Dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system

Abstract

According to the dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system provided by the invention, in an MPPT (Maximum Power Point Tracking) operation interval, a grid-side DC / AC (Direct Current / Alternating Current) converter adopts inertia synchronous control, and meanwhile, the voltage balance of a direct current bus is maintained through various MPPT algorithms and the maximum output power of an inverter is achieved; in a constant power operation interval, the photovoltaic array autonomously maintains the stability of the DC bus voltage according to the active power output by the inverter, the grid-side converter uses virtual synchronous control, the effect of photovoltaic array-grid-side converter power balance is achieved by controlling the output power of the grid-side DC / AC converter, and the bidirectional primary frequency modulation function is achieved. Besides, when switching is carried out in different operation intervals, the two working modes operate at the same time, a final loop is judged and output through a dual-mode parallel competition autonomous strategy, smooth switching of the equipment in different operation intervals is achieved, and the dynamic performance in the switching process is improved.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation equipment technology, specifically to a dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system. Background Technology

[0002] The desert-based photovoltaic (PV) base possesses abundant photovoltaic resources, but its remote location far from load centers hinders its development. Centralized PV inverters, as one of the basic power generation units in this region, currently employ grid-connected control, exhibiting "current source" characteristics. This necessitates significant derating of power transmission channels, making power delivery difficult and requiring numerous synchronous condensers, severely restricting the development of new energy sources. Against this backdrop, modifying the PV inverter control strategy to simulate the operating characteristics of a synchronous generator, enabling active support for grid transient voltages, inertial response, and primary frequency regulation, thus exhibiting "voltage source" characteristics, has become a hot topic in centralized PV control research in the desert-based scenario.

[0003] Current research on voltage source control in centralized photovoltaic (PV) power generation systems mainly focuses on systems where parallel energy storage is connected to the DC bus voltage to maintain its stability, and the grid-side converter employs virtual synchronous control. Research on centralized PV power generation systems without DC-side energy storage and without a Chopper is limited. Therefore, the grid-side control structure is crucial for achieving voltage source characteristics in centralized PV power generation systems across multiple operating ranges. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system.

[0005] The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system provided by the present invention includes:

[0006] Photovoltaic arrays and grid-side converters;

[0007] The grid-side converter includes various DC / AC converters;

[0008] The photovoltaic array is connected to the same DC bus, and the DC bus is connected to the grid via a DC / AC converter.

[0009] During the MPPT operating range, inertial synchronous control is used in conjunction with MPPT control to achieve the maximum active power output of the photovoltaic array; during the constant power operating range, virtual synchronous control is used, and the photovoltaic array autonomously maintains the DC bus voltage stability based on the active power output of the inverter.

[0010] During the MPPT operating range, constant power operating range, or low-voltage grid operating range, the grid-side DC / AC converter's inertial synchronization control loop and virtual synchronization control loop operate simultaneously; in different operating ranges, autonomous smooth dynamic switching is achieved through a dual-mode parallel competition autonomous strategy.

[0011] Preferably, the self-synchronizing voltage source control strategy for the MPPT operating range includes:

[0012] The photovoltaic array operates at its maximum power point, achieving maximum power output under current conditions. The grid-side DC / AC converter operates under inertial synchronous control, and the grid-side synchronous loop switching switch S... ω In M1 mode, disturbances to the DC bus voltage are introduced into the grid-connection frequency of the grid-side DC / AC converter. This maintains the stability of the DC bus voltage while simultaneously synchronizing the inverter with the grid. The phase angle of the inverter output modulation voltage is:

[0013]

[0014] In the formula: ω0 represents the reference value of the power grid frequency, k pdc k represents the inertial synchronization proportional coefficient. idc V represents the inertial synchronization integral coefficient. dc This represents the actual value of the DC bus voltage, V. dcrefG This represents the given value of the grid-side inertial synchronous DC bus voltage; s represents the Laplace expression method for differential calculation.

[0015] Since inertial synchronization lacks damping, stabilizing damping is added during the generation of the modulated wave voltage amplitude. Its expression is as follows:

[0016]

[0017] In the formula: V t0 Q represents the given value of the peak potential within the inverter; gref Q represents the given value of reactive power in the power grid. g This represents the actual value of the current reactive power of the power grid; k pt and k it D represents the proportional and integral coefficients of the reactive power control loop, respectively; pss V represents the voltage damping stabilization compensation amount; t Indicates the magnitude of the modulated wave voltage; voltage stabilization switch S D In M1 mode; D pss The disturbance ΔV of the DC bus voltage dc get:

[0018]

[0019] In the formula: k pss T represents the damping stability proportional coefficient;c This represents the time constant of the high-pass filter.

