Modular three-phase photovoltaic inverter cascade topology distributed control method

Abstract

This application specifically relates to a distributed control method for a modular three-phase photovoltaic inverter cascaded topology, comprising: establishing a modular three-phase photovoltaic inverter cascaded topology including multiple sub-modules and local controllers connected to each sub-module; obtaining the actual three-phase current value, three-phase current reference value, output voltage reference value, and target output voltage value on the output side of each sub-module; based on the oscillation frequency corresponding to each sub-module, obtaining the current difference of each sub-module according to the actual three-phase current value and the three-phase current reference value on the output side of each sub-module, and obtaining the voltage control equation of each sub-module according to the current difference, output voltage reference value, and output voltage target value; and calculating the α and β components of the actual output voltage of each sub-module to generate the PWM control signal of the three-phase inverter in each sub-module, modulating the amplitude of the output AC voltage of each sub-module. Thus, accurate power tracking is achieved.

Description

Technical Field

[0001] This application relates to the fields of power electronics and photovoltaic power generation technology, and in particular to a distributed control method for a modular three-phase photovoltaic inverter cascade topology. Background Technology

[0002] In the field of new energy power generation, traditional grid-connected control methods have revealed significant drawbacks due to their inherent characteristics such as volatility, intermittency, and uncertainty. Grid-connected control is essentially a current source control strategy, which limits its support effectiveness for the power grid, leading to poor stability during application. To effectively overcome these challenges, grid-connected control strategies have been proposed in related technologies.

[0003] In related technologies, when the inverter is in grid-connected operation mode, it needs to be able to accurately follow the power command issued by the upper system in order to achieve the dispatchability of power output, so as to better integrate into the overall operation and dispatch system of the power grid. In islanded operation mode, the inverter not only has to bear the heavy responsibility of supporting the stable operation of the power grid, but also needs to reasonably allocate power according to its own capacity ratio, while ensuring that the system voltage is always maintained within an acceptable safe range. Virtual oscillator control (VOC) is an advanced control strategy that combines the two key capabilities of grid-connected power control and grid support. Based on the characteristic of unified frequency across the entire network, this method can achieve accurate tracking and allocation of active power during grid connection. In related technologies, method (1) proposes an adaptive virtual impedance control scheme to eliminate reactive power allocation errors in islanded mesh microgrids, thereby achieving power tracking; method (2) proposes to dynamically change the voltage reference value of AHO by calculating the power flow feasible point in real time to achieve error-free tracking of reactive power.

[0004] However, reactive power control remains a major challenge for various VOC control methods. Scholars in related fields have proposed using virtual oscillators to control the inverter's current feedback gain to regulate active or reactive power, but this method suffers from drawbacks such as reliance on PI parameters, limitations in linear approximation, and computational complexity. Method (1) relies on a centralized controller and communication system, which has certain limitations; method (2) requires prior knowledge of system parameters for power flow calculations. Furthermore, when applied to cascaded topologies, its tracking capability is significantly reduced once an intra-phase power imbalance occurs, a problem that urgently needs to be addressed. Summary of the Invention

[0005] This application provides a distributed control method for a modular three-phase photovoltaic inverter cascaded topology to solve the problems of large reactive power error and power tracking divergence in traditional AHO control under power imbalance in related technologies.

[0006] The first aspect of this application provides a distributed control method for a modular three-phase photovoltaic inverter cascaded topology, including the following steps:

[0007] A modular three-phase photovoltaic inverter cascade topology is established, wherein the modular three-phase photovoltaic inverter cascade topology includes multiple sub-modules and a local controller connected to each sub-module.

[0008] The actual three-phase current value on the output side of each submodule, the reference three-phase current value of each submodule calculated by the local controller, the reference output voltage value of each submodule, and the target output voltage value of each submodule are obtained.

[0009] Based on the oscillation frequency corresponding to each submodule, the current difference of each submodule is obtained according to the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule. The voltage control equation of each submodule is obtained according to the current difference of each submodule, the reference value of the output voltage of each submodule and the target value of the output voltage of each submodule.

[0010] The α and β components of the actual output voltage of each submodule are calculated based on the voltage control equation of each submodule, and the PWM control signal of the three-phase inverter in each submodule is generated based on the α and β components of the actual output voltage of each submodule, so as to modulate the amplitude of the output AC voltage of each submodule through the PWM control signal of the three-phase inverter in each submodule.

[0011] Optionally, obtaining the actual three-phase current value on the output side of each submodule and the reference three-phase current value of each submodule calculated by the local controller of each submodule includes:

[0012] Based on a preset sampling strategy, the actual three-phase current values ​​on the output side of each submodule are collected, and it is determined whether the local controller of each submodule receives the reference power information sent by the corresponding central controller.

[0013] If reference power information is received from the corresponding central controller, the local controller of each submodule calculates the three-phase current reference value of each submodule based on the received reference power information.

