; and communication devices 1209. Communication device 1209 allows electronic devices to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 12 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown, and more or fewer devices may be implemented or have instead.

[0119] In particular, according to embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present invention include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device 1209, or installed from a memory 1208, or installed from a ROM 1202. When the computer program is executed by the processor 1201, it performs the functions defined in the flexible capacity expansion method for new energy distribution transformers according to embodiments of the present invention.

[0120] Figure 12 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of use of the embodiments of the present invention.

[0121] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code. When the software or computer code is accessed and executed by the computer, processor, or hardware, the flexible capacity expansion method for new energy transformer substations shown in the above embodiments is implemented.

[0122] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for flexible capacity expansion of transformers in new energy distribution areas, characterized in that, The method includes: A circuit model of a transformer and a flexible parallel unit in a new energy distribution area is established. The flexible parallel unit includes a transformer branch, a DC converter on the energy storage side, a series converter, and a parallel converter. One end of the transformer branch is connected to the new energy distribution area, and the other end of the transformer branch is connected to the power grid. One end of the series converter is connected to the transformer branch, and the other end of the series converter is connected to one end of the parallel converter via a DC bus. The other end of the parallel converter is connected to the transformer branch, and the DC converter on the energy storage side is connected to the DC bus. Based on the energy storage-side DC converter, a dual closed-loop control strategy for voltage and current is adopted to stabilize the DC bus voltage. Based on the series converter, the steady-state current of the parallel transformer branch is distributed by current control, and transient inertia compensation is provided for the system by using transient current feedforward compensation. Based on parallel converters, a virtual synchronous network control strategy is adopted to aggregate and control the grid port voltage, thereby reshaping the grid port characteristics.

2. The flexible capacity expansion method for new energy distribution transformers according to claim 1, characterized in that, The transformer branch includes: a first transformer and a second transformer, wherein... The primary winding of the first transformer is connected in series between the new energy power generation station and the secondary winding of the second transformer, and the secondary winding of the first transformer is connected in parallel to the series converter. The primary winding of the second transformer is connected to the power grid, and the secondary winding of the second transformer is connected in parallel to the parallel converter.

3. The flexible capacity expansion method for new energy distribution transformers according to claim 2, characterized in that, The DC bus voltage is stabilized using a dual closed-loop control strategy based on the energy storage-side DC converter, including: Based on the deviation between the DC bus voltage and the DC bus voltage reference, a DC converter-side current reference is generated through the outer loop control of the DC bus voltage. Based on the deviation between the DC converter side current and the DC converter side current reference, an intermediate control quantity is generated through DC current inner loop control. The supercapacitor voltage is superimposed on the intermediate control quantity to perform feedforward compensation, thereby generating a DC converter modulation wave on the energy storage side. The modulation wave of the energy storage-side DC converter is sinusoidally pulse-width modulated to obtain the switching signal of the energy storage-side DC converter.

4. The flexible capacity expansion method for new energy distribution transformers according to claim 2, characterized in that, Based on a series converter, the steady-state current of the parallel transformer branch is distributed through current control, and transient inertia compensation is provided for the system using transient current feedforward compensation, including: Based on the turns ratio and power distribution coefficient of the first transformer and the current of the new energy distribution transformer, the series-side tracking current reference is calculated. The series-side tracking current reference is transformed to obtain the current reference vector in the stationary coordinate system. Based on the capacity limitation of the parallel converter, the transient current feedforward coefficient on the series side is calculated; During system transients, when the impulse power demand exceeds the capacity of the parallel converter, the transient current feedforward coefficient is superimposed to perform feedforward compensation on the current reference vector to generate the output current reference on the series side in the stationary coordinate system. Based on the output current reference, a proportional resonant controller is used to perform closed-loop calculations to generate a series converter modulation wave. The modulation wave of the series converter is pulse-width modulated to output the switching drive signal of the series converter.

5. The flexible capacity expansion method for new energy distribution transformers according to claim 2, characterized in that, Based on parallel converters, a virtual synchronous grid control strategy is adopted to aggregate and control the grid port voltage, thereby reshaping the grid port characteristics, including: Collect the grid-side current and filter capacitor voltage, and calculate the first active power and the first reactive power output from the grid port; Based on the deviation between the supercapacitor voltage and the supercapacitor voltage reference, a second active power reference for the virtual synchronous machine is generated through the active power controller, and based on the deviation between the first reactive power and the reactive power reference at the grid port, a second reactive power reference for the virtual synchronous machine is generated through the reactive power controller. Based on the second active power reference, the second reactive power reference, the first active power, and the first reactive power, the voltage frequency deviation and amplitude deviation of the grid port are calculated by virtual synchronous mechanism network control, combined with virtual inertia and damping coefficient. Based on the voltage frequency deviation and the amplitude deviation, the port voltage reference in the rotating coordinate system is calculated; The port voltage reference is transformed to obtain the port voltage reference vector in the stationary coordinate system; Based on the port voltage reference vector, the grid port voltage is aggregated and controlled through the voltage and current dual closed-loop control of the parallel converter.

6. The flexible capacity expansion method for new energy distribution transformers according to claim 5, characterized in that, Based on the port voltage reference vector, the grid port voltage is aggregated and controlled through the voltage and current dual closed-loop control of the parallel converter, including: Based on the deviation between the port voltage reference vector and the filter capacitor voltage, a port current reference is generated through voltage loop control; Based on the deviation between the port current reference and the port current, a modulated wave for the parallel converter is generated through current loop control. The modulation wave of the parallel converter is sinusoidally pulse-width modulated to generate the switching drive signal of the parallel converter.

7. The flexible capacity expansion method for new energy distribution transformers according to claim 5, characterized in that, Based on the capacity of the parallel converter, the second active power reference of the virtual synchronous machine is limited.

8. A flexible capacity expansion device for transformers in new energy distribution areas, characterized in that, The device includes: The model building module is used to establish the circuit model of the transformer and flexible parallel unit in the new energy distribution area. The flexible parallel unit includes a transformer branch, an energy storage-side DC converter, a series converter, and a parallel converter. One end of the transformer branch is connected to the new energy distribution area, and the other end of the transformer branch is connected to the power grid. One end of the series converter is connected to the transformer branch, and the other end of the series converter is connected to one end of the parallel converter through a DC bus. The other end of the parallel converter is connected to the transformer branch, and the energy storage-side DC converter is connected to the DC bus. The energy storage side control module is used to stabilize the DC bus voltage based on the energy storage side DC converter using a dual closed-loop control strategy of voltage and current. The series-side control module is used to distribute the steady-state current of the parallel transformer branch through current control based on the series converter, and to provide transient inertia compensation for the system by using transient current feedforward compensation. The parallel-side control module is used to aggregate and control the grid port voltage based on the parallel converter and adopt a virtual synchronous network control strategy, thereby reshaping the grid port characteristics.

9. An electronic device, characterized in that, include: The system includes a memory and a processor, which are interconnected. The memory stores computer instructions, and the processor executes the computer instructions to perform the flexible capacity expansion method for new energy distribution transformers as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions, which are used to cause the computer to execute the flexible capacity expansion method for new energy distribution transformers as described in any one of claims 1 to 7.

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