[0020] Preferably, when operating within the MPPT range, the photovoltaic power generation system reduces active power output as the grid frequency increases, causing the PV curve operating point to shift to the right from the MPPT operating point, and the active power reference P... ref The instruction is:

[0021] P ref =V PV ·I PV +ΔP t (4)

[0022] In the formula, V PV Represented as the photovoltaic panel port voltage, I PV ΔP represents the output current of the photovoltaic panel. t This refers to the active power command for the photovoltaic power generation system participating in the grid frequency response offset;

[0023] Under inertial synchronous control, the DC bus voltage maps to the grid frequency, ΔP t Written as:

[0024] ΔP t =K c ·s·ΔV dc +K t ·ΔV dc (5)

[0025] Where: K c K represents the inertial response coefficient. c This represents the primary frequency modulation factor; -0.2P GN <ΔP t <0, P GN This refers to the rated power of the grid-side DC / AC converter.

[0026] Preferably, the grid-side synchronous loop switching switch S for the constant power operation range and the low-voltage operation range of the power grid ω In M2 mode, the grid-side DC / AC converter employs virtual synchronization control. The error signal between the power reference command and the actual value of the grid output active power is introduced into the grid-connection angle frequency of the grid-side DC / AC converter through a virtual synchronization transfer function. The phase angle of its output modulation voltage is:

[0027]

[0028] In the formula: ω p Indicates the virtual synchronous output grid angular frequency error value; P gref Indicates the reference command for active power of the power grid; P g J represents the actual active power output of the grid-side converter; PD represents the virtual inertia coefficient of the virtual synchronization link. P This represents the virtual damping coefficient of the virtual synchronization link.

[0029] Preferably, when virtual synchronous control is used, damped stabilization already exists in the photovoltaic power generation system, and the output of the stabilization element is:

[0030] D pss =0 (7)

[0031] Grid-side synchronous switching switch S ω In M2 mode, voltage stabilization switch S D In M2 mode, the active power output of the photovoltaic inverter is adjusted while grid frequency synchronization is achieved. Under conditions of enhanced solar illumination and no grid faults, the grid-side converter participates in the grid frequency response. Its virtual synchronization control active power reference command is:

[0032]

[0033] Where: K tc K represents the primary frequency modulation coefficient of the grid-side converter. gc This represents the inertia response coefficient of the grid-side converter; -0.2P GN <ΔP t <0.1P GN .

[0034] Preferably, during steady-state operation of the power grid, in the MPPT operating range, the grid-side synchronization loop switching switch S ω In M1 mode, as sunlight intensity increases and the output power of the photovoltaic modules increases, the grid-side active power output lags due to the small DC capacitance, leading to an increase in bus voltage, V dc Increase, V dcrefG ω remains unchanged dc Reduce; the active power P output of the grid-side converter g Get bigger, P gref ω remains unchanged p The output of the network side is reduced to ω, representing the dual-mode parallel competitive autonomous strategy selection. p Switch S D When operating in M2 mode, the photovoltaic power generation system automatically switches to the constant power operating range.

[0035] Preferably, during the constant power operation range, the grid-side synchronous loop switching switch S ω In M2 mode, as sunlight decreases, the photovoltaic output power decreases, the grid-side DC / AC converter output active power exceeds the input active power, the DC bus voltage gradually decreases, and the photovoltaic PV operating point shifts to the lower left, with its output V... dc Slightly decrease, ω dcDecrease; the grid-side output active power gradually decreases until it equals the input active power, ω p Increase, dual-mode parallel competitive autonomous strategy selection network-side output is ω dc Switch S D When operating in M1 mode, the photovoltaic power generation system automatically switches to the MPPT operating range.

[0036] Preferably, during a low-voltage grid fault, the active power output of the grid-side DC / AC converter is blocked, the DC bus voltage rises, and the photovoltaic operating point shifts to the right on the original PV curve, resulting in a decrease in the output V. dc Increase, net side ω dc Increase; P gref It decreases as the grid voltage decreases, and is related to P. g Keep it consistent, ω p The dual-mode parallel competitive autonomous strategy selection network-side output remains unchanged at ω. p Switch S D It operates in M2 mode.

[0037] Preferably, when the fault is recovered, the output power of the grid-side DC / AC converter is greater than the input power of the photovoltaic array, the DC bus voltage decreases, the photovoltaic returns to its original maximum power point, and the output V... dc Decrease, net side ω dc Decrease; P gref With P g Keep it consistent, ω p The dual-mode parallel competitive autonomous strategy selection network-side output remains unchanged at ω. dc Switch S D It operates in M2 mode and automatically switches when a fault occurs or ends.

