A photovoltaic energy storage direct current power supply system for a relay protection power supply system and a control method thereof

Abstract

The application discloses a photovoltaic energy storage direct current power supply system for a relay protection power supply system and a control method thereof, and the system comprises a photovoltaic array, an MPPT converter, an energy storage battery pack, a bidirectional DC / DC converter, a DC / DC converter, a state monitoring module and a control module, is connected in parallel with an existing operating power supply to form a double-redundant power supply architecture without electrical interference. The control method realizes intelligent cooperation of the photovoltaic energy storage and the power grid through multi-dimensional state sensing, illumination adaptive mode configuration, double-closed-loop constant voltage regulation, millisecond-level seamless switching and storage battery health management. The application solves the problem of long-time power failure of a traditional power supply, significantly improves power supply reliability, reduces the operation cost of the system in the whole life cycle, and is suitable for relay protection power supply systems of various power plants and transformer substations.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection and power supply technology, and in particular to a photovoltaic energy storage DC power supply system and its control method for a relay protection power supply system. Background Technology

[0002] Relay protection systems ensure the safe and stable operation of power systems, and their normal operation depends on a stable operating power supply. The operating power supply provides electrical energy to equipment such as relay protection devices and circuit breaker operating mechanisms, and the continuity and stability of the power supply directly affect the reliability of the relay protection system's operation.

[0003] Currently, the relay protection operating power supplies used in power systems are mainly divided into two categories: DC operating power supplies and AC operating power supplies. 1. DC Operating Power Supply: This is the current mainstream form. It converts AC power from the grid into DC power through a rectifier, charging the battery bank before supplying power to the load. Its advantage is that the battery bank can store electrical energy, maintaining power supply for a certain period even during a complete grid outage. However, it has disadvantages: battery capacity decays rapidly, has a short lifespan, requiring regular replacement and increasing operation and maintenance costs; its energy storage capacity is limited, and prolonged power outages may cause relay protection devices to lose power; the system relies on grid power and lacks independent backup energy. 2. AC operating power supply: It draws energy directly from current transformers or voltage transformers, resulting in low investment costs and simple operation and maintenance. However, the reliability of the power supply depends on the operating status of the primary system. When a short circuit or grounding fault occurs in the power system, the transformer output may be interrupted, causing the relay protection device to lose power. Furthermore, AC power supply is susceptible to grid voltage fluctuations and harmonic interference, resulting in unstable power supply quality. Furthermore, existing operating power systems mostly employ a single power supply method, lacking independent redundant power supply means. Some dual-grid power supply schemes, due to their shared power source, will still fail simultaneously during large-scale grid outages. Summary of the Invention

[0004] To address the shortcomings of existing technologies, there is an urgent need to construct redundant operating power supply systems with independent energy supply and high reliability, thereby resolving the aforementioned problems of traditional power supplies. To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A photovoltaic energy storage DC power supply system for a relay protection power supply system includes a photovoltaic array, an MPPT converter, an energy storage battery pack, a bidirectional DC / DC converter, a DC / DC converter, a status monitoring module, and a control module. The output of the photovoltaic array is connected to the input of the MPPT converter; the output of the MPPT converter is connected to the DC bus; the positive and negative terminals of the energy storage battery pack are connected to the low-voltage side port of the bidirectional DC / DC converter; the bidirectional DC / DC converter adopts a non-electrically isolated bidirectional topology and can operate in charging and discharging modes, with the high-voltage side port connected to the DC bus; the input of the DC / DC converter is connected to the DC bus, and the output is connected to the power supply input of the relay protection device and automatic device; The status monitoring module's acquisition terminals are connected to the AC grid side, DC bus, photovoltaic array output terminal, energy storage battery pack, and DC / DC converter output terminal, respectively, while the signal output terminal is connected to the control module's input terminal. The control module's control output terminals are connected to the MPPT converter, bidirectional DC / DC converter, and DC / DC converter control terminal, respectively. The control module enables the photovoltaic energy storage DC power supply system to be connected in parallel with the existing relay protection operating power supply to form a dual redundant power supply architecture without direct electrical interference, and dynamically compensates for the source load supply and demand deficit to maintain a constant DC bus voltage.

