A multi-path direct current convergence photovoltaic inverter network construction control method and device

Abstract

The application belongs to the technical field of new energy power generation control, and discloses a kind of multi-path direct current convergence photovoltaic inverter network construction control method and device, method includes: selecting at least one photovoltaic branch as leading branch, the rest photovoltaic branch as subordinate branch;Leading branch operates in maximum power point tracking mode, subordinate branch operates in fast power control mode;Coordination controller generates global power reference instruction based on direct current bus voltage deviation, and combines the output capacity reference provided by leading branch and the actual output power of inverter, generates the active power instruction of each subordinate branch and issues to each subordinate branch;Coordination controller adaptively adjusts inverter active instruction based on the relationship between actual output power of inverter and photovoltaic branch estimated output limit;Direct current / alternating current controller obtains inverter active instruction, generates driving signal of inverter power switch based on network construction type control strategy through current-voltage double closed loop regulation, to realize the dynamic coordination of multi-path photovoltaic power.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation control technology, specifically relating to a grid control method and device for a photovoltaic inverter with multi-channel DC convergence. Background Technology

[0002] The large-scale deployment of photovoltaic power generation places higher demands on the stable operation of the power grid. Traditional grid-connected inverters rely on grid voltage and frequency for synchronization, which can easily lead to wide-frequency oscillations in weak grid scenarios. In recent years, grid-connected control has gradually become a research hotspot. By simulating the external characteristics of synchronous generators, inverters can autonomously establish and regulate grid voltage and frequency, effectively enhancing the system's inertia and damping characteristics.

[0003] With the continuous increase in the penetration rate of new energy sources, the installed capacity of photovoltaic power plants is constantly expanding. The photovoltaic inverter structure with multiple DC convergence has been widely used due to its modular design, high fault tolerance, and good scalability. However, this architecture also faces important technical challenges, mainly including the power coupling effect between the input channels and the coordinated control of multiple channels during dynamic processes.

[0004] In DC convergence photovoltaic systems, each branch forms a strong physical coupling through a common DC bus, which brings about the following two problems: internal circulating current and power loss. If the port voltage equalization control fails, circulating current or additional ripple current will be generated between channels; the risk of dynamic stability increases. Power fluctuations in a single channel may propagate to other channels through the coupling path, causing local disturbances to evolve into global oscillations, which may lead to system control instability in severe cases.

[0005] Existing research mostly focuses on traditional grid-connected control modes and generally adopts the maximum power point tracking control framework, failing to fully consider the dynamic interaction and coordination requirements between branches in the grid-connected mode. In addition, in traditional schemes, all photovoltaic branches participate in global optimization, resulting in slow system response and difficulty in meeting the frequency regulation, voltage regulation, and inertial damping support requirements of grid-connected inverters in large-scale renewable energy access scenarios. Summary of the Invention

[0006] To address the issues of slow response and strong AC / DC coupling in existing multi-DC convergence photovoltaic systems under grid-connection mode, this invention provides a grid-connection control method and device for multi-DC convergence photovoltaic inverters, which achieves dynamic coordination and optimized allocation of multi-channel photovoltaic power, effectively improving the inverter's dynamic response speed and stability.

[0007] This invention provides the following technical solution: The primary objective of this invention is to provide a grid control method for a photovoltaic inverter with multi-channel DC convergence, comprising: At least one photovoltaic branch is selected as the dominant branch, and the remaining photovoltaic branches are designated as subordinate branches; the dominant branch operates in maximum power point tracking mode, and the subordinate branches operate in fast power control mode. The coordinating controller generates a global power reference command based on the DC bus voltage deviation, and combines the output capacity benchmark provided by the main branch and the actual output power of the inverter to generate active power commands for each subordinate branch and send them to each subordinate branch. The coordinating controller adaptively adjusts the active power command of the inverter based on the relationship between the actual output power of the inverter and the estimated output limit of the photovoltaic branch. The DC / AC controller acquires the active power command from the inverter and generates the drive signal for the inverter power switch through dual closed-loop regulation of current and voltage based on the grid-type control strategy.

[0008] The dominant branch is selected for maximum power point tracking to estimate the output capacity benchmark of the photovoltaic branch. Combined with the DC bus voltage deviation and the actual inverter output power, the power control of the subordinate branches is coordinated. Through differentiated control of the master and slave branches, the response lag caused by all parallel branches participating in global optimization is avoided, effectively improving the inverter's response speed and tracking accuracy to power commands. Simultaneously, the differentiated control of the master and slave branches decouples the strong relationship between AC-side grid control and DC bus voltage regulation, allowing the inverter to move beyond a single voltage regulation constraint and achieve more flexible grid control.

