Control method and system of efficient micro-grid topological structure based on hybrid distribution transformer

Abstract

The invention discloses a control method and system for a high-efficiency micro-grid topological structure based on a hybrid distribution transformer, and belongs to the technical field of micro-grids. The control method comprises a grid-connected operation mode and an island operation mode. During grid connection, the parallel inverter controls the direct current bus voltage and reactive power, the series inverter stabilizes the load voltage, and photovoltaic and energy storage execute maximum power point tracking and double-closed-loop control respectively. And in an island, the series inverter stops outputting, and the parallel inverter is converted into a voltage control mode to support the voltage. When a power grid fails, island operation is automatically converted; and after the power grid is recovered, smooth grid connection is realized through phase pre-synchronization control. According to the method, by optimizing the topological structure and the control strategy, the potential of the HDT inverter is brought into full play in the island mode, the problem that the capacity of the HDT inverter in the island mode in the prior art cannot be effectively utilized is solved, and therefore the overall efficiency and economical efficiency of the system are improved.

Description

Technical Field

[0001] This invention belongs to the field of microgrid technology, specifically relating to a control method and system for a high-efficiency microgrid topology based on a hybrid distribution transformer. Background Technology

[0002] Renewable energy refers to resources that can be replenished naturally at a rate far exceeding their consumption. In recent years, with the rapid development of related technologies and the application of new electronic materials, the cost of utilizing these energy sources has decreased significantly, laying a solid foundation for a clean and sustainable energy future. Among numerous renewable energy sources, solar photovoltaic (PV) has become a focal point due to its widespread natural distribution and diverse applications, ranging from small-scale devices to large-scale power generation systems. However, the rapid development of PV technology has also brought about problems such as power fluctuations caused by energy intermittency. Especially during the grid connection of large-scale solar power generation, these problems pose significant challenges to power quality, system reliability and security, and control capabilities.

[0003] The widespread distribution of nonlinear and stochastic power electronic loads in modern power systems further increases system complexity. To address these challenges, power converter technology has gradually developed into a key means of connecting renewable energy sources, energy storage devices, and critical loads to microgrids. Therefore, researching efficient microgrid converter control methods has become one of the key directions for solving complex power system problems.

[0004] Microgrids are flexible power distribution networks capable of operating efficiently in grid-connected or islanded modes, enabling deep integration of renewable energy with the public grid. Advanced microgrids can monitor and control multiple interconnected loads and distributed energy sources, thereby improving system performance, reliability, resilience, and sustainability. In microgrid systems, power quality is a crucial indicator for evaluating system effectiveness and control performance. Existing research has systematically explored the causes, consequences, and mitigation techniques of power quality problems. Among these studies, hybrid distribution transformers (HDTs) have attracted significant attention due to their efficiency in improving voltage and current-related power quality issues.

[0005] In recent years, significant progress has been made in research on different topologies and control strategies for HDTs. However, current research focuses primarily on improving power quality, with less attention paid to optimizing system efficiency and cost control. When a microgrid switches to islanded mode, the inverters in the HDT are often not fully utilized due to the lack of AC support from the main grid, resulting in ineffective capacity utilization. This phenomenon exposes the limitations of existing designs in islanded mode. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a control method and system for a high-efficiency microgrid topology based on a hybrid distribution transformer, so as to solve the problem that the inverter of the HDT cannot be fully utilized during the switching between islanded mode and grid-connected mode in the prior art.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A control method for a high-efficiency microgrid topology based on a hybrid distribution transformer, the method being based on a microgrid topology including a switch, a high-efficiency distribution transformer (HDT), a photovoltaic module, and an energy storage module; The two sides of the switch are respectively connected to the power grid and the high-voltage side of the HDT, and the low-voltage side of the HDT is connected to an AC load. The HDT includes a transformer body, a parallel compensation inverter, a series compensation inverter, and a DC bus capacitor. The series compensation inverter and the secondary side of the transformer body are connected in series and connected to the AC load. The parallel compensation inverter and the tertiary side of the transformer body are connected in parallel. The parallel compensation inverter, the series compensation inverter, and the DC bus capacitor are connected in parallel. The photovoltaic module is connected in parallel with the DC bus capacitor through a Boost circuit. The energy storage module is connected in parallel with the DC bus capacitor through a bidirectional DC-DC circuit. The control method includes grid-connected mode and islanded mode; In the grid-connected mode, the switching drive signal of the parallel compensation inverter is generated through the power outer loop and the current inner loop control to achieve independent control of the DC bus voltage and reactive power; the load voltage generates the drive signal of the series compensation inverter based on its reference value and the collected three-phase load voltage signal; the photovoltaic module controls the control signal of the Boost circuit switching transistor through the maximum power point tracking algorithm, and the energy storage module responds through dual closed-loop control. In the islanded mode, the output voltage of the series compensation inverter is set to 0, the parallel compensation inverter is switched to voltage outer loop control, the photovoltaic module is in voltage regulation mode, and the control strategy of the energy storage module is the same as that in the grid-connected mode. When switching from grid-connected mode to islanded mode, the switch will disconnect if there is a grid anomaly. When switching from islanded mode to grid-connected mode, phase pre-synchronization is initiated after the grid is restored, gradually aligning the grid phases, and the switch is closed after the parameters are normal.

