Series-parallel hybrid five-port energy router capable of realizing transformer area interconnection and control method of series-parallel hybrid five-port energy router

Abstract

The invention discloses a series-parallel hybrid five-port energy router capable of realizing transformer area interconnection and a control method of the series-parallel hybrid five-port energy router. The five-port energy router comprises four low-voltage alternating current ports AC1, AC2, AC3 and AC4, a direct current port DC, two parallel converters PCM1 and PCM3, and two series converters SCM2 and SCM4. AC ports of the PCM1 and the PM3 are respectively connected with the AC1 and the AC3, and AC ports of the SCM2 and the SCM4 are respectively connected with the AC2 and the AC4 through series transformers; dC ports of the PCM1, the SCM2, the PCM3 and the SCM4 are connected together to form a common DC bus; dC is led out from the common DC bus. The five-port energy router supports parallel connection-series connection and parallel connection-parallel connection power flow mutual aid modes, DC bus voltage is stabilized through the PCM, reactive power and active power are controlled through the PCM, voltage amplitude and phase control active power flow are adjusted through the SCM, and the required configuration capacity is small. According to the invention, the flexible interconnection of the low-voltage transformer area can be realized, the dynamic capacity increase of the transformer area and the fault rapid transfer are realized, and the power supply reliability and the distributed power supply acceptance capability are improved.

Description

Technical Field

[0001] This invention relates to the application of power electronics technology in the field of flexible interconnection of distribution networks, specifically to a series-parallel hybrid five-port energy router and its control method that can realize the interconnection of transformer substations. Background Technology

[0002] In recent years, rural electricity consumption has increased rapidly, leading to severe overload problems in distribution transformer areas and power lines. This mismatch between power supply and demand, coupled with the concentrated peak hours of electricity consumption in rural areas, has exacerbated low voltage issues. On the other hand, with the increasing growth of DC loads such as electric vehicle charging stations, data centers, DC appliances, and communication equipment, as well as the large-capacity, high-proportion distributed DC power sources like photovoltaics, the current power grid's source-load-storage DC characteristics are becoming increasingly pronounced. Therefore, interconnecting multiple distribution transformers within the same area can, to some extent, improve load balancing and energy optimization capabilities, alleviating the pressure of power grid upgrades and renovations.

[0003] Flexible interconnection of low-voltage distribution areas enables dynamic capacity expansion and rapid fault transfer, improving power supply reliability and the capacity to accommodate distributed power sources. However, current methods for interconnecting and power supply between distribution areas based on traditional AC methods mostly employ topology reconfiguration, switch combination state switching, and changes in operating modes. Their mutual power controllability and load balancing capabilities are insufficient to support the rapid development needs of both the source and load ends within the current distribution areas. To address these issues, the paper "Practical Application of Low-Voltage Flexible Interconnection Technology in New Rural Distribution Networks," published in the Rural Electrification Journal (Vol. 3, No. 6, 2023), proposes a three-terminal common DC bus type low-voltage flexible DC interconnection topology. Three distribution areas (No. 1, No. 2, and No. 5) are each connected to a ±375V DC bus via a 250kW AC / DC bidirectional converter, forming a common DC bus structure. Power dispatch, load balancing, and fault switching are achieved through a central controller and a local monitoring station. Also addressing the issue of low-voltage distribution area interconnection, the paper "Power Mutual Aid Strategy Across Distribution Areas in Flexible Interconnection Systems of Low-Voltage Distribution Areas" published in the Ningxia Electric Power Journal in 2023, Issue 2, proposes an adaptive control strategy based on an improved droop algorithm to achieve adaptive power mutual aid between interconnected distribution areas. This distribution area consists of six distribution areas connected to a shared 750V DC bus via their respective AC / DC converters.

[0004] It should be noted that in the above low-voltage flexible DC interconnect topology, all AC / DC bidirectional converters are connected in parallel with the DC bus and operate in full-power mode, resulting in large hardware capacity and high cost. Furthermore, each unit requires additional communication, complicating system control. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a hybrid series-parallel five-port energy router.

