Grid-connected distributed photovoltaic inverter control method and system

Abstract

The invention discloses a grid-connected distributed photovoltaic inverter control method and system. The method comprises the following steps: selecting a first control object, and establishing a first controller based on the first control object; establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller; and controlling the grid-connected distributed photovoltaic inverter according to the second controller. Through the control method, the power grid operation state change when the voltage of the power grid drops can be effectively handled, and the stability and reliability of the grid-connected distributed photovoltaic inverter are improved. When the voltage of the power grid drops, the voltage of the direct current link capacitor is kept constant, so that the voltage of the direct current link can be prevented from exceeding the voltage limit of the capacitor, and the off-network phenomenon caused by triggering the protection device is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected distributed photovoltaic inverter control, and in particular to a grid-connected distributed photovoltaic inverter control method and system. Background Art

[0002] Distributed photovoltaic arrays are often connected to the distribution network in a two-stage three-phase grid-connected form. This two-stage structure consists of a boost converter connected to the photovoltaic array and an inverter connected to the grid. When a fault occurs in the distribution network and causes a voltage drop on the grid side, the grid-connected photovoltaic array will be disconnected from the distribution network to go off the grid for self-protection. Low Voltage Ride Through (LVRT) means that when a grid fault occurs and the grid connection point voltage drops, the photovoltaic power generation system can continue to maintain connection with the grid and return to normal and stable operation after the fault is resolved.

[0003] During the voltage drop, the power delivered to the grid by the distributed photovoltaic array through the two-level structure is significantly reduced. At the same time, the distributed photovoltaic array still uses the maximum power point tracking (MPPT) strategy to control the photovoltaic voltage, and the active power generated by the photovoltaic array maintains the power peak. The difference between the power generated by the distributed photovoltaic array and the power delivered to the grid causes the DC link voltage to increase severely, exceeding the voltage limit of the capacitor, triggering the protection device, and causing a large area of ​​the distributed photovoltaic array to be disconnected from the grid.

[0004] At present, there are various problems in the design of sliding mode control strategy for low voltage ride through of grid-connected photovoltaic arrays. Some adopt first-order sliding mode control, but cannot guarantee the zero dynamic stability of DC / DC boost converter; some are improved on the original basis and adopt second-order sliding mode control to ensure the fast response and stability of the controller, but cannot guarantee finite time convergence. Therefore, it is necessary to design a finite time convergence second-order sliding mode controller to take into account the response speed, stability and convergence of the control. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above existing problems, the present invention is proposed.

[0007] Therefore, the present invention provides a grid-connected distributed photovoltaic inverter control method and system, which can solve the problems mentioned in the background technology.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a grid-connected distributed photovoltaic inverter control method, comprising:

[0010] Selecting a first control object, and establishing a first controller based on the first control object;

[0011] Establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller;

[0012] The grid-connected distributed photovoltaic inverter is controlled according to the second controller.

[0013] As a preferred solution of the grid-connected distributed photovoltaic inverter control method of the present invention, the selecting of the first control object includes:

[0014] Establishing a first control parameter set of a target grid-connected distributed photovoltaic inverter;

[0015] The first control parameter set is a set of control parameters in the target grid-connected distributed photovoltaic inverter;

[0016] Any control parameter in the first control parameter set is selected as a first control object.

[0017] As a preferred solution of the grid-connected distributed photovoltaic inverter control method of the present invention, wherein: the establishment of the first controller based on the first control object includes:

[0018] determining a control condition of the first controller with respect to the first controlled object;

[0019] Establishing a first objective function and a first constraint condition based on the control condition;

[0020] The control conditions include at least a control target of the first controller, a control law of the first controller, a convergence speed of the first controller, and a stability of the first controller.

[0021] As a preferred solution of the grid-connected distributed photovoltaic inverter control method of the present invention, the grid-connected distributed photovoltaic inverter control according to the second controller includes:

[0022] Determining a power grid operation state, wherein the power grid operation state includes a first operation state and a second operation state;

[0023] When the power grid enters the second operating state, the second controller is used to control the grid-connected distributed photovoltaic inverter.

[0024] As a preferred solution of the grid-connected distributed photovoltaic inverter control method described in the present invention, the first objective function is an arbitrary function that keeps the voltage of the DC link capacitor constant when the grid voltage drops.

