Alternating current and direct current hybrid power distribution system

Abstract

The invention discloses an AC-DC hybrid power distribution system, and belongs to the technical field of power distribution control. The device is applied to a low-voltage side of a distribution transformer area of a power distribution network and supports alternating-current power distribution and direct-current power distribution at the same time. Comprising an MPR controller, an alternating-current power distribution unit and a direct-current power distribution unit which are arranged in a power distribution cabinet, and the MPR controller is connected with the alternating-current power distribution unit and the direct-current power distribution unit for bidirectional communication; the medium-voltage direct-current bus is connected with the alternating-current power distribution unit through a bidirectional four-leg PCS and is connected with the direct-current power distribution unit; the bidirectional four-bridge-arm PCS realizes electric energy bidirectional conversion between the AC power distribution unit and the medium-voltage DC bus, and provides a stable DC power supply for the DC power distribution unit. According to the invention, scenes such as rated grid connection and margin absorption of photovoltaic power generation are formed by adding energy storage and micro-grid control, so that the stability of power supply is ensured; the bidirectional four-bridge-arm PCS is used for solving the electric energy quality problems of three-phase imbalance, harmonic waves, reactive compensation and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of power distribution control, specifically relating to an AC / DC hybrid power distribution system. Background Technology

[0002] With the advancement of the construction of new power systems, the distribution network is gradually transforming from a simple power network that receives and distributes electricity to users into a power network that integrates and interacts with power sources, grids, loads, and storage, and is flexibly coupled with the upper-level power grid. At the same time, new and old problems in areas such as the local consumption of distributed power sources, the carrying of new loads, end-side interconnection and mutual assistance, and local power quality are becoming increasingly prominent, requiring new system solutions to address these issues and keep pace with the development of new power systems.

[0003] The aforementioned issues are all concentrated on the distribution side and are close to the end of the power consumption process. Dedicated transformer users all have self-maintained transformers, while public transformer users are powered by substation areas. Addressing power quality issues such as load, absorption, peak shaving, peak load, overload, three-phase imbalance, and low end voltage around the substation area can effectively ensure the power grid's power quality and energy efficiency.

[0004] Distribution areas fall under the category of power distribution networks, which are generally divided into urban power grid scenarios and rural power grid scenarios. Distribution areas are also divided into urban power grid distribution areas and rural power grid distribution areas.

[0005] Urban power grid scenario: Peak shaving, valley filling, and peak replenishment are achieved through energy storage and energy storage loads, providing a flexible and dispatchable solution for the stable operation of the power grid. Energy storage achieves peak shaving and valley filling through two charging and two discharging operations, while electric vehicle V2G and energy storage simultaneously meet the replenishment needs when the power grid is insufficient.

[0006] Rural power grid scenario: The already poor power quality, fluctuating power load and photovoltaic power generation have amplified the problems faced by the distribution area. The core issues are voltage deviation, three-phase imbalance, power factor, overload and absorption.

[0007] The large-scale construction of grid-connected photovoltaic projects is now impacting the power grid and transformer substations, causing phenomena such as power grid flow fluctuations, transformer substation directional overload, and inability to alleviate capacity issues. Summary of the Invention

[0008] To address the technical problems existing in the background art, the present invention provides an AC / DC hybrid power distribution system.

[0009] This invention adopts the following technical solution: an AC / DC hybrid power distribution system, applied on the low-voltage side of a common power distribution transformer area in a power distribution network, supporting both AC and DC power distribution; the AC / DC hybrid power distribution system includes: a distribution cabinet, in which an MPR controller, an AC power distribution unit, and a DC power distribution unit are configured; the MPR controller is connected to the AC power distribution unit and the DC power distribution unit for bidirectional communication; It also includes: a medium-voltage DC bus, which is connected to the AC power distribution unit via a bidirectional four-arm PCS and to the DC power distribution unit; wherein, the bidirectional four-arm PCS realizes bidirectional power conversion between the AC power distribution unit and the medium-voltage DC bus, and provides a stable DC power supply for the DC power distribution unit.

[0010] In a further embodiment, the AC power distribution unit includes: The first branch is used to connect the MPR controller and the low-voltage side; the bidirectional four-bridge PCS is correspondingly connected to the first branch. The second branch is connected in parallel to the first branch and is located at the input of the bidirectional four-arm PCS; an important load is connected to the second branch, which is an AC load with high power supply reliability requirements.

