Dual-path energy supply power stabilization system and control method

Abstract

The application relates to a dual-path energy supply stabilizing system and a control method, which comprises a 1# power distribution circuit and a 2# power distribution circuit in parallel connection, the two power distribution circuits are connected through an AC / AC module, and the AC low-voltage side of the 2# power distribution circuit is connected with a DC micro-grid through an AC / DC module; the AC / AC module comprises a first power unit and a second power unit, the AC output end of the first power unit is a first port of the AC / AC module, the AC output end of the second power unit is a second port of the AC / AC module, the first power unit and the second power unit share a DC input end, and the DC input end is a third port of the AC / AC module; the AC bus of the low-voltage side of the 1# power distribution circuit is connected with the AC / AC module through the first port, the AC bus of the low-voltage side of the 2# power distribution circuit is connected with the AC / AC module through the second port, and the DC bus of the DC micro-grid is connected with the AC / AC module through the third port.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to a dual-source power supply stability system and control method. Background Technology

[0002] With the increasing popularity of new energy electric vehicles, the number of high-power AC / DC charging piles in highway service areas is constantly increasing, making it difficult for the transformer capacity of the existing AC power grid to meet the load requirements. To solve this problem, it is necessary to build large-scale AC and DC microgrids to provide energy for the increased high-power DC charging piles. However, the use of renewable energy generation in AC and DC microgrids means that for service areas without grid connection qualifications, the surplus electricity generated needs to be controlled to avoid feeding back into the grid and causing impacts, or to restrict renewable energy generation to avoid energy waste. In addition, for old distribution lines that do not contain renewable energy microgrids, not only is their power capacity limited and unable to meet the increased electricity load, but they also cannot continue to supply power to the load in the event of a grid outage. Summary of the Invention

[0003] In view of the problems existing in the new and old power supply systems mentioned in the prior art, the present invention designs a dual-energy power supply stability system that can establish a connection between the new and old power supply systems, realize the power capacity expansion of the old lines, and enable the new and old power supply systems to operate in an off-grid state. This not only improves the power supply stability of the original distribution network, but also improves the efficiency of new energy utilization.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A dual-energy power supply stability system includes a No. 1 distribution line and a No. 2 distribution line that supply power to their respective loads in parallel, and an ACAC module connecting the No. 1 distribution line and the No. 2 distribution line; the AC low-voltage side of the No. 2 distribution line supplies power to the AC loads through an AC bus, and is also connected to a DC microgrid containing a new energy power generation system through an AC / DC module.

[0006] The ACAC module comprises two interconnected three-phase inverter modules: a first power unit and a second power unit. The AC output of the first power unit is its first port, which is connected to the AC bus on the low-voltage side of distribution line #1. The AC bus on the low-voltage side of distribution line #1 is equipped with a #1 electricity meter module, which is connected to the ACAC module via serial communication. The AC output of the second power unit is its second port, which is connected to the AC bus on the low-voltage side of distribution line #2. The AC bus on the low-voltage side of distribution line #2 is equipped with a #2 electricity meter module, which is connected to both the AC / DC module and the ACAC module on the low-voltage side of distribution line #2 via serial communication. The first and second power units share a DC input terminal, which is a third port. The DC bus of the DC microgrid is connected to the ACAC module via this third port.

[0007] Furthermore, the DC microgrid includes DC-DC energy storage modules, DC-DC photovoltaic modules, DC loads, and DC-DC charging piles connected in parallel to the DC bus.

[0008] Furthermore, each of the first and second power units includes six IGBTs and an LC series resonant circuit. The IGBTs in the first power unit are Q1, Q2, Q3, Q4, Q5, and Q6. The emitter of Q1 is connected to the collector of Q2, the emitter of Q3 is connected to the collector of Q4, and the emitter of Q5 is connected to the collector of Q6. The IGBTs in the second power unit are Q7, Q8, Q9, Q10, Q11, and Q12. The emitter of Q7 is connected to the collector of Q8, the emitter of Q9 is connected to the collector of Q10, and the emitter of Q11 is connected to the collector of Q12. The collectors of Q1, Q3, Q5, Q7, Q9, and Q11 are connected, and the emitters of Q2, Q4, Q6, Q8, Q10, and Q12 are connected.