[0025] As a preferred solution of the grid-connected distributed photovoltaic inverter control method described in the present invention, the first equivalent control signal is an arbitrary signal for controlling the duty cycle.

[0026] As a preferred solution of the grid-connected distributed photovoltaic inverter control method of the present invention, the grid-connected distributed photovoltaic inverter control according to the second controller further includes:

[0027] When the power grid enters the first operating state, a first maximum power point tracking strategy is used to control the grid-connected distributed photovoltaic inverter.

[0028] In a second aspect, the present invention provides a grid-connected distributed photovoltaic inverter control system, comprising:

[0029] A first controller establishing module, used for selecting a first control object and establishing a first controller based on the first control object;

[0030] A second controller establishing module, used for establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller;

[0031] A control module is used to control the grid-connected distributed photovoltaic inverter according to the second controller.

[0032] In a third aspect, the present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above-mentioned method when executing the computer program.

[0033] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the method described above when executed by a processor.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention proposes a control method and system for a grid-connected distributed photovoltaic inverter, selects a first control object, and establishes a first controller based on the first control object; establishes a first equivalent control signal, and updates the first controller based on the first equivalent control signal to obtain a second controller; and performs grid-connected distributed photovoltaic inverter control according to the second controller. Through the above control method, the present application can effectively cope with the change of the grid operation state when the grid voltage drops, and improve the stability and reliability of the grid-connected distributed photovoltaic inverter. When the grid voltage drops, by keeping the voltage of the DC link capacitor constant, the DC link voltage can be prevented from exceeding the voltage limit of the capacitor, thereby avoiding the disconnection phenomenon caused by triggering the protection device. In addition, the control method of the present application can also quickly return to the maximum power point tracking state after the grid resumes normal operation, ensuring the power generation efficiency of the photovoltaic array. By using the second controller for control, the present application realizes the precise control of the grid-connected distributed photovoltaic inverter, improves the dynamic response speed and stability of the system, and ensures the efficient operation of the photovoltaic inverter under various grid operation conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0036] Figure 1 A method flow chart of a grid-connected distributed photovoltaic inverter control method and system provided by an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a two-stage grid-connected photovoltaic array DC / DC converter control strategy for a grid-connected distributed photovoltaic inverter control method and system provided by an embodiment of the present invention;

[0038] Figure 3 A schematic diagram of a typical duty cycle and frequency width ratio based on pulse width modulation control of a grid-connected distributed photovoltaic inverter control method and system provided by an embodiment of the present invention;

[0039] Figure 4 An internal structural diagram of a computer device of a grid-connected distributed photovoltaic inverter control method and system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0041] Example 1

[0042] Reference Figure 1-Figure 4 , which is the first embodiment of the present invention, provides a grid-connected distributed photovoltaic inverter control method and system, including:

[0043] There are some problems in the existing related technologies. For example, when the grid voltage drops, the traditional grid-connected distributed photovoltaic inverter control method cannot effectively maintain the voltage stability of the DC link capacitor, causing the DC link voltage to exceed the voltage limit of the capacitor, triggering the protection device, and thus causing large-scale grid disconnection. In addition, the traditional control strategy cannot quickly return to the maximum power point tracking state after the grid voltage returns to normal, affecting the power generation efficiency of the photovoltaic array.

[0044] The present application provides a method that can effectively solve the above-mentioned problems. Next, multiple embodiments will be combined to explain in detail how to implement the grid-connected distributed photovoltaic inverter control method;

[0045] Figure 1 A method flow chart of a grid-connected distributed photovoltaic inverter control method and system is shown, including:

[0046] S101, selecting a first control object, and establishing a first controller based on the first control object;

[0047] In the embodiment of the present application, selecting the first control object includes:

[0048] Establishing a first control parameter set of a target grid-connected distributed photovoltaic inverter;

[0049] The first control parameter set is a set of control parameters in the target grid-connected distributed photovoltaic inverter;

[0050] Any control parameter in the first control parameter set is selected as a first control object.

[0051] In an optional embodiment, the control parameters in the target grid-connected distributed photovoltaic inverter may at least include but are not limited to DC link voltage, AC side current, DC side current, photovoltaic array output power, etc. By selecting appropriate control parameters as the control object, the operating state of the grid-connected distributed photovoltaic inverter can be more accurately controlled.

