Inertia control method and device for direct current side of photovoltaic storage direct current flexible participation in power grid frequency modulation

Abstract

Embodiments of the present disclosure provide a DC side inertia control method and device for power grid frequency modulation of a photovoltaic energy storage DC flexible participation power system. The method comprises: obtaining an operating state of the photovoltaic energy storage DC flexible participation power system and a state of charge of an energy storage unit, and collecting a DC bus voltage and an energy storage unit current; performing voltage recovery control, virtual inertia control and DC bus voltage control to determine a DC bus current reference value; determining an energy storage unit current reference value and an AC power grid current reference value; performing DC bus current control according to the energy storage unit current and the energy storage unit current reference value to control output power of an energy storage unit converter; and performing feedforward decoupling control according to the AC power grid current reference value to control output power of an AC power grid converter. In this way, inertia power can be provided for the photovoltaic energy storage DC flexible participation power system, DC voltage fluctuation can be reduced, and frequency modulation disturbance can be suppressed.

Description

Technical Field

[0001] The embodiments disclosed herein generally relate to the field of power distribution networks, and more specifically, to a method and apparatus for DC-side inertia control in which photovoltaic, energy storage, DC and flexible photovoltaic systems participate in power grid frequency regulation. Background Technology

[0002] To improve the absorption capacity of new energy power generation, traditional power systems must be upgraded and transformed, leading to the concept of DC distribution networks. In a DC distribution network, power generation equipment is directly connected to the DC bus via DC / DC converters, saving on converter construction costs and facilitating capacity expansion for new energy power generation equipment. During power transmission, the DC distribution network only transmits active power, allowing direct connection to DC equipment such as DC-driven appliances, electric vehicle charging stations, and large data centers, reducing the complexity of power consumption. A DC distribution network encompassing new energy photovoltaic power generation equipment, energy storage equipment, DC loads, and AC flexible loads can be called a photovoltaic-storage-DC-flexible distribution system. This system is connected to the AC grid via DC / AC converters. For the power grid, the entire photovoltaic-storage-DC-flexible distribution system alters the traditional power balance relationship between the supply and load sides. The system can adjust the power it draws from the grid within a wider range based on the grid's supply and demand. From the grid's perspective, the system becomes a flexible load, allowing each device within the system to adjust its power consumption according to the grid's supply and demand.

[0003] The photovoltaic-storage-DC-flexible power distribution system needs to actively participate in the frequency regulation of the AC power grid. The renewable energy generation equipment is the main power generation equipment in this system. The converter connected to the DC bus is a static device with relatively low inherent inertia. This results in poor ability to mitigate disturbances through inertial power. In this case, the flexibility of energy storage unit capacity configuration can be utilized to provide virtual inertia to the AC power grid through a reasonable control strategy, increasing the grid's inertia and mitigating power imbalances caused by disturbances. Simultaneously, some load units in the DC distribution network can actively change their power consumption to balance the disturbance power, improving the stability of the AC power grid frequency. Generally, power sources with variable output power can provide virtual inertia through additional virtual inertia control strategies. However, the control strategy for energy storage unit converters lacks flexibility, does not consider the coordination between the energy storage unit and the AC power grid in providing virtual inertia power, and ignores the actual state of the energy storage unit when providing virtual inertia power, making it less friendly to the charging and discharging of the energy storage equipment and potentially leading to overcharging and over-discharging problems. Therefore, research on the virtual inertial control strategy of photovoltaic-storage-DC-flexible power distribution system and the auxiliary frequency regulation control strategy of the system on the AC power grid has important academic and practical application value. Summary of the Invention

[0004] According to embodiments of this disclosure, a method, apparatus, electronic device, and computer-readable storage medium for DC-side inertia control of photovoltaic-storage-DC-flexible grid frequency regulation are provided.

[0005] In a first aspect of this disclosure, a method for DC-side inertia control in a photovoltaic-storage-DC-flexible grid frequency regulation system is provided. The method includes:

[0006] Acquire the operating status of the photovoltaic-storage-DC-flexible power distribution system and the state of charge of the energy storage units, and collect the DC bus voltage and energy storage unit current;

[0007] Based on the DC bus voltage and the preset DC bus voltage reference value, voltage recovery control, virtual inertia control, and DC bus voltage control are performed to determine the DC bus current reference value.

[0008] Based on the operating status of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage unit, and the reference value of the DC bus current, the reference value of the current of the energy storage unit and the reference value of the current of the AC power grid are determined.

[0009] Based on the current of the energy storage unit and the current reference value of the energy storage unit, DC bus current control is performed to control the output power of the energy storage unit converter.

[0010] Based on the current reference value of the AC power grid, feedforward decoupling control is performed to control the output power of the AC power grid converter.

[0011] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein the step of performing voltage recovery control, virtual inertia control, and DC bus voltage control based on the DC bus voltage and a preset DC bus voltage reference value, and determining a DC bus current reference value, includes:

[0012] Based on the DC bus voltage and the preset DC bus voltage reference value, a voltage restorer is used for voltage recovery control to determine the given value of the DC side current;

[0013] The output current at the load grid connection point is collected, and virtual inertial control is performed based on the given value of the DC side current, the reference value of the DC bus voltage, and the output current at the load grid connection point to determine the reference value of the DC bus voltage.

[0014] Based on the DC bus voltage and the DC bus voltage reference value, a DC bus voltage controller is used to control the DC bus voltage and determine the DC bus current reference value.

