A method and system for maximum power tracking of photovoltaic direct-drive heating

Abstract

The present invention relates to the field of photovoltaic modules and discloses a method and system for maximum power tracking of photovoltaic direct-drive heating, comprising: obtaining electrical parameters of the photovoltaic module; determining a matching degree based on the output power and the maximum output power; determining a load resistance matching coefficient interval of the external circuit of the photovoltaic module based on the matching degree; determining a load resistance matching interval based on the load resistance matching coefficient interval and the internal resistance; and determining a load voltage matching coefficient interval of the external circuit of the photovoltaic module based on the matching degree. The present invention obtains detailed electrical parameters and optimizes the selection of load voltage and resistance in combination with the matching degree, thereby more accurately finding the maximum power point and improving the energy efficiency of the system; and by adjusting the load resistance and voltage matching interval in real time according to the output power of different photovoltaic modules and environmental changes, it ensures that the system can always maintain a state close to the maximum power point under different light intensity or temperature conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic modules, and in particular to a method and system for maximum power tracking applied to photovoltaic direct-drive heating. Background Art

[0002] In the field of new energy technologies, Maximum Power Point Tracking (MPPT) technology is particularly important. Its purpose is to achieve maximum power output in various situations. It has been widely used in photovoltaic power plant systems connected to the power grid, and has also been well applied in photovoltaic power generation systems.

[0003] Photovoltaic direct drive technology is a technology that directly applies photovoltaic electricity. It is currently mainly used in photovoltaic direct drive heating systems and photovoltaic direct drive air source heat pump systems. Because it does not require inverters and power storage, it reduces losses during energy conversion and improves energy efficiency. It also has advantages such as simple structure, low cost, and easy maintenance, and is increasingly attracting attention from the industry.

[0004] Application No. 202110008621.4 uses big data technology and mathematical statistics methods to introduce the matching factor α to give the optimal matching algorithm for photovoltaic direct-driven resistive loads. Combined with application Nos. 202420125069.6, ZL202420059313.3 and ZL202420188318.6, it has been successfully used in photovoltaic water heater stand-alone mode and centralized household mode; however, this matching algorithm maximizes the power generated by photovoltaic power on the load resistance within a day by configuring a suitable load resistance, and does not achieve the tracking of the maximum power point, that is, the photovoltaic power is not utilized to the greatest extent; Application No. 202220239498.7 only gives a "variable load concept" without any theoretical basis or implementation method; Application No. 202010057626.1 gives a relatively cumbersome photovoltaic water heater performance detection method. Although it includes efficiency detection, it does not involve how to improve efficiency. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for maximum power tracking of photovoltaic direct-drive heating, comprising:

[0006] Obtaining electrical parameters of the photovoltaic module; wherein the electrical parameters include output power, maximum output power, internal resistance, open circuit voltage, short circuit current, and voltage at maximum power; determining a matching degree based on the output power and the maximum output power;

[0007] Determine the load resistance matching coefficient interval of the external circuit of the photovoltaic module based on the matching degree; determine the load resistance matching interval based on the load resistance matching coefficient interval and the internal resistance; determine the load voltage matching coefficient interval of the external circuit of the photovoltaic module based on the matching degree; and determine the load voltage matching interval based on the load voltage matching coefficient interval and the voltage at maximum power.

[0008] Preferably, the method further comprises:

[0009] Setting a voltage adjustment direction of the power converter so that the input voltage of the power converter changes in a positive trend or a negative trend; detecting the input voltage and input current of the power converter at a first moment, calculating a first power, and recording a first input voltage value corresponding to the first power;

[0010] detecting an input voltage and an input current of the power converter at a second moment, calculating a second power, and recording a second input voltage value corresponding to the second power;

[0011] detecting an input voltage and an input current of the power converter at a third moment, calculating a third power, and recording a third input voltage value corresponding to the third power;

[0012] When the first power, the second power, and the third power satisfy a continuously decreasing relationship, and the third input voltage value is outside the load voltage matching interval, changing the voltage adjustment direction to reverse the change trend of the input voltage;

