Photovoltaic off-grid power supply system and control method thereof

Abstract

The application relates to a photovoltaic off-grid power supply system and a control method thereof, and the system comprises a plurality of inverter voltage boosting units, a power flow coordination controller, a bus switch cabinet, a plurality of groups of transmitting optical fibers and receiving optical fibers; wherein the power flow coordination controller is connected with the plurality of inverter voltage boosting units in one-to-one correspondence through the plurality of groups of transmitting optical fibers and receiving optical fibers, and the output ends of the inverter voltage boosting units are connected with off-grid loads after being connected in parallel in the bus switch cabinet. The application specifies the master and the slave through the power flow coordination controller, sends a phase synchronization signal and a voltage amplitude instruction, each inverter unit generates an output voltage reference according to the instruction, and the stable operation and the accurate control of the multi-machine parallel off-grid power supply are realized.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power generation and supply technology, and in particular to a photovoltaic off-grid power supply system and its control method. Background Technology

[0002] In photovoltaic (PV) power generation applications, off-grid power supply systems are a key solution for providing electricity to areas without grid coverage or independent microgrids. Traditional off-grid PV systems typically require battery energy storage units to provide voltage and frequency support for off-grid PV and address the instantaneous power balance issue between PV output fluctuations and load power demand. However, the introduction of battery energy storage units brings problems such as high system cost, large footprint, complex maintenance, and limited battery life.

[0003] With the expansion of photovoltaic power plant scale and the increasing demands for power supply reliability, multiple inverter boost units are typically required to operate in parallel to expand system capacity and provide redundant power supply. However, operating multiple inverter units in parallel off-grid mode without energy storage presents even more severe technical challenges: the system must achieve real-time balance between photovoltaic input power and load power consumption through the inverter's own rapid response, without energy storage buffer; simultaneously, the output phases of each unit must be strictly synchronized to avoid circulating current, the output voltage amplitude must be coordinated and controlled to ensure power distribution, and the system must be able to maintain voltage stability during sudden changes in illumination or load switching. How to maintain voltage and frequency stability in an off-grid power supply system without energy storage is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a photovoltaic off-grid power supply system and its control method to solve the problems of high cost, complex maintenance and low reliability caused by the need to equip energy storage units in the existing off-grid photovoltaic system, as well as the defects of power balance difficulty and poor voltage stability when multiple inverter units are connected in parallel without energy storage. At the same time, it can realize the maximum power point tracking (MPPT) operation of photovoltaic modules under the condition of no energy storage.

[0005] To achieve the above objectives, the present invention provides the following solution: A photovoltaic off-grid power supply system includes: several inverter boost units, a power flow coordination controller, a combiner switch cabinet, and several sets of transmitting and receiving optical fibers; The power flow coordination controller is connected to several inverter boost units one by one through several sets of transmitting and receiving optical fibers. The output of the inverter boost units is connected in parallel in the combiner switch cabinet and then connected to the off-grid load.

[0006] Optionally, the inverter boost unit includes: a photovoltaic module, an input-side DC switch, a capacitor energy storage module, an inverter module, an AC filter module, a first AC switch, a boost transformer, and a second AC switch connected in sequence. An AC voltage and current sampling module is installed between the inverter module and the AC filter module to collect output voltage and current signals and transmit them to the inverter control unit. The inverter control unit is connected to a sampling unit, which is used to collect the output voltage and current of the inverter module.

[0007] Optionally, the capacitor energy storage module is composed of an energy storage capacitor or a bidirectional buck-boost circuit composed of an energy storage capacitor, an inductor and a switching transistor. The bidirectional buck-boost circuit includes: a bridge arm consisting of a first switch and a second switch connected in series, which is connected in parallel between the positive and negative terminals of the input bus; the midpoint of the bridge arm is connected to one end of an inductor; the other end of the inductor is connected to the positive terminal of an energy storage capacitor; and the negative terminal of the energy storage capacitor is connected to the negative terminal N of the input bus.

[0008] Optionally, the inverter module is any one of a two-level three-phase full-bridge inverter circuit, a diode-clamped three-level inverter circuit, or a T-type three-level inverter circuit.