[0038] Preferably, the inverter power reference command design during a low-voltage grid fault includes:

[0039] During low-voltage ride-through, the photovoltaic inverter injects a dynamic reactive current into the power system that varies with the grid connection point voltage. This dynamic reactive current command is expressed as follows:

[0040] I Tq =K i (0.9-V orms )I N 0.2≤V orms ≤0.9 (9)

[0041] In the formula: I Tq The command K represents dynamic reactive current. i I represents the dynamic reactive current proportional gain of a photovoltaic inverter. N K represents the rated current of the photovoltaic inverter, under conditions of high reactive current output. iThe inverter's reactive current varies with the terminal voltage, ensuring it outputs three times the normal current regardless of any percentage drop in grid voltage. orms Indicates the effective value of the grid voltage at the grid connection point;

[0042] Due to inverter capacity limitations, the active current reference command is as follows:

[0043]

[0044] In the formula: I Td Indicates the variable of active current that the inverter needs to output; I lim This indicates the maximum current limit that the inverter can output;

[0045] Under current source control, because the phase-locked loop locks the inverter phase angle with the grid phase angle, its active and reactive power are decoupled. Active power has a linear relationship with the d-axis current, and reactive power has a linear relationship with the q-axis current. Under voltage source control, there is a phase difference between the inverter and the grid, making decoupling impossible. In this case, the relationships between active and reactive power and the d-axis and q-axis currents are as follows:

[0046]

[0047] From sh(11)s, the active and reactive power reference commands during low-voltage ride-through are obtained:

[0048]

[0049] The voltage support function is achieved by modifying the power command as described above.

[0050] Among them, V od Indicates the D-axis component of the generated modulated wave voltage; I fd V represents the D-axis component of the generated output current; oq Indicates the Q-axis component of the generated modulated wave voltage; I fq This represents the Q-axis component of the generated output current.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] This invention provides a dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system. The grid-side converter adopts self-synchronizing voltage source control. By simultaneously operating two grid-type control methods and using competitive dominance to achieve autonomous switching between the two control methods, self-synchronizing voltage source control in multiple operating ranges can be realized. While meeting the voltage source control requirements of different operating ranges, it also takes into account maximum power point tracking and DC bus voltage control, achieving a smooth transition during operating range switching and improving the stability, reliability and safety of the equipment. Attached Figure Description

[0053] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0054] Figure 1 This is a schematic diagram of a centralized photovoltaic inverter topology.

[0055] Figure 2 This is a diagram showing the operating status of a photovoltaic power generation system under full sunlight.

[0056] Figure 3 This is a block diagram of the self-synchronizing voltage source control for a centralized photovoltaic power generation system.

[0057] Figure 4 The strategy is a dual-mode parallel competition switching strategy;

[0058] Figure 5 Figures (a) to (c) in the figure show the simulation results of frequency modulation in the MPPT operating range;

[0059] Figure 6 Figures (a) to (c) in the figure show the simulation results of frequency modulation in the constant power operation range;

[0060] Figure 7 The figure shows the simulation results of a dual-mode parallel autonomous switching strategy under low-voltage ride-through conditions. Detailed Implementation

[0061] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0062] Example

[0063] This invention provides a dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system. Based on the needs of different operating ranges, corresponding centralized photovoltaic voltage source strategies are proposed. When switching between different ranges, a dual-mode parallel competitive autonomous switching method is used, with both modes operating simultaneously. Through the dual-mode parallel competitive autonomous strategy, a smooth switching effect is achieved, improving the safety and stability of the equipment.

[0064] The centralized photovoltaic power generation system includes a photovoltaic array and a grid-side converter; the grid-side converter includes various DC / AC converters, and the topology diagram of the centralized photovoltaic inverter is shown below. Figure 1 ;

[0065] The photovoltaic power generation system employs voltage source control; different control strategies are adopted according to different operating ranges of the photovoltaic system: in the MPPT operating range, inertial synchronous control is used, combined with MPPT control to achieve maximum active power output of the photovoltaic array; in the constant power range, virtual synchronous control is used, and the photovoltaic array autonomously maintains DC bus voltage stability based on the active power output of the inverter. The different operating ranges of the centralized photovoltaic power generation system under different light intensities are as follows: Figure 2 The control block diagram of the self-synchronizing voltage source of the centralized photovoltaic power generation system is as follows: Figure 3 ;

[0066] The dual-mode parallel autonomous switching strategy of the photovoltaic power generation system refers to the simultaneous operation of the grid-side DC / AC converter's inertial synchronization control loop and virtual synchronization control loop, regardless of whether it is in the MPPT operating range, constant power operating range, or low-voltage grid operating range. Autonomous smooth dynamic switching is achieved through a dual-mode parallel competitive autonomous strategy in different operating ranges.