[0013] When the first power, the second power, and the third power satisfy a continuously decreasing relationship, and the third input voltage value is within the load voltage matching interval, maintaining the voltage adjustment direction unchanged, and updating the voltage at maximum power based on the current irradiance;

[0014] When the first power, the second power, and the third power satisfy a continuously increasing relationship, and the third input voltage value exceeds an upper limit of the load voltage matching interval, changing the voltage adjustment direction, detecting the input voltage and input current at a fourth moment, calculating a fourth power, and recording a fourth input voltage value corresponding to the fourth power;

[0015] When the fourth input voltage value is not greater than the open-circuit voltage and the fourth power is greater than the third power, the voltage adjustment direction is maintained unchanged.

[0016] Preferably, the method further comprises:

[0017] When it is detected that the short-circuit current change rate of the PV module exceeds the preset threshold, the current voltage adjustment direction is locked and the direction reversal operation is suspended until the short-circuit current stabilizes and tracking is restarted;

[0018] In response to the voltage adjustment direction being changed, continuously collecting N input powers, and restoring the original voltage adjustment direction when M of the N input powers satisfy the condition that the N input powers are greater than the M input powers and the input voltage value is within the load voltage matching interval; wherein N>3 and M>2;

[0019] When it is detected that the power continues to decrease after the original voltage adjustment direction is restored, the voltage adjustment direction is reversed, and the voltage adjustment step is set to a proportional value based on the open circuit voltage and the voltage at the maximum power.

[0020] Preferably, the method further comprises:

[0021] For a fixed resistance load, the ratio change of the open circuit voltage and the voltage at the maximum power is monitored in real time, and when the ratio change exceeds a preset range, the voltage adjustment direction is triggered to reverse;

[0022] For adjustable resistance loads, when the input power is detected to be lower than the preset efficiency threshold, the load resistance is dynamically adjusted to the load resistance matching range;

[0023] For segmented load regulation, when it is detected that the input voltage exceeds a preset segment threshold, it switches to the adjacent resistance segment and reinitializes the voltage adjustment direction; wherein, the segment threshold is dynamically optimized based on historical power data.

[0024] Preferably, the method further comprises:

[0025] Compare the ratio of the current power to the historical maximum power in real time. When the ratio is lower than a preset value, start the global scan mode, adjust the input voltage bidirectionally with a preset step size, and record the maximum power point.

[0026] In response to a power rising edge detected in the global sweep mode, the sweep is immediately terminated and restored to the normal tracking mode, while retaining the power extreme point data obtained during the sweep process;

[0027] By integrating ambient light sensor data, when a sudden change in irradiance is detected, the voltage adjustment direction is temporarily frozen and the current operating point is maintained until the irradiance stabilizes and the tracking parameters are reinitialized.

[0028] Preferably, the calculation formula of the load resistance matching coefficient interval is as follows:

[0029] ;

[0030] in, Indicates the load resistance matching coefficient range, Indicates the degree of matching.

[0031] Preferably, the calculation formula of the load resistance matching interval is as follows:

[0032] ;

[0033] in, Indicates the load resistance matching range, Indicates internal resistance.

[0034] Preferably, the calculation formula of the load voltage matching coefficient interval is as follows:

[0035] ;

[0036] in, Indicates the load voltage matching coefficient range.

[0037] Preferably, the calculation formula of the load voltage matching interval is as follows:

[0038] ;

[0039] in, Indicates the load voltage matching range, Indicates the voltage at maximum power.

[0040] A system for maximum power point tracking of photovoltaic direct-drive heating, which is applicable to the above-mentioned method for maximum power point tracking of photovoltaic direct-drive heating, comprises:

[0041] a matching determination unit, the matching determination unit being configured to obtain electrical parameters of the photovoltaic module; wherein the electrical parameters include output power, maximum output power, internal resistance, open circuit voltage, short circuit current, and voltage at maximum power; and determining a matching degree based on the output power and the maximum output power;

[0042] an interval determination unit, the interval determination unit being configured to determine a load resistance matching coefficient interval of an external circuit of the photovoltaic assembly based on the matching degree; determine a load resistance matching interval based on the load resistance matching coefficient interval and the internal resistance; determine a load voltage matching coefficient interval of the external circuit of the photovoltaic assembly based on the matching degree; and determine a load voltage matching interval based on the load voltage matching coefficient interval and the voltage at maximum power;

