Photovoltaic system and power control method

Abstract

The invention relates to a photovoltaic system and a power control method. Relates to the field of solar power generation. And performing hierarchical power optimization on the photovoltaic module. In the preceding-stage power optimization, the gain of a direct-current converter used for implementing power conversion on the photovoltaic module is guided to be close to a preset value; in post-stage power optimization, the inverter performs maximum power point tracking on a string internally connected with a plurality of photovoltaic modules in series, and the plurality of photovoltaic modules corresponding to the multi-stage direct-current converters connected in series form one string. Through power optimization of front and back stages, when the gain of any DC converter reaches a preset value, the corresponding photovoltaic module reaches a power optimization point.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of solar power generation, and more specifically, to a photovoltaic system and a related power control method. Background Art

[0002] In photovoltaic systems, the maximum power point tracking of photovoltaic arrays means that when external environmental conditions such as solar illumination intensity and external temperature change, the system changes the output current or voltage of the photovoltaic array to keep the array operating at the maximum power point. Conventional MPPT algorithms (such as perturbation observation method, hill climbing method, etc.) have a good tracking and control effect for single-peak power. However, in the case of partial shading, the power and voltage curves of the photovoltaic array present a multi-peak problem with multiple power extreme points, and conventional MPPT algorithms are prone to fall into local extreme values.

[0003] There are many reasons for the mismatch of solar panels, mainly caused by the mismatch of voltage and current. Local foreign objects and floating clouds, nearby objects, surface pollution, different installation angles and orientations, aging and temperature changes and many other factors, the mismatch of photovoltaic modules induces unbalanced power loss in photovoltaic modules. As a result, the entire photovoltaic power generation system cannot operate at the maximum output power point.

[0004] Artificial intelligence methods (such as neural networks and particle swarm methods) are effective for local shading situations, but the neural network method requires long-term targeted training for different photovoltaic array systems. The particle swarm method can improve the accuracy of the results, but the implementation process is more complicated, which will lead to a significant increase in hardware equipment costs.

[0005] Current photovoltaic power optimization usually only attempts to achieve the optimal working current multiplied by the optimal working voltage of the battery module from the perspective of the battery module user end, or only uses a centralized inverter to centrally optimize the series-parallel system of all battery modules. The coexistence of user-end optimization and centralized optimization will cause some problems. The power optimization of the battery module user end and the power optimization of the photovoltaic inverter will interfere with each other. How to guide this constrained relationship to mutually adapt and adaptively meet the optimization needs of both parties and achieve power optimization is a more difficult problem. Summary of the invention

[0006] The present application relates to a power control method, comprising:

[0007] Using a DC converter to perform DC to DC power conversion on photovoltaic modules;

[0008] The multi-level DC converters are connected in series, and a plurality of photovoltaic modules corresponding to a group of multi-level DC converters connected in series are regarded as a group string;

[0009] Using an inverter to convert the output power provided by the multi-level DC converter from DC to AC;

[0010] In terms of global power optimization, the maximum power point tracking of the strings is performed through the inverter;

[0011] In terms of local power optimization, the gain of the DC converter is guided to approach the preset value;

[0012] Based on the coordinated cooperation of global power optimization and local power optimization, the goal of increasing and optimizing the operating power of photovoltaic modules can be achieved together.

[0013] In the above method, the DC converter is equipped with a microprocessor for driving the DC converter to perform voltage or current conversion. The microprocessor adjusts the gain by changing the duty cycle of the DC converter to make it closer to a preset value.

[0014] In the above method, the multi-stage DC converters connected in series form a series branch, which can supply power to the inverter. The magnitude of the series voltage provided by the series branch is adjusted by changing the preset value.

[0015] In the above method, the DC converter is selected from any one of a Cuk circuit, a buck converter, a boost converter, and a buck-boost converter.

[0016] In the above method, the gain moving closer to the preset value includes reducing the difference between the voltage gain and the preset value; or the gain moving closer to the preset value includes reducing the difference between the current gain and the preset value.

[0017] In the above method, when the gain of any DC converter reaches its preset value, the corresponding photovoltaic module reaches its own power optimization point.

[0018] In the above method, in the same string, if all photovoltaic modules are not blocked, the gains of the multi-stage DC converters corresponding to the same string reach the corresponding preset values. At this time, all photovoltaic modules in the same string operate at their respective maximum power points.

[0019] In the above method, if some photovoltaic modules in the same string are blocked, the gains of the multi-stage DC converters corresponding to the same string all reach the corresponding preset values. At this time, the unblocked photovoltaic modules in the same string all operate at their respective maximum power points, and the blocked photovoltaic modules do not operate at their respective maximum power points.

[0020] The present application relates to a power control method, comprising:

[0021] Using a DC converter to perform DC to DC power conversion on photovoltaic modules;

[0022] Connecting multiple DC converters in parallel;

[0023] Using an inverter to convert the output power provided by the multi-level DC converter from DC to AC;

[0024] In terms of global power optimization, the maximum power point tracking is performed on the output power provided by each parallel DC converter through the inverter;

[0025] In terms of local power optimization, the gain of the DC converter is guided to approach the preset value;

[0026] Based on the coordinated cooperation of global power optimization and local power optimization, the goal of increasing and optimizing the operating power of photovoltaic modules can be achieved together.

[0027] The present application relates to a power control method, comprising:

[0028] Using a DC converter to perform DC to DC power conversion on photovoltaic modules;

[0029] Connecting multiple DC converters in series;

[0030] Using an inverter to convert the output power provided by the multi-level DC converter from DC to AC;

[0031] In terms of global power optimization, the maximum power point tracking is performed on the output power provided by each DC converter connected in series through the inverter;

[0032] In terms of local power optimization, the gain of the DC converter is guided to approach the preset value;

[0033] Based on the coordinated cooperation of global power optimization and local power optimization, the goal of increasing and optimizing the operating power of photovoltaic modules can be achieved together.

[0034] The present application relates to a photovoltaic system, comprising:

[0035] A DC converter, used for performing DC to DC power conversion on the photovoltaic modules, wherein a plurality of photovoltaic modules corresponding to a group of multi-stage DC converters connected in series are regarded as a group string;

[0036] Inverter, which is powered by a multi-level DC converter connected in series;

[0037] By performing maximum power point tracking on the strings through the inverter and guiding the gain of the DC converter to approach the preset value, the goal of optimizing and increasing the operating power of the PV panels is achieved.

[0038] In the above photovoltaic system, the gain includes voltage gain or current gain.

[0039] In the above photovoltaic system, the multi-stage DC converters connected in series form a series branch, and the multiple series branches connected in parallel supply power to the same inverter.

[0040] In the photovoltaic system described above, the preset values ​​corresponding to different series-connected branches with unequal numbers of DC converters are also set to be different.

[0041] In the photovoltaic system described above, the preset value of the DC converter corresponding to the series-connected branch with a small number of DC converters is set to be larger than the preset value of the DC converter corresponding to the series-connected branch with a large number of DC converters.

[0042] In the photovoltaic system described above, among the multi-stage DC converters corresponding to any series-connected branch, the preset values ​​of different DC converters are set to be different or the same.

[0043] In the above-mentioned photovoltaic system, when the gain of any DC converter reaches a preset value, a photovoltaic component corresponding to any DC converter operates at its maximum power point under the premise of no shading; or, a photovoltaic component corresponding to any DC converter operates at a non-maximum power point under the premise of shading.

[0044] In the above photovoltaic system, the DC converter is selected from any one of a Cuk circuit, a buck converter, a boost converter, and a buck-boost converter.

[0045] In the above photovoltaic system, when the gain of any DC converter reaches its preset value, the corresponding photovoltaic module reaches its own power optimization point.

[0046] In the above photovoltaic system, the DC converter is equipped with a microprocessor for driving the DC converter to perform voltage or current conversion. The microprocessor adjusts the gain by changing the duty cycle of the DC converter so that the gain approaches a preset value. The preset value is changed by programming the microprocessor to adjust the gain.

[0047] The present application relates to a photovoltaic system, comprising:

[0048] A DC converter, used for performing DC to DC power conversion on the photovoltaic module;

[0049] An inverter, which is powered by a multi-level DC converter connected in parallel;

[0050] Based on the maximum power point tracking of the output power provided by each DC converter through the inverter, and by guiding the gain of the DC converter to approach the preset value, the purpose of optimizing and increasing the operating power of the photovoltaic module is achieved together.

[0051] The present application relates to a power control method for implementing hierarchical power optimization of photovoltaic modules, including:

[0052] In the front-stage power optimization, the gain of the DC converter used to implement power conversion for the photovoltaic module is guided to approach the preset value;

[0053] In the post-stage power optimization, the inverter performs maximum power point tracking on a string of multiple PV modules connected in series, and multiple PV modules corresponding to a group of multi-level DC converters connected in series are regarded as one string;

[0054] Through power optimization of the previous and next stages, when the gain of any DC converter reaches a preset value, the corresponding photovoltaic module reaches the power optimization point.

[0055] In the above method, when the gain of any DC converter reaches a preset value, the power optimization point of a photovoltaic module corresponding to any DC converter is the maximum power point under the premise of no shading.

[0056] In the above method, when the gain of any DC converter reaches a preset value, the power optimization point of a photovoltaic module corresponding to any DC converter is a non-maximum power point under the premise of shading.

[0057] In the above method, the DC converter is equipped with a microprocessor for driving the DC converter to perform voltage or current conversion. The microprocessor adjusts the gain by changing the duty cycle of the DC converter so that the gain approaches a preset value. The preset value is changed by programming the microprocessor to adjust the gain.

[0058] The present application relates to a power control method for implementing hierarchical power optimization of photovoltaic modules, including:

[0059] In the front-stage power optimization, the gain of the DC converter used to implement power conversion for the photovoltaic module is guided to approach the preset value;

[0060] In the post-stage power optimization, the inverter performs maximum power point tracking on the output power provided by each DC converter connected in parallel;

[0061] Through power optimization of the previous and next stages, when the gain of any DC converter reaches a preset value, the corresponding photovoltaic module reaches the power optimization point.

[0062] The present application relates to a photovoltaic system for implementing hierarchical power optimization of photovoltaic modules, including:

[0063] A DC converter is used to perform DC to DC power conversion on the photovoltaic module; wherein the multi-stage DC converters are connected in series, and a plurality of photovoltaic modules corresponding to a group of multi-stage DC converters connected in series are regarded as a group string;

[0064] An inverter for converting the output power provided by the multi-stage DC converter from DC to AC;

[0065] In the front-stage power optimization, the gain of the DC converter is guided to approach the preset value;

[0066] In the post-stage power optimization, the inverter performs maximum power point tracking on the strings;

[0067] Through the power optimization of the front and rear stages, when the gain of any DC converter reaches a preset value, the corresponding photovoltaic component reaches the power optimization point.

[0068] The present application relates to a power control method, comprising:

[0069] Using a DC converter to perform DC to DC power conversion on photovoltaic modules;

[0070] Connecting multiple DC converters in parallel or in series;

[0071] Using a DC conversion device to perform DC to DC power conversion on the output power provided by the multi-stage DC converter;

[0072] In terms of global power optimization, the output power provided by each DC converter connected in parallel or in series is tracked by the DC conversion device to perform maximum power point tracking;

[0073] In terms of local power optimization, the gain of the DC converter is guided to approach the preset value (or set value);

[0074] Based on the coordinated cooperation of global power optimization and local power optimization, the goal of increasing and optimizing the operating power of photovoltaic modules can be achieved together. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] In order to make the above purposes, features and advantages more understandable, the following text will explain the specific implementation methods in detail in conjunction with the drawings. After reading the following description and referring to the following drawings, the features and advantages of the present application will become apparent.

[0076] Figure 1 Multiple photovoltaic modules are connected in series and the inverter performs unified power optimization on the photovoltaic modules.

[0077] Figure 2 It is to perform one-to-one power optimization on each photovoltaic module from the perspective of the photovoltaic module user.