[0014] Optionally, obtaining the output voltage reference value and the target output voltage value of each submodule includes:

[0015] Determine the power flow equation for each submodule, and calculate the output voltage reference value for each submodule based on the power flow equation for each submodule;

[0016] Obtain the output quantity corresponding to each submodule, and use the output quantity corresponding to each submodule to compensate the output voltage reference value of each submodule;

[0017] Based on a preset limiting strategy, the output voltage reference value of each submodule after compensation is limited to obtain the target value of the output voltage of each submodule.

[0018] Optionally, obtaining the output quantity corresponding to each submodule includes:

[0019] Obtain the active power reference value and actual active power value for each submodule, and the reactive power reference value and actual reactive power value for each submodule;

[0020] Calculate the first product of the difference between the active power reference value and the actual active power value corresponding to each submodule and the sine of the line impedance angle corresponding to each submodule; and calculate the second product of the difference between the reactive power reference value and the actual reactive power value corresponding to each submodule and the cosine of the line impedance angle corresponding to each submodule.

[0021] The first product and the second product are summed, and the summation result is processed by a PI controller to obtain the output quantity corresponding to each submodule.

[0022] Optionally, after obtaining the current difference value of each submodule based on the oscillation frequency corresponding to each submodule, according to the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule, the method further includes:

[0023] The input signal of the virtual oscillator in the local controller corresponding to each submodule is obtained by performing a rotation matrix transformation and current coefficient scaling on the current difference of each submodule.

[0024] A second aspect of this application provides a distributed control device for a modular three-phase photovoltaic inverter cascaded topology, comprising:

[0025] A building module is used to establish a modular three-phase photovoltaic inverter cascade topology, wherein the modular three-phase photovoltaic inverter cascade topology includes multiple sub-modules and a local controller connected to each sub-module.

[0026] The acquisition module is used to acquire the actual three-phase current value on the output side of each submodule, the reference value of the three-phase current of each submodule calculated by the local controller, the reference value of the output voltage of each submodule, and the target value of the output voltage of each submodule.

[0027] The determination module is used to determine the current difference of each submodule based on the oscillation frequency corresponding to each submodule, the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule, and to determine the voltage control equation of each submodule based on the current difference of each submodule, the reference value of the output voltage of each submodule and the target value of the output voltage of each submodule.

[0028] The modulation module is used to calculate the α and β components of the actual output voltage of each submodule according to the voltage control equation of each submodule, and generate the PWM control signal of the three-phase inverter in each submodule according to the α and β components of the actual output voltage of each submodule, so as to modulate the amplitude of the output AC voltage of each submodule through the PWM control signal of the three-phase inverter in each submodule.

[0029] Optionally, the acquisition module is specifically used for:

[0030] Based on a preset sampling strategy, the actual three-phase current values ​​on the output side of each submodule are collected, and it is determined whether the local controller of each submodule receives the reference power information sent by the corresponding central controller.

[0031] If reference power information is received from the corresponding central controller, the local controller of each submodule calculates the three-phase current reference value of each submodule based on the received reference power information.

[0032] Optionally, the acquisition module is specifically used for:

[0033] Determine the power flow equation for each submodule, and calculate the output voltage reference value for each submodule based on the power flow equation for each submodule;

[0034] Obtain the output quantity corresponding to each submodule, and use the output quantity corresponding to each submodule to compensate the output voltage reference value of each submodule;

[0035] Based on a preset limiting strategy, the output voltage reference value of each submodule after compensation is limited to obtain the target value of the output voltage of each submodule.

[0036] Optionally, the acquisition module is specifically used for:

[0037] Obtain the active power reference value and actual active power value for each submodule, and the reactive power reference value and actual reactive power value for each submodule;

[0038] Calculate the first product of the difference between the active power reference value and the actual active power value corresponding to each submodule and the sine of the line impedance angle corresponding to each submodule; and calculate the second product of the difference between the reactive power reference value and the actual reactive power value corresponding to each submodule and the cosine of the line impedance angle corresponding to each submodule.

[0039] The first product and the second product are summed, and the summation result is processed by a PI controller to obtain the output quantity corresponding to each submodule.

[0040] Optionally, after determining the current difference of each submodule based on the oscillation frequency corresponding to each submodule, according to the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule, the determining module is further configured to:

[0041] The input signal of the virtual oscillator in the local controller corresponding to each submodule is obtained by performing a rotation matrix transformation and current coefficient scaling on the current difference of each submodule.

[0042] A third aspect of this application provides an electronic device, including: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being configured to perform a distributed control method for a modular three-phase photovoltaic inverter cascaded topology as described in the above embodiments.

[0043] A fourth aspect of this application provides a computer-readable storage medium having a computer program stored thereon, which is executed by a processor to implement a distributed control method for a modular three-phase photovoltaic inverter cascaded topology as described in the above embodiments.

[0044] A fifth aspect of this application provides a computer program product storing a computer program that, when executed by a processor, implements a distributed control method for a modular three-phase photovoltaic inverter cascaded topology as described in the above embodiments.