[0009] As a preferred option, the calculation of the output capacity benchmark includes: The local controller of the dominant branch monitors the output voltage and current of the dominant branch in real time, calculates the maximum power reference value of the dominant branch using a maximum power point tracking (MPPT) algorithm, and uploads this maximum power reference value as the output capacity benchmark to the coordinating controller. By utilizing the dominant branch to detect environmental physical limits in real time, a reliable basis is provided for power allocation by the coordinating controller, ensuring the scientific nature of power scheduling.

[0010] Preferably, the coordinating controller generates active power commands for each subordinate branch, including: Based on the DC bus voltage deviation, a global power reference command is generated through voltage closed-loop control. Based on the global power reference command, the output capacity benchmark provided by the dominant branch, and the actual output power of the inverter, the total output of the subordinate branches other than the dominant branch is calculated, and the total output is evenly distributed to each subordinate branch.

[0011] Based on the power balance relationship between the AC and DC sides of the inverter, the global power reference command is reasonably allocated to ensure that the DC side power can dynamically adjust in line with the AC side power, so that the AC side of the inverter can get rid of the traditional voltage regulation constraint and achieve more flexible grid control.

[0012] Preferably, the coordination controller adaptively adjusts the inverter's active power command based on the relationship between the inverter's actual output power and the estimated output limit of the photovoltaic branch, including: The estimated output limit of the photovoltaic branch includes the early warning output limit and the safe output limit; The coordinating controller generates an inverter operating range flag signal based on the relationship between the actual output power of the inverter and the early warning output limit and safe output limit of the photovoltaic branch. The coordinating controller determines the inverter's operating mode based on the operating range flag signal and adaptively adjusts the inverter's active power command based on the inverter's operating mode.

[0013] By designing dual thresholds for early warning and safety, a safety boundary for system operation is established to avoid system instability caused by excessive issuance of instructions and to ensure the safe operation of the system under conditions such as sudden changes in irradiation.

[0014] Preferably, the operating modes include normal mode, early warning mode, and adjustment mode; If the actual output power of the inverter is less than or equal to the warning output limit of the photovoltaic branch, the inverter is in normal mode and maintains active power command. If the actual output power of the inverter is greater than the warning output limit of the photovoltaic branch and less than or equal to the safe output limit of the photovoltaic branch, the inverter enters the warning mode and performs a limit operation on the active power command. The active power command at the moment of entering the warning mode is used as the upper limit of the subsequent active power command. If the actual output power of the inverter exceeds the safe output limit of the photovoltaic branch, the inverter enters the regulation mode and adaptively adjusts the active power command based on the power response deviation of each subordinate branch.

[0015] Further refine the instruction adjustment strategies under different operating modes to achieve a balance between maximizing the utilization of photovoltaic branch response capabilities and ensuring safety. When the system approaches or exceeds physical limits, limit-down (early warning mode) or negative feedback correction (regulation mode) is used to maximize the utilization of photovoltaic response capabilities. In regulation mode, negative feedback is used to forcibly reduce active power commands, ensuring that AC and DC power can quickly recover balance under extreme conditions and preventing system disconnection from the grid.

[0016] Preferably, the active power command is adaptively corrected within a preset time after the operating mode switches from the warning mode and / or regulation mode back to the normal mode. This ensures a smooth transition of power commands when the system recovers from the warning mode and / or regulation mode back to the normal mode, preventing the warning from being triggered again due to sudden changes in commands.

[0017] Preferably, the output power of the subordinate branch is less than the output capacity benchmark provided by the dominant branch.

[0018] Taking advantage of the flat voltage-power characteristic to the left of the maximum power point, it can effectively suppress DC bus voltage fluctuations when irradiation drops rapidly, and enhance the operational stability of subordinate branches under sudden environmental changes.

[0019] Preferably, the grid-based control strategy includes droop control, virtual synchronous machine control, virtual impedance control, or adaptive damping algorithms. It supports multiple grid-based algorithms, enabling large-scale photovoltaic systems to provide simulated inertia, damping support, or suppression of broadband oscillations according to the actual needs of the power grid.

[0020] Preferably, the coordination controller maintains communication with the local controller and DC / AC controller of each photovoltaic branch. During the control cycle, it acquires the status data of the inverter and each photovoltaic branch in real time, updates and sends the active power command of each subordinate branch to the local controller of each subordinate branch, and updates and sends the active power command of the inverter to the DC / AC controller.