[0011] In a further embodiment, the AC power distribution unit further includes: The third branch is connected in parallel to the first branch; the second branch is connected to a non-critical load, which is an AC load with low requirements for power supply reliability. The fourth branch is connected in parallel to the first branch; the third branch is connected to a power device.

[0012] In a further embodiment, the AC power distribution unit further includes: The switching unit is connected in series on the first branch and located at the input of the important load.

[0013] In a further embodiment, the DC power distribution unit includes an energy storage unit; the energy storage unit includes at least: The fifth branch is connected in parallel to the medium-voltage DC bus; the fifth branch is connected to the high-voltage box via a bidirectional DC / DC converter; The sixth branch is connected in parallel to the medium-voltage DC bus; the sixth branch is connected to the photovoltaic module via the MPPT converter.

[0014] In a further embodiment, the DC power distribution unit includes a charging unit; the charging unit includes: The seventh branch is connected in parallel to the medium-voltage DC bus; a V2G charging pile is connected to the seventh branch through a bidirectional DC / DC converter; The eighth branch is connected in parallel to the medium-voltage DC bus; a conventional charging pile is connected to the eighth branch through a unidirectional DC / DC converter.

[0015] In a further embodiment, the power distribution cabinet is further equipped with at least: a power distribution unit focused on the AC side, a switch control unit, a circuit protection unit, and a metering and monitoring unit.

[0016] In a further embodiment, the bidirectional four-arm PCS is configured to determine whether to start or stop charging the energy storage battery based on a first judgment condition, and adjust the charging power in real time; the first judgment condition is the SOC value of the energy storage battery or a decision variable collected within a specified time period. Correspondingly, the AC power distribution unit and the DC power distribution unit are currently in charging operation mode, while the switching unit remains in grid-connected mode.

[0017] In a further embodiment, the bidirectional four-arm PCS is configured to determine whether to start or stop discharging the energy storage battery based on a second judgment condition, and adjust the discharge power in real time; the second judgment condition is the loss of power on the AC side grid, the SOC value of the energy storage battery, or a decision variable collected within a specified time period. Correspondingly, the AC power distribution unit and the DC power distribution unit are currently in a discharge operation state, and the static switching switch remains in either grid-connected or off-grid state.

[0018] In a further embodiment, the switching unit collects the real-time voltage of each phase of the AC side power grid. When the AC side power grid loses power, it quickly disconnects the connection between the AC side power grid and the DC side microgrid and transmits the off-grid switching signal to the bidirectional four-arm PCS. When the bidirectional four-arm PCS switches from current source mode to voltage source mode, the AC / DC hybrid power distribution system switches from grid-connected state to off-grid state.

[0019] In a further embodiment, the bidirectional four-arm PCS is configured to adjust the total power carried by each phase during charging or discharging.

[0020] The beneficial effects of this invention are as follows: By adding energy storage and microgrid control, scenarios such as rated grid connection, surplus consumption, and energy storage without power generation are formed, which maximizes the investor value of photovoltaic power generation while ensuring the power supply to residents; the use of bidirectional four-arm PCS solves problems such as three-phase imbalance; and the use of adjustable transformers solves dynamic capacity adjustment during capacity overload and loss, which is a key mode to ensure the safe, stable, and efficient operation of power systems containing microgrids, and helps to improve the overall performance of the entire power supply network and achieve the effect of micro-distribution synergy.

[0021] Furthermore, the AC power distribution unit and DC power distribution unit of this invention are connected via a medium-voltage DC bus to form a hybrid power supply system. Moreover, the use of a hybrid connection method with two different current types, rather than a simple series or parallel connection, effectively solves the problems of three-phase imbalance, reactive power compensation, and power quality.

[0022] By using a static switching switch to achieve seamless switching between on-grid and off-grid operations, the switching time can be controlled within 20ms, ensuring that critical loads can operate uninterruptedly under any circumstances.

[0023] Furthermore, this system can significantly reduce the impact on the power grid when new energy sources are connected to the grid, enabling the local consumption of photovoltaic energy. The energy storage system acts as a buffer, meeting the needs of diverse application scenarios such as peak shaving and valley filling, and serving as an off-grid emergency backup power source.