[0008] A further improvement of the present invention is that: Preferably, during grid-connected mode control, the DC bus voltage and grid reactive power on the parallel compensation inverter side are independently controlled through power outer loop control, generating d-axis and q-axis reference values ​​of grid current. Combined with grid current inner loop control, the switching transistor drive signal of the parallel compensation inverter is obtained.

[0009] Preferably, the dual closed-loop control includes an outer power loop control and an inner grid current loop control, wherein the outer power loop control detects the bus voltage error and the inner grid current loop controls the energy storage module.

[0010] Preferably, when switching from grid-connected mode to islanded mode, the abnormal grid conditions include deviations in the amplitude, phase, or frequency of the grid voltage from the normal range.

[0011] Preferably, in the islanded mode, the parallel compensation inverter generates drive signals for six switches by acquiring the three-phase load voltage signal and combining it with a reference value; The process of acquiring the three-phase load voltage signal is as follows: when the grid-side voltage amplitude is lower than 0.7 pu, a dual phase-locked loop is used to detect the phase of the load voltage and the grid voltage respectively. The phase difference between the two is sinusoidally smoothed and then input into the PI controller, which outputs the frequency deviation. The deviation is superimposed with the load frequency and integrated to generate the target phase, so that the load voltage phase gradually tracks the grid voltage.

[0012] Preferably, when switching from islanded mode to grid-connected mode, phase pre-synchronization is initiated when the amplitude of the grid voltage recovers to more than 80% of the normal value; during phase synchronization, all parameters of the grid are synchronously detected until they recover to the normal range, and then the switch is closed.

[0013] Preferably, the maximum power point tracking algorithm is a boost converter that adjusts the duty cycle to make the photovoltaic module operate at the maximum power point voltage.

[0014] Preferably, when the grid-connected mode is converted to the islanded mode, the following conditions are met: the phase difference between the grid-side voltage and the load voltage is <3°, the voltage amplitude difference is <0.05, and the frequency difference is <0.3Hz; When the islanded mode is converted to the grid-connected mode, the following conditions must be met: the voltage amplitude difference between the grid-side voltage and the load voltage is <0.3 pu, the frequency difference is <0.3Hz, and the phase difference is <3°.

[0015] Preferably, when switching from grid-connected mode to islanded mode, the series-compensated inverter operates in grid-connected mode for a delay time, and then switches to islanded mode; when switching from islanded mode to grid-connected mode, the system remains in islanded mode for a delay time, and switches to grid-connected mode after the delay time ends.