[0005] Preferably, the system uses the DC bus voltage as the sole indicator of power balance, and satisfies the following global power coupling constraint equations under any operating state: ; in, The output power of the existing relay protection operating power supply, For the output power of the photovoltaic array, For energy storage battery packs to absorb or output power, This refers to the total load power of relay protection devices and automatic devices. The equivalent total power loss of the system operation and transformation link is defined in the model as positive for power output and negative for absorption.

[0006] Preferably, the dynamic characteristics of the DC bus voltage satisfy the following differential equation: ; in, This is the DC bus voltage. This is the DC bus capacitance value.

[0007] Preferably, the control module has an embedded multi-mode power supply priority determiner, which automatically configures the system into either a photovoltaic and energy storage independent main power supply + operating power backup or an operating power main power supply + photovoltaic and energy storage independent backup mode based on historical sunshine data and real-time photovoltaic output prediction, thus isolating AC system short circuit and harmonic voltage fluctuation interference.

[0008] Preferably, the control method of the system includes the following steps: S1. The status monitoring module samples the voltage of the existing operating power supply side, the DC bus voltage of the photovoltaic and energy storage, the output current of the photovoltaic array, the charging and discharging current of the energy storage battery pack, the DC load output current, and the battery state of charge data at a frequency of not less than 1kHz, and sends them to the control module. S2. The control module extracts the time-series photovoltaic power output characteristics, combines historical sunshine data to evaluate the energy sufficiency of the application scenario environment, adaptively configures the primary and secondary power supply roles in the dual redundancy architecture, and activates the multi-mode collaborative control strategy under the corresponding priority. S3. Calculate the power imbalance based on the dynamic characteristics of the DC bus voltage, generate the target reference command for energy storage charging and discharging, and drive the bidirectional DC / DC converter to maintain the balance of DC bus power supply. S4. The control module calculates the bus voltage drop rate of the current main power supply in real time. When it determines that the power failure occurs due to exceeding the limit, it executes a hardware-level fast redirection and switching command in milliseconds and puts the backup link in the corresponding mode to provide emergency full-load power supply. S5. The control module dynamically adjusts the photovoltaic charging power and the battery charge / discharge depth based on the real-time state of charge of the energy storage battery pack to avoid overcharging and over-discharging of the battery.

[0009] Preferably, the specific execution logic of the multi-mode collaborative control strategy in step S2 is as follows: In areas lacking solar resources, the existing operating power supply is used as the main power source, with independent photovoltaic and energy storage backup. Under normal conditions, the total load is mainly borne by the existing power supply. The photovoltaic array's power is first used to charge the energy storage battery bank to maintain maximum backup capacity. After the battery bank is fully charged, the photovoltaic modules enter standby mode or use redundant power to supplement the load. In the event of a failure of the operating power supply, the operating power supply is immediately cut off and photovoltaic and energy storage power is switched on. At the same time, the photovoltaic modules continue to generate power to supplement the battery bank, extending the emergency power supply time. In areas with abundant solar resources, the system is locked into a mode of independent main power supply for solar power and energy storage, plus backup operating power: Under normal conditions, the original operating power supply is in a standby emergency state with no output, and the solar power and energy storage system directly serves as the main output; when the solar power and energy storage system equipment fails or the battery is depleted, the operating power supply is switched on in reverse.

[0010] Preferably, the energy storage control objective in step S3 satisfies the following current balance equation: ; in, To provide current to the energy storage battery pack For the photovoltaic array output current, The current output by the DC / DC converter to the DC load. This is the system's equivalent loss current.