[0024] In summary, different transformer substations have their own important benefits in different usage scenarios. For example, in public transformer substations with high penetration of distributed power sources, they can improve the utilization rate of new energy sources and improve power quality, and are suitable for 200kVA transformers. Urban distribution network substations can improve power quality, improve power supply reliability, and regulate substation load peaking, and are suitable for 4-500kVA transformers. Public and private transformer substations that frequently have power supply needs can quickly connect to mobile energy storage to achieve zero-second power supply, and are suitable for 500kVA transformers. These beneficial effects in different scenarios play a key role in the stable and efficient operation of the corresponding substations. Attached Figure Description

[0025] Figure 1 This is a diagram of the architecture of a hybrid AC / DC power distribution system.

[0026] Figure 2 This is the schematic diagram of a static switching switch. Detailed Implementation

[0027] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0028] Example 1 like Figure 1 As shown, the AC / DC hybrid power distribution system disclosed in this embodiment is applied to the low-voltage side of the public distribution transformer area in the power distribution network, and supports both AC and DC power distribution. For example, it can be connected starting from the 400V outgoing line of the 10kV transformer area.

[0029] Furthermore, for ease of dispatching and installation, the AC / DC hybrid power distribution system is integrated into the distribution cabinet. Therefore, the distribution cabinet is equipped with an MPR controller, an AC power distribution unit, and a DC power distribution unit; the MPR controller is connected to the AC power distribution unit and the DC power distribution unit for bidirectional communication.

[0030] It also includes: a medium-voltage DC bus, which is connected to the AC power distribution unit via a bidirectional four-arm PCS and to the DC power distribution unit; wherein, the bidirectional four-arm PCS realizes bidirectional power conversion between the AC power distribution unit and the medium-voltage DC bus, and provides a stable DC power supply for the DC power distribution unit.

[0031] It is worth mentioning that the power distribution cabinet described in this embodiment is also equipped with: a power distribution unit focused on the AC side, a switch control unit, a circuit protection unit, and a metering and monitoring unit.

[0032] In other words, the power distribution cabinet in this embodiment adds an AC / DC hybrid power distribution system to the existing functional units. Therefore, this AC / DC hybrid power distribution system actually includes the functional units of the existing technology, such as the following basic functions: The circuit can be disconnected by operating the corresponding air switch to prevent electric shock; it can also automatically trip and disconnect the circuit in case of overload, short circuit or other abnormal conditions.

[0033] When an excessive current occurs in the circuit (such as an internal short circuit in the equipment), the fuse element melts due to overheating, cutting off the circuit in time and preventing the equipment from being burned out due to overcurrent.

[0034] It can monitor parameters such as voltage, current, and power in AC circuits in real time, record users' electricity consumption, and upload electricity data to the power management system to facilitate power companies in calculating electricity bills and analyzing electricity usage.

[0035] This embodiment of the bidirectional four-arm PCS is a three-phase four-arm PCS, with a topology consisting of an arm section and a filtering section. The arm section comprises four arms, each containing two power switching devices (typically IGBTs, etc.), with the upper and lower switching devices complementing each other's conduction. By controlling the on / off combinations of the switching devices in each arm, the system achieves either DC-to-three-phase AC inversion or three-phase AC-to-DC rectification.

[0036] The filtering section includes a filter circuit composed of an inductor (L) and a capacitor (C). The inductor is used to suppress sudden current changes, while the capacitor is used to stabilize the output voltage and filter out high-frequency harmonics. After passing through this filter circuit, the three-phase AC output produces a smoother and more stable AC power, improving power quality.

[0037] When the PCS operates in inverter mode, the DC-side voltage serves as the input. The control circuit drives the power switching devices on the bridge arms to alternately turn on and off according to a specific pulse width modulation (PWM) strategy. Taking a three-phase sinusoidal output as an example, by controlling the on-time and sequence of each phase bridge arm, a three-phase sinusoidal AC current is synthesized on the AC side. For example, phase A bridge arm turns on and off according to a certain pattern within one cycle, generating the phase A AC voltage waveform. Similarly, phases B and C are also controlled, thus outputting a three-phase AC current.

[0038] In rectification mode, with a three-phase AC power input, the power switching devices are turned on according to the control signal, rectifying the three-phase AC power into DC power, which is then stored in the DC-side energy storage device (such as a battery). The filter circuit also serves to stabilize the DC voltage and filter out harmonics.