[0009] The present invention also discloses a control method for the above-mentioned power supply stabilization system, comprising:

[0010] When the No. 1 distribution line is connected to the grid, the first power unit of the ACAC module uses the PQ power control method to adjust the output power of the first port, and converts the generated power of the DC microgrid into AC power to increase the power capacity of the No. 1 distribution line load.

[0011] When the No. 1 distribution line is off-grid, the first power unit of the ACAC module operates in voltage and frequency control mode, converting the generated power of the DC microgrid into AC power to supply the load of the No. 1 distribution line.

[0012] When the No. 2 distribution line is off-grid and the AC / DC module can operate normally, the second power unit of the AC / DC module operates in virtual synchronous machine or droop mode, and operates in parallel with the AC / DC module's AC and DC, drawing power from the DC bus of the DC microgrid to supply power to the AC load of the No. 2 distribution line.

[0013] When the No. 2 distribution line is disconnected from the grid and the AC / DC module fails, the second power unit of the AC / DC module operates in voltage and frequency control mode, draws power from the DC bus of the DC microgrid, and converts it into AC power through the second power unit to supply AC load to the No. 2 distribution line.

[0014] Furthermore, when the No. 1 distribution line is connected to the grid, the control modes of the first power unit in the ACAC module are divided into line capacity expansion mode, new energy high-efficiency utilization mode, and transformer high-efficiency state mode. The first power unit selects and executes the corresponding mode according to the power data collected by the No. 1 metering module from the No. 1 distribution line.

[0015] Furthermore, when the first power unit executes the line capacity expansion mode, it acquires the apparent power S of the transformer of distribution line #1. 1_RATED Obtain the AC load power P of distribution line #1. 1_LOAD Determine whether relation (1) is satisfied:

[0016] P 1_LOAD ≥a·S 1_RATED (Equation 1)

[0017] In the above formula, a is the calculation adjustment coefficient of the No. 1 distribution line, which is the ratio of the maximum apparent load power to the rated apparent power of the transformer when the transformer is running stably for a long time.

[0018] If relation (1) is satisfied, then the power control setpoint P of the first port is... 1_AC_REF Calculate according to relation (2):

[0019] P 1_AC_REF =P 1_LOAD -a·S 1_RATED +P 1_MARGIN (Equation 2)

[0020] In the above formula, P 1_MARGIN This indicates the operating margin power of the AC / DC module in power distribution line #2;

[0021] If relation (1) is not satisfied, then the power control setpoint P of the first port is... 1_AC_REF It is 0.

[0022] Furthermore, when the first power unit executes the high-efficiency utilization mode of new energy, it obtains the output power P of the AC / DC module in the No. 2 distribution line. ACDCObtain the rated power P of the AC / DC module. ACDC_RATED Determine whether relation (3) is satisfied:

[0023] |P ACDC |≥c·P ACDC_RATED (Equation 3)

[0024] In the above formula, c is the margin power output of the first port;

[0025] If relation (3) is satisfied, then continue to determine whether relation (4) is satisfied:

[0026] a·S 1_RATED ≥P 1_LOAD ≥P 1_TH (Equation 4)

[0027] In the above formula, S 1_RATED P represents the apparent power of transformer #1 in distribution line. 1_LOAD P represents the AC load power of distribution line #1. 1_TH Adjust the power threshold for distribution line #1; 'a' is the calculated adjustment coefficient for distribution line #1, which is the ratio of the maximum apparent load power to the rated apparent power of the transformer when the transformer is running stably for a long time.

[0028] If relation (4) is satisfied, then the power control setpoint P of the first port is... 1_AC_REF Calculate according to relation (5):

[0029] P 1_AC_REF =P 1_LOAD -P 1_TH (Equation 5)

[0030] If relation (4) is not satisfied, then the power control setpoint P of the first port is... 1_AC_REF =0;

[0031] If relation (3) is not satisfied, then the line capacity expansion mode is executed.