[0021] The second objective of this invention is to provide a multi-channel DC convergence photovoltaic inverter grid control device for the above-mentioned method, comprising: The coordinating controller is configured to generate a global power reference based on the DC bus voltage deviation, and combine the output capacity benchmark provided by the main branch with the actual output power of the inverter to generate active power commands for each subordinate branch and send them to each subordinate branch. Based on the relationship between the actual output power of the inverter and the estimated output limit of the photovoltaic branch, it adaptively adjusts the active power commands of the inverter. Multiple local controllers are connected to their respective photovoltaic branches. At least one local controller is configured to operate in maximum power point tracking mode to estimate the power output capability benchmark and upload it to the coordinating controller. The remaining local controllers are configured to operate in fast power control mode to respond to the active power command issued by the coordinating controller. The DC / AC controller is configured to generate drive signals for the inverter power switch through dual closed-loop regulation of current and voltage based on a grid-type control strategy. The coordination controller is communicatively connected to each of the local controllers and the DC / AC controller.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a master-slave power control architecture, selecting the dominant branch to operate in maximum power point tracking mode to estimate the photovoltaic system's output capacity benchmark, while the remaining subordinate branches operate in power control mode. This avoids the slow response problem caused by all photovoltaic branches participating in global optimization in traditional solutions, effectively improving the response speed and tracking accuracy of multi-DC converged photovoltaic systems to power commands, and enhancing the system's robustness in real-time scheduling. Simultaneously, the coordinating controller generates global power based on the DC bus voltage deviation and allocates power according to the output capacity benchmark and the actual inverter output power, decoupling the strong coupling between AC-side grid control and DC bus voltage regulation, enabling rapid DC-side power response to AC-side grid demand.

[0023] This invention is based on a multi-branch limit control architecture, which implements differentiated collaborative control for the dominant and subordinate branches. It determines the operating range based on the relationship between the actual output power of the inverter and the estimated output limit, and adaptively adjusts the active power command of the inverter. This realizes the full utilization of the response capability of each photovoltaic branch, effectively preserves the frequency and voltage regulation capability and inertial damping support characteristics of the grid-type inverter in the scenario of large-scale new energy access, and improves the reliability and scheduling flexibility of the photovoltaic system over a wide operating range. Attached Figure Description

[0024] Figure 1 A control block diagram of a photovoltaic inverter grid control method for multi-channel DC convergence provided by the present invention; Figure 2 A schematic diagram of the operation mode of a photovoltaic inverter grid control method with multi-channel DC convergence provided by the present invention; Figure 3 A schematic diagram illustrating the implementation process of a multi-channel DC convergence photovoltaic inverter grid control method provided by the present invention; Figure 4 The present invention provides a control block diagram of the local controller of each photovoltaic branch of a photovoltaic inverter for a multi-DC convergence photovoltaic inverter network control method. Figure 5 The simulation operation effect of the photovoltaic inverter grid control method with multi-DC convergence provided by the present invention under uniform irradiance conditions is shown in the figure. Figure 6 Simulation results of a multi-DC convergence photovoltaic inverter grid control method provided by the present invention under non-uniform irradiance conditions. Figure 7 Simulation results of a multi-DC convergence photovoltaic inverter grid control method provided by the present invention under islanded operation conditions; Figure 8 A schematic diagram of a photovoltaic inverter grid control device for multi-channel DC convergence provided by the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0026] The present invention will now be described in further detail with reference to the accompanying drawings: Example 1: like Figure 1 and Figure 3 As shown, this embodiment provides a grid control method for a photovoltaic inverter with multi-channel DC convergence, the method including the following steps: At least one photovoltaic branch is selected as the dominant branch, and the remaining photovoltaic branches are designated as subordinate branches; the dominant branch operates in maximum power point tracking mode, and the subordinate branches operate in fast power control mode. The coordinating controller generates a global power reference command based on the DC bus voltage deviation, and combines the output capacity benchmark provided by the main branch and the actual output power of the inverter to generate active power commands for each subordinate branch and send them to each subordinate branch. The coordinating controller adaptively adjusts the active power command of the inverter based on the relationship between the actual output power of the inverter and the estimated output limit of the photovoltaic branch. The DC / AC controller acquires the active power command from the inverter and generates the drive signal for the inverter power switch through dual closed-loop regulation of current and voltage based on the grid-type control strategy.