[0052] In an optional embodiment, parameters such as DC link voltage, AC side current, DC side current, and photovoltaic array output power are put into the first control parameter set as control parameters;

[0053] In an optional embodiment, by real-time monitoring of changes in these parameters, dynamic adjustment of the inverter operating state can be achieved. For example, when the DC link voltage exceeds a set safety threshold, the first controller can automatically adjust the power output of the inverter to avoid equipment damage caused by excessive voltage.

[0054] In another optional embodiment, real-time monitoring of the AC side current and the DC side current helps prevent overload conditions and ensure stable operation of the system. Monitoring of the output power of the photovoltaic array can optimize the energy conversion efficiency and adjust the working state of the inverter according to the real-time lighting conditions, thereby improving the overall power generation efficiency. Through comprehensive consideration of these control parameters, the first controller can achieve fine control of the grid-connected distributed photovoltaic inverter to ensure its efficient and safe operation under various environmental conditions.

[0055] In an optional embodiment, relevant technicians can select the first control object based on historical monitoring data. For example, parameters with greater impact on the system or higher volatility in historical monitoring data, such as DC link voltage and photovoltaic array output power, are selected as priority control objects. By analyzing the historical change trends of these parameters, their future behavior patterns can be predicted, so that corresponding control adjustments can be made in advance.

[0056] In another optional embodiment, for example, if historical data shows that the DC link voltage has an upward trend in a specific time period, then during this time period, the first controller can reduce the power output of the inverter in advance to prevent the voltage from exceeding the safety threshold. Similarly, the prediction of the output power of the photovoltaic array can help the inverter adjust the working state before the lighting conditions change to maintain the optimization of power generation efficiency. This control strategy based on historical data makes the operation of the inverter more intelligent and adaptive, further improving the stability and efficiency of the system.

[0057] In the embodiment of the present application, the photovoltaic current of the distributed photovoltaic array is taken as the first control object;

[0058] In an embodiment of the present application, establishing a first controller based on the first control object includes:

[0059] determining a control condition of the first controller with respect to the first controlled object;

[0060] Establishing a first objective function and a first constraint condition based on the control condition;

[0061] The control conditions include at least a control target of the first controller, a control law of the first controller, a convergence speed of the first controller, and a stability of the first controller.

[0062] In an optional embodiment, the first objective function may be designed by any part of the control target of the first controller, the control law of the first controller, the convergence speed of the first controller, and the stability of the first controller;

[0063] In an optional embodiment, the first constraint condition may be designed by any part of the control objective of the first controller, the control law of the first controller, the convergence speed of the first controller, and the stability of the first controller;

[0064] In the embodiment of the present application, the first objective function is an arbitrary function that keeps the voltage of the DC link capacitor constant when the grid voltage drops.

[0065] In an optional embodiment, the first objective function can be designed in different ways, for example, by optimizing control parameters to achieve accurate control of the DC link capacitor voltage. For example, an objective function can be designed that adjusts the output power of the inverter to keep the DC link capacitor voltage within a safe range when the grid voltage drops.

[0066] It should be noted that such an objective function can be a function of the DC link capacitor voltage, a function of the inverter output power, or a combination of the two. In this way, even when the grid voltage is unstable, the stable operation of the inverter can be ensured, and the protection device can be avoided from being triggered due to excessive voltage, thereby reducing the occurrence of grid disconnection.

[0067] In an optional embodiment, the design of the first objective function may also use an optimization algorithm, such as particle swarm optimization (PSO) or genetic algorithm (GA), to achieve a better control effect. Through these algorithms, the best solution that satisfies all control conditions can be found, thereby improving the overall performance of the system. In addition, the design of the first objective function may also consider the efficiency and cost factors of the inverter to achieve a balance between economy and efficiency. In practical applications, the design of the first objective function needs to comprehensively consider the specific requirements and environmental conditions of the system to ensure the applicability and effectiveness of the control strategy.

[0068] In an optional embodiment, the first controller may adopt a sliding mode control strategy, which has good dynamic performance and robustness and can adapt to rapid changes in grid voltage. The sliding mode control strategy ensures that the system state can reach and remain on the sliding mode surface by designing the sliding mode surface and the arrival condition, thereby achieving precise control of the dynamic behavior of the system.