[0015] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein determining the current reference value of the energy storage unit and the current reference value of the AC power grid based on the operating state of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage unit, and the DC bus current reference value includes:

[0016] Based on the state of charge of the energy storage unit, determine the upper limit value of the state of charge, the lower limit value of the state of charge, and the current state of charge value of the energy storage unit;

[0017] The allocation factor of the reference current is determined based on the upper limit of the state of charge of the energy storage unit, the lower limit of the state of charge, and the current state of charge.

[0018] Determine whether the DC bus current reference value is equal to 0; if yes, set both the current reference value of the energy storage unit and the current reference value of the AC grid to 0; if no, determine the current reference value of the energy storage unit and the current reference value of the AC grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system and the allocation factor of the reference current.

[0019] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein the control of the DC bus current based on the energy storage unit current and the current reference value of the energy storage unit to control the output power of the energy storage unit converter includes:

[0020] DC bus current control is performed using a DC bus current controller based on the current of the energy storage unit and the current reference value of the energy storage unit.

[0021] The difference between the energy storage unit voltage and the output of the DC bus current controller is obtained, and the ratio of the difference to the DC bus voltage is used as the duty cycle signal.

[0022] The duty cycle signal is input into the PWM generator to generate a PWM switching signal, which is then used to control the output power of the energy storage unit converter.

[0023] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein the step of performing feedforward decoupling control based on the current reference value of the AC grid to control the output power of the AC grid converter includes:

[0024] The current reference value of the AC power grid is transformed by dq to obtain the d-axis component and q-axis component of the current reference value of the AC power grid.

[0025] Based on the d-axis and q-axis components of the current reference value of the AC power grid, feedforward decoupling control is performed to determine the d-axis control signal and the q-axis control signal.

[0026] The d-axis control signal and the q-axis control signal are subjected to dq inverse transformation to obtain the SPWM modulation signal. The AC grid converter switching signal is generated by the SPWM generator and the output power of the AC grid converter is controlled by the AC grid converter switching signal.

[0027] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein determining the current reference value of the energy storage unit and the current reference value of the AC power grid based on the operating state of the photovoltaic-storage-DC-flexible power distribution system and the allocation factor of the reference current includes:

[0028] If the photovoltaic-storage-DC-flexible power distribution system is in grid-connected operation, then the current reference value of the energy storage unit and the current reference value of the AC grid are determined according to the allocation factor of the reference current and the reference value of the DC bus current.

[0029] If the photovoltaic-storage-DC-flexible power distribution system is in off-grid operation, then determine whether the DC bus current reference value is greater than 0; if yes, then set the current reference value of the energy storage unit to equal the DC bus current reference value, and the current reference value of the AC grid to 0; if no, then determine whether the allocation factor of the reference current is less than the preset reference current allocation factor threshold.

[0030] If the allocation factor of the reference current is less than the preset threshold of the allocation factor of the reference current, then the current reference value of the energy storage unit is made equal to the DC bus current reference value, and the current reference value of the AC grid is 0.

[0031] If the allocation factor of the reference current is not less than the preset allocation factor threshold of the reference current, then the photovoltaic system is controlled to operate in non-MPPT mode.

[0032] In addition to the aspects described above and any possible implementations, a further implementation is provided, wherein determining the current reference value of the energy storage unit and the current reference value of the AC grid based on the allocation factor of the reference current and the DC bus current reference value includes:

[0033] Determine whether the DC bus current reference value is greater than 0;

[0034] If so, then the current reference value of the AC grid is equal to the product of 1 minus the allocation factor of the reference current and the DC bus current reference value, and the current reference value of the energy storage unit is equal to the product of the DC bus current reference value and the allocation factor of the reference current.

[0035] If not, then the current reference value of the AC grid is equal to the product of the DC bus current reference value and the allocation factor of the reference current, and the current reference value of the energy storage unit is equal to the product of 1 minus the allocation factor of the reference current and the DC bus current reference value.

[0036] In a second aspect of this disclosure, a DC-side inertia control device for photovoltaic-storage-DC-flexible grid frequency regulation is provided. The device includes: a data acquisition module, a reference current control module, an energy storage unit converter control module, and an AC grid converter control module.

[0037] The data acquisition module is used to acquire the operating status of the photovoltaic-storage-DC-flexible power distribution system and the state of charge of the energy storage units, and to collect the DC bus voltage and the energy storage unit current.

[0038] The reference current control module is used to perform voltage recovery control, virtual inertia control, and DC bus voltage control based on the DC bus voltage and a preset DC bus voltage reference value, and to determine the DC bus current reference value; it is also used to determine the current reference value of the energy storage unit and the current reference value of the AC grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage unit, and the DC bus current reference value.

[0039] The energy storage unit converter control module is used to control the DC bus current based on the energy storage unit current and the current reference value of the energy storage unit, thereby controlling the output power of the energy storage unit converter.

[0040] The AC grid converter control module is used to perform feedforward decoupling control based on the current reference value of the AC grid, thereby controlling the output power of the AC grid converter.

[0041] In a third aspect of this disclosure, an electronic device is provided. The electronic device includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the program to implement the method described above.

[0042] In a fourth aspect of this disclosure, a computer-readable storage medium is provided having a computer program stored thereon that, when executed by a processor, implements the methods as described in the first and / or second aspects of this disclosure.