[0078] Figure 3 Power optimization is implemented from the photovoltaic module usage end and from the inverter end based on voltage gain.

[0079] Figure 4 Power optimization is implemented from the PV panel usage end and from the inverter end based on current gain.

[0080] Figure 5 It is a characteristic that is manifested by implementing power optimization from the end of series component use and the inverter end.

[0081] Figure 6 It is a DC converter that uses integrated buck conversion, boost conversion and buck-boost conversion functions.

[0082] Figure 7 It is the power fluctuation caused by the change of gain on the gain and maximum power curve.

[0083] Figure 8 It is the change of preset value on the voltage power curve of the photovoltaic module that causes the optimization point to be different.

[0084] Fig. 9 It is a characteristic that is manifested by implementing power optimization from the parallel component usage end and the inverter end. DETAILED DESCRIPTION

[0085] The technical solutions disclosed in the present application will be clearly and completely described below in conjunction with specific embodiments. However, the embodiments described are only embodiments used for narrative explanation in the present application and are not all embodiments. Based on these embodiments, technicians in this field should realize that any solution obtained without creative work falls within the scope of protection of the present application.

[0086] See also Figure 1 After the photovoltaic modules PV1-PVN are connected in series, the inverter INVT uniformly optimizes the power of all the photovoltaic modules connected in series. At this time, the maximum power point tracking MPPT is executed.

[0087] See also Figure 1 , the full name of the power optimizer or MPPT (Maximum Power Point Tracking) controller is the maximum power point tracking solar controller. The method used to achieve the best power of the photovoltaic module is MPPT. At present, it is common to connect all photovoltaic modules to a single inverter INVT to perform MPPT. This method centrally controls the MPPT function by the photovoltaic inverter, so power optimization related control operations are required.

[0088] See also Figure 1, when the lighting conditions of the photovoltaic modules are consistent, this photovoltaic system can work normally, but when some photovoltaic modules are not matched or shaded, the power efficiency of the photovoltaic system will be greatly reduced. As shown in the figure, it can be assumed that the lighting conditions of photovoltaic module PV1 are very good, and the radiation of photovoltaic modules PV2 and PVN is low. For example, they are shaded. When the inverter INVT performs MPPT on the string, the photovoltaic module PV1 reaches its maximum power point, while the photovoltaic modules PV2 and PVN do not reach the maximum power point.

[0089] See also Figure 1 Assuming that the lighting conditions of the photovoltaic component PV1 are very good, its power-voltage curve is represented by CV1, and the horizontal axis represents the operating voltage of the photovoltaic component PV1, and the vertical axis represents the power of the photovoltaic component PV1. As shown in the figure, this photovoltaic component PV1 can reach its maximum power point.

[0090] See also Figure 1 Assuming that the lighting condition of photovoltaic module PV2 is relatively weak, its power-voltage curve is represented by CV2, and the horizontal axis represents the working voltage of photovoltaic module PV2, and the vertical axis represents the power of photovoltaic module PV2. As shown in the figure, this photovoltaic module PV2 cannot reach its maximum power point.

[0091] See also Figure 1 Assuming that the photovoltaic component PVN is blocked from light, its power-voltage curve is represented by CVN, and the horizontal axis represents the operating voltage of the photovoltaic component PVN, and the vertical axis represents the power of the photovoltaic component PVN. As shown in the figure, this photovoltaic component PVN cannot reach its maximum power point.

[0092] See also Figure 1 , multiple photovoltaic modules PV1-PVN are connected in series between busbars LA and LB: If multiple photovoltaic modules PV1-PVN are defined to form a string, then multiple strings are connected in parallel between busbars LA and LB. The photovoltaic power optimization shown in the figure often only attempts to achieve the optimal operating current of the DC bus multiplied by the optimal operating voltage from the perspective of the photovoltaic inverter INVT end, that is, to pursue the bus current I BUS Multiply by bus voltage V BUS The string current, i.e., bus current, and string voltage, i.e., bus voltage, of a single string can be set at their maximum power point.

[0093] See also Figure 1 Due to the series connection of the photovoltaic modules PV1-PVN in the string, the bus current flowing through them is the same and the inverter INVT is in this bus current I BUS The power of each PV group is uniformly adjusted. If the working conditions of each PV module in the string are inconsistent, there will inevitably be power differences as shown in the figure.

[0094] See also Figure 1 , power optimization The photovoltaic power generation system that is currently widely used connects all components in series and parallel directly to a centralized inverter to transmit electricity to the grid system. The framework structure shown in the figure can only adjust the maximum power of the entire system, and cannot track and control the individual power of each panel or component of each string in the photovoltaic system through MPPT, so it cannot guarantee the maximum power output of each panel. As long as any panel in each string is shaded by light, the other panels in this string will be affected, and the output voltage will be pulled to an unreasonable value, resulting in energy loss. Therefore, it is necessary to improve the centralized optimization.

[0095] See also Figure 2 , the photovoltaic module array is the basis of the photovoltaic system's conversion of light energy into electrical energy. The photovoltaic module array is equipped with a battery string, which is composed of photovoltaic modules PV1 to PVN connected in series. Each photovoltaic module or photovoltaic panel is equipped with a DC converter or power optimizer that performs maximum power tracking calculations. In a battery string, for example, the electric energy generated by the first-level photovoltaic module PV1 shown in the figure is converted by the first-level power optimizer OP1 to perform power optimization, and the electric energy generated by the second-level photovoltaic module PV2 is converted by the second-level power optimizer OP2 to perform power optimization. And so on, until the electric energy generated by the N-th photovoltaic module PVN is converted by the N-th power optimizer OPN to perform power optimization. N is a positive integer not less than 1.

[0096] See also Figure 2 ,and Figure 1 Compared with the centralized MPPT, MPPT is performed individually at the PV module, so each PV module can reach its own maximum power point independently. This is equivalent to configuring the working voltage and working current of the PV module to have no direct correlation with the output voltage and output current of the power optimizer.

[0097] See also Figure 2 Assuming that the lighting conditions of the photovoltaic component PV1 are very good, its power-voltage curve is represented by CV1, and the horizontal axis represents the operating voltage of the photovoltaic component PV1, and the vertical axis represents the power of the photovoltaic component PV1. As shown in the figure, this photovoltaic component PV1 can reach the maximum power point under very good lighting conditions.

[0098] See also Figure 2 Assuming that the lighting conditions of photovoltaic component PV2 are relatively weak, its power-voltage curve is represented by CV2, and the horizontal axis represents the working voltage of photovoltaic component PV2, and the vertical axis represents the power of photovoltaic component PV2. As shown in the figure, this photovoltaic component PV2 can reach the maximum power point under relatively weak lighting conditions.

[0099] See also Figure 2 Assuming that the photovoltaic component PVN is blocked from light, its power-voltage curve is represented by CVN, and the horizontal axis represents the operating voltage of the photovoltaic component PVN, and the vertical axis represents the power of the photovoltaic component PVN. As shown in the figure, this photovoltaic component PVN can reach the maximum power point under the condition of blocked light.

[0100] See also Figure 2 The PV power optimization shown in the figure only attempts to achieve the optimal working current multiplied by the optimal working voltage of the PV module from the perspective of the local end of the PV module: For example, the power optimizer OPN attempts to achieve the working current I of the PV module PVN from the perspective of the local end of the PV module PVN PVN Multiply by the operating voltage V PVN If this product is maximized, the power optimizer OPN has successfully implemented power optimization for the photovoltaic module PVN.

[0101] See also Figure 2 , the output voltage of the first stage power optimizer OP1 is V O1 , the output voltage V corresponding to the second-stage power optimizer OP2 O2 , ... and so on, until the output voltage V of the Nth-stage power optimizer OPN ON The total string voltage of any photovoltaic cell string is calculated to be approximately V O1 +V O2 +…V ON =V BUS The power optimizer used in this case is also called a maximum power point tracker, which usually uses a specific type of topology circuit to search for the maximum power point and allow the DC converter to extract the maximum possible power from the PV panel.

[0102] See also Figure 2 If no measures are taken, assuming that the conventional power optimizer OP1-OPN has achieved the working current I of the photovoltaic module such as PVN through maximum power tracking PVN Multiply by the operating voltage V PVN Maximization. In this balanced state where the power is at its maximum, if the photovoltaic inverter INVT performs power optimization again, it means that the photovoltaic inverter INVT will change the bus current and bus voltage to pursue the bus current I BUS Multiply by bus voltage V BUS It is obvious that the tracking action of the inverter INVT will break the power balance of the traditional power optimizer OP1-OPN. At this time, it is extremely difficult to achieve working adaptation between the traditional power optimizer and the photovoltaic inverter and meet the optimization requirements of both.

[0103] See also Figure 2In order to solve the above problems, the MPPT function of the photovoltaic inverter INVT can be abandoned. The optimization products currently on the market have adopted this kind of solution. For example, the power optimization solution of Israel Solar Anji Company is to perform power optimization only in the photovoltaic module PV1-PVN locally instead of in the inverter INVT. The inverter simply performs the inversion of DC to AC conversion. This solution also has great inconvenience: because the existing photovoltaic inverters in photovoltaic power stations basically have MPPT function, and the photovoltaic MPPT function is standard. Few inverter merchants will cancel the photovoltaic MPPT function to adapt to the local optimization of photovoltaic modules PV1-PVN. Therefore, this makes it difficult for the power optimization function configured on the DC converter side to adapt to the market demand. Whether it is a distributed photovoltaic power station or a centralized photovoltaic power station, it would rather give up the DC converter with MPPT function than give up the MPPT function of the inverter. This is a comprehensive result based on the cost considerations of the photovoltaic power station, the final power optimization effect, and the convenience of use.

[0104] See also Figure 2 , especially the current photovoltaic system is compatible with photovoltaic inverters with MPPT function. The various software architectures and hardware parts of the current photovoltaic system are based on catering to photovoltaic inverters with MPPT function. Such photovoltaic inverters have adapted to the ecological chain of standard photovoltaic systems. The software and hardware systems of photovoltaic power stations are also designed and laid out based on photovoltaic inverters with maximum power tracking. Abandoning the MPPT function of photovoltaic inverter INVT is unacceptable for many existing photovoltaic power stations or newly built photovoltaic power stations, and it will also lose the opportunity for secondary optimization.

[0105] See also Figure 3 In the example shown in the figure, the optimization of the photovoltaic module user end and the centralized optimization coexist. In a battery string, for example, the electric energy generated by the first-level photovoltaic module PV1 shown in the figure is converted and optimized by the first-level DC converter H1, and the electric energy generated by the second-level photovoltaic module PV2 is converted and optimized by the second-level DC converter H2. And so on, until the electric energy generated by the N-th photovoltaic module PVN is converted and optimized by the N-th DC converter HN. N is a positive integer not less than 1.

[0106] See also Figure 3 , assuming that the output voltage U of the first-stage DC converter H1 is H1 , the output voltage U corresponding to the second-stage DC converter H2 H2 , ... and so on, until the output voltage U of the Nth-stage DC converter HN HN The total string voltage of any photovoltaic cell string is calculated to be approximately U H1 +U H2 +…UHN =V BUS . The DC converter used in this occasion is also called a photovoltaic power optimizer, which searches for the power optimization point (Power Optimization Point). Note that the power optimization point can be either the maximum power point (Maximum Power Point) or a non-maximum power point. It is easy to understand that the power optimization point is the maximum power point, but it is worth explaining that the power optimization point is a non-maximum power point. The power optimization point of one or several photovoltaic components can still bring many advantages to the photovoltaic system at a non-maximum power point: for example, ensuring that the remaining photovoltaic components in the string reach the maximum power point as much as possible, maintaining the overall power of the photovoltaic system is increased, allowing the string to match the secondary power optimization of the external inverter, facilitating the flexible adjustment of the number of photovoltaic components inside the string, allowing the string to conveniently float its own string voltage and realize free parallel connection of the strings, etc. This is the advantage of the specific solution of the present application.

