Low-voltage amplitude limiting control method and system based on optical storage VSG system

Abstract

The invention discloses a low-voltage amplitude limiting control method and system based on an optical storage VSG system, and the method comprises the steps: firstly building a coordination control strategy of a VSG and an energy storage DC / DC converter, and reflecting the difference relation between the output power of an inverter and the power demand of a power grid through the size of a DC bus voltage; if the direct-current bus voltage in the current control period is higher than the normal operation lower limit value of the direct-current bus voltage, a coordination control strategy is adopted; and if the DC bus voltage in the current control period is lower than the normal operation lower limit value of the DC bus voltage and is higher than the threshold value of the low-voltage relay, adding low-voltage amplitude limiting control on the basis of the coordination control strategy. And if the direct-current bus voltage in the current control period continuously drops to be lower than the low-voltage relay threshold value, a low-voltage protection relay needs to be triggered. Low-voltage amplitude limiting control is added on the basis of a basic coordination control strategy, under the condition that the output power of an inverter is smaller than the power requirement of a power grid, it is preferentially considered that a low-voltage relay is prevented from being triggered, and the optical storage VSG system is prevented from being separated from the power grid.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic energy storage control technology, specifically relating to a low-voltage limiting control method and system based on a photovoltaic-energy storage VSG system. Background Technology

[0002] With the dwindling availability of fossil fuels and increasing environmental pollution, humanity is facing an unprecedented crisis. Solar energy, as a new type of green energy, meets the demands of daily life and production and has great development potential, with photovoltaic power generation being the most widely used application.

[0003] Photovoltaic power generation is affected by factors such as temperature and environment, resulting in randomness and intermittency in its output. To ensure the maximum power output from the photovoltaic system, it is necessary to ensure that the system operates at its maximum power point (MPP). The MPPT algorithm is typically used to adjust the operating voltage of the photovoltaic system to operate at its maximum power under different weather conditions.

[0004] Due to the intermittent and fluctuating output characteristics of residential photovoltaic power generation, large-scale grid connection of residential distributed photovoltaic power poses a significant challenge to the stable operation of low-voltage distribution networks. In particular, the impact on the voltage of the distribution network is becoming increasingly prominent. In recent years, with the continuous maturation of energy storage technology and its significant cost reduction, the application of distributed energy storage in improving the voltage quality and renewable energy absorption capacity of low-voltage distribution networks has received widespread attention. Therefore, for the voltage limit exceeding problem caused by high proportion of residential photovoltaic power connected to low-voltage distribution networks, the design and research of voltage control strategies using photovoltaic inverters and distributed energy storage to coordinate voltage is extremely necessary. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems by proposing a low-voltage limiting control method, system, and application based on a photovoltaic-storage VSG system. This invention calculates the additional increment of angular frequency by summing the product of the DC bus voltage low-voltage relay error value and the proportional coefficient 1 and the integral coefficient 1 and the integral value of the DC bus voltage low-voltage relay error value. When the system bus voltage is about to exceed the lower limit, the system bus voltage is controlled to operate stably within the safe range.

[0006] Technical Solution: To achieve the aforementioned objectives, this invention proposes a low-voltage limiting control method and system based on a photovoltaic-storage VSG system.

[0007] The method includes the following steps:

[0008] First, establish a coordinated control strategy between the VSG and the energy storage DC / DC converter;

[0009] Obtain the oscillation equation of the synchronous machine and the equation relating the DC link capacitor voltage to the input and output power;

[0010] By combining the two equations above, the rotational inertia proportionality coefficient of VSG can be derived.

[0011] The output angular frequency change is obtained by multiplying the reciprocal of the proportional coefficient of rotational inertia and the change in DC bus voltage during the current control cycle. The output angular frequency change is then added to the rated angular frequency to obtain the output angular frequency of the inverter.

[0012] Obtain the DC bus voltage for the current control cycle;

[0013] If the DC bus voltage of the current control cycle is higher than the normal operating lower limit of the DC bus voltage, then the inverter output angular frequency is the sum of the rated angular frequency and the change in the output angular frequency.

[0014] If the DC bus voltage of the current control cycle is lower than the normal operating limit of the DC bus voltage, then the DC bus voltage of the current control cycle is compared with the low-voltage relay threshold.

