A tunnel direct current power supply system control system containing a single-stage networked photovoltaic power generation unit

Abstract

The application provides a tunnel direct current power supply system containing a single-stage network-structured photovoltaic power generation unit. The system is composed of a commercial power supply unit, a single-stage network-structured photovoltaic power generation unit, an alternating current bus, an alternating current-direct current converter (AC / DC) and a tunnel direct current lighting system, wherein the AC / DC realizes the power conversion from commercial alternating current 380V to direct current 400V. The network-structured photovoltaic power generation unit is connected to the alternating current bus and adopts a matching control strategy based on the direct current side voltage deviation driving, and through the mapping relationship between the direct current voltage and the output frequency or power, the self-synchronous operation and power adaptive adjustment of the photovoltaic unit are realized.

Description

Technical Field

[0001] This invention relates to the fields of power electronics and new energy power generation technology, and in particular to a control system for a tunnel DC power supply system containing a single-stage grid-connected photovoltaic power generation unit, specifically belonging to the field of photovoltaic power generation grid-connected control and DC power supply system integration technology. Background Technology

[0002] With the continuous increase in the operating mileage of highways, the number of tunnels and other special road sections is also growing. As an important infrastructure for ensuring driving safety, tunnel lighting places high demands on the continuity and stability of the power supply system. Existing highway tunnels are mostly located in mountainous or remote areas, and their power supply usually relies on long-distance lines. This results in problems such as long power supply paths and significant susceptibility to external environmental influences. Under extreme weather or fault conditions, voltage fluctuations or even short-term power outages are prone to occur, making it difficult to meet the high reliability power supply requirements of tunnel lighting.

[0003] To improve power supply reliability and energy efficiency, photovoltaic (PV) power generation systems are increasingly being applied to tunnel power supply scenarios. However, most existing PV power generation systems adopt a grid-connected control method, relying on the upstream power grid for voltage and frequency support. The PV inverters themselves do not have the ability to independently adjust the AC bus voltage and frequency. When the power grid experiences disturbances or power outages, grid-connected PV systems typically cannot continue operating, making it difficult to provide continuous power to tunnel loads.

[0004] Furthermore, during grid-connected operation, traditional photovoltaic systems lack effective power regulation and constraint mechanisms, making them prone to reverse power transmission to the upstream grid. This not only affects grid operation safety but also limits the promotion of photovoltaics in specific application scenarios. Simultaneously, existing systems typically lack inertial response and frequency regulation capabilities, making it difficult to provide effective dynamic support under load fluctuations or system disturbances.

[0005] Therefore, there is an urgent need for a power supply system and its control method suitable for highway tunnel scenarios, which enables photovoltaic power generation units to have maximum power point tracking (MPPT), voltage and frequency support capabilities, achieve stable grid connection when the grid is operating normally, and be able to operate independently and maintain power supply when the grid is abnormal or disconnected. At the same time, it has the ability to suppress reverse power flow and improve the dynamic performance of the system, thereby improving the safety, reliability and adaptability of the tunnel power supply system. Summary of the Invention

[0006] This invention addresses the problems of insufficient continuous power supply capacity, lack of voltage and frequency support capabilities, easy occurrence of reverse power flow, and limited dynamic response capabilities in DC power supply systems for highway tunnels. It provides a control method, system, and structure for a tunnel DC power supply system based on a single-stage grid-connected photovoltaic power generation unit. This system integrates a photovoltaic array, a DC combiner device, a single-stage DC-AC converter (DC / AC), and its control device into a grid-connected photovoltaic power generation unit, which is then connected to the AC bus to support the AC bus voltage and frequency. Through a matched control strategy, the grid-connected photovoltaic power generation unit can adaptively adjust its output power according to the DC side voltage deviation, achieving self-synchronous operation. Simultaneously, the system has a power limiting mechanism to suppress reverse power flow and possesses inertial response and primary frequency regulation capabilities, enabling the photovoltaic power generation unit to provide dynamic support under load fluctuations or disturbances. In the event of a mains power outage or fault, the single-stage grid-connected photovoltaic power generation unit can maintain AC bus stability, achieving seamless islanded operation, thereby ensuring continuous power supply to the tunnel DC load and improving the system's stability, reliability, and safety.