[0006] In a first aspect, this application provides a series-parallel hybrid five-port energy router capable of interconnecting distribution substations, comprising: four low-voltage AC ports AC1, AC2, AC3 and AC4, one DC port DC, two parallel converters PCM1 and PCM3, and two series converters SCM2 and SCM4; the AC port of PCM1 is connected to AC1, the AC port of SCM2 is connected to AC2 through a first series transformer SIT2; the AC port of PCM3 is connected to AC3, and the AC port of SCM4 is connected to AC4 through a second series transformer SIT4; the DC ports of PCM1, SCM2, PCM3 and SCM4 are connected together to form a common DC bus; the DC is led out from the common DC bus.

[0007] In one possible implementation, a circuit breaker is connected in series on each of the four low-voltage AC ports; a current-limiting protection module is connected in series between each series converter and its corresponding series transformer.

[0008] Secondly, this application provides a control method for a five-port energy router, wherein the five-port energy router is any one of the energy routers described in claims 1-3; the control method includes at least two operating modes: a first operating mode is a parallel-series mutual assistance mode, including power flow mutual assistance between AC1 and AC2, AC1 and AC4, AC2 and AC3, and AC3 and AC4; and a second operating mode is a parallel-parallel mutual assistance mode, including power flow mutual assistance between AC1 and AC3.

[0009] In one possible implementation, when operating in the first operating mode, the control process includes:

[0010] By employing current inner-loop control and power outer-loop control on the parallel converter PCMh, the active and reactive power of the AC port ACh connected to PCMh can be controlled.

[0011] By adjusting the amplitude and phase angle of the output voltage of the series converter SCMk, the active and reactive power of the AC port ACk connected to SCMk can be controlled.

[0012] The power compensation amount is generated by the outer loop PI controller of the DC bus voltage, and the power command allocated to ACh is dynamically corrected to maintain the stability of the DC bus voltage.

[0013] In one possible implementation, the SCMk employs pre-synchronous phase-locked loop control, and its phase angle dynamic adjustment rate is given by the formula... Determine, in the formula, This represents the synchronization coefficient of the phase-locked loop. The frequency of the AC power grid connected to ACk. The AC power grid reference frequency is used to ensure the phase angle at the moment of grid connection. =0.

[0014] In one possible implementation, when operating in the second operating mode, the control process includes:

[0015] Both of the two parallel converters PCM1 and PCM3 of the mutual aid system adopt a dual closed-loop control strategy, including an inner current loop control and an outer current loop control. By maintaining the stability of the DC bus voltage, the active power between the two corresponding AC ports AC1 and AC3 is automatically balanced.

[0016] In one possible implementation, the formula for the current inner loop control is:

[0017] ;

[0018] in, and These represent the d-axis and q-axis components of the output voltage of the parallel converter, respectively. and These are reference values ​​for the d-axis and q-axis components of the AC side current of the parallel converter; and These represent the d-axis and q-axis components of the output current of the parallel converter, respectively. and These represent the proportional and integral coefficients of the current inner-loop PI control, respectively. and These are the d / q axis components of the grid voltage to which the parallel converter is connected; This refers to the filter inductance value on the AC side of the parallel converter. The grid angular frequency of the AC power grid to which the parallel converter is connected; The equivalent resistance of the filter inductor; For integration operators;

[0019] In one possible implementation, the outer loop control uses DC voltage averaging control to generate reference values ​​for the d-axis and q-axis components of the AC side current, and uses an inverse power model to calculate the feedforward current command.

[0020] Thirdly, this application provides a flexible interconnection system for a distribution network, characterized in that it includes at least one of the aforementioned five-port energy routers for interconnecting multiple low-voltage distribution areas, thereby achieving dynamic capacity expansion, fault transfer, load balancing, and efficient consumption of distributed energy.