[0011] Preferably, the constant voltage regulation of energy storage in step S3 adopts a voltage and current dual closed-loop PI control algorithm, and the specific steps are as follows: Calculate the rated reference setting voltage of the DC bus With real-time sampling bus voltage Deviation values ​​between: ; Deviation The reference current value for the energy storage side is obtained after processing by the voltage loop PI regulator. The voltage loop compensation calculation formula is as follows: ; in, This is the proportional coefficient for the voltage loop control. The integral coefficient for voltage loop control; Reference value of the reference current With real-time sampled energy storage current The comparison yields the current deviation value, which is then processed by the current loop PI regulator, while also incorporating the feedforward current. and The corrected integrated drive signal is used to generate the required PWM duty cycle to trigger the power switch.

[0012] Preferably, the transient seamless switching between primary and backup power supplies in step S4 meets the following hard requirements: When a fault is detected and the backup switching action is initiated, the high-frequency PWM timing latch inside the control module ensures that the backup system outputs a rated operating current of not less than 10A within 0.1s from the start of the action. After the main power supply returns to normal and operates stably for 3-5 seconds, the control module performs a smooth switching operation. During the switching process, the DC bus voltage fluctuation does not exceed ±5% of the rated value.

[0013] Preferably, the battery health energy management strategy in step S5 is as follows: When the state of charge of the energy storage battery pack reaches the upper limit of the safe full charge threshold, and the net input power of the DC bus source end is still greater than the total power consumed by the back end, the MPPT converter actively jumps out of maximum power point tracking and enters constant voltage power limiting clamping mode, or the control module cuts off the excess photovoltaic string array until the system experiences a power demand gap again. When the state of charge of the energy storage battery pack drops to the lower safety threshold, the control module limits the discharge power of the battery pack and prioritizes the power supply to the core relay protection device.

[0014] Compared with existing relay protection operating power supply technology, the present invention has the following advantages: 1. This invention independently connects to a photovoltaic energy storage DC power supply system in parallel with an existing relay protection operating power supply, forming a dual-redundancy power supply mode without direct electrical interference. When any power supply link fails, the other link can seamlessly switch within milliseconds, ensuring that critical equipment such as relay protection devices and circuit breakers continuously receive power. In areas and periods with sufficient sunlight, the photovoltaic array can continuously generate power and buffer power supply through energy storage battery banks, solving the problems of limited battery capacity and protection device failure after prolonged power outages in traditional DC operating power supplies. 2. Utilize solar power generation to supplement or replace part of the grid's electrical energy, reducing dependence on external power grids and lowering long-term operating electricity costs. Intelligent collaborative management of photovoltaic charging and battery charging / discharging is achieved through a control module, optimizing battery charging / discharging frequency and depth, mitigating battery capacity degradation, extending battery bank lifespan, and reducing equipment replacement and maintenance costs. 3. The photovoltaic energy storage power supply system is completely electrically isolated from the AC primary system, fundamentally avoiding the impact of AC system faults on the power supply to the relay protection device. The DC bus voltage is precisely constant-voltage controlled by the energy storage bidirectional DC / DC converter, resulting in low voltage ripple and high stability, providing a clean and reliable power supply for the relay protection device. 4. This invention adopts a modular design, eliminating the need for large-scale modifications to existing relay protection operating power supply systems. It can be directly connected in parallel to existing systems, resulting in low modification costs and short construction periods. The system can adaptively configure itself into two operating modes based on regional solar resource conditions: "photovoltaic-storage main supply + grid backup" or "grid main supply + photovoltaic-storage backup," making it suitable for regions with varying solar conditions. Furthermore, this system can be extended to applications such as power communication systems and automated monitoring systems, where high power supply reliability is required. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the photovoltaic energy storage DC power supply system for relay protection power supply system of the present invention; Figure 2 This is a coupled power supply architecture diagram of the photovoltaic energy storage DC power supply system of the present invention; Figure 3 This is a block diagram of the constant voltage control of the bidirectional DC / DC converter for energy storage in this invention; Figure 4 This is a diagram illustrating the multi-mode control strategy of the photovoltaic energy storage power supply system used in the relay protection device according to the present invention. Figure 5 This is a diagram showing the main power supply of the photovoltaic energy storage DC power supply system of this invention; Figure 6 This is a diagram of the backup power supply for the photovoltaic energy storage DC power supply system of the present invention. Detailed Implementation