[0043] The beneficial effects of this disclosure are as follows:

[0044] This disclosure allows for flexible determination of the reference current allocation factor based on the state of charge of the energy storage unit, enabling unified management of the current flowing from the energy storage unit and the AC grid to the DC bus. By reallocating the respective reference currents according to the allocation factor, the converters of the energy storage unit and the AC grid operate under their respective reference currents. This rationally allocates the output power of the energy storage unit and the AC grid based on the actual operating state of the photovoltaic-storage-DC-flexible power distribution system, avoiding overcharging and over-discharging of the energy storage unit and making the charging and discharging process more user-friendly. Furthermore, by introducing virtual inertial control during the coordination between the energy storage unit and the AC grid, this disclosure enhances the system inertia of the AC grid, reducing DC bus voltage fluctuations caused by AC grid disturbances and smoothing frequency disturbances in the AC system. This enables the photovoltaic-storage-DC-flexible system to participate in AC grid auxiliary frequency regulation.

[0045] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of this disclosure, nor is it intended to restrict the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0046] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. In the drawings, the same or similar reference numerals denote the same or similar elements, wherein:

[0047] Figure 1 A flowchart is shown of a DC-side inertia control method for photovoltaic-storage-DC-flexible grid frequency regulation according to an embodiment of the present disclosure;

[0048] Figure 2 A control structure diagram for generating a DC bus reference current according to an embodiment of the present disclosure is shown;

[0049] Figure 3 A schematic diagram illustrating the process of determining the current reference value of the energy storage unit and the current reference value of the AC power grid according to an embodiment of the present disclosure is shown.

[0050] Figure 4 A control structure diagram of an energy storage unit converter according to an embodiment of the present disclosure is shown;

[0051] Figure 5 A control structure diagram of an AC grid converter according to an embodiment of the present disclosure is shown;

[0052] Figure 6 A topology diagram of a photovoltaic-storage-DC-flexible power distribution system according to an embodiment of the present disclosure is shown;

[0053] Figure 7 The output power and load power curves of a photovoltaic array in Example 1 according to an embodiment of the present disclosure are shown;

[0054] Figure 8 A DC bus voltage curve is shown in Example 1, an embodiment of the present disclosure;

[0055] Figure 9 The output power and load power curves of a photovoltaic array in Example 2 according to an embodiment of the present disclosure are shown;

[0056] Figure 10 A DC bus voltage curve is shown in Example 2 according to an embodiment of the present disclosure;

[0057] Figure 11 The output power and load power curves of a photovoltaic array in Example 3 according to an embodiment of the present disclosure are shown;

[0058] Figure 12 The output power curves of the battery pack, AC grid, and photovoltaic array at SOC = 65% are shown in Example 3 of an embodiment of the present disclosure.

[0059] Figure 13 The output power curves of the battery pack, AC grid, and photovoltaic array at SOC = 35% are shown in Example 3 of an embodiment of the present disclosure.

[0060] Figure 14 The output power and load power curves of a photovoltaic array in Example 4 according to an embodiment of the present disclosure are shown;

[0061] Figure 15 The output power curves of the battery pack, AC grid, and photovoltaic array at SOC = 65% are shown in Example 4 of an embodiment of the present disclosure.

[0062] Figure 16 The output power curves of the battery pack, AC grid, and photovoltaic array are shown in Example 4 of an embodiment of the present disclosure when SOC = 35%.

[0063] Figure 17 The AC power grid frequency response curves under different disturbance conditions are shown in Example 5, an embodiment of the present disclosure.

[0064] Figure 18 A schematic diagram of the structure of a DC-side inertia control device for photovoltaic-storage-DC-flexible grid frequency regulation according to an embodiment of the present disclosure is shown.

[0065] Figure 19 A block diagram of an exemplary electronic device according to an embodiment of the present disclosure is shown. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0067] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0068] In this disclosure, a reference value for the DC bus current is determined based on the measured DC bus voltage and a preset DC bus voltage reference value. A distribution factor for the reference current is calculated based on the current state of charge of the energy storage unit and the operating status of the photovoltaic-storage-DC-flexible power distribution system, thereby determining the reference current values ​​for the energy storage unit and the AC grid. Inverter control of the energy storage unit is implemented based on its current reference value, and AC grid converter control is implemented based on the AC grid current reference value. This disclosure can provide inertial power to the photovoltaic-storage-DC-flexible power distribution system, thereby reducing DC bus voltage fluctuations and smoothing AC system frequency fluctuations.

[0069] Figure 1 A flowchart of a DC-side inertia control method 100 for photovoltaic-storage-DC-flexible grid frequency regulation according to an embodiment of the present disclosure is shown.

[0070] In box 110, the operating status of the photovoltaic-storage-DC-flexible power distribution system and the state of charge of the energy storage units are acquired, and the DC bus voltage u is collected. dc and energy storage unit current i b In some embodiments, it is also necessary to collect the AC grid current i. g Output current i at the load grid connection point out .

[0071] In box 120, according to the DC bus voltage u dc and the preset DC bus voltage reference value u dcn Voltage recovery control, virtual inertia control, and DC bus voltage control are performed to determine the reference value of DC bus current.

[0072] like Figure 2 As shown, the step based on the DC bus voltage u dc and the preset DC bus voltage reference value u dcnThis involves performing voltage recovery control, virtual inertia control, and DC bus voltage control to determine the DC bus current reference value, including:

[0073] According to the DC bus voltage u dc and the preset DC bus voltage reference value u dcn ,use Figure 2 The voltage restorer shown performs voltage recovery control to determine the given value i of the DC side current. set .

[0074] The transfer function of the voltage restorer is G. rc (s)=k prc +k irc / s;

[0075] Where, k prc k represents the proportional coefficient of the voltage restorer. irc represents the integral coefficient of the voltage restorer, and s represents the Laplace operator.