[0039] In a further embodiment, combined with Figure 1The AC power distribution unit includes: a first branch for connecting the MPR controller and the low-voltage side; the bidirectional four-arm PCS is correspondingly connected to the first branch; the AC power from the low-voltage side is connected to the system through the first branch, and the MPR controller obtains real-time electrical parameter information from the low-voltage side, such as voltage, current, and power, through this branch. This data is crucial for the MPR controller to determine the system's operating status, enabling it to perform corresponding control according to preset strategies. The bidirectional four-arm PCS performs bidirectional AC-DC power conversion on the first branch. During charging, it converts the AC power from the low-voltage side to DC power to charge the energy storage unit; during discharging, it converts the DC power from the energy storage unit back to AC power to feed it back to the low-voltage grid.

[0040] The second branch is connected in parallel to the first branch and located at the input of the bidirectional four-arm PCS. An important load is connected to the second branch; this important load is an AC load with high power supply reliability requirements, ensuring that the important load receives a stable AC power supply. In this embodiment, the important load could be: reaction equipment in a chemical plant, data center servers in an internet company, equipment in a hospital's intensive care unit, etc.

[0041] The third branch is connected in parallel to the first branch; the second branch is connected to a non-critical load, which is an AC load with low power supply reliability requirements. In this embodiment, the non-critical load can be: ordinary lighting fixtures, general office equipment, etc.

[0042] The fourth branch is connected in parallel to the first branch; a power device is connected to the third branch. The power device may be an electric motor, etc.

[0043] To ensure continuous power supply to critical loads during grid outages or faults, a static transfer switch (STS) is connected in series on the first branch and located at the input of the critical load. In this embodiment, the STS is selected. Considering the load power during grid connection and the scenario of the PCS charging at full power, the actual power on the incoming AC side will be twice the full-load power of the PCS. Therefore, the STS power is 200kW.

[0044] The principle of the static switching switch in this embodiment can be combined with... Figure 2 To understand, Figure 2 The left side is labeled "Load Side," with three connection points: U, V, and W, for connecting to the load device; the right side is labeled "Grid Side," with three connection points: R, S, and T, for connecting to the grid power supply. The bidirectional thyristor in the middle (black arrow symbol in the diagram) serves as the core switching element, connecting or disconnecting the load side and grid side circuits under the drive of the main control circuit.

[0045] Its functions are as follows: It collects voltage and current signals from the load side in real time and feeds these signals back to the main control circuit. The main control circuit then uses the collected data to determine the operating status of the load, such as whether there are any abnormalities like overload or short circuit.

[0046] The system collects voltage signals from the power grid side and monitors parameters such as the amplitude, frequency, and phase of the grid voltage. When the grid voltage becomes abnormal (such as power failure, overvoltage, or undervoltage), the main control circuit controls the STS to perform a switching operation based on this signal, achieving uninterrupted power supply to the load within 20ms.

[0047] It receives instructions from the main control circuit, provides trigger signals to the bidirectional thyristor, and controls its conduction and turn-off, thereby realizing the switching of the load between the grid power supply and the backup power supply (the backup power supply connection is not shown in the figure, but it exists in actual applications).

[0048] Provide a stable DC power supply for the entire STS control circuit (including voltage / current sampling, drive circuit, main control circuit, etc.) to ensure the normal operation of the control circuit.

[0049] In another embodiment, the DC power distribution unit includes an energy storage unit; the energy storage unit includes at least: The fifth branch is connected in parallel to the medium-voltage DC bus; this fifth branch is connected to the high-voltage box via a bidirectional DC / DC converter. The other end of the high-voltage box is connected to an energy storage battery. Further, the energy storage battery is configured with the following standard: single cell 3.2V / 280Ah, battery pack 51.2V / 280Ah, and energy storage system 750V / 280Ah. This enables the storage and release of electrical energy, effectively solving the problem of spatial and temporal imbalance between power supply and demand, and improving system stability, economy, and renewable energy absorption capacity.

[0050] Specifically, this manifests as peak shaving and valley filling: storing electrical energy during off-peak hours and releasing it during peak hours reduces the peak load on the power grid, improves equipment utilization efficiency, and lowers system operating costs.

[0051] Backup power supply: In the event of grid failure, power outage or power fluctuation, the module can serve as a backup power supply to provide continuous power to critical loads and improve power supply reliability.