[0045] Therefore, this application establishes a modular three-phase photovoltaic inverter cascade topology including multiple sub-modules and a local controller connected to each sub-module; it obtains the actual three-phase current value, reference three-phase current value, reference output voltage value, and target output voltage value on the output side of each sub-module; based on the oscillation frequency corresponding to each sub-module, it obtains the current difference of each sub-module according to the actual three-phase current value and the reference three-phase current value on the output side of each sub-module, and obtains the voltage control equation of each sub-module according to the current difference, reference output voltage value, and target output voltage value; it also calculates the α and β components of the actual output voltage of each sub-module to generate the PWM control signal of the three-phase inverter in each sub-module, modulating the amplitude of the output AC voltage of each sub-module. This solves the problems of large reactive power error and power point tracking divergence in traditional AHO control under power imbalance in related technologies, achieving accurate power tracking.

[0046] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0047] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0048] Figure 1 This is a flowchart illustrating a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application.

[0049] Figure 2 This is a schematic diagram of an adaptive voltage regulation control strategy for a distributed control method of a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application;

[0050] Figure 3 This is a schematic diagram of the internal control of a submodule of a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application;

[0051] Figure 4 This is a schematic diagram of a modular three-phase photovoltaic inverter cascaded structure circuit, which is provided in an embodiment of the present application for a distributed control method of a modular three-phase photovoltaic inverter cascaded topology.

[0052] Figure 5 This is a schematic diagram of the power waveform when using a conventional control strategy for in-phase power balance in a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application;

[0053] Figure 6This is a schematic diagram of the power waveform after the inverter output voltage amplitude is dynamically adjusted according to the requirements of the power flow equation during the phase power balance of a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application.

[0054] Figure 7 This is a schematic diagram of the power and amplitude waveforms after the inverter output voltage amplitude is dynamically adjusted according to the requirements of the power flow equation when there is power imbalance within the phase of a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application.

[0055] Figure 8 This is a schematic diagram of the power and amplitude waveforms after a voltage compensation control loop is superimposed on a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application, which allows the inverter output voltage amplitude to be dynamically adjusted according to the requirements of the power flow equation when there is power imbalance within the phase. The diagram shows the power and amplitude waveforms after the module reference voltage changes according to a given power ratio.

[0056] Figure 9 This is a schematic diagram of a distributed control device for a modular three-phase photovoltaic inverter cascade topology provided in an embodiment of this application;

[0057] Figure 10 This is a schematic diagram of the structure of an electronic device provided according to an embodiment of this application. Detailed Implementation

[0058] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0059] The following describes a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to embodiments of this application, with reference to the accompanying drawings. Addressing the problems mentioned in the background art regarding the large reactive power error and power tracking divergence of traditional AHO control under power imbalance, this application provides a distributed control method for a modular three-phase photovoltaic inverter cascaded topology. In this method, embodiments of this application establish a modular three-phase photovoltaic inverter cascaded topology including multiple sub-modules and local controllers connected to each sub-module; obtain the actual three-phase current value, reference three-phase current value, reference output voltage value, and target output voltage value on the output side of each sub-module; based on the oscillation frequency corresponding to each sub-module, obtain the current difference of each sub-module according to the actual three-phase current value and reference three-phase current value on the output side of each sub-module; obtain the voltage control equation for each sub-module according to the current difference, reference output voltage value, and target output voltage value; and calculate the α and β components of the actual output voltage of each sub-module to generate the PWM control signal of the three-phase inverter in each sub-module, modulating the amplitude of the output AC voltage of each sub-module. This solves the problems of large reactive power error and power tracking divergence in traditional AHO control when power is unbalanced, thus achieving accurate power tracking.

[0060] Specifically, Figure 1 This is a flowchart illustrating a distributed control method for a modular three-phase photovoltaic inverter cascaded topology provided in an embodiment of this application.

[0061] like Figure 1 As shown, the distributed control method for this modular three-phase photovoltaic inverter cascaded topology includes the following steps:

[0062] In step S101, a modular three-phase photovoltaic inverter cascade topology is established, wherein the modular three-phase photovoltaic inverter cascade topology includes multiple sub-modules and a local controller connected to each sub-module.

[0063] Specifically, in this embodiment, PSIM simulation software is used to model the cascaded topology of a five-module three-phase photovoltaic inverter. In order to verify the effectiveness of the AHO (Andronov-Hopf Oscillator) grid-connected self-synchronization control strategy, a constant voltage source is used to replace the input terminal of the three-phase cascaded H-bridge unit.

[0064] In step S102, the actual three-phase current value of the output side of each submodule, the reference three-phase current value of each submodule calculated by the local controller, the reference output voltage value of each submodule, and the target output voltage value of each submodule are obtained.

[0065] Optionally, in some embodiments, obtaining the actual three-phase current value on the output side of each submodule and the reference three-phase current value of each submodule calculated by the local controller of each submodule includes: collecting the actual three-phase current value on the output side of each submodule based on a preset sampling strategy, and determining whether the local controller of each submodule has received the reference power information sent by the corresponding central controller; if the reference power information sent by the corresponding central controller is received, then the local controller of each submodule calculates the reference three-phase current value of each submodule based on the received reference power information.