[0016] A photovoltaic energy storage DC power supply system for relay protection power supply systems, such as Figure 1 As shown, it includes a photovoltaic array, an MPPT converter, an energy storage battery pack, a bidirectional DC / DC converter, a DC / DC converter, a status monitoring module, and a control module; The photovoltaic array output is connected to the MPPT converter input, converting solar radiation into DC power output. The MPPT converter output is connected to the DC bus, adjusting its operating point in real time to ensure the photovoltaic array always operates at its maximum power point, maximizing solar energy capture. The energy storage battery pack's positive and negative terminals are connected to the low-voltage side of the bidirectional DC / DC converter, serving as a system energy buffer and backup unit. It absorbs and stores energy when photovoltaic power is excessive and releases energy when photovoltaic power is insufficient, at night, or under fault conditions. The bidirectional DC / DC converter adopts a non-electrically isolated bidirectional topology, capable of operating in charging and discharging modes. Its high-voltage side is connected to the DC bus, enabling bidirectional power flow between the energy storage battery pack and the DC bus. The DC / DC converter input is connected to the DC bus, and its output is connected to the power input of the relay protection device and automatic device, completing voltage level matching and converting the DC bus power into a stable DC output that meets load requirements. The status monitoring module's acquisition terminals are connected to the AC grid side, DC bus, photovoltaic array output terminal, energy storage battery bank, and DC / DC converter output terminal, respectively, to sample AC grid side voltage, DC bus voltage, photovoltaic array output current, energy storage battery bank charging and discharging current, DC load output current, and battery state of charge data at a frequency of not less than 1kHz; the status monitoring module's signal output terminal is connected to the control module's input terminal to upload the collected real-time operating parameters to the control module; the control module's control output terminal is connected to the MPPT converter, bidirectional DC / DC converter, and DC / DC converter control terminal, respectively. like Figure 2 As shown, the control module connects the photovoltaic energy storage DC power supply system in parallel with the existing relay protection operating power supply to form a dual redundant power supply architecture without direct electrical interference, and dynamically compensates for the supply and demand gap of the source load to maintain a constant DC bus voltage.

[0017] In the preferred scheme, the system uses the DC bus voltage as the sole indicator of power balance, and satisfies the following global power coupling constraint equations under any operating state: ; in, The output power of the existing relay protection operating power supply, For the output power of the photovoltaic array, For energy storage battery packs to absorb or output power, This refers to the total load power of relay protection devices and automatic devices. The equivalent total power loss of the system operation and conversion links is defined in the model as positive for power output and negative for absorption. When the system power reaches dynamic equilibrium, the DC bus voltage remains constant; when the photovoltaic output or load changes abruptly, the power difference is compensated by adjusting the charging and discharging power of the energy storage battery pack, thus maintaining the stability of the bus voltage.

[0018] In the preferred embodiment, the dynamic characteristics of the DC bus voltage satisfy the following differential equation: ; in, This is the DC bus voltage. This is the DC bus capacitance value; This equation intuitively reflects the relationship between the power imbalance and the rate of change of the DC bus voltage. The control module calculates the power deficit based on this equation and generates energy storage charging and discharging control commands.