[0027] The method provided in this embodiment is applied to a photovoltaic inverter system containing multiple photovoltaic branches. Through a hierarchical collaborative control architecture, it achieves dynamic coordination and optimized allocation of photovoltaic power, ensuring the stable operation of the system in grid-connected mode.

[0028] In multi-DC convergence photovoltaic systems, if each branch participates in global optimization, it not only consumes large computational resources but also results in lag in response to sudden changes in irradiance. This embodiment adopts a "master-slave division of labor" strategy, selecting only a portion of the branches as master branches, allowing them to operate in maximum power point tracking mode to sense the maximum available power under the current environment; while the remaining branches are designated as slave branches, operating in fast power control mode, responsible for executing active power commands issued by the coordinating controller. This division of labor mechanism effectively improves the response speed and tracking accuracy of the multi-DC convergence photovoltaic system to power commands, enhancing the system's robustness in real-time scheduling.

[0029] The control methods of the local controllers for each photovoltaic branch are as follows: Figure 4As shown. Specifically, the local controller of the main branch monitors the output voltage in real time. With current And calculate the power value at the maximum power point. and will The output capacity benchmark is sent to the coordination controller, and the specific calculation process is as follows:

[0030] Where z represents the current sampling time, and z-1 represents the previous sampling time. These represent the real-time voltage change rate and power change rate of the dominant branch, respectively. To preset the tracking step size, For symbolic functions, This is the reference voltage for the maximum power point. When When the voltage disturbance is in the correct direction, it indicates that the current operating point is to the left of the maximum power point, and the voltage disturbance direction is correct; adjustment should continue in the same direction. When this occurs, it indicates that the operating point has exceeded the maximum power point and the voltage needs to be adjusted in reverse. As a result, the main branch can quickly lock the maximum power point under the current environment and upload the power value corresponding to that point as the output capacity benchmark to the coordinating controller.

[0031] When master-slave power control architectures are applied to larger-scale or modular, distributed photovoltaic power plants, the estimation strategy for available system power (i.e., output capacity baseline) needs to be adaptively adjusted. Two methods can be used for estimation: First, global estimation, which selects multiple photovoltaic modules as the dominant branches and operates them in maximum power point tracking mode, estimating the total available system power based on the average of their output power. Second, local estimation, suitable for modular distributed systems, selects one string as the dominant branch within each block, estimating the available power of that block based on its maximum output power, achieving regional autonomy and coordination. In practical applications, the selection of dominant photovoltaic modules needs to comprehensively consider geographical environment and economic factors.

[0032] The local controller of the subordinate branch operates in fast power control mode, receiving active power commands from the coordinating controller in real time. Based on this, a voltage inner loop reference signal is generated. The specific calculation formula is as follows:

[0033] in, i Number the branch roads For transfer functions, , All of these are control parameters.

[0034] Based on voltage inner loop reference signal The local controller of the subordinate branch generates the gate drive signal of the Boost converter through voltage inner loop control. This is to control the response of subordinate branches to coordinated active power commands.

[0035] It should be noted that in the operating region to the right of the maximum power point, photovoltaic modules exhibit a large instantaneous voltage change rate. Rapid decreases in irradiance can easily trigger DC bus voltage fluctuations, affecting system stability. In contrast, operating to the left of the maximum power point results in a smoother voltage-power characteristic. Even under rapid changes in irradiance, there will be no significant voltage drop or entry into open-circuit conditions, which is more conducive to system stability. Therefore, the operating range of the subordinate branch is limited to the left of the maximum power point.

[0036] The coordinating controller collects DC bus voltage in real time. Compare it with a preset reference voltage. By comparing the values ​​and using voltage closed-loop control, a global power reference command is generated. The calculation formula is as follows:

[0037] in, For transfer functions, , All of these are control parameters.

[0038] In grid-connected applications, fluctuations in the DC bus voltage directly reflect the power imbalance between the AC and DC sides. When an increase in AC load causes a drop in the DC bus voltage, the coordinating controller generates a global power reference through voltage closed-loop control, indicating the total increase in DC output required. The coordinating controller combines this with the output capacity reference. Global Power Reference Command and the actual output power of the inverter Calculate the active power command for each subordinate branch. The instructions are then sent to the local controllers of each subordinate branch, which then execute the commands accordingly. Dynamically adjust output to meet system scheduling requirements. Active power command for subordinate branches. The calculation formula is as follows:

[0039] in, This represents the total output required from subordinate branches after removing the contribution of the dominant branch; This indicates the number of parallel branches on the DC side of the inverter.