[0007] The tunnel DC power supply system includes a mains power source, a single-stage grid-type photovoltaic power generation unit, an AC bus, an AC-DC converter (AC / DC), a DC bus, and tunnel DC loads. The mains power source is connected to the AC bus to provide power frequency AC energy. The single-stage grid-type photovoltaic power generation unit is connected to the AC bus to supply power to the AC bus and support its voltage and frequency. The AC-DC converter is connected to the AC bus to convert AC energy into DC energy and connect it to the DC bus. The tunnel DC loads are connected to the DC bus to obtain DC energy.

[0008] The single-stage grid-type photovoltaic power generation unit includes a photovoltaic array, a DC combiner device, a single-stage DC-AC converter and its control device; wherein, the photovoltaic array is used to convert solar energy into DC power, the DC combiner device is used to collect the outputs of multiple photovoltaic arrays and send them to the DC / AC converter, and the DC / AC converter is used to convert DC power into AC power and output it to the AC bus.

[0009] The AC-DC converter is used to convert mains power or AC bus power into DC power and connect it to the system DC bus to provide power for the tunnel's DC load. The input terminal of the AC-DC converter is connected to the AC bus, and the output terminal is connected to the DC bus. In specific implementations, the AC-DC converter can adopt a power electronic rectifier or a multi-pulse rectifier structure, including but not limited to uncontrolled rectifiers, multi-pulse rectifiers, three-phase two-level rectifier converters, three-phase three-level rectifier converters, or modular multilevel converters (MMC).

[0010] The single-stage grid-type photovoltaic power generation unit operates in different states under varying illumination and load conditions. When the photovoltaic power generation is less than the load demand, the system is supplied by both the mains power and the photovoltaic power generation unit. When the photovoltaic power generation exceeds the load demand, the photovoltaic power generation unit undertakes the main power supply task and adjusts the output power through control strategies to maintain stable system operation. The operating range of the photovoltaic power generation system under different operating conditions is described.

[0011] To achieve the above functions, the single-stage grid-type photovoltaic power generation unit adopts a control method based on a matched control strategy. This control strategy establishes an adjustment relationship between the output frequency or power based on the deviation between the DC-side voltage and its reference value, enabling the photovoltaic power generation unit to achieve self-synchronous operation and adaptive power adjustment. Simultaneously, by introducing a dynamic adjustment element, the system possesses a certain inertial response and frequency regulation capability, thereby providing dynamic support under load fluctuations or system disturbances.

[0012] In addition, a power detection and regulation mechanism is set at the grid connection point of the single-stage grid-type photovoltaic power generation unit. When a reverse power transmission trend to the upper-level grid is detected, the power generation is limited by adjusting the output power reference value of the photovoltaic power generation unit or the DC side voltage control target, thereby suppressing reverse power flow and improving the safety of system operation.

[0013] The synchronization signal ω constructed based on DC bus voltage synchronization (or matched control type synchronization) dc The control includes a method for synchronizing the DC bus voltage. This synchronization control has various expressions; this application uses a single-k type method as an example, but those skilled in the art will understand that the DC voltage synchronization in this application is not limited to this expression. (1) In the formula, ω dc To calculate the angular frequency for DC voltage synchronization, V dcref This is the DC voltage reference value, V dc k is the actual value of the DC bus voltage. pdc This is the proportionality coefficient.

[0014] The MPPT control enables the photovoltaic power generation unit and photovoltaic array to operate at their maximum power point, achieving maximum power output under the current operating conditions. The output power of the photovoltaic array is directly proportional to the port voltage. The DC / AC converter uses matching control to introduce disturbances in the DC bus voltage into the grid-connected frequency of the DC / AC converter, simultaneously stabilizing the DC bus voltage and achieving grid synchronization. The phase angle of the inverter output modulation voltage is: (2) In the formula, ω0 represents the reference value of the power grid frequency, and θsyn This refers to the phase angle of the grid connection.

[0015] In the excitation control process of a single-stage grid-type photovoltaic power generation unit, a reactive power regulation loop based on voltage deviation is constructed to support and regulate the AC bus voltage. This regulation loop uses a proportional-integral controller, and its expression is: (3) In the formula, V t V is the internal potential reference value. t0 k is the rated internal potential. pq With k iq These are the proportional and integral coefficients of the PI controller, Q. ref Q is the reactive power reference value. g k represents the actual reactive power value. q V is the reactive power droop factor. oref Reference value for grid connection point voltage, V o Actual value of grid connection point voltage.