[0021] Beneficial effects:

[0022] This invention addresses the high and low voltage issues and poor carrying capacity of current power distribution networks by proposing a five-port energy router suitable for distribution networks, thus meeting the challenges posed by renewable energy integration and other complex factors. This structure retains a DC bus to allow for flexible access to diverse and heterogeneous resources in distribution areas, ensuring the energy exchange needs of flexible interconnection between different distribution areas and new energy sources such as photovoltaics, energy storage, and charging piles are met. Simultaneously, the modular design provides higher redundancy and economy during system expansion. Compared to traditional flexible DC solutions, the SCM has lower capacity configuration requirements, effectively reducing system hardware costs. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a five-port energy router structure in one embodiment of this application;

[0024] Figure 2 This is a PQ control strategy in one embodiment of this application;

[0025] Figure 3 The AC1 voltage and current in the simulation experiment of this application;

[0026] Figure 4 The AC2 voltage and current in the simulation experiment of this application;

[0027] Figure 5 The AC3 voltage and current in the simulation experiment of this application;

[0028] Figure 6 The waveform of active power flowing through the converter in the simulation experiment of this application is shown.

[0029] Figure 7 This refers to the DC bus voltage used in the simulation experiment of this application. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present application, the technical solution of the present application will be further described in detail below with reference to the embodiments and accompanying drawings.

[0031] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application 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 for the embodiments of this application 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.

[0032] Furthermore, the terms "installation," "setup," "equipped with," "connection," "linked," and "socketing" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0033] In this embodiment of the disclosure, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0034] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0035] This invention proposes a hybrid series-parallel five-port energy router. This structure retains the DC bus of the flexible DC solution, facilitating the addition of transformer substations (plug-and-play) and distributed resource access. The interconnection architecture can be adjusted according to actual site selection, and some port converters do not operate at full power, thus improving efficiency.

[0036] The following will refer to Figure 1 A specific implementation method according to this application is described.

[0037] Example 1:

[0038] like Figure 1 As shown in the embodiment of this application, a five-port energy router capable of implementing a hybrid series-parallel configuration is provided.

[0039] The five-port energy router includes four low-voltage AC ports and one DC port. The four low-voltage AC ports are designated as AC1, AC2, AC3, and AC4.

[0040] AC1~AC4 can be connected to the low-voltage AC busbar of the low-voltage distribution area; DC can be connected to distributed photovoltaic, energy storage or charging piles.

[0041] The low voltage in the low voltage distribution area, low voltage AC bus, and low voltage AC port refers to AC voltage levels of 1000V and below (such as 400V and below).

[0042] In one embodiment of this application, the specific operating voltage is the standard civilian voltage of 220V phase voltage or 380V line voltage.

[0043] The five-port energy router includes two parallel converters (PCMs) and two series converters (SCMs); the two parallel converters are PCM1 and PCM3; the two series converters are SCM2 and SCM4; both PCMs and SCMs can realize bidirectional AC / DC power conversion.

[0044] The AC port ac1 of PCM1 is connected to AC1, and the AC port ac2 of SCM2 is connected to AC2 through the first series transformer SIT2; the AC port ac3 of PCM3 is connected to AC3, and the AC port ac4 of SCM4 is connected to AC4 through the second series transformer SIT4; the DC ports dc1 of PCM1, dc2 of SCM2, dc3 of PCM3, and dc4 of SCM4 are connected together to form a common DC bus; the DC port DC is led out from the common DC bus.

[0045] To improve system reliability, all four low-voltage AC port line networks are equipped with series circuit breakers (QF); a circuit breaker (CRM) is installed between the SCM and the series transformer.

[0046] To better understand the technical solution of this application, the devices involved in this application are explained.

[0047] PCM, short for Parallel Converter Module, is used to realize bidirectional AC / DC power conversion, stabilize DC bus voltage, control the bidirectional flow of reactive power in the control zone, and precisely regulate the active and reactive power of the connected AC ports.

[0048] SCM, short for Series Converter Module, is used to realize bidirectional AC / DC power conversion. It is used to adjust the amplitude and phase (interconnection point voltage) of the output voltage and control the bidirectional transmission of active power flow between interconnected stations.