[0067] The MPPT operating range self-synchronizing voltage source control strategy can be designed so that the photovoltaic array operates at its maximum power point, achieving maximum power output under the current operating conditions. The grid-side DC / AC converter operates under inertial synchronization control, and the grid-side synchronization loop switching switch S... ω In M1 mode, disturbances to the DC bus voltage are introduced into the grid-connection frequency of the grid-side DC / AC converter. This maintains the stability of the DC bus voltage while simultaneously synchronizing the inverter with the grid. The phase angle of the inverter output modulation voltage is:

[0068]

[0069] In the formula: ω0 represents the reference value of the power grid frequency, k pdc k represents the inertial synchronization proportional coefficient. idc V represents the inertial synchronization integral coefficient. dc This represents the actual value of the DC bus voltage, V. dcrefG represents the given value of the grid-side inertial synchronous DC bus voltage; s represents the Laplace expression for differential calculation.

[0070] Since inertial synchronization lacks damping, stabilizing damping can be added during the generation of the modulated wave voltage amplitude. The expression for this is:

[0071]

[0072] In the formula: V t0 Q represents the given value of the peak potential within the inverter; gref Q represents the given value of reactive power in the power grid. g This represents the actual value of the current reactive power of the power grid; k pt and k it D represents the proportional and integral coefficients of the reactive power control loop, respectively;pss This indicates the voltage damping stabilization compensation amount. Voltage stabilization switch S D In M1 mode.

[0073] D pss The disturbance V of the DC bus voltage can be used as a measure. dc get:

[0074]

[0075] In the formula: k pss T represents the damping stability proportional coefficient; c This represents the time constant of the high-pass filter.

[0076] When operating within the MPPT (Maximum Active Power Response Time) range, the photovoltaic (PV) power generation system has already reached its maximum active power output and cannot provide more active power to the grid. Therefore, when the grid frequency fluctuates, the system can only reduce its active power output as the grid frequency increases, causing the PV curve operating point to shift to the right from the MPPT operating point. The active power reference P... ref The instruction is:

[0077] P ref =V PV ·I PV +ΔP t (16)

[0078] In the formula V PV Represented as the photovoltaic panel port voltage, I PV ΔP represents the output current of the photovoltaic panel. t This represents the active power command for the photovoltaic power generation system participating in the grid frequency response offset. Under inertial synchronous control, the DC bus voltage maps to the grid frequency, ΔP. t It can be written as:

[0079] ΔP t =K c ·s·ΔV dc +K t ·ΔV dc (17)

[0080] Where: K c K represents the inertial response coefficient. c This represents the primary frequency modulation coefficient. Since ΔP t It cannot be greater than 0, nor can it be too small to reduce the accuracy of the MPPT algorithm; therefore, it is set to -0.2P. GN <ΔP t <0, P GN This refers to the rated power of the grid-side DC / AC converter.

[0081] The grid-side synchronous ring switching switch S for the constant power operation range and the low voltage operation range of the power grid ωIn M2 mode, the grid-side DC / AC converter employs virtual synchronization control. The error signal between the power reference command and the actual value of the grid output active power is introduced into the grid-connected frequency of the grid-side DC / AC converter through a virtual synchronization transfer function. The phase angle of its output modulation voltage is:

[0082]

[0083] In the formula: ω p Indicates the virtual synchronous output grid angular frequency error value; P gref Indicates the reference command for active power of the power grid; P g J represents the actual active power output of the grid-side converter; P D represents the virtual inertia coefficient of the virtual synchronization link. P This represents the virtual damping coefficient of the virtual synchronization link.

[0084] When using virtual synchronous control, damped stabilization already exists in the system. The output of the stabilization element is then:

[0085] D pss =0 (19)

[0086] Grid-side synchronous switching switch S ω In M2 mode, voltage stabilization switch S D In M2 mode, the active power output of the photovoltaic inverter is adjusted while simultaneously achieving grid frequency synchronization. Under conditions of enhanced solar illumination and no grid faults, the grid-side converter needs to participate in the grid frequency response, and its virtual synchronization control active power reference command is as follows:

[0087]

[0088] Where: K tc K represents the primary frequency modulation coefficient of the grid-side converter. gc This represents the inertia response coefficient of the grid-side converter. Since the photovoltaic power generation system operates in a constant power region, the photovoltaic array has an active power margin, thus allowing for increased output active power when the grid frequency decreases, achieving bidirectional frequency regulation. Currently, the inverter can output 1.1P of active power under unity power factor operation. GN It can be set to -0.2P. GN <ΔP t <0.1P GN .