[0016] A control system for a high-efficiency microgrid topology based on a hybrid distribution transformer includes: The grid-connected module, when the microgrid is in the grid-connected mode, generates the switching drive signal of the parallel compensation inverter through the power outer loop and current inner loop control, realizing independent control of DC bus voltage and reactive power; the load voltage generates the drive signal of the series compensation inverter based on its reference value and the collected three-phase load voltage signal; the photovoltaic module controls the control signal of the Boost circuit switching transistor through the maximum power point tracking algorithm, and the energy storage module responds through dual closed-loop control. In the islanded module, when the microgrid is in the islanded mode, the output voltage of the series compensation inverter is set to 0, the parallel compensation inverter is switched to voltage outer loop control, the photovoltaic module is in voltage regulation mode, and the control strategy of the energy storage module is the same as that of the grid-connected mode. The grid-connected switching islanding module disconnects when the microgrid switches from grid-connected mode to islanded mode, in case of grid anomalies. The islanding to grid-connected module initiates phase pre-synchronization after the grid is restored when the microgrid switches from islanding mode to grid-connected mode. It gradually aligns the grid phases and closes the switch once the parameters are normal.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a control method for a high-efficiency microgrid topology based on a hybrid distribution transformer (HDT). It provides control algorithms applicable to both grid-connected and islanded modes, as well as a pre-synchronization strategy for mode switching. This invention enables smooth switching between grid-connected and islanded modes in a hybrid AC / DC microgrid system based on HDT. In particular, the application of the phase pre-synchronization strategy effectively avoids system instability during switching, improving operational reliability and smoothness.

[0018] This invention proposes a hybrid AC / DC microgrid system based on HDT. By optimizing the topology and control strategy, the potential of HDT inverters is fully utilized in islanded mode, solving the problem of ineffective utilization of HDT inverter capacity in islanded mode in existing technologies, thereby improving the overall efficiency and economy of the system. Attached Figure Description

[0019] Figure 1 This is a topology diagram of the hybrid AC / DC microgrid based on HDT involved in this invention.

[0020] Figure 2 This invention relates to the series compensation inverter control strategy for HDT.

[0021] Figure 3 This invention relates to the parallel compensation inverter control strategy for HDT.

[0022] Figure 4 This is the control strategy for the photovoltaic module involved in this invention.

[0023] Figure 5 This refers to the control strategy for the energy storage module involved in this invention.

[0024] Figure 6 This refers to the island mode phase generation strategy involved in this invention.

[0025] Figure 7 This is a control logic diagram for microgrid mode switching involved in this invention.

[0026] Figure 8 This is a timing diagram of microgrid mode switching involved in this invention. Detailed Implementation

[0027] Hereinafter, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first," "second," "third," or "fourth" may explicitly or implicitly include one or more of that feature.

[0028] The synchronization method provided in this application can be applied to mobile phones, tablets, wearable devices, in-vehicle devices, augmented reality (AR) / virtual reality (VR) devices, laptops, and ultra-mobile personal computers. In this application, the specific type of terminal device is not limited to terminal devices such as mobile personal computers (UMPCs), netbooks, and personal digital assistants (PDAs).

[0029] It should be noted that the terms "first," "second," etc., used in the specification and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0030] This invention proposes a hybrid AC / DC microgrid topology based on a High-Density Transformer (HDT). This topology includes a switch, one end of which is connected to the power grid, and the other end to the HDT. The HDT consists of a three-winding transformer, a series-compensated inverter, a parallel-compensated inverter, and a DC bus capacitor, and is connected to the load through its other end. A photovoltaic array is connected to the HDT's DC bus capacitor via a Boost circuit, while energy storage devices are connected to the DC bus capacitor via a bidirectional DC-DC circuit, enabling bidirectional energy flow and flexible system operation.

[0031] This invention discloses a microgrid control algorithm applicable to the above-mentioned topology, including control algorithms for grid-connected operation mode, islanded operation mode, and mode switching process.

[0032] In grid-connected mode, this invention achieves independent control of the DC bus voltage and grid reactive power on the parallel compensation inverter side through an outer power control system, thereby generating d-axis and q-axis reference values ​​for grid current control. Combined with an inner grid current control system, these reference values ​​are used to generate drive signals for the six switches of the parallel compensation inverter. Simultaneously, by acquiring three-phase load voltage signals and combining them with reference values, a load voltage control system generates drive signals for the six switches of the series compensation inverter. The photovoltaic DC bus voltage control system uses a maximum power point tracking (MPPT) algorithm to generate reference values ​​and, combined with the acquired photovoltaic voltage signals, generates drive signals for the Boost circuit switches through a control algorithm, thereby achieving efficient utilization of photovoltaic energy. Furthermore, the energy storage module adopts a dual closed-loop control structure, where the outer voltage loop detects bus voltage errors, and the inner grid current loop controls the bidirectional DC-DC converter of the energy storage module to achieve rapid dynamic response.