[0032] Furthermore, when the first power unit executes the transformer high-efficiency mode, it acquires the apparent power S of the transformer of distribution line #1. 1_RATED Obtain the AC load power P of distribution line #1. 1_LOAD Determine whether relation (6) is satisfied:

[0033] P 1_LOAD ≥b·S 1_RATED (Equation 6)

[0034] In the above formula, b is the adjustment coefficient under the high-efficiency operation state of transformer #1 of the distribution line;

[0035] If relation (6) is satisfied, then the power control setpoint P of the first port is... 1_AC_REF Calculate according to relation (7):

[0036] P 1_AC_REF =P 1_LOAD -b·S 1_RATED +P 1_MARGIN (Equation 7)

[0037] In the above formula, P 1_MARGIN This indicates the operating margin power of the AC / DC module in power distribution line #2;

[0038] If relation (6) is not satisfied, then the power control setpoint P of the first port is... 1_AC_REF It is 0.

[0039] This invention uses an ACAC module to connect two parallel AC power distribution lines. Distribution line #1 can be considered an existing power supply line. To avoid overloading the transformer on this line or failing to meet the power demand of newly added charging piles, distribution line #2 can be considered a newly built power supply line to meet the needs of a large number of newly added AC / DC charging piles. Distribution line #2 is equipped with a new energy power generation system (i.e., a DC microgrid). To fully utilize the surplus power generated by the new energy source, the DC output terminal of the ACAC module is connected to the DC microgrid. When the transformer capacity of distribution line #1 is insufficient, the power generated by the new energy source can be inverted through the ACAC module to provide power to the load of distribution line #1, avoiding the need for new energy to feed into the grid and preventing energy waste. When distribution line #1 experiences a power outage, the new energy source can also be used to power the load of distribution line #1, ensuring its off-grid operation. When power is lost on distribution line #2, the AC / DC module operates off-grid. The second power unit in the ACAC module operates in parallel with the AC / DC module, providing AC and DC power. It can obtain power from the DC bus of the DC microgrid to increase the capacity of the AC bus of distribution line #2. When power is lost on distribution line #2 and the AC / DC module fails, the ACAC module, through its third and second ports, establishes a connection between the AC and DC buses of distribution line #2, allowing it to still invert and supply the generated power from new energy sources to the load on distribution line #2. The power supply stabilization system designed in this invention not only achieves stable AC power supply but also allows both distribution lines to operate off-grid. Attached Figure Description

[0040] Figure 1 This is a circuit diagram of the dual-energy power supply stability system in the embodiment;

[0041] Figure 2 for Figure 1 Control strategy diagram of ACAC module during grid-connected operation of distribution line #1;

[0042] Figure 3 for Figure 1 Control strategy diagram of ACAC module when the No. 1 distribution line is off-grid;

[0043] Figure 4 for Figure 1 Control strategy diagram of ACAC module when the No. 2 distribution line is off-grid. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0045] This embodiment first discloses a dual-power supply stability system, the circuit structure of which is as follows: Figure 1 As shown, the system includes two power distribution lines, #1 and #2, which supply power to their respective loads in parallel, and an AC / AC module connecting them. Power distribution line #1 is an existing power supply line. Its transformer has a #1 circuit breaker on the low-voltage side, and AC loads and several high-power AC / DC charging piles are connected in parallel to its AC bus. Power distribution line #2 is a newly constructed line built to meet the increasing power demand from the expanding load. Its transformer has a #2 circuit breaker on the low-voltage side, and AC loads and several high-power AC / DC charging piles are also connected in parallel to its AC bus. The AC bus of power distribution line #2 is also connected to the DC bus of a DC microgrid via an AC / DC module. The DC bus of the DC microgrid has DC / DC energy storage modules, DC / DC photovoltaic modules, DC loads, and several high-power DC / DC charging piles connected in parallel.