[0076] Collect the output current i at the load grid connection point out According to the given value i of the DC side current set The DC bus voltage reference value u dcn The output current i at the point where the load is connected to the grid out , proceed as Figure 2 The virtual inertial control shown determines the DC bus voltage reference value. Virtual damping D is used in the virtual inertial control process. v and virtual capacitance C v .

[0077] According to the DC bus voltage u dc and the DC bus voltage reference value After subtracting the two values, a DC bus voltage controller is used for... Figure 2 The DC bus voltage control shown determines the DC bus current reference value.

[0078] The transfer function of the DC bus voltage controller is: G dc (s)=k pdc +k idc / s.

[0079] Where, k pdc k represents the proportional gain of the DC bus voltage controller. idc represents the integral coefficient of the DC bus voltage controller, and s represents the Laplace operator.

[0080] In box 130, based on the operating status of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage unit, and the reference value of the DC bus current... Determine the current reference value for the energy storage unit Reference value of current in AC power grid

[0081] like Figure 3 As shown, the operation status of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage unit, and the reference value of the DC bus current are all considered. Determine the current reference value for the energy storage unit Reference value of current in AC power grid include:

[0082] Based on the state of charge of the energy storage unit, determine the upper limit of the state of charge (SOC) of the energy storage unit. max State of Charge (SOC) min and the current state of charge (SOC);

[0083] Based on the upper limit of the state of charge (SOC) of the energy storage unit max State of Charge (SOC) min Given the current state of charge (SOC), determine the allocation factor x for the reference current;

[0084] The allocation factor x of the reference current is calculated using the following formula:

[0085]

[0086] Determine the DC bus current reference value Is it equal to 0? If so, then set the current reference value of the energy storage unit to 0. Reference value of current in AC power grid If all values ​​are 0, then the current reference value of the energy storage unit is determined based on the operating status of the photovoltaic-storage-DC-flexible power distribution system and the allocation factor x of the reference current. Reference value of current in AC power grid

[0087] In some embodiments, the current reference value of the energy storage unit is determined based on the operating status of the photovoltaic-storage-DC-flexible power distribution system and the allocation factor x of the reference current. Reference value of current in AC power grid include:

[0088] Based on the grid-connected and off-grid operation status of the photovoltaic-storage-DC-flexible power distribution system, determine E n The value; if the system is operating in grid-connected mode, then E n =1; if the system is running offline, then E n =0.

[0089] If the photovoltaic-storage-DC-flexible power distribution system is operating in grid-connected mode, i.e., E n =1, then based on the allocation factor x of the reference current and the reference value of the DC bus current... Determine the current reference value for the energy storage unit Reference value of current in AC power grid

[0090] In some embodiments, the allocation factor x based on the reference current and the DC bus current reference value are... Determine the current reference value for the energy storage unit Reference value of current in AC power grid include:

[0091] Determine the DC bus current reference value Is it greater than 0?

[0092] If so, then set the current reference value of the AC power grid. The result is equal to 1 minus the allocation factor x of the reference current and the DC bus current reference value. The product of these, the current reference value of the energy storage unit. Equal to the DC bus current reference value The product of the allocation factor x of the reference current, i.e.

[0093] If not, then set the current reference value of the AC power grid. Equal to the DC bus current reference value The current reference value of the energy storage unit is the product of the allocation factor x of the reference current. The result is equal to 1 minus the allocation factor x of the reference current and the DC bus current reference value. The product of, i.e.

[0094] If the photovoltaic-storage-DC-flexible power distribution system is operating in off-grid mode, i.e., E n If the value is 0, then the reference value of the DC bus current is determined. Is it greater than 0? If so, then set the current reference value of the energy storage unit to 0. Equal to the DC bus current reference value AC power grid current reference value If the value is 0, then determine whether the allocation factor x of the reference current is less than the preset allocation factor threshold of the reference current; the preset allocation factor threshold of the reference current is 1.

[0095] If the allocation factor x of the reference current is less than the preset threshold value of the allocation factor of the reference current, then the reference value of the energy storage unit is set to... Equal to the DC bus current reference value AC power grid current reference value The value is 0. When x equals 0, a portion of the non-critical loads in the AC power grid should also be disconnected.

[0096] If the allocation factor x of the reference current is not less than the preset allocation factor threshold of the reference current, in order to avoid the problem of the DC bus voltage of the system rising due to the net residual power, it is necessary to control the photovoltaic to operate in non-MPPT mode, or to disconnect some photovoltaic power generation units from the system.

[0097] In box 140, DC bus current control is performed based on the energy storage unit current and the current reference value of the energy storage unit to control the output power of the energy storage unit converter.

[0098] In some embodiments, the method based on the energy storage unit current i b and the current reference value of the energy storage unit DC bus current control is implemented to control the output power of the energy storage unit converter, including:

[0099] like Figure 4 As shown, based on the energy storage unit current i b and the current reference value of the energy storage unit A DC bus current controller is used for DC bus current control; the transfer function of the DC bus current controller is G. i (s), G i (s)=k pi +k ii / s, where k pi k is the proportional coefficient of the DC bus current controller. ii is the integral coefficient of the DC bus current controller, and s is the Laplace operator.

[0100] Obtain the voltage u of the energy storage unit b The difference Δu between the output u of the DC bus current controller and the output u is multiplied by 1 / u. dc This is then used as the duty cycle signal;

[0101] The duty cycle signal is input into the PWM generator to generate a PWM switching signal, which is then used to control the output power of the energy storage unit converter.

[0102] exist Figure 4 In this context, B-DC represents a bidirectional DC / DC converter circuit.