[0049] SIT, short for Series Isolation Transformer, is used in conjunction with SCM to achieve electrical isolation, ensuring a safe connection between the SCM and the AC port, while also adapting to different voltage levels to ensure the stability of power transmission.

[0050] QF stands for Circuit Breaker, and it is used to protect circuits. When a short circuit or other fault occurs in the corresponding AC port line, it can quickly disconnect the circuit to prevent the fault from escalating and improve system reliability.

[0051] CRM, short for Current Limiting and Protection Module, is a module connected in series between the SCM and SIT to limit the fault current amplitude, prevent excessive current from damaging core components such as the SCM and SIT, and assist in the implementation of fault protection functions.

[0052] Example 2:

[0053] This application provides a control method for a five-port energy router, wherein the five-port energy router is the energy router described in Embodiment 1; the control method includes at least two working modes: a first working mode is a parallel-series mutual assistance mode, including power flow mutual assistance between AC1 and AC2, AC1 and AC4, AC2 and AC3, and AC3 and AC4; and a second working mode is a parallel-parallel mutual assistance mode, including power flow mutual assistance between AC1 and AC3.

[0054] The five-port power router described above can achieve bidirectional power transfer between its ports. There are two typical working modes (power flow transfer modes) between the ports: the first working mode is parallel-series power transfer, such as power flow transfer between AC1 and AC2, AC1 and AC4, AC2 and AC3, and AC3 and AC4; the second working mode is parallel-parallel power transfer, such as power flow transfer between AC1 and AC3.

[0055] The aforementioned five-port energy router retains the plug-and-play and scalability of the flexible DC interconnection architecture; the interconnection of some AC substations adopts a series architecture, and the PCM and SCM do not need to operate at full power, thereby improving system operating efficiency.

[0056] First operating mode: Parallel-series mutual assistance:

[0057] The h-th low-voltage AC port ACh and the k-th low-voltage AC port ACk achieve power flow mutual assistance through the h-th parallel converter PCMh and the k-th series converter PCMh; where h=1 or 3, k=2 or 4;

[0058] 1. Active and reactive power control in ACh:

[0059] The h-th parallel converter PCMh controls the active power P1 and reactive power Q1 of the h-th low-voltage AC port ACh. The instantaneous active power and instantaneous reactive power on the output side in the dq coordinate system are as follows:

[0060]

[0061] In the formula, Let ACh be the d-axis equivalent component of the voltage vector. and These are the d-axis and q-axis equivalent components of the ACh current vector, respectively.

[0062] To simplify power calculations, the above scheme uses a directional strategy to align the d-axis of the dq coordinate system with the direction of the ACh voltage vector. Therefore, the ACh voltage vector... , .in, It is the imaginary unit.

[0063] ACh current vector .

[0064] ACh instantaneous power:

[0065]

[0066] The inner current loop uses a PI controller with feedforward decoupling.

[0067]

[0068] In the formula, and These represent the d-axis and q-axis components of the PCMh output voltage, respectively. Represents the output current vector of PCMh; and These represent the d-axis and q-axis components of the PCMh output current command, respectively. and These represent compensation for cross-coupling terms; This refers to the filter inductance value on the AC side of PCMh. The grid angular frequency of the AC power grid to which PCMh is connected; The d-axis equivalent component of the ACh voltage vector represents grid voltage feedforward, improving disturbance rejection. and The proportional and integral coefficients of the inner-loop PI controller are respectively determined. For integration operators;

[0069] Power outer loop current generation command:

[0070]

[0071] In the formula, and These are the reference values ​​for active and reactive power in ACh, respectively.

[0072] 2. Active and reactive power control of ACk:

[0073] SCMk adjusts the output voltage and phase angle Controlling the active power of ACk and reactive power The power equation is:

[0074]

[0075] In the formula, The equivalent reactance of SITk The voltage amplitude of the AC power grid connected to ACk;

[0076] Active power control loop:

[0077]

[0078]

[0079] In the formula, Indicates the output voltage of SCMk and The initial reference phase angle difference between them This represents the reference value for active power ACk;

[0080] Phase angle dynamic correction amount:

[0081]

[0082] In the formula, This is the dynamic correction amount for the phase angle. and These are the proportional coefficient and integral coefficient of the active power control loop, respectively.