[0016] In the matching control strategy, to enable the single-stage grid-type photovoltaic power generation unit to have inertial response capability, this invention introduces an inertial response element by adjusting the DC-side voltage reference value. Specifically, the voltage reference value is dynamically corrected according to the DC-side voltage change rate, so that the voltage reference value is adaptively adjusted with changes in system energy.

[0017] When the system power experiences a sudden change, the DC-side voltage will change, and its rate of change reflects the degree of energy imbalance in the system. By introducing this rate of change term, the DC voltage reference value can be adjusted, and then the output frequency can be influenced through a matched control strategy to achieve inertial response characteristics similar to a synchronous generator, thereby improving the dynamic stability of the system. The inertial response expression is: (4) In the formula, △V ine k is the inertial response bus voltage deviation value. ine This is the proportionality coefficient.

[0018] Its time-domain expression is: (5) In the control method described above, an adaptive adjustment mechanism is constructed based on frequency deviation to achieve the primary frequency regulation function of the single-stage grid-type photovoltaic power generation unit. Specifically, when the system frequency deviation is within a preset range, the single-stage grid-type photovoltaic power generation unit maintains the basic matching control coefficient; when the frequency deviation exceeds a set threshold, the matching control coefficient is adjusted so that the system output power increases with the increase of frequency deviation, thereby achieving rapid support for system frequency drops.

[0019] Specifically, the system output frequency and the DC-side voltage deviation satisfy the following relationship: (6) In the formula, △ω sup For primary frequency modulation support value, k sup The primary frequency modulation ratio, Δω th .

[0020] By combining equations (1), (2), and (6), it can be seen that the primary frequency modulation expression is the same as the proportional coefficient term of the matching control. Primary frequency modulation can be achieved by adjusting the output voltage of the photovoltaic array. However, the difference is that equation (6) only takes effect when the frequency deviation value is greater than the threshold.

[0021] The system is equipped with an anti-reverse current device, which acts on the DC-side voltage control link of the single-stage grid-type photovoltaic power generation unit. The anti-reverse current device is used to detect the direction of active power flow of the single-stage grid-type photovoltaic power generation unit at the grid connection point. When a tendency for the system to send power in reverse to the upstream grid is detected, the output power of the photovoltaic power generation unit is limited by adjusting the DC-side voltage reference value or its control quantity.

[0022] Specifically, the anti-reverse current device dynamically adjusts the DC-side voltage control reference value based on the active power detection value at the grid connection point. When the active power exceeds a set threshold, it indicates that the DC / AC is feeding current back to the grid. This reduces the output power of the single-stage grid-type photovoltaic power generation unit, thereby suppressing the generation of reverse power flow. This adjustment process, through the synergistic effect of the DC-side voltage control link and the matching control strategy, effectively constrains reverse power without changing the basic control structure of the system.

[0023] The control system includes a voltage outer loop and a current inner loop control structure. The voltage outer loop is used to generate control reference quantities, and the current inner loop is used to achieve rapid adjustment of the converter output current. Both the voltage outer loop and the current inner loop can be implemented using a proportional-integral (PI) control strategy or a virtual admittance control structure. These control methods are all conventional techniques in this field and will not be elaborated further.

[0024] The tunnel DC power supply system, in addition to the photovoltaic converter control, also includes an AC bus, an AC-DC converter, a DC bus, tunnel DC loads, and related protection and limiting devices. The AC bus connects to the mains power supply and the single-stage grid-type photovoltaic power generation units. The mains power supply provides basic DC power when sunlight or photovoltaic power is insufficient, and ensures continuous power supply to the tunnel loads. The AC-DC converter connects to the AC bus and provides DC power to the DC bus, maintaining DC bus voltage stability and providing stable DC power to the tunnel DC loads. The AC-DC converter can employ uncontrolled rectification, multi-pulse rectification, three-phase two-level, or three-level rectification topologies, or a modular multilevel converter (MMC) to adapt to different system capacities and power quality requirements.

[0025] The DC bus is used to collect DC power from the mains and photovoltaic power generation units and supply power to the tunnel's DC loads. These tunnel DC loads mainly include DC lighting fixtures and their drivers, and may also include other DC loads and their corresponding power conversion devices. The photovoltaic power generation units can supply power independently when the mains power is disconnected, achieving seamless islanded operation and ensuring the continuity and safety of tunnel lighting.