[0069] In another optional embodiment, the first controller may also adopt a fuzzy control strategy, which can handle uncertainty and nonlinear factors and improve the adaptability and flexibility of control. The fuzzy control strategy converts precise input variables into fuzzy variables by defining fuzzy rules and membership functions, and then performs reasoning based on the fuzzy rules to finally output control decisions. This control strategy is particularly suitable for processing complex nonlinear systems, such as grid-connected distributed photovoltaic inverters, because it can adapt to changes in grid conditions and fluctuations in inverter internal parameters.

[0070] In another optional embodiment, the first controller can also adopt an adaptive control strategy, which can automatically adjust the control parameters according to the system operating state and the changes in the external environment to achieve the best control effect. The adaptive control strategy dynamically adjusts the control rules and parameters to adapt to the grid voltage fluctuations and load changes by real-time monitoring of system performance indicators and environmental parameters. This strategy is particularly suitable for grid-connected distributed photovoltaic inverters because it can ensure the stability and efficiency of the system under various operating conditions.

[0071] In the embodiment of the present application, the first controller is designed using a sliding mode controller;

[0072] For example, the design is as follows Figure 2 As shown in the schematic diagram of the control strategy of the two-stage grid-connected photovoltaic array DC / DC converter, during the low voltage ride-through, the maximum power point tracking control strategy is no longer applicable to the DC / DC converter. According to the requirements of the power grid technical specifications, the grid-connected photovoltaic array is obliged to reduce the generation of active power during the voltage drop and allocate part of its inverter capacity to reactive power, which is contrary to the maximum power point tracking control strategy. To solve this problem, the finite-time sliding mode control (FTSMC) strategy is used to control the DC / DC converter instead of the maximum power point tracking strategy during the low voltage ride-through. Sliding mode control can effectively respond to the adverse effects of external interference and can adapt well to operating conditions with uncertain model parameters.

[0073] Among them, the dynamic equation of the photovoltaic array DC / DC converter is:

[0074]

[0075] Among them, u is the switch gate signal, which represents the logical state of the DC / DC converter power switch. The signal appears in the form of "0" and "1" switching commands. C is capacitance, L is inductance; v dc is the DC link voltage, i pv is the photovoltaic array current, i dcis the DC link current, v pv is the PV array voltage.

[0076] Furthermore, the control target is selected. The goal of the controller based on the finite time sliding mode control strategy is to keep the voltage of the DC link capacitor constant when the grid voltage drops. To achieve this goal, it is necessary to maintain the change of the energy stored in the capacitor to zero, which can be further expressed mathematically as:

[0077]

[0078] Where C is the capacitance, v dc is the DC link voltage, i pv is the photovoltaic array current, v pv is the photovoltaic array voltage; P pv and P dc They represent the power generated by the PV array and the power of the DC link respectively.

[0079] In an optional embodiment, assuming that the loss of the DC / AC inverter can be ignored, it can be obtained that:

[0080] P dc ≈P grid (4)

[0081] Among them, P grid is the active power delivered to the grid.

[0082] Furthermore, the photovoltaic voltage can be written as a function of the photovoltaic current:

[0083]

[0084] Where n p and n s are the number of PV array modules in parallel and series respectively; the coefficients are charge q, Boltzmann constant κ, ambient temperature T, diode saturation current I sat , short circuit current I sc .

[0085] Furthermore, after rearranging the above formula, the current reference value for keeping the DC link voltage constant is obtained: The relationship with the active power delivered to the grid is as follows:

[0086]

[0087] Therefore, for each power value output to the grid, the above equation can be solved to find the reference current of the photovoltaic array: By controlling the output current i of the photovoltaic array pv , achieving the goal of maintaining DC link voltage stability during low voltage ride-through.1 is the photovoltaic array current error:

[0088]

[0089] Furthermore, the control law of sliding mode control is designed. The basic principle of sliding mode control is to design a specific sliding surface in its control law so that the trajectory of the state variable points to the desired origin when it coincides. For the DC / DC converter, the control law is first designed using the switching function as follows:

[0090]

[0091] Where u is the switch gate signal, representing the logical state of the DC / DC converter power switch. The signal appears in the form of "0" and "1" switching commands; sgn is the sign function, and the control law indicates that the gate signal u is determined by the sliding surface. S SMC Decide.

