Photovoltaic inverter mode determination method and device and photovoltaic inverter control method and system

Abstract

The invention discloses a photovoltaic inverter mode determination method and device and a photovoltaic inverter control method and system, and relates to the field of photovoltaic technology. The method for determining the mode of the photovoltaic inverter comprises the steps that the power generation benefit Me, the compensation benefit Mc and the current mode of the photovoltaic inverter are obtained, the compensation benefit Mc is determined according to a first benefit Mch and a second benefit Mcq, the first benefit Mch is the benefit generated by treating harmonic current, and the second benefit Mcq is the benefit generated by compensating reactive power; determining a target mode of the photovoltaic inverter according to the power generation benefit Me, the compensation benefit Mc and the current mode; wherein each of the current mode and the target mode comprises one of a power generation mode and an electric energy management mode. According to the embodiment of the invention, the method can carry out the harmonic control and reactive compensation, and can better support the stable operation of a power grid.

Description

Technical Field

[0001] This application belongs to the field of photovoltaic technology, and particularly relates to a method and device for determining the mode of a photovoltaic inverter, a control method and system for a photovoltaic inverter. Background Art

[0002] The main circuit structure of a photovoltaic inverter is similar to that of a Static Var Generator (SVG) and an Active Power Filter (APF). The difference is that the photovoltaic inverter mainly outputs active components, while SVG and APF mainly output reactive components.

[0003] In the related art, the photovoltaic inverter only focuses on power generation, aiming at the maximum power output on the photovoltaic (PV) side, and is not responsible for the power quality of the distribution network. Due to the access of photovoltaic power generation, the deterioration of the power quality of the distribution network is aggravated, resulting in an increase in harmonic content and a low reactive power in the distribution network, which affects the safe operation of transformers and load equipment, and further leads to insufficient stability of the power grid. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a method and device for determining the mode of a photovoltaic inverter, a control method and system for a photovoltaic inverter in view of the above deficiencies in the prior art. Using the method for determining the mode of the photovoltaic inverter, the working mode of the photovoltaic inverter can be dynamically adjusted, so that the photovoltaic inverter can not only focus on maximum active power generation, but also perform harmonic suppression and reactive power compensation, thereby better supporting the stable operation of the power grid, improving the stability of the power grid, and increasing the adaptability and flexibility of the photovoltaic inverter.

[0005] In a first aspect, an embodiment of this application provides a method for determining the mode of a photovoltaic inverter, including:

[0006] Obtain the power generation benefit Me, compensation benefit Mc and current mode of the photovoltaic inverter. The compensation benefit Mc is determined according to the first benefit Mch and the second benefit Mcq. The first benefit Mch is the benefit generated by suppressing harmonic current, and the second benefit Mcq is the benefit generated by compensating reactive power;

[0007] Determine the target mode of the photovoltaic inverter according to the power generation benefit Me, compensation benefit Mc and current mode;

[0008] Wherein, both the current mode and the target mode include one of a power generation mode and a power governance mode.

[0009] In some embodiments of the first aspect, obtaining the power generation benefit Me of the photovoltaic inverter specifically includes:

[0010] Obtain the maximum output power Ppv on the AC side of the photovoltaic inverter and the time-of-use electricity price;

[0011] Determine the power generation benefit Me of the PV inverter by multiplying the maximum AC-side output power Ppv by the time-of-use electricity price.

[0012] In some embodiments of the first aspect, obtaining the maximum AC-side output power Ppv of the PV inverter specifically includes:

[0013] Obtain the maximum DC-side output power of the PV inverter and the maximum active power received by the AC-side distribution network of the PV inverter;

[0014] When the maximum DC-side output power is greater than or equal to the maximum active power, determine the maximum active power as the maximum AC-side output power Ppv of the PV inverter;

[0015] Or,

[0016] When the maximum DC-side output power is less than the maximum active power, determine the maximum DC-side output power as the maximum AC-side output power Ppv of the PV inverter.

[0017] In some embodiments of the first aspect, obtaining the compensation benefit Mc of the PV inverter includes:

[0018] Obtain the first benefit Mch and the second benefit Mcq;

[0019] Determine the sum of the first benefit Mch and the second benefit Mcq as the compensation benefit Mc of the PV inverter.

[0020] In some embodiments of the first aspect, obtaining the first benefit Mch specifically includes:

[0021] Obtain the harmonic current component Ilh in the harmonic suppression unit benefit coefficient Kh, the grid voltage Ue, and the load current Il;

[0022] Determine the first benefit Mch according to the harmonic suppression unit benefit coefficient Kh, the grid voltage Ue, and the harmonic current component Ilh.

[0023] In some embodiments of the first aspect, obtaining the harmonic suppression unit benefit coefficient Kh specifically includes:

[0024] Obtain the first benefit coefficient Kh1, the second benefit coefficient Kh2, and the third benefit coefficient Kh3; the first benefit coefficient Kh1 is the benefit coefficient for the improvement of power consumption satisfaction brought by harmonic current suppression; the second benefit coefficient Kh2 is the benefit coefficient for the additional loss brought by harmonic current suppression; the third benefit coefficient Kh3 is the benefit coefficient for the extension of equipment life brought by harmonic current suppression;

[0025] Determine the sum of the first benefit coefficient Kh1, the second benefit coefficient Kh2, and the third benefit coefficient Kh3 as the harmonic benefit coefficient Kh of the governance unit.

[0026] In some embodiments of the first aspect, determine the first benefit Mch according to the harmonic benefit coefficient Kh of the governance unit, the grid voltage Ue, and the harmonic current component Ilh, specifically including:

[0027] Substitute the harmonic benefit coefficient Kh of the governance unit, the grid voltage Ue, and the harmonic current component Ilh into formula (1) to calculate the first benefit Mch;

[0028] Formula (1) includes:

[0029] Mch = Ue * Ilh * Kh (1).

[0030] In some embodiments of the first aspect, obtain the second benefit Mcq, specifically including:

[0031] Obtain the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq in the load current Il;

[0032] Determine the second benefit Mcq according to the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq.

[0033] In some embodiments of the first aspect, obtain the reactive power benefit coefficient Kq of the compensation unit, specifically including:

[0034] Obtain the fourth benefit coefficient Kq1 and the fifth benefit coefficient Kq2; the fourth benefit coefficient Kq1 is the electricity price reduction benefit coefficient brought by the photovoltaic inverter improving the power factor; the fifth benefit coefficient is the energy-saving benefit coefficient brought by the reactive power governance of the photovoltaic inverter;

[0035] Determine the sum of the fourth benefit coefficient Kq1 and the fifth benefit coefficient Kq2 as the reactive power benefit coefficient of the compensation unit.

[0036] In some embodiments of the first aspect, determine the second benefit Mcq according to the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq, specifically including:

[0037] Substitute the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq into formula (2) to calculate the second benefit Mcq;

[0038] Formula (2) includes:

[0039] Mcq = Ue * Ilq * Kq (2).

[0040] In some embodiments of the first aspect, determining the target mode of the PV inverter according to the power generation revenue Me, the compensation benefit Mc, and the current mode specifically includes:

[0041] When the current mode is the power generation mode, obtain the starting power management coefficient Kc;

[0042] When Mc > Me * Kc, determine the target mode of the PV inverter as the power management mode;

[0043] Or,

[0044] When Mc ≤ Me * Kc, determine the target mode of the PV inverter as the power generation mode.

[0045] In some embodiments of the first aspect, determining the target mode of the PV inverter according to the power generation revenue Me, the compensation benefit Mc, and the current mode specifically includes:

[0046] When the current mode is the power management mode, obtain the return power generation mode coefficient Kd;

[0047] When Mc < Me * Kd, determine the target mode of the PV inverter as the power generation mode;

[0048] Or,

[0049] When Mc ≥ Me * Kd, determine the target mode of the PV inverter as the power management mode.

[0050] In some embodiments of the first aspect, before determining the target mode of the PV inverter according to the power generation revenue Me, the compensation benefit Mc, and the current mode, the method further includes:

[0051] Obtain multiple power generation benefits Me and multiple compensation benefits Mc of the PV inverter within a preset time period t;

[0052] Determine the average value of the multiple power generation benefits Me as the target power generation benefit Me of the PV inverter, and determine the average value of the multiple compensation benefits Mc as the target compensation benefit of the PV inverter;

[0053] Determining the target mode of the PV inverter according to the power generation revenue Me, the compensation benefit Mc, and the current mode includes:

[0054] Determine the target mode of the PV inverter according to the target power generation revenue, the target compensation benefit, and the current mode.

[0055] In some embodiments of the first aspect, before determining the average value of the multiple power generation benefits Me as the power generation benefit Me of the PV inverter and determining the average value of the multiple compensation benefits Mc as the compensation benefit Mc of the PV inverter, the method further includes:

[0056] Adopt the moving average method to solve the average value of multiple power generation benefits Me and the average value of multiple compensation benefits Mc.