[0009] Optionally, the power flow coordination controller includes a computing chip, a crystal oscillator circuit, an auxiliary power supply, and several sets of fiber optic transmitting interfaces and fiber optic receiving interfaces. The several sets of fiber optic transmitting interfaces are connected one-to-one with the fiber optic receiving interfaces of several inverter control units through several sets of transmitting optical fibers, and are used to send phase synchronization pulse signals and communication signals. The several sets of fiber optic receiving interfaces are connected one-to-one with the fiber optic transmitting interfaces of several inverter control units through several sets of receiving optical fibers, and are used to receive the status information of each inverter boost unit.

[0010] The present invention also provides a control method applied to the aforementioned photovoltaic off-grid power supply system, comprising: S1. Obtain the status information of several inverter boost units; S2. Use one of the inverter boost units as the master and the remaining inverter boost units as slaves; S3. Broadcast phase synchronization pulse signals to all inverter boost units at fixed intervals via phase synchronization optical fiber; S4. Control the output of the inverter module of the host and the output of the inverter module of the slave according to the phase synchronization pulse signal.

[0011] Optionally, controlling the inverter module output of the host includes: The inverter control unit of the host receives the phase synchronization pulse signal and captures the rising edge to generate the host real-time phase angle; The maximum power point tracking algorithm (MPPT) is executed. Based on the current output power-voltage characteristics of the photovoltaic module, the DC voltage reference value that maximizes the power is calculated by perturbation observation method or incremental conductance method, and the target amplitude of the output voltage is obtained. Based on the real-time phase angle of the host and the target amplitude, a voltage reference command for the host is generated and output to control the output of the host's inverter module.

[0012] Optionally, controlling the output of the inverter module of the slave unit includes: The inverter control unit of the host receives the phase synchronization pulse signal and captures the rising edge to generate the real-time phase angle of the slave. Based on the real-time phase angle of the slave device and the voltage reference command of the master device, a voltage reference command for the slave device is generated to control the output of the inverter module of the slave device.

[0013] The beneficial effects of this invention are as follows: By eliminating the energy storage unit, this invention significantly reduces system investment costs and operational complexity, and improves system reliability in harsh environments; the use of fiber optic communication to achieve hard real-time transmission of phase synchronization signals ensures the phase synchronization accuracy of multiple units in parallel under energy storage conditions, effectively suppressing circulating currents; through master-slave voltage amplitude coordination control, dynamic distribution of load power among each inverter unit is achieved, maintaining system voltage stability; the control strategy within the inverter unit organically combines the MPPT algorithm with off-grid voltage control, enabling photovoltaic modules to always operate at their maximum power point even without energy storage, improving the utilization rate of photovoltaic energy; the diversified design of the capacitor energy storage module enhances the system's adaptability to instantaneous power fluctuations. This invention is particularly suitable for cost-sensitive, difficult-to-maintain, and power-adjustable load applications. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the structure of a photovoltaic off-grid power supply system according to an embodiment of the present invention; Figure 2 The diagram below shows the structure of the capacitor energy storage module provided in the embodiment of the present invention, wherein (a) is the basic structure and (b) is the enhanced structure including a bidirectional buck-boost circuit; Figure 3This is a schematic diagram of the inverter module in an embodiment of the present invention, wherein (a) is a two-level three-phase full-bridge inverter circuit, (b) is a diode-clamped three-level inverter circuit, and (c) is a T-type three-level inverter circuit; Figure 4 This is a schematic diagram of the power flow coordination controller according to an embodiment of the present invention; Figure 5 A schematic diagram of the control method for a photovoltaic off-grid power supply system provided as a real-time example of the present invention; Among them, 101-Input-side DC switch, 102-Capacitor energy storage module, 103-Inverter module, 104-AC voltage and current sampling module, 105-AC filter module, 106-First AC switch, 107-Step-up transformer, 108-Second AC switch, 110-Inverter control unit, 111-Sampling unit, 114-Power flow coordination controller, 212-Transmitting optical fiber, 213-Receiving optical fiber, 115-Bus switch cabinet, 116-Photovoltaic module, 117-Off-grid load, 1021-Bus capacitor, 1022-Inductor, 1023-Energy storage capacitor, 1024 - First switch transistor, 1025 - Second switch transistor, 301 - Third switch transistor, 302 - Fourth switch transistor, 303 - Fifth switch transistor, 304 - Sixth switch transistor, 305 - Seventh switch transistor, 306 - Eighth switch transistor, 307 - Third capacitor, 308 - Fourth capacitor, 311 - Ninth switch transistor, 312 - Tenth switch transistor, 313 - Eleventh switch transistor, 314 - Twelfth switch transistor, 315 - First diode, 316 - Second diode, 317 - Thirteenth switch transistor, 318 - Fourteenth switch transistor, 319 - Fifteenth switch transistor, 320 - ... 16th switch transistor, 321-3rd diode, 322-4th diode, 323-17th switch transistor, 324-18th switch transistor, 325-19th switch transistor, 326-20th switch transistor, 327-5th diode, 328-6th diode, 331-5th capacitor, 332-6th capacitor, 333-21st switch transistor, 334-22nd switch transistor, 335-23rd switch transistor, 336-24th switch transistor, 337-25th switch transistor, 338-26th switch transistor, 339-27th switch transistor, 340-28th switch transistor Switching transistor, 341-29th switching transistor, 342-30th switching transistor, 343-31st switching transistor, 344-32nd switching transistor, 401-operational chip, 402-crystal oscillator circuit, 403-auxiliary power supply, 404-first fiber optic transmitting interface, 405-first fiber optic receiving interface, 406-second fiber optic transmitting interface, 407-second fiber optic receiving interface, 4041-first phase synchronization pulse transmitting module, 4042-first communication fiber optic transmitting module, 4061-second phase synchronization pulse transmitting module, 4062-second communication fiber optic transmitting module. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] This embodiment proposes a photovoltaic off-grid power supply system, including: several inverter boost units, power flow coordination controller 114, combiner switch cabinet 115, and several sets of transmitting optical fibers and receiving optical fibers; The power flow coordination controller 114 is connected to several inverter boost units one by one through several sets of transmitting optical fibers and receiving optical fibers. The output terminals of the inverter boost units are connected in parallel in the combiner switch cabinet 115 and then connected to the off-grid load 117.