[0107] See also Figure 3 It is necessary to retain the MPPT function of the photovoltaic inverter INVT, but as mentioned above, how to achieve adaptation between the DC converter H1-HN and the inverter INVT and meet the optimization requirements of both is a difficult point in the design of the photovoltaic system. Even if some solutions have designed two MPPT coexistence architectures, the mainstream idea is to realize the current I of the photovoltaic module PVN in the local DC converter H1-HN. PVN Multiply the voltage V PVN Maximize and realize the current I at the busbar BUS Multiply the voltage V BUS Maximization, the coexistence of the two MPPTs still has irreconcilable difficulties. For example, facing different PV module application scenarios (different degrees of shading of PV modules, different numbers of PV modules in series in different strings, and randomness of the number of strings in parallel string relationships, etc.), how to programmably correct and adjust the maximum power tracking is a great challenge. In other words, simply realizing the current I of the PV module at the PVN of the PV module is not enough. PVN Multiply the voltage V PVN The maximization of the optimization effect is almost equivalent to letting it run freely. The local photovoltaic power optimization of the photovoltaic module and the post-stage photovoltaic power optimization of the inverter still interfere with and constrain each other. These traditional solutions lack the flexibility and freedom to cope with different photovoltaic module application scenarios, and the optimization effect is not optimal.

[0108] See also Figure 3The present application discloses a power control method, including: using a DC converter such as HN to implement DC to DC power conversion on the corresponding photovoltaic module PVN. The DC converters H1-HN are connected in series, and a group of multi-stage DC converters H1-HN connected in series correspond to a plurality of photovoltaic modules PV1-PVN as a string. At this time, it is necessary to use an inverter INVT to implement DC to AC power conversion on the output power provided by the DC converter H1-HN (i.e., the cumulative value of the output power provided by all DC converters H1-HN).

[0109] See also Figure 3 , the power optimization point of the DC converter H1-HN is the DC to DC power conversion.

[0110] See also Figure 3 , the power optimization point of the inverter INVT is the power conversion from DC to AC.

[0111] See also Figure 3 The present application discloses a power control method, which involves two aspects: global power optimization of a photovoltaic system and local power optimization of a photovoltaic system.

[0112] See also Figure 3 In terms of global power optimization, as shown in the figure, the maximum power point tracking is performed on a single string or multiple strings in parallel by the inverter INVT. In an optional embodiment, for example, the curve SAB represents the execution of the bus current I BUS Multiply the bus voltage V BUS Maximum Power Point Tracking (MPPT), the coordinate system where the curve SAB is located is the bus voltage and the ordinate is the power on the DC bus.

[0113] See also Figure 3 In terms of local power optimization, as shown in the figure, the gain of the DC converter H1-HN is guided to approach the preset value or set value. In an optional embodiment, for example, the curve CVN represents the power optimization performed at the photovoltaic module PVN but not directly the maximum power point tracking (MPPT), and the coordinate system where the curve CVN is located has the horizontal axis being the operating voltage of the photovoltaic module and the vertical axis being the power of the photovoltaic module.

[0114] See also Figure 3 The power optimization mentioned in this article includes: maximum power tracking implemented to reach the maximum power point, power increase implemented to get as close to the maximum power point as possible, power boost implemented when the maximum power point cannot be reached but the attempt is made to approach the maximum power point, and any optimization behavior to increase the power of photovoltaic modules.

[0115] See also Figure 3Based on the coordinated cooperation of global power optimization and local power optimization, the purpose of increasing and optimizing the operating power of photovoltaic modules PV1-PVN is achieved. In an optional embodiment, through the coordinated cooperation of global power optimization and local power optimization, when the gain Gain of the DC converter HN reaches the preset value Target0_VN, the photovoltaic module PVN corresponding to the DC converter HN reaches its power optimization point.

[0116] See also Figure 3 , the multi-level DC converters H1-HN are connected in series, and the photovoltaic inverter INVT performs power conversion on the output power provided by the multi-level DC converters H1-HN, that is, performs power conversion on the sum of the output powers of the multi-level DC converters H1-HN, which is the same meaning. The total electric energy provided by the photovoltaic component array is transmitted to the photovoltaic inverter INVT by the DC bus. There are many types of photovoltaic inverters INVT in the industry. In the illustrated embodiment, it is almost compatible with any inverter with MPPT.

[0117] See also Figure 3 , the photovoltaic inverter INVT has a maximum power tracking function, and the photovoltaic inverter INVT implements maximum power tracking for the photovoltaic components PV1-PVN corresponding to the multi-level DC converters H1-HN in series as a whole. Note that the photovoltaic inverter INVT used in almost all distributed or centralized photovoltaic power stations currently has a maximum power tracking function, which brings some disadvantages: the local power optimization of the photovoltaic components PV1-PVN and the power optimization of the photovoltaic inverter INVT will interfere with each other. How to guide this constraint relationship to the mutual adaptation of the DC converter H1-HN and the inverter INVT to adapt to each other and meet the optimization needs of both parties and achieve system and power optimization is a difficult problem.

[0118] See also Figure 3 In order to solve the above-mentioned drawbacks, the power optimizer involved in the present application uses the aforementioned DC converters H1-HN, for example. Taking the DC converter H1 as an example, the DC converter H1 converts the electric energy captured from the corresponding photovoltaic component PV1 into the output power of the DC converter H1. The actual gain of the DC converter H1 is Gain1 and the gain Gain1 of the DC converter H1 needs to be guided to approach the preset value Target0_V1.

[0119] See also Figure 3 , for DC converter H1, U H1 is the output voltage of DC converter H1 and U P1 This is the input voltage of the DC converter H1. In Buck or Boost or Buck-Boost circuits, Gain1 = U H1 / U P1The gain Gain1 of the DC converter H1 needs to be guided to approach the preset value Target0_V1 to optimize the power of PV1. Under the step-down circuit, Gain1 = D BU , the D BU It is the duty cycle of the DC converter H1 when using the step-down circuit. Under the step-up circuit, Gain1=1 / (1-D BO ), the D BO It is the duty cycle of the DC converter H1 when using the boost circuit. Under the buck-boost circuit, Gain1 = D BU / (1-D BO ), the D BU and D BO The buck duty cycle and boost duty cycle of the DC converter H1 when using the buck-boost circuit are shown respectively. It can be seen that the gain is closely related to the circuit form.

[0120] See also Figure 3 When the gain Gain1 of the DC converter H1 reaches the preset value Target0_V1, in an optional embodiment, the photovoltaic component PV1 corresponding to the DC converter H1 reaches its power optimization point.

[0121] See also Figure 3 Taking the DC converter H2 as an example, the DC converter H2 converts the electric energy captured from the corresponding photovoltaic component PV2 into the output power of the DC converter H2. The actual gain of the DC converter H2 is Gain2 and the gain Gain2 of the DC converter H2 needs to be guided to approach the preset value Target0_V2.

[0122] See also Figure 3 , for DC converter H2, U H2 is the output voltage of DC converter H2 and U P2 This is the input voltage of the DC converter H2. In Buck or Boost or Buck-Boost circuits, Gain2 = U H2 / U P2 The gain Gain2 of the DC converter H2 needs to be guided to approach the preset value Target0_V2 to optimize the power of PV2.

[0123] See also Figure 3 When the gain Gain2 of the DC converter H2 reaches the preset value Target0_V2, in an optional embodiment, the photovoltaic component PV2 corresponding to the DC converter H2 reaches its power optimization point.

[0124] See also Figure 3Taking the DC converter HN as an example, the DC converter HN converts the electric energy captured from the corresponding photovoltaic module PVN into the output power of the DC converter HN. The actual gain of the DC converter HN is GainN and the gain GainN of the DC converter HN needs to be guided to approach the preset value Target0_VN.

[0125] See also Figure 3 , for DC converter HN, U HN is the output voltage of the DC converter HN and U PN It is the input voltage of the DC converter HN. In Buck or Boost or Buck-Boost circuit, GainN=U HN / U PN The gain GainN of the DC converter HN needs to be guided toward the preset value Target0_VN to implement power optimization for PVN.

[0126] See also Figure 3 When the gain GainN of the DC converter HN reaches the preset value Target0_VN, in an optional embodiment, the photovoltaic component PVN corresponding to the DC converter HN reaches its power optimization point.

[0127] See also Figure 3 In an optional embodiment, in the same group of strings including PV1-PVN, if all photovoltaic modules are not shaded, when the gains of the multi-stage DC converters H1-HN corresponding to the same group of strings reach the corresponding preset values, such as gain Gain1 = Target0_V1 and Gain2 = Target0_V2 and GainN = Target0_VN, all photovoltaic modules PV1-PVN in the same group of strings are working at their respective maximum power points. This outcome is based on the coordinated cooperation of global power optimization and local power optimization to jointly optimize the power of photovoltaic modules PV1-PVN. In this embodiment, the power optimization point is the maximum power point (Maximum Power Point) of the photovoltaic module.

[0128] See also Figure 3In an optional embodiment, in the same group of strings including PV1-PVN, if some photovoltaic components are shaded, such as photovoltaic component PV2 is shadowed, the remaining photovoltaic components are not shadowed. After global and local power optimization, when the gains of the multi-stage DC converters H1-HN corresponding to the same group of strings reach the corresponding preset values, such as gains Gain1=Target0_V1, Gain2=Target0_V2, and GainN=Target0_VN, the unshaded photovoltaic components in the same group of strings, such as PV1, PV3-PVN, all operate at their respective maximum power points, and the shaded photovoltaic components, such as photovoltaic component PV2, do not operate at their maximum power points.

[0129] See also Figure 3 , the power optimization point of one or several photovoltaic components such as PV2 can still bring many advantages at non-maximum power points: for example, to ensure that the remaining photovoltaic components in the string reach the maximum power point as much as possible, which requires the maximum power tracking MPPT function on the inverter side. For example, to maintain the overall power of the photovoltaic system is increased, so that the string can match the MPPT function of the external inverter. Another example is to facilitate the flexible adjustment of the number of photovoltaic components in the string, because any change in the gain of any DC converter can cause the string voltage to change by a certain amplitude, so that the string can conveniently float its own string voltage and realize the free parallel connection of the string, which will be introduced below.

[0130] See also Figure 3 In an optional embodiment, the preset values ​​Target0_V1 and Target0_V2 and Target0_VN or the preset values ​​Target0_V3 to Target0_V(N-1) set by the DC converters H3 to H(N-1) may be the same or different.

[0131] See also Figure 3 In an optional embodiment, the multi-level DC converters H1-HN connected in series form a series branch and the series branch supplies power to the inverter INVT, and the series voltage provided by the series branch is adjusted by changing the preset values ​​Target0_V1 to Target0_VN, such as the bus voltage V BUS The size.

[0132] See also Figure 3 In an optional embodiment, changing the preset value Target0_V1 will adjust the output voltage U of the DC converter H1. H1 However, through the coordination of global power optimization and local power optimization, the photovoltaic module PV1 can still reach the desired optimal power optimization point. Similarly, changing the preset value Target0_V2 will adjust the output voltage U of the DC converter H2. H2However, through the coordination of global power optimization and local power optimization, the photovoltaic module PV2 can still reach the desired optimal power optimization point. Furthermore, changing the preset value Target0_VN will adjust the output voltage U of the DC converter HN. HN However, through the coordination of global power optimization and local power optimization, the photovoltaic module PVN can still reach the desired optimal power optimization point. In other words, the optimization scheme of the present application can be completely coupled with any maximum power tracking algorithm of the external inverter INVT. By modifying the preset values ​​such as Target0_VN, the DC converter or power optimizer can be easily matched to different components. In addition, the bus voltage V BUS The size can be adjusted arbitrarily without affecting the power optimization results of the photovoltaic system, which is beneficial for inverters INVT with different rated input voltages. Figure 2 It is difficult for traditional power optimizers to take into account the coordination between optimizers and between optimizers and inverters.