[0066] Understandably, based on a preset sampling strategy, this application embodiment typically uses current sensors installed on the output side of each submodule to collect the actual three-phase current value on the output side of each submodule in real time; checks whether the local controller of each submodule has successfully received the reference power information sent from the central controller; once it is confirmed that the local controller has received the correct reference power information, it uses this information to calculate the three-phase current reference value of each submodule through the local controller. This process involves converting the received reference power into a specific current reference value to guide the inverter to generate the corresponding output current and ensure that the system operation meets the expected power requirements.

[0067] Optionally, in some embodiments, obtaining the output voltage reference value and the target output voltage value of each submodule includes: determining the power flow equation of each submodule and calculating the output voltage reference value of each submodule based on the power flow equation of each submodule; obtaining the output quantity corresponding to each submodule and compensating the output voltage reference value of each submodule using the output quantity corresponding to each submodule; and limiting the compensated output voltage reference value of each submodule based on a preset limiting strategy to obtain the target output voltage value of each submodule.

[0068] Among them, the power flow equation is used to calculate the output voltage reference value of each submodule, describing the relationship between the active and reactive power and voltage at each node in the power system.

[0069] Understandably, the output voltage reference value of each submodule is calculated based on the defined power flow equations for each submodule. This is determined based on the current operating state of the system and the desired power distribution. For example... Figure 2 As shown, Figure 2This diagram illustrates an adaptive voltage regulation control strategy for a distributed control method of a modular three-phase photovoltaic inverter cascaded topology, provided in one embodiment of this application. A quantity is calculated to compensate for the output voltage reference value. This compensation quantity is applied to the output voltage reference value to adjust its value, enabling the submodules to more accurately meet the set power requirements. After compensation, the compensated output voltage reference value is limited based on a preset limiting strategy. The limiting strategy ensures that the output voltage does not exceed a safe or effective range, thereby protecting the equipment and maintaining system stability. The output voltage reference value after limiting is the target output voltage value for each submodule. This target output voltage value will guide the actual operation of the inverter, making its output voltage as close as possible to this target value.

[0070] Optionally, in some embodiments, obtaining the output quantity corresponding to each submodule includes: obtaining the active power reference value and the actual active power value, and the reactive power reference value and the actual reactive power value corresponding to each submodule; calculating the first product of the difference between the active power reference value and the actual active power value corresponding to each submodule and the sine of the line impedance angle corresponding to each submodule, and calculating the second product of the difference between the reactive power reference value and the actual reactive power value corresponding to each submodule and the cosine of the line impedance angle corresponding to each submodule; summing the first product and the second product, and processing the summed result through a PI controller to obtain the output quantity corresponding to each submodule.

[0071] Understandably, in order to achieve accurate tracking of active and reactive power when there is power imbalance between modules, the reference value of the output voltage of each submodule is calculated based on the power flow equation. The difference between the active power reference value and the actual value is multiplied by the sine of the line impedance angle, and the difference between the reactive power reference value and the actual value is multiplied by the cosine of the line impedance angle. The results of these two multiplications are summed, and the sum is processed by a PI controller. Its output is used to compensate for the reference value of the submodule output voltage. In this way, the output of each submodule is precisely adjusted to ensure that even in the presence of power imbalance, the system can effectively reduce power error and maintain stable operation.

[0072] In step S103, based on the oscillation frequency corresponding to each submodule, the current difference of each submodule is obtained according to the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule. The voltage control equation of each submodule is obtained according to the current difference of each submodule, the reference value of the output voltage of each submodule and the target value of the output voltage of each submodule.

[0073] Specifically, for each submodule, the difference between the actual and reference values ​​of its three-phase current is calculated. This current difference is then transformed into a form suitable for input to the virtual oscillator through rotation matrix transformation and current coefficient scaling. This helps convert the error signal into a control signal that can be used to adjust the inverter output. Based on the current difference, output voltage reference value, and target output voltage value of each submodule, a voltage control equation is formed to calculate the component of the actual output voltage of the submodule. This ensures that even in the event of power imbalance within the system, the output voltage of each submodule can be precisely adjusted to track the set power reference value, thereby achieving efficient and stable power output.

[0074] Optionally, in some embodiments, after obtaining the current difference of each submodule based on the oscillation frequency corresponding to each submodule and the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule, the method further includes: performing a rotation matrix transformation and current coefficient scaling on the current difference of each submodule to obtain the input signal of the virtual oscillator in the local controller corresponding to each submodule.

[0075] Understandably, in order to convert the current difference value of each submodule into a signal suitable for controlling the inverter, a rotation matrix transformation of the current difference value is required. This helps adjust the angle of the signal to meet the requirements of the inverter control system. The current difference value, scaled based on the current coefficient, forms the input signal for the virtual oscillator (e.g., AHO) in the local controller. This input signal is used to drive the oscillator, thereby generating the inverter's output voltage control signal.

[0076] In step S104, the α and β components of the actual output voltage of each submodule are calculated according to the voltage control equation of each submodule, and the PWM control signal of the three-phase inverter in each submodule is generated according to the α and β components of the actual output voltage of each submodule, so as to modulate the amplitude of the output AC voltage of each submodule through the PWM control signal of the three-phase inverter in each submodule.