[0083] Phase angle Dynamic correction: ;

[0084] Reactive power control loop (regulation) ):

[0085]

[0086] In the formula, This indicates the reference value for the output voltage amplitude of SCMk. This represents the actual value of the output voltage amplitude of SCMk. This represents the reference value for reactive power ACk;

[0087] Voltage dynamic correction amount:

[0088]

[0089] In the formula, This is the dynamic correction amount for the phase angle. and These are the proportional coefficient and integral coefficient of the reactive power control loop, respectively.

[0090] 3. DC bus voltage regulation and power coordination:

[0091] When maintaining DC bus voltage When it remains unchanged, we can obtain Further, we can obtain ;in, and These represent the DC-side currents of PCMh and SCMk, respectively. This represents the total system loss.

[0092] The equation for the energy storage of the DC bus capacitor is:

[0093]

[0094] In the formula, This is the DC bus capacitor.

[0095] Further linearize it:

[0096]

[0097] In the formula, This is the rated voltage of the DC bus. This refers to the DC bus voltage deviation. ; and These are the changes in active power, ACh and ACk, respectively.

[0098] Finally, a PI controller is designed to generate the power compensation amount:

[0099]

[0100] In the formula, Indicates the amount of power compensation. and These represent the proportional and integral coefficients of the voltage outer loop PI control, respectively; This indicates the reference value for the DC bus voltage;

[0101] The power grids distribute the power compensation amount obtained in the previous step through power command allocation. Assigned to ACh: The power command received by ACk: . This is the initial active power reference value.

[0102] SCMk employs pre-synchronous phase-locked loop control to ensure instantaneous grid connection. To avoid inrush current.

[0103]

[0104] In the formula, This represents the synchronization coefficient of the phase-locked loop. The frequency (measured value) of the AC power grid connected to ACk. The reference frequency for AC power grids is 50Hz.

[0105] Second working mode: Parallel-parallel mutual assistance, that is, power flow mutual assistance between AC1 and AC3;

[0106] Power flow is mutually supported between AC1 and AC3 through two parallel converters.

[0107] First, under normal grid-connected conditions, the parallel converter's dynamic differential equations in the abc three-phase stationary coordinate system are written according to Kirchhoff's laws. The abc axis is then transformed into the dq axis, and the equations are as follows:

[0108]

[0109] In the formula, This refers to the filter inductance value on the AC side of the parallel converter. The grid angular frequency (2π×50Hz) of the AC grid to which the parallel converter is connected. This is the equivalent resistance of the filter inductor;

[0110] Define the d-axis and q-axis components of the switching modulation function of the parallel converter as follows: , .

[0111]

[0112] When switching losses are ignored, the power flow of AC1 and AC3 is described as follows:

[0113]

[0114] In the formula For the first The active power flowing out of the AC side of the parallel converter ; Indicates the first AC output voltage of a parallel converter Axial components, For the first The current flowing into the DC side of the parallel converter. While maintaining the DC bus voltage. When it remains unchanged, we can obtain Further, we can obtain The power flow at both ports reaches a state of equilibrium. Therefore, as long as the DC-side voltage remains constant, stable transmission of active power between the two ends can be achieved.

[0115] The AC side current of the parallel converter can be obtained. , These are proportional to active power and reactive power, respectively, therefore, by controlling... , The active and reactive power of the system can be controlled, and the inner-loop control equations can be designed as follows:

[0116]

[0117] in, and These are the reference values ​​for the d-axis and q-axis components of the AC side current of the parallel converter. and These represent the proportional and integral coefficients of the current inner-loop PI control, respectively. and These are the d / q axis components of the grid voltage to which the parallel converter is connected; and Cross-coupling terms in a rotating coordinate system; The equivalent resistance of the filter inductor;

[0118] When the energy router operates in steady state, it needs to maintain the DC-side voltage stable near its rated value. Therefore, the outer loop of the dual closed-loop control adopts DC voltage averaging control.