[0019] Furthermore, the inverter boost unit includes: a photovoltaic module 116, an input-side DC switch 101, a capacitor energy storage module 102, an inverter module 103, an AC filter module 105, a first AC switch 106, a boost transformer 107, and a second AC switch 108 connected in sequence. An AC voltage and current sampling module 104 is installed between the inverter module 103 and the AC filter module 105 to collect output voltage and current signals and transmit them to the inverter control unit 110. The inverter control unit 110 is connected to a sampling unit 111, which is used to collect the output voltage and current of the inverter module 103.

[0020] Specifically, such as Figure 1 As shown, the off-grid photovoltaic power supply system of this embodiment includes M inverter boost units (M is an integer greater than or equal to 2), a power flow coordination controller 114, M sets of transmitting optical fibers, M sets of receiving optical fibers, and a combiner switch cabinet 115. Each inverter boost unit consists of an input-side DC switch 101, a capacitor energy storage module 102, an inverter module 103, an AC voltage and current sampling module 104, an AC filter module 105, a first AC switch 106, a boost transformer 107, a second AC switch 108, a combiner switch cabinet 115, an inverter control unit 110, and a sampling unit 111.

[0021] One end of the input-side DC switch 101 is connected to the photovoltaic module 116, and the other end is connected to the input terminal of the capacitor storage module 102. The output terminal of the capacitor storage module 102 is connected to the DC side of the inverter module 103. The AC output terminal of the inverter module 103 is connected to the input terminal of the AC filter module 105, and the output terminal of the AC filter module 105 is connected to the low-voltage side of the step-up transformer 107 via the first AC switch 106. The high-voltage side of the step-up transformer 107 is connected to the input busbar of the combiner switch cabinet 115 via the second AC switch 108. The output terminals of the M inverter step-up units are connected in parallel in the combiner switch cabinet 115 and then connected to the off-grid load 117 through the combiner switch cabinet. In this embodiment, the load is a resistive load, and the load power changes when the voltage amplitude output by the step-up inverter unit changes.

[0022] An AC voltage and current sampling module 104 is installed between an inverter module 103 and an AC filter module 105 to collect output voltage and current signals and transmit them to an inverter control unit 110.