[0077] Understandably, by converting the actual output voltage of each submodule into α and β components, the inverter's output voltage can be controlled more accurately, effectively simplifying the complexity of a three-phase AC system into a problem in a two-phase stationary coordinate system, facilitating precise control. Using techniques such as space vector modulation or sinusoidal pulse width modulation to generate PWM signals can optimize the operation of the inverter's switching devices, improve the system's dynamic response speed, and enhance its stability and robustness. The control methods of the local controller, such as... Figure 3 As shown, Figure 3This is a schematic diagram of the internal control of a submodule of a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application. By using a PI controller to compensate for active and reactive power errors, the power error in the system can be significantly reduced, making the inverter output closer to the set target value, especially maintaining high tracking accuracy under power imbalance conditions.

[0078] Therefore, the local controller of a single submodule receives reference power information from the central controller and calculates the current reference value accordingly. The actual values ​​of the three-phase currents are sampled in real time on the three-phase output side of the inverter, and the sampled data is quickly transmitted to the local controller. The local controller then compares and analyzes the actual values ​​of the three-phase currents with the reference values, calculates the difference, and this difference is processed by rotation matrix transformation and current coefficient scaling to obtain the input signal for the oscillator. Furthermore, the control circuit in this embodiment does not require actual hardware and can be implemented digitally. Each inverter module is programmed to simulate the dynamic changes of the nonlinear oscillator in the local controller. The multi-converter system outputs high voltage by connecting multiple submodules in series, and the controller of each submodule is implemented locally in each unit of the stack. Each module's controller uses the inverter's three-phase output current as a feedback signal and sequentially modulates the amplitude and frequency of the AC voltage, thereby achieving non-communicative synchronization between the inverter and the grid.

[0079] To facilitate those skilled in the art to further understand the distributed control method of the modular three-phase photovoltaic inverter cascade topology in the embodiments of this application, the following is combined with... Figures 4 to 8 The embodiments shown will be described in detail.

[0080] Specifically, this application embodiment uses PSIM simulation software to model the cascaded topology of a five-module three-phase photovoltaic inverter, as follows: Figure 4 As shown, Figure 4 This is a schematic diagram of a modular three-phase photovoltaic inverter cascaded structure circuit, illustrating a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to one embodiment of this application. To verify the effectiveness of the AHO grid-connected self-synchronization control strategy, a constant voltage source was used to replace the input terminal of the three-phase cascaded H-bridge unit. Simulations were performed using a traditional AHO control strategy, a control optimization strategy that allows the inverter output voltage amplitude to be dynamically adjusted according to the requirements of the power flow equation, and the adaptive voltage control strategy with added voltage compensation loop proposed in this invention, simulating both intra-phase power balance and inter-phase power balance scenarios. The simulation was set with a given active power reference value P for the five inverter sub-modules. ref The initial values ​​of all reactive power are 0W, and they all step to 500W at 0.25s. At the same time, in order to ensure that the system operates at unity power factor, a reactive power reference value Q is set.ref Always set to 0Var; set the P of the five submodules ref The initial values ​​of all modules are 0W. At 0.25s, the active power of the five sub-modules jumps to 300W, 350W, 400W, 450W, and 500W respectively. At this point, the active power of each module is no longer balanced, and the reference value of reactive power is Q. ref Always set to 0Var, the rotation angle of AHO is the line impedance angle;

[0081] Furthermore, the active and reactive power tracking under different conditions are compared in the simulation results. The simulated waveforms of the output voltage frequency and amplitude of the five-module three-phase inverter are recorded. To intuitively demonstrate the reactive power tracking, this embodiment of the application plots a power error simulation waveform diagram according to the defined reactive power error calculation method. The reactive power error Q of the j-th sub-module defined in this embodiment of the application is... errj The expression is:

[0082]

[0083] Among them, Q errj Let Q be the reactive power error of the j-th submodule. refj This is the reference value for the reactive power of the j-th submodule.

[0084] Under the above conditions, the power waveform when using the traditional AHO control strategy is read as follows: Figure 5 As shown, Figure 5 This diagram illustrates the power waveforms during phase-to-phase power balance using a conventional control strategy in a distributed control method for a modular three-phase photovoltaic inverter cascaded topology, according to one embodiment of this application. The rotation angle of AHO is π / 2, and the system is inductive. It can be seen that when the phase-to-phase power is balanced, in the inductive network, the instantaneous active power output by the inverter can accurately and stably track the active power reference value, demonstrating good active power tracking performance. However, the reactive power Q and its setpoint Q... ref There is a significant tracking error between them, with a reactive power error of 35% after entering steady state. Simulation results show that, under the assumption of an inductive network, although the AHO controller can achieve accurate tracking of active power, it will also absorb a certain amount of reactive power from the grid side.

[0085] Furthermore, the power waveform is read when a control optimization strategy is adopted that allows the inverter output voltage amplitude to be dynamically adjusted according to the requirements of the power flow equation, such as... Figure 6 As shown, Figure 6This diagram illustrates the power waveform of a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application. During phase-to-phase power balance, the inverter output voltage amplitude is dynamically adjusted according to the power flow equation. The rotation angle of AHO is taken as the system power angle. It can be seen that when the phase-to-phase power is balanced, the instantaneous active power of all five modules accurately and stably tracks the active power reference value. After adopting the optimized control strategy, the maximum reactive power error is 14.6% when the given power changes; after entering steady state, this error further decreases to 7.5%. In stark contrast, the reactive power error is as high as 35% when using the traditional control strategy. Therefore, the optimized control strategy is significantly effective in reducing reactive power error. The reactive power output of all five inverter modules can accurately track the reactive power setpoint, verifying that the optimized control strategy can improve the controller's power tracking performance during module power balance.