[0046] The ACAC module in the above scheme mainly consists of two three-phase inverter modules, which can be divided into a first power unit and a second power unit. Each power unit is composed of six IGBTs and an LC series resonant circuit. The first power unit includes six IGBTs numbered Q1, Q2, Q3, Q4, Q5, and Q6, an LC series circuit composed of L1 and C1, an LC series circuit composed of L2 and C2, and an LC series circuit composed of L3 and C3. The emitter of Q1 is connected to the collector of Q2, the emitter of Q3 is connected to the collector of Q4, and the emitter of Q5 is connected to the collector of Q6. One end of L1 is connected to the emitter of Q5, one end of L2 is connected to the emitter of Q3, and one end of L3 is connected to the emitter of Q1. The other ends of C1, C2, and C3 are connected together. The other ends of L1, L2, and L3 serve as the three-phase AC output terminals of the first power unit, i.e., the first port. The low-voltage side AC bus of the #1 distribution line establishes an electrical connection with the ACAC module through the first port.

[0047] The second power unit comprises six IGBTs numbered Q7, Q8, Q9, Q10, Q11, and Q12, an LC series circuit consisting of L4 and C4, an LC series circuit consisting of L5 and C5, and an LC series circuit consisting of L6 and C6. The emitter of Q7 is connected to the collector of Q8, the emitter of Q9 is connected to the collector of Q10, and the emitter of Q11 is connected to the collector of Q12. One end of L4 is connected to the emitter of Q7, one end of L5 is connected to the emitter of Q9, and one end of L6 is connected to the emitter of Q11. The other ends of C4, C5, and C6 are connected together. The other ends of L4, L5, and L6 serve as the three-phase AC output terminals of the second power unit, i.e., the second port. The low-voltage side AC bus of the #2 distribution line is electrically connected to the ACAC module through the second port.

[0048] The collectors of Q1, Q3, Q5, Q7, Q9, and Q11 in the two power units are connected together and lead out to one terminal of the DC input of the ACAC module. The emitters of Q2, Q4, Q6, Q8, Q10, and Q12 are connected together and lead out to another terminal of the DC input of the ACAC module. The two terminals constitute the third port of the ACAC module. The DC bus of the DC microgrid is connected to the ACAC module through the third port.

[0049] To coordinate the power supply status of the two distribution lines and achieve the goal of rationally scheduling the ACAC module control strategy, the power supply stabilization system described above also includes a #1 metering module on the AC low-voltage side of distribution line #1. This module collects the AC bus power consumption data of distribution line #1. The #1 metering module is connected to the ACAC module via serial communication, feeding back the collected data to the ACAC module. Simultaneously, a #2 metering module is installed on the AC low-voltage side of distribution line #2 to collect the AC bus power consumption data of distribution line #2. This #2 metering module is connected to both the AC / DC module and the ACAC module on the low-voltage side of distribution line #2 via serial communication. The metering modules can collect the AC power capacity of the two distribution lines in real time. With the help of a certain power scheduling control strategy, excess power generated by new energy sources can be converted into AC / DC power for distribution line #1 through the third port to the first port, increasing its power capacity. Furthermore, when the grid power supply to distribution line #1 fails, it can provide AC power to its loads, ensuring its normal operation off-grid. When the No. 2 distribution line is de-energized, and the AC / DC module is functioning normally, the second power unit and the AC / DC equipment form a drooping dual-machine parallel connection. The new energy power generation of the DC microgrid is used to supply power to the load of the No. 2 distribution line, thereby achieving reasonable and efficient use of new energy power generation, increasing grid capacity, preventing the new energy power from being fed into the grid, and enabling both distribution lines to have the ability to operate off-grid.

[0050] This embodiment also provides a control method for the aforementioned dual-energy power supply stability system, combined with... Figures 2 to 4 The specific control method is explained below:

[0051] When the No. 1 distribution line is connected to the grid, the first power unit of the ACAC module uses the PQ power control method to adjust the output power of the first port, and converts the generated power of the DC microgrid into AC power to increase the power capacity of the No. 1 distribution line load.

[0052] When the No. 1 distribution line is off-grid, the first power unit of the ACAC module operates in voltage and frequency control mode, converting the generated power of the DC microgrid into AC power to supply the load of the No. 1 distribution line.

[0053] When the No. 2 distribution line is off-grid and the AC / DC module can operate normally, the second power unit of the AC / DC module operates in virtual synchronous machine or droop mode, and operates in parallel with the AC / DC module's AC and DC, drawing power from the DC bus of the DC microgrid to supply power to the AC load of the No. 2 distribution line.