[0133] See also Figure 3 , DC converters belong to power electronic devices, and their main purpose is to achieve the function of power point tracking of individual photovoltaic modules. Buck circuit, boost circuit, buck-boost circuit and CUK circuit are the main circuit topologies suitable for photovoltaic DC converters. These main circuit topologies are essentially still in the category of switching power supply SMPS system. The switching power supply system usually uses power semiconductor devices as switching elements and adjusts the output voltage by periodically switching on and off to control the duty cycle of the switching elements. The power conversion achieved by the switching power supply is its core part. In order to meet the high power density requirements, the converter needs to work in a high frequency state and the switching transistors need to use power switches with high switching speed and short conduction and off time, such as power thyristors, power field effect transistors and insulated bipolar transistors. The main control methods of the switching converter are divided into pulse width modulation, pulse frequency modulation and other methods, and pulse width modulation schemes are commonly used. The switching power converter shown in the figure is a DC to DC buck or boost or buck-boost DC converter. After the DC converter optimizes the power of a single photovoltaic module, the energy is transmitted to the inverter for DC to AC processing for local use or grid connection. The inverter INVT is usually an inverter device equipped with maximum power tracking MPPT (for example, maximizing the product of bus voltage and bus current).

[0134] See also Figure 3, the DC converters H1-HN still need to achieve power optimization of the corresponding photovoltaic components PV1-PVN but no longer simply track the MPPT (for example, maximizing the product of the output current and output voltage of the photovoltaic component). In other words, the power optimization pursued by the DC converters H1-HN in this application may not be the maximum power point of the corresponding photovoltaic components PV1-PVN but the optimal power optimization, provided that it can achieve a high degree of adaptation with the MPPT of the inverter INVT. The optimal power may be the maximum power point of the photovoltaic components PV1-PVN, or it may not be their maximum power point. Note that the optimal power optimization has taken into account the coordination and cooperation with the MPPT of the inverter INVT.

[0135] See also Figure 3 Strictly speaking, the power optimization of the DC converter H1-HN at this time is not MPPT, but another power optimization method that can work in coordination with the MPPT of the inverter INVT. This design is based on the local DC converter H1-HN and the secondary photovoltaic MPPT of the inverter INVT mentioned above, which may cause some mutual constraints and interference with each other, causing the photovoltaic components that have been parked at the maximum power point to deviate from the maximum power point, or to be in a see-saw change state of entering the maximum point and escaping the maximum point. Generally speaking, photovoltaic components and the DC converters installed locally on the photovoltaic components, as well as photovoltaic supporting equipment such as junction boxes and inverters are not purchased from the same merchant. Current photovoltaic inverters are all equipped with MPPT functions, but the power optimization function of the local DC converter has poor adaptability and cannot cooperate well with the MPPT function of the inverter. The power optimizer involved in this application can just solve this type of problem.

[0136] See also Figure 4 Taking the DC converter H1 as an example, the DC converter H1 converts the electric energy captured from the corresponding photovoltaic component PV1 into the output power of the DC converter H1. The actual gain of the DC converter H1 is gain1 and the gain gain1 of the DC converter H1 needs to be guided to approach the preset value Target0_I1.

[0137] See also Figure 4 , for DC converter H1, I H1 is the output current of DC converter H1 and I P1 This is the input current of the DC converter H1. In Buck or Boost or Buck-Boost circuits, gain1 = I H1 / I P1 It is necessary to guide the gain gain1 of the DC converter H1 to approach the preset value Target0_I1 to implement power optimization for PV1.

[0138] See also Figure 4When the gain gain1 of the DC converter H1 reaches the preset value Target0_I1, in an optional embodiment, the photovoltaic component PV1 corresponding to the DC converter H1 reaches its power optimization point.

[0139] See also Figure 4 Taking the DC converter H2 as an example, the DC converter H2 converts the electric energy captured from the corresponding photovoltaic component PV2 into the output power of the DC converter H2. The actual gain of the DC converter H2 is gain2 and the gain gain2 of the DC converter H2 needs to be guided to approach the preset value Target0_I2.

[0140] See also Figure 4 , for DC converter H2, I H2 is the output current of DC converter H2 and I P2 This is the input current of the DC converter H2. In Buck or Boost or Buck-Boost circuits, gain2 = I H2 / I P2 It is necessary to guide the gain gain2 of the DC converter H2 to approach the preset value Target0_I2 to optimize the power of PV2.

[0141] See also Figure 4 When the gain gain2 of the DC converter H2 reaches the preset value Target0_I2, in an optional embodiment, the photovoltaic component PV2 corresponding to the DC converter H2 reaches its power optimization point.

[0142] See also Figure 4 Taking the DC converter HN as an example, the DC converter HN converts the electric energy captured from the corresponding photovoltaic module PVN into the output power of the DC converter HN. The actual gain of the DC converter HN is gainN and the gain gainN of the DC converter HN needs to be guided to approach the preset value Target0_IN.

[0143] See also Figure 4 , for DC converter HN, I HN is the output current of the DC converter HN and I PN This is the input current of the DC converter HN. In Buck or Boost or Buck-Boost circuits, gainN = I HN / I PN It is necessary to guide the gain gainN of the DC converter HN to approach the preset value Target0_IN to implement power optimization for PVN.

[0144] See also Figure 4When the gain gainN of the DC converter HN reaches the preset value Target0_IN, in an optional embodiment, the photovoltaic component PVN corresponding to the DC converter HN reaches its power optimization point.

[0145] See also Figure 4 In an optional embodiment, in the same group of strings including PV1-PVN, if all photovoltaic modules are not shaded, when the gains of the multi-stage DC converters H1-HN corresponding to the same group of strings reach the corresponding preset values, such as gain gain1 = Target0_I1 and gain2 = Target0_I2 and gainN = Target0_IN, all photovoltaic modules PV1-PVN in the same group of strings work at their respective maximum power points. This outcome is based on the coordinated cooperation of global power optimization and local power optimization, and jointly optimizes the power of photovoltaic modules PV1-PVN. In this embodiment, the power optimization point is the maximum power point of the photovoltaic module.

[0146] See also Figure 4 In an optional embodiment, in the same group of strings including PV1-PVN, if some photovoltaic components are shaded, such as photovoltaic component PV2 is shadowed, and the remaining photovoltaic components are not shadowed, after global and local power optimization, when the gains of the multi-stage DC converters H1-HN corresponding to the same group of strings reach the corresponding preset values, such as gain gain1=Target0_I1 and gain2=Target0_I2 and gainN=Target0_IN, the unshaded photovoltaic components in the same group of strings, such as PV1, PV3-PVN, all operate at their respective maximum power points, and the shaded photovoltaic components, such as photovoltaic component PV2, operate at non-maximum power points.

[0147] See also Figure 4 In an optional embodiment, the preset values ​​Target0_I1 and Target0_I2 and Target0_IN or the preset values ​​Target0_I3 to Target0_I(N-1) set by the DC converters H3 to H(N-1) may be the same or different.

[0148] See also Figure 5 The multi-level DC converters H1-HN connected in series form a series branch, which supplies power to the inverter INVT. The series voltage provided by the series branch, such as V BUS The cascade voltage provided by the series branch, such as V BUS The size.

[0149] See also Figure 5 , different groups of batteries are connected in series and parallel between busbars LA and LB: if multi-level DC converters H1-HN are defined to form a series branch, different series branches are connected in parallel between busbars LA and LB. If DC converter H1-HK forms another branch, it is also connected between busbars LA and LB. This parallel relationship of strings will bring some disadvantages in terms of optimization: if the number of components connected in series N and K are not equal, that is, as mentioned above, facing different PV component application scenarios, the MPPT of inverter INVT guides the string (PV1-PVN) to work at the maximum power point, but it may not be able to make the string (PV1-PVK) work at the maximum power point. In fact, the total power that a larger number of PV modules can provide is usually much greater than that of a smaller number of PV modules. K is a positive integer not less than 1.

[0150] See also Figure 5 The tricky problem is that each DC converter H1-HN corresponding to the string (PV1-PVN), such as HN, tries to maximize the power of the corresponding PV module, such as PVN. In this working state, the output voltages of the DC converters H1-HN will inevitably generate a string voltage U H1 +U H2 +…U HN .

[0151] See also Figure 5 In contrast, each DC converter such as HK in the DC converter H1-HK corresponding to the other string (PV1-PVK) attempts to maximize the power of the corresponding PV module such as PVK. In this working state, the output voltage of each DC converter H1-HK will inevitably generate another string voltage U H1 +U H2 +…U HK .

[0152] See also Figure 5 In most cases, U H1 +U H2 +…U HN and U H1 +U H2 +…U HKNot equal. However, for the photovoltaic inverter INVT, there is only one bus voltage value corresponding to the maximum power point of the DC bus, so there is a matching problem between different strings, which leads to the disorder of the photovoltaic inverter INVT in executing MPPT. At this time, the great advantages of the present application are fully demonstrated. As long as the preset values ​​of different strings are slightly modified, the bus voltages contributed by different strings can be infinitely close. For example: If N>K, the preset values ​​of the DC converters H1-HN corresponding to the strings (PV1-PVN) are designed to be smaller than the preset values ​​of the DC converters H1-HK corresponding to the strings (PV1-PVK), the string voltage U can be easily made. H1 +U H2 +…U HN and U H1 +U H2 +…U HK Equal or close. In particular, the preset value of each DC converter can be adjusted to be the same or different, which is extremely helpful for making the string voltages of different strings equal or close when the inverter INVT performs power optimization. There is no doubt that this is an intuitive reflection of the coordination and adaptation between the power optimization function of the DC converter H1-HN and the MPPT function of the inverter INVT or the photovoltaic inverter INVT.

[0153] See also Figure 5 , we need to consider the overall power of the photovoltaic system. In other words, we cannot only look at the power change trend of the photovoltaic system from the perspective of global power optimization, nor can we only look at the power change trend of the photovoltaic system from the perspective of local power optimization. The horizontal axis is the gain GAIN of the DC converter H1-HN, and the vertical axis is the set of maximum power points of the overall power. The vertical axis is P MAX This optional example shows how global power optimization and local power optimization can work together to increase and optimize the operating power of PV panels.

[0154] See also Figure 5 , according to GAIN-P MAX The curve shows that on the one hand, the gain GAIN of each DC converter H1-HN can be adjusted locally in each photovoltaic module to adjust the overall power SysP of the photovoltaic system. In the previous article, the DC converter HN has been used as an example for explanation. GAIN is, for example, the voltage-based gain GainN of the DC converter HN or the current-based gain gainN of the DC converter HN. A change in GAIN means a change in SysP.

[0155] See also Figure 5 , according to GAIN-P MAXThe curve shows that on the other hand, the overall power SysP of the photovoltaic system can be adjusted through the maximum power point tracking MPPT function at the inverter INVT end.

[0156] See also Figure 5 In an optional embodiment, the multi-stage DC converters are connected in series. As shown in the figure, a group of DC converters H1-HK can be connected in series, a group of DC converters H1-HN can be connected in series, or more other groups of multi-stage DC converters not shown can be connected in series, and different groups of DC converters are connected in parallel. For example, the series branch of the multi-stage DC converter H1-HK is connected in parallel with the series branch of the multi-stage DC converter H1-HN. If there are other series branches of multi-stage DC converters, then the different series branches are all connected in parallel.

[0157] See also Figure 5 In an optional embodiment, an inverter INVT performs power conversion on the output power provided by the multi-level DC converter (in this example, H1-HK and H1-HN as shown in the figure), and the inverter INVT can have a maximum power tracking MPPT function. Therefore, the photovoltaic inverter INVT performs maximum power tracking, that is, performs MPPT (for example, maximizing the product of bus voltage and bus current) on multiple photovoltaic components such as PV1-PVN and PV1-PVK corresponding to the series-connected multi-level DC converter (in this example, H1-HK and H1-HN as shown in the figure).

[0158] See also Figure 5 In an optional embodiment, a plurality of photovoltaic modules PV1-PVN corresponding to a group of multi-level DC converters H1-HN connected in series can be regarded as a group string (PV-string1), and a plurality of photovoltaic modules PV1-PVK corresponding to a multi-level DC converter H1-HK can be regarded as another group string (PV-string2). More groups of strings are not shown in the figure.