[0057] Based on the same inventive concept, in a second aspect, an embodiment of the present application further provides a photovoltaic inverter control method, including:

[0058] Determine the target mode of the photovoltaic inverter according to the photovoltaic inverter mode determination method in the first aspect;

[0059] Control the photovoltaic inverter to execute the target mode.

[0060] Based on the same inventive concept, in a third aspect, an embodiment of the present application provides a photovoltaic inverter mode determination device, including:

[0061] A first acquisition module, configured to acquire the power generation benefit Me, the compensation benefit Mc and the current mode of the photovoltaic inverter. The compensation benefit Mc is determined according to the first benefit Mch and the second benefit Mcq. The first benefit Mch is the benefit generated by suppressing harmonic current, and the second benefit Mcq is the benefit generated by compensating reactive power;

[0062] A first determination module, connected to the first acquisition module, configured to determine the target mode of the photovoltaic inverter according to the power generation benefit Me, the compensation benefit Mc and the current mode;

[0063] Wherein, both the current mode and the target mode include one of a power generation mode and an electric energy governance mode.

[0064] In some embodiments of the third aspect, the first acquisition module is specifically configured to:

[0065] Acquire the maximum AC-side output power Ppv of the photovoltaic inverter and the time-of-use electricity price;

[0066] Determine the product of the maximum AC-side output power Ppv and the time-of-use electricity price as the power generation benefit Me of the photovoltaic inverter.

[0067] In some embodiments of the third aspect, the first acquisition module is specifically configured to:

[0068] Acquire the first benefit Mch and the second benefit Mcq;

[0069] Determine the sum of the first benefit Mch and the second benefit Mcq as the compensation benefit Mc of the photovoltaic inverter.

[0070] In some embodiments of the third aspect, the first determination module is specifically configured to:

[0071] When the current mode is the power generation mode, acquire the starting power governance coefficient Kc;

[0072] When Mc > Me * Kc, the target mode of the photovoltaic inverter is determined as the power energy management mode;

[0073] Or,

[0074] When Mc ≤ Me * Kc, the target mode of the photovoltaic inverter is determined as the power generation mode.

[0075] Based on the same inventive concept, in a fourth aspect, an embodiment of the present application further provides a photovoltaic inverter control system, including:

[0076] The photovoltaic inverter mode determination device according to the third aspect, which is used to determine the target mode of the photovoltaic inverter;

[0077] A control device, connected to the photovoltaic inverter mode determination device, which is used to control the photovoltaic inverter to execute the target mode.

[0078] According to the photovoltaic inverter mode determination method and device, photovoltaic inverter control method and system provided by the embodiments of the present application, first obtain the power generation benefit Me, compensation benefit Mc and current mode of the photovoltaic inverter, and then determine the target mode of the photovoltaic inverter according to the power generation benefit Me, compensation benefit Mc and current mode. That is to say, in the embodiments of the present application, by comprehensively considering the power generation benefit Me of the photovoltaic inverter, the first benefit Mch generated by harmonic current governance, the second benefit Mcq generated by reactive power compensation, and the current mode, the working mode of the photovoltaic inverter is dynamically adjusted, so that the photovoltaic inverter can not only focus on maximum active power generation, but also perform harmonic governance and reactive power compensation to improve or solve the problems in the related art that the harmonic content in the distribution network increases, the reactive power is low, and the safe operation of transformers and load equipment is affected, thereby better supporting the stable operation of the power grid, improving the stability of the power grid, and increasing the adaptability and flexibility of the photovoltaic inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 An electrical diagram showing the connection of the photovoltaic inverter to the distribution network;

[0080] Figure 2 A schematic flowchart showing a method for determining the mode of a photovoltaic inverter provided by an embodiment of the present application;

[0081] Figure 3 Another schematic flowchart showing a method for determining the mode of a photovoltaic inverter provided by an embodiment of the present application;

[0082] Figure 4 A schematic structural diagram showing a device for determining the mode of a photovoltaic inverter provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0083] To enable those skilled in the art to better understand the technical solutions of this application, the following further describes this application in detail with reference to the accompanying drawings and embodiments.

[0084] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the following further describes this application in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain this application and are not configured to limit this application. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of this application by showing examples of this application.

[0085] It should be noted that in this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including", or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or device. Without further limitation, elements defined by the statement "comprising..." do not preclude the presence of additional identical elements in the process, method, article, or device comprising the said elements.

[0086] It should be understood that the term " / and" used herein is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A / and B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally represents an "or" relationship between the associated objects before and after.

[0087] To better understand the photovoltaic inverter mode determination method and device, and the photovoltaic inverter control method and device provided by the embodiments of this application, the related technologies that may be involved in the embodiments of this application are described below.

[0088] The current relevant research on reactive power compensation and harmonic suppression of photovoltaic inverters mainly focuses on the feasibility of control strategies under the condition of multi - function in one device. For example, some patents propose methods for estimating grid - side harmonic current through grid - side voltage and compensating harmonic current using current closed - loop control, enabling the photovoltaic grid - connected inverter to have the function of APF; that is, from how to extract harmonic components of grid voltage and current, and then perform closed - loop control through voltage or current control commands to manage power quality. Another example is that some literature proposes that there are differences in the remaining capacity of photovoltaic inverters under different output conditions, and a dynamic power quality optimization method with maximum active power and power quality management as the objective function is constructed.

[0089] However, the technical solutions in the related technologies all ignore that in the distributed application scenario of photovoltaic inverters, the available capacity at the grid connection point is often limited, and the power generation of photovoltaic power is limited. In the self - consumption mode, if the photovoltaic power is fed back to the grid, there will also be an embarrassing situation of being fined. In addition, with the access of photovoltaic grid - connected inverters, users often face the problem of deteriorating power quality of the power consumption system, manifested as abnormal voltage and current harmonics, abnormal operation of protection devices, too low power factor, and high power factor adjustment charges.

[0090] The electrical diagram of the photovoltaic inverter connected to the distribution network in the related technology is as Figure 1 shown. The photovoltaic inverter is connected to the grid at the low - voltage side of the line transformer. In the distributed generation application scenario, there are still a large number of loads in the line, including linear loads and nonlinear loads, continuous working loads and short - time working loads. Taking iron and steel metallurgy users as an example, there are a large number of nonlinear loads, mainly rolling mills, electric arc furnaces, etc. These loads have strong volatility, low power factor, and serious pollution to the power supply system. In the related technology, the photovoltaic grid - connected inverter only focuses on power generation, aiming at the maximum power output of the PV side, and is not responsible for the power quality of the distribution network. In recent years, with the continuous increase in the penetration rate of photovoltaic power generation and the insufficient grid connection capacity, photovoltaic power generation faces the problem of being limited in power, and the equipment capacity is not fully utilized; on the other hand, due to the access of photovoltaic power generation, the deterioration of the power quality of the distribution network is aggravated, resulting in an increase in harmonic content and low reactive power in the distribution network, affecting the safe operation of transformers and load equipment, and generating high power factor adjustment costs.

[0091] It should be noted that for the connection relationship between the line transformer, photovoltaic inverter, photovoltaic module, nonlinear load, power electronic device, and distribution breaker, please refer to Figure 1 and will not be elaborated here.

[0092] Based on this, the embodiments of the present application provide a method and device for determining the mode of a photovoltaic inverter, a control method and system for a photovoltaic inverter, so as to solve at least some of the above problems.

[0093] Embodiment 1

[0094] The photovoltaic inverter mode determination method provided by the embodiments of the present application is applicable to the distributed power generation application scenario in the process of solar photovoltaic power generation. The photovoltaic inverter mode determination method provided by the embodiments of the present application can be executed by a controller of a photovoltaic inverter, a photovoltaic inverter mode determination device, an electronic device, etc. Hereinafter, an example will be given where the photovoltaic inverter mode determination method is executed by a controller.

[0095] As Figure 2 shown, the photovoltaic inverter mode determination method provided by the embodiments of the present application may include steps S110 to S120.

[0096] S110. Obtain the power generation benefit Me, the compensation benefit Mc, and the current mode of the photovoltaic inverter. The compensation benefit Mc is determined according to the first benefit Mch and the second benefit Mcq. The first benefit Mch is the benefit generated by controlling harmonic current, and the second benefit Mcq is the benefit generated by compensating reactive power.

[0097] S120. Determine the target mode of the photovoltaic inverter according to the power generation benefit Me, the compensation benefit Mc, and the current mode.

[0098] Among them, both the current mode and the target mode include one of a power generation mode and a power quality control mode.