[0089] The principle of the dual-mode parallel autonomous switching strategy:

[0090] (1) During steady-state operation of the power grid, in the MPPT operating range, the grid-side synchronization loop switching switch S ωIn M1 mode, as sunlight intensity increases and the output power of the photovoltaic modules increases, the grid-side active power output lags due to the small DC capacitance, leading to an increase in bus voltage, V dc Increase, V dcrefG ω remains unchanged dc Reduce; the active power P output of the grid-side converter g Get bigger, P gref ω remains unchanged p The output of the network side is reduced to ω, representing the dual-mode parallel competitive autonomous strategy selection. p Switch S D When operating in M2 mode, the system will automatically switch to the constant power operating range.

[0091] (2) During the constant power operation range, the grid-side synchronous loop switching switch S ω In M2 mode, as sunlight decreases, the photovoltaic output power decreases, the grid-side DC / AC converter output active power exceeds the input active power, the DC bus voltage gradually decreases, and the photovoltaic PV operating point shifts to the lower left, with its output V... dc Slightly decrease, ω dc Decrease; the grid-side output active power gradually decreases until it equals the input active power, ω p Increase, dual-mode parallel competitive autonomous strategy selection network-side output is ω dc Switch S D When operating in M1 mode, the system will automatically switch to the MPPT operating range.

[0092] (3) During a low-voltage fault in the power grid, the active power output of the grid-side DC / AC converter is blocked, the DC bus voltage rises, the photovoltaic operating point shifts to the right on the original PV curve, and the output V dc Increase, net side ω dc Increase; P gref It will decrease as the grid voltage decreases, and is related to P. g Keep it consistent, ω p The dual-mode parallel competitive autonomous strategy selection network-side output remains unchanged at ω. p Switch S D It operates in M2 mode.

[0093] (4) When the fault is recovered, the output power of the grid-side DC / AC converter is greater than the input power of the photovoltaic array, the DC bus voltage decreases, the photovoltaic returns to its original maximum power point, and the output V dc Decrease, net side ω dc Decrease; P gref With P g Keep it consistent, ω p The dual-mode parallel competitive autonomous strategy selection network-side output remains unchanged at ω. dc Switch S DOperating in M2 mode, it can autonomously switch over upon fault occurrence and termination. The dual-mode parallel contention switching strategy is as follows: Figure 4 As shown.

[0094] The inverter power reference command design during low-voltage grid faults is as follows: During low-voltage ride-through, the photovoltaic inverter needs to inject a dynamic reactive current into the power system that varies with the grid connection point voltage. The dynamic reactive current command is expressed as follows:

[0095] I Tq =K i (0.9-V orms )I N 0.2≤V orms ≤0.9 (21)

[0096] In the formula: I Tq The command K represents dynamic reactive current. i I represents the dynamic reactive current proportional gain of a photovoltaic inverter. N This represents the rated current of the photovoltaic inverter. K is used when the output reactive current is high. i It can vary with the terminal voltage, allowing the inverter to output 3 times the reactive current when the grid voltage drops by any proportion.

[0097] Due to inverter capacity limitations, the active current reference command is as follows:

[0098]

[0099] In the formula: I Td This represents the active current variable that the inverter needs to output.

[0100] Under current source control, because the phase-locked loop locks the inverter phase angle to the grid phase angle, its active and reactive power can be decoupled. Active power has a linear relationship with the d-axis current, and reactive power has a linear relationship with the q-axis current. However, under voltage source control, there is a phase difference between the inverter and the grid phase angle, so decoupling is not possible. In this case, the relationship between active and reactive power and the d-axis and q-axis currents is as follows:

[0101]

[0102] From (11), the active and reactive power reference commands during low-voltage ride-through can be obtained:

[0103]

[0104] The voltage support function is achieved by modifying the power command as described above.

[0105] Among them, V od Indicates the D-axis component of the generated modulated wave voltage; I fd V represents the D-axis component of the generated output current;oq Indicates the Q-axis component of the generated modulated wave voltage; I fq This represents the Q-axis component of the generated output current.

[0106] This invention relates to a self-synchronizing voltage source control strategy for a centralized photovoltaic power generation system, which achieves voltage source control by changing the control strategy of the grid-side DC / AC converter without changing the topology of the centralized photovoltaic power generation system.

[0107] Step 1: Design the MPPT operation range control structure based on the centralized photovoltaic power generation system according to equations (1) to (5), including the inertial synchronization control of the grid-side DC / AC converter, the design of the proportional coefficient, integral coefficient, stabilization link control parameters and frequency modulation commands based on the grid-side DC / AC converter system parameters, etc.

[0108] Step 2: Design the constant power operation range control structure based on the centralized photovoltaic power generation system according to equations (6) to (8), including the virtual synchronization control of the grid-side DC / AC converter, the design of the virtual synchronization inertia coefficient and damping coefficient based on the system parameters of the grid-side DC / AC converter, and the frequency modulation command, etc.

