A two-step cooperative constant voltage control system and method for a plurality of distributed photovoltaic power generation units

Abstract

The application provides a two-step coordinated constant-voltage control system and method of a plurality of distributed photovoltaic power generation units, and the autonomous operation of the plurality of distributed photovoltaic power generation units to a medium-voltage direct-current system is realized through the coordinated constant-voltage control strategy of a main photovoltaic power generation unit in the plurality of distributed photovoltaic power generation units and the droop control strategy of a secondary photovoltaic power generation unit. When a disturbance occurs in the system, the unbalanced power in the system can be accommodated, the direct-current bus voltage is maintained constant, and the stable operation of the medium-voltage direct-current system is ensured.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, specifically to a two-step collaborative constant voltage control system and method for multiple distributed photovoltaic power generation units. Background Technology

[0002] In recent years, my country's photovoltaic (PV) power generation has achieved rapid development, with the installed capacity of PV in the power grid increasing day by day. my country's PV power generation development model combines centralized and distributed generation. Due to the relatively scarce land resources in the central and eastern regions, distributed generation is the primary mode of PV power generation.

[0003] Typically, photovoltaic (PV) power generation systems prioritize preventing curtailment of solar power to maximize output. Therefore, PV systems need to coordinate with energy storage systems to ensure stable operation of the DC power grid. Current research on coordinated PV-storage operation has yielded significant results. However, the lifespan of energy storage systems is generally shorter than that of PV modules, and their cost is far higher. Although energy storage systems can reduce power disturbances and improve system stability through self-charging and discharging, providing continuous power to the load and thus increasing system utilization, a growing number of power companies are increasingly interested in providing voltage support for PV systems to reduce investment and maintenance costs associated with energy storage systems.

[0004] Existing research on photovoltaic constant voltage control strategies mainly focuses on applications in low-voltage DC systems. This is because the adjustable voltage capability range of a single photovoltaic power generation unit is small, and the control strategy is simple, such as... Figure 1 As shown.

[0005] Currently, there are several collaborative control strategies, including PQ control, V / f control, and droop control. However, in DC systems, f and Q do not exist; therefore, multiple distributed photovoltaic power generation units can operate collaboratively using a droop control strategy. Droop control has a significant drawback: it distributes unbalanced power in a proportional manner, failing to achieve error-free regulation. Therefore, improvements to droop control are needed. Researchers have developed three main methods: The first method uses a Washout filter to replace the droop coefficient, transforming the proportional error input into a proportional-integral (PI) form to eliminate steady-state error. The second method superimposes the PI output of the DC voltage error onto the droop control reference value, utilizing the steady-state error-free characteristic of PI to achieve error-free DC voltage regulation. The third method actively adjusts the active power reference value of the droop control, achieving error-free DC voltage regulation by shifting the droop curve.

[0006] As the above analysis shows, photovoltaic power generation systems can operate under a constant voltage control strategy in low-voltage DC systems without needing to coordinate with other photovoltaic power generation units. However, existing technologies cannot adapt to off-grid operation scenarios without energy storage in medium-voltage DC systems, leading to unstable operation of such systems. Summary of the Invention

[0007] To address the aforementioned issues, for off-grid medium-voltage DC systems without energy storage, this invention first considers the voltage support capability of a single photovoltaic power generation unit. Then, it combines the coordinated operation of multiple distributed photovoltaic units under droop control strategies to enable the multiple distributed photovoltaic power generation units to absorb unbalanced power in the system, maintain a constant DC bus voltage, and ensure the stable operation of the medium-voltage DC system.

[0008] Specifically, according to a first aspect of the present invention, a two-step coordinated constant voltage control system for multiple distributed photovoltaic power generation units is provided, comprising multiple coordinated distributed photovoltaic power generation units, including a primary photovoltaic power generation unit and multiple secondary photovoltaic power generation units, wherein the irradiance of the primary photovoltaic power generation unit is greater than that of the secondary photovoltaic power generation units, the primary photovoltaic power generation unit includes an MPPT strategy module and a constant voltage control strategy module, and the secondary photovoltaic power generation units include an MPPT strategy module and a droop control strategy module. In the primary photovoltaic power generation unit, the MPPT strategy module and the constant voltage control strategy module can be switched selectively by a first control switch, and in the secondary photovoltaic power generation units, the MPPT strategy module and the droop control strategy module can be switched selectively by a second control switch. The system also includes a control unit, which controls the switching of the first control switch and the second control switch based on the load fluctuation of the multiple distributed photovoltaic power generation units.