[0086] Furthermore, the power waveform is read when a control optimization strategy is adopted that allows the inverter output voltage amplitude to be dynamically adjusted according to the requirements of the power flow equation, such as... Figure 7 As shown, Figure 7 This is a schematic diagram of the power and amplitude waveforms after allowing the inverter output voltage amplitude to be dynamically adjusted according to the requirements of the power flow equation when there is power imbalance within the phase in a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to an embodiment of this application. The simulation results show that when the module power is unbalanced, the reactive power error shows a divergent trend when the given power changes after using the control optimization strategy. The error increases continuously with time, so each sub-module cannot accurately track the active and reactive power reference values, and the voltage of each module cannot change automatically according to the power ratio.

[0087] Furthermore, the power waveform of the adaptive voltage control strategy with added voltage compensation loop proposed in the embodiments of this application is read as follows: Figure 8 As shown, Figure 8This paper presents a distributed control method for a modular three-phase photovoltaic inverter cascaded topology according to one embodiment of this application. When there is power imbalance within a phase, a voltage compensation control loop is superimposed on the method, allowing the inverter output voltage amplitude to be dynamically adjusted according to the power flow equation. This allows the module reference voltage to change according to a given power ratio, resulting in power and amplitude waveforms. When the power of each module is unbalanced, after optimization by the adaptive voltage control strategy of this embodiment, the maximum reactive power error is 93.3% at the instant the given power changes; after entering steady state, this maximum error is only 2%, and the active and reactive power of each sub-module can accurately track the given power reference value. The output voltage of the five modules is adaptively adjusted according to the given active power ratio of 10:9:8:7:6, eventually reaching a stable state. Therefore, the proposed adaptive voltage control strategy can achieve stable tracking of active and reactive power in both power balance and power imbalance between modules, with power errors smaller than the previous two control strategies, demonstrating superior power tracking performance.

[0088] Therefore, this embodiment of the application, through a control optimization method that allows the inverter output voltage amplitude to be dynamically adjusted according to the requirements of the power flow equation, reduces the module power tracking error from 35% to 7% when the power is balanced within the phase. Furthermore, by allowing the module reference voltage to change proportionally to a given power value, the submodule can automatically adjust its output voltage amplitude proportionally to a given power value when the power is unbalanced within the phase, reducing the power error to 2%. This embodiment of the application achieves power distribution and communication-free synchronization among submodules in a cascaded system without the need for external synchronization signals or complex communication protocols, greatly simplifying system wiring and improving the flexibility and scalability of the modular system. It ensures that the cascaded topology of the modular photovoltaic inverter has high tracking capability for both active and reactive power in both phase-balanced and phase-unbalanced power conditions.

[0089] According to the distributed control method for the modular three-phase photovoltaic inverter cascade topology proposed in this application, this application establishes a modular three-phase photovoltaic inverter cascade topology including multiple sub-modules and local controllers connected to each sub-module; obtains the actual three-phase current value, three-phase current reference value, output voltage reference value, and target output voltage value on the output side of each sub-module; based on the oscillation frequency corresponding to each sub-module, the current difference of each sub-module is obtained according to the actual three-phase current value and the three-phase current reference value on the output side of each sub-module, and the voltage control equation of each sub-module is obtained according to the current difference, output voltage reference value, and output voltage target value; and the α component and β component of the actual output voltage of each sub-module are calculated to generate the PWM control signal of the three-phase inverter in each sub-module, modulating the amplitude of the output AC voltage of each sub-module. This solves the problems of large reactive power error and power point tracking divergence in traditional AHO control under power imbalance in related technologies, achieving accurate power tracking.

[0090] Next, referring to the accompanying drawings, a distributed control device for a modular three-phase photovoltaic inverter cascade topology proposed according to an embodiment of this application is described.

[0091] Figure 9 This is a block diagram of a distributed control device for a modular three-phase photovoltaic inverter cascade topology according to an embodiment of this application.

[0092] like Figure 9 As shown, the distributed control device 1000 of the modular three-phase photovoltaic inverter cascade topology includes: a construction module 100, an acquisition module 200, a determination module 300, and a modulation module 400.

[0093] The construction module 100 is used to establish a modular three-phase photovoltaic inverter cascade topology, which includes multiple sub-modules and a local controller connected to each sub-module.

[0094] The acquisition module 200 is used to acquire the actual three-phase current value on the output side of each submodule, the reference value of the three-phase current of each submodule calculated by the local controller, the reference value of the output voltage of each submodule, and the target value of the output voltage of each submodule.