[0040] Based on the above power control, the key to DC bus voltage stabilization lies in Whether it can be responded to accurately. Based on the power balance relationship between the AC and DC sides of the inverter, this demand can be reasonably allocated to the output power of each DC-side component. AC side output power Under this control architecture, the DC-side power (the output power of each photovoltaic branch) It can follow the AC side power (the actual output power of the photovoltaic inverter). Dynamic adjustment enables the AC side of the inverter to break free from traditional voltage regulation constraints and achieve more flexible grid control.

[0041] The coordination controller assesses the system's current power generation capacity based on the actual output power of the photovoltaic inverters and the estimated output limit of each photovoltaic branch, and generates corresponding operating range commands. flag .

[0042] If the actual output power of the photovoltaic inverter does not exceed the warning output limit of the photovoltaic branch, then flag The value is 0, maintaining the current inverter active power command. Unchanged; if the actual output power of the photovoltaic inverter exceeds the warning output limit of the photovoltaic branch, but does not exceed the safe output limit of the photovoltaic branch under the current environmental conditions, then flag A value of 1 triggers an alert and imposes restrictions. Increased power generation scheduling; if the active power output exceeds the safe output limit, then flag 2, adaptive correction Until the system returns to a safe operating range.

[0043] The above logical relationship can be expressed as:

[0044] in, As the early warning coefficient, The adjustment coefficient; the operating mode of the photovoltaic inverter is as follows: Figure 2 As shown.

[0045] To reduce the bias in available power estimation caused by differences in irradiance between branches and improve system operational stability, an early warning coefficient is adopted. Flexibly set safe output range. Warning coefficient. The value of is related to the uniformity of irradiance between arrays: if the difference in irradiance is small, near As the differences increase, The corresponding reduction allows for a reasonable limitation of the safe output range. In this embodiment, the warning coefficient... Take 0.7.

[0046] Adjustment coefficient This is used to define the adjustment range for triggering adaptive power command correction when the system output approaches the maximum output limit under the current environment; in addition, it further reduces the adjustment coefficient. It can also realize power reserve control function. In this embodiment, the adjustment coefficient Take 0.85.

[0047] exist flag In the normal mode where the value is 0, the active power instruction is generated as follows:

[0048] in, This is the initial setting value for the active power command. When the photovoltaic array has full output capability, the command value remains unchanged. This is a power command adaptive correction term, used when the system switches back to normal mode from warning mode or adjustment mode. flag Drop to 0, after switching The value should be set to a reasonable reference value generated after the adjustment process before switching, so as to prevent the system from triggering a warning immediately due to the command exceeding the limit after returning to normal mode; It is a decay term introduced through an integrator with an initial value of 1. As a decay time constant, this term ensures that the adaptive correction term remains constant over time. It then slowly decays to 0, so that when sufficient light resources are restored, the unit can fully follow the set power command again, achieving maximum regulation.

[0049] exist flag In the warning mode of 1, the inverter active power command generation method is as follows:

[0050] in, In order to be in flag The active power reference value recorded at the moment the warning state is triggered by the rising edge. Once the system triggers the warning, it indicates that the photovoltaic output capacity has approached the output limit under the current environment. In order to avoid excessive issuance of commands that would cause the system to enter a dangerous operating state, the controller uses the power command at the moment of mode switching as the upper limit of subsequent commands.

[0051] exist flag In adjustment mode 2, the active power command generation method is as follows:

[0052] When the power demand exceeds the system output capacity, the command values ​​of each subordinate branch... Compared with actual output A deviation will occur between them, and the amount of this deviation is... By introducing a negative feedback loop into the inverter's active power command set-off loop, adaptive correction of the command is achieved: the greater the deviation, the stronger the negative feedback effect, and the active power command is adjusted accordingly until the AC and DC power are restored to balance, thus enabling each branch to accurately follow the command.

[0053] The DC / AC controller collects the three-phase voltage at the grid connection point of the photovoltaic inverter in real time. Inverter output current and grid-connected current signal After coordinate transformation, calculate the inverter output active power. With reactive power The calculation formula is as follows:

[0054] in, , The three-phase voltages are respectively d shaft and q Components on the axis, , The inverter output current is respectively at d shaft and q Components on the axis; Compare output power with power reference value , By comparison, a reference voltage is generated through the grid-type power outer loop, and the calculation formula is as follows:

[0055] in, As a reference for the inverter output angular frequency, For the output voltage phase, , These are the rated angular frequency and the rated voltage amplitude, respectively. This is a reference value for reactive power. for d Shaft voltage reference value, , Both are transfer functions. , , All of these are control parameters.