[0092] Furthermore, the sliding surface of the sliding mode control is designed, which determines the convergence speed, stability and overall performance of the controller. SMC The proportional derivative sliding surface is selected and defined as:

[0093]

[0094] In the formula, α 1 , α 2 , α 3 is the control parameter, satisfying α 1 >0,α 2 >0 and 0<α 3 <1;

[0095] Furthermore, the stability condition of sliding mode control, in order to ensure the stability of the proposed sliding mode controller, the following Lyapunov candidate function is selected:

[0096]

[0097] The following conditions must be met to determine the local reachability of the state variable trajectory:

[0098]

[0099] Where S SMC The first-order derivative of is:

[0100]

[0101] Furthermore, combining the previous formula, the first-order and second-order derivatives of the photovoltaic current error e can be obtained:

[0102]

[0103] In an optional embodiment, the following two cases are considered for the stability of the proposed sliding mode controller:

[0104] when hour:

[0105]

[0106] when hour:

[0107]

[0108] In summary, the stability of the sliding mode controller needs to meet the following conditions:

[0109]

[0110] where α 1 , α 2 , α 3 To ensure the stability of the sliding mode controller, the selection of these control parameters should satisfy the above inequality.

[0111] Furthermore, the finite time convergence condition of sliding mode control, according to the principle of sliding surface, when the tracking error is very close to the origin to be converged, S SMC =0, it is necessary to ensure that the following formula converges in finite time:

[0112]

[0113] By integrating the convergence time, we get the following:

[0114]

[0115] Therefore, the tracking error will converge to the sliding surface in finite time:

[0116]

[0117] It should be noted that selecting a first control object and establishing a first controller based on the first control object can effectively reduce the fluctuation and interference of the power grid and improve the overall stability of the system by accurately controlling the output current of the photovoltaic array. When designing a sliding mode controller, it is necessary to consider the dynamic response and anti-interference ability of the system to ensure that good performance can be maintained under various working conditions. By reasonably selecting control parameters, the performance of the sliding mode controller can be optimized so that it can meet the stability requirements while also having the ability of fast response and high-precision control. In practical applications, this control method and system can effectively improve the operating efficiency of grid-connected distributed photovoltaic inverters and reduce maintenance costs, and has broad application prospects.

[0118] S102, establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller;

[0119] In the embodiment of the present application, the first equivalent control signal is established as an arbitrary signal for controlling the duty cycle.

[0120] In an optional embodiment, the first equivalent control signal can be generated using a proportional integral derivative (PID) controller, which can dynamically adjust control parameters according to the real-time output of the photovoltaic array and feedback information from the power grid. In this way, the first equivalent control signal can reflect the system state in real time and guide the first controller to perform precise current control.

[0121] In an optional embodiment, the embodiment may also include an adaptive algorithm for automatically adjusting the parameters of the PID controller according to the working environment and load changes of the photovoltaic inverter to further improve the control accuracy and the robustness of the system.

[0122] In an optional embodiment, the first equivalent control signal can also be generated by a fuzzy logic controller, which can handle uncertainty and nonlinear factors, thereby providing a more flexible and adaptable control strategy during the operation of the photovoltaic inverter. The fuzzy logic controller simulates the human decision-making process through a set of fuzzy rules, which are based on fuzzy sets and membership functions of input variables and can handle the fuzziness and imprecision of input data.

[0123] It should be noted that, in this way, the first equivalent control signal can better adapt to environmental changes and load fluctuations, and ensure the stability and efficiency of the photovoltaic inverter under various working conditions.

[0124] In an optional embodiment, the first equivalent control signal may also be designed through a control scheme based on pulse width modulation to achieve precise control of the inverter output voltage waveform.

[0125] It should be noted that this control scheme uses pulse width modulation technology to control the frequency and amplitude of the inverter output voltage by adjusting the on and off time of the switching device. This control scheme based on pulse width modulation can effectively reduce the harmonic distortion of the output voltage and improve the power quality. At the same time, it can also dynamically adjust the output power according to the load demand, thereby optimizing the performance of the entire system.