[0109] Step 3: Design a switching strategy for different operating ranges of the centralized photovoltaic power generation system based on the principle of dual-mode parallel competitive switching strategy;

[0110] Step 4: Design the power command of the grid-side DC / AC converter based on the centralized photovoltaic power generation system during low-voltage grid faults according to equations (9) to (12).

[0111] To demonstrate the proposed self-synchronizing voltage source control strategy based on a centralized photovoltaic inverter, PSCAD / EMTDC is used in conjunction with a specific simulation example to further illustrate and verify the above method. A 3300kW centralized photovoltaic inverter grid-connected system was established. The main circuit parameters of the system are shown in Table 1. Based on the steps described, a voltage source control strategy based on the centralized photovoltaic inverter's inertial synchronization control and virtual synchronization control was designed. A frequency modulation strategy based on the centralized photovoltaic inverter's voltage source control strategy and a smooth switching control strategy between different voltage source controls of the centralized photovoltaic inverter were also designed. The simulation results, including the output power waveform, DC bus voltage waveform, and grid-side DC / AC converter frequency waveform, are attached. Figure 5 Appendix Figure 6 and attached Figure 7 As shown.

[0112] Table 1 System Main Circuit Parameters

[0113] parameter value parameter value Rated output power 3300kW Rated output voltage 600V Maximum MPPT voltage 1450V Minimum MPPT voltage 875V Output filter inductor 0.07μH Output filter capacitor 3*55.8μF Single-unit bus support capacitor 27mF Rated output frequency 50Hz

[0114] Appendix Figure 5Simulation results show that during the MPPT operating range, from 3s to 8s, the grid-side DC / AC converter employs an inertial synchronous control strategy, utilizing MPPT to achieve maximum power output on the DC side. From 3s to 4s, the illuminance is 400W / m². 2 The output active power is 0.4 pu, the photovoltaic DC voltage is 1.01 pu, and the grid-side converter angular frequency is 1 pu; between 4s and 5.5s, the irradiance is reduced to 200W / m². 2 The output active power dropped to 0.2 pu. During this process, the DC voltage dropped to a minimum of 0.8 pu and eventually stabilized at 1.01 pu, while the grid-side converter frequency dropped to a minimum of 0.998 pu. Within 7 to 8 seconds, the illuminance recovered to 400 W / m². 2 The output active power recovered from 0.2 pu to 0.4 pu. During this process, the photovoltaic DC voltage rose to a maximum of 1.15 pu, and the grid-side converter frequency rose to a maximum of 1.002 pu. Simulation results show that, within the MPPT operating range, inertial synchronous control can achieve autonomous response to the grid frequency in centralized photovoltaic systems.

[0115] Appendix Figure 6 Simulation results show that during the constant power operation range, from 8s to 13s, the photovoltaic array maintains a stable DC bus voltage based on the active power output of the inverter. The grid-side DC / AC converter employs virtual synchronous control, achieving power balance between the photovoltaic array and the grid-side DC / AC converter by controlling the grid-side output power, while simultaneously realizing autonomous grid frequency response. When the grid frequency changes, the inverter reflects this through changes in active power. From 8s to 9s, the irradiance is 600W / m². 2 The output active power is 0.5 pu, the photovoltaic DC voltage is 1.12 pu, and the grid-side converter frequency is 1 pu; from 9s to 10.5s, the irradiance increases to 800W / m². 2 At this point, virtual synchronous control is used, and the output power is the rated power of the DC / AC converter. Therefore, the output active power remains at 0.5 pu, the photovoltaic DC voltage rises to 1.18 pu, and the GFM frequency stabilizes at 1 pu. When the load drops at 9.5s and 10s, the active power drops to a minimum of 0.4 pu, the photovoltaic DC voltage rises to a maximum of 1.2 pu, and the grid-side converter frequency rises to a maximum of 1.003 pu. When a low-voltage fault occurs at 10.5s, the output active power drops to 0, the output reactive power rises from 0 to 0.2 pu, the photovoltaic DC voltage rises to 1.2 pu, and the GFM frequency remains at 1 pu. At 11s, the fault is recovered, and the irradiance is 800W / m². 2The output active power is 0.5 pu, the photovoltaic DC voltage is 1.18 pu, and the grid-side converter frequency is 1 pu. Simulation results show that centralized photovoltaic systems in the constant power operation zone can achieve bidirectional autonomous adjustment of the grid frequency using virtual synchronization.