[0043] a power conversion unit configured to set a voltage adjustment direction of a power converter so that an input voltage of the power converter changes in a positive or negative trend; detect an input voltage and an input current of the power converter at a first moment, calculate a first power, and record a first input voltage value corresponding to the first power;

[0044] An interval tracking unit is configured to detect the input voltage and input current of the power converter at a second moment, calculate a second power, and record a second input voltage value corresponding to the second power; detect the input voltage and input current of the power converter at a third moment, calculate a third power, and record a third input voltage value corresponding to the third power; and change the voltage adjustment direction to reverse the changing trend of the input voltage when the first power, the second power, and the third power satisfy a continuously decreasing relationship and the third input voltage value is outside the load voltage matching interval.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The present invention optimizes the selection of load voltage and resistance by obtaining detailed electrical parameters and combining them with matching, thereby finding the maximum power point more accurately and improving the energy efficiency of the system. Furthermore, the load resistance and voltage matching interval are adjusted in real time according to the output power of different photovoltaic modules and environmental changes, thereby ensuring that the system can always remain close to the maximum power point under different light intensity or temperature conditions, thereby avoiding power loss caused by environmental changes. Furthermore, by dynamically adjusting the matching interval of the external circuit according to the actually measured electrical parameters, the matching between the photovoltaic module and the load can be optimized.

[0047] (2) By detecting the input voltage, current, and power at multiple moments, the present invention can accurately track the power change trend and timely adjust the voltage adjustment direction when the power continuously decreases or increases. This enables the system to dynamically adapt to different working environments, avoids power loss, and ensures that the photovoltaic system always operates at a position close to the maximum power point. Moreover, by setting the voltage adjustment direction and real-time adjustment strategy, the method automatically tracks the maximum power point and responds to environmental changes, which improves the system's automation level and reduces the need for human intervention and adjustment.

[0048] (3) The present invention can suspend the voltage reversal operation when the short-circuit current change rate of the photovoltaic module exceeds a threshold, and restart the tracking after the short-circuit current stabilizes, effectively avoiding system instability caused by electrical fluctuations. Moreover, when the power ratio is detected to be lower than a preset value, the method starts a global scanning mode, automatically adjusts the voltage and searches for the maximum power point. At the same time, it can respond to sudden environmental changes and avoid system performance degradation caused by sudden environmental changes. The scanning mode helps the system find a new maximum power point and quickly resumes normal mode when a power increase is detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 PV curves of photovoltaic modules under different irradiances in one embodiment of the present invention;

[0050] Figure 2 In one embodiment of the present invention, the function Relationship diagram with matching degree, load resistance matching coefficient range and load resistance matching range;

[0051] Figure 3 A table showing resistance matching coefficient intervals and voltage matching coefficient intervals under different power matching degrees in one embodiment of the present invention;

[0052] Figure 4 A structural diagram of an energy storage capacitor implementing maximum power interval tracking in one embodiment of the present invention;

[0053] Figure 5 This is a control logic diagram of a fixed load in one embodiment of the present invention;

[0054] Figure 6 This is a control logic diagram for continuously adjusting loads in one embodiment of the present invention;

[0055] Figure 7 This is a control logic diagram of a system capable of adjusting load resistance in sections according to an embodiment of the present invention;

[0056] Figure 8 This is a topological diagram of a parallel multi-heating unit system in one embodiment of the present invention;

[0057] Figure 9 A schematic flow chart of the steps of the overall method in one embodiment of the present invention;

[0058] Figure 10 FIG. 1 is a schematic diagram of the system architecture of the overall system in one embodiment of the present invention.