[0126] In the embodiment of the present application, the first equivalent control signal is designed by a control scheme based on pulse width modulation, specifically:

[0127] A control scheme based on pulse width modulation, in which the control signal is compared with a ramp waveform to generate a discrete gate pulse signal. Its advantage is that since the switching function is performed by the pulse width modulator, no additional hardware circuit is required and its transient response will not deteriorate.

[0128] First, in sliding mode control, the discrete control input gate signal u can be theoretically expressed as the equivalent control signal u eq , which can be generated by using the invariance condition.

[0129] In an optional embodiment, the sliding mode control system equation obtained from the dynamic equation of the DC / DC converter satisfies the following form:

[0130] i pv =f(i pv ,u) (18)

[0131] Where u = {0, 1}. In the ideal sliding mode control process, the state trajectory controlled by the gate signal u always moves along the sliding plane, that is, S SMC =0, and in the absence of high-frequency oscillation, Assume that the equivalent control signal u eq The controlled state trajectory is completely equivalent to the ideal sliding mode control trajectory. The state trajectory equation is can be rewritten as Solve the equation G·f(i pv ,u eq )=0, the equivalent control signal u eq , as follows:

[0132]

[0133] The equivalent control signal u eq Substituting back into the dynamic equation of the DC / DC converter, we obtain Achieve equivalent control.

[0134] In an alternative embodiment, at high switching frequencies, the equivalent control is actually a duty cycle control. In each switching period of duration Δ, the control input gate signal u switches between 1 and 0 once. The moment when the switching occurs is determined by the sampled value of the state variable at the beginning of each switching period. The duty cycle is the portion of the switching period where the control maintains a value of 1, usually the state vector x(t) (the state vector of the DC / DC converter controlled by the sliding mode is i pv (t)) is expressed as d(x), 0<d(x)<1. For each switching cycle interval Δ, the control input gate signal u is expressed as follows:

[0135]

[0136] The following general system expression To derive the system dynamic equation under duty cycle control:

[0137]

[0138] In an optional embodiment, when the duty cycle frequency tends to infinity, that is, the switching period duration Δ→0, the pulse width modulation control system adopts an ideal average model, and the above formula is expressed as:

[0139]

[0140] It is called an average pulse width modulation control system. Therefore, when the duty cycle frequency tends to infinity, the state trajectory of the pulse width control control system is controlled by the duty cycle d(x). Since the duty cycle is basically also a smooth analytical function of the discrete control pulses in the pulse width modulation, the pulse width modulation-based sliding mode controller can be obtained by mapping the equivalent control function to the duty cycle function of the pulse width modulator, that is:

[0141]

[0142] It should be noted that the finite-time convergent sliding mode control law can be further modified into a finite-time convergent sliding mode control based on pulse width modulation, retaining the dynamic response characteristics of the controller.

[0143] It should also be noted that establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller can achieve precise control of the inverter output voltage waveform. In this way, the output voltage of the inverter will be more stable, and harmonic distortion will be effectively suppressed, thereby improving the power quality of the entire system. In addition, the control scheme based on pulse width modulation can also dynamically adjust the output power according to the change of the load to ensure the optimal performance of the system under different working conditions. In practical applications, this control method can significantly reduce the operating cost of the inverter, extend the service life of the equipment, and has a high market application value due to its high efficiency and stability.

[0144] S103: Control the grid-connected distributed photovoltaic inverter according to the second controller.

[0145] In an embodiment of the present application, controlling the grid-connected distributed photovoltaic inverter according to the second controller includes:

[0146] Determining a power grid operation state, wherein the power grid operation state includes a first operation state and a second operation state;

[0147] When the power grid enters the second operating state, the second controller is used to control the grid-connected distributed photovoltaic inverter.

[0148] In the embodiment of the present application, the controlling of the grid-connected distributed photovoltaic inverter according to the second controller further includes:

[0149] When the power grid enters the first operating state, a first maximum power point tracking strategy is used to control the grid-connected distributed photovoltaic inverter.