[0119]

[0120] in, DC-side voltage setpoint of parallel converter The average value of the DC-side voltage of the parallel converter. This is the setpoint for the reactive power on the AC side of the parallel converter. This represents the actual reactive power value on the AC side of the parallel converter.

[0121] The control block diagram of the parallel converter can be obtained from the above derivation, as follows: Figure 2As shown, the outer loop control target is the average capacitor voltage. The error between the average voltage and the setpoint voltage is used by the outer loop PI controller to generate the setpoint value of the d-axis component of the inner loop input current. The dq component of the input current is then passed through the inner loop PI controller and superimposed with the decoupled component to generate the dq-axis component of the modulated wave. The dq-abc transformation is then used to generate the sinusoidal modulated wave on the three-phase input side. The drive signal is generated by the CPS-SPWM modulation module.

[0122] The control strategy on the output side (e.g., AC3-PCM3) is similar to that on the input side (e.g., AC1-PCM1), also employing a dual closed-loop control strategy of outer loop (power / voltage) - inner loop (current). As can be seen from the port power flow equation, the outer loop control, when controlling id through active power P, is affected by iq, and when controlling iq through reactive power Q, it is affected by id. To eliminate these effects, the power flow formula is transformed and rearranged to obtain an inverse power model, which is then introduced into the control outer loop.

[0123]

[0124] in, and Representing the d-axis and q-axis components of the current command in the inverse model feedforward, respectively, introducing... and It can better reduce overshoot during PI regulation; and These are the active power reference value and the reactive power reference value, respectively. and The d / q axis components of the grid voltage are respectively.

[0125] The final reference value for the d-axis component of the AC side current of the parallel converter is: ;

[0126] The final reference value for the q-axis component of the AC side current of the parallel converter is: .

[0127] Example 3:

[0128] This application provides a flexible interconnection system for a power distribution network, characterized in that it includes at least one of the aforementioned five-port energy routers, used to realize interconnection between multiple low-voltage distribution areas, thereby achieving dynamic capacity expansion, fault transfer, load balancing, and efficient consumption of distributed energy.

[0129] The specific implementations of the five-port energy router, control method, and flexible interconnection system for distribution networks provided in Embodiments 1, 2, and 3 of this application can be referred to each other, and will not be elaborated here.

[0130] The effectiveness of the series-parallel hybrid five-port energy router and its control method for interconnecting transformer substations provided in this application is verified by simulation experiments. The simulation parameters are shown in Table 1.

[0131]

[0132] Simulation results are as follows Figures 3-7 As shown.

[0133] Figures 3-5 These are the voltage and current curves for AC1, AC2, and AC3 in the simulation experiment of this application; the horizontal axis represents time (unit: s), and the vertical axis represents voltage (unit: V) and current (unit: A), with voltage and current represented by curves of different colors. Figures 3-5 As can be seen, due to the use of the controller state tracking control method, no sudden changes in the output voltage of the port converter were caused during operation. Although the current dropped sharply at the beginning, it remained basically stable in subsequent operation. The relative stability of the voltage ensured the relative stability of the current, and the PQ control provided voltage amplitude and frequency support for the power-off load, realizing uninterrupted and stable power supply to the power-off load.

[0134] Figure 6 This is a waveform diagram of the active power flowing through the converter in the simulation experiment of this application, where the horizontal axis is time (unit: s) and the vertical axis is active power (unit: W or kW); where P1 is the output power of AC1; P2 is the output power of AC2; and P3 is the output power of AC3. Figure 6 As can be seen from the active power response waveform curve at the port output, in PQ control mode, the low-voltage AC port of the converter automatically allocates active power according to the power flow balance constraint, satisfying P1+P2+P3=0.