[0052] The energy storage unit also includes a sixth branch, connected in parallel to the medium-voltage DC bus; the sixth branch is connected to a photovoltaic module via an MPPT converter. The rationale for including the photovoltaic module is as follows: Energy Conversion: Photovoltaic modules can directly convert solar energy into direct current (DC) electricity, achieving clean power generation and reducing fossil fuel consumption and environmental pollution. They can be installed on rooftops, carports, ground surfaces, etc., offering flexibility and convenience.

[0053] Self-consumption and surplus power sold to the grid: Photovoltaic power generation can prioritize meeting its own electricity needs, and surplus power can be sold to the grid to achieve a win-win situation for both the economy and the environment.

[0054] The DC power distribution unit includes a charging unit; the charging unit includes: a seventh branch, which is connected in parallel to the medium-voltage DC bus; the seventh branch is connected to a V2G charging pile through a bidirectional DC / DC converter. The eighth branch is connected in parallel to the medium-voltage DC bus; a conventional charging pile is connected to the eighth branch through a unidirectional DC / DC converter.

[0055] Based on the above description, the bidirectional four-arm PCS is configured to determine whether to start or stop charging the energy storage battery based on a first judgment condition, and adjust the charging power in real time. The first judgment condition is the SOC value of the energy storage battery or a decision variable collected within a specified time period. Correspondingly, the AC distribution unit and the DC distribution unit are currently in a charging operation state, and the static switching switch remains in a grid-connected state. For example, constant current charging is used in the initial stage of battery charging, and constant voltage charging is used in the later stage to protect the battery and improve charging efficiency. The decision variables collected within the specified time period include: photovoltaic power generation, current load, etc.

[0056] Alternatively, the bidirectional four-arm PCS is configured to determine whether to start or stop discharging the energy storage battery based on a second judgment condition, and adjust the discharge power in real time. For example, when the system load suddenly increases, the PCS quickly increases the discharge power to maintain system stability. The second judgment condition is the loss of power on the AC side of the grid, the SOC value of the energy storage battery, or decision variables collected within a specified time period; correspondingly, the current AC distribution unit and DC distribution unit are in a discharging operation state, and the static switching switch remains in a grid-connected or off-grid state. Furthermore, the decision variables here can be based on factors such as system dispatch instructions, load demand, or electricity prices.

[0057] Therefore, in this embodiment, the static switching switch collects the real-time voltage of each phase of the AC power grid. When a power outage is detected on the AC side, it quickly disconnects the connection between the AC power grid and the DC microgrid and transmits a switching off-grid signal to the bidirectional four-arm PCS. The bidirectional four-arm PCS switches from current source mode to voltage source mode, and the AC / DC hybrid power distribution system switches from grid-connected state to off-grid state. The grid-connected to off-grid switching is seamless and does not affect the power consumption on the DC side, ensuring that other load units outside the microgrid are unaffected. The switching requires planned power outages, but important loads cannot be disconnected, and it does not affect power inspection and maintenance.

[0058] The bidirectional four-arm PCS is configured to adjust the total power carried by each phase during charging or discharging.

[0059] In summary, this embodiment acquires various operational data from the AC power distribution unit through the MPR controller. By using sensors connected to each branch, real-time electrical parameters such as voltage, current, and power on the AC side are obtained to monitor the stability of the AC power supply and the operating status of the load. It can also acquire status information of various switches, contactors, and other equipment in the AC power distribution unit to understand their opening and closing status, ensuring the normal operation of power distribution.

[0060] The MPR controller sends control commands to the AC distribution unit based on the system's operating strategy and acquired information. For the DC distribution unit, the MPR controller first acquires key data from the batteries in the energy storage unit, such as battery voltage, current, and state of charge (SOC), to understand the energy storage status of the energy storage system and provide a basis for charge and discharge control. It can also acquire information such as the photovoltaic unit's power generation, DC bus voltage, and the power consumption of each DC load to understand the power supply and demand situation on the DC side. For example, when the photovoltaic unit's power generation suddenly drops, the MPR controller can detect this in time and adjust the energy storage unit's discharge strategy to maintain stable system operation.

[0061] Based on the acquired information, the MPR controller issues commands to the DC power distribution unit. During charging, based on factors such as the battery's SOC, photovoltaic power generation, and current load, the MPR controller sends commands to the bidirectional DC / DC converter to control its charging process, including whether to initiate charging and adjusting the charging current and voltage. During discharging, it similarly controls the bidirectional DC / DC converter to adjust the battery's discharge power according to system demands, such as grid failures or sudden load increases. For the charging pile unit within the DC power distribution unit, the MPR controller can control the charging power and time of the charging pile based on the vehicle's charging needs and the overall energy distribution of the system, achieving orderly charging.