[0019] In the preferred scheme, such as Figure 4 As shown, the control module has an embedded multi-mode power supply priority determiner. Based on historical solar irradiance data and real-time photovoltaic output prediction, it automatically configures the system into either a photovoltaic and energy storage independent main power supply + operating power backup or an operating power main power supply + photovoltaic and energy storage independent backup mode, thus isolating AC system short circuit and harmonic voltage fluctuation interference. In areas with abundant solar resources, the system operates in a photovoltaic-storage independent main power supply mode: under normal conditions, the original operating power supply is in standby with no output, and the load is directly supplied by the photovoltaic array, with excess power charging the energy storage battery pack; when the photovoltaic output is insufficient or at night, the energy storage battery pack discharges to supplement the power; when the photovoltaic-storage system fails or the battery charge level is lower than the lower threshold, it automatically switches to the existing operating power supply. In areas lacking solar resources, the system operates in a main operating power supply mode: under normal conditions, the existing operating power supply bears the main load, and the photovoltaic array generates electricity to charge the energy storage battery bank first. After the battery is fully charged, the photovoltaic power directly supplements the load; when the existing operating power supply fails, it immediately switches to the photovoltaic-storage system for power supply, while the photovoltaic array continues to generate electricity to supplement the battery energy, extending the emergency power supply time.

[0020] In the preferred scheme, such as Figure 3 As shown, the control module uses a voltage and current dual closed-loop PI control algorithm to perform constant voltage regulation on the bidirectional DC / DC converter. The energy storage control objective satisfies the following current balance equation: ; in, To provide current to the energy storage battery pack For the photovoltaic array output current, The current output by the DC / DC converter to the DC load. This represents the system's equivalent loss current. The specific control process is as follows: Calculate the rated reference voltage of the DC bus. With real-time sampling bus voltage Deviation value between ; to deviation The reference current value for the energy storage side is obtained after processing by the voltage loop PI regulator. ,in This is the proportional coefficient for the voltage loop control. The integral coefficient for voltage loop control; the reference current value is compared with the real-time sampled energy storage current. The comparison yields the current deviation value, which is then processed by the current loop PI regulator, while also incorporating the feedforward current. and The corrected integrated drive signal is used to generate the required PWM duty cycle to trigger the power switch.

[0021] In the preferred scheme, the main and backup power supply switching adopts a hardware fast switching mechanism. The control module calculates the bus voltage drop rate of the current main power supply in real time. When it is determined that the main power supply exceeds the limit and a power outage fault occurs, the switching command is executed in milliseconds. like Figure 5 As shown, in the main power supply mode of the photovoltaic-storage system, if the photovoltaic-storage system fails within 1.5 seconds, the operating power supply can be quickly connected to continuously supply 10A to the relay protection system. like Figure 6 As shown, in the backup power supply mode of the photovoltaic energy storage system, if the operating power supply fails at 0.5s, the photovoltaic energy storage power supply system can switch in within milliseconds and provide stable power supply to the relay protection system with a current of 10A within 0.1s. After the switching action is initiated, the backup system can reach a steady-state output current of no less than 10A within 0.1s; when the main power supply returns to normal and operates stably for 3-5 seconds, the control module performs a smooth back-switching operation, and the DC bus voltage fluctuation during the switching process does not exceed ±5% of the rated value.

[0022] In the preferred embodiment, the control module has a battery health energy management function: when the state of charge of the energy storage battery pack reaches the upper limit of the safe full charge threshold, and the net input power at the DC bus source end is still greater than the total power consumed by the downstream, the MPPT converter actively jumps out of maximum power point tracking and enters the constant voltage power limiting clamping mode, or the control module cuts off excess photovoltaic string arrays to prevent the battery from overcharging; when the state of charge of the energy storage battery pack drops to the lower limit of the safe threshold, the control module limits the discharge power of the battery pack, prioritizes the power supply of the core relay protection device, and avoids the battery from being over-discharged.