[0054] When the No. 2 distribution line is disconnected from the grid and the AC / DC module fails, the second power unit of the AC / DC module operates in voltage and frequency control mode, draws power from the DC bus of the DC microgrid, and converts it into AC power through the second power unit to supply AC load to the No. 2 distribution line.

[0055] Further explanation of the above control method: When the No. 1 distribution line is connected to the grid, the control mode of the first power unit in the ACAC module is divided into three types: line capacity expansion mode, new energy high-efficiency utilization mode, and transformer high-efficiency state mode. The first power unit selects and executes the corresponding mode according to the power data collected by the No. 1 metering module from the No. 1 distribution line.

[0056] Specifically, when the AC load power of distribution line #1, as monitored by the metering module of meter #1, continuously increases and approaches the rated power of the transformer of distribution line #1, the first power unit activates the line capacity expansion mode, dispatching the power generated by the DC microgrid to provide power to the AC load under distribution line #1. When the AC load power of distribution line #1, as monitored by the metering module of meter #1, continuously increases but has not yet approached the rated power of the transformer of distribution line #1, in order to improve the operating efficiency of transformer #1, it is usually allowed to operate at 60%-70% of its rated power to minimize its own losses. In this state, the first power unit should activate the transformer high-efficiency mode. In addition to the above two situations, in order to maximize the utilization of new energy power generation, the first power unit should activate the new energy high-efficiency utilization mode, that is, all the excess electricity generated by the DC microgrid is transmitted to distribution line #1 to provide power to its AC load, reducing the amount of electricity drawn from the AC grid of distribution line #1.

[0057] Specifically, when the first power unit executes the line capacity expansion mode, such as Figure 2 As shown, the apparent power S of the transformer of the No. 1 distribution line is obtained by the No. 1 metering module. 1_RATED Obtain the AC load power P of distribution line #1. 1_LOAD First, determine whether relation (1) is satisfied:

[0058] P 1_LOAD ≥a·S 1_RATED (Equation 1)

[0059] In the above formula, a is the calculation adjustment coefficient of the No. 1 distribution line, which is the ratio of the maximum apparent load power to the rated apparent power of the transformer when the transformer is running stably for a long time.

[0060] If relation (1) is satisfied, then the power control setpoint P of the first port is... 1_AC_REF Calculate according to relation (2):

[0061] P 1_AC_REF =P 1_LOAD -a·S 1_RATED +P 1_MARGIN (Equation 2)

[0062] In the above formula, P 1_MARGIN This indicates the operating margin power of the AC / DC module in power distribution line #2;

[0063] If relation (1) is not satisfied, then the power control setpoint P of the first port is... 1_AC_REF It is 0.

[0064] When the first power unit executes the high-efficiency utilization mode of new energy, the #2 metering module obtains the output power P of the AC / DC module in the #2 distribution line.ACDC Obtain the rated power P of the AC / DC module. ACDC_RATED First, determine whether relation (3) is satisfied:

[0065] |P ACDC |≥c·P ACDC_RATED (Equation 3)

[0066] In the above formula, c is the margin power output of the first port, which is mainly set to prevent the transformer from operating at full load;

[0067] If relation (3) is satisfied, then continue to determine whether relation (4) is satisfied:

[0068] a·S 1_RATED ≥P 1_LOAD ≥P 1_TH (Equation 4)

[0069] In the above formula, P 1_TH The power threshold for distribution line #1 can be adjusted to the power of the maximum AC load without buffer start function.

[0070] If relation (4) is satisfied, then the power control setpoint P of the first port is... 1_AC_REF Calculate according to relation (5):

[0071] P 1_AC_REF =P 1_LOAD -P 1_TH (Equation 5)

[0072] If relation (4) is not satisfied, then the power control setpoint P of the first port is... 1_AC_REF =0;

[0073] If relation (3) is not satisfied, then the line capacity expansion mode is executed.