[0159] See also Figure 5 In an optional embodiment, multiple strings connected in parallel supply power to the photovoltaic inverter INVT. In this example, the inverter INVT converts the string current of a single string (PV1-PVN), i.e., I N And the string voltage V BUS Set it at its maximum power point and also set the string current of a single string (PV1-PVK), that is, I K And the string voltage V BUS Set at its maximum power point. String current I N is the output current of the DC converters H1-HN connected in series, the string current I K It is the output current of the DC converters H1-HK connected in series.

[0160] See also Figure 3 In an optional embodiment, a single string supplies power to the photovoltaic inverter INVT. In this example, the inverter converts the string current of a single string, i.e., I BUS And the string voltage V BUS Set it to its maximum power point. In this example, there is only one string, so the bus current is directly the string current or string level current of the single string in the figure, and the bus voltage is the string voltage or string level voltage of the single string in the figure.

[0161] See also Figure 5 In an optional embodiment, multiple strings supply power to the photovoltaic inverter INVT. In this example, the inverter converts the sum of the string currents of all strings, i.e., the bus current I BUS And the string voltage is the bus voltage V BUS Set at its maximum power point. In this example, multiple strings are connected in parallel, so the bus current is the sum of the string currents or string-level currents of the multiple strings shown in the figure (for example, in the case of two strings, the bus current is the string current I N Add string current I K ), the bus voltage is the same string voltage or string-level voltage for each of the multiple strings shown in the figure.

[0162] See also Figure 5 In an optional embodiment, among the multi-stage DC converters corresponding to a single string (such as PV-string1), the preset values ​​of different DC converters H1-HN are set to be different or the same.

[0163] See also Figure 5 In an optional embodiment, when multiple strings connected in parallel supply power to the photovoltaic inverter INVT, the preset values ​​of the DC converters corresponding to different strings (e.g., PV-string1, PV-string2) with unequal numbers of photovoltaic components are also set to be different. N and K are different, for example, the preset value Target0_S1 of the DC converter H1-HN is set to be different from the preset value Target0_S2 of the DC converter H1-HK. Note that the preset values ​​of different DC converters in the DC converters H1-HN can be set to be the same, for example, Target0_S1, and the preset values ​​of different DC converters in other DC converters H1-HK can be set to be the same, for example, Target0_S2.

[0164] See also Figure 5 In an optional embodiment, the preset value of the DC converter H1-HK corresponding to the string with a small number of photovoltaic components (such as PV-string2), such as Target0_S2, is larger than the preset value of the DC converter H1-HN corresponding to the string with a large number of photovoltaic components (such as PV-string1), such as Target0_S1.

[0165] See also Figure 5 ,Common MPPT tracking methods include constant voltage method, conductance increment method, ,perturbation observation method, etc. They are suitable for inverter INVT in global power optimization, and also for optimization actions of local power optimization.

[0166] See also Figure 5 In an optional embodiment, the global power optimization and local power optimization are coordinated. Without changing the MPPT architecture of the existing photovoltaic inverter INVT, the multi-level DC converter H1-HN or power optimizer can be fully coupled with the MPPT algorithm of the external inverter INVT. The local power optimization of the photovoltaic module and the centralized power optimization of the inverter will not interfere with each other. For the overall power SysP of the photovoltaic system, the local power optimizer of the photovoltaic module can cooperate with the maximum power tracking algorithm of the photovoltaic inverter to achieve the best optimization effect of SysP.

[0167] See also Figure 5 Based on the above advantages, the DC converter or power optimizer disclosed in this application is easier to adapt to different types or different vendors' photovoltaic inverters than traditional power optimizers. Moreover, by modifying the so-called preset value, the DC converter or power optimizer disclosed in this application can easily match different types of photovoltaic modules: it should be noted that the voltage and current parameters of photovoltaic modules of different types or different vendors are not completely consistent, and even the voltage and current parameters of the same type of photovoltaic modules of the same vendor are not completely consistent (for example, in different production batches).

[0168] See also Figure 5 In contrast, traditional Figure 2 A major drawback of the power optimizer is that the battery characteristics of different photovoltaic modules in the network are different. In order to adaptably cooperate with photovoltaic modules in the same string but with different characteristics, the traditional power optimizer requires certain restrictions on the battery characteristics of photovoltaic modules. A typical example is to limit the various parameters of photovoltaic modules such as voltage, current, nominal power, etc., which leads to a significant increase in the cost of photovoltaic modules that can be networked. The power optimizer disclosed in this article implements power optimization by modifying the so-called preset value, which does not necessarily require the execution of MPPT. Then the change of the preset value allows the power optimizer to adapt to photovoltaic modules with different battery characteristics and different parameters, allowing power optimization of various types of photovoltaic modules with poor consistency under a wide parameter range such as wide voltage and wide current. Traditional power optimizers are difficult to achieve this and cannot construct SysP curves.

[0169] See also Figure 5In an optional embodiment, the photovoltaic system includes a DC converter H1-HN for implementing DC to DC power conversion for the photovoltaic modules PV1-PVN, and the photovoltaic system also includes an inverter INVT, and the inverter INVT is powered by the multi-stage DC converters H1-HN connected in series. The photovoltaic system performs maximum power point tracking based on the total output power provided by each DC converter H1-HN through the inverter INVT, and the photovoltaic system guides the respective gains of the DC converters H1-HN to approach the corresponding preset values, so as to achieve the purpose of optimizing and increasing the operating power of the photovoltaic module.

[0170] See also Figure 5 In an optional embodiment, the DC converters H1-HN implement DC to DC power conversion for the photovoltaic components PV1-PVN. The multi-stage DC converters H1-HN are connected in series. An inverter INVT is used to implement DC to AC power conversion for the total output power provided by the multi-stage DC converters H1-HN. In terms of global power optimization, the inverter INVT performs maximum power point tracking on the output power provided by each DC converter H1-HN in series, for example, performing maximum power point tracking at the DC bus LA-LB. In terms of local power optimization, the gains of each DC converter H1-HN are guided to approach the corresponding preset values. Based on the coordinated cooperation of global power optimization and local power optimization, the purpose of increasing and optimizing the operating power of photovoltaic components such as PV1-PVN is achieved together.

[0171] See also Figure 5 In an optional embodiment, hierarchical power optimization is implemented for the photovoltaic modules PV1-PVN. In the front-stage power optimization, the gains of the DC converters H1-HN used to implement power conversion for the photovoltaic modules PV1-PVN are guided to approach the corresponding preset values. In the back-stage power optimization, the inverter INVT performs maximum power point tracking on the total output power provided by the series-connected DC converters H1-HN. Through the front- and back-stage power optimization, when the gain of any DC converter such as HN reaches the preset value, the corresponding photovoltaic module PVN reaches the power optimization point.

[0172] See also Figure 6 The DC converter HK mentioned in the previous article that the available switching power supply SMPS can be used, and the specific circuit topologies include Buck circuit, Boost circuit, Buck-Boost circuit, etc. Figure 6 It is one of the typical categories of Buck-Boost circuits, and can be adaptively changed into a Buck circuit or a Boost circuit. This goal can be achieved by modifying the software of the controller 400 or directly by modifying the components and hardware circuits.

[0173] See also Figure 6 Although the DC converter HK or DC / DC converter belongs to the category of switching power supply SMPS, its optional topology is not limited to a specific type. In this example, the DC converter HK preferably has both a boost circuit and a buck circuit. The main topology circuit of the power optimizer has been introduced above. The photovoltaic module PVK uses the DC converter HK shown in the figure (assuming that K can be a number from 1 to N) to generate the desired output voltage and perform the desired power optimization. The first input terminal IN1 of the input side of the DC converter HK is coupled to the positive terminal of the photovoltaic module PVK and the second input terminal IN2 is coupled to the negative terminal of the photovoltaic module PVK. The corresponding DC converter HK provides an output voltage and output power between the first output terminal NO1 and the second output terminal NO2 on the output side. In addition, the input capacitor C1 can be set in the topology to be connected between the first input terminal IN1 and the second input terminal IN2, and the output capacitor C2 can be set to be connected between the first output terminal NO1 and the second output terminal NO2.

[0174] See also Figure 6 , the DC converter or power optimizer performs DC / DC voltage conversion on the DC power of the photovoltaic module and synchronously performs power optimization tracking calculation. In the topological structure, the power switch S1 and the power switch S2 of the buck conversion circuit module in the DC converter HK are connected in series between the first input terminal IN1 and the second input terminal IN2, and the power switch S3 and the power switch S4 of the boost conversion circuit of the DC converter HK are connected in series between the first output terminal NO1 and the second output terminal NO2. Therefore, the main topological circuit adopts a switching power supply that can step up and down, and the buck conversion circuit and the boost conversion circuit share the same inductor device L.

[0175] See also Figure 6 , the power switch S1 and the power switch S2 are both connected to the first interconnection node X1, and the power switch S3 and the power switch S4 in the boost conversion circuit module are both connected to the second interconnection node X2, and an inductor element L is set between the first interconnection node X1 where the front power switches S1-S2 are connected and the second interconnection node X2 where the rear power switches S3-S4 are connected in the buck-boost circuit topology. The second output terminal NO2 and the second input terminal IN2 can be directly coupled together or their potentials can be set to be substantially the same.

[0176] See also Figure 6 The controller 400 configured for the DC converter HK, such as the pulse width modulator of the microprocessor MCU, sends several pulse modulation signals D1-D4 for driving the power switches S1-S4. The controller 400 can use a driver with stronger driving capability to amplify the driving capability of the signals D1-D4 and then drive the power switches S1-S4.

[0177] See also Figure 6 , a DC converter such as HK is equipped with a microprocessor MCU for driving the DC converter HK to perform voltage conversion or current conversion. The microprocessor MCU adjusts the gain GainK or gainK of the DC converter HK by changing the duty cycle of the DC converter HK when it is working, for example, by changing the duty cycle to make GainK approach the preset value Target0_VK based on voltage or to make gainK approach the preset value Target0_IK based on current. The preset value stored by the microprocessor itself or transmitted to it by the outside is programmable, and Target0_VK or Target0_IK can be adjusted at any time according to actual needs. If the preset value is changed, the gain GainK or gainK is also changed accordingly.

[0178] See also Figure 6 When multiple stages of DC converters are connected in series, the first output terminal NO1 of the DC converter HK can be coupled to the second output terminal NO2 of the adjacent previous stage DC converter H(K-1).

[0179] See also Figure 6 When multiple stages of DC converters are connected in series, the second output terminal NO2 of the DC converter HK can be coupled to the first output terminal NO1 of the adjacent subsequent stage of DC converter H(K+1).

[0180] See also Figure 6 , the power switch is typically an insulated gate bipolar transistor or a semiconductor field effect transistor, etc. The DC converter HK shown in the figure preferably has both a buck circuit and a boost circuit: for example, the power switches S1-S2 constitute a buck single arm of the buck circuit, and the D1 and D2 signals provided by the pulse width modulator of the controller 400 can be used to drive the complementary switches S1 and S2 of the buck circuit respectively. S1-S2 switch at high frequency but they are not allowed to be turned on at the same time. The duty cycle of the pulse modulation signal for the buck circuit refers to the duty cycle of the power switch S1, and the power switch S2 is a synchronous freewheeling switch.

[0181] See also Figure 6 If only the Buck circuit is retained, S3 and S4 can be discarded, such as replacing S4 with a wire or directly deleting S3 in the circuit topology. Alternatively, the pulse modulation signal D4 of the controller 400 is required to continuously turn on S4, but the pulse modulation signal D3 needs to continuously control S3 to turn it off. The power switch S2 can also be replaced by a freewheeling diode.

[0182] See also Figure 6, the boost circuit Boost function of the DC converter is opposite to the buck circuit. The DC converter HK shown in the figure has a boost circuit opposite to the buck circuit: for example, the power switches S3-S4 constitute the boost arm of the boost circuit, and the D3 and D4 signals provided by the pulse width modulator of the controller 400 can be used to drive the complementary switches S3 and S4 of the boost circuit respectively. S3-S4 switch at high frequency but they are not allowed to be turned on at the same time. The duty cycle of the pulse modulation signal for the boost circuit refers to the duty cycle of the power switch S3, and the power switch S4 is a synchronous freewheeling switch.