[0023] Example 1: Areas with abundant solar resources (independent main power supply mode for solar power and energy storage): This embodiment is applied to the relay protection system of a 110kV photovoltaic power station substation in Northwest China. The local average annual sunshine duration is 3200 hours, with abundant solar resources. The control process is as follows: Figure 4 As shown, the fault switching waveform is as follows: Figure 5 As shown; S1. The status monitoring module samples grid-side voltage, 240V DC bus voltage, photovoltaic array output current, energy storage battery pack charging and discharging current, 10A rated DC load current and battery state of charge data at a high frequency of 1kHz, and sends them to the control module in real time. S2. The control module combines historical sunshine data and real-time photovoltaic output to assess the environmental energy sufficiency and automatically configures it into a photovoltaic and energy storage independent main supply + operation power backup mode, while the original grid operation power enters a zero-output standby state. S3, control module based on Figure 3 The voltage and current dual closed-loop PI control algorithm shown performs constant voltage regulation: when the irradiance is 960W / m², the photovoltaic output power is 2.5kW, meeting the 1.8kW load demand, with the excess 0.7kW used to charge the battery; after 1 second, when the irradiance drops to 500W / m², the photovoltaic output power drops to 1.3kW, and the control module adjusts according to the current balance equation: Calculate the energy storage compensation current to drive the bidirectional DC / DC converter to output 0.5kW power while maintaining the DC bus voltage within the range of 240V±2%. S4, such as Figure 5 As shown, a fault occurred in the photovoltaic-storage system within 1.5 seconds. The control module detected that the bus voltage drop rate exceeded the preset threshold and executed a hardware switching command within 0.0008 seconds, switching on the grid operating power supply. Within 0.1 seconds, a steady-state output current of 10A was reached. After the photovoltaic-storage system returned to normal and operated stably for 4 seconds, the control module executed a smooth back-switch. During the switching process, the bus voltage fluctuation was 3.2%. S5. When the battery state of charge reaches the upper limit threshold of 95%, the MPPT converter exits maximum power point tracking and enters constant voltage power limiting mode; when the battery state of charge drops to the lower limit threshold of 20% at night, it automatically switches to grid operation power supply.

[0024] Example 2: Areas lacking solar resources (independent backup mode for solar power and energy storage): This embodiment is applied to the relay protection system of a 35kV substation in a mountainous area in Southwest China. The local average annual sunshine duration is 1100 hours, and sunlight resources are scarce. The control process is as follows: Figure 4 As shown, the fault switching waveform is as follows: Figure 6 As shown; T1, the status monitoring module samples grid-side voltage, 120V DC bus voltage, photovoltaic array output current, energy storage battery pack charging and discharging current, 10A rated DC load current and battery state of charge data at a high frequency of 1kHz, and sends them to the control module in real time. T2. The control module assesses that the environmental energy sufficiency is insufficient and automatically configures it to the existing operating power supply as the main power supply + independent photovoltaic and energy storage backup mode. Under normal conditions, the grid operating power supply will bear all the load. T3, control module based on Figure 3 The dual closed-loop control algorithm shown is used for adjustment: the output power of the photovoltaic array is used to charge the battery first. After the battery is fully charged, the photovoltaic power directly supplements part of the load; the power difference is dynamically compensated by the bidirectional DC / DC converter to maintain the stability of the DC bus voltage. T4, such as Figure 6 As shown, a grid operation power supply failure occurs at 0.5s. The control module detects that the bus voltage drop rate exceeds the limit and executes a hardware switching command within 0.0009s to activate the photovoltaic-storage system. Within 0.1s, a steady-state output current of 10A is achieved. At the same time, the photovoltaic array continuously generates electricity to replenish the battery, extending the emergency power supply time from the traditional 8 hours to more than 72 hours. After the grid power supply is restored and stabilized for 3 seconds, the control module executes a smooth back-off. T5. When the battery state of charge drops to the lower threshold of 15%, the control module cuts off the power supply to non-core monitoring equipment and prioritizes the power supply to the relay protection device and the circuit breaker trip coil. When the battery state of charge reaches the upper threshold of 90%, the MPPT converter enters standby mode.