[0023] The power flow coordination controller 114 is connected to the inverter control unit 110 in each inverter boost unit via a set of transmitting optical fibers 212 and a set of receiving optical fibers 213. The transmitting optical fibers include a phase synchronization optical fiber and a communication signal transmitting optical fiber, while the receiving optical fiber is a communication signal receiving optical fiber. This fiber optic communication method ensures hard real-time transmission of the phase synchronization signal and effectively avoids electromagnetic interference.

[0024] Furthermore, the capacitor energy storage module 102 is composed of an energy storage capacitor 1023 or a bidirectional buck-boost circuit composed of an energy storage capacitor 1023, an inductor, and a switching transistor. The bidirectional buck-boost circuit includes: the positive and negative terminals of the bus capacitor 1021 are respectively connected to the positive and negative terminals of the DC bus; a bridge arm formed by the series connection of the first switch transistor 1024 and the second switch transistor 1025 is connected in parallel between the positive and negative terminals of the input bus; the midpoint of the bridge arm is connected to one end of the inductor 1022; the other end of the inductor 1022 is connected to the positive terminal of the energy storage capacitor 1023; and the negative terminal of the energy storage capacitor 1023 is connected to the negative terminal N of the input bus.

[0025] Specifically, such as Figure 2 As shown, there are two preferred implementation methods for the capacitor energy storage module 2. Figure 2 (a) is the basic structure: at least one set of capacitors C are connected in parallel between the positive terminal P and the negative terminal N of the input bus to provide instantaneous energy buffer. Figure 2(b) An enhanced structure including a bidirectional buck-boost circuit: A bridge arm formed by the series connection of the first switch 1024 and the second switch 1025 is connected in parallel between the positive and negative terminals of the input bus. The midpoint of the bridge arm is connected to one end of the inductor 1022, and the other end of the inductor 1022 is connected to the positive terminal of the energy storage capacitor 1023. The negative terminal of the energy storage capacitor 1023 is connected to the negative terminal N of the input bus. This circuit allows energy to flow bidirectionally and actively adjusts the DC bus voltage when photovoltaic power fluctuates, enhancing system stability.

[0026] Furthermore, the inverter module 103 is any one of a two-level three-phase full-bridge inverter circuit, a diode-clamped three-level inverter circuit, or a T-type three-level inverter circuit.

[0027] Furthermore, such as Figure 3 As shown, inverter module 3 can adopt various circuit topologies. Figure 3 (a) is a two-level three-phase full-bridge inverter circuit, which consists of six switching transistors and has a simple structure. The third switching transistor 301 and the fourth switching transistor 302 are connected in series to form the A-phase bridge arm, the fifth switching transistor 303 and the sixth switching transistor 304 are connected in series to form the B-phase bridge arm, and the seventh switching transistor 305 and the eighth switching transistor 306 are connected in series to form the A-phase bridge arm.

[0028] Figure 3 (b) is a three-level inverter circuit based on diode clamping, which can reduce output voltage harmonics and switching transistor voltage stress. The three-level inverter circuit based on diode clamping includes two sets of capacitors, namely the third capacitor 307 and the fourth capacitor 308, which are connected in series; the ninth switch 311, the tenth switch 312, the eleventh switch 313, and the twelfth switch 314 are connected in series and clamped by the first diode 315 and the second diode 316 to form the A-phase bridge arm; similarly, the thirteenth switch 317, the fourteenth switch 318, the fifteenth switch 319, and the sixteenth switch 320 are connected in series and clamped by the third diode 321 and the fourth diode 322 to form the B-phase bridge arm; the seventeenth switch 323, the eighteenth switch 324, the nineteenth switch 325, and the twentieth switch 326 are connected in series and clamped by the fifth diode 327 and the sixth diode 328 to form the C-phase bridge arm.