[0074] When the first power unit executes the transformer high-efficiency mode, the apparent power S of the transformer of the No. 1 distribution line is obtained by the No. 1 metering module. 1_RATED Obtain the AC load power P of distribution line #1. 1_LOAD First, determine whether relation (6) is satisfied:

[0075] P 1_LOAD ≥b·S 1_RATED (Equation 6)

[0076] In the above formula, b is the adjustment coefficient of the No. 1 distribution line transformer under high-efficiency operation, that is, the optimal operating efficiency of the transformer.

[0077] If relation (6) is satisfied, then the power control setpoint P of the first port is... 1_AC_REF Calculate according to relation (7):

[0078] P 1_AC_REF =P 1_LOAD -b·S 1_RATED +P 1_MARGIN (Equation 7)

[0079] If relation (6) is not satisfied, then the power control setpoint P of the first port is... 1_AC_REF It is 0.

[0080] When the No. 1 circuit breaker in the No. 1 distribution line is disconnected, the first power unit of the ACAC module can operate in an off-grid state. The first power unit operates in voltage frequency control mode (VF) to convert the power generated by the DC microgrid into AC power to supply the load of the No. 1 distribution line, ensuring that the No. 1 distribution line can work stably when the grid is cut off.

[0081] When the No. 2 circuit breaker in the No. 2 distribution line is disconnected and the AC / DC module can work normally, the second power unit of the AC / DC module operates in virtual synchronous machine (VSG) or droop mode (DROOP), and runs in parallel with the AC / DC module in both AC and DC modes. Both are powered by the DC bus of the DC microgrid, which increases the capacity of the AC bus of the No. 2 distribution line.

[0082] When the circuit breaker in distribution line #2 trips and the AC / DC module malfunctions, energy conversion between AC and DC cannot occur. In this situation, the electricity generated by the renewable energy source in the DC microgrid cannot be used in the AC grid. The AC load in distribution line #2 can only draw power from the AC grid, failing to fully utilize the renewable energy source. Therefore, in the power supply stabilization system of this invention, an AC / AC module is used to establish a connection between distribution line #2 and the DC bus of the DC microgrid. This allows renewable energy to be inverted from the third port to the second port and converted into AC power to supply the AC load of distribution line #2. At this time, the second power unit of the AC / AC module operates in voltage-frequency control (VF) mode, increasing the redundancy of the power supply network.