[0026] To ensure safe system operation, the system can be equipped with protection and limiting mechanisms, including overcurrent and overvoltage protection, as well as DC-side voltage and output current limiting. Combined with the anti-reverse current device, it can prevent photovoltaic power from flowing back to the upstream grid while maintaining system output stability.

[0027] During system operation, a coordinated control relationship is formed between the photovoltaic power generation units, the AC-DC converter, the DC bus, and the tunnel load. The photovoltaic power generation units adjust their output power according to the irradiance conditions and load demand, the AC-DC converter maintains the DC bus voltage stability, and the DC load continues to operate according to the system's power supply. The entire system can achieve dynamic coordination under multiple operating conditions, including grid connection, independent photovoltaic power supply, and islanding switching scenarios.

[0028] The system control method is achieved through the coordinated control of photovoltaic converters, DC bus voltage regulation, and anti-reverse current regulation. This method ensures that the system can smoothly switch operating modes under different lighting conditions and load changes, improving photovoltaic power utilization and system power supply reliability. It also features dynamic frequency regulation and voltage support functions, meeting the safety and stability requirements of power supply in highway tunnels.

[0029] Through the tunnel DC power supply system containing single-stage grid-type photovoltaic power generation units, the present invention can realize the active and reactive power support of the single-stage grid-type photovoltaic system to the system during changes in system operating status or fluctuations in illumination conditions, achieve effective coordination under different control modes, increase the photovoltaic absorption rate of the system, reduce electricity costs, ensure the smooth transition of the tunnel DC power supply system under multiple operating conditions, and improve the system's dynamic response capability, operational stability, and control robustness. Attached Figure Description

[0030] Figure 1 This is a tunnel DC power supply system containing a single-stage grid-connected photovoltaic power generation unit; Figure 2 This is a schematic diagram of the operating range of a photovoltaic power generation system under different lighting conditions; Figure 3 This is a structural diagram of a single-stage photovoltaic converter system; Figure 4 This is a control block diagram of a single-stage photovoltaic converter based on a matching control strategy. Figure 5 A flowchart of a control method for a tunnel DC power supply system containing a single-stage grid-connected photovoltaic power generation unit; Figure 6 This is a flowchart of a control method for a tunnel DC power supply system containing a single-stage grid photovoltaic power generation unit. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are used to illustrate the technical solutions of the present invention, so that those skilled in the art can understand and implement the present invention, but are not intended to limit the scope of protection of the present invention. It should be noted that, for those skilled in the art, various modifications and improvements can be made to the present invention without departing from the technical concept of the present invention, and all such modifications and improvements should fall within the scope of protection of the present invention.

[0032] This invention relates to a tunnel DC power supply system comprising a single-stage grid-connected photovoltaic (PV) power generation unit. The system consists of a mains power supply, an AC bus, an AC-DC converter, a single-stage grid-connected PV power generation unit, a DC bus, and a tunnel DC load. The grid-connected PV power generation unit outputs PV power to the AC bus through a single-stage conversion and achieves adaptive power regulation through DC-side voltage matching control, inertia response, and primary frequency regulation mechanisms. Simultaneously, anti-reverse current constraints ensure that power does not flow back to the upstream grid. During system operation, the PV power generation unit, AC-DC converter, and DC bus form a coordinated control relationship, achieving parallel operation and coordination of maximum power point tracking control and bus voltage control. This ensures that the system maintains continuous and stable DC power supply even under conditions of fluctuating sunlight, load disturbances, or mains power outages, thereby significantly improving the dynamic response capability, operational stability, and control robustness of the tunnel DC power supply system.

[0033] This embodiment, by selecting a suitable converter topology according to specific application requirements, can be applied to tunnel DC power supply systems of different scales, thereby achieving good technical results.

[0034] like Figure 1 As shown, this embodiment provides a tunnel DC power supply system including a single-stage grid-connected photovoltaic power generation unit, comprising a mains power supply, an AC bus, an AC-DC converter, a single-stage grid-connected photovoltaic power generation unit, a DC bus, and tunnel DC loads. The mains power supply is connected to the DC bus through the AC-DC converter, providing basic DC power to the DC bus; the single-stage grid-connected photovoltaic power generation unit directly outputs power to the AC bus through a single-stage converter, and provides support for the AC bus voltage and frequency; the tunnel DC loads are connected to the DC bus to obtain DC power and power tunnel lighting and other DC loads.