[0029] Figure 3(c) is a T-type three-level inverter circuit. According to the attached diagram, the DC side of the T-type three-level inverter circuit includes a positive bus P, a negative bus N, and a neutral point O formed by a series capacitor group consisting of the fifth capacitor 331 and the sixth capacitor 332. The specific connection relationships of the switching transistors in the attached diagram are as follows: the emitter of the twenty-first switch 333 is connected to the neutral point O, and its collector is connected to the collector of the twenty-second switch 334; the emitter of the twenty-second switch 334 is connected to output phase A; the emitter of the twenty-third switch 335 is connected to the neutral point O, and its collector is connected to the collector of the twenty-fourth switch 336; the emitter of the twenty-fourth switch 336 is connected to output phase B; the emitter of the twenty-fifth switch 337 is connected to the neutral point O, and its collector is connected to the collector of the twenty-sixth switch 338. Connections: The emitter of the 26th switch transistor 338 is connected to the output phase C; the collector of the 27th switch transistor 339 is connected to the positive P bus and the emitter is connected to the output phase A; the collector of the 28th switch transistor 340 is connected to the output phase B and the emitter is connected to the negative N bus; the collector of the 29th switch transistor 341 is connected to the positive P bus and the emitter is connected to the output phase B; the collector of the 30th switch transistor 342 is connected to the output phase B and the emitter is connected to the negative N bus; the collector of the 31st switch transistor 343 is connected to the positive P bus and the emitter is connected to the output phase C; the collector of the 32nd switch transistor 344 is connected to the output phase C and the emitter is connected to the neutral point O.

[0030] Furthermore, the power flow coordination controller 114 includes a computing chip 401, a crystal oscillator circuit 402, an auxiliary power supply 403, and several sets of fiber optic transmitting interfaces and fiber optic receiving interfaces. The several sets of fiber optic transmitting interfaces are connected one-to-one with the fiber optic receiving interfaces of several inverter control units 110 through several sets of transmitting optical fibers, and are used to send phase synchronization pulse signals and communication signals. The several sets of fiber optic receiving interfaces are connected one-to-one with the fiber optic transmitting interfaces of several inverter control units 110 through several sets of receiving optical fibers, and are used to receive the status information of each inverter boost unit 110.

[0031] Specifically, such as Figure 4As shown, the power flow coordination controller includes a computing chip 401, a crystal oscillator circuit 402, an auxiliary power supply 403, and M sets of fiber optic transmitting interfaces and M sets of fiber optic receiving interfaces. Each set of first fiber optic transmitting interfaces 404, second fiber optic transmitting interfaces 406, etc., is connected to a corresponding transmitting fiber (phase synchronization fiber and communication signal transmitting fiber), and each set of first fiber optic receiving interfaces 405, second fiber optic receiving interfaces 407, etc., is connected to a corresponding receiving fiber (communication signal receiving fiber). Each set of transmitting fiber optic interfaces includes two optical transmitting modules. For example, the first fiber optic transmitting interface 404 includes a first phase synchronization pulse transmitting module 4041 and a first communication fiber optic transmitting module 4042, and the second fiber optic transmitting interface 406 includes a second phase synchronization pulse transmitting module 4061 and a second communication fiber optic transmitting module 4062. The computing chip 401 communicates at high speed with each inverter control unit through the fiber optic interface, sending phase synchronization pulses and voltage amplitude commands, and receiving power, voltage, and other information uploaded by each unit. The crystal oscillator circuit 402 provides a high-precision clock source to ensure the accuracy of the phase synchronization signal. The auxiliary power supply 403 supplies power to the internal circuitry of the controller.

[0032] This embodiment also provides a control method applied to a photovoltaic off-grid power supply system, including: S1. Obtain the status information of several inverter boost units; S2. Use one of the inverter boost units as the master and the remaining inverter boost units as slaves; S3. Broadcast phase synchronization pulse signals to all inverter boost units at fixed intervals via phase synchronization optical fiber; S4. Control the output of the inverter module of the host and the output of the inverter module of the slave according to the phase synchronization pulse signal.

[0033] Furthermore: the output of the inverter module controlling the host includes: The inverter control unit of the host receives the phase synchronization pulse signal and captures the rising edge to generate the host real-time phase angle; The maximum power point tracking algorithm (MPPT) is executed. Based on the current output power-voltage characteristics of the photovoltaic module, the DC voltage reference value that maximizes the power is calculated by perturbation observation method or incremental conductance method, and the target amplitude of the output voltage is obtained. Based on the real-time phase angle of the host and the target amplitude, a voltage reference command for the host is generated and output to control the output of the host's inverter module.

[0034] Furthermore, controlling the output of the slave inverter module includes: The inverter control unit of the host receives the phase synchronization pulse signal and captures the rising edge to generate the real-time phase angle of the slave. Based on the real-time phase angle of the slave device and the voltage reference command of the master device, a voltage reference command for the slave device is generated to control the output of the inverter module of the slave device.