[0015] If the DC bus voltage of the current control cycle is higher than the low-voltage relay threshold, the inverter output angular frequency is the sum of the rated angular frequency, the change in output angular frequency, and the additional increment of angular frequency.

[0016] If the DC bus voltage of the current control cycle is lower than the low-voltage relay threshold, the low-voltage protection relay is triggered.

[0017] Repeat the above steps in each control cycle, and run the entire system while ensuring that the bus voltage is controlled within the lower limit of the bus voltage.

[0018] The change in output angular frequency when the DC bus voltage of the current control cycle is higher than the normal operating lower limit of the DC bus voltage is the quotient of the change in DC bus voltage of the current control cycle and the proportional coefficient of the moment of inertia.

[0019] When the DC bus voltage of the current control cycle is lower than the normal operating lower limit of the DC bus voltage and higher than the low-voltage relay threshold, the change in output angular frequency is the product of the rotational inertia proportional coefficient and the change in DC bus voltage of the current control cycle. The additional increment of angular frequency is the sum of the product of the low-voltage relay error value of the DC bus voltage in the current control cycle and the proportional coefficient 1, and the product of the integral coefficient 1 and the integral value of the low-voltage relay error value of the DC bus voltage mentioned above.

[0020] The proportional coefficient 1 and integral coefficient 1 are set to fixed values. The normal reference error value of the DC bus voltage is the difference between the DC bus voltage in the current control cycle and the normal operating lower limit value of the DC bus voltage. The error value of the DC bus voltage low-voltage relay is the difference between the DC bus voltage in the current control cycle and the low-voltage relay threshold value.

[0021] The determined normal reference error value for DC bus voltage is ,in, This is the DC bus voltage value for the current control cycle. This is the lower limit of normal operation for the DC bus voltage; the error value of the DC bus voltage low-voltage relay is... ,in, This is the DC bus voltage value for the current control cycle. This represents the lower limit of normal operation of the DC bus voltage; the change in output angular frequency is... ,in This is the normal reference error value for the DC bus voltage in the current control cycle. The moment of inertia proportionality coefficient; the additional increment of angular frequency is ,in , The proportional coefficient is 1 and the integral coefficient is 1, respectively. The DC bus voltage is the low-voltage relay error value; the inverter output angular frequency for the current control cycle is... ,in The rated angular frequency, This represents the change in angular frequency output during the previous control cycle. Add an increment to the angular frequency of the previous control cycle;

[0022] The system specifies a lower limit for normal operation of the DC bus voltage and a threshold for the low-voltage relay. If the energy storage is under normal operating conditions, the bus voltage will be controlled above the lower limit for normal operation while the photovoltaic system tracks the maximum power point, combined with the charging and discharging function of the energy storage. If the energy storage is under extreme operating conditions and can no longer discharge, and continuing to track the maximum power point cannot guarantee that the output power can meet the grid's needs, and the bus voltage is lower than the lower limit for normal operation of the DC bus voltage, then the low-voltage protection relay will be avoided, allowing the system to continue outputting power to the grid.

[0023] Compare the relationship between the DC bus voltage and the normal operating lower limit of the DC bus voltage and the low-voltage relay threshold.

[0024] A low-voltage limiting control system based on a photovoltaic-storage VSG system includes the following modules:

[0025] The real-time voltage acquisition module is configured to acquire the bus voltage of the current control cycle;

[0026] The DC bus voltage normal reference error value acquisition module is configured to acquire the DC bus voltage normal reference error value for the current control cycle.

[0027] The DC bus voltage low-voltage relay error value acquisition module is configured to acquire the DC bus voltage low-voltage relay error value for the current control cycle.

[0028] The addition module is configured to add the product of the DC bus voltage low-voltage relay error value and the proportional coefficient 1 in the current control cycle to the product of the integral coefficient 1 and the integral value of the DC bus voltage low-voltage relay error value.

[0029] The addition module is configured to add the rated angular frequency, the change in output angular frequency, and the additional increment of angular frequency.

[0030] The division module is configured to divide the change in DC bus voltage and the proportionality coefficient of rotational inertia in the current control cycle.

[0031] The integration module is configured to integrate the DC bus voltage low-voltage relay error value over time for the current control cycle;

[0032] The comparison module is configured to compare the angular frequency of the current control cycle with an increment added to 0;

[0033] The comparison module is configured to compare the angular frequency of the current control cycle with the rated angular frequency plus an increment.