[0025] The table below compares two typical application scenarios:

[0026] The two typical embodiments described above fully verify the effectiveness and engineering applicability of the multi-mode adaptive control strategy of this invention. Regardless of whether the region has abundant or scarce solar resources, the system can automatically configure the optimal power supply architecture, achieving dual redundancy power supply. Compared with traditional relay protection operating power supplies, this invention not only solves the industry pain point of protection device loss due to prolonged power outages, but also reduces the system's total lifecycle operating cost through intelligent energy management. All performance indicators meet or exceed power industry standards, and it can be directly applied to the renovation and new construction of relay protection power supply systems in various power plants, substations, and power facilities.

Claims

1. A photovoltaic energy storage DC power supply system for a relay protection power supply system, characterized in that, It includes a photovoltaic array, MPPT converter, energy storage battery pack, bidirectional DC / DC converter, DC / DC converter, condition monitoring module and control module; The output of the photovoltaic array is connected to the input of the MPPT converter; the output of the MPPT converter is connected to the DC bus; the positive and negative terminals of the energy storage battery pack are connected to the low-voltage side port of the bidirectional DC / DC converter; the bidirectional DC / DC converter adopts a non-electrically isolated bidirectional topology and can operate in charging and discharging modes, with the high-voltage side port connected to the DC bus; the input of the DC / DC converter is connected to the DC bus, and the output is connected to the power supply input of the relay protection device and automatic device; The status monitoring module's acquisition terminals are connected to the AC grid side, DC bus, photovoltaic array output terminal, energy storage battery pack, and DC / DC converter output terminal, respectively, while the signal output terminal is connected to the control module's input terminal. The control module's control output terminals are connected to the MPPT converter, bidirectional DC / DC converter, and DC / DC converter control terminal, respectively. The control module enables the photovoltaic energy storage DC power supply system to be connected in parallel with the existing relay protection operating power supply to form a dual redundant power supply architecture without direct electrical interference, and dynamically compensates for the source load supply and demand deficit to maintain a constant DC bus voltage.

2. The photovoltaic energy storage DC power supply system for relay protection power supply system according to claim 1, characterized in that, The system uses the DC bus voltage as the sole indicator of power balance and satisfies the following global power coupling constraint equations under any operating state: ； in, The output power of the existing relay protection operating power supply, For the output power of the photovoltaic array, For energy storage battery packs to absorb or output power, This refers to the total load power of relay protection devices and automatic devices. The equivalent total power loss of the system operation and transformation link is defined in the model as positive for power output and negative for absorption.

3. The photovoltaic energy storage DC power supply system for relay protection power supply system according to claim 2, characterized in that, The dynamic characteristics of the DC bus voltage satisfy the following differential equation: ； in, This is the DC bus voltage. This is the DC bus capacitance value.

4. The photovoltaic energy storage DC power supply system for relay protection power supply system according to claim 1, characterized in that, The control module has an embedded multi-mode power supply priority determiner. Based on historical sunshine data and real-time photovoltaic output prediction, it automatically configures the system into either a photovoltaic and energy storage independent main power supply + operating power backup or an operating power main power supply + photovoltaic and energy storage independent backup mode, thus isolating AC system short circuit and harmonic voltage fluctuation interference.

5. The photovoltaic energy storage DC power supply system for a relay protection power supply system according to any one of claims 1 to 4, characterized in that, The control method of this system includes the following steps: S1. The status monitoring module samples the existing operating power supply side voltage, photovoltaic-storage DC bus voltage, photovoltaic array output current, energy storage battery pack charging and discharging current, DC load output current and battery state of charge data at a frequency of not less than 1kHz, and sends them to the control module. S2. The control module extracts the time-series photovoltaic output characteristics, combines historical sunshine data to evaluate the energy sufficiency of the application scenario environment, adaptively configures the primary and secondary power supply roles in the dual redundancy architecture, and activates the multi-mode collaborative control strategy under the corresponding priority. S3. Calculate the power imbalance based on the dynamic characteristics of the DC bus voltage, generate the target reference command for energy storage charging and discharging, and drive the bidirectional DC / DC converter to maintain the balance of DC bus power supply. S4. The control module calculates the bus voltage drop rate of the current main power supply in real time. When it determines that the power failure occurs due to exceeding the limit, it executes a hardware-level fast redirection and switching command in milliseconds and puts the backup link in the corresponding mode to provide emergency full-load power supply. S5. The control module dynamically adjusts the photovoltaic charging power and the battery charge / discharge depth based on the real-time state of charge of the energy storage battery pack to avoid overcharging and over-discharging of the battery.