[0009] In one embodiment, the control unit is configured to: when the load fluctuates, switch the main photovoltaic power generation unit to the constant voltage control strategy module and switch the secondary photovoltaic power generation unit to the droop control strategy module.

[0010] In one embodiment, the control unit is configured to: when the load is stable, switch the main photovoltaic power generation unit to the constant voltage control strategy module and switch the secondary photovoltaic power generation unit to the MPPT strategy module.

[0011] In one embodiment, the constant voltage control strategy module includes a PI controller, an adjustment module, and a PWM module in sequence. The adjustment module calculates the power change caused by load fluctuations based on the DC bus voltage change and the DC bus current, calculates the photovoltaic cell port voltage change based on the power change and the actual slope of the photovoltaic cell PU curve, and calculates the converter turn-off angle based on the photovoltaic cell port voltage change and the PV cell voltage reference value.

[0012] According to a second aspect of the present invention, a control method is provided based on a two-step collaborative constant voltage control system for multiple distributed photovoltaic power generation units. The unbalanced power in the system is allocated proportionally according to the maximum output power capacity of each photovoltaic power generation unit. The total absorption power is the sum of the absorption power of the main photovoltaic power generation unit and the absorption power of the multiple distributed secondary photovoltaic power generation units based on droop control.

[0013] In one embodiment, the power consumption control of each secondary photovoltaic power generation unit in the multi-distributed secondary photovoltaic power generation unit is as follows:

[0014] In the formula, k PV,i Let ΔP be the slope of the monotonically increasing interval of the PU curve of the photovoltaic cell in the i-th photovoltaic power generation unit. PV_droop This refers to the power absorbed by the multi-distributed secondary photovoltaic power generation unit based on droop control.

[0015] In one embodiment, the constant pressure control is implemented as follows:

[0016] S100, based on DC bus voltage reference value and the actual DC bus voltage value U DC Calculate the DC bus voltage change ΔU DC ,

[0017] S210, based on DC bus voltage change ΔU DC and the current I of the DC bus DC Calculate the power change ΔP caused by load fluctuations. DC ,

[0018] S220, based on power change ΔP DC And the actual slope k of the PU curve of photovoltaic cells PV Calculate the change in photovoltaic cell port voltage ΔU PV ,

[0019] S230, based on the change in photovoltaic cell port voltage ΔU PV and PV cell voltage reference value Calculate the turn-off angle β of the converter.

[0020] S300 performs pulse width modulator (PWM) voltage regulation control and boost converter voltage conversion based on the converter's turn-off angle β.

[0021] In one embodiment, the droop control is implemented as follows:

[0022]

[0023] In the formula, e(t) is the error value of the photovoltaic power generation unit; P * P and P represent the reference and actual active power values ​​of the photovoltaic power generation unit, respectively. and U DC These are the reference and actual values ​​for the medium-voltage DC bus voltage, respectively; K d This is the droop coefficient.

[0024] According to a third aspect of the present invention, a terminal is provided, characterized in that it includes: at least one processor and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to cause the at least one processor to perform the control method of the second aspect.

[0025] According to a fourth aspect of the present invention, a computer-readable storage medium is provided, characterized in that the computer-readable storage medium stores computer instructions for causing the computer to perform the control method of the second aspect.

[0026] This invention employs a two-step collaborative control strategy involving multiple distributed photovoltaic (PV) power generation units. For off-grid, non-storage medium-voltage DC (DC) systems, PV power generation units provide voltage support to ensure a constant DC bus voltage. This enables autonomous operation of the medium-voltage DC system by the multiple distributed PV power generation units. When disturbances occur in the system, it can absorb unbalanced power, maintain a constant DC bus voltage, and ensure stable operation of the medium-voltage DC system. Attached Figure Description

[0027] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0028] Figure 1 This is a block diagram of a constant pressure control principle;

[0029] Figure 2 This invention relates to the PU output characteristics of photovoltaic cells at room temperature.

[0030] Figure 3 This is a schematic diagram of a constant pressure control principle according to the present invention;

[0031] Figure 4 This is a diagram of the droop control structure of a single photovoltaic power generation unit of the present invention;

[0032] Figure 5This is a diagram illustrating the droop control operation characteristics of a single photovoltaic power generation unit according to the present invention.