[0034] The iterative control module is configured to limit the angular frequency increment of the current control cycle to 0 if the angular frequency increment of the current control cycle is greater than 0, and to proceed to the next comparison stage if the angular frequency increment of the current control cycle is less than 0.

[0035] The iterative control module is configured such that if the angular frequency increment of the current control cycle is greater than the rated angular frequency, the angular frequency increment of the current control cycle remains unchanged; if the angular frequency increment of the current control cycle is less than the rated angular frequency, the angular frequency increment of the current control cycle is limited to the rated angular frequency.

[0036] The iterative control module also includes a module for calculating the additional angular frequency increment, which is configured to calculate the additional angular frequency increment based on the sum of the product of the DC bus voltage low-voltage relay error value and the proportional coefficient 1 and the integral coefficient 1 and the integral value of the DC bus voltage low-voltage relay error value.

[0037] It includes a computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the steps described in the low-voltage limiting control method based on an optical storage VSG system.

[0038] The invention includes an electronic device comprising a memory and a processor, and computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the steps in the method described in the low-voltage limiting control method based on a photoelectric storage VSG system.

[0039] The invention includes a photovoltaic system employing steps in a low-voltage limiting control method based on a photovoltaic-storage VSG system, comprising a low-voltage limiting control system or a readable storage medium or electronic device based on a photovoltaic-storage VSG system.

[0040] Beneficial effects:

[0041] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0042] Photovoltaic power generation is characterized by intermittent and fluctuating output. Large-scale grid-connected residential distributed photovoltaic systems pose significant challenges to the stable operation of low-voltage distribution networks, particularly affecting the voltage. To maintain the bus voltage of the photovoltaic-storage system within a safe range, energy storage is required to participate in bus voltage control. Conventional constant voltage control technologies for energy storage, when operating under extreme conditions, may damage the energy storage and cause the bus voltage to exceed the lower limit for safe operation. Therefore, this invention specifies a lower limit for normal DC bus voltage operation and a low-voltage relay threshold. If the energy storage is operating normally, it prioritizes tracking the photovoltaic maximum power point; if it is operating under extreme conditions, it prioritizes controlling the bus voltage above the low-voltage relay threshold.

[0043] This invention solves the problem of bus voltage exceeding limits when energy storage is under extreme operating conditions, thereby effectively maintaining the stable operation of the system. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0045] Figure 1 This is a system structure diagram of the low-voltage limiting control method based on a photovoltaic energy storage system according to the present invention.

[0046] Figure 2 This is a flowchart of the low-voltage limiting control method based on a photovoltaic energy storage system according to the present invention.

[0047] Figure 3 This is the PU characteristic curve of the photovoltaic array provided in the low-voltage limiting control method based on the photovoltaic-storage VSG system of the present invention.

[0048] Figure 4 This is a simulation waveform of the maximum power point tracking method of the low-voltage limiting control method based on the photovoltaic-storage VSG system of the present invention.

[0049] Figure 5 This is a simulated waveform of the bus voltage under extreme operating conditions of the energy storage system based on the low-voltage limiting control method of the photovoltaic-storage VSG system of this invention. Detailed Implementation

[0050] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0051] like Figure 1 The diagram illustrates the system structure of a high-voltage limiting control method based on a photovoltaic energy storage system according to the present invention. It mainly includes a photovoltaic array, an energy storage device, a sampling module, an MPPT control module, a PWM drive module, a DC / DC module connected to the photovoltaic array, a DC / DC module connected to the energy storage, a DC / AC module, a DC link capacitor, and a power grid. The output of the MPPT control module is connected to the input of the PWM drive module; the output of the PWM drive module is connected to the control signal input of the DC / DC module; the output of the DC / DC module connected to the photovoltaic array is connected to the DC link capacitor; the output of the energy storage device is connected to the input of the DC / DC module; the output of the DC / DC module connected to the energy storage is connected to the DC link capacitor; the input of the voltage acquisition module is connected to the DC link capacitor; its output is connected to the VSG module; the VSG module is connected to the input of the PWM drive module; the output of the PWM drive module is connected to the input of the DC / AC module; and the DC / AC output is connected to the power grid module.