[0135] Figure 7 This is the DC bus voltage curve from the simulation experiment of this application, where the horizontal axis represents time (in seconds) and the vertical axis represents voltage (in V). Figure 7 As can be seen, the DC bus can quickly stabilize to the target value (750V) during system operation.

[0136] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A series-parallel hybrid five-port energy router capable of interconnecting distribution transformer areas, characterized in that, include: The system includes four low-voltage AC ports AC1, AC2, AC3, and AC4; one DC port DC; two parallel converters PCM1 and PCM3; and two series converters SCM2 and SCM4. The AC port of PCM1 is connected to AC1, and the AC port of SCM2 is connected to AC2 via a first series transformer SIT2. The AC port of PCM3 is connected to AC3, and the AC port of SCM4 is connected to AC4 via a second series transformer SIT4. The DC ports of PCM1, SCM2, PCM3, and SCM4 are connected together to form a common DC bus. The DC converter is led out from the common DC bus.

2. The five-port energy router according to claim 1, characterized in that, Each of the four low-voltage AC ports is connected in series with a circuit breaker; a current limiting protection module is connected in series between each series converter and its corresponding series transformer.

3. A control method for a five-port energy router, characterized in that, The five-port energy router is any one of the energy routers described in claims 1-3; the control method includes at least two working modes: the first working mode is a parallel-series mutual assistance mode, including power flow mutual assistance between AC1 and AC2, AC1 and AC4, AC2 and AC3, and AC3 and AC4; and the second working mode is a parallel-parallel mutual assistance mode, including power flow mutual assistance between AC1 and AC3.

4. The control method according to claim 3, characterized in that, When operating in the first operating mode, the control process includes: By employing current inner-loop control and power outer-loop control on the parallel converter PCMh, the active and reactive power of the AC port ACh connected to PCMh can be controlled. By adjusting the amplitude and phase angle of the output voltage of the series converter SCMk, the active and reactive power of the AC port ACk connected to SCMk can be controlled. The power compensation amount is generated by the outer loop PI controller of the DC bus voltage, and the power command allocated to ACh is dynamically corrected to maintain the stability of the DC bus voltage.

5. The method according to claim 4, characterized in that, The SCMk employs pre-synchronous phase-locked loop control, and its dynamic phase angle adjustment rate is given by the formula. Determine, in the formula, This represents the synchronization coefficient of the phase-locked loop. The frequency of the AC power grid connected to ACk. The AC power grid reference frequency is used to ensure the phase angle at the moment of grid connection. =0.

6. The method according to claim 4, characterized in that, When operating in the second operating mode, the control process includes: Both of the two parallel converters PCM1 and PCM3 of the mutual aid system adopt a dual closed-loop control strategy, including an inner current loop control and an outer current loop control. By maintaining the stability of the DC bus voltage, the active power between the two corresponding AC ports AC1 and AC3 is automatically balanced.

7. The method according to claim 7, characterized in that, The formula for the current inner loop control is: ； in, and These represent the d-axis and q-axis components of the output voltage of the parallel converter, respectively. and These are reference values ​​for the d-axis and q-axis components of the AC side current of the parallel converter; and These represent the d-axis and q-axis components of the output current of the parallel converter, respectively. and These represent the proportional and integral coefficients of the current inner-loop PI control, respectively. and These are the d / q axis components of the grid voltage to which the parallel converter is connected; This refers to the filter inductance value on the AC side of the parallel converter. The grid angular frequency of the AC power grid to which the parallel converter is connected; The equivalent resistance of the filter inductor; It is an integral operator.

8. The method according to claim 7, characterized in that, The outer loop control uses DC voltage mean control to generate reference values ​​for the d-axis and q-axis components of the AC side current, and uses the power inverse model to calculate the feedforward current command.

9. A flexible interconnection system for power distribution networks, characterized in that, It includes at least one five-port energy router as described in any one of claims 1-3, for interconnecting multiple low-voltage distribution areas, thereby achieving dynamic capacity expansion, fault transfer, load balancing and efficient consumption of distributed energy.

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