[0183] See also Figure 6 If only the Boost circuit is retained, S1 and S2 can be discarded, such as replacing S1 with a wire and directly deleting S2 in the circuit topology. Alternatively, the pulse modulation signal D1 of the controller 400 is required to continuously turn on S1, but the pulse modulation signal D2 needs to continuously control S2 to turn it off. The power switch S4 can also be replaced by a freewheeling diode.

[0184] See also Figure 6 In summary, the topology of the DC converter HK is not limited to any specific restrictions. It can be the buck-boost circuit shown in the figure, or it can be modified to only retain the Buck circuit or the Boost circuit. The Buck circuit has many variations in the industry, and the Boost circuit also has many variations in the industry. Other DC converters that replace the circuit topology shown in the figure typically include the CUK circuit and the inverse SEPIC circuit.

[0185] See also Figure 6 , the multi-level DC converters H1-HN are all equipped with a controller 400, and power optimization can be specifically implemented by the pulse width modulation signal output by the controller for driving the DC converter. The controller and its configured peripheral hardware can collect various target parameters of photovoltaic components such as PVK or DC converters such as HK, which is equivalent to a data collector. Capturing these target parameter data is helpful to achieve power optimization. In an optional example, the peripheral hardware can collect a series of related specified target parameter information such as the voltage, current and power of the photovoltaic component as well as the temperature and power generation: the voltage parameter is collected by the voltage sensor 111, and the current parameter is collected by the current sensor 112. The temperature parameter can be collected by the peripheral hardware such as the temperature sensor and the light radiation intensity is collected by the light sensor. In addition, the output voltage of the DC converter HK can also be detected by the voltage sensor 113, and the output current of the DC converter HK can be detected by the current sensor 114.

[0186] See also Figure 6The more types of peripheral hardware used for data collection, the more types of target parameters related to photovoltaic modules that the controller 400 can obtain. In a more complex embodiment, the various target parameters may also include data of environmental factors of the photovoltaic modules detected by an environmental monitor: ambient temperature and humidity, wind speed, light intensity, air pressure, etc. The environmental monitor is a highly integrated data collector.

[0187] See also Figure 6 Target parameters related to the photovoltaic module PVK, such as the working voltage and working current of the photovoltaic module, are transmitted to the controller 400 by the corresponding voltage sensor 111 and current sensor 112. The working voltage and working current are actually the input voltage and input current of the DC converter HK.

[0188] See also Figure 6 Target parameters related to the DC converter HK, such as the output voltage and output current of the DC converter, are transmitted to the controller 400 by the corresponding voltage sensor 113 and current sensor 114 .

[0189] See also Figure 6 The controller 400 is selected from a field programmable gate array, a processor, a state machine, a software-driven control device or a complex programmable logic device, a semi-custom ASIC, a microprocessor, a logic circuit, and a single-chip microcomputer.

[0190] See also Figure 3 , the DC converters H1-HN are connected in series according to the following rule: the second output terminal of the previous DC converter is coupled to the first output terminal of the adjacent next DC converter. The second output terminal of the first DC converter H1 is connected to the first output terminal of the second DC converter H2, and the second output terminal of the second DC converter H2 is connected to the first output terminal of the adjacent third DC converter H3. And so on, until the second output terminal of the N-1th DC converter H(N-1) is connected to the first output terminal of the Nth DC converter HN. Therefore, it can also be considered that the series voltage provided by the multi-stage DC converters H1-HN connected in series is equal to the superposition value of their respective output voltages. The total series voltage generated by the DC converters H1-HN can be provided between the bus LA coupled to the first output terminal of the first-stage DC converter H1 and the bus LB coupled to the second output terminal of the Nth-stage DC converter HN.

[0191] See also Figure 7 , the current photovoltaic power optimization only uses a centralized inverter to centrally optimize the series-parallel system of all battery components, as shown in Figure 1 Or just from the perspective of the battery module user end to try to achieve the best working current of the battery module multiplied by the best working voltage, as Figure 2 described. Figure 7 It aims to explain how to solve the problem of crosstalk between power optimization at the user end of battery components and power optimization at the inverter, and how to guide this constrained relationship to mutually adapt and adaptively meet the optimization needs of both parties and achieve power optimization.

[0192] See also Figure 7 ,contrast Figure 2 For example, the traditional power curve CVN and Figure 7 The power curve SysP of the photovoltaic system in the figure. The working principle of the traditional power optimizer is different from that of the power optimizer in this article. The former pursues the working current I of the photovoltaic module PVN at the photovoltaic module end. PVN Multiply by the operating voltage V PVN The latter is to pursue the optimal power processing of the photovoltaic module PVN at the photovoltaic module end (under the optimal processing I PVN Multiply by V PVN It may or may not be the maximum). It is worth noting that this paper does not calculate I PVN Multiply by V PVN Therefore, this article usually does not need to know whether PVN itself is at the maximum power point. This is a typical difference between the two.

[0193] See also Figure 7 The difference between searching for the power optimization point (POP) and searching for the maximum power point (MPP) in the traditional scheme is Figure 7 Will be introduced in detail.

[0194] See also Figure 7 Based on the above-mentioned conditions, different strings in the traditional power optimizer lack sufficient layout flexibility, and usually require that the number of PV modules used in different strings should not differ too much. For example, it is required that the N and K of the strings PV-string1 and PV-string2 in the network should be the same or similar. Figure 5 . This requirement is very unrealistic or too demanding in many PV system applications. Some sites allow a larger number of PV modules, such as N, while some sites can only arrange a smaller number of PV modules, such as K. N and K are not equal, and the number of PV modules used in different strings is usually quite different. Traditional power optimizers are not very practical at this time, because the specific power optimization function of pursuing the maximum power point limits the voltage floating range of the power optimizer, otherwise it will cause at least some of the PV modules to drift from the maximum power point when catering to the parallel connection between multiple strings.

[0195] See also Figure 7Based on the above-mentioned distinguishing conditions, the different strings networked by the power optimizer in this article have sufficient layout flexibility, for example, the number of photovoltaic modules used in different strings is allowed to be designed differently. For example, the N and K of the two networked strings PV-string1 and PV-string2 are allowed to be freely and flexibly adjusted. For example, in an optional embodiment, it is assumed that the string PV-string2 uses fewer photovoltaic modules, K<N. At this time, some or all of the DC converters in the DC converter H1-HK only need to fine-tune their so-called preset values. Under this condition, the power optimizer pursuing power optimization has a larger voltage floating range, because the change of the so-called preset value is equivalent to the input and output voltage of the DC converter H1-HK can be flexibly expanded. It can still be guaranteed that different strings have the same string voltage.

[0196] See also Figure 7 In the embodiments of the strings PV-string1 and PV-string2, the principle that the power optimizer pursuing power optimization has a larger voltage floating range is now explained: the horizontal axis GAIN is fine-tuned.

[0197] See also Figure 7 , take the N photovoltaic modules in the string PV-string1 as an example. Figure 5 The power optimizer has a larger voltage floating range. For example, Gain1 = U H1 / U P1 , the preset value Target0_V1 is fine-tuned, because power optimization requires the gain Gain1 to be close to the preset value Target0_V1, and Target0_V1 fine-tuning will change U H1 Similarly, power optimization requires the gain GainN to be close to the preset value Target0_VN. Fine-tuning Target0_VN will change U HN It is obvious that for the DC converter H1-HN corresponding to this string PV-string1, the series voltage U H1 , U H2 ,…U HN This can be done by fine-tuning the GAIN of each of the DC converters H1-HN (in this case, GAIN is, for example, the voltage-based gain GainN of the DC converter HN, etc.). H1 +U H2 +…U HN This fine-tuning action occurs during local power optimization and also during global power optimization, and SysP is still optimizing.

[0198] See also Figure 7 , taking the K photovoltaic modules of the string PV-string2 as an example. Figure 5The same principle applies to the DC converter H1-HK corresponding to the string PV-string2, the series voltage U H1 , U H2 ,…U HK This can be done by fine-tuning the GAIN of each of the DC converters H1-HK (in this case, GAIN is, for example, the voltage-based gain GainK of the DC converter HK). H1 +U H2 +…U HK The target voltage can be reached. This fine-tuning action occurs during the local power optimization and the global power optimization. SysP is still optimizing. H1 +U H2 +…U HN and U H1 +U H2 +…U HK The fact that the number of PV modules in different strings is the same or different does not affect the tracking of the power optimization point POP, nor does it affect the tracking of the overall power SysP of the photovoltaic system at the system level.

[0199] See also Figure 7 As explained above, the power optimizer in this paper is to pursue the optimal power processing of photovoltaic modules at the photovoltaic module end such as PVN (under the optimal processing I PVN Multiply by V PVN The result of the optimal power processing is to obtain the power optimization point POP. The DC converter HN (N = 1, 2, 3 ...) can continuously maintain the corresponding photovoltaic module PVN in a power optimization state when freely configuring the output voltage and input voltage.

[0200] See also Figure 7 Based on the above-mentioned distinguishing conditions, the advantages of the present application include: when strings of different lengths are connected in parallel, the preset value Target0 of each DC converter can be flexibly set to achieve parallel matching (the preset value Target0 is, for example, the preset value Target0_V1 to Target0_VN or Target0_I1 to Target0_IN recorded above).

[0201] See also Figure 7 , through the coordinated cooperation of global and local power optimization, when the gain of any DC converter such as HN reaches a preset value such as Target0, its corresponding photovoltaic module PVN reaches the power optimization point POP.

[0202] See also Figure 7As mentioned above, the intuitive performance of the optimal power processing of the present application is also reflected in: when the multi-stage DC converters are connected in series, any DC converter HN can flexibly configure its output voltage and input voltage, then the cascade voltage U output by the multi-stage DC converters H1-HN H1 +U H2 +…U HN There will be considerable flexibility, and the free expansion of the string voltage will not affect the power optimization point POP tracking of the multi-level DC converter H1-HN.

[0203] See also Figure 2 In contrast, traditional power optimizers OP1-OPN cannot freely configure the adjustment range of the string voltage in a large range. The way to change the string voltage is either to increase the number of PV modules in the string and the number of paired power optimizers, or to reduce the number of PV modules in the string and the number of paired power optimizers. This requires on-site construction in the PV power station, involving the dismantling and construction of PV modules and power optimizers.

[0204] See also Figure 2 , continue to compare the power optimizer in this article with the traditional power optimizer. It is known that when the traditional power optimizer performs power optimization on the corresponding photovoltaic module PVN (N = 1, 2, 3 ...), it tracks the working current I PVN Multiply it by its operating voltage V PVN The bus voltage is the sum of the output voltages of the power optimizers in series, and the bus current is the sum of the currents flowing through the series structures in parallel. A series structure includes multiple DC converters in series, such as H1-HN or H1-HK. If the inverter INVT frequently adjusts the bus voltage V BUS and bus current I BUS When tracking bus MPPT, the output voltage and output current of the traditional power optimizer are forced to change to cater to the bus voltage V BUS and bus current I BUS The traditional power optimizer OP1-OPN is difficult to reconcile this contradiction.