[0052] The PWM module consists of two modules: one PWM module is connected to the output of the MPPT control module, transmitting the control signals from the MPPT control module to the DC / DC module connected to the photovoltaic array; the other PWM module is connected to the output of the VSG module, transmitting the control signals from the VSG module to the DC / AC module.

[0053] Photovoltaic power generation is characterized by intermittent and fluctuating output. Large-scale grid-connected residential distributed photovoltaic systems pose significant challenges to the stable operation of low-voltage distribution networks, particularly affecting the voltage. To maintain the bus voltage of the photovoltaic-storage system within a safe range, energy storage is required to participate in bus voltage control. Conventional constant voltage control technologies for energy storage, when operating under extreme conditions, may damage the energy storage and cause the bus voltage to exceed the lower limit for safe operation. Therefore, this invention specifies a lower limit for normal DC bus voltage operation and a low-voltage relay threshold. If the energy storage is operating normally, it prioritizes tracking the photovoltaic maximum power point; if it is operating under extreme conditions, it prioritizes controlling the bus voltage above the low-voltage relay threshold.

[0054] like Figure 2 , Figure 3 , Figure 4 , Figure 5 As shown, the present invention provides a low-voltage limiting control method based on a photovoltaic-storage VSG system. Based on the coordinated control strategy of the VSG and the energy storage DC / DC converter, an additional angular frequency increment is introduced according to the relationship between the DC bus voltage and the low-voltage relay threshold. The method determines whether to introduce the additional angular frequency increment by comparing the DC bus voltage with the normal operating lower limit of the DC bus voltage. This ensures that the DC bus voltage of the photovoltaic-storage VSG system can continue to transmit power to the grid even at a low level, and minimizes the triggering of the low-voltage relay.

[0055] This method includes the following specific steps:

[0056] Step S1: Obtain the oscillation equation of the synchronizing machine: The equation relating DC link capacitor voltage to input and output power is as follows: .

[0057] Step S2: Solve the two equations simultaneously to derive the proportionality coefficient of the VSG's moment of inertia. : .

[0058] Step S3: Adjust the rotational inertia proportionality coefficient The reciprocal of the current control cycle and the change in DC bus voltage. Multiplying them together yields the change in output angular frequency. ,Right now The change in output angular frequency is compared with the rated angular frequency. The output angular frequency of the inverter is obtained by adding them together. ,Right now Next, proceed to step S4.

[0059] Step S4: Obtain the DC bus voltage for the current control cycle. ;

[0060] Step S5: If the DC bus voltage of the current control cycle is higher than the normal operating lower limit of the DC bus voltage. Then the inverter output angular frequency is the sum of the rated angular frequency and the change in output angular frequency. Otherwise, proceed to step S6.

[0061] Step S6: If the DC bus voltage of the current control cycle is lower than the normal operating limit of the DC bus voltage. Then, the DC bus voltage of the current control cycle is compared with the low-voltage relay threshold; and the process proceeds to step S7.

[0062] Step S7: If the DC bus voltage of the current control cycle is higher than the low-voltage relay threshold... The inverter output angular frequency is the sum of the rated angular frequency, the change in output angular frequency, and the additional increment of angular frequency. Then proceed to step S8.

[0063] Step S8: If the DC bus voltage of the current control cycle is lower than the low-voltage relay threshold, the low-voltage protection relay is triggered.

[0064] Step S9: Update Udc(k-1) by setting Udc(k-1) = Udc(k).

[0065] Example 1:

[0066] A composite MPPT control model of the photovoltaic array Boost circuit was built in the Matlab / Simulink environment. The simulation parameters of the photovoltaic array are set as follows:

[0067] Parameter name Parameter value Short-circuit current Isc 313.6A Open circuit voltage Uoc 363V Maximum power point current Impp 294A Maximum power point voltage Umpp 290V Irradiance 1000W / m2 temperature 25℃

[0068] A high-voltage limiting control model for the DC / DC module of an energy storage device was built using Matlab / Simulink. The simulation parameters for the energy storage device are set as shown in the table below:

[0069] Parameter name Parameter value Rated voltage 500V Rated capacity 400Ah Initial capacity state 80% Battery response time 30s

[0070] The simulation was conducted at a temperature of 25℃ and a light intensity of 1000 W / m². The operating condition was set so that the energy storage device reached its limit condition and disconnected from the system after 1 second. The characteristic curve of the photovoltaic array is shown below. Figure 3 As shown, under the simulation conditions in this case, the maximum power point voltage Umpp = 460.8V and the maximum power point power Pmpp = 36080.6W.