[0103] In box 150, based on the current reference value of the AC power grid. Feedforward decoupling control is implemented to control the output power of the AC grid converter.

[0104] like Figure 5 As shown, the reference current value of the AC power grid is... To implement feedforward decoupling control and control the output power of the AC grid converter, including:

[0105] The current reference value of the AC power grid Perform dq transformation to obtain the d-axis component of the AC power grid current reference value. and q-axis components

[0106] Based on the d-axis component of the current reference value of the AC power grid and q-axis components Perform feedforward decoupling control to determine the d-axis control signal. and q-axis control signal

[0107] The d-axis control signal and q-axis control signal Perform an inverse dq transform to obtain an SPWM modulation signal, generate an AC grid converter switching signal using an SPWM generator, and use the AC grid converter switching signal to control the output power of the AC grid converter.

[0108] Figure 5 In the diagram, G-VSC stands for AC grid converter, and L... g For filter inductance, ω is the angular frequency. and These are the d-axis and q-axis components of the measured AC power grid current, u gd and u gq These represent the d-axis and q-axis components of the measured AC grid voltage, respectively. and These are the d-axis and q-axis components of the voltage deviation signal given value, respectively.

[0109] To verify the effectiveness of the embodiments of this disclosure, a system was built using Matlab / Simulink as follows. Figure 6 The simulation model is shown. Table 1 shows the parameter values ​​for the virtual inertial control strategy. The parameters of each unit in the system are described below:

[0110] (1) AC power grid: The AC power grid consists of permanent magnet synchronous generators (PMSG) with a rated power of 25kW. Its stator resistance is 0.432Ω, stator inductance is 4.24mH, and flux linkage is 0.932Wb.

[0111] (2) Photovoltaic Unit: The photovoltaic unit consists of a 5×40 photovoltaic array. Each photovoltaic module has a power generation capacity of 150W. After calculation, the rated power of the photovoltaic unit is 30kW.

[0112] (3) Energy storage unit: The energy storage unit consists of a battery pack with a rated voltage of 200V and a stored energy of 10kWh.

[0113] (4) Load Unit: The load unit consists of DC load and AC load.

[0114] Table 1. Parameter values ​​for virtual inertial control strategy

[0115]

[0116] In Table 1, L b r is the equivalent inductance of the battery. b r is the equivalent resistance of the battery. g The resistance of the filter inductor.

[0117] The photovoltaic unit has a power generation capacity of 30kW. The load unit consists of AC and DC loads, with the AC load consuming 18kW and the DC load consuming 20kW, for a total power consumption of 38kW. The net surplus power of 8kW is provided by the energy storage unit.

[0118] Example 1: The photovoltaic array of the system is operating at a light intensity of S = 1000 W / m 2 At a temperature T = 25℃, the output power is 30kW, with a DC load of 20kW and an AC load of 10kW in each load unit, totaling 30kW. At the 2nd second, the DC load increases by 10kW, bringing the total load power to 40kW. At the 6th second, the AC load increases by 5kW, bringing the total load power to 45kW. The photovoltaic array output power and load power curves are shown below. Figure 7 As shown, the DC bus voltage curve of the system is as follows: Figure 8 As shown.

[0119] At times 2s and 6s, the AC and DC loads of the system load units change successively, causing the DC bus voltage to fluctuate accordingly. Under traditional control strategies, the DC bus voltage exhibits significant fluctuations and overshoot. Using the control method and apparatus in the embodiments of this disclosure, virtual inertial control is employed, resulting in slower voltage fluctuations and a significantly reduced overshoot when the DC bus voltage is disturbed. Based on virtual inertial control, a voltage restorer is used for voltage recovery control, which eliminates steady-state errors and restores the DC bus voltage to its state before the disturbance.

[0120] Example 2: With a constant ambient temperature T = 25℃, the irradiance of the photovoltaic array exhibits a step-like change, with an initial irradiance S = 1000 W / m². 2 The light intensity decreased to S = 400 W / m² in 2 seconds. 2 The light intensity increased to S = 600 W / m² in 6 seconds. 2 The photovoltaic arrays have output powers of 30kW, 12kW, and 20kW. The load units consist of a 25kW DC load and a 10kW AC load, totaling 35kW. The output power and load power curves of the photovoltaic arrays are shown below. Figure 9 As shown, the DC bus voltage curve of the system is as follows: Figure 10 As shown.

[0121] At times 2s and 6s, the illumination intensity S of the photovoltaic array changes, and the DC bus voltage fluctuates accordingly. Example 2 shows the same DC bus voltage variation as in Example 1 under three different control strategies: conventional control, virtual inertial control, and virtual inertial control with an additional voltage restorer.

[0122] Example 3: The photovoltaic array of the system is operating at a light intensity of S = 1000 W / m 2 At a temperature T = 25℃, the output power is 30kW, and the maximum state of charge (SOC) of the battery pack is... max =80%, minimum state of charge (SOC) min =20%, current state of charge (SOC) = 65%. The initial power of the load unit is 25kW, increasing by 10kW at 2s, increasing by 5kW at 4s, decreasing by 5kW at 6s, and decreasing by 10kW at 8s. The output power of the photovoltaic unit and the load unit are as follows: Figure 11 As shown, the output power curves of the battery pack and the AC grid are as follows: Figure 12 As shown. The current state of charge of the battery pack is changed to SOC = 35%, while other system parameters remain unchanged. Simulation analysis is performed, and the output power curves of the battery pack and the AC grid are shown below. Figure 13 As shown.