[0033] Figure 6 This is a diagram showing the droop control operation points of the present invention;

[0034] Figure 7 This is a diagram showing the overall control structure of the photovoltaic power generation unit of the present invention;

[0035] Figure 8 This is a schematic diagram of a multi-distributed photovoltaic power generation unit based on a two-step collaborative control strategy according to the present invention;

[0036] Figure 9 This is a control logic diagram for a multi-distributed photovoltaic power generation unit according to the present invention. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0038] For off-grid medium-voltage DC systems without energy storage, maintaining stable operation requires the use of photovoltaic (PV) power generation units to provide voltage support and ensure a constant DC bus voltage. This invention first considers the voltage support capability of a single PV power generation unit, and then combines this with the coordinated operation of multiple distributed PV units operating under a droop control strategy. This enables the distributed PV power generation units to absorb unbalanced power in the system, maintain a constant DC bus voltage, and ensure stable operation of the medium-voltage DC system.

[0039] Depend on Figure 2 It is known that although the PU characteristic curves of photovoltaic cells show the same trend under different environments, their maximum power generation is greater when the light intensity is stronger. Therefore, to ensure that the medium-voltage DC bus voltage operates within a stable range and to allow the DC bus voltage to recover to its rated value as quickly as possible during load switching, this invention proposes a two-step cooperative control strategy. Under this cooperative strategy, one photovoltaic power generation unit with a large dynamic operating range acts as the main photovoltaic power generation unit, operating under a constant voltage control strategy. The other multiple distributed photovoltaic power generation units all operate under droop control with power regulation capabilities. According to their droop characteristics and their respective power regulation capabilities, they provide power to the load and absorb unbalanced power.

[0040] Specifically, according to one aspect of the present invention, a two-step coordinated constant voltage control method for multiple distributed photovoltaic power generation units is provided, comprising multiple photovoltaic power generation units with coordinated output, wherein the photovoltaic power generation unit with the highest irradiance uses constant voltage control as the main precise control of the DC bus voltage, and the remaining power generation units coordinate to absorb unbalanced power in the system based on droop control.

[0041] In one embodiment, the constant voltage control strategy may employ an improved constant voltage control module, such as... Figure 3 As shown, an adjustment module 20 is placed between the PI controller 10 and the PWM module 30. (The figure shows...) and These are the reference values ​​for the DC bus and photovoltaic (PV) cell voltages, ΔU. DC for The difference between the two values ​​is the change in DC bus voltage after passing through the PI controller, I DC The current ΔP is the current of the DC bus. DC k represents the change in power caused by load fluctuations. PV ΔU represents the slope of the monotonically increasing interval of the PU curve of a photovoltaic cell under different environmental conditions. PV β represents the change in photovoltaic cell port voltage corresponding to the monotonically increasing interval of the PU curve caused by load changes, and β is the turn-off angle of the converter.

[0042] Therefore, the improved constant pressure control module is implemented as follows:

[0043] S100, based on DC bus voltage reference value and the actual DC bus voltage value U DC Calculate the DC bus voltage change ΔU DC .

[0044] Preferably, the DC bus voltage change ΔU DC The control steady-state error is eliminated by a proportional-integral (PI) controller.

[0045] S210, based on DC bus voltage change ΔU DC and the current I of the DC bus DC Calculate the power change ΔP caused by load fluctuations. DC .

[0046] S220, based on power change ΔP DC And the actual slope k of the PU curve of photovoltaic cells PV Calculate the change in photovoltaic cell port voltage ΔU PV .

[0047] S230, based on the change in photovoltaic cell port voltage ΔU PV and PV cell voltage reference value Calculate the turn-off angle β of the converter.

[0048] The S300 uses pulse width modulator (PWM) voltage regulation control and boost converter (Boost converter) based on the converter's turn-off angle β. This allows for precise control of the DC bus voltage and suppression of disturbances.

[0049] The control structure diagram and operating characteristics of droop control for a single photovoltaic power generation unit are as follows: Figure 4 , Figure 5 As shown, by Figure 4 We can obtain:

[0050]

[0051] In the formula, e(t) is the error value of the photovoltaic power generation unit; P * P and P represent the reference and actual active power values ​​of the photovoltaic power generation unit, respectively. and U DC These are the reference and actual values ​​for the medium-voltage DC bus voltage, respectively; K d This is the droop coefficient.