[0099] According to the photovoltaic inverter mode determination method provided by the embodiments of the present application, first obtain the power generation benefit Me, the compensation benefit Mc, and the current mode of the photovoltaic inverter, and then determine the target mode of the photovoltaic inverter according to the power generation benefit Me, the compensation benefit Mc, and the current mode. That is to say, in the embodiments of the present application, by comprehensively considering the power generation benefit Me of the photovoltaic inverter, the first benefit Mch generated by controlling harmonic current, the second benefit Mcq generated by compensating reactive power, and the current mode, the working mode of the photovoltaic inverter is dynamically adjusted, so that the photovoltaic inverter can not only focus on maximum active power generation, but also perform harmonic control and reactive power compensation to improve or solve the problems in the related art that the harmonic content in the distribution network increases, the reactive power is low, and the safe operation of transformers and load equipment is affected, thereby better supporting the stable operation of the power grid, improving the stability of the power grid, and increasing the adaptability and flexibility of the photovoltaic inverter.

[0100] The following introduces the specific implementation manners of the above steps.

[0101] In step S110, exemplarily, the photovoltaic inverter can be any photovoltaic inverter that needs to confirm the mode. The photovoltaic inverter can be a grid-connected photovoltaic inverter.

[0102] Exemplarily, the power generation benefit Me can be the benefit obtained by the photovoltaic inverter through the power generation mode.

[0103] Exemplarily, the current mode may be the current operating mode of the photovoltaic inverter. The current mode may be a power generation mode or a power management mode.

[0104] In some embodiments, obtaining the power generation benefit Me of the photovoltaic inverter specifically includes:

[0105] Obtaining the maximum AC-side output power Ppv of the photovoltaic inverter and the time-of-use electricity price;

[0106] Determining the product of the maximum AC-side output power Ppv and the time-of-use electricity price as the power generation benefit Me of the photovoltaic inverter.

[0107] In this embodiment, determining the product of the maximum AC-side output power Ppv and the time-of-use electricity price as the power generation benefit Me of the photovoltaic inverter can improve the accuracy of determining the power generation benefit Me of the photovoltaic inverter.

[0108] Exemplarily, the controller may respond to the user's time-of-use voltage input operation based on the photovoltaic inverter operation and maintenance interface to obtain the time-of-use electricity price, where the time-of-use voltage input operation may be an operation for inputting the time-of-use voltage. Alternatively, the time-of-use electricity price may be pre-stored in the controller for subsequent direct invocation.

[0109] Through extensive research by the inventors, it is found that in a distributed application scenario, the active power output by the photovoltaic inverter is restricted by the following two aspects: The first aspect is the maximum power and components that the photovoltaic panels on the DC side can output; the second aspect is the maximum active power of photovoltaic power generation that the AC-side power distribution network can accept.

[0110] Based on this, in some examples, obtaining the maximum AC-side output power Ppv of the photovoltaic inverter specifically includes:

[0111] Obtaining the maximum DC-side output power of the photovoltaic inverter and the maximum active power accepted by the AC-side power distribution network of the photovoltaic inverter;

[0112] In the case where the maximum DC-side output power is greater than or equal to the maximum active power, determining the maximum active power as the maximum AC-side output power Ppv of the photovoltaic inverter;

[0113] Or,

[0114] In the case where the maximum DC-side output power is less than the maximum active power, determining the maximum DC-side output power as the maximum AC-side output power Ppv of the photovoltaic inverter.

[0115] In this example, the smaller value between the maximum output power on the DC side and the maximum active power accepted by the AC-side distribution network is taken as the maximum output power Ppv of the PV inverter on the AC side. Then, the maximum output power Ppv on the AC side is multiplied by the time-of-use electricity price to calculate the power generation benefit Me that the PV inverter can obtain. In the case where the PV panel is damaged and cannot generate electricity, the grid cannot accommodate enough power and does not allow PV grid connection, or PV does not generate electricity at night, the power generation revenue Me is 0. That is to say, taking the smaller value between the maximum output power on the DC side and the maximum active power accepted by the AC-side distribution network as the maximum output power Ppv of the PV inverter on the AC side can further improve the accuracy of determining the power generation benefit Me of the PV inverter.

[0116] Exemplarily, the maximum output power on the DC side can be obtained in the following way: The PV module obtains real-time data through an irradiance sensor and a temperature sensor, determines the current maximum power that can be generated by the PV module by combining the theoretical maximum output power estimated from the PV module characteristic curve, and transmits the current maximum power that can be generated by the PV module to the controller of the PV inverter through communication.

[0117] Exemplarily, the maximum active power accepted by the AC-side distribution network of the PV inverter, that is, the maximum active power of PV power generation that the AC-side distribution network of the PV inverter can accept. This maximum active power can be the power limit value transmitted by the superior grid dispatching through communication, or can be the power limit value transmitted by the anti-backflow device of the PV (the anti-backflow device needs to be installed in the scenario where only self-use of generated power is allowed and the surplus power cannot be fed into the grid).

[0118] In some embodiments, obtaining the compensation benefit Mc of the PV inverter includes:

[0119] Obtaining the first benefit Mch and the second benefit Mcq;

[0120] Determining the sum of the first benefit Mch and the second benefit Mcq as the compensation benefit Mc of the PV inverter.

[0121] In this embodiment, by determining the sum of the first benefit Mch and the second benefit Mcq as the compensation benefit Mc of the PV inverter, the benefits generated by harmonic current governance and reactive power compensation of the PV inverter can be comprehensively considered, enabling the PV inverter to not only focus on maximum active power generation but also perform harmonic governance and reactive power compensation to improve or solve the problems in the related art of increased harmonic content and low reactive power in the distribution network, which affect the safe operation of transformers and load equipment, thereby better supporting the stable operation of the grid to improve the stability of the grid, and increasing the adaptability and flexibility of the PV inverter.

[0122] That is to say, the compensation benefit Mc satisfies formula (3), and formula (3) includes:

[0123] Mc = Mch + Mcq (3).

[0124] In some other examples, the compensation benefit Mc can satisfy: Mc = k1 * Mch + k2 * Mcq. Wherein, k1 is the weight corresponding to the first benefit Mch, and k2 is the weight corresponding to the second benefit Mcq. k1 + k2 = 1. The values of k1 and k2 can be preset in the controller according to the actual situation, or can be obtained by responding to the user's weight input operation based on the photovoltaic inverter operation and maintenance interface. In this example, by setting weights for the first benefit Mch and the second benefit Mcq, and determining the compensation benefit Mc based on the set weights, the first benefit Mch and the second benefit Mcq, the compensation benefit Mc can be flexibly adjusted, improving the adaptability and flexibility of the photovoltaic inverter.

[0125] In some examples, obtaining the first benefit Mch specifically includes:

[0126] Obtaining the harmonic benefit coefficient Kh of the governance unit, the grid voltage Ue, and the harmonic current component Ilh in the load current Il;

[0127] Determining the first benefit Mch according to the harmonic benefit coefficient Kh of the governance unit, the grid voltage Ue, and the harmonic current component Ilh.

[0128] In this example, through the harmonic benefit coefficient Kh of the governance unit, the grid voltage Ue, and the harmonic current component Ilh, the first benefit Mch can be determined quickly and accurately.

[0129] Exemplarily, the grid voltage Ue can be collected through the controller of the photovoltaic inverter.

[0130] Exemplarily, a current transformer (CT) can be used to collect the grid current Ie on the low-voltage side where the photovoltaic inverter is connected to the power grid, and transmit the grid current Ie to the controller; then the controller collects the output current Ipv of the photovoltaic inverter; the sum of the grid current Ie and the output current Ipv is determined as the load current Il; the harmonic current component Ilh in the load current I1 can be extracted based on methods such as the instantaneous reactive power theory (ip-iq method), and the reactive current component Ilq in the load current Il involved below can be extracted.

[0131] That is to say, the load current Il satisfies formula (4), and formula (4) includes:

[0132] Il = Ie + Ipv (4).

[0133] In some examples, obtaining the harmonic benefit coefficient Kh of the governance unit specifically includes:

[0134] Obtain the first benefit coefficient Kh1, the second benefit coefficient Kh2, and the third benefit coefficient Kh3; the first benefit coefficient Kh1 is the benefit coefficient for the improvement of power consumption satisfaction brought about by harmonic current governance; the second benefit coefficient Kh2 is the benefit coefficient for the additional loss brought about by harmonic current governance; the third benefit coefficient Kh3 is the benefit coefficient for the extension of equipment life brought about by harmonic current governance;

[0135] Determine the sum of the first benefit coefficient Kh1, the second benefit coefficient Kh2, and the third benefit coefficient Kh3 as the harmonic governance benefit coefficient Kh for a unit.

[0136] In this example, by determining the sum of the first benefit coefficient Kh1, the second benefit coefficient Kh2, and the third benefit coefficient Kh3 as the harmonic governance benefit coefficient Kh for a unit, the accuracy and reliability of the harmonic governance benefit coefficient Kh for a unit can be improved.