[0150] In the embodiment of the present application, under normal circumstances, the maximum power point tracking strategy is adopted to evaluate di in each sample. pv / dv pv and -i pv / v pv The relationship between is calculated by adjusting the DC / DC converter duty cycle d to achieve the maximum power and ensure that the photovoltaic array generates peak active power. When the grid voltage drops suddenly, switch to the pulse width modulation-based finite time convergence sliding mode controller to generate the DC / DC converter duty cycle during the low voltage ride-through period. Using the control law introduced in the previous formula and the given sliding surface, it can be ensured that no matter what the initial state of the photovoltaic array is, the current converges to the sliding surface, further maintaining the DC link capacitor voltage stability, and switch to the maximum power point tracking strategy after the fault is cleared.

[0151] In an optional embodiment, relevant technicians can design more operating states to switch control strategies to adapt to different grid conditions and fault conditions. For example, in addition to grid voltage sag, grid frequency anomalies, current overload and other conditions can also be considered. In these cases, the inverter control system can switch to corresponding control strategies, such as frequency adaptive control or current limiting control, to ensure the stable operation of the system and the safety of the equipment. In this way, the inverter can not only operate efficiently under normal conditions, but also provide necessary support when the grid is abnormal, enhancing the robustness and reliability of the entire power system.

[0152] In summary, the present invention proposes a control method for a grid-connected distributed photovoltaic inverter, selects a first control object, and establishes a first controller based on the first control object; establishes a first equivalent control signal, and updates the first controller based on the first equivalent control signal to obtain a second controller; and performs grid-connected distributed photovoltaic inverter control according to the second controller. Through the above control method, the present application can effectively cope with the change of the grid operation state when the grid voltage drops, and improve the stability and reliability of the grid-connected distributed photovoltaic inverter. When the grid voltage drops, by keeping the voltage of the DC link capacitor constant, the DC link voltage can be prevented from exceeding the voltage limit of the capacitor, thereby avoiding the disconnection phenomenon caused by triggering the protection device. In addition, the control method of the present application can also quickly return to the maximum power point tracking state after the grid resumes normal operation, ensuring the power generation efficiency of the photovoltaic array. By using the second controller for control, the present application realizes the precise control of the grid-connected distributed photovoltaic inverter, improves the dynamic response speed and stability of the system, and ensures the efficient operation of the photovoltaic inverter under various grid operation conditions.

[0153] Example 2

[0154] In a preferred embodiment, designing a finite time convergent sliding mode controller includes selecting a control object distributed photovoltaic array photovoltaic current i pv , design sliding surface S SMC , analyze the stability conditions and finite time convergence conditions of the sliding mode controller, and finally output the switch gate signal u to control the DC / DC boost converter; design a sliding mode controller based on pulse width modulation, by using the equivalent control signal u eq Instead of the discrete switch command signal u, it is further mapped to the duty cycle function d of the pulse width modulator. The low voltage ride-through control strategy for grid-connected distributed photovoltaic inverters is designed.

[0155] like Figure 2 The schematic diagram of the control strategy of the two-stage grid-connected photovoltaic array DC / DC converter is shown in Figure 1. The photovoltaic array (PVArray) is the power supply part of the system, which consists of multiple photovoltaic cells and is used to convert solar energy into DC power. Voltage and current: The output voltage v of the photovoltaic array is marked in the figure. pv and current i pv. DC / DC Converter: This part of the circuit is used to adjust the DC voltage output by the photovoltaic array to make it suitable for the needs of subsequent circuits. Inductor (L) and Capacitor (C): Inductors and capacitors are used to filter and smooth current. Switch (d): The switch is used to control the flow of current and achieve voltage adjustment. Maximum Power Point Tracking (MPPT): This is a control strategy used to ensure that the photovoltaic array always operates at the maximum power point under different light and temperature conditions, thereby improving the efficiency of the system. Control Signal: The control signal is marked in the figure, including the duty cycle (DutyCycle) and the gate signal (Gate Signal). DC / AC InverterDC / AC Inverter: This part of the circuit converts DC power into AC power so that it can be connected to the power grid or used by AC loads. Three-Phase Inverter: The figure shows a three-phase inverter, which consists of six switches to control the output of three-phase AC power. Filter: This part of the circuit is used to smooth the AC power output by the inverter, reduce the harmonic content, and improve the power quality. The figure shows a filter with a resistor (R f ) and inductance (L f ) filter. Grid This is the output part of the system. The AC power output by the inverter is connected to the grid after passing through the filter and exchanges power with the grid. Voltage and current: The voltage v of the grid is marked in the figure. abc and current i abc . Power calculation (PowerCalculation): This part of the circuit is used to calculate the active power (P) and reactive power (Q) of the system in order to perform power factor correction and grid management. Control signal: Multiple control signals are marked in the figure, including gate signal (Gate Signal), equivalent signal (Equivalent Signal) and duty cycle (Duty Cycle). These signals are used to control the switches in the circuit to achieve normal operation of the system. Maximum power point tracking (MPPT): By adjusting the duty cycle (Duty Cycle), ensure that the photovoltaic array always operates at the maximum power point. Finite time convergence sliding mode control: This is a control strategy used to quickly adjust the system state to ensure stable operation of the system. Low voltage ride-through (LVRT) decision: When the grid voltage is abnormal, the system needs to make a decision to ensure the stable operation of the system.