[0205] See also Figure 7The intuitive performance of the power optimization point POP processing is reflected in the following: when the DC converter HN performs power optimization on the corresponding photovoltaic module PVN (N = 1, 2, 3 ...), it guides the gain of the DC converter HN, such as the Gain mentioned above, to approach the preset value Target0 to implement local optimization of the photovoltaic module PVN. In terms of global power optimization, the inverter INVT will naturally frequently adjust the bus voltage V when it performs maximum power tracking MPPT. BUS and bus current I BUS Tracking the busbar MPPT and striving to push the PV modules PV1-PVN to their respective maximum power points is the essence of MPPT tracking. At the same time, taking the DC converter HN as an example, it will actively guide the gain such as Gain to approach the preset value Target0. Considering the inverter INVT adjusting V BUS and I BUS This is the action required for maximum power tracking. Under this condition, the gain is changed by the optimization behavior of the DC converter HN, so that the U HN and I HN The adjustable power of the inverter INVT meets the MPPT requirements of the inverter. The power tracking MPPT of the inverter and the power optimization of the DC converter HN will naturally not interfere with each other. Instead, the two will achieve a win-win effect of mutual cooperation and promotion, improving the power conversion rate. There is no doubt that this is another manifestation of the mutual coordination and adaptation between the power optimization of the DC converter H1-HN and the MPPT of the inverter INVT.

[0206] See also Figure 7 , analyze the system-level power PysP curve: Assume that the gain Gain = GAIN1 represents that the actual gain of the DC converters H1-HN is lower than the expected preset value Target0, GAIN1 < Target0, even if the power tracking of each string is implemented through the MPPT function of the inverter INVT, the power PysP does not reach the optimal level.

[0207] See also Figure 7 , we still analyze the curve of the overall power PysP: Assuming that the gain Gain=GAIN2 represents that the actual gain of the DC converters H1-HN exceeds the expected preset value Target0, GAIN2>Target0, even if the power tracking of each string is implemented through the MPPT function of the inverter INVT, the power PysP does not reach the optimal level.

[0208] See also Figure 7, we still analyze the curve of the overall power PysP: Assuming that the gain Gain≈Target0 represents that the actual gain of the DC converters H1-HN is close to the expected preset value Target0, PysP is almost maximum, so when the power tracking of each string is implemented through the MPPT function of the inverter INVT, the power PysP is optimized.

[0209] See also Figure 7 In an optional embodiment, the global power optimization and the local power optimization are coordinated so that when the gain of any one of the DC converters H1-HN, such as HN, such as the voltage-based gain GainN or the current-based gain gainN of HN, reaches a preset value Target0 (such as Target0_VN or Target0_IN), it can be basically considered that the photovoltaic component PVN corresponding to the DC converter HN reaches the power optimization point POP.

[0210] See also Figure 7 At present, in distributed or centralized photovoltaic power stations, the problem that needs to be paid attention to is: shadow blocking causes mismatch between many photovoltaic modules. The problem also lies in: the battery output characteristics of photovoltaic modules are reflected in the close relationship between output voltage and output current and external factors such as light intensity and ambient temperature. The uncertainty of external environmental factors causes the maximum output power and the corresponding voltage of the maximum power point to change with the changes of external factors.

[0211] See also Figure 7 In an optional embodiment, when the gain of any one of the DC converters H1-HN, such as HN, reaches a preset value Target0, the power optimization point POP of a photovoltaic component PVN corresponding to any DC converter, such as HN, is the maximum power point MPP under the premise of no shading.

[0212] See also Figure 7 In an optional embodiment, when the gain of any one of the DC converters H1-HN, such as HN, reaches a preset value Target0, a power optimization point POP of a photovoltaic component PVN corresponding to any DC converter, such as HN, is not a maximum power point MPP under the premise of shading.

[0213] See also Figure 7 In an optional embodiment, any DC converter, such as HN, is equipped with a controller 400 for controlling the DC converter HN to perform voltage conversion or current conversion. Figure 6, the controller 400 adjusts the gain (e.g., gain GainN or gain gainN) by changing the duty cycle of the DC converter HN when it is working. Generally, if the DC converter HN is working in the buck state, the duty cycle of the Buck circuit is changed; if the DC converter HN is working in the boost state, the duty cycle of the Boost circuit is changed; if the DC converter HN is working in the buck-boost state, the buck duty cycle and the boost duty cycle of the buck-boost circuit are changed.

[0214] See also Figure 7 In an optional embodiment, the DC converter HN is used to convert the electric energy captured from the photovoltaic module PVN into the output power of the DC converter HN itself, based on the cooperation of performing maximum power point tracking on the string through the inverter INVT and guiding the gain of the DC converter HN to approach the preset value, so as to achieve the purpose of optimizing and increasing the operating power of the photovoltaic module PVN. The gain approaching the preset value includes reducing the difference between the voltage gain and the first type of preset value, or approaching the preset value includes reducing the difference between the current gain and the second type of preset value. There are various schemes for approaching the preset value. For example, the calculation of optimizing the power SP can be implemented for the photovoltaic module PVN, and the scheme for approaching the preset value is as described below. For example, the scheme of optimizing SP = pow / (1+abs(Target0_VN-GainN)×k1) and approaching the voltage-based gain GainN to the first type of preset value Target0_VN can achieve the purpose of optimization. The microprocessor can perform the optimization operation on SP. For example, the optimization of SP = pow / (1+abs(Target0_IN-gainN)×k2) can achieve the optimization purpose by moving the current-based gain N closer to the second type of preset value Target0_IN. The symbol abs in the formula represents the absolute value, and pow represents the power of the photovoltaic module PVN. PVN *V PVN The values ​​of the coefficients k1 and k2 that appear respectively are different, and they represent preset coefficient values ​​that can be set in advance as needed and can be adjusted at any time.

[0215] See also Figure 7 In an optional embodiment, the power SP of the photovoltaic module PVN is still optimized, and the scheme of approaching the preset value is as follows. For example, SP = pow × (1 - (Target0_VN - GainN) Q ×k'1) optimization, the solution of moving the voltage-based gain GainN closer to the first type of preset value Target0_VN can achieve the optimization purpose. The microprocessor can perform optimization operations on SP. For example, SP = pow × (1-(Target0_IN-gainN) Q×k'2) optimization, the scheme of moving the current-based gain gainN closer to the second type of preset value Target0_IN can achieve the optimization purpose. The values ​​of the coefficients k'1 and k'2 that appear respectively are different. The non-zero even superscript Q represents the power symbol or several powers. k'1 and k'2 represent the preset coefficient values ​​that can be set in advance as needed and can be adjusted at any time.

[0216] See also Figure 7 In an optional embodiment, the power SP of the photovoltaic module PVN is still optimized, and the scheme of approaching the preset value is as follows. For example, SP = pow / (1+(Target0_VN-GainN) Q ×k3) optimization, the solution of moving the voltage-based gain GainN closer to the first type of preset value Target0_VN can achieve the optimization purpose. The microprocessor can perform optimization operations on SP. For example, SP = pow / (1+(Target0_IN-gainN) Q ×k4) optimization, the scheme of moving the current-based gain gainN closer to the second type of preset value Target0_IN can achieve the optimization purpose. The values ​​of the coefficients k3 and k4 that appear respectively are different. The non-zero even superscript Q represents the power symbol or several powers. k3 and k4 represent the preset coefficient values ​​that can be set in advance as needed and can be adjusted at any time. The calculation of the optimized power SP can still use the traditional conductivity increment method or perturbation observation method and similar optimization methods to track the maximum value of SP.

[0217] See also Figure 7 In an optional embodiment, the previous operating gain will correspond to the previous SP value. If the previous operating gain is increased to the next operating gain, the next operating gain will correspond to the next SP value. Assuming that the traditional perturbation observation method is used and the next SP value is increased compared to the previous SP value, the operating gain will continue to be increased. Otherwise, the perturbation direction is changed, such as reducing the DC converter operating gain. This process can be repeated until the optimized power SP is maximized.

[0218] See also Figure 7In an optional embodiment, when a DC converter such as HN is actually running, it does not actually know what the corresponding gain is when the corresponding photovoltaic component PVN or itself is at maximum power output, because the DC converter does not actually perform MPPT. Therefore, the tracking method for adjusting SP by the DC converter HN can have the above-mentioned or more implementation methods, which have a common goal: to make its gain (such as GainN or gainN) close to or close to or approximately equal to the expected preset value. Or make the gain close to or close to or approximately equal to the expected preset value required when the photovoltaic component PVN is at the power optimization point POP, for example, by means of the MPPT function of the photovoltaic inverter INVT, that is, global power optimization and by means of local local power optimization. It is worth noting that even if the gain cannot reach the preset value Target0, as long as the gain of the DC converter is guided to approach the preset value, such as reducing the difference between the voltage gain and the first type of preset value or reducing the difference between the current gain and the second type of preset value, it meets the expectation of this application: that is, the purpose of increasing and optimizing the operating power of the photovoltaic component. Therefore, even if the power optimization point POP cannot be reached, it is allowed. Whether the PV module reaches its power optimization point is not a necessary restriction for power control or power optimization.

[0219] See also Figure 8 In an optional embodiment, the present application relates to a power control method for implementing hierarchical power optimization for photovoltaic modules. In the front-stage power optimization, the gains of the DC converters H1-HN used for power conversion of the photovoltaic modules PV1-PVN (e.g., series gain values ​​Gain1, Gain2, ... GainN) are guided to approach their respective corresponding preset values ​​(e.g., series preset values ​​Target0_V1, Target0_V2, ... Target0_VN). Or the gains of the DC converters H1-HN (e.g., series gain values ​​gain1, gain2, ... gainN) are approached to their respective corresponding preset values ​​(e.g., series preset values ​​Target0_I1, Target0_I2, ... Target0_IN). In the back-stage power optimization, the inverter INVT performs maximum power point tracking, i.e., MPPT, on the strings of multiple photovoltaic modules PV1-PVN connected in series, and the multiple photovoltaic modules corresponding to a group of multi-stage DC converters H1-HN connected in series are regarded as a string PV-string1. Of course, more strings such as PV-string2 can be connected. Through the pre-stage power optimization and post-stage power optimization, when the gain of any DC converter such as HN reaches the preset value, the corresponding PV module reaches the power optimization point POP. The pre-stage power optimization is the optimization seen from the PV module locally, and the post-stage power optimization is the optimization seen from the inverter INVT.

[0220] See also Figure 8, if the DC converter such as HK is set to a so-called preset value based on voltage, such as Figure 6 The voltage sensors 111 and 113 shown collect the input voltage and output voltage of HK respectively, and the controller 400 such as a microprocessor calculates the actual gain of the output voltage and the input voltage from the voltage data collected by these voltage sensors 111 and 113. For example, the microprocessor collects the working current of the photovoltaic component through the current sensor 112, and calculates the power of the photovoltaic component PVK according to the working current and working voltage of the photovoltaic component PVK. When driving the DC converter HK, the microprocessor can adjust the actual gain of its output voltage and input voltage to approach the preset value Target0_VK.

[0221] See also Figure 8 , if the DC converter such as HK is set based on the so-called preset value of current, such as Figure 6 The current sensors 112 and 114 shown collect the input current and output current of HK respectively, and the controller 400 such as a microprocessor calculates the actual gain of the output current and the input current from the current data collected by these current sensors 112 and 114. For example, the microprocessor collects the working voltage of the photovoltaic component through the voltage sensor 111, and calculates the power of the photovoltaic component PVK according to the working current and working voltage of the photovoltaic component PVK. When driving the DC converter HK, the microprocessor can adjust the actual gain of its output current and input current to approach the preset value Target0_IK.

[0222] See also Figure 8 As mentioned above, the DC converter such as HN does not actually perform MPPT, so it does not know what the gain of the DC converter such as HN should be when the corresponding photovoltaic module PVN is at the maximum power point, i.e., the MPP point. If the preset value is set to Figure 8 It is obvious that the photovoltaic module is optimized according to the power voltage curve CVN from the inverter INVT of the rear power optimization end, so as to assist the front power optimization end, i.e., the DC converter HN, and push the photovoltaic module PVN to the MPP point. In contrast, if the preset value is improved to Figure 8 Another value Target2 in the PV module, under this condition, the power situation of the PVN PV module is slightly better, but it is still necessary to optimize from the inverter INVT at the rear power optimization end, so as to assist the DC converter HN, i.e. the front power optimization end, to push the PV module PVN to the MPP point. After comparing Target1 and Target2, it can be learned that the local optimization of the PV module can only partially improve the power situation. Preferably, it is necessary to perform maximum power point tracking on the string through the inverter INVT and guide the gain of the DC converter HN to the preset value, so as to achieve the purpose of optimizing and increasing the operating power of the PV module PVN.