[0137] Exemplarily, the value range of the first benefit coefficient Kh1 can be [0.05, 0.3]. For the number of precision devices connected to the distribution network, excessive harmonic current can cause malfunction or shutdown of the devices, resulting in production interruption, data loss, etc. That is, the first benefit coefficient Kh1 is related to the number of precision devices connected to the distribution network and the harmonic current. More specifically, for precision manufacturing / data centers, the value of this first benefit coefficient Kh1 can be taken a little larger, and for ordinary industries / commercial areas, the value of this first benefit coefficient Kh1 can be taken a little smaller.

[0138] Exemplarily, the value range of the second benefit coefficient Kh2 can be [0.1, 0.4]. For the line impedance in the distribution network, excessive harmonic current can lead to additional losses in transformers and loads in the line. That is, the second benefit coefficient Kh2 is related to the line impedance in the distribution network and the harmonic current. More specifically, for high-harmonic power grids such as metallurgical plants, the value of this second benefit coefficient Kh2 can be taken a little larger, and for low-harmonic areas such as residential areas, the value of this second benefit coefficient Kh2 can be taken a little smaller.

[0139] Exemplarily, the value range of the third benefit coefficient Kh3 can be [0.05, 0.25]. For the load type in the distribution network, excessive harmonic current can lead to a reduction in the life of equipment such as capacitors, motors, and frequency converters. That is, the third benefit coefficient Kh3 is related to the load type in the distribution network and the harmonic current. More specifically, in scenarios where there are more sensitive devices and the equipment replacement cost is high, the value of this third benefit coefficient Kh3 is taken as large, and vice versa, the value of this third benefit coefficient Kh3 is taken as small. Among them, sensitive devices refer to key devices that are highly sensitive to environmental parameters, power fluctuations, or changes in technical conditions during system operation, and their performance directly affects the photovoltaic power generation efficiency, system stability, and safety.

[0140] That is to say, the harmonic governance benefit coefficient Kh for a unit satisfies formula (5), and formula (5) includes:

[0141] Kh = Kh1 + Kh2 + Kh3 (5).

[0142] In some examples, according to the harmonic benefit coefficient Kh of the governance unit, the grid voltage Ue, and the harmonic current component Ilh, the first benefit Mch is determined, specifically including:

[0143] Substitute the harmonic benefit coefficient Kh of the governance unit, the grid voltage Ue, and the harmonic current component Ilh into formula (1) to calculate and obtain the first benefit Mch;

[0144] Formula (1) includes:

[0145] Mch = Ue * Ilh * Kh (1).

[0146] In this example, through the above formula (1), the first benefit Mch can be determined quickly and accurately.

[0147] In some embodiments, obtaining the second benefit Mcq specifically includes:

[0148] Obtain the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq in the load current Il;

[0149] According to the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq, determine the second benefit Mcq.

[0150] In this embodiment, through the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq, the second benefit Mcq can be determined quickly and accurately.

[0151] In some examples, obtaining the reactive power benefit coefficient Kq of the compensation unit specifically includes:

[0152] Obtain the fourth benefit coefficient Kq1 and the fifth benefit coefficient Kq2; the fourth benefit coefficient Kq1 is the electricity price unit reduction benefit coefficient brought by the photovoltaic inverter improving the power factor; the fifth benefit coefficient is the energy-saving benefit coefficient brought by the reactive power governance of the photovoltaic inverter;

[0153] Determine the sum of the fourth benefit coefficient Kq1 and the fifth benefit coefficient Kq2 as the reactive power benefit coefficient of the compensation unit.

[0154] In this example, by determining the sum of the fourth benefit coefficient Kq1 and the fifth benefit coefficient Kq2 as the reactive power benefit coefficient Kq of the compensation unit, the accuracy and reliability of the reactive power benefit coefficient Kq of the compensation unit can be improved.

[0155] Exemplarily, the value range of the fourth benefit coefficient Kq1 can be [0.02, 0.15]. The fourth benefit coefficient Kq1 is related to the reward and punishment policy of the local power company. For example, for the reward and punishment policy, for every 0.01 increase in the power factor above the standard value, the electricity fee reduction ratio is usually 0.1%-1%. For large industrial users, the electricity price is high, the load base is large, the electricity fee is much, and the unit reactive power compensation income is higher. The value of this fourth benefit coefficient Kq1 is taken as large, and for general industrial and commercial users, the value of this fourth benefit coefficient Kq1 is taken as a little smaller.

[0156] Exemplarily, the value range of the fifth benefit coefficient Kq2 can be [0.03, 0.12]. The fifth benefit coefficient Kq2 is related to the resistance losses of the lines and transformers in the distribution network and the reduction of line current by reactive power compensation. More specifically, the reduction of losses is proportional to the square of the current. In a distribution network with high-impedance lines and transformers with high loads, the value of this fifth benefit coefficient Kq2 is taken as large, and vice versa, the value of this fifth benefit coefficient Kq2 is taken as small.

[0157] That is to say, the benefit coefficient Kq for compensating unit reactive power satisfies formula (6), and formula (6) includes:

[0158] Kq = Kq1 + Kq2 (6).

[0159] It should be added that the specific values of the first benefit coefficient Kh1 to the fifth benefit coefficient Kq2 in the embodiments of the present application can be set according to actual situations, and their values can be pre-stored in the controller or input through the operation and maintenance interface of the photovoltaic inverter, which is not limited herein.

[0160] In some examples, according to the benefit coefficient Kq for compensating unit reactive power, the grid voltage Ue, and the reactive current component Ilq, the second benefit Mcq is determined, which specifically includes:

[0161] Substitute the benefit coefficient Kq for compensating unit reactive power, the grid voltage Ue, and the reactive current component Ilq into formula (2) to calculate and obtain the second benefit Mcq;

[0162] Formula (2) includes:

[0163] Mcq = Ue * Ilq * Kq (2).

[0164] In this example, according to the above formula (2), the second benefit Mcq can be determined quickly and accurately.

[0165] In step S120, after the controller obtains the power generation benefit Me, the compensation benefit Mc, and the current mode of the photovoltaic inverter, it can also determine the target mode of the photovoltaic inverter according to the power generation income Me, the compensation benefit Mc, and the current mode.

[0166] Exemplarily, the target mode can be the next operating mode of the current mode of the photovoltaic inverter.

[0167] Exemplarily, an identifier corresponding to the current mode can be stored in the controller, and the current mode can be determined through this identifier. For example, when the identifier is 0, it can indicate that the current mode is the power generation mode, and when the identifier is 1, it can indicate that the current mode is the power quality management mode.

[0168] It should be noted that the default current mode of the photovoltaic inverter is the power generation mode.

[0169] In some embodiments, the target mode of the photovoltaic inverter is determined according to the power generation revenue Me, the compensation benefit Mc, and the current mode, specifically including:

[0170] When the current mode is the power generation mode, obtain the start power quality management coefficient Kc;

[0171] When Mc > Me * Kc, determine the target mode of the photovoltaic inverter as the power quality management mode;

[0172] Or,

[0173] When Mc ≤ Me * Kc, determine the target mode of the photovoltaic inverter as the power generation mode.

[0174] In this embodiment, when Mc > Me * Kc, the target mode of the photovoltaic inverter is determined as the power quality management mode for power quality management; or, when Mc ≤ Me * Kc, the target mode of the photovoltaic inverter is determined as the power generation mode, so that the photovoltaic inverter can reflect the grid demand from the perspective of economic benefits, dynamically adjust the operating mode of the photovoltaic inverter, not only focus on maximum active power generation, but also be able to perform harmonic governance and reactive power compensation when necessary, thereby better supporting the stable operation of the grid. In addition, by introducing the start power quality management coefficient Kc, the problem that the compensation benefit Mc and the power generation benefit Me are close in value for a period of time, resulting in frequent mode switching of the photovoltaic inverter, can be improved or solved.

[0175] Exemplarily, the value range of the start power quality management coefficient Kc can be [1.1, 1.5]. More specifically, in an industrial scenario, where harmonic and reactive power fluctuations are large, the value of Kc can be taken to be smaller; for example: the grid has severe harmonics and extremely high compensation benefits (such as a metallurgical plant); in a commercial scenario, where the grid fully absorbs the photovoltaic power generation, the harmonic and reactive power contents are small, and the photovoltaic power generation revenue is dominant, the value of Kc is taken to be larger.

[0176] It should be noted that the value range of the start power quality management coefficient Kc can be set according to the actual situation, and its value can be pre-stored in the controller or input through the operation and maintenance interface of the photovoltaic inverter, which is not limited here.

[0177] Exemplarily, the power generation mode can be a mode capable of generating electricity; the power management mode can be a mode capable of performing power management.