[0071] In the simulation of the high-voltage limiting control method based on a photovoltaic energy storage system proposed in this invention, the lower limit of normal operation of the DC bus voltage and the low-voltage relay threshold are first determined, and then the proportional coefficient Kp1 and integral coefficient Ki1 are determined. The simulation output diagram using the low-voltage limiting control method of the bus voltage proposed in this invention is shown below. Figure 4 and Figure 5 As shown, within 0 to 1 second, the power demand of the grid is 35 kW, and the power generated by the photovoltaic system can meet the power demand, and the DC bus voltage is stable at 750 V. Within 1 to 2 seconds, the power demand of the grid increases to 155 kW. At this time, the power generated by the photovoltaic system and energy storage is 42 kW, which cannot meet the power demand, and the bus voltage drops. After algorithm control, it stabilizes at around the low-voltage relay threshold in about 0.1 seconds to prevent the bus voltage from dropping further.

[0072] The table below shows the simulation results of the low-voltage limiting control technology based on the photovoltaic-storage VSG system. It can be seen that the low-voltage limiting control technology based on the photovoltaic-storage VSG system proposed in this invention has a short control time and small oscillation after reaching steady state.

[0073] plan Time required to reach steady state / s Steady-state DC bus voltage / V Improved 0.1 700

[0074] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-voltage limiting control method based on a photovoltaic-storage VSG system, characterized by: The method includes the following steps: First, establish a coordinated control strategy between the VSG and the energy storage DC / DC converter; Obtain the oscillation equation of the synchronous machine and the equation relating the DC link capacitor voltage to the input and output power; By combining the two equations above, the rotational inertia proportionality coefficient of VSG can be derived. The output angular frequency change is obtained by multiplying the reciprocal of the proportional coefficient of rotational inertia and the change in DC bus voltage during the current control cycle. The output angular frequency change is then added to the rated angular frequency to obtain the output angular frequency of the inverter. Obtain the DC bus voltage for the current control cycle; If the DC bus voltage of the current control cycle is higher than the normal operating lower limit of the DC bus voltage, then the inverter output angular frequency is the sum of the rated angular frequency and the change in the output angular frequency. If the DC bus voltage of the current control cycle is lower than the normal operating limit of the DC bus voltage, then the DC bus voltage of the current control cycle is compared with the low-voltage relay threshold. If the DC bus voltage of the current control cycle is higher than the low-voltage relay threshold, the inverter output angular frequency is the sum of the rated angular frequency, the change in output angular frequency, and the additional increment of angular frequency. If the DC bus voltage of the current control cycle is lower than the low-voltage relay threshold, the low-voltage protection relay is triggered. Repeat the above steps in each control cycle, and run the entire system while ensuring that the bus voltage is controlled within the lower limit of the bus voltage. The change in output angular frequency when the DC bus voltage of the current control cycle is higher than the normal operating lower limit of the DC bus voltage is the quotient of the change in DC bus voltage of the current control cycle and the proportional coefficient of the moment of inertia. When the DC bus voltage of the current control cycle is lower than the normal operating lower limit of the DC bus voltage and higher than the low-voltage relay threshold, the change in output angular frequency is the product of the rotational inertia proportional coefficient and the change in DC bus voltage of the current control cycle. The additional increment of angular frequency is the sum of the product of the low-voltage relay error value of the DC bus voltage in the current control cycle and the proportional coefficient 1, and the product of the integral coefficient 1 and the integral value of the low-voltage relay error value of the DC bus voltage mentioned above. The proportional coefficient 1 and integral coefficient 1 are set to fixed values. The normal reference error value of the DC bus voltage is the difference between the DC bus voltage in the current control cycle and the normal operating lower limit value of the DC bus voltage. The error value of the DC bus voltage low-voltage relay is the difference between the DC bus voltage in the current control cycle and the low-voltage relay threshold value. The determined normal reference error value for DC bus voltage is ,in, This is the DC bus voltage value for the current control cycle. This is the lower limit of normal operation for the DC bus voltage; the error value of the DC bus voltage low-voltage relay is... ,in, This is the DC bus voltage value for the current control cycle. This represents the lower limit of normal operation of the DC bus voltage; the change in output angular frequency is... ,in This is the normal reference error value for the DC bus voltage in the current control cycle. The moment of inertia proportionality coefficient; the additional increment of angular frequency is ,in , The proportional coefficient is 1 and the integral coefficient is 1, respectively. The DC bus voltage is the low-voltage relay error value; the inverter output angular frequency for the current control cycle is... ,in The rated angular frequency, This represents the change in angular frequency output during the previous control cycle. Add an increment to the angular frequency of the previous control cycle; The system specifies a lower limit for normal operation of the DC bus voltage and a threshold for the low-voltage relay. If the energy storage is under normal operating conditions, the bus voltage will be controlled above the lower limit for normal operation while the photovoltaic system tracks the maximum power point, combined with the charging and discharging function of the energy storage. If the energy storage is under extreme operating conditions and can no longer discharge, and continuing to track the maximum power point cannot guarantee that the output power can meet the grid's needs, and the bus voltage is lower than the lower limit for normal operation of the DC bus voltage, then the low-voltage protection relay will be avoided, allowing the system to continue outputting power to the grid.