[0059] In the figure: 1. Match determination unit; 2. Interval determination unit. DETAILED DESCRIPTION

[0060] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] For example 1, please refer to Figure 1-Figure 3 as well as Figure 9 The present invention provides a technical solution: a method for maximum power tracking applied to photovoltaic direct-drive heating, comprising:

[0062] S1. Obtain electrical parameters of the photovoltaic module, wherein the electrical parameters include output power, maximum output power, internal resistance, open circuit voltage, short circuit current, and voltage at maximum power; determine the matching degree based on the output power and maximum output power;

[0063] S2. Determine the load resistance matching coefficient interval of the external circuit of the photovoltaic module based on the matching degree; determine the load resistance matching interval based on the load resistance matching coefficient interval and the internal resistance; determine the load voltage matching coefficient interval of the external circuit of the photovoltaic module based on the matching degree; determine the load voltage matching interval based on the load voltage matching coefficient interval and the voltage at maximum power.

[0064] It should be noted that there are four core parameters for photovoltaic modules: maximum power , voltage at maximum power , open circuit voltage , short-circuit current These parameters are based on the standard ambient temperature and 1000 These four parameters are particularly important and must be calibrated by photovoltaic module manufacturers according to regulations. Figure 1 According to the PV curve of the photovoltaic module, we know the three characteristics of the photovoltaic module: the first characteristic is that the maximum output power of the photovoltaic module is basically proportional to the irradiance acting on the photovoltaic module; the second characteristic is that the voltage at the maximum power point increases with the decrease of the irradiance acting on the photovoltaic module, but the increase is Not big; characteristic three is open circuit voltage As the irradiance acting on the photovoltaic modules decreases, the reduction rate compared to is much larger, and as the irradiance acting on the photovoltaic modules decreases, and Gradually approaching equality; characteristic 1 reflects the importance of photovoltaic direct drive applications, and characteristics 2 and 3 provide the core basis for maximum power point tracking in photovoltaic direct drive; because the photovoltaic direct drive system is a closed circuit, according to Ohm's law of closed circuit, the current in the circuit can be expressed as:

[0065] ;

[0066] in, represents the current in the circuit, is the electromotive force of the power supply, Represents the external circuit resistance, Indicates the internal resistance of the power supply;

[0067] Power supply output power It can be expressed as current With the terminal voltage The product of , that is:

[0068] ;

[0069] Due to the terminal voltage Equal to electromotive force Subtract internal resistance The voltage drop across is:

[0070] ;

[0071] The terminal voltage Substituting the expression into the output power formula, we get:

[0072] ;

[0073] Substituting the current expression into the above formula, the output power of the closed circuit power supply can be obtained after simplification: The expression:

[0074] ;

[0075] At any given moment, the irradiance acting on this photovoltaic module is constant, so the electromotive force Can be regarded as a constant, internal resistance It can also be regarded as a constant. At this time, its output power Can be regarded as only with external resistance Related functions ,Right now:

[0076] ;

[0077] In order to find the maximum output power at this moment ,right about Find the derivative and let its derivative , which can be solved as hour, Reaching the maximum value, the maximum output power for:

[0078] ;

[0079] In summary, in a photovoltaic direct drive system, the output power of the component and its electromotive force , external circuit load resistance and component internal resistance When the external circuit load resistance and component internal resistance When the power output is equal to the power output, the efficiency is the highest. Based on this conclusion, the maximum power of the four core parameters of the photovoltaic module can be calculated. , voltage at maximum power , open circuit voltage , short-circuit current , we can get the other three parameters of the photovoltaic module, namely the working current of the photovoltaic module at the maximum power point , the internal resistance and external resistance of the volt component at the maximum power point .

[0080] The so-called maximum power point tracking of photovoltaic direct drive system is nothing more than adjusting the load resistance of the external circuit , tracking the internal circuit resistance that changes with irradiance , make them equal or as close as possible. Output power matching Not only does it reflect the internal resistance With external resistance Matching relationship, resistance matching coefficient interval calculated according to λ It is the range of adjusting external resistance to achieve maximum power tracking, and according to Calculated voltage matching coefficient range This provides a basis for determining how to adjust through voltage detection.