[0033] In islanded mode, the control strategy differs significantly from that in grid-connected mode. The output voltage of the series-compensated inverter is set to 0, while the parallel-compensated inverter switches to outer-loop voltage control. This involves acquiring the three-phase load voltage signal and combining it with a reference value to generate the drive signals for its six switching transistors. Furthermore, to achieve smooth system mode switching, this invention also designs a reference phase generation strategy in islanded mode and a phase pre-synchronization strategy when switching from islanded to grid-connected mode, ensuring the stability and smoothness of mode transitions.

[0034] The system switches from grid-connected mode to islanded mode according to the following logic: When the sampling module detects that the amplitude, phase, or frequency of the grid voltage deviates from the normal range, the controller immediately issues a command to disconnect the switch, switching the system to islanded mode. During this process, to prevent system instability caused by the time delay when the switch is disconnected, the series-compensated inverter will continue to operate in grid-connected mode for a short period to ensure that the power supply to the load is not affected. After the delay period ends, the output voltage of the series-compensated inverter is set to 0, and the system officially enters islanded mode, switching to the control logic of islanded mode to ensure the stability and power quality of the system during islanded operation.

[0035] The system switches from islanded mode to grid-connected mode according to the following logic: When the sampling module detects that the grid voltage amplitude gradually recovers to more than 80% of its normal value, the system initiates a phase pre-synchronization strategy. The parallel-compensated inverter gradually adjusts the load voltage phase to align with the grid phase, thereby achieving phase matching with the grid. During phase synchronization, the system continuously monitors the grid voltage amplitude, frequency, and phase difference to ensure all parameters return to normal ranges. Once these conditions are met, the controller issues a command to close the switch, completing the grid-connected operation. Considering the switching delay, the system maintains the islanded mode control strategy for a short period after closing the switch until it is confirmed that the switch is fully closed and the system is operating stably before switching to the grid-connected mode control logic, ensuring the smoothness and reliability of the entire process.

[0036] The standard three-winding structure corresponding to this invention is typically difficult to physically connect in parallel between the CVSE and CVSH outputs. To address this inherent limitation, this invention employs a simpler and more practical strategy in islanded operation mode: instructing the CVSE to stop actively outputting (e.g., controlling its output voltage to zero, or putting it into a bypass / short-circuit state), while the islanded power supply task is entirely handled independently by the parallel-compensated inverter CVSH, which then switches to voltage source control mode. This "single-unit main supply, auxiliary unit on standby" scheme effectively reduces the complexity of the control algorithm in islanded mode and decreases the reliance on hardware switching devices.

[0037] The following description, in conjunction with specific embodiments, provides further details.

[0038] This invention discloses a hybrid AC / DC microgrid system based on HDT, as shown in the attached figure. Figure 1 As shown, the main circuit topology of the hybrid AC / DC microgrid involved consists of four parts: a switch, a high-voltage transformer (HDT), photovoltaic modules, and an energy storage module. One side of the switch is connected to the grid, and the other side is connected to the high-voltage side of the HDT. The HDT mainly consists of a transformer body, two voltage-source inverters connected in parallel to compensate for the inverter CV. SH and series compensated inverter CVSE It consists of DC bus capacitors. The transformer body is a three-phase power frequency transformer with three windings, and its high-voltage side winding W... 1φ One end is connected to the switch in a delta configuration, while the secondary low-voltage winding W 2φ and the third-side control winding W 3φ All use a neutral-lead star connection; W 2φ After passing through an LCR filter and CV SE After being connected in series to the low-voltage distribution network side, W 3φ After passing through an LCL filter and then CV SH Connected (φ represents the phase sequence subscript of a three-phase system; φ can be a, b, or c). W 2φ and W 3φ The neutral lines are connected together and then connected to the midpoint of the split capacitor. CV SH and CV SE Both adopt a three-phase bridge inverter circuit topology and a DC bus capacitor C. D The photovoltaic modules are connected in parallel to form the DC bus on the inverter side. In addition, the photovoltaic array of the photovoltaic module is connected in parallel to both ends of the DC bus on the inverter side through a boost circuit, while the energy storage module is connected in parallel to both ends of the DC bus through a bidirectional DC-DC circuit.