2. The low-voltage limiting control method based on a photovoltaic-storage VSG system according to claim 1, characterized in that, Compare the relationship between the DC bus voltage and the normal operating lower limit of the DC bus voltage and the low-voltage relay threshold.

3. A low-voltage limiting control system based on a photovoltaic-storage VSG system, characterized in that, Includes the following modules, The real-time voltage acquisition module is configured to acquire the bus voltage of the current control cycle; The DC bus voltage normal reference error value acquisition module is configured to acquire the DC bus voltage normal reference error value for the current control cycle. The DC bus voltage low-voltage relay error value acquisition module is configured to acquire the DC bus voltage low-voltage relay error value for the current control cycle. The addition module is configured to add the product of the DC bus voltage low-voltage relay error value and the proportional coefficient 1 in the current control cycle to the product of the integral coefficient 1 and the integral value of the DC bus voltage low-voltage relay error value. The addition module is configured to add the rated angular frequency, the change in output angular frequency, and the additional increment of angular frequency. The division module is configured to divide the change in DC bus voltage and the proportionality coefficient of rotational inertia in the current control cycle. The integration module is configured to integrate the DC bus voltage low-voltage relay error value over time for the current control cycle; The comparison module is configured to compare the angular frequency of the current control cycle with an increment added to 0; The comparison module is configured to compare the angular frequency of the current control cycle with the rated angular frequency plus an increment. The iterative control module is configured to limit the angular frequency increment of the current control cycle to 0 if the angular frequency increment of the current control cycle is greater than 0, and to proceed to the next comparison stage if the angular frequency increment of the current control cycle is less than 0. The iterative control module is configured such that if the angular frequency increment of the current control cycle is greater than the rated angular frequency, the angular frequency increment of the current control cycle remains unchanged; if the angular frequency increment of the current control cycle is less than the rated angular frequency, the angular frequency increment of the current control cycle is limited to the rated angular frequency.

4. A low-voltage limiting control system based on a photovoltaic-storage VSG system according to claim 3, characterized in that, The iterative control module also includes a module for calculating the additional angular frequency increment, which is configured to calculate and determine the additional angular frequency increment based on the sum of the product of the DC bus voltage low-voltage relay error value and the proportional coefficient 1 and the integral coefficient 1 and the integral value of the DC bus voltage low-voltage relay error value.

5. A low-voltage limiting control system based on a photovoltaic-storage VSG system according to claim 3, characterized in that, The invention includes a computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the steps of the method according to any one of claims 1-2.

6. A low-voltage limiting control system based on a photovoltaic-storage VSG system according to claim 3, characterized in that, The invention includes an electronic device comprising a memory and a processor, and computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the steps of the method according to any one of claims 1-2.

7. A low-voltage limiting control system based on a photovoltaic-storage VSG system according to claim 3, characterized in that, The invention includes a photovoltaic system employing the steps of the method according to any one of claims 1-2, comprising the control system according to claim 3 or 4, the readable storage medium according to claim 5, or the electronic device according to claim 6.

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