[0178] In some other embodiments, the target mode of the PV inverter is determined according to the power generation benefit Me, the compensation benefit Mc, and the current mode, specifically including:

[0179] When the current mode is the power management mode, obtain the return power generation mode coefficient Kd;

[0180] When Mc < Me * Kd, determine the target mode of the PV inverter as the power generation mode;

[0181] Or,

[0182] When Mc ≥ Me * Kd, determine the target mode of the PV inverter as the power management mode.

[0183] In this embodiment, when Mc < Me * Kd, the target mode of the PV inverter is determined as the power generation mode, or when Mc ≥ Me * Kd, the target mode of the PV inverter is determined as the power management mode for power quality management. In this way, the PV inverter can reflect the grid demand according to the economic benefit index, dynamically adjust the working mode of the PV inverter, not only focus on maximum active power generation, but also be able to perform harmonic governance and reactive power compensation when necessary, so as to better support the stable operation of the grid. In addition, by introducing the start power management coefficient Kc, the problem that the compensation benefit Mc and the power generation benefit Me are close in value for a period of time, resulting in frequent mode switching of the PV inverter, can be improved or solved.

[0184] Exemplarily, the value range of the return power generation mode coefficient Kd is [0.8, 0.95]. In the application scenario of large industries, the harmonic and reactive power loads work continuously and have a large content, and it is necessary to ensure sufficient compensation, so the Kd value is taken a little smaller; in the commercial application scenario, the load and harmonic load work for a short time and have a small content, and the power generation benefit is the main, so the Kd value is taken a little larger.

[0185] It should be noted that the value ranges of the return power generation mode coefficient Kd, the start power management coefficient Kc, and the first benefit coefficient Kh1 to the fifth benefit coefficient Kq2 in the embodiments of the present application are estimated based on engineering practice and ideal speculation. In actual applications, these parameters need to be debugged, and users can set them according to their actual situations.

[0186] In some embodiments, before determining the target mode of the PV inverter according to the power generation benefit Me, the compensation benefit Mc, and the current mode, the method further includes:

[0187] Obtain multiple power generation benefits Me and multiple compensation benefits Mc of the photovoltaic inverter within a preset time period t;

[0188] Determine the average value of the multiple power generation benefits Me as the target power generation benefit Me of the photovoltaic inverter, and determine the average value of the multiple compensation benefits Mc as the target compensation benefit of the photovoltaic inverter;

[0189] Determine the target mode of the photovoltaic inverter according to the power generation benefit Me, the compensation benefit Mc, and the current mode, including:

[0190] Determine the target mode of the photovoltaic inverter according to the target power generation benefit, the target compensation benefit, and the current mode.

[0191] In this embodiment, by determining the average value of the multiple power generation benefits Me as the target power generation benefit Me of the photovoltaic inverter, and determining the average value of the multiple compensation benefits Mc as the target compensation benefit of the photovoltaic inverter; then, according to the target power generation benefit, the target compensation benefit, and the current mode, determine the target mode of the photovoltaic inverter, which can improve or solve the problem that the fluctuations of the harmonic current and the reactive current of the load on the line where the photovoltaic inverter is located, as well as the fluctuations of the photovoltaic power generation, result in inaccurate determination of the target mode of the photovoltaic inverter, that is, it can improve the accuracy of the target mode determination.

[0192] Exemplarily, the preset time period t can be set according to the actual situation, and its value can be pre-stored in the controller or input through the operation and maintenance interface of the photovoltaic inverter, which is not limited here. For example, the value range of the preset time period t can be 1 - 15 minutes (min).

[0193] In this embodiment, when Mc > Me * Kc, determine the target mode of the photovoltaic inverter as the power quality governance mode for power quality governance. In addition, by introducing the starting power quality governance coefficient Kc, it can improve or solve the problem that the compensation benefit Mc and the power generation benefit Me are close in value within a certain period of time, resulting in frequent mode switching of the photovoltaic inverter.

[0194] In some examples, before determining the average value of the multiple power generation benefits Me as the power generation benefit Me of the photovoltaic inverter, and determining the average value of the multiple compensation benefits Mc as the compensation benefit Mc of the photovoltaic inverter, the method further includes:

[0195] Adopt the moving average method to solve the average value of the multiple power generation benefits Me and the average value of the multiple compensation benefits Mc.

[0196] In this embodiment, through the moving average method, the average value of the multiple power generation benefits Me and the average value of the multiple compensation benefits Mc can be solved quickly and accurately.

[0197] To better understand the photovoltaic inverter mode determination method provided by the embodiments of the present application, a specific calculation process will be described below.

[0198] Assume that the maximum DC-side output power is 100 kilowatts (kW), the maximum active power is 110 kW, then the maximum AC-side output power Ppv of the photovoltaic inverter is determined to be 100 kW, and the time-of-use electricity price is 0.5 yuan, then the power generation benefit Me = 50000 is calculated; assume that the grid current Ie = 180 amperes (A), the output current Ipv = 30 A, then according to the formula (4) in step S110, the load current Il = 210 A is calculated; assume that the harmonic current component Ilh extracted from the load current Il is 10.5 A, and the reactive current component Ilq is 150 A. Assume that the first benefit coefficient Kh1 is 0.05, the second benefit coefficient Kh2 is 0.1, and the third benefit coefficient Kh3 is 0.05, then according to the formula (5) in step S110, the harmonic governance benefit coefficient Kh per unit is calculated to be 0.2. Assume that the fourth benefit coefficient Kq1 is 0.1 and the fifth benefit coefficient Kq2 is 0.1, then according to the formula (6) in step S110, the reactive power compensation benefit coefficient Kq per unit is calculated to be 0.2. Assume that the grid voltage Ue is 380 V, then according to the formula (1) in step S110, the first benefit Mch = 798 is calculated, and according to the formula (2) in step S110, the second benefit Mcq = 11400 is calculated. According to the formula (3) in step S110, the compensation gain Mc = 12198 is calculated. Assume that the starting power governance coefficient Kc is 1.2 and the power generation mode coefficient Kd is 0.9. When the current mode is the power governance mode, Me * Kd = 45000, that is, Mc < Me * Kd, then the target mode of the photovoltaic inverter is determined to be the power generation mode; when the current mode is the power generation mode, Me * Kc = 6000, that is, Mc ≤ Me * Kc, then the target mode of the photovoltaic inverter is determined to be the power generation mode.

[0199] To better understand the photovoltaic inverter mode determination method provided by the embodiments of the present application, a specific implementation manner will be described below.

[0200] Most of the existing technologies mainly focus on how to extract the harmonic components of the grid voltage and current, and then perform closed-loop control through voltage or current control commands to manage power quality. There are also papers that have proposed that there are differences in the remaining capacity of photovoltaic inverters under different output conditions, and a dynamic optimization method for power quality with the maximization of active power and power quality management as the objective function has been constructed. However, it does not pay attention to how to correctly evaluate the benefits generated by photovoltaic inverters for harmonic governance and reactive power compensation. Based on this, the embodiments of this application propose a model for reasonably estimating the benefits of harmonic and reactive power compensation of photovoltaic inverters. By obtaining the compensation benefits through the harmonic benefit coefficient per unit of governance and the reactive power benefit coefficient per unit of compensation, and then comparing with the power generation benefits, with the goal of maximizing user benefits, the photovoltaic grid-connected inverter can autonomously choose to operate in the photovoltaic power generation mode or the power quality management mode, enhancing the adaptability and flexibility of the photovoltaic inverter in actual application scenarios.

[0201] The electrical diagram of a common photovoltaic grid-connected inverter connected to the distribution network is as follows Figure 1 As shown, the photovoltaic grid-connected inverter is connected to the grid on the low-voltage side of the line transformer. In the distributed generation application scenario, there are also a large number of loads in the line, including linear and non-linear loads, continuous working loads, and short-time working loads. Taking iron and steel metallurgy users as an example, there are a large number of non-linear loads, mainly rolling mills, electric arc furnaces, etc. These loads have strong volatility, low power factor, and serious pollution to the power supply system. In the traditional mode, the photovoltaic grid-connected inverter only focuses on power generation, aiming to achieve the maximum power output on the PV side and is not responsible for the power quality of the distribution network. In recent years, with the continuous increase in the penetration rate of photovoltaic power generation, the power grid's consumption capacity is insufficient, and photovoltaic power generation faces the problem of power rationing and insufficient utilization of equipment capacity. On the other hand, due to the access of photovoltaic power generation, it has exacerbated the deterioration of the power quality of the distribution network, resulting in an increase in harmonic content and a low reactive power in the distribution network, affecting the safe operation of transformers and load equipment, and generating high power factor adjustment fees.