[0056] It should be noted that by coordinating the controller, the strong coupling between AC-side grid control and DC bus voltage regulation is eliminated, enabling dynamic coordination and optimized allocation of multiple photovoltaic power sources. This design allows the inverter control strategy to be no longer limited to a single grid configuration mode, but can be flexibly configured according to the actual needs of the grid. For example, droop control can be used to achieve autonomous power distribution; virtual synchronous machine control can be introduced to provide inertia and damping support; or virtual impedance can be combined to optimize parallel current sharing, or adaptive damping algorithms can be used to suppress broadband oscillations.

[0057] Subsequently, through voltage and current dual closed-loop control, generation is achieved. d Shaft reference modulation voltage , q Shaft reference modulation voltage To drive the inverter power switch, the expression is as follows:

[0058] in, , Both are transfer functions. This is the capacitance value of the filter capacitor. This is the inductance value of the filter inductor.

[0059] The coordinating controller maintains communication with the local controllers of each photovoltaic branch and the DC / AC controllers, exchanging system status and command data in real time. Within each control cycle, the coordinating controller recalculates the DC-side power command (the active power command of each subordinate branch) based on the DC bus voltage, power feedback from each subordinate branch, and the system operating mode. ), Generate flag signal flag Calculate AC power measurement command (inverter active power command) The updated instructions are then sent to the local controllers and DC / AC controllers of each subordinate branch.

[0060] Example 2: Please refer to Figure 5 This embodiment provides the simulation operation effect of a multi-DC converged photovoltaic inverter grid control method under uniform irradiance conditions. In this embodiment, uniform irradiance conditions refer to the situation where the irradiance of all three photovoltaic arrays is the same, and the irradiance changes synchronously. For details, please refer to [reference needed]. Figure 5 The diagram shows the variation curve of irradiance. In this embodiment, the DC side of the photovoltaic inverter connects to three photovoltaic arrays with a total rated power of 1MW, with the first array serving as the dominant array. The system active power setpoint changes stepwise with a period of 1 second within the rated power range; starting from the 5th second, the irradiance received by each photovoltaic array also changes stepwise synchronously with a period of 2 seconds. Figure 5 The output waveforms of the flag signal, the active power at the inverter grid connection point, the active power of each photovoltaic array, the irradiance variation, the DC bus voltage, and the reactive power at the grid connection point are presented sequentially. The results show that after a step change in the photovoltaic inverter power command, the system can respond quickly and accurately to the power dispatch demand, with an overall response time of less than 150ms. Simultaneously, the DC / AC controller can adaptively correct the power reference value on the inverter's AC side based on the estimated maximum generateable power, enabling the photovoltaic inverter to track the power regulation command as closely as possible.

[0061] Example 3: Please refer to Figure 6 This embodiment provides a simulation of the operation of a multi-DC converged photovoltaic inverter grid control method under non-uniform irradiance conditions. In this embodiment, the photovoltaic inverter connects three photovoltaic arrays with a total rated power of 1MW on the DC side, with the first array as the dominant array. The system active power setpoint changes abruptly with a period of 1 second within the rated power range, and all photovoltaic arrays are under non-uniform irradiance conditions. In this embodiment, non-uniform irradiance conditions refer to situations where the irradiance of the three photovoltaic arrays is not completely the same, and the irradiance changes by different amounts at the same time. See [reference needed] for details. Figure 6 The graph shows the variation in irradiance. Simulation results demonstrate that, after adopting the grid control method proposed in Example 1, when the system power command or irradiance undergoes abrupt changes, the coordinating controller can accurately allocate the power command to each controllable photovoltaic branch. This control strategy achieves intelligent power allocation and dynamic coordination among multiple photovoltaic arrays, fully proving the feasibility and effectiveness of the method provided in Example 1.