[0039] Specifically, one end of the switch is connected to the grid via an inductor, and the voltage obtained is... u Gφ The other end of the switch is connected to the high-voltage side winding W. 1φ The connection is such that the high-voltage side receives the injected current from the grid side. i Psφ The injection voltage is u 1φ The secondary winding W 2φ One end is connected to an AC load, and the other end is connected through an inductor L. SE and CV SE Connections, secondary winding and inductor L SE At the connection point, an anti-parallel diode is connected to the neutral line, and a branch capacitor C is connected in series at the connection point between the secondary side and the AC load. f and resistance R f resistance R f one end and capacitor C f One end is connected to the neutral line, and the secondary side draws current from the AC load. i 2k The voltage obtained is u 2φ The current drawn by the AC load from the neutral line is i 2n ,; third side W 3φ One end is through LSH and CV SH The connection is made at one end and the other end is connected to the neutral line. The voltage obtained on the third side is... u 3φ The output current is i 3n The DC bus capacitor consists of two C capacitors. D It consists of a DC bus capacitor connected in parallel with a DC load, a photovoltaic module, and an energy storage module.

[0040] The control strategy for this hybrid AC / DC microgrid system is as follows: Series-compensated inverter CV for HDT SE Control strategies such as Figure 2 As shown. When the system is in grid-connected mode, the sampling module samples the three-phase load voltage signal, then converts it into d-axis, q-axis, and 0-axis signals through coordinate transformation. These signals are then combined with reference values ​​and used by a PI controller to generate CV. SE The six switching transistor drive signals are adjusted to ±50% duty cycle when the system is in islanded mode, so that CV... SE The output voltage becomes 0, which means that in islanded operation mode, the CV SE Not working; the specific load voltage control system control process is as follows: when the system is in grid-connected mode, the sampling module samples the three-phase load voltage signal. u 2a , u 2b , u 2c Then, it is converted into a d-axis signal through coordinate transformation. u 2d q-axis signal u 2q and 0 axis signal u 20 Then, it is combined with the d-axis signal reference value generated on the inverter side. u 2dref and the q-axis signal reference value generated by the power grid reactive power control u 2qref and 0-axis signal reference value u 20ref The PI controller generates drive signals for the six switching transistors of the CVSE. When the system is in islanded mode, the drive signals for the six switching transistors are adjusted to a duty cycle of ±50%, enabling the CVSE to function correctly. SE The output voltage becomes 0, which means that in islanded operation mode, the CV SE Not working.

[0041] Parallel Compensated Inverter CV for HDT SH Control strategies such as Figure 3As shown. The specific process is as follows: for the parallel compensation inverter CV of HDT. SH Control strategies such as Figure 3 As shown. Specifically, when the system is in grid-connected mode, the control process of the power outer loop control system is as follows: combining the d-axis signal reference value generated by the DC bus voltage control on the parallel inverter side and the q-axis signal reference value generated by the grid reactive power control. Subsequently, the control process of the grid current inner loop control system is as follows: the sampling module samples the three-phase grid side current signal. i ga , i gb , i gc Then, it is converted into a d-axis signal through coordinate transformation. i gd q-axis signal i gq and 0 axis signal i g0 Then, the d-axis signal reference value generated by the DC bus voltage control on the parallel inverter side is combined with the reference value. i gdref and the q-axis signal reference value generated by the power grid reactive power control i gqref CV is generated through the grid current inner loop controller. SH The six switching transistor drive signals. When the system is in islanded mode, the sampling module samples the three-phase load voltage signal, then converts it into d-axis, q-axis, and 0-axis signals through coordinate transformation. These signals are then combined with reference values ​​and used by the PI controller to generate CV. SH The six switching transistor drive signals.