[0202] Based on this, the embodiments of this application propose a calculation model for the benefits generated by harmonic governance and reactive power compensation. This model proposes a harmonic benefit coefficient per unit of governance and a reactive power benefit coefficient to calculate the size of the compensation benefits generated by the photovoltaic inverter for auxiliary power quality management, and then compares with the power generation benefits generated by the photovoltaic inverter's output of active power. By setting the start power quality management coefficient and the return power generation mode coefficient, the working mode is dynamically adjusted, enabling the photovoltaic inverter to not only focus on maximum active power generation but also perform harmonic governance and reactive power compensation when necessary, thereby better supporting the stable operation of the power grid, increasing the adaptability and flexibility of the photovoltaic grid-connected inverter, and also improving user benefits.

[0203] As Figure 3As shown in the figure, the specific implementation is as follows. At the low-voltage side where photovoltaic power generation is connected, a current CT sensor is used to collect the grid current Ie data and transmit it to the photovoltaic inverter. Then, based on data such as the grid voltage Ue and the output current Ipv collected by the inverter, data such as the load current Il and power factor PFl on the current line can be calculated. According to the calculated load current Il, the harmonic current component Ilh and reactive current component Ilq in the load current are extracted.

[0204] For users, the photovoltaic grid-connected inverter earns income through the power generation mode. Then, according to the time-of-use electricity price in the user's local area, it can be set on the operation and maintenance interface of the photovoltaic inverter, and then multiplied by the active power output by the inverter to calculate the power generation income of the inverter at the current moment. In a distributed application scenario, the active power output by the inverter is restricted by the maximum power that the photovoltaic panels on the DC side can output and the components on the one hand, and on the other hand, it is also restricted by the maximum active power of photovoltaic power generation that the AC-side distribution network can accept. In the embodiments of this application, the smaller value of the two is used as the maximum power Ppv that can be output on the AC side of the photovoltaic inverter, and then multiplied by the time-of-use electricity price to calculate the power generation income Me that the photovoltaic inverter can obtain. Then, in the case where the photovoltaic panels are damaged and cannot generate electricity, the grid cannot accommodate enough power and does not allow photovoltaic grid connection, or photovoltaic does not generate electricity at night, the power generation income Me is 0.

[0205] If the photovoltaic inverter selects the power quality governance mode (i.e., the power governance mode), according to the principles of APF and SVG, the generated reverse compensation current Ic cancels out the harmonic current component Ilh and reactive current component Ilq of the load current, so as to achieve the purpose of harmonic governance and reactive power compensation. The embodiments of this application consider that the benefits generated by harmonic current governance are mainly reflected in the improvement of power quality, thereby reducing production delay accidents caused by equipment failures, reducing line losses and improving transmission capacity, and increasing the service life of transformers and load equipment, thereby reducing the later maintenance cost. Among them, according to the principle of APF, the generated compensation current Ic1 is equal in magnitude and opposite in direction to the harmonic current Ilh in the load current; according to the principle of SVG, the generated compensation current Ic2 is equal in magnitude and opposite in direction to the reactive current Ilq in the load current; Ic = Ic1 + Ic2.

[0206] In the embodiments of this application, the harmonic benefit coefficient Kh of the governance unit is used to calculate the harmonic governance income of the unit. Specifically, Kh includes the benefit coefficient Kh1 of the improved power consumption satisfaction brought by the harmonic current governance, the additional loss benefit coefficient Kh2, and the equipment life extension benefit coefficient Kh3. The harmonic benefit coefficient Kh of the governance unit = Kh1 + Kh2 + Kh3. The power company assesses the power factor index of users. The power factor of large industrial users should reach above 0.9, and that of general industrial and commercial users should reach above 0.85. If the power factor is higher than the standard power factor, a certain amount of electricity fee reduction ratio will be obtained. If the power factor is lower than the standard power factor, a certain proportion of penalty will be suffered. Specifically, the income coefficient Kq of the compensation unit reactive power mainly includes: the income coefficient Kq1 of the reduction of the electricity price unit brought by the improved power factor and the energy-saving benefit coefficient Kq2 brought by the reactive power governance. Here, Kq = Kq1 + Kq2.

[0207] In summary, the compensation benefit Mc of the photovoltaic inverter is equal to the benefit Mch generated by the harmonic current governance and the benefit Mcq generated by the reactive power compensation. The specific calculation formulas are shown as follows (1) to (3).

[0208] Mch = Ue*Ilh*Kh (1)

[0209] Mcq = Ue*Ilq*Kq (2)

[0210] Mc = Mch + Mcq (3)

[0211] The income coefficient Kh (A / yuan) of the governance unit harmonic current and the income coefficient Kq (A / yuan) of the compensation unit reactive current can be set in the operation and maintenance interface of the photovoltaic inverter, which is convenient for users to calculate the above coefficient values according to the situation of their own loads.

[0212] According to the above photovoltaic grid-connected inverter, the photovoltaic power generation benefit Me and the compensation benefit Mc can be calculated in real time. When the photovoltaic inverter judges and switches between the power generation mode and the power quality control mode, considering the volatility of the harmonic current and reactive current of the load on the line and the volatility of photovoltaic power generation, the method of sliding window averaging is adopted, and the average value of the two in a period of time is used as the judgment basis for mode switching. The window time t can be set on the operation and maintenance interface of the photovoltaic inverter, and the range is 1 - 15 minutes. In addition, considering that the average values of the compensation benefit Mc and the power generation benefit Me may be close in a period of time, resulting in frequent mode switching of the photovoltaic inverter. The embodiment of the present application uses hysteresis judgment. The photovoltaic inverter defaults to the grid-connected power generation mode. When the compensation benefit Mc is greater than the power generation benefit Me multiplied by the starting power quality control mode coefficient Kc, the mode switches to the power quality mode, where the starting power quality control coefficient Kc can be set; when the device is operating in the power quality control mode, and the compensation benefit Mc is less than the power generation benefit Me multiplied by the return power generation mode coefficient Kd, the device switches back to the power generation mode, where the return power generation mode coefficient Kd can be set. The starting power quality control coefficient Kc and the return power generation mode coefficient Kd can be set on the operation and maintenance interface of the photovoltaic inverter. The former value is greater than the latter value, and the difference between the two values is the width of the hysteresis interval. See the specific switching logic flowchart below Figure 2 as shown

[0213] It should be noted that traditional photovoltaic grid-connected inverters only focus on maximum active power generation and are helpless in the face of insufficient grid accommodation and deteriorated power quality caused by the continuous increase in the current photovoltaic power generation penetration rate.

[0214] The embodiment of the present application proposes a method for economic response harmonic governance and reactive power compensation of a photovoltaic inverter, which has the following advantages:

[0215] ①. It improves the economic benefits of users. When the photovoltaic grid-connected inverter is prohibited from sending power to the grid, at night, on rainy or cloudy days, etc., when there is basically no active output, it can still perform power quality governance, further improving the asset return rate of the photovoltaic grid-connected inverter.

[0216] ②. It increases the adaptability and flexibility of the photovoltaic grid-connected inverter. By real-time monitoring of the power quality parameters of the power grid, the inverter can dynamically adjust its working mode according to the economic benefit index, which reflects the demand of the power grid from the side. It not only focuses on maximum active power generation but also can perform harmonic governance and reactive power compensation when necessary, thus better supporting the stable operation of the power grid.

[0217] ③. The photovoltaic grid-connected inverter has the functions of power generation, harmonic governance, and reactive power compensation, reducing the repeated investment in relevant power quality governance equipment.

[0218] It should be added that the current CT sensor in the embodiment of the present application is placed on the low-voltage side to collect the grid current, and can also be placed on the high-voltage side. The high-voltage side current is converted to the low-voltage side through transformer ratio conversion. The main purpose is to obtain grid current data through the current sensor CT to calculate the harmonic current and reactive current that need to be compensated in the line.

[0219] ②. The current CT sensor in the embodiment of the present application can also be replaced by an anti-backflow device. The anti-backflow device has its own current CT that can collect grid current data.

[0220] ③. In the photovoltaic inverter power generation mode and power management mode in the embodiment of the present application, taking into account the simultaneous power generation and power quality, the DC capacitor of the photovoltaic power generation inverter is difficult to decouple the active power and reactive power, which will reduce the output capacity of the inverter and is more complicated to control. Therefore, a method of operating the power generation mode and the power management mode separately is adopted.

[0221] Example 2

[0222] The embodiment of the present application also provides a photovoltaic inverter control method, which can be applied to distributed power generation application scenarios in the process of solar photovoltaic power generation. The photovoltaic inverter control method provided in the embodiment of the present application can be executed by a photovoltaic inverter controller, a photovoltaic inverter control system, and an electronic device.

[0223] The photovoltaic inverter control method provided in the embodiment of the present application may include steps S210 to S220.

[0224] S210: Determine a target mode of the photovoltaic inverter according to the photovoltaic inverter mode determination method of embodiment 1.