[0052] Let ΔP = P * -P, When seeking an error value e(t) that is zero:

[0053]

[0054] Based on equations (1) and (2), the following can be drawn: Figure 5 The droop characteristic curve. When a power disturbance occurs in the medium-voltage DC system, the photovoltaic power generation unit will follow a curve with a slope of -K. d The downward curve moves to the operating point (P1,U1) or (P2,U2), thereby absorbing the unbalanced power. Therefore, while the photovoltaic power generation unit provides an incremental ΔP, the DC bus voltage will inevitably experience a voltage deviation ΔU. DC .

[0055] The active power flowing into the DC bus is defined as positive, and the outflow as negative. Let P be the total active power of m photovoltaic power generation units operating under vertical control in the initial time state. PV_droop for:

[0056]

[0057] In the formula, P i,0 This represents the active power of the photovoltaic power generation unit based on droop control in the initial steady state.

[0058] m photovoltaic power generation units satisfy:

[0059]

[0060] The total active power P of n photovoltaic power generation units operating under maximum power point tracking (MPPT) control PV_MPPT for:

[0061]

[0062] In the formula, Pj,0 This represents the active power of the photovoltaic power generation unit based on MPPT control in the initial steady state.

[0063] Medium-voltage DC systems satisfy energy conservation.

[0064] P PV_droop +P PV_MPPT +P load =0 (6)

[0065] In the formula, P load For DC loads, the value is negative under the specified power flow direction.

[0066] If the output of a photovoltaic power generation unit based on the MPPT control strategy or the switching of loads causes a power change of ΔP in the medium-voltage DC system p Then equation (4) is changed to:

[0067]

[0068] In the formula, ΔP i,1 =P i,1 -P i,0 ΔU DC,i,1 =U DC,i,1 -U DC,i,0 , where P i,1 and U DC,i,1 These are the DC bus voltages after power fluctuations.

[0069] Equation (7) - Equation (4) yields

[0070]

[0071] After the power disturbance, equation (6) becomes:

[0072]

[0073] Equation (9) - Equation (6) yields

[0074]

[0075] Substituting equation (8) into equation (10), we get

[0076]

[0077] Because the DC voltage of the photovoltaic power generation system changes synchronously, that is, the average DC voltage change ΔU of each photovoltaic power generation unit. DC,1 =ΔU DC,i,1 Equation (11) becomes:

[0078]

[0079] Equation (12) reveals that ΔUDC,1 Same power disturbance ΔP P It is directly proportional to the sum of the derivatives of the droop coefficients of m photovoltaic power generation units. That is, when power fluctuations occur in the system, the photovoltaic power generation units based on droop control work together to automatically move along the droop characteristic curve and cooperate to complete the unbalanced power absorption.

[0080] Schematic diagram of the operating point of a photovoltaic power generation unit based on the droop control strategy Figure 6 As shown in the figure. Ignoring DC grid losses, the photovoltaic power generation system operates at point F1.

[0081] At this time, the photovoltaic power generation unit satisfies:

[0082]

[0083] The active power of a photovoltaic power generation unit can also be expressed as:

[0084]

[0085] If the system change is ΔP P Then the running point moves from point F1 to point F2 along the downward curve 1. At this time, equations (13) and (14) can be written as:

[0086]

[0087]

[0088] To achieve error-free DC voltage correction, it means that the operating point F2 must move to point F3 and operate stably. Figure 6 It can be seen that the drooping curve 1 needs to be translated ΔP along the P-axis. P At this point, equations (13) and (14) can be written as:

[0089]

[0090]

[0091] Equation (17) matches equations (7), (8), and (15), but the left-hand sides of equations (16) and (18) are the same, and the right-hand sides violate the principle of uniqueness. Therefore, it can be concluded that the system cannot operate stably at point F3. Thus, [the following is a continuation of the previous sentence, but the context is unclear]. Figure 6 Translation of the sag curve 1 by ΔP P Without PI regulation, the voltage will move along the droop curve 2, passing point F3, and reaching the stable point F4. In summary, photovoltaic power generation units cannot achieve error-free DC voltage correction solely through droop control. However, through the two-step collaborative control strategy of the multi-distributed photovoltaic power generation units of this invention, one photovoltaic power generation unit acts as the master, precisely controlling the DC bus voltage, while other photovoltaic power generation units employ droop control, coordinating to absorb unbalanced power in the system.