[0062] Example 4: Please refer to Figure 7 This embodiment provides the simulation effect of the multi-DC convergence photovoltaic inverter grid control method under islanded operation conditions; islanded operation is off-grid operation, i.e., as shown in the example. Figure 1 The PCC shown on the right is not connected to the power grid but operates directly under load. In this embodiment, the DC side of the photovoltaic inverter connects to three photovoltaic arrays with a total rated power of 1MW, with the first array serving as the dominant array. The load demand fluctuates approximately every 2 seconds, and all photovoltaic arrays operate under non-uniform irradiance conditions. In this embodiment, non-uniform irradiance conditions refer to situations where the irradiance of the three photovoltaic arrays is not entirely the same, and the irradiance exhibits the same amount of variation at different times. See [reference needed] for details. Figure 7 The irradiance variation curve is shown in the figure. Simulation results demonstrate that, using the grid-connected control method proposed in Example 1, the coordinating controller can quickly schedule photovoltaic arrays to accurately respond to load changes and effectively maintain the stability of the DC bus voltage when irradiance changes abruptly. Simultaneously, the DC / AC controller adaptively adjusts the inverter output power based on real-time load demand and the output capacity of each photovoltaic array. The system exhibits excellent voltage and frequency support capabilities under grid-connected control.

[0063] Example 5: Please refer to Figure 8 This embodiment provides a multi-channel DC convergence photovoltaic inverter grid control device for implementing the method described in Embodiment 1. The device includes: DC analog photovoltaic power supply 1, whose circuit topology consists of a current source, diodes, series equivalent resistors and parallel equivalent resistors, is used to simulate the time-varying output characteristics of a photovoltaic array affected by the environment. A DC / AC controller includes a DC / DC converter 2 and a DC / AC converter 3; wherein, the DC / DC converter 2 is used to convert the unregulated DC power output from the DC analog photovoltaic power supply into a target DC voltage to achieve optimized power regulation; The DC / AC converter 3 includes a main power conversion circuit and an LCL-type filter circuit. The main power conversion circuit realizes DC / AC power conversion, and the LCL-type filter circuit consists of a filter inductor on the converter side. Filter capacitor and grid-side filter inductor The composition, its topological connection method is that the AC side of the main power conversion circuit is connected in series. , , Then connected to the power grid; AC analog power supply 4 is used to simulate the actual main power grid and provide voltage and frequency support for the photovoltaic system; The coordination controller 5 employs a cooperative control architecture. In the DC voltage control unit 511, the DC bus voltage is acquired in real time, and the maximum power reference value generated by the dominant photovoltaic module (6i) and the power response deviation feedback from each subordinate photovoltaic module (61~6n) are received. Simultaneously, the actual output power of the photovoltaic inverter is obtained. Closed-loop control is performed based on the deviation between the sampled DC bus voltage value and the set reference value to generate a global active power reference value. In the DC-side power command generation unit 512, power commands are calculated and issued to each subordinate photovoltaic module based on the maximum power point of the dominant photovoltaic module and the actual output power of the inverter.

[0064] In the operation mode determination unit 521, the current operation mode of the system is determined by comparing the actual output power of the inverter with the estimated upper limit of the output power of each photovoltaic array; the flag signal generation unit 522 generates a corresponding flag signal based on the determination result; then, the AC side power command generation unit 523 adaptively adjusts the active power command of the inverter according to the flag signal, and outputs the adjusted command to the grid control unit 531.

[0065] In the grid control unit 531, the grid connection point voltage, inverter output current and grid connection current are collected synchronously. Based on the grid-type control strategy, the drive signal of the power switching device is generated in the voltage and current control unit 532 through the voltage-current dual closed-loop regulation mechanism.

[0066] The DC local controller 6 includes local controllers for the dominant photovoltaic module and slave photovoltaic modules. In the dominant photovoltaic module local controller 6i, the maximum power point under the current operating condition is calculated in real time by running a maximum power point tracking algorithm, and this value is uploaded to the coordinating controller 5. In the slave photovoltaic module local controllers 61-6n, a fast power control mode is adopted. Based on the power command issued by the coordinating controller, the drive signal of the front-end Boost converter is generated through power-voltage closed-loop control, and the power response deviation is fed back to the AC side power command generation unit 523.

[0067] Furthermore, the coordination controller 5 and the DC local controller 6 are equipped with processors and memory as signal processing units. The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0068] The memory can be a plug-in hard drive, a smart media card (SMC), a secure digital card (SD), a flash card, etc. The memory is used to store the computer program and other programs and data required by the large-scale photovoltaic grid-connected device. The memory can also be used to temporarily store data that has already been output or will be output.

[0069] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0070] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0071] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0072] In the embodiments provided by this invention, it should be understood that the disclosed apparatus / terminal devices and methods can be implemented in other ways. For example, the apparatus / terminal device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0073] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some units can be selected to achieve the purpose of this embodiment according to actual needs.