[0035] In this embodiment, the control of the single-stage grid-type photovoltaic power generation unit determines the system operation mode based on the illumination conditions and DC load demand. For example... Figure 2 As shown, the photovoltaic converter can use a matched control strategy to control the output voltage and power of the photovoltaic array. In this case, the DC side voltage is controlled by V. dc The matching strategy is the primary strategy, combined with inertial response and primary frequency regulation mechanisms to achieve adaptive adjustment of photovoltaic power and load support; when the photovoltaic power output exceeds the load demand, the anti-reverse current device sends a signal to adjust V. dcref The DC bus voltage is kept stable through a bus voltage control strategy, while the photovoltaic units can still supply power independently, achieving seamless off-grid capability.

[0036] like Figure 3 and Figure 4As shown, a single-stage grid-type photovoltaic power generation unit includes a photovoltaic array, a DC combiner device, a single-stage DC / AC converter, and a control algorithm. The control system constructs a voltage outer loop and a current inner loop. The grid-type photovoltaic system employs a matched control strategy, through V... dc Self-synchronization is achieved, and inertial response, primary frequency modulation, and anti-reverse current constraints are combined to ensure the stability of photovoltaic output power and bus voltage. The voltage outer loop uses the excitation output signal as the input signal, and the current inner loop is used to quickly track the reference signal generated by the voltage outer loop to regulate the output current of the single-stage converter.

[0037] Through the synergistic effect of the above structure and control strategy, the single-stage grid-type photovoltaic power generation unit can adaptively adjust its power output under different illumination conditions and load disturbances, while ensuring the stability of the DC bus voltage and realizing the smooth operation of the system.

[0038] Figure 5 A flowchart illustrating a tunnel DC power supply system comprising a single-stage grid-connected photovoltaic power generation unit according to an exemplary embodiment is shown. The single-stage grid-connected photovoltaic power generation unit includes a single-stage converter and its matching control strategy, including: The mains power is connected to the AC bus to provide a voltage reference value; according to Figure 4 The control strategy generates conversion commands, and the DC / AC unit performs photovoltaic to AC bus power conversion; The system operates according to the matching control strategy, dynamically adjusts the output characteristics based on the anti-backflow device, and judges the mains power operation status. The system dynamically adapts to the photovoltaic output and load power to determine the optimal operating conditions and AC bus voltage control mode of the system. AC / DC converters convert DC bus power into DC power, providing stable DC bus power.

[0039] Figure 6 A flowchart illustrating another tunnel DC power supply system containing a single-stage grid-type photovoltaic power generation unit according to an exemplary embodiment is shown. The specific implementation steps are as follows: Step 1: Connect the mains power supply to the AC bus to provide voltage and frequency references for the system; Step 2: Detect the lighting conditions. When the lighting is insufficient, the single-stage grid-type photovoltaic power generation unit will not be put into operation. The mains power will supply power to the DC bus through AC / DC and maintain the normal operation of the tunnel DC load. Step 3: When there is sufficient sunlight and the output voltage of the photovoltaic array reaches the set threshold, the single-stage grid-type photovoltaic power generation unit is put into operation, and the single-stage DC / AC converter begins to output power to the AC bus. Step 4: The control device of the single-stage grid-type photovoltaic power generation unit generates control quantities based on the DC-side voltage and its reference value, and determines the DC-side voltage reference value V.dcref , used to adjust the output power of photovoltaic power generation units; Step 5: The anti-reverse current device detects the direction of active power at the grid connection point. When it detects reverse power flow to the upstream grid, it adjusts the DC side voltage reference value V. dcref Adjustments are made to reduce photovoltaic output power; when there is no reverse power flow, the current control state is maintained. Step 6: Detect the mains power status at the grid connection point. When the mains power fails or disconnects, the system switches to islanded operation mode; when the mains power is normal, the system operates in grid-connected mode. Step 7: Based on the system operation mode, the single-stage grid-connected photovoltaic power generation unit uses a grid control strategy to generate control commands, including active power regulation based on matched control, dynamic correction based on inertia response and primary frequency regulation, and reactive power regulation based on voltage deviation, thereby generating the synchronous phase angle θ. syn and excitation voltage reference signal; Step 8: Use the outer loop control signal as the inner loop current input, and generate a PWM drive signal through the current controller to control the switching action of the single-stage DC / AC converter; Step 9: Based on the relationship between photovoltaic output power and load demand, determine the AC bus power supply mode, which can be supplied by a single-stage grid-type photovoltaic power generation unit alone or in coordination with the mains power supply. Step 10: The AC-DC converter converts the AC bus power into stable DC power and outputs it to the DC bus to continuously supply power to the tunnel DC load and ensure the stable operation of the tunnel lighting system.