[0092] Depend on Figure 2 It is known that the greater the light intensity, the larger the dynamic operating range and the greater the adjustable power margin of the photovoltaic power generation unit. Therefore, this invention selects the photovoltaic power generation unit with the highest light intensity to operate under a constant voltage control strategy to precisely control the DC bus voltage, while other distributed photovoltaic power generation units operate under a droop control strategy. Due to the different light intensities, the output power range of the distributed photovoltaic power generation units based on droop control also varies. To make reasonable use of the dynamic operating capability, the unbalanced power in the system is allocated proportionally according to the maximum output power capability of each photovoltaic power generation unit, as shown in the following formula:

[0093] ΔP P =ΔP PV_CVC +ΔP PV_droop (19)

[0094] In the formula, ΔP PV_CVC The main photovoltaic power generation unit's absorption capacity; ΔP PV_droop This refers to the power absorption capacity of multi-distributed photovoltaic power generation units based on droop control.

[0095] The power absorption capacity of each photovoltaic power generation unit in the multi-distributed photovoltaic power generation unit is:

[0096]

[0097] In the formula, k PV,i Let be the slope of the monotonically increasing interval of the PU curve of the photovoltaic cell in the i-th photovoltaic power generation unit.

[0098] According to equation (20), the unbalanced power in the system is distributed to each photovoltaic power generation unit for absorption, thereby maintaining the stability of the DC bus voltage.

[0099] Figure 7 A general control structure diagram of a photovoltaic (PV) power generation unit is presented. CVC is the main PV power generation unit's power control, and the MPPT strategy and the main PV power generation unit's power control are switched via a switch K. When the switch is 0, the MPPT strategy is executed, adjusting the PV cell port voltage U according to environmental conditions. PV , ensure U PV =U MPP This achieves maximum power point tracking control. When the switch is in position 1, a constant voltage control strategy is implemented, adjusting the photovoltaic cell port voltage U according to load fluctuations. PV This ensures that the power output of the photovoltaic cells equals the power required by the load, thereby stabilizing the DC bus voltage.

[0100] In one embodiment, taking three photovoltaic power generation units connected to the grid as an example, such as... Figure 8As shown, these are the control logic 100 for the first photovoltaic power generation unit (PV1), the control logic 200 for the second photovoltaic power generation unit (PV2), and the control logic 300 for the third photovoltaic power generation unit (PV3), where the light intensity of PV1 > the light intensity of PV2 > the light intensity of PV3. K1, K2, and K3 are the control switching switches for PV1, PV2, and PV3, respectively. This enables... Figure 9 Control methods:

[0101] Initially, (K1,K2,K3) = (1,0,0), meaning that the first photovoltaic power generation unit (PV1) adopts a constant voltage control strategy, while the second photovoltaic power generation unit (PV2) and the third photovoltaic power generation unit (PV3) adopt an MPPT strategy, with PV1 maintaining the DC bus voltage stability.

[0102] When the load fluctuates, let (K1,K2,K3)=(1,1,1), that is, the first photovoltaic power generation unit (PV1) adopts a constant voltage control strategy, and the second photovoltaic power generation unit (PV2) and the third photovoltaic power generation unit (PV3) adopt a droop control strategy. The droop control of PV2 and PV3 automatically takes effect, absorbing the unbalanced power according to the ratio of formula (20). PV1 operates under the constant voltage control strategy, and the voltage at the photovoltaic cell port is at... Nearby adjustments are made to achieve differential voltage regulation of the DC bus, thereby ensuring stable operation of the medium-voltage DC system.

[0103] When the load returns to a stable state, (K1,K2,K3) = (1,0,0) can be set so that PV1 maintains the DC bus voltage stability and achieves maximum power point tracking control.

[0104] Of course, as can be seen from formula (20), there can be multiple photovoltaic power generation units that implement droop control, not just two.

[0105] To implement the above control logic, one aspect of this invention proposes a two-step collaborative constant voltage control system for multiple distributed photovoltaic power generation units, including multiple collaborative distributed photovoltaic power generation units, including a main photovoltaic power generation unit and multiple secondary photovoltaic power generation units. The irradiance of the main photovoltaic power generation unit is greater than that of the secondary photovoltaic power generation units. The main photovoltaic power generation unit includes an MPPT strategy and a constant voltage control strategy, and the secondary photovoltaic power generation units include an MPPT strategy and a droop control strategy. In the main photovoltaic power generation unit, the MPPT strategy and the constant voltage control strategy can be switched by a first control switch K1. In the secondary photovoltaic power generation units, the MPPT strategy and the droop control strategy can be switched by a second control switch K2 and K3. The system also includes a control unit, which controls the switching of the first control switch and the second control switch based on the load fluctuation of the multiple distributed photovoltaic power generation units.