[0042] Control strategies for photovoltaic modules, such as Figure 4 As shown. When operating in grid-connected mode or under high load demand, the photovoltaic (PV) modules preferentially operate in MPPT mode. In this mode, the boost converter adjusts the duty cycle to ensure the PV modules operate at their maximum power point voltage, maximizing power generation. The MPPT algorithm continuously tracks the power curve of the PV array, adapting to changes in irradiance and ambient temperature. In islanded mode or under low load demand (excess power generation), the system switches to voltage regulation mode. In this mode, the control objective shifts from tracking the maximum power point to regulating the stability of the DC bus voltage. The PV modules operate at voltages below the maximum power point, and the DC bus voltage is maintained stable by adjusting the output voltage of the boost converter. The control strategy for the PV modules is as follows: Figure 4 As shown, the specific control process of the photovoltaic DC bus voltage control system is as follows: The photovoltaic system control strategy detects the output voltage of the photovoltaic array in real time. u pv and current i pvThe voltage corresponding to the maximum power point is calculated using the MPPT (Maximum Power Point Tracking) algorithm. u mpp and use it as a reference value. u pvref Compare it with the actual voltage u pv The difference is input to the PI controller; the PI controller generates a PWM modulation signal by comparing this signal with a carrier signal (such as a triangular wave) in a comparator. S pv Ultimately, it drives the power switching devices.

[0043] Control strategies for energy storage modules, such as Figure 5 As shown. By adjusting the switching signal of the bidirectional converter, the charging and discharging current of the battery can be precisely controlled, thereby achieving DC bus voltage regulation and system power balance. Regardless of changes in load power or photovoltaic output power, the energy storage module ensures that the DC bus voltage remains stable near the set value through charging and discharging. The control strategy for the energy storage module is as follows: Figure 5 As shown, the system monitors the DC bus voltage in real time. u dc and compare it with the reference value. u dcref A comparison is performed to generate an error signal, which is then input to the PI controller's output current reference value. i bcref The difference between this value and the current is input to the PI controller, which outputs a control signal. This control signal is then directly compared with a carrier wave (such as a triangular wave) in a comparator to generate the switching signal for the bidirectional converter. S b1 and S b2 (Complementarity is ensured through the "Not" logic gate), and the charging and discharging current of the battery can be precisely controlled by adjusting the switching signal of the bidirectional converter.

[0044] In islanded mode, the phase signal used for coordinate transformation is obtained through, for example... Figure 6 The algorithm shown generates the voltage when the grid-side voltage is... u G When the amplitude is less than 0.7 (per unit), the phase is obtained by integrating with respect to the power frequency. When the grid-side voltage amplitude is less than 0.7 (per unit), the system uses two phase-locked loops (PLLs) to detect the phase of the load voltage u2 and the grid voltage uG, respectively. The two phase signals are then subtracted and smoothed. sine The smoothed phase difference is fed into a PI controller, whose output is a frequency component representing the frequency deviation that needs to be adjusted. This frequency component is related to the load frequency. Δ ω2) After summing, the summation is passed as input to the integration module. The integration module generates the target phase for all three-phase parallel converters based on the adjusted frequency. Due to the frequency adjustment, the load voltage gradually matches the phase of the grid voltage.

[0045] The method for determining when the system switches from grid-connected mode to islanded mode and when it switches back from islanded mode to grid-connected mode is as follows: Figure 7 As shown. Switching from islanded mode to grid-connected mode: When the system is in islanded operation mode, if the grid becomes available again, the system will perform the following checks: grid-side voltage. U Gk With load voltage U 2k Phase difference |Ф G -Ф2|Is it less than 3°, voltage amplitude difference| U Gk - U 2k |Whether it is less than 0.05 (per unit), frequency difference| f G - f 2| Is it less than 0.3Hz? If all the above conditions are met, the system will switch from islanded mode to grid-connected mode, i.e., Ds(t) = 1. Operational checks in grid-connected mode: If the system is already in grid-connected mode, the system will also check the following conditions: voltage amplitude difference | U Gk - U 2k |Whether the frequency difference is within 0.3 per unit | f G - f 2| Whether it is less than 0.3Hz, and the phase difference |Ф G If -Ф2|<3° meets the requirements, the system will switch to island mode.