[0156] Example 3

[0157] This embodiment also provides a grid-connected distributed photovoltaic inverter control system, including:

[0158] A first controller establishing module, used for selecting a first control object and establishing a first controller based on the first control object;

[0159] A second controller establishing module, used for establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller;

[0160] A control module is used to control the grid-connected distributed photovoltaic inverter according to the second controller.

[0161] The above-mentioned unit modules may be embedded in or independent of a processor in a computer device in the form of hardware, or may be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to the above-mentioned modules.

[0162] This embodiment also provides a computer device, which may be a terminal, and its internal structure diagram may be as shown in FIG. Figure 4 As shown. The computer device includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, a grid-connected distributed photovoltaic inverter control method is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covered on the display screen, or a button, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse, etc.

[0163] This embodiment further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the following steps are implemented:

[0164] Selecting a first control object, and establishing a first controller based on the first control object;

[0165] Establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller;

[0166] The grid-connected distributed photovoltaic inverter is controlled according to the second controller.

[0167] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0168] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0169] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0170] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0171] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1The steps for the functions specified in one or more boxes.

[0172] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0173] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A grid-connected distributed photovoltaic inverter control method, characterized in that: include: Selecting a first control object, and establishing a first controller based on the first control object; Establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller; The grid-connected distributed photovoltaic inverter is controlled according to the second controller.

2. The grid-connected distributed photovoltaic inverter control method according to claim 1, characterized in that: The selecting the first control object comprises: Establishing a first control parameter set of a target grid-connected distributed photovoltaic inverter; The first control parameter set is a set of control parameters in the target grid-connected distributed photovoltaic inverter; Any control parameter in the first control parameter set is selected as a first control object.

3. The grid-connected distributed photovoltaic inverter control method according to claim 2, characterized in that: The establishing of the first controller based on the first control object comprises: determining a control condition of the first controller with respect to the first controlled object; Establishing a first objective function and a first constraint condition based on the control condition; The control conditions include at least a control target of the first controller, a control law of the first controller, a convergence speed of the first controller, and a stability of the first controller.

4. The grid-connected distributed photovoltaic inverter control method according to claim 3, characterized in that: The controlling of the grid-connected distributed photovoltaic inverter according to the second controller includes: Determining a power grid operation state, wherein the power grid operation state includes a first operation state and a second operation state; When the power grid enters the second operating state, the second controller is used to control the grid-connected distributed photovoltaic inverter.

5. The grid-connected distributed photovoltaic inverter control method according to claim 4, characterized in that: The first objective function is an arbitrary function that keeps the voltage of the DC link capacitor constant when the grid voltage decreases.

6. The grid-connected distributed photovoltaic inverter control method according to claim 5, characterized in that: The first equivalent control signal is established as an arbitrary signal for controlling the duty cycle.

7. The grid-connected distributed photovoltaic inverter control method and system according to claim 6, characterized in that: The controlling of the grid-connected distributed photovoltaic inverter according to the second controller further includes: When the power grid enters the first operating state, a first maximum power point tracking strategy is used to control the grid-connected distributed photovoltaic inverter.

8. A grid-connected distributed photovoltaic inverter control system, characterized in that: include: A first controller establishing module, used for selecting a first control object and establishing a first controller based on the first control object; A second controller establishing module, used for establishing a first equivalent control signal, and updating the first controller based on the first equivalent control signal to obtain a second controller; A control module is used to control the grid-connected distributed photovoltaic inverter according to the second controller.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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