6. The photovoltaic energy storage DC power supply system for relay protection power supply system according to claim 5, characterized in that, The specific execution logic of the multi-mode collaborative control strategy in step S2 is as follows: In areas lacking solar resources, the existing operating power supply is used as the main power source, with independent photovoltaic and energy storage backup. Under normal conditions, the total load is mainly borne by the existing power supply. The photovoltaic array's power is first used to charge the energy storage battery bank to maintain the maximum backup capacity. After the battery bank is fully charged, the photovoltaic modules enter standby mode or use redundant power to supplement the load. In the event of a failure of the operating power supply, the operating power supply is immediately cut off and photovoltaic and energy storage power supply is activated. At the same time, the photovoltaic modules continue to generate power to supplement the battery bank, extending the emergency power supply time. In areas with abundant solar resources, the system is locked into a mode of independent main power supply for solar power and energy storage, plus backup operating power: Under normal conditions, the original operating power supply is in a standby emergency state with no output, and the solar power and energy storage system directly serves as the main output; when the solar power and energy storage system equipment fails or the battery is depleted, the operating power supply is switched on in reverse.

7. The photovoltaic energy storage DC power supply system for relay protection power supply system according to claim 5, characterized in that, In step S3, the energy storage control objective satisfies the following current balance equation: ； in, To provide current to the energy storage battery pack For the photovoltaic array output current, The current output by the DC / DC converter to the DC load. This is the system's equivalent loss current.

8. The photovoltaic energy storage DC power supply system for relay protection power supply system according to claim 7, characterized in that, In step S3, the constant voltage regulation of energy storage adopts a voltage and current dual closed-loop PI control algorithm. The specific steps are as follows: Calculate the rated reference setting voltage of the DC bus With real-time sampling bus voltage Deviation values ​​between: ; Deviation The reference current value for the energy storage side is obtained after processing by the voltage loop PI regulator. The voltage loop compensation calculation formula is as follows: ； in, This is the proportional coefficient for the voltage loop control. The integral coefficient for voltage loop control; Reference value of the reference current With real-time sampled energy storage current The comparison yields the current deviation value, which is then processed by the current loop PI regulator, while also incorporating the feedforward current. and The corrected integrated drive signal is used to generate the required PWM duty cycle to trigger the power switch.

9. The photovoltaic energy storage DC power supply system for relay protection power supply system according to claim 5, characterized in that, In step S4, the seamless transient switching between primary and backup power supplies must meet the following hard requirements: When a fault is detected and the backup switching action is initiated, the high-frequency PWM timing latch inside the control module ensures that the backup system outputs a rated operating current of not less than 10A within 0.1s from the start of the action. After the main power supply returns to normal and operates stably for 3-5 seconds, the control module performs a smooth switching operation. During the switching process, the DC bus voltage fluctuation does not exceed ±5% of the rated value.

10. The photovoltaic energy storage DC power supply system for relay protection power supply system according to claim 5, characterized in that, The battery health energy management strategy in step S5 is as follows: When the state of charge of the energy storage battery pack reaches the upper limit of the safe full charge threshold, and the net input power of the DC bus source end is still greater than the total power consumed by the back end, the MPPT converter actively jumps out of maximum power point tracking and enters constant voltage power limiting clamping mode, or the control module cuts off the excess photovoltaic string array until the system experiences a power demand gap again. When the state of charge of the energy storage battery pack drops to the lower safety threshold, the control module limits the discharge power of the battery pack and prioritizes the power supply to the core relay protection device.

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