[0046] Furthermore, considering the certain delay between the opening and closing of the switch, this invention designs a smooth switching strategy, with the switching timing logic as follows: Figure 8 As shown in Figure D. S D is the control signal for the switch. SH For CV SH The mode control signal, D SE For CV SEThe mode control signal is 0, indicating that the module has entered islanded mode; a control signal of 1 indicates that the module has entered grid-connected mode. The switching logic from grid-connected to islanded mode is as follows: The sampling module monitors the voltage amplitude, phase, and frequency of the power grid in real time. When any parameter (amplitude, phase, or frequency) deviates from the normal range, the system determines that the power grid is abnormal and triggers the switching logic. The controller immediately issues a disconnect switch command, physically isolating the system from the power grid and entering islanded mode. SH Switch to islanded operation mode. Due to a brief time delay when the switch is turned off, to avoid system instability caused by this delay, CV... SE During this transition period, the control logic continues to operate according to the grid-connected mode. Once the delay time ends and the switch is completely open, the CV... SE The output voltage is gradually set to 0, ceasing response to the grid. During the switchover logic from islanded mode to grid-connected mode, the sampling module monitors the grid voltage amplitude, frequency, and phase in real time. When the grid voltage amplitude gradually recovers to more than 80% of its rated value, the system considers the grid to have essentially recovered and enters the switching preparation phase. The system initiates phase pre-synchronization logic, and the parallel-compensated inverter takes over the synchronization control task. By finely adjusting the phase of the load voltage, it gradually approaches the phase of the grid voltage, ultimately achieving phase matching. During this process, the speed and range of phase adjustment are strictly regulated by the controller to avoid large disturbances or rapid changes that could lead to system instability. When all conditions are met, the controller issues a command to close the switch, completing the physical connection between the system and the grid. Considering the time delay in switch closure, the system continues to maintain the islanded mode control logic for a short period after switch closure to ensure that the stability of the load voltage and frequency is not affected during the transition phase.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A control method of a high-efficiency microgrid topology based on a hybrid distribution transformer, characterized by, The method is based on a micro-grid topology, the micro-grid topology comprising a switch, an HDT, a photovoltaic module and an energy storage module; Two sides of the switch are connected with a power grid and a high-voltage side of the HDT respectively, and a low-voltage side of the HDT is connected with an alternating current load; the HDT comprises a transformer body, a parallel compensation inverter, a series compensation inverter and a direct current bus capacitor; the series compensation inverter and a secondary side of the transformer body are connected in series and connected with the alternating current load, and the parallel compensation inverter and a tertiary side of the transformer body are connected in parallel; the parallel compensation inverter, the series compensation inverter and the direct current bus capacitor are connected in parallel, the photovoltaic module is connected with the direct current bus capacitor in parallel through a Boost circuit, and the energy storage module is connected with the direct current bus capacitor in parallel through a bidirectional DC-DC circuit; The control method comprises a grid-connected mode and an island mode; In the grid-connected mode, a switch driving signal of the parallel compensation inverter is generated through power outer loop control and current inner loop control, so as to realize independent control of the direct current bus voltage and the reactive power; a driving signal of the series compensation inverter is generated based on a reference value and an acquired three-phase load voltage signal of the load voltage; a control signal of a Boost circuit switch tube of the photovoltaic module is controlled through a maximum power point tracking algorithm, and the energy storage module is controlled through double closed loop control; In the island mode, an output voltage of the series compensation inverter is set to 0, the parallel compensation inverter is switched to voltage outer loop control, the photovoltaic module is in a voltage regulation mode, and the control strategy of the energy storage module is consistent with that in the grid-connected mode; When the grid-connected mode is converted to the island mode, the switch is turned off when the power grid is abnormal; When the island mode is converted to the grid-connected mode, the switch is turned on after the power grid is restored and phase pre-synchronization is started, the power grid phase is gradually aligned, and the switch is turned off after the parameters are normal.

2. The control method of the high-efficiency micro-grid topology based on the hybrid distribution transformer according to claim 1, characterized in that, In the grid-connected mode control process, independent control of the direct current bus voltage on the parallel compensation inverter side and the reactive power of the power grid is realized through power outer loop control, d-axis and q-axis reference values of the power grid current are generated, and switch tube driving signals of the parallel compensation inverter are obtained through combination of power grid current inner loop control.