[0123] A virtual inertial control strategy based on the State of Charge (SOC) of energy storage units manages the current of the battery bank and the AC grid in a unified manner and allocates it rationally through a reference current allocation factor. When the system is disturbed, the system can output inertial power through the virtual inertial control strategy to improve the fluctuation of DC bus voltage caused by the disturbance. When the battery bank's SOC is 65%, it releases more electricity when discharging and absorbs less electricity when charging. When the battery bank's SOC is 35%, it releases less electricity when discharging and absorbs more electricity when charging.

[0124] Example 4: Simulation analysis of the system considering fluctuations in two sets of photovoltaic arrays. The load unit power is 30kW, and the photovoltaic array 1 of the system operates at an irradiance of S = 800W / m². 2 The output power is 25kW at a temperature T = 25℃, and the photovoltaic array 2 of the system outputs 25kW at a light intensity S = 400W / m². 2 At a temperature T = 25℃, the output power is 12kW. The output power of photovoltaic array 1 and photovoltaic array 2 will vary depending on the amount of sunlight. The output power of the photovoltaic unit and the load unit are as follows: Figure 14 This indicates the maximum state of charge (SOC) of the battery pack. max =80%, minimum state of charge (SOC) min =20%, current state of charge (SOC) = 65%. The output power curves of the battery bank and the AC grid are as follows: Figure 15 As shown. The current state of charge of the battery pack is changed to SOC = 35%, while other system parameters remain unchanged. Simulation analysis is performed, and the output power curves of the battery pack and the AC grid are shown below. Figure 16 As shown.

[0125] A virtual inertial control strategy based on the battery's State of Charge (SOC) is established. When the battery pack's SOC is high, it releases more energy while discharging and absorbs less energy while charging. Conversely, when the SOC is low, it releases less energy while discharging and absorbs more energy while charging. This verifies the effectiveness of the virtual inertial control strategy considering the energy storage unit's SOC.

[0126] Example 5: AC power grid frequency variation curves under different AC power grid load disturbances are shown below. Figure 17 As shown.

[0127] Scenario 1: If the AC grid load suddenly increases by 9kW, the frequency characteristic of the AC grid is shown in curve L1. At this time, the frequency offset Δf = 0.19Hz, which does not exceed the system frequency regulation threshold Δf. th =0.2Hz, the photovoltaic-storage-DC-flexible power distribution system does not need to participate in the AC power grid frequency regulation process.

[0128] Scenario 2: The AC grid load suddenly increases by 14kW. When the photovoltaic-storage-DC-flexible power distribution system does not participate in the AC grid frequency regulation, the frequency characteristics are shown as curve L2. At this time, the frequency offset Δf = 0.35Hz, which has exceeded the threshold.

[0129] Scenario 3: The AC grid load suddenly increases by 14kW. The photovoltaic-storage-DC-flexible distribution system participates in AC grid frequency regulation 3.2s after the AC grid disturbance occurs. It provides virtual inertial power to the AC grid through the G-VSC converter, ensuring that the frequency change of the AC grid does not exceed the system frequency regulation threshold Δf. th The frequency characteristic curve of the AC power grid is shown in curve L3.

[0130] Scenario 4: The AC grid load suddenly increases by 22kW. When the photovoltaic-storage-DC-flexible distribution system does not participate in AC grid frequency regulation, the frequency characteristic curve is shown as curve L4. The frequency offset Δf = 0.5Hz, which exceeds the system frequency regulation threshold Δf under normal AC grid operation. th .

[0131] Scenario 5: The AC grid load suddenly increases by 22kW. The photovoltaic-storage-DC-flexible distribution system immediately participates in the frequency regulation of the AC grid at the moment the disturbance occurs. The frequency characteristics of the AC grid are shown in curve L5. The change in the AC grid frequency will still exceed the system frequency regulation threshold Δf. th However, the situation has been greatly improved. At this point, the AC power grid itself needs to perform emergency control measures such as load shedding to ensure that the frequency deviation does not exceed the system frequency regulation threshold.

[0132] Simulation results show that the DC-side inertia control method and apparatus for photovoltaic-storage-DC-flexible grid frequency regulation according to the embodiments of this disclosure determines the degree of participation based on the timing of the system's power supply to the AC grid. When the AC grid disturbance is small, the system does not participate in AC grid frequency regulation; when the disturbance is large, the system selectively participates in AC grid frequency regulation, providing virtual inertial power to the AC grid at a selected moment; when the disturbance is large, the system provides virtual inertial power to the AC grid as soon as the disturbance occurs. Therefore, the control method and apparatus proposed in this disclosure can effectively suppress frequency disturbances in AC systems.

[0133] According to the embodiments of this disclosure, the following technical effects are achieved:

[0134] This disclosure allows for flexible determination of the reference current allocation factor based on the state of charge of the energy storage unit, enabling unified management of the current flowing from the energy storage unit and the AC grid to the DC bus. By reallocating the respective reference currents according to the allocation factor, the converters of the energy storage unit and the AC grid operate under their respective reference currents. This rationally allocates the output power of the energy storage unit and the AC grid based on the actual operating state of the photovoltaic-storage-DC-flexible power distribution system, avoiding overcharging and over-discharging of the energy storage unit and making the charging and discharging process more user-friendly. Furthermore, this disclosure introduces virtual inertial control through the coordination between the energy storage unit and the AC grid, enhancing the system inertia of the AC grid. This reduces DC bus voltage fluctuations after AC grid disturbances, smooths AC system frequency disturbances, and enables photovoltaic-storage-DC-flexible power distribution to participate in AC grid auxiliary frequency regulation.