[0035] Specifically, such as Figure 5 As shown, the control methods of this system include power flow coordination control method 501 and inverter unit control method 502, wherein the power flow coordination control method 501 is specifically implemented as follows: The first step, status information acquisition 5011: The power flow coordination controller periodically acquires information such as active power P, reactive power Q, input voltage Vdc, output voltage Vout, and current voltage amplitude command status of M inverter boost units through communication signal receiving optical fiber.

[0036] The second step, master / slave designation 5012: After system startup, the power flow coordination controller designates one inverter boost unit as the master unit and the rest as slave units through internal settings or dynamic election. The selection of the master unit can be based on factors such as unit number and photovoltaic power generation capacity.

[0037] The third step is the phase synchronization signal broadcast 5013: The power flow coordination controller uses its internal crystal oscillator circuit to generate a high-precision clock, which broadcasts phase synchronization pulses to all inverter boost units at a fixed period (e.g., 20ms) via the phase synchronization fiber. The rising edge of this pulse serves as the reference for calculating the phase angle of each unit.

[0038] Step 4: Voltage Amplitude Command Issuance 5014: The power flow coordination controller monitors the current output voltage amplitude of the master unit and uses this amplitude as a reference value. It then sends a voltage amplitude command to all slave units via fiber optic communication. The slave units will use this command as the target for their own output voltage amplitude.

[0039] Inverter unit control method 502 is divided into master inverter unit control method and slave inverter unit control method. The control method of the master control unit is as follows: The first step is phase acquisition and calculation 5021. The inverter control unit of the main unit receives the phase synchronization fiber optic signal from the power flow coordination controller and detects the rising edge of the pulse through the capture unit. Each time a rising edge is captured, the internal unit performs integration to calculate the real-time phase angle and generates the real-time phase angle θ.

[0040] The second step involves the main unit controlling the 5022 via MPPT. The main unit's inverter control unit executes the photovoltaic maximum power point tracking (MPPT) algorithm. Based on the current output power-voltage characteristics of the photovoltaic modules, it calculates the DC voltage reference value that maximizes power using methods such as perturbation observation or incremental conductance, thereby obtaining the required AC output voltage amplitude Vref_master. This amplitude is dynamically adjusted to adapt to changes in sunlight and temperature.

[0041] The third step is output voltage control 5023. The host computer generates the three-phase voltage reference command Vref_abc = Vref_master based on the real-time phase θ and voltage amplitude Vref_master. sin(θ + φ), where φ is the three-phase phase offset (0, 120°, 240°). The inverter control unit 110 compares the voltage reference command with the actual voltage and current fed back by the sampling module 104, and generates a PWM trigger pulse through a voltage and current dual closed-loop control algorithm (such as PI regulation) to drive the switching transistors of the inverter module 103, so that the inverter output voltage accurately tracks the command.

[0042] The slave control method is as follows: The first step is phase acquisition and calculation 5024. The slave inverter control unit also receives the phase synchronization fiber optic signal and calculates the real-time phase angle θ in the same way to ensure strict phase synchronization with the master unit.

[0043] The second step involves the slave unit controlling the 5022 MPPT. The slave unit receives the voltage amplitude command Vref_slave (i.e., the master unit's voltage amplitude) from the power flow coordination controller via fiber optic communication. Based on the real-time phase θ and the received voltage amplitude Vref_slave, the slave unit generates the three-phase voltage reference command Vref_abc = Vref_slave. sin(θ + φ). Where φ is the compensation phase angle. The output power of the slave device is adjusted by φ to realize the MPPT function.

[0044] The third step is output voltage control 5026. The slave inverter control unit also generates PWM pulses through closed-loop control to drive the inverter module, making its output voltage amplitude consistent with that of the master unit, thereby achieving power distribution and system stability.