3. The control method of the high-efficiency micro-grid topology based on the hybrid distribution transformer according to claim 1, characterized in that, The double closed loop control comprises power outer loop control and power grid current inner loop control, the power outer loop control detects bus voltage error, and the power grid current inner loop control controls the energy storage module.

4. The control method of the high-efficiency micro-grid topology based on the hybrid distribution transformer according to claim 1, characterized in that, When the grid-connected mode is converted to the island mode, the abnormal conditions of the power grid include that the amplitude, phase or frequency of the power grid voltage deviates from the normal range.

5. The control method of the high efficient microgrid topology based on the hybrid distribution transformer according to claim 1, characterized in that, In the island mode, driving signals of six switches are generated through acquisition of three-phase load voltage signals and combination of reference values by the parallel compensation inverter; The process of acquiring the three-phase load voltage signals is as follows: when the grid-side voltage amplitude is lower than 0.7 p.u., double phase-locked loops are used to detect the phases of the load voltage and the power grid voltage respectively, a phase difference between the two is input into a PI controller after sinusoidal smoothing, and a frequency deviation amount is output; The deviation amount and the load frequency are superimposed, and a target phase is generated through integration, so that the phase of the load voltage gradually tracks the phase of the power grid voltage.

6. The control method of a high-efficiency microgrid topology based on a hybrid distribution transformer according to claim 1, characterized in that, When the island mode is converted to the grid-connected mode, phase pre-synchronization is started when the amplitude of the power grid voltage is restored to more than 80% of the normal value. In the phase synchronization process, all parameters of the grid are detected until they return to the normal range, and the switch is closed.

7. The control method of a high-efficiency microgrid topology based on a hybrid distribution transformer according to claim 1, characterized in that, The maximum power point tracking algorithm is used to operate the photovoltaic module at the maximum power point voltage by adjusting the duty cycle of the boost converter.

8. The control method of the high-efficiency microgrid topology based on the hybrid distribution transformer according to claim 1, characterized in that, When the grid-connected mode is converted to the island mode, the following conditions are met: the phase difference between the grid-side voltage and the load voltage is less than 3°, the voltage amplitude difference is less than 0.05, and the frequency difference is less than 0.3 Hz. When the island mode is converted to the grid-connected mode, the following conditions are met: the voltage amplitude difference between the grid-side voltage and the load voltage is less than 0.3 p.u, the frequency difference is less than 0.3 Hz, and the phase difference is less than 3°.

9. The control method of the high-efficiency microgrid topology based on the hybrid distribution transformer according to claim 1, characterized in that, When switching from the grid-connected mode to the island mode, the series compensation inverter works in the grid-connected mode for a delay time and then switches to the island mode; when switching from the island mode to the grid-connected mode, the system still works in the island mode for a delay time and then switches to the grid-connected mode.

10. A control system for a high efficiency microgrid topology based on a hybrid distribution transformer, characterized by, The grid-connected module generates the switch driving signal of the parallel compensation inverter through power outer loop and current inner loop control when the microgrid is in the grid-connected mode, realizing independent control of the DC bus voltage and reactive power; the load voltage generates the driving signal of the series compensation inverter based on its reference value and the collected three-phase load voltage signal; the photovoltaic module controls the control signal of the Boost circuit switch tube through the maximum power point tracking algorithm, and the energy storage module responds through double closed loop control; The island module sets the output voltage of the series compensation inverter to 0 when the microgrid is in the island mode, and the parallel compensation inverter switches to voltage outer loop control; the photovoltaic module is in voltage regulation mode, and the control strategy of the energy storage module is consistent with that in the grid-connected mode; The grid-connected-to-island module opens the switch when the microgrid is converted from the grid-connected mode to the island mode when the grid is abnormal. The island-to-grid-connected module starts phase pre-synchronization after the grid recovers when the microgrid is converted from the island mode to the grid-connected mode, gradually aligns the grid phase, and closes the switch when the parameters are normal. ​

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