[0135] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this disclosure is not limited to the described order of actions, because according to this disclosure, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily essential to this disclosure.

[0136] The above is an introduction to the method embodiments. The following describes the solution described in this disclosure further through device embodiments.

[0137] Figure 18 A block diagram of a DC-side inertia control device 1800 for photovoltaic-storage-DC-flexible grid frequency regulation according to an embodiment of the present disclosure is shown. Figure 18 As shown, the device 1800 includes: a data acquisition module 1810, a reference current control module 1820, an energy storage unit converter control module 1830, and an AC grid converter control module 1840.

[0138] The data acquisition module 1810 is used to acquire the operating status of the photovoltaic-storage-DC-flexible power distribution system and the state of charge of the energy storage unit, and to collect the DC bus voltage and the energy storage unit current.

[0139] The reference current control module 1820 is used to perform voltage recovery control, virtual inertia control, and DC bus voltage control based on the DC bus voltage and a preset DC bus voltage reference value, and to determine the DC bus current reference value; it is also used to determine the current reference value of the energy storage unit and the current reference value of the AC grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage unit, and the DC bus current reference value.

[0140] The energy storage unit converter control module 1830 is used to control the DC bus current based on the energy storage unit current and the current reference value of the energy storage unit, thereby controlling the output power of the energy storage unit converter.

[0141] The AC grid converter control module 1840 is used to perform feedforward decoupling control based on the current reference value of the AC grid, thereby controlling the output power of the AC grid converter.

[0142] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the described module can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0143] Figure 19 A schematic block diagram of an electronic device 1900 that can be used to implement embodiments of the present disclosure is shown. Figure 19 As shown, device 1900 includes a CPU 1901, which can perform various appropriate actions and processes according to computer program instructions stored in ROM 1902 or loaded into RAM 1903 from storage unit 1908. RAM 1903 can also store various programs and data required for the operation of device 1900. CPU 1901, ROM 1902, and RAM 1903 are interconnected via bus 1904. I / O interface 1905 is also connected to bus 1904.

[0144] Multiple components in device 1900 are connected to I / O interface 1905, including: input unit 1906, such as keyboard, mouse, etc.; output unit 1907, such as various types of monitors, speakers, etc.; storage unit 1908, such as disk, optical disk, etc.; and communication unit 1909, such as network card, modem, wireless transceiver, etc. Communication unit 1909 allows device 1900 to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.

[0145] Processing unit 1901 executes the various methods and processes described above, such as method 100. For example, in some embodiments, method 100 may be implemented as a computer software program tangibly contained in a machine-readable medium, such as storage unit 1908. In some embodiments, part or all of the computer program may be loaded and / or installed on device 1900 via ROM 1902 and / or communication unit 1909. When the computer program is loaded into RAM 1903 and executed by CPU 1901, one or more steps of method 100 described above may be performed. Alternatively, in other embodiments, CPU 1901 may be configured to execute method 100 by any other suitable means (e.g., by means of firmware).

[0146] The functions described above in this document can be performed, at least in part, by one or more hardware logic components. For example, exemplary types of hardware logic components that can be used, without limitation, include: field programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), system-on-a-chip (SoCs), complex programmable logic devices (CPLDs), and so on.

[0147] The program code used to implement the methods of this disclosure may be written in any combination of one or more programming languages. This program code may be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing apparatus, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may be executed entirely on a machine, partially on a machine, as a standalone software package partially on a machine and partially on a remote machine, or entirely on a remote machine or server.

[0148] In the context of this disclosure, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, RAM, ROM, EPROM, optical fibers, CD-ROMs, optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0149] Furthermore, although the operations are described in a specific order, this should be understood as requiring that such operations be performed in the specific order shown or in sequential order, or requiring that all illustrated operations be performed to achieve the desired result. In certain environments, multitasking and parallel processing may be advantageous. Similarly, although several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of this disclosure. Certain features described in the context of individual embodiments may also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be implemented individually or in any suitable sub-combination in multiple implementations.

[0150] Although the subject matter has been described using language specific to structural features and / or methodological logic, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are merely illustrative examples of implementing the claims.

Claims

1. A method for controlling the DC-side inertia of photovoltaic-storage-DC-flexible grid frequency regulation, characterized in that, The method includes: acquiring the operating status of the photovoltaic-storage-DC-flexible power distribution system and the state of charge of the energy storage units; collecting the DC bus voltage and the energy storage unit current; performing voltage recovery control, virtual inertia control, and DC bus voltage control based on the DC bus voltage and a preset DC bus voltage reference value to determine a DC bus current reference value; determining the current reference value of the energy storage unit and the current reference value of the AC grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage units, and the DC bus current reference value; performing DC bus current control based on the energy storage unit current and the current reference value of the energy storage unit to control the output power of the energy storage unit converter; and performing feedforward decoupling control based on the current reference value of the AC grid to control the output power of the AC grid converter. The step of determining the current reference value of the energy storage unit and the current reference value of the AC power grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage unit, and the DC bus current reference value includes: Based on the state of charge of the energy storage unit, determine the upper limit value of the state of charge, the lower limit value of the state of charge, and the current state of charge value of the energy storage unit; The allocation factor of the reference current is determined based on the upper limit of the state of charge of the energy storage unit, the lower limit of the state of charge, and the current state of charge. Determine whether the DC bus current reference value is equal to 0; if yes, set both the current reference value of the energy storage unit and the current reference value of the AC grid to 0; if no, determine the current reference value of the energy storage unit and the current reference value of the AC grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system and the allocation factor of the reference current.