[0095] The determination module 300 is used to determine the current difference of each submodule based on the oscillation frequency corresponding to each submodule, the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule, and to determine the voltage control equation of each submodule based on the current difference of each submodule, the reference value of the output voltage of each submodule and the target value of the output voltage of each submodule.

[0096] The modulation module 400 is used to calculate the α and β components of the actual output voltage of each submodule according to the voltage control equation of each submodule, and generate the PWM control signal of the three-phase inverter in each submodule according to the α and β components of the actual output voltage of each submodule, so as to modulate the amplitude of the output AC voltage of each submodule through the PWM control signal of the three-phase inverter in each submodule.

[0097] Optionally, the acquisition module 200 is specifically used to: acquire the actual value of the three-phase current on the output side of each submodule based on a preset sampling strategy, and determine whether the local controller of each submodule has received the reference power information sent by the corresponding central controller; if the reference power information sent by the corresponding central controller is received, the local controller of each submodule calculates the reference value of the three-phase current of each submodule based on the received reference power information.

[0098] Optionally, the acquisition module 200 is specifically used for: determining the power flow equation of each submodule, and calculating the output voltage reference value of each submodule based on the power flow equation of each submodule; acquiring the output quantity corresponding to each submodule, and compensating the output voltage reference value of each submodule using the output quantity corresponding to each submodule; and limiting the compensated output voltage reference value of each submodule based on a preset limiting strategy to obtain the target value of the output voltage of each submodule.

[0099] Optionally, the acquisition module 200 is specifically used for: acquiring the active power reference value and actual active power value, and the reactive power reference value and actual reactive power value corresponding to each sub-module; calculating the first product of the difference between the active power reference value and the actual active power value corresponding to each sub-module and the sine of the line impedance angle corresponding to each sub-module, and calculating the second product of the difference between the reactive power reference value and the actual reactive power value corresponding to each sub-module and the cosine of the line impedance angle corresponding to each sub-module; summing the first product and the second product, and processing the summed result through a PI controller to obtain the output quantity corresponding to each sub-module.

[0100] Optionally, after determining the current difference of each submodule based on the oscillation frequency corresponding to each submodule, according to the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule, module 300 is further used to: perform rotation matrix transformation and current coefficient scaling on the current difference of each submodule to obtain the input signal of the virtual oscillator in the local controller corresponding to each submodule.

[0101] It should be noted that the explanation of the aforementioned embodiment of the distributed control method for the cascaded topology of modular three-phase photovoltaic inverters also applies to the distributed control device for the cascaded topology of modular three-phase photovoltaic inverters in this embodiment, and will not be repeated here.

[0102] According to the distributed control device based on the modular three-phase photovoltaic inverter cascade topology proposed in this application, this application establishes a modular three-phase photovoltaic inverter cascade topology including multiple sub-modules and local controllers connected to each sub-module; obtains the actual three-phase current value, three-phase current reference value, output voltage reference value, and output voltage target value on the output side of each sub-module; based on the oscillation frequency corresponding to each sub-module, obtains the current difference of each sub-module according to the actual three-phase current value and the three-phase current reference value on the output side of each sub-module, and obtains the voltage control equation of each sub-module according to the current difference, output voltage reference value, and output voltage target value; and calculates the α component and β component of the actual output voltage of each sub-module to generate the PWM control signal of the three-phase inverter in each sub-module, modulating the amplitude of the output AC voltage of each sub-module. Thus, it solves the problems of large reactive power error and power tracking divergence in traditional AHO control under power imbalance in related technologies, achieving accurate power tracking.

[0103] Figure 10 A schematic diagram of the structure of an electronic device provided in an embodiment of this application. The electronic device may include:

[0104] The memory 1001, the processor 1002, and the computer program stored on the memory 1001 and capable of running on the processor 1002.

[0105] When the processor 1002 executes the program, it implements the distributed control method for the modular three-phase photovoltaic inverter cascade topology provided in the above embodiments.

[0106] Furthermore, electronic devices also include:

[0107] Communication interface 1003 is used for communication between memory 1001 and processor 1002.

[0108] The memory 1001 is used to store computer programs that can run on the processor 1002.

[0109] The memory 1001 may include high-speed RAM memory, and may also include non-volatile memory, such as at least one disk storage device.

[0110] If the memory 1001, processor 1002, and communication interface 1003 are implemented independently, then the communication interface 1003, memory 1001, and processor 1002 can be interconnected via a bus to complete communication between them. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be categorized into address buses, data buses, control buses, etc. For ease of representation, Figure 10 The bus is represented by a single thick line, but this does not mean that there is only one bus or one type of bus.

[0111] Optionally, in a specific implementation, if the memory 1001, processor 1002, and communication interface 1003 are integrated on a single chip, then the memory 1001, processor 1002, and communication interface 1003 can communicate with each other through an internal interface.

[0112] The processor 1002 may be a central processing unit (CPU), an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of this application.

[0113] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the distributed control method for the modular three-phase photovoltaic inverter cascade topology described above.