[0083] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A control method for a dual-energy power supply stability system, characterized in that: The dual-path energy supply stabilization system includes a No. 1 distribution line and a No. 2 distribution line that supply power to their respective loads in parallel, and also includes an ACAC module connecting the No. 1 distribution line and the No. 2 distribution line; the AC low-voltage side of the No. 2 distribution line supplies power to the AC loads through the AC bus, and is also connected to a DC microgrid containing a new energy power generation system through an AC / DC module. The ACAC module comprises two interconnected three-phase inverter modules: a first power unit and a second power unit. The AC output terminal of the first power unit is the first port, which is connected to the AC bus on the low-voltage side of distribution line #1. The AC bus on the low-voltage side of distribution line #1 is equipped with a #1 electricity meter module, which is connected to the ACAC module via serial communication. The AC output terminal of the second power unit is the second port, which is connected to the AC bus on the low-voltage side of distribution line #2. The AC bus on the low-voltage side of distribution line #2 is equipped with a #2 electricity meter module, which is connected to both the AC / DC module and the ACAC module on the low-voltage side of distribution line #2 via serial communication. The first and second power units share a DC input terminal, which is the third port. The DC bus of the DC microgrid is connected to the ACAC module via the third port. The DC microgrid includes DC-DC energy storage modules, DC-DC photovoltaic modules, DC loads, and DC-DC charging piles connected in parallel to the DC bus. The first power unit and the second power unit each include six IGBTs and an LC series resonant circuit. The IGBTs in the first power unit are Q1, Q2, Q3, Q4, Q5, and Q6. The emitter of Q1 is connected to the collector of Q2, the emitter of Q3 is connected to the collector of Q4, and the emitter of Q5 is connected to the collector of Q6. The IGBTs in the second power unit are Q7, Q8, Q9, Q10, Q11, and Q12. The emitter of Q7 is connected to the collector of Q8, the emitter of Q9 is connected to the collector of Q10, and the emitter of Q11 is connected to the collector of Q12. The collectors of Q1, Q3, Q5, Q7, Q9, and Q11 are connected, and the emitters of Q2, Q4, Q6, Q8, Q10, and Q12 are connected. The control method of the dual-energy power supply stability system includes: When the No. 1 distribution line is connected to the grid, the first power unit of the ACAC module uses the PQ power control method to adjust the output power of the first port, and converts the generated power of the DC microgrid into AC power to increase the power capacity of the No. 1 distribution line load. When the No. 1 distribution line is off-grid, the first power unit of the ACAC module operates in voltage and frequency control mode, converting the generated power of the DC microgrid into AC power to supply the load of the No. 1 distribution line. When the No. 2 distribution line is off-grid and the AC / DC module can operate normally, the second power unit of the AC / DC module operates in virtual synchronous machine or droop mode, and operates in parallel with the AC / DC module's AC and DC, drawing power from the DC bus of the DC microgrid to supply power to the AC load of the No. 2 distribution line. When the No. 2 distribution line is disconnected from the grid and the AC / DC module fails, the second power unit of the ACAC module operates in voltage and frequency control mode, draws power from the DC bus of the DC microgrid, and converts it into AC power through the second power unit to supply AC load of the No. 2 distribution line. When the No. 1 distribution line is connected to the grid, the control modes of the first power unit in the ACAC module are divided into line capacity expansion mode, new energy high-efficiency utilization mode, and transformer high-efficiency state mode. The first power unit selects and executes the corresponding mode according to the power data collected by the No. 1 metering module from the No. 1 distribution line. When the first power unit executes the line capacity expansion mode, it acquires the apparent power of the transformer of distribution line #1. S 1_RATED Obtain the AC load power of distribution line #1 P 1_LOAD Determine whether relation (1) is satisfied: (Equation 1) In the above formula, a The calculation adjustment coefficient for distribution line #1 is the ratio of the maximum apparent load power to the rated apparent power of the transformer when the transformer is running stably for a long time. If relation (1) is satisfied, then the power control setpoint of the first port is... P 1_AC_REF Calculate according to relation (2): (Equation 2) In the above formula, P 1_MARGIN This indicates the operating margin power of the AC / DC module in power distribution line #2; If relation (1) is not satisfied, then the power control setpoint of the first port is... P 1_AC_REF =0; When the first power unit executes the high-efficiency utilization mode of new energy, it obtains the output power of the AC / DC module in the No. 2 distribution line. P ACDC Obtain the rated power of the AC / DC module. P ACDC_RATED Determine whether relation (3) is satisfied: (Equation 3) In the above formula, c This is the margin power output from the first port; If relation (3) is satisfied, then continue to determine whether relation (4) is satisfied: (Equation 4) In the above formula, S 1_RATED The apparent power of the transformer for distribution line #1. P 1_LOAD This refers to the AC load power of distribution line #1. P 1_TH Adjust the power threshold for distribution line #1; a The calculation adjustment coefficient for distribution line #1 is the ratio of the maximum apparent load power to the rated apparent power of the transformer when the transformer is running stably for a long time. If relation (4) is satisfied, then the power control setpoint of the first port is... P 1_AC_REF Calculate according to relation (5): (Equation 5) If relation (4) is not satisfied, then the power control setpoint of the first port is... P 1_AC_REF =0; If relation (3) is not satisfied, then the line capacity expansion mode is executed; When the first power unit executes the transformer high-efficiency mode, it acquires the apparent power of the transformer of distribution line #1. S 1_RATED Obtain the AC load power of distribution line #1 P 1_LOAD Determine whether relation (6) is satisfied: (Equation 6) In the above formula, b This is the adjustment coefficient for the transformer of distribution line #1 operating under high-efficiency conditions; If relation (6) is satisfied, then the power control setpoint of the first port is... P 1_AC_REF Calculate according to relation (7): (Equation 7) In the above formula, P 1_MARGIN This indicates the operating margin power of the AC / DC module in power distribution line #2; If relation (6) is not satisfied, then the power control setpoint of the first port is... P 1_AC_REF It is 0.

Images