[0225] S220: Control the photovoltaic inverter to execute the target mode.

[0226] In the embodiment of the present application, by comprehensively considering the power generation benefit Me of the photovoltaic inverter, the first benefit Mch of controlling harmonic current, the second benefit Mcq of compensating reactive power, and the current mode, the working mode of the photovoltaic inverter is dynamically adjusted, so that the photovoltaic inverter can not only focus on the maximum active power generation, but also perform harmonic control and reactive power compensation, so as to improve or solve the problems of increased harmonic content and low reactive power in the distribution network of the related technology, which affect the safe operation of transformers and load equipment, thereby better supporting the stable operation of the power grid, improving the stability of the power grid, and increasing the adaptability and flexibility of the photovoltaic inverter.

[0227] In some implementations, the first acquisition module 310 is specifically configured to:

[0228] Obtain the maximum output power Ppv of the PV inverter on the AC side and the time-of-use electricity price;

[0229] Determine the power generation benefit Me of the photovoltaic inverter as the product of the maximum output power Ppv on the AC side and the time-of-use electricity price.

[0230] In some embodiments, the first acquisition module 310 is specifically configured to:

[0231] Obtain the maximum output power on the DC side of the photovoltaic inverter and the maximum active power received by the AC side distribution network of the photovoltaic inverter;

[0232] When the maximum output power on the DC side is greater than or equal to the maximum active power, determine the maximum active power as the maximum output power Ppv on the AC side of the photovoltaic inverter;

[0233] Or,

[0234] When the maximum output power on the DC side is less than the maximum active power, determine the maximum output power on the DC side as the maximum output power Ppv on the AC side of the photovoltaic inverter.

[0235] In some embodiments, the first acquisition module 310 is specifically configured to:

[0236] Obtain the first benefit Mch and the second benefit Mcq;

[0237] Determine the sum of the first benefit Mch and the second benefit Mcq as the compensation benefit Mc of the photovoltaic inverter.

[0238] In some embodiments, the first acquisition module 310 is specifically configured to:

[0239] Obtain the harmonic current component Ilh in the harmonic benefit coefficient Kh for unit governance, the grid voltage Ue, and the load current Il;

[0240] Determine the first benefit Mch according to the harmonic benefit coefficient Kh for unit governance, the grid voltage Ue, and the harmonic current component Ilh.

[0241] In some embodiments, the first acquisition module 310 is specifically configured to:

[0242] Obtain the first benefit coefficient Kh1, the second benefit coefficient Kh2, and the third benefit coefficient Kh3; the first benefit coefficient Kh1 is the benefit coefficient for the improvement of power consumption satisfaction brought by the governance of harmonic current; the second benefit coefficient Kh2 is the benefit coefficient for the additional loss brought by the governance of harmonic current; the third benefit coefficient Kh3 is the benefit coefficient for the extension of equipment life brought by the governance of harmonic current;

[0243] Determine the sum of the first benefit coefficient Kh1, the second benefit coefficient Kh2, and the third benefit coefficient Kh3 as the harmonic benefit coefficient Kh for unit governance.

[0244] In some embodiments, the first acquisition module 310 is specifically configured to:

[0245] Substitute the harmonic benefit coefficient Kh of the governance unit, the grid voltage Ue, and the harmonic current component Ilh into formula (1) to calculate the first benefit Mch;

[0246] Formula (1) includes:

[0247] Mch = Ue * Ilh * Kh (1).

[0248] In some embodiments, the first acquisition module 310 is specifically configured to:

[0249] Obtain the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq in the load current Il;

[0250] Determine the second benefit Mcq according to the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq.

[0251] In some embodiments, the first acquisition module 310 is specifically configured to:

[0252] Obtain the fourth benefit coefficient Kq1 and the fifth benefit coefficient Kq2; the fourth benefit coefficient Kq1 is the electricity price reduction benefit coefficient brought by the photovoltaic inverter to improve the power factor; the fifth benefit coefficient is the energy-saving benefit coefficient brought by the reactive power governance of the photovoltaic inverter;

[0253] Determine the sum of the fourth benefit coefficient Kq1 and the fifth benefit coefficient Kq2 as the reactive power benefit coefficient of the compensation unit.

[0254] In some embodiments, the first acquisition module 310 is specifically configured to:

[0255] Substitute the reactive power benefit coefficient Kq of the compensation unit, the grid voltage Ue, and the reactive current component Ilq into formula (2) to calculate the second benefit Mcq;

[0256] Formula (2) includes:

[0257] Mcq = Ue * Ilq * Kq (2).

[0258] In some embodiments, the first determination module 320 is specifically configured to:

[0259] In the case where the current mode is the power generation mode, obtain the starting power governance coefficient Kc;

[0260] In the case where Mc > Me * Kc, determine the target mode of the photovoltaic inverter as the power governance mode;

[0261] Or,

[0262] When Mc ≤ Me * Kc, the target mode of the photovoltaic inverter is determined as the power generation mode.

[0263] In some embodiments, the first determination module 320 is specifically configured to:

[0264] When the current mode is the power management mode, obtain the return power generation mode coefficient Kd;

[0265] When Mc < Me * Kd, the target mode of the photovoltaic inverter is determined as the power generation mode;

[0266] Or,

[0267] When Mc ≥ Me * Kd, the target mode of the photovoltaic inverter is determined as the power management mode.

[0268] In some embodiments, the device further includes:

[0269] A second acquisition module, configured to acquire a plurality of power generation benefits Me and a plurality of compensation benefits Mc of the photovoltaic inverter within a preset time period t;

[0270] A second determination module, connected to the second acquisition module, configured to determine the average value of the plurality of power generation benefits Me as the target power generation benefit Me of the photovoltaic inverter, and determine the average value of the plurality of compensation benefits Mc as the target compensation benefit of the photovoltaic inverter;

[0271] The first determination module 320 is specifically configured to:

[0272] Determine the target mode of the photovoltaic inverter according to the target power generation benefit, the target compensation benefit, and the current mode.

[0273] In some embodiments, the device further includes:

[0274] A solution module, configured to use the moving average method to solve the average value of the plurality of power generation benefits Me and the average value of the plurality of compensation benefits Mc.

[0275] The photovoltaic inverter control method provided by the embodiments of the present application has the beneficial effects and implementation manners of the photovoltaic inverter mode determination method provided by Embodiment 1 of the present application. Specifically, reference may be made to the specific description of the photovoltaic inverter mode determination method in the above Embodiment 1, and details are not described herein again in this embodiment.

[0276] Embodiment 3

[0277] As Figure 4 shown, the photovoltaic inverter mode determination device provided by the embodiments of the present application includes a first acquisition module 310 and a first determination module 320.

[0278] Among them, the first acquisition module 310 is configured to acquire the power generation benefit Me, compensation benefit Mc, and current mode of the photovoltaic inverter. The compensation benefit Mc is determined according to the first benefit Mch and the second benefit Mcq. The first benefit Mch is the benefit generated by controlling harmonic current, and the second benefit Mcq is the benefit generated by compensating reactive power.

[0279] The first determination module 320 is connected to the first acquisition module 310 and is configured to determine the target mode of the photovoltaic inverter according to the power generation benefit Me, compensation benefit Mc, and current mode.

[0280] Among them, both the current mode and the target mode include one of a power generation mode and a power energy control mode.

[0281] The photovoltaic inverter mode determination device provided by the embodiment of the present application can be used to execute the photovoltaic inverter mode determination method in Embodiment 1, that is, it has the beneficial effects and implementation manners of the photovoltaic inverter mode determination method provided by Embodiment 1 of the present application. Specifically, reference can be made to the specific description of the photovoltaic inverter mode determination method in the above Embodiment 1, and details are not described herein again in this embodiment.

[0282] Embodiment 4

[0283] The embodiment of the present application provides a photovoltaic inverter control system, including:

[0284] The photovoltaic inverter mode determination device of Embodiment 3 is configured to determine the target mode of the photovoltaic inverter;

[0285] The control device is connected to the photovoltaic inverter mode determination device and is configured to control the photovoltaic inverter to execute the target mode.

[0286] The photovoltaic inverter control system provided by the embodiment of the present application can be used to execute the photovoltaic inverter control method in Embodiment 2, that is, it has the beneficial effects and implementation manners of the photovoltaic inverter control method provided by Embodiment 2 of the present application. Specifically, reference can be made to the specific description of the photovoltaic inverter control method in the above Embodiment 2, and details are not described herein again in this embodiment.

[0287] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present application. However, the present application is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present application, and these modifications and improvements are also regarded as the protection scope of the present application.