2. The method according to claim 1, characterized in that, The process of determining a DC bus current reference value based on the DC bus voltage and a preset DC bus voltage reference value includes: voltage recovery control, virtual inertia control, and DC bus voltage control. Based on the DC bus voltage and the preset DC bus voltage reference value, a voltage restorer is used for voltage recovery control to determine the given value of the DC side current; The output current at the load grid connection point is collected, and virtual inertial control is performed based on the given value of the DC side current, the reference value of the DC bus voltage, and the output current at the load grid connection point to determine the reference value of the DC bus voltage. Based on the DC bus voltage and the DC bus voltage reference value, a DC bus voltage controller is used to control the DC bus voltage and determine the DC bus current reference value.

3. The method according to claim 1, characterized in that, The step of controlling the DC bus current based on the energy storage unit current and the energy storage unit current reference value to control the output power of the energy storage unit converter includes: DC bus current control is performed using a DC bus current controller based on the current of the energy storage unit and the current reference value of the energy storage unit. The difference between the energy storage unit voltage and the output of the DC bus current controller is obtained, and the ratio of the difference to the DC bus voltage is used as the duty cycle signal. The duty cycle signal is input into the PWM generator to generate a PWM switching signal, which is then used to control the output power of the energy storage unit converter.

4. The method according to claim 1, characterized in that, The step of performing feedforward decoupling control based on the current reference value of the AC power grid to control the output power of the AC power grid converter includes: The current reference value of the AC power grid is transformed by dq to obtain the d-axis component and q-axis component of the current reference value of the AC power grid. Based on the d-axis and q-axis components of the current reference value of the AC power grid, feedforward decoupling control is performed to determine the d-axis control signal and the q-axis control signal. The d-axis control signal and the q-axis control signal are subjected to dq inverse transformation to obtain the SPWM modulation signal. The AC grid converter switching signal is generated by the SPWM generator and the output power of the AC grid converter is controlled by the AC grid converter switching signal.

5. The method according to claim 1, characterized in that, The step of determining the current reference value of the energy storage unit and the current reference value of the AC power grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system and the allocation factor of the reference current includes: If the photovoltaic-storage-DC-flexible power distribution system is in grid-connected operation, then the current reference value of the energy storage unit and the current reference value of the AC grid are determined according to the allocation factor of the reference current and the reference value of the DC bus current. If the photovoltaic-storage-DC-flexible power distribution system is in off-grid operation, then determine whether the DC bus current reference value is greater than 0; if yes, then set the current reference value of the energy storage unit to equal the DC bus current reference value, and the current reference value of the AC grid to 0; if no, then determine whether the allocation factor of the reference current is less than the preset reference current allocation factor threshold. If the allocation factor of the reference current is less than the preset threshold of the allocation factor of the reference current, then the current reference value of the energy storage unit is made equal to the DC bus current reference value, and the current reference value of the AC grid is 0. If the allocation factor of the reference current is not less than the preset allocation factor threshold of the reference current, then the photovoltaic system is controlled to operate in non-MPPT mode.

6. The method according to claim 5, characterized in that, The step of determining the current reference value of the energy storage unit and the current reference value of the AC power grid based on the allocation factor of the reference current and the reference value of the DC bus current includes: Determine whether the DC bus current reference value is greater than 0; If so, then the current reference value of the AC grid is equal to the product of 1 minus the allocation factor of the reference current and the DC bus current reference value, and the current reference value of the energy storage unit is equal to the product of the DC bus current reference value and the allocation factor of the reference current. If not, then the current reference value of the AC grid is equal to the product of the DC bus current reference value and the allocation factor of the reference current, and the current reference value of the energy storage unit is equal to the product of 1 minus the allocation factor of the reference current and the DC bus current reference value.

7. A DC-side inertia control device for photovoltaic-storage-DC-flexible grid frequency regulation, characterized in that, The device includes: a data acquisition module, a reference current control module, an energy storage unit converter control module, and an AC grid converter control module; The data acquisition module is used to acquire the operating status of the photovoltaic-storage-DC-flexible power distribution system and the state of charge of the energy storage unit, and to collect the DC bus voltage and the energy storage unit current. The reference current control module is used to perform voltage recovery control, virtual inertia control, and DC bus voltage control based on the DC bus voltage and a preset DC bus voltage reference value, and to determine the DC bus current reference value; it is also used to determine the current reference value of the energy storage unit and the current reference value of the AC grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system, the state of charge of the energy storage unit, and the DC bus current reference value. The energy storage unit converter control module is used to control the DC bus current based on the energy storage unit current and the current reference value of the energy storage unit, thereby controlling the output power of the energy storage unit converter. The AC grid converter control module is used to perform feedforward decoupling control based on the current reference value of the AC grid, thereby controlling the output power of the AC grid converter. The reference current control module is specifically used for: Based on the state of charge of the energy storage unit, determine the upper limit value of the state of charge, the lower limit value of the state of charge, and the current state of charge value of the energy storage unit; The allocation factor of the reference current is determined based on the upper limit of the state of charge of the energy storage unit, the lower limit of the state of charge, and the current state of charge. Determine whether the DC bus current reference value is equal to 0; if yes, set both the current reference value of the energy storage unit and the current reference value of the AC grid to 0; if no, determine the current reference value of the energy storage unit and the current reference value of the AC grid based on the operating status of the photovoltaic-storage-DC-flexible power distribution system and the allocation factor of the reference current.

8. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the program, it implements the method as described in any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 6.

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