[0114] This application also provides a computer program product that stores a computer program that, when executed by a processor, implements the distributed control method for the modular three-phase photovoltaic inverter cascade topology described above.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0117] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more N executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

[0118] It should be understood that the various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, the N steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0119] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

Claims

1. A distributed control method for a modular three-phase photovoltaic inverter cascaded topology, characterized in that, Includes the following steps: A modular three-phase photovoltaic inverter cascade topology is established, wherein the modular three-phase photovoltaic inverter cascade topology includes multiple sub-modules and a local controller connected to each sub-module. The actual three-phase current value on the output side of each submodule, the reference three-phase current value of each submodule calculated by the local controller, the reference output voltage value of each submodule, and the target output voltage value of each submodule are obtained. Based on the oscillation frequency corresponding to each submodule, the current difference of each submodule is obtained according to the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule. The voltage control equation of each submodule is obtained according to the current difference of each submodule, the reference value of the output voltage of each submodule and the target value of the output voltage of each submodule. The α and β components of the actual output voltage of each submodule are calculated based on the voltage control equation of each submodule, and the PWM control signal of the three-phase inverter in each submodule is generated based on the α and β components of the actual output voltage of each submodule, so as to modulate the amplitude of the output AC voltage of each submodule through the PWM control signal of the three-phase inverter in each submodule.

2. The method according to claim 1, characterized in that, The process of obtaining the actual three-phase current value on the output side of each submodule and the reference three-phase current value of each submodule calculated by the local controller of each submodule includes: Based on a preset sampling strategy, the actual three-phase current values ​​on the output side of each submodule are collected, and it is determined whether the local controller of each submodule receives the reference power information sent by the corresponding central controller. If reference power information is received from the corresponding central controller, the local controller of each submodule calculates the three-phase current reference value of each submodule based on the received reference power information.

3. The method according to claim 1, characterized in that, The process of obtaining the output voltage reference value and the target output voltage value of each submodule includes: Determine the power flow equation for each submodule, and calculate the output voltage reference value for each submodule based on the power flow equation for each submodule; Obtain the output quantity corresponding to each submodule, and use the output quantity corresponding to each submodule to compensate the output voltage reference value of each submodule; Based on a preset limiting strategy, the output voltage reference value of each submodule after compensation is limited to obtain the target value of the output voltage of each submodule.

4. The method according to claim 3, characterized in that, The process of obtaining the output quantity corresponding to each submodule includes: Obtain the active power reference value and actual active power value for each submodule, and the reactive power reference value and actual reactive power value for each submodule; Calculate the first product of the difference between the active power reference value and the actual active power value corresponding to each submodule and the sine of the line impedance angle corresponding to each submodule; and calculate the second product of the difference between the reactive power reference value and the actual reactive power value corresponding to each submodule and the cosine of the line impedance angle corresponding to each submodule. The first product and the second product are summed, and the summation result is processed by a PI controller to obtain the output quantity corresponding to each submodule.

5. The method according to claim 1, characterized in that, After obtaining the current difference value of each submodule based on the oscillation frequency corresponding to each submodule, according to the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule, the method further includes: The input signal of the virtual oscillator in the local controller corresponding to each submodule is obtained by performing a rotation matrix transformation and current coefficient scaling on the current difference of each submodule.

6. A distributed control device for a modular three-phase photovoltaic inverter cascaded topology, characterized in that, include: A building module is used to establish a modular three-phase photovoltaic inverter cascade topology, wherein the modular three-phase photovoltaic inverter cascade topology includes multiple sub-modules and a local controller connected to each sub-module. The acquisition module is used to acquire the actual three-phase current value on the output side of each submodule, the reference value of the three-phase current of each submodule calculated by the local controller, the reference value of the output voltage of each submodule, and the target value of the output voltage of each submodule. The determination module is used to determine the current difference of each submodule based on the oscillation frequency corresponding to each submodule, the actual value of the three-phase current on the output side of each submodule and the reference value of the three-phase current of each submodule, and to determine the voltage control equation of each submodule based on the current difference of each submodule, the reference value of the output voltage of each submodule and the target value of the output voltage of each submodule. The modulation module is used to calculate the α and β components of the actual output voltage of each submodule according to the voltage control equation of each submodule, and generate the PWM control signal of the three-phase inverter in each submodule according to the α and β components of the actual output voltage of each submodule, so as to modulate the amplitude of the output AC voltage of each submodule through the PWM control signal of the three-phase inverter in each submodule.

7. The apparatus according to claim 6, characterized in that, The acquisition module is specifically used for: Based on a preset sampling strategy, the actual three-phase current values ​​on the output side of each submodule are collected, and it is determined whether the local controller of each submodule receives the reference power information sent by the corresponding central controller. If reference power information is received from the corresponding central controller, the local controller of each submodule calculates the three-phase current reference value of each submodule based on the received reference power information.

8. An electronic device, characterized in that, include: The memory, the processor, and the computer program stored in the memory and executable on the processor, the processor executing the program to implement the distributed control method for the modular three-phase photovoltaic inverter cascaded topology as described in any one of claims 1-5.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, The program is executed by the processor to implement the distributed control method for the modular three-phase photovoltaic inverter cascade topology as described in any one of claims 1-5.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the distributed control method for the modular three-phase photovoltaic inverter cascade topology as described in any one of claims 1-5.

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