[0106] The two-step coordinated constant voltage control method for multiple distributed photovoltaic power generation units provided in this invention can be implemented as a software functional module and sold or used as an independent product, and can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0107] This invention addresses the issue of distributed photovoltaic (PV) systems being collected into a medium-voltage DC system via DC transmission. It proposes a two-step collaborative control strategy for multiple distributed PV power generation units, which enables the distributed PV system to maintain a constant medium-voltage DC bus voltage and avoids the situation where the medium-voltage DC system without energy storage cannot operate stably when off-grid.

[0108] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A two-step coordinated constant-voltage control system for multiple distributed photovoltaic power generation units, comprising multiple coordinated distributed photovoltaic power generation units, including a primary photovoltaic power generation unit and multiple secondary photovoltaic power generation units, wherein the light intensity of the primary photovoltaic power generation unit is greater than the light intensity of the secondary photovoltaic power generation units, characterized in that, The main photovoltaic power generation unit includes an MPPT strategy module and a constant voltage control strategy module. The secondary photovoltaic power generation unit includes an MPPT strategy module and a droop control strategy module. In the main photovoltaic power generation unit, the MPPT strategy module and the constant voltage control strategy module can be switched selectively via a first control switch. In the aforementioned photovoltaic power generation unit, the MPPT strategy module and the droop control strategy module can be selectively switched via a second control switch. It also includes a control unit, which controls the switching of the first control switch and the second control switch based on the load fluctuation of multiple distributed photovoltaic power generation units; The control unit is configured to: when the load fluctuates, switch the main photovoltaic power generation unit to the constant voltage control strategy module and switch the secondary photovoltaic power generation unit to the droop control strategy module; when the load is stable, switch the main photovoltaic power generation unit to the constant voltage control strategy module and switch the secondary photovoltaic power generation unit to the MPPT strategy module.

2. The two-step collaborative constant voltage control system for multiple distributed photovoltaic power generation units as described in claim 1, characterized in that, The constant voltage control strategy module includes a PI controller, an adjustment module, and a PWM module. The adjustment module calculates the power change caused by load fluctuations based on the DC bus voltage change and the DC bus current, calculates the photovoltaic cell port voltage change based on the power change and the actual slope of the photovoltaic cell PU curve, and calculates the converter turn-off angle based on the photovoltaic cell port voltage change and the PV cell voltage reference value.

3. A control method for a two-step cooperative constant voltage control system for multiple distributed photovoltaic power generation units according to any one of claims 1-2, characterized in that, The unbalanced power in the system is distributed proportionally according to the maximum output power capacity of each photovoltaic power generation unit. The total absorption power is the sum of the absorption power of the main photovoltaic power generation unit and the absorption power of the multi-distributed secondary photovoltaic power generation units based on droop control.

4. The control method as described in claim 3, characterized in that, The power consumption control of each secondary photovoltaic power generation unit in the multi-distributed secondary photovoltaic power generation unit is as follows: In the formula, k PV,i For the first i Photovoltaic cells of a photovoltaic power generation unit PU The slope of the monotonically increasing interval of the curve, Δ P PV_droop This refers to the power absorbed by the multi-distributed secondary photovoltaic power generation unit based on droop control.

5. The control method as described in claim 4, characterized in that, The constant pressure control is implemented as follows: S100, based on DC bus voltage reference value and actual DC bus voltage value U DC Calculate the DC bus voltage change Δ U DC , S210, based on DC bus voltage change Δ U DC and DC bus current I DC Calculate the power change Δ caused by load fluctuations. P DC , S220, based on power change Δ P DC Actual slope of photovoltaic cell PU curve k PV Calculate the change in photovoltaic cell port voltage Δ U PV , S230, based on the change in photovoltaic cell port voltage Δ U PV and PV cell voltage reference value Calculate the turn-off angle of the converter β , S300, based on the converter's turn-off angle β Perform pulse width modulator (PWM) voltage regulation control and boost converter voltage conversion.

6. The control method as described in claim 4, characterized in that, The droop control is implemented as follows: In the formula, e ( t The error value is that of the photovoltaic power generation unit. P * and P These are the reference value and the actual value of the active power of the photovoltaic power generation unit, respectively; and U DC These are the reference value and the actual value of the medium-voltage DC bus voltage, respectively. K d This is the droop coefficient.

7. A terminal, characterized in that, include: At least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to cause the at least one processor to perform the control method according to any one of claims 3-6.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to perform the control method according to any one of claims 3-6.

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