[0045] When sunlight changes or load switching occurs, the main unit adjusts the voltage amplitude via MPPT (Multi-Phase Transmission Timing), and the power flow coordination controller synchronizes this amplitude to the slave units in real time. All units adjust their output voltage synchronously, while the instantaneous buffering capacity of the capacitor storage module ensures a smooth transition. Due to strict phase synchronization and consistent voltage amplitude, there is almost no circulating current between units, achieving stable off-grid operation without energy storage and maximizing the utilization of photovoltaic energy.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A photovoltaic off-grid power supply system, characterized in that, include: Several inverter boost units, power flow coordination controller (114), combiner switch cabinet (115), several sets of transmitting optical fibers (212) and receiving optical fibers (213). The power flow coordination controller (114) is connected to several inverter boost units one by one through several sets of transmitting optical fibers (212) and receiving optical fibers (213). The output end of the inverter boost unit is connected in parallel in the combiner switch cabinet (115) and then connected to the off-grid load (117).

2. The photovoltaic off-grid power supply system according to claim 1, characterized in that, The inverter boost unit includes: a photovoltaic module (116), an input-side DC switch (101), a capacitor energy storage module (102), an inverter module (103), an AC filter module (105), a first AC switch (106), a boost transformer (107), and a second AC switch (108) connected in sequence. An AC voltage and current sampling module (104) is installed between the inverter module (103) and the AC filter module (105) to collect output voltage and current signals and transmit them to the inverter control unit (110). The inverter control unit (110) is connected to a sampling unit (111), which is used to collect the output voltage and current of the inverter module (103).

3. The photovoltaic off-grid power supply system according to claim 2, characterized in that, The capacitor energy storage module (102) is composed of an energy storage capacitor (1023) or a bidirectional buck-boost circuit composed of an energy storage capacitor (1023), an inductor and a switching transistor; The bidirectional buck-boost circuit includes: a bridge arm formed by a first switch (1024) and a second switch (1025) connected in series is connected in parallel between the positive and negative terminals of the input bus. The midpoint of the bridge arm is connected to one end of an inductor (1022). The other end of the inductor (1022) is connected to the positive terminal of an energy storage capacitor (1023). The negative terminal of the capacitor (1023) is connected to the negative terminal N of the input bus.

4. The photovoltaic off-grid power supply system according to claim 2, characterized in that, The inverter module (103) is any one of a two-level three-phase full-bridge inverter circuit, a diode-clamped three-level inverter circuit, or a T-type three-level inverter circuit.

5. The photovoltaic off-grid power supply system according to claim 2, characterized in that, The power flow coordination controller (114) includes a computing chip (401), a crystal oscillator circuit (402), an auxiliary power supply (403), and several sets of fiber optic transmitting interfaces and fiber optic receiving interfaces. The several sets of fiber optic transmitting interfaces are connected one-to-one with the fiber optic receiving interfaces of several inverter control units (110) through several sets of transmitting optical fibers, and are used to send phase synchronization pulse signals and communication signals. The several sets of fiber optic receiving interfaces are connected one-to-one with the fiber optic transmitting interfaces of several inverter control units (110) through several sets of receiving optical fibers, and are used to receive the status information of each inverter boost unit (110).

6. A control method applied to the photovoltaic off-grid power supply system according to any one of claims 1-5, characterized in that, include: S1. Obtain the status information of several inverter boost units; S2. Use one of the inverter boost units as the master and the remaining inverter boost units as slaves; S3. Broadcast phase synchronization pulse signals to all inverter boost units at fixed intervals via phase synchronization optical fiber; S4. Control the output of the inverter module of the host and the output of the inverter module of the slave according to the phase synchronization pulse signal.

7. The control method according to claim 6, characterized in that, The output of the inverter module controlling the host includes: The inverter control unit of the host receives the phase synchronization pulse signal and captures the rising edge to generate the host real-time phase angle; The maximum power point tracking algorithm (MPPT) is executed. Based on the current output power-voltage characteristics of the photovoltaic module, the DC voltage reference value that maximizes the power is calculated by perturbation observation method or incremental conductance method, and the target amplitude of the output voltage is obtained. Based on the real-time phase angle of the host and the target amplitude, a voltage reference command for the host is generated and output to control the output of the host's inverter module.

8. The control method according to claim 7, characterized in that, The output of the inverter module controlling the slave unit includes: The inverter control unit of the host receives the phase synchronization pulse signal and captures the rising edge to generate the real-time phase angle of the slave. Based on the real-time phase angle of the slave device and the voltage reference command of the master device, a voltage reference command for the slave device is generated to control the output of the inverter module of the slave device.

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