[0074] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0075] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0076] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A grid control method for a photovoltaic inverter with multi-channel DC convergence, characterized in that, include: At least one photovoltaic branch is selected as the dominant branch, and the remaining photovoltaic branches are designated as subordinate branches; the dominant branch operates in maximum power point tracking mode, and the subordinate branches operate in fast power control mode. The coordinating controller generates a global power reference command based on the DC bus voltage deviation, and combines the output capacity benchmark provided by the main branch and the actual output power of the inverter to generate active power commands for each subordinate branch and send them to each subordinate branch. The coordinating controller adaptively adjusts the active power command of the inverter based on the relationship between the actual output power of the inverter and the estimated output limit of the photovoltaic branch. The DC / AC controller acquires the active power command from the inverter and generates the drive signal for the inverter power switch through dual closed-loop regulation of current and voltage based on the grid-type control strategy.

2. The method according to claim 1, characterized in that, The calculation of the output capacity benchmark includes: The local controller of the main branch monitors the output voltage and output current of the main branch in real time, calculates the maximum power reference value of the main branch using the maximum power point tracking algorithm, and uploads the maximum power reference value as the output capacity benchmark to the coordinating controller.

3. The method according to claim 1, characterized in that, The coordinating controller generates active power commands for each subordinate branch, including: Based on the DC bus voltage deviation, a global power reference command is generated through voltage closed-loop control. Based on the global power reference command, the output capacity benchmark provided by the dominant branch, and the actual output power of the inverter, the total output of the subordinate branches other than the dominant branch is calculated, and the total output is evenly distributed to each subordinate branch.

4. The method according to claim 1, characterized in that, The coordination controller adaptively adjusts the inverter's active power command based on the relationship between the inverter's actual output power and the estimated output limit of the photovoltaic branch, including: The estimated output limit of the photovoltaic branch includes the early warning output limit and the safe output limit; The coordinating controller generates an inverter operating range flag signal based on the relationship between the actual output power of the inverter and the early warning output limit and safe output limit of the photovoltaic branch. The coordinating controller determines the inverter's operating mode based on the operating range flag signal and adaptively adjusts the inverter's active power command based on the inverter's operating mode.

5. The method according to claim 4, characterized in that, The operating modes include normal mode, early warning mode, and adjustment mode; If the actual output power of the inverter is less than or equal to the warning output limit of the photovoltaic branch, the inverter is in normal mode and maintains active power command. If the actual output power of the inverter is greater than the warning output limit of the photovoltaic branch and less than or equal to the safe output limit of the photovoltaic branch, the inverter enters the warning mode and performs a limit operation on the active power command. The active power command at the moment of entering the warning mode is used as the upper limit of the subsequent active power command. If the actual output power of the inverter exceeds the safe output limit of the photovoltaic branch, the inverter enters the regulation mode and adaptively adjusts the active power command based on the power response deviation of each subordinate branch.

6. The method according to claim 5, characterized in that, Within a preset time after the operating mode switches from warning mode and / or adjustment mode back to normal mode, the active power command is adaptively corrected.

7. The method according to claim 1, characterized in that, The output power of the subordinate branch is less than the output capacity benchmark provided by the dominant branch.

8. The method according to claim 1, characterized in that, The network-based control strategy includes droop control, virtual synchronous machine control, virtual impedance control, or adaptive damping algorithm.

9. The method according to claim 1, characterized in that, The coordination controller maintains communication with the local controllers of each photovoltaic branch and the DC / AC controller. During the control cycle, it acquires the status data of the inverter and each photovoltaic branch in real time, updates and sends the active power command of each subordinate branch to the local controller of each subordinate branch, and updates and sends the active power command of the inverter to the DC / AC controller.

10. A multi-channel DC convergence photovoltaic inverter grid control device, used to implement the method as described in any one of claims 1 to 9, characterized in that, include: The coordinating controller is configured to generate a global power reference based on the DC bus voltage deviation, and combine the output capacity benchmark provided by the main branch with the actual output power of the inverter to generate active power commands for each subordinate branch and send them to each subordinate branch. Based on the relationship between the actual output power of the inverter and the estimated output limit of the photovoltaic branch, it adaptively adjusts the active power commands of the inverter. Multiple local controllers are connected to their respective photovoltaic branches. At least one local controller is configured to operate in maximum power point tracking mode to estimate the power output capability benchmark and upload it to the coordinating controller. The remaining local controllers are configured to operate in fast power control mode to respond to the active power command issued by the coordinating controller. The DC / AC controller is configured to generate drive signals for the inverter power switch through dual closed-loop regulation of current and voltage based on a grid-type control strategy. The coordination controller is communicatively connected to each of the local controllers and the DC / AC controller.

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