Claims

1. A method for determining a photovoltaic inverter mode, characterized in that, Including: Obtain the power generation benefit Me, compensation benefit Mc and current mode of the photovoltaic inverter. The compensation benefit Mc is determined according to the first benefit Mch and the second benefit Mcq. The first benefit Mch is the benefit generated by harmonic current governance, and the second benefit Mcq is the benefit generated by reactive power compensation. Determine the target mode of the photovoltaic inverter according to the power generation benefit Me, the compensation benefit Mc and the current mode. Wherein, both the current mode and the target mode include one of a power generation mode and an electric energy governance mode.

2. The method according to claim 1, wherein Obtaining the power generation benefit Me of the photovoltaic inverter specifically includes: Obtain the maximum AC-side output power Ppv of the photovoltaic inverter and the time-of-use electricity price. Determine the product of the maximum AC-side output power Ppv and the time-of-use electricity price as the power generation benefit Me of the photovoltaic inverter.

3. The method according to claim 2, wherein The obtaining of the maximum AC-side output power Ppv of the photovoltaic inverter specifically includes: Obtain the maximum DC-side output power of the photovoltaic inverter and the maximum active power accepted by the AC-side distribution network of the photovoltaic inverter. When the maximum DC-side output power is greater than or equal to the maximum active power, determine the maximum active power as the maximum AC-side output power Ppv of the photovoltaic inverter. Or, When the maximum DC-side output power is less than the maximum active power, determine the maximum DC-side output power as the maximum AC-side output power Ppv of the photovoltaic inverter.

4. The method according to claim 1, wherein Obtaining the compensation benefit Mc of the photovoltaic inverter includes: Obtain the first benefit Mch and the second benefit Mcq. Determine the sum of the first benefit Mch and the second benefit Mcq as the compensation benefit Mc of the photovoltaic inverter.

5. The method according to claim 4, characterized in that, Obtaining the first benefit Mch specifically includes: Obtain the harmonic current component Ilh in the harmonic benefit coefficient Kh per unit of governance, grid voltage Ue and load current Il. Determine the first benefit Mch according to the harmonic benefit coefficient Kh per unit of governance, the grid voltage Ue and the harmonic current component Ilh.

6. The method according to claim 5, characterized in that, Obtaining the harmonic benefit coefficient Kh per unit of governance specifically includes: Obtain the first benefit coefficient Kh1, the second benefit coefficient Kh2 and the third benefit coefficient Kh3. The first benefit coefficient Kh1 is the benefit coefficient for the improvement of power consumption satisfaction brought by harmonic current governance; the second benefit coefficient Kh2 is the benefit coefficient for the additional loss brought by harmonic current governance; the third benefit coefficient Kh3 is the benefit coefficient for the extension of equipment life brought by harmonic current governance. Determine the sum of the first benefit coefficient Kh1, the second benefit coefficient Kh2 and the third benefit coefficient Kh3 as the harmonic benefit coefficient Kh per unit of governance.

7. The method according to claim 5, characterized in that The determination of the first benefit Mch according to the harmonic benefit coefficient Kh per unit of governance, the grid voltage Ue and the harmonic current component Ilh specifically includes: Substitute the harmonic benefit coefficient Kh per unit of governance, the grid voltage Ue and the harmonic current component Ilh into formula (1) to calculate the first benefit Mch. The formula (1) includes: Mch = Ue*Ilh*Kh (1).

8. The method according to claim 4, characterized in that Obtaining the second benefit Mcq specifically includes: Obtain the reactive power benefit coefficient \(K_q\) of the compensation unit, the grid voltage \(U_e\), and the reactive current component \(I_{lq}\) of the load current \(I_l\); Determine the second benefit \(M_{cq}\) according to the reactive power benefit coefficient \(K_q\) of the compensation unit, the grid voltage \(U_e\), and the reactive current component \(I_{lq}\).

9. The method according to claim 8, wherein Obtaining the reactive power benefit coefficient \(K_q\) of the compensation unit specifically includes: Obtain the fourth benefit coefficient \(K_{q1}\) and the fifth benefit coefficient \(K_{q2}\); the fourth benefit coefficient \(K_{q1}\) is the benefit coefficient of the reduced electricity price per unit due to the power factor improvement of the PV inverter; the fifth benefit coefficient is the energy-saving benefit coefficient brought by the reactive power management of the PV inverter; Determine the sum of the fourth benefit coefficient \(K_{q1}\) and the fifth benefit coefficient \(K_{q2}\) as the reactive power benefit coefficient of the compensation unit.

10. The method according to claim 8, characterized in that, The step of determining the second benefit \(M_{cq}\) according to the reactive power benefit coefficient \(K_q\) of the compensation unit, the grid voltage \(U_e\), and the reactive current component \(I_{lq}\) specifically includes: Substitute the reactive power benefit coefficient \(K_q\) of the compensation unit, the grid voltage \(U_e\), and the reactive current component \(I_{lq}\) into formula (2) to calculate the second benefit \(M_{cq}\); The formula (2) includes: \(M_{cq}=U_e\times I_{lq}\times K_q\) (2).

11. The method according to claim 1, characterized in that, The step of determining the target mode of the PV inverter according to the power generation benefit \(M_e\), the compensation benefit \(M_c\), and the current mode specifically includes: When the current mode is the power generation mode, obtain the starting power management coefficient \(K_c\); When \(M_c > M_e\times K_c\), determine the target mode of the PV inverter as the power management mode; Or, When \(M_c\leq M_e\times K_c\), determine the target mode of the PV inverter as the power generation mode.

12. The method according to claim 1, characterized in that, The step of determining the target mode of the PV inverter according to the power generation benefit \(M_e\), the compensation benefit \(M_c\), and the current mode specifically includes: When the current mode is the power management mode, obtain the coefficient \(K_d\) for returning to the power generation mode; When \(M_c < M_e\times K_d\), determine the target mode of the PV inverter as the power generation mode; Or, When \(M_c\geq M_e\times K_d\), determine the target mode of the PV inverter as the power management mode.

13. The method according to claim 1, wherein Before determining the target mode of the PV inverter according to the power generation benefit \(M_e\), the compensation benefit \(M_c\), and the current mode, the method further includes: Obtain multiple power generation benefits \(M_e\) and multiple compensation benefits \(M_c\) of the PV inverter within a preset time period \(t\); Determine the average value of multiple power generation benefits \(M_e\) as the target power generation benefit \(M_e\) of the PV inverter, and determine the average value of multiple compensation benefits \(M_c\) as the target compensation benefit of the PV inverter; The step of determining the target mode of the PV inverter according to the power generation benefit \(M_e\), the compensation benefit \(M_c\), and the current mode includes: Determine the target mode of the PV inverter according to the target power generation benefit \(M_e\), the target compensation benefit, and the current mode.

14. The method according to claim 13, characterized in that, Before determining the average value of multiple power generation benefits Me as the power generation benefit Me of the PV inverter and determining the average value of multiple compensation benefits Mc as the compensation benefit Mc of the PV inverter, the method further includes: Using the moving average method to solve the average value of multiple power generation benefits Me and the average value of multiple compensation benefits Mc.

15. A photovoltaic inverter control method, characterized in that, Including: Determining the target mode of the PV inverter according to the PV inverter mode determination method according to any one of claims 1-14; Controlling the PV inverter to execute the target mode.

16. A photovoltaic inverter mode determination device, characterized in that, Including: A first acquisition module for acquiring the power generation benefit Me, compensation benefit Mc and current mode of the PV inverter, where the compensation benefit Mc is determined according to a first benefit Mch and a second benefit Mcq, the first benefit Mch is the benefit generated by harmonic current governance, and the second benefit Mcq is the benefit generated by reactive power compensation; A first determination module connected to the first acquisition module for determining the target mode of the PV inverter according to the power generation benefit Me, the compensation benefit Mc and the current mode; Wherein, both the current mode and the target mode include one of a power generation mode and a power energy governance mode.

17. The device according to claim 16, wherein The first acquisition module is specifically used for: Acquiring the maximum output power Ppv on the AC side of the PV inverter and the time-of-use electricity price; Determining the product of the maximum output power Ppv on the AC side and the time-of-use electricity price as the power generation benefit Me of the PV inverter; And / or The first acquisition module is specifically used for: Acquiring the first benefit Mch and the second benefit Mcq; Determining the sum of the first benefit Mch and the second benefit Mcq as the compensation benefit Mc of the PV inverter; And / or The first determination module is specifically used for: When the current mode is the power generation mode, acquiring the starting power energy governance coefficient Kc; When Mc > Me * Kc, determining the target mode of the PV inverter as the power energy governance mode; Or When Mc ≤ Me * Kc, determining the target mode of the PV inverter as the power generation mode.

18. A photovoltaic inverter control system, characterized in that, Including: Determining the target mode of the PV inverter according to the PV inverter mode determination device according to claim 16 or 17; A control device connected to the PV inverter mode determination device for controlling the PV inverter to execute the target mode.

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