[0116] Appendix Figure 7 Simulation results show that, using a dual-mode parallel autonomous switching control strategy: from 5.5s to 6s, the grid-side converter employs inertial synchronous control; in the event of a low-voltage fault, the grid-side output power drops to 0, and the photovoltaic DC voltage rises from 1pu to 1.18pu. From 10.5s to 11s, the grid-side converter adopts a virtual synchronous control strategy; in the event of a low-voltage fault, it switches to inertial synchronous control, the output active power drops from 0.5pu to 0, and the photovoltaic DC voltage rises from 1.18pu to 1.21pu. The simulation results under both modes demonstrate that, when faults occur and exit, the loop competition control switching method results in a smooth DC bus voltage transition without overshoot or fluctuations, ensuring stable inverter operation.

[0117] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0118] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0119] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system, characterized in that, include: Photovoltaic arrays and grid-side converters; The grid-side converter includes various DC / AC converters; The photovoltaic array is connected to the same DC bus, and the DC bus is connected to the grid via a DC / AC converter. During the MPPT operating range, inertial synchronous control is used in conjunction with MPPT control to achieve the maximum active power output of the photovoltaic array; during the constant power operating range, virtual synchronous control is used, and the photovoltaic array autonomously maintains the DC bus voltage stability based on the active power output of the inverter. During the MPPT operating range, constant power operating range, or low-voltage grid operating range, the grid-side DC / AC converter's inertial synchronization control loop and virtual synchronization control loop operate simultaneously; in different operating ranges, autonomous smooth dynamic switching is achieved through a dual-mode parallel competition autonomous strategy.

2. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 1, characterized in that, The self-synchronization voltage source control strategy for the MPPT operating range includes: The photovoltaic array operates at its maximum power point, achieving maximum power output under current conditions. The grid-side DC / AC converter operates under inertial synchronous control, and the grid-side synchronous loop switching switch S... ω In M1 mode, disturbances to the DC bus voltage are introduced into the grid-connection frequency of the grid-side DC / AC converter. This maintains the stability of the DC bus voltage while simultaneously synchronizing the inverter with the grid. The phase angle of the inverter output modulation voltage is: In the formula: ω0 represents the reference value of the power grid frequency, k pdc k represents the inertial synchronization proportional coefficient. idc V represents the inertial synchronization integral coefficient. dc This represents the actual value of the DC bus voltage, V. dcrefG This represents the given value of the grid-side inertial synchronous DC bus voltage; s represents the Laplace expression method for differential calculation. Since inertial synchronization lacks damping, stabilizing damping is added during the generation of the modulated wave voltage amplitude. Its expression is as follows: In the formula: V t0 Q represents the given value of the peak potential within the inverter; gref Q represents the given value of reactive power in the power grid. g This represents the actual value of the current reactive power of the power grid; k pt and k it D represents the proportional and integral coefficients of the reactive power control loop, respectively; pss V represents the voltage damping stabilization compensation amount; t Indicates the magnitude of the modulated wave voltage; voltage stabilization switch S D In M1 mode; D pss By the amount of disturbance ΔV of the DC bus voltage dc It is obtained: where: k pss represents the damping stabilizing proportionality coefficient; T c represents the high-pass link time constant.

3. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 2, characterized in that, When operating within the MPPT range, the photovoltaic power generation system reduces active power output as grid frequency increases, causing the PV curve operating point to shift to the right from the MPPT operating point. The active power reference P... ref The instruction is: P ref =V PV ·I PV +ΔP t (28) where V PV represents the photovoltaic panel port voltage, I PV represents the photovoltaic panel output current, ΔP t represents the photovoltaic generation system active power instruction for participating in the grid frequency response deviation; Under the inertia synchronous control, the DC bus voltage maps the grid frequency, ΔP t is written as: ΔP t = K c · s · ΔV dc + K t · ΔV dc (29) In the formula: K c K represents the inertial response coefficient. c This represents the primary frequency modulation factor; -0.2P GN <ΔP t <0, P GN This refers to the rated power of the grid-side DC / AC converter.

4. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 3, characterized in that, The grid-side synchronous loop switching switch S for constant power operation range and low-voltage grid operation range ω In M2 mode, the grid-side DC / AC converter employs virtual synchronization control. The error signal between the power reference command and the actual value of the grid output active power is introduced into the grid-connection angle frequency of the grid-side DC / AC converter through a virtual synchronization transfer function. The phase angle of its output modulation voltage is: In the formula: ω p Indicates the virtual synchronous output grid angular frequency error value; P gref Indicates the power grid active power reference command; P g J represents the actual active power output of the grid-side converter; P D represents the virtual inertia coefficient of the virtual synchronization link; P This represents the virtual damping coefficient of the virtual synchronization link.

5. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 4, characterized in that, When using virtual synchronous control, damped stabilization already exists in the photovoltaic power generation system. The output of the stabilization stage is then: D pss ＝0 (31) Grid-side synchronous switching switch S ω In M2 mode, voltage stabilization switch S D In M2 mode, the active power output of the photovoltaic inverter is adjusted while grid frequency synchronization is achieved. Under conditions of enhanced solar illumination and no grid faults, the grid-side converter participates in the grid frequency response. Its virtual synchronization control active power reference command is: P gref = P GN + ΔP g (32) = P GN + (-K tc · ω p -K gc · s · ω p ) where: K tc represents the grid-side converter primary frequency modulation coefficient; K gc represents the grid-side converter inertia response coefficient; -0.2P GN <ΔP t <0.1P GN .

6. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 5, characterized in that, During steady-state operation of the power grid, in the MPPT operating range, the grid-side synchronization loop switching switch S... ω In M1 mode, as sunlight intensity increases and the output power of the photovoltaic modules increases, the grid-side active power output lags due to the small DC capacitance, leading to an increase in bus voltage, V dc Increase, V dcrefG ω remains unchanged dc Reduce; the active power P output of the grid-side converter g Get bigger, P gref ω remains unchanged p The output of the network side is reduced to ω, representing the dual-mode parallel competitive autonomous strategy selection. p Switch S D When operating in M2 mode, the photovoltaic power generation system automatically switches to the constant power operating range.

7. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 6, characterized in that, During constant power operation, the grid-side synchronous loop switching switch S ω In M2 mode, as sunlight decreases, the photovoltaic output power decreases, the grid-side DC / AC converter output active power exceeds the input active power, the DC bus voltage gradually decreases, and the photovoltaic PV operating point shifts to the lower left, with its output V... dc Slightly decrease, ω dc Decrease; the grid-side output active power gradually decreases until it equals the input active power, ω p Increase, dual-mode parallel competitive autonomous strategy selection network-side output is ω dc Switch S D When operating in M1 mode, the photovoltaic power generation system automatically switches to the MPPT operating range.

8. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 7, characterized in that, During a low-voltage fault in the power grid, the active power output of the grid-side DC / AC converter is blocked, the DC bus voltage rises, and the photovoltaic operating point shifts to the right on the original PV curve, resulting in a decrease in output V. dc Increase, net side ω dc Increase; P gref It decreases as the grid voltage decreases, and is related to P. g Keep it consistent, ω p The dual-mode parallel competitive autonomous strategy selection network-side output remains unchanged at ω. p Switch S D It operates in M2 mode.

9. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 8, characterized in that, When the fault is recovered, the output power of the grid-side DC / AC converter exceeds the input power of the photovoltaic array, the DC bus voltage decreases, the photovoltaic array returns to its original maximum power point, and the output V... dc Decrease, net side ω dc Decrease; P gref With P g Keep it consistent, ω p The dual-mode parallel competitive autonomous strategy selection network-side output remains unchanged at ω. dc Switch S D It operates in M2 mode and automatically switches when a fault occurs or ends.

10. The dual-mode parallel competitive autonomous self-synchronizing voltage source centralized photovoltaic power generation system according to claim 9, characterized in that, The inverter power reference command design during low-voltage grid faults includes: During low-voltage ride-through, the photovoltaic inverter injects a dynamic reactive current into the power system that varies with the grid connection point voltage. This dynamic reactive current command is expressed as follows: I Tq =K i (0.9-V orms )I N , 0.2≤V orms ≤0.9 (33) In the formula: I Tq The command K represents dynamic reactive current. i I represents the dynamic reactive current proportional gain of a photovoltaic inverter. N K represents the rated current of the photovoltaic inverter, under conditions of high reactive current output. i The inverter's reactive current varies with the terminal voltage, ensuring it outputs three times the normal current regardless of any percentage drop in grid voltage. orms Indicates the effective value of the grid voltage at the grid connection point; Due to inverter capacity limitations, the active current reference command is as follows: In the formula: I Td Indicates the variable of active current that the inverter needs to output; I lim This indicates the maximum current limit that the inverter can output; Under current source control, because the phase-locked loop locks the inverter phase angle with the grid phase angle, its active and reactive power are decoupled. Active power has a linear relationship with the d-axis current, and reactive power has a linear relationship with the q-axis current. Under voltage source control, there is a phase difference between the inverter and the grid, making decoupling impossible. In this case, the relationships between active and reactive power and the d-axis and q-axis currents are as follows: From sh(35)s, the active and reactive power reference commands during low-voltage ride-through are obtained: The voltage support function is achieved by modifying the power command as described above. Among them, V od Indicates the D-axis component of the generated modulated wave voltage; I fd V represents the D-axis component of the generated output current; oq Indicates the Q-axis component of the generated modulated wave voltage; I fq This represents the Q-axis component of the generated output current.

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