[0040] Through the above control methods, the system can achieve coordinated operation of maximum power point tracking control and bus voltage control under conditions of varying illumination or load disturbances. Based on the relationship between photovoltaic output power and load demand, the optimal power supply mode of the system is ultimately determined. The power generation unit adopts a grid-based control strategy to improve the system's operational stability and dynamic response capability.

[0041] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A tunnel DC power supply system containing a single-stage grid-connected photovoltaic power generation unit, characterized in that, The system mainly consists of a mains power supply, a single-stage grid-type photovoltaic power generation unit, an AC bus, an AC-DC converter (AC / DC), and a tunnel DC load. The connection relationships and functions between the various devices are as follows: The mains power supply is used to provide industrial frequency AC power and is connected to the AC bus; The single-stage grid-type photovoltaic power generation unit is connected to the AC bus to provide power to the AC bus and support its voltage and frequency. The AC / DC converter has its input terminal connected to the AC bus and its output terminal connected to the DC bus, and is used to convert AC power into DC power and supply power to DC loads. The tunnel DC load is connected to the DC bus and is used to consume DC power. The single-stage grid-type photovoltaic power generation unit includes a photovoltaic array, a DC combiner device, a single-stage DC-AC converter, and a control device. The photovoltaic array is used to convert solar energy into direct current (DC) electricity. The DC combiner is connected to the photovoltaic array at one end and to the DC / AC converter at the other end, and is used to collect DC power output from multiple photovoltaic arrays. The DC / AC converter is used to convert DC power into AC power and output it to the AC bus. The control device is used to control the DC / AC converter and to construct an output frequency or power adjustment mechanism based on the DC side voltage deviation, so as to realize the self-synchronous operation and power adaptive adjustment of the grid-type photovoltaic power generation unit.

2. The tunnel DC power supply system according to claim 1, characterized in that, AC / DC converters convert alternating current into direct current. These AC / DC converters include, but are not limited to, uncontrolled rectifier converters, multi-pulse rectifier converters, three-phase two-level converters, three-phase three-level converters, and modular multilevel converters.

3. The tunnel DC power supply system according to claim 1, characterized in that, The grid-type photovoltaic power generation unit includes a photovoltaic array and a single-stage DC-AC converter, which is used to realize single-stage energy conversion from DC to AC.

4. The tunnel DC power supply system according to claim 1, characterized in that, The control device employs a matching control strategy based on DC-side voltage deviation to control the grid-type photovoltaic power generation unit.

5. The matching control strategy according to claim 4, characterized in that, The controller achieves maximum power point tracking of the photovoltaic array by controlling the DC side voltage, i.e., the voltage at the photovoltaic panel port.

6. The matching control strategy according to claim 4, characterized in that, In the matching control strategy, the output frequency or power is related to the deviation between the DC side voltage and its reference value, and the mapping relationship includes a proportional element or a transfer function containing dynamic characteristics.

7. The grid-type photovoltaic power generation unit according to claim 4 or 5, characterized in that, The matching control strategy further includes an inertia response stage and / or a frequency droop control stage, so that the grid-type photovoltaic power generation unit has inertia response and primary frequency regulation capability.

8. The tunnel DC power supply system according to claim 1, characterized in that, The system also includes a power detection and regulation device for detecting the direction of active power flow between the grid-connected photovoltaic power generation unit and the upstream grid. When reverse power transmission to the upstream grid is detected, the power generation is limited by adjusting the output power reference value or DC side voltage control target value of the grid-connected photovoltaic power generation unit. The power detection is based on the active power measurement value at the grid connection point. When the active power is greater than the set threshold, the power limiting mechanism is triggered.

9. The tunnel DC power supply system according to claim 1, characterized in that, When the mains power supply is disconnected or fails, the grid-connected photovoltaic power generation unit maintains stable AC bus voltage and frequency, achieving a seamless switch from grid-connected operation to islanded operation.

10. The tunnel DC power supply system according to claim 1, characterized in that, The tunnel DC load includes DC lighting fixtures and their driving converters, as well as other DC loads and their corresponding power conversion devices; the AC-DC converter and the grid-type photovoltaic power generation unit work together to balance the system power, so as to maintain the stable operation of the AC bus and the DC bus.

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