[0223] See also Fig. 9 , the inverter INVT can be replaced with a DC conversion device with an MPPT function. The DC conversion device includes, for example, a DC / DC converter and the aforementioned DC converter. Conventional Buck, Boost, Buck-Boost, cuk and other conversion circuits are typical examples of DC conversion devices. In an optional example, a DC converter H1-HN is used to implement DC to DC power conversion on the photovoltaic module. The multi-level DC converters H1-HN are connected in parallel or in series. A DC conversion device with an MPPT function that replaces the inverter is used to implement DC to DC power conversion on the total output power provided by the multi-level DC converter H1-HN. In terms of global power optimization, the output power provided by the parallel or series DC converters H1-HN is tracked to the maximum power point by using a DC conversion device that replaces the inverter INVT. In terms of local power optimization, the gains of the DC converters H1-HN are guided to approach the corresponding preset values. Based on the coordinated cooperation of global power optimization and local power optimization, the purpose of increasing and optimizing the operating power of the photovoltaic module is achieved together. Note that the DC conversion device not shown in the figure is used to replace the inverter INVT in the figure of this application. The inverter INVT usually converts the DC power on the DC bus into AC power, and the DC conversion device that replaces the inverter INVT converts the DC power on the DC bus into another form of DC power, such as DC power with a voltage / current different from that of the DC bus, that is, the DC conversion device is used to implement DC to DC power conversion on the output power provided by the multi-stage DC converter H1-HN, but it is worth noting that at this time, the MPPT function of the inverter INVT, etc. needs to be transplanted to the DC conversion device.

[0224] See also Fig. 9 In an optional embodiment, the multi-level DC converters H1-HN are connected in parallel, and the inverter INVT is still used to perform power conversion on the output power provided by the multi-level DC converters H1-HN. As mentioned above, the inverter INVT has a maximum power tracking MPPT function, and the inverter INVT performs maximum power tracking on the multiple photovoltaic components PV1-PVN corresponding to the parallel multi-level DC converters H1-HN as a whole. This is different from the series connection of the multi-level DC converters mentioned above. In addition, the DC converters H1-HK are also connected in parallel, and the inverter INVT is still used to perform power conversion on the output power provided by the multi-level DC converters H1-HK. As mentioned above, the inverter INVT has a maximum power tracking MPPT function, and the inverter INVT performs maximum power tracking on the multiple photovoltaic components PV1-PVK corresponding to the parallel multi-level DC converters H1-HK as a whole. In the parallel relationship, the two output ends of each DC converter are respectively coupled to the bus LA and the bus LB.

[0225] See also Fig. 9 , except that the series architecture is changed to parallel architecture, this embodiment and Figure 5 Similarly, for example, by trying to reduce the difference between the gain of the DC converter and the corresponding preset value, the photovoltaic module can be locally optimized. In some cases, only a few of the gains of the DC converters in the system can work at their preset value positions, or in other words, the gains of most or even all DC converters cannot work completely at their preset value positions, but this does not affect the power optimization implemented by this application for individual photovoltaic modules and the power optimization implemented for the entire photovoltaic system. Therefore, this article implements power optimization for photovoltaic modules by guiding the gain of the DC converter to approach the corresponding preset value, which means that the situation where the gain of the DC converter is not equal to the preset value is allowed. In an optional embodiment, the difference between the gain and the preset value does not exceed a predetermined critical value or is within a predetermined setting range, and it is considered that the power optimization of the photovoltaic module is achieved. Or in other optional embodiments, the gain of the DC converter and the corresponding preset value have a previous difference at present, and the gain of the DC converter continues to approach the preset value. After they have the next difference, the power of the photovoltaic module under the next difference is larger than the power of the photovoltaic module under the previous difference, and it is considered that the power optimization of the photovoltaic module is achieved. Based on the condition of the previous difference, the DC converter gain approaches the corresponding preset value, so the next difference is less than the previous difference. The above examples are actually in line with the main purpose of this application, that is, by guiding the DC converter gain to approach the preset value, implementing power optimization on the photovoltaic component or increasing the power of the photovoltaic component. The above examples can still best optimize the power SysP.

[0226] See also Fig. 9 In an optional embodiment, the DC converter H1-HN performs DC to DC power conversion on the photovoltaic components PV1-PVN. The multi-level DC converters H1-HN are connected in parallel. An inverter INVT is used to perform DC to AC power conversion on the total output power provided by the multi-level DC converters H1-HN. In terms of global power optimization, the inverter INVT performs maximum power point tracking on the output power provided by each parallel DC converter H1-HN, for example, performing maximum power point tracking at the DC bus LA-LB. In terms of local power optimization, the gains of each DC converter H1-HN are guided to approach the corresponding preset values. Based on the coordinated cooperation of global power optimization and local power optimization, the purpose of increasing and optimizing the operating power of photovoltaic components such as PV1-PVN is achieved together.

[0227] See also Fig. 9In an optional embodiment, the photovoltaic system includes a DC converter H1-HN for implementing DC to DC power conversion for the photovoltaic modules PV1-PVN, and the photovoltaic system also includes an inverter INVT, and the multi-level DC converters H1-HN connected in parallel supply power to the inverter INVT. The photovoltaic system performs maximum power point tracking based on the total output power provided by each DC converter H1-HN through the inverter INVT, and the photovoltaic system guides the respective gains of the DC converters H1-HN to approach the corresponding preset values, thereby jointly achieving the purpose of optimizing and increasing the operating power of the photovoltaic modules.

[0228] See also Fig. 9 In an optional embodiment, hierarchical power optimization is implemented for the photovoltaic modules PV1-PVN. In the front-stage power optimization, the gains of the DC converters H1-HN used to implement power conversion for the photovoltaic modules PV1-PVN are guided to approach the corresponding preset values. In the back-stage power optimization, the inverter INVT performs maximum power point tracking on the total output power provided by the DC converters H1-HN connected in parallel. Through the front- and back-stage power optimization, when the gain of any DC converter such as HN reaches the preset value, the corresponding photovoltaic module PVN reaches the power optimization point.

[0229] The above description and drawings provide typical embodiments of specific structures of specific embodiments, and the above invention provides existing preferred embodiments, but these contents are not intended to be limiting. For those skilled in the art, various changes and modifications will undoubtedly be obvious after reading the above description. Therefore, the attached claims should be regarded as covering all changes and modifications to the true intent and scope of the present invention. Any and all equivalent scopes and contents within the scope of the claims should be considered to still be within the intent and scope of the present invention.

Claims

1. A power control method, characterized in that: include: Using a DC converter to perform DC to DC power conversion on photovoltaic modules; The multi-level DC converters are connected in series, and a plurality of photovoltaic modules corresponding to a group of multi-level DC converters connected in series are regarded as a group string; Using an inverter to convert the output power provided by the multi-level DC converter from DC to AC; In terms of global power optimization, the maximum power point tracking of the strings is performed through the inverter; In terms of local power optimization, the gain of the DC converter is guided to approach the preset value; Based on the coordinated cooperation of global power optimization and local power optimization, the goal of increasing and optimizing the operating power of photovoltaic modules can be achieved together.

2. The method according to claim 1, characterized in that: The DC converter is equipped with a microprocessor for driving the DC converter to perform voltage or current conversion. The microprocessor adjusts the gain by changing the duty cycle of the DC converter when it is working so as to make it close to the preset value.

3. The method according to claim 1, characterized in that: The multi-stage DC converters connected in series form a series branch, which supplies power to the inverter. The magnitude of the series voltage provided by the series branch is adjusted by changing the preset value.

4. The method according to claim 1, characterized in that: The DC converter is selected from any one of a buck converter, a boost converter, and a buck-boost converter.

5. The method according to claim 1, characterized in that: The gain moving closer to the preset value comprises reducing the difference between the voltage gain and the preset value; or The gain moving closer to the preset value includes reducing the difference between the current gain and the preset value.

6. A power control method, characterized in that: include: Using a DC converter to perform DC to DC power conversion on photovoltaic modules; Connecting multiple DC converters in parallel or in series; Using an inverter to convert the output power provided by the multi-level DC converter from DC to AC; In terms of global power optimization, the maximum power point tracking is performed on the output power provided by each DC converter connected in parallel or in series through the inverter; In terms of local power optimization, the gain of the DC converter is guided to approach the preset value; Based on the coordinated cooperation of global power optimization and local power optimization, the goal of increasing and optimizing the operating power of photovoltaic modules can be achieved together.

7. A photovoltaic system, characterized in that: include: A DC converter, used for performing DC to DC power conversion on the photovoltaic modules, wherein a plurality of photovoltaic modules corresponding to a group of multi-stage DC converters connected in series are regarded as a group string; Inverter, which is powered by a multi-level DC converter connected in series; By performing maximum power point tracking on the strings through the inverter and guiding the gain of the DC converter to approach the preset value, the goal of optimizing and increasing the operating power of the PV panels is achieved.

8. The photovoltaic system according to claim 7, characterized in that: The gain includes a voltage gain or a current gain.

9. The photovoltaic system according to claim 7, characterized in that: The multi-level DC converters connected in series form a series branch, and the multiple series branches connected in parallel supply power to the same inverter.

10. The photovoltaic system according to claim 9, characterized in that: The preset values ​​corresponding to different series-connected branches with unequal numbers of DC converters are also set to be different.

11. The photovoltaic system according to claim 10, characterized in that: The preset value of the DC converter corresponding to the series-connected branch with a small number of DC converters is set to be larger than the preset value of the DC converter corresponding to the series-connected branch with a large number of DC converters.

12. The photovoltaic system according to claim 9, characterized in that: Among the multi-stage DC converters corresponding to any series-connected branch, the preset values ​​of different DC converters are set to be different or the same.

13. A photovoltaic system, characterized in that: include: A DC converter, used for performing DC to DC power conversion on the photovoltaic module; An inverter, which is powered by a multi-level DC converter connected in parallel; Based on the maximum power point tracking of the output power provided by each DC converter through the inverter, and by guiding the gain of the DC converter to approach the preset value, the purpose of optimizing and increasing the operating power of the photovoltaic module is achieved together.

14. A power control method, characterized in that: Implement hierarchical power optimization for photovoltaic modules, including: In the front-stage power optimization, the gain of the DC converter used to implement power conversion for the photovoltaic module is guided to approach the preset value; In the post-stage power optimization, the inverter performs maximum power point tracking on a string of multiple PV modules connected in series, and multiple PV modules corresponding to a group of multi-level DC converters connected in series are regarded as one string; Through power optimization of the previous and next stages, when the gain of any DC converter reaches a preset value, the corresponding photovoltaic module reaches the power optimization point.

15. The method according to claim 14, characterized in that: The DC converter is equipped with a microprocessor for driving the DC converter to perform voltage or current conversion. The microprocessor adjusts the gain by changing the duty cycle of the DC converter so that the gain approaches a preset value.

16. A power control method, characterized in that: Implement hierarchical power optimization for photovoltaic modules, including: In the front-stage power optimization, the gain of the DC converter used to implement power conversion for the photovoltaic module is guided to approach the preset value; In the post-stage power optimization, the inverter performs maximum power point tracking on the output power provided by each DC converter connected in parallel; Through power optimization of the previous and next stages, when the gain of any DC converter reaches a preset value, the corresponding photovoltaic module reaches the power optimization point.

17. A power control method, characterized in that: include: Using a DC converter to perform DC to DC power conversion on photovoltaic modules; Connecting multiple DC converters in parallel or in series; Using a DC conversion device to perform DC to DC power conversion on the output power provided by the multi-stage DC converter; In terms of global power optimization, the output power provided by each DC converter connected in parallel or in series is tracked by the DC conversion device to perform maximum power point tracking; In terms of local power optimization, the gain of the DC converter is guided to approach the set value; Based on the coordinated cooperation of global power optimization and local power optimization, the goal of increasing and optimizing the operating power of photovoltaic modules can be achieved together.

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