Claims

1. An AC / DC hybrid power distribution system, characterized in that, It is applied on the low-voltage side of the public distribution transformer area in the distribution network, and supports both AC and DC power distribution; the AC / DC hybrid power distribution system includes: a distribution cabinet, in which an MPR controller, an AC power distribution unit, and a DC power distribution unit are configured; the MPR controller is connected to the AC power distribution unit and the DC power distribution unit for bidirectional communication; It also includes: a medium-voltage DC bus, which is connected to the AC power distribution unit via a bidirectional four-arm PCS and to the DC power distribution unit; wherein, the bidirectional four-arm PCS realizes bidirectional power conversion between the AC power distribution unit and the medium-voltage DC bus, and provides a stable DC power supply for the DC power distribution unit.

2. The AC / DC hybrid power distribution system according to claim 1, characterized in that, The AC power distribution unit includes: The first branch is used to connect the MPR controller and the low-voltage side; the bidirectional four-bridge PCS is correspondingly connected to the first branch. The second branch is connected in parallel to the first branch and is located at the input of the bidirectional four-arm PCS; an important load is connected to the second branch, which is an AC load with high power supply reliability requirements.

3. The AC / DC hybrid power distribution system according to claim 2, characterized in that, The AC power distribution unit also includes: The third branch is connected in parallel to the first branch; the second branch is connected to a non-critical load, which is an AC load with low requirements for power supply reliability. The fourth branch is connected in parallel to the first branch; the third branch is connected to a power device.

4. The AC / DC hybrid power distribution system according to claim 2, characterized in that, The AC power distribution unit also includes: The switching unit is connected in series on the first branch and located at the input of the important load.

5. The AC / DC hybrid power distribution system according to claim 1, characterized in that, The DC power distribution unit includes an energy storage unit; the energy storage unit includes at least: The fifth branch is connected in parallel to the medium-voltage DC bus; the fifth branch is connected to the high-voltage box via a bidirectional DC / DC converter; The sixth branch is connected in parallel to the medium-voltage DC bus; the sixth branch is connected to the photovoltaic module via the MPPT converter.

6. The AC / DC hybrid power distribution system according to claim 1, characterized in that, The DC power distribution unit includes a charging unit; the charging unit includes: The seventh branch is connected in parallel to the medium-voltage DC bus; a V2G charging pile is connected to the seventh branch through a bidirectional DC / DC converter; The eighth branch is connected in parallel to the medium-voltage DC bus; a conventional charging pile is connected to the eighth branch through a unidirectional DC / DC converter.

7. The AC / DC hybrid power distribution system according to claim 1, characterized in that, The power distribution cabinet is also equipped with at least the following: a power distribution unit focused on the AC side, a switch control unit, a circuit protection unit, and a metering and monitoring unit.

8. The AC / DC hybrid power distribution system according to claim 1, characterized in that, The bidirectional four-arm PCS is configured to determine whether to start or stop charging the energy storage battery based on a first judgment condition, and adjust the charging power in real time; the first judgment condition is the SOC value of the energy storage battery or a decision variable collected within a specified time period. Correspondingly, the AC power distribution unit and the DC power distribution unit are currently in charging operation mode, while the switching unit remains in grid-connected mode.

9. The AC / DC hybrid power distribution system according to claim 1, characterized in that, The bidirectional four-arm PCS is configured to determine whether to start or stop discharging the energy storage battery based on a second judgment condition, and adjust the discharge power in real time; the second judgment condition is the loss of power on the AC side grid, the SOC value of the energy storage battery, or a decision variable collected within a specified time period. Correspondingly, the AC power distribution unit and the DC power distribution unit are currently in a discharge operation state, and the static switching switch remains in either grid-connected or off-grid state.

10. The AC / DC hybrid power distribution system according to claim 4, characterized in that, The switching unit collects the real-time voltage of each phase of the AC power grid. When it detects that the AC power grid has lost power, it quickly disconnects the connection between the AC power grid and the DC microgrid and transmits the off-grid switching signal to the bidirectional four-arm PCS. When the bidirectional four-arm PCS switches from current source mode to voltage source mode, the AC / DC hybrid power distribution system switches from grid-connected state to off-grid state.

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