[0081] According to the characteristics of photovoltaic modules, for different irradiances acting on photovoltaic modules, ,and , maximum output power It can be expressed as:

[0082] ;

[0083] According to the second and third characteristics of photovoltaic modules, compared to Very small, and increases only with decreasing irradiance, at a given power matching Finally, for some applications, As the maximum power point voltage , calculate the voltage matching coefficient interval , thus obtaining the maximum power tracking voltage range Since the irradiance is less than 1000 in normal environment , for some applications, you can also As the maximum power tracking voltage range, as long as the actual voltage detected is within this range, the output power efficiency can be guaranteed to be no less than .

[0084] Compared with traditional technology, the power point tracking is changed to power range tracking. A photovoltaic array is composed of The same parameters of the photovoltaic modules, each PV panels form a series group. The groups are connected in series and then in parallel to form a photovoltaic array.

[0085] Obviously, for a photovoltaic array, the four parameters of the maximum power of a photovoltaic panel component are , voltage at maximum power , open circuit voltage , short-circuit current , the four core parameters of the photovoltaic array can be obtained:

[0086] Maximum power: ;

[0087] Voltage at maximum power: ;

[0088] Open circuit voltage: ;

[0089] Short-circuit current: ;

[0090] Since they are all multiple relationships, all the conclusions of this application are applicable not only to single photovoltaic panel components of any parameters, but also to any photovoltaic array.

[0091] For photovoltaic direct drive systems, the load R can be divided into three categories: the first category is the load R with a fixed resistance, such as photovoltaic water heaters, photovoltaic heaters, etc.; the second category is the load R whose resistance can be continuously or nearly continuously adjusted, such as various DC variable frequency loads; the third category is the load R whose resistance can be adjusted in sections, such as electric boiler systems, electric drying systems, electric steam generator systems, etc.

[0092] In an optional embodiment, the method further includes:

[0093] When the first power, the second power, and the third power satisfy a continuously decreasing relationship, and the third input voltage value is within the load voltage matching interval, the voltage adjustment direction is maintained unchanged, and the voltage at maximum power is updated based on the current irradiance;

[0094] When the first power, the second power, and the third power satisfy a continuously increasing relationship, and the third input voltage value exceeds an upper limit of the load voltage matching interval, changing the voltage adjustment direction, detecting the input voltage and the input current at a fourth moment, calculating a fourth power, and recording a fourth input voltage value corresponding to the fourth power;

[0095] When the fourth input voltage value is not greater than the open-circuit voltage and the fourth power is greater than the third power, the voltage adjustment direction is maintained unchanged.

[0096] In an optional embodiment, the method further includes:

[0097] Setting a voltage adjustment direction of the power converter so that the input voltage of the power converter changes in a positive trend or a negative trend; detecting the input voltage and input current of the power converter at a first moment, calculating a first power, and recording a first input voltage value corresponding to the first power;

[0098] detecting an input voltage and an input current of the power converter at a second moment, calculating a second power, and recording a second input voltage value corresponding to the second power;

[0099] detecting an input voltage and an input current of the power converter at a third moment, calculating a third power, and recording a third input voltage value corresponding to the third power;

[0100] When the first power, the second power, and the third power satisfy a continuously decreasing relationship, and the third input voltage value is outside the load voltage matching interval, changing the voltage adjustment direction to reverse the change trend of the input voltage;

[0101] When it is detected that the short-circuit current change rate of the PV module exceeds the preset threshold, the current voltage adjustment direction is locked and the direction reversal operation is suspended until the short-circuit current stabilizes and tracking is restarted;

[0102] In response to the change in voltage adjustment direction, continuously collect N input powers. When M of the N input powers satisfy the condition that the N input powers are greater than the M input powers, and the input voltage value is within the load voltage matching range, restore the original voltage adjustment direction; where N>3 and M>2;

[0103] When a continuous power drop is detected after the original voltage adjustment direction is restored, the voltage adjustment direction is reversed, and the voltage adjustment step is set to a proportional value based on the open circuit voltage and the voltage at maximum power.

[0104] In an optional embodiment, the method further includes:

[0105] For a fixed resistance load, the ratio change between the open circuit voltage and the voltage at maximum power is monitored in real time. When the ratio change exceeds the preset range, the voltage adjustment direction is reversed.

[0106] For adjustable resistance loads, when the input power is detected to be lower than the preset efficiency threshold, the load resistance is dynamically adjusted to the load resistance matching range;

[0107] For segmented load regulation, when the input voltage is detected to exceed the preset segment threshold, it switches to the adjacent resistance segment and reinitializes the voltage adjustment direction; among which, the segment threshold is dynamically optimized based on historical power data.

[0108] In an optional embodiment, the method further includes:

[0109] Compare the ratio of current power to historical maximum power in real time. When the ratio is lower than the preset value, start the global scan mode, adjust the input voltage in both directions with the preset step size and record the maximum power point.

[0110] In response to a power rising edge detected in the global sweep mode, the sweep is immediately terminated and restored to the normal tracking mode, while retaining the power extreme point data obtained during the sweep process;

[0111] By integrating ambient light sensor data, when a sudden change in irradiance is detected, the voltage adjustment direction is temporarily frozen and the current operating point is maintained until the irradiance stabilizes and the tracking parameters are reinitialized.

[0112] In an optional embodiment, the calculation formula of the load resistance matching coefficient interval is as follows:

[0113] ;

[0114] in, Indicates the load resistance matching coefficient range, Indicates the degree of matching.

[0115] In an optional embodiment, the calculation formula of the load resistance matching interval is as follows:

[0116] ;

[0117] in, Indicates the load resistance matching range, Indicates internal resistance.

[0118] It should be noted that due to the electromotive force of photovoltaic modules and internal resistance It changes with the change of the irradiance of sunlight acting on the photovoltaic modules. For fixed photovoltaic modules, the irradiance acting on the modules cannot be changed, so the only way to change it is to change the load resistance. , so that it is consistent with the corresponding internal resistance Only when the loads are equal can the output power be maximized, which is also the goal pursued in photovoltaic direct drive applications;

[0119] In order to achieve the above purpose, we first analyze the impact on output power when the internal resistance is not equal to the external resistance.

[0120] Because at any moment, only When the output power is the maximum , at a given matching degree (0< <100%), according to The value of can be inferred from the corresponding and , thus obtaining The value range of The specific reverse calculation process and corresponding formula are as follows:

[0121] According to the closed circuit power supply output power The expression of , after expansion, can be obtained:

[0122] ;

[0123] Will Substituting in and further sorting out, we get:

[0124] ;

[0125] Then Substituting in and further sorting out, we get:

[0126] ;

[0127] This is a The quadratic equation of one variable, because 0< <100%, according to the root-finding formula:

[0128] ;

[0129] make It is called the lower limit matching coefficient of the load resistance. It is called the upper limit matching coefficient of the load resistance. It is called the load resistance matching coefficient range. back, It is a constant that is independent of other parameters.

[0130] when hour, , , the efficiency is highest when the internal and external resistance values ​​are equal; hour, The output power is 0, there is only short-circuit current, The output power is 0, only the open circuit voltage.

[0131] In an optional embodiment, the calculation formula of the load voltage matching coefficient interval is as follows:

[0132] ;

[0133] in, Indicates the load voltage matching coefficient range.

[0134] In an optional embodiment, the calculation formula of the load voltage matching interval is as follows:

[0135] ;

[0136] in, Indicates the load voltage matching range, Indicates the voltage at maximum power.

[0137] It should be noted that according to the above and the above 、 、 and 、 The analysis can be described more clearly in the form of PR curve;

[0138] See Figure 2 , it can be seen that in When the maximum output power , and the corresponding load resistance and output voltage ,have ;

[0139] exist Sometimes, there are , so we have:

[0140] ;

[0141] Right now:

[0142] ;

[0143] Similarly, we can get:

[0144]

[0145] make It is called the lower limit of the load voltage matching coefficient. It is called the upper limit of the load voltage matching coefficient. It is called the load voltage matching coefficient interval. back, It is a constant that is independent of other parameters.

[0146] Based on this, different power matching degrees can be obtained Under this condition, the load resistance matching coefficient range is and load voltage coefficient range For details, please refer to the table Figure 3 .

[0147] For example 2, please refer to Figure 4 and Figure 5 , this application is loaded It is an application of fixed resistance value. Application No. 202110008621.4 introduces the matching factor α to provide the optimal matching algorithm for photovoltaic direct drive resistive load. By configuring the appropriate load resistance, the power generated by photovoltaic power on the load resistance within a day is maximized, but the maximum power tracking is not achieved. In order to achieve the tracking of the maximum power range, the power storage device C and the anti-backflow device D are added to the photovoltaic direct drive circuit, as well as the photovoltaic power on / off device K. The load The resistance value can be obtained by For the basic structure diagram, please refer to Figure 4 , its algorithm and control logic diagram can be found in Figure 5 As shown, it is obvious that when K is disconnected, the voltage V across C begins to increase and store energy. When K is turned on, the photovoltaic power and the energy stored in C jointly supply power to the load R; when the load voltage V The load keeps working until the load voltage V is lower than When , K is disconnected again, and this process repeats.

[0148] The larger the capacity of the power storage device C, the lower the switching frequency of K; The closer it is to 100%, the higher the on-off frequency of K. To accommodate frequent on-off switching and prevent DC arcing, K should use a contactless switch. Actual testing using a photovoltaic water heater revealed that, compared to the method in application number 202110008621.4, output power can be increased by 6% on sunny days, by 10% to 20% in partly to overcast conditions, and by over 30% on cloudy days.

[0149] For example three, please refer to Figure 6 , this application is loaded The resistance value can be adjusted continuously or approximately continuously (adjustment step For photovoltaic direct drive systems, the maximum power of the photovoltaic power supply part , voltage at maximum power and It can be considered as known, assuming that the load resistance can be divided into n DC load intervals, the load increment And satisfy: For its algorithm and control logic, please refer to Figure 6 .

[0150] For the adjustment step , which can be a resistive load or other DC load, so this method can be directly used in DC frequency conversion systems.

[0151] For example 4, please refer to Figure 7 The present application is an application in which the load resistance R can be adjusted in sections. The so-called load resistance R can be adjusted in sections, which is to form m different load resistances through different connection combinations according to the needs. , and satisfy: , because the load resistance R is known at any stage, the current output power can be calculated based on the detected load voltage V. As long as the output power is not reduced, the relative current resistance is given. Voltage required to increase resistance switching Or the voltage that needs to be switched to reduce resistance , that is, the resistance Working voltage range , the maximum power range tracking can be achieved. For its algorithm and control logic, please refer to Figure 7 .

[0152] For example five, please refer to Figure 8 The present application is applied to parallel multi-heating unit systems. In the field of electric heating, many scenarios use parallel multiple electric heating tubes for heating, such as electric boiler systems, electric drying systems, electric steam generator systems, etc. Because the core electric heating parts of these systems have the same topological structure, and generally the resistance of each heating unit is the same, refer to Figure 8 The connection and disconnection of the on-off switches K1, K2, ..., Kn determine the size of the total load resistance R. Assuming that there are k heating units connected, according to the calculation formula of the parallel resistance:

[0153] ;

[0154] Especially in the resistance of each heating unit At the same time, there are , relative to the entire heating system, n different load resistance values ​​can be obtained:

[0155] .

[0156] For example 2, please refer to Figure 10 The present invention provides a technical solution: a system for maximum power tracking of photovoltaic direct-drive heating, which is applicable to the above-mentioned method for maximum power tracking of photovoltaic direct-drive heating, comprising:

[0157] Matching determination unit 1, matching determination unit 1 is used to obtain electrical parameters of the photovoltaic module; wherein the electrical parameters include output power, maximum output power, internal resistance, open circuit voltage, short circuit current and voltage at maximum power; and determine the matching degree based on the output power and maximum output power;

[0158] The interval determination unit 2 is used to determine the load resistance matching coefficient interval of the external circuit of the photovoltaic module according to the matching degree; determine the load resistance matching interval according to the load resistance matching coefficient interval and the internal resistance; determine the load voltage matching coefficient interval of the external circuit of the photovoltaic module according to the matching degree; and determine the load voltage matching interval according to the load voltage matching coefficient interval and the voltage at maximum power.

[0159] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for maximum power tracking applied to photovoltaic direct drive heating, characterized in that: include: Obtaining electrical parameters of the photovoltaic module; wherein the electrical parameters include output power, maximum output power, internal resistance, open circuit voltage, short circuit current, and voltage at maximum power; determining a matching degree based on the output power and the maximum output power; Determining a load resistance matching coefficient interval of the external circuit of the photovoltaic assembly based on the matching degree; determining a load resistance matching interval based on the load resistance matching coefficient interval and the internal resistance; determining a load voltage matching coefficient interval of the external circuit of the photovoltaic assembly based on the matching degree; determining a load voltage matching interval based on the load voltage matching coefficient interval and the voltage at maximum power; The calculation formula of the load resistance matching coefficient range is as follows: ； in, Indicates the load resistance matching coefficient range, Indicates the degree of matching; The calculation formula of the load voltage matching coefficient interval is as follows: ； in, Indicates the load voltage matching coefficient range; The output power is calculated as follows: ； in, Indicates the output power, Indicates the maximum output power.

2. The method for maximum power tracking applied to photovoltaic direct-drive heating according to claim 1, characterized in that: The method further comprises: Setting a voltage adjustment direction of the power converter so that the input voltage of the power converter changes in a positive trend or a negative trend; detecting the input voltage and input current of the power converter at a first moment, calculating a first power, and recording a first input voltage value corresponding to the first power; detecting an input voltage and an input current of the power converter at a second moment, calculating a second power, and recording a second input voltage value corresponding to the second power; detecting an input voltage and an input current of the power converter at a third moment, calculating a third power, and recording a third input voltage value corresponding to the third power; When the first power, the second power, and the third power satisfy a continuously decreasing relationship, and the third input voltage value is outside the load voltage matching interval, changing the voltage adjustment direction to reverse the change trend of the input voltage; When the first power, the second power, and the third power satisfy a continuously decreasing relationship, and the third input voltage value is within the load voltage matching interval, maintaining the voltage adjustment direction unchanged, and updating the voltage at maximum power based on the current irradiance; When the first power, the second power, and the third power satisfy a continuously increasing relationship, and the third input voltage value exceeds an upper limit of the load voltage matching interval, changing the voltage adjustment direction, detecting the input voltage and input current at a fourth moment, calculating a fourth power, and recording a fourth input voltage value corresponding to the fourth power; When the fourth input voltage value is not greater than the open-circuit voltage and the fourth power is greater than the third power, the voltage adjustment direction is maintained unchanged.

3. The method for maximum power tracking applied to photovoltaic direct-drive heating according to claim 2, characterized in that: The method further comprises: When it is detected that the short-circuit current change rate of the PV module exceeds the preset threshold, the current voltage adjustment direction is locked and the direction reversal operation is suspended until the short-circuit current stabilizes and tracking is restarted; In response to the voltage adjustment direction being changed, continuously collecting N input powers, and restoring the original voltage adjustment direction when M of the N input powers satisfy the condition that the N input powers are greater than the M input powers and the input voltage value is within the load voltage matching interval; wherein N>3 and M>2; When it is detected that the power continues to decrease after the original voltage adjustment direction is restored, the voltage adjustment direction is reversed, and the voltage adjustment step is set to a proportional value based on the open circuit voltage and the voltage at the maximum power.

4. The method for maximum power tracking applied to photovoltaic direct-drive heating according to claim 3, characterized in that: The method further comprises: For a fixed resistance load, the ratio change of the open circuit voltage and the voltage at the maximum power is monitored in real time, and when the ratio change exceeds a preset range, the voltage adjustment direction is triggered to reverse; For adjustable resistance loads, when the input power is detected to be lower than the preset efficiency threshold, the load resistance is dynamically adjusted to the load resistance matching range; For segmented load regulation, when it is detected that the input voltage exceeds a preset segment threshold, it switches to the adjacent resistance segment and reinitializes the voltage adjustment direction; wherein, the segment threshold is dynamically optimized based on historical power data.

5. The method for maximum power tracking applied to photovoltaic direct-drive heating according to claim 4, characterized in that: The method further comprises: Compare the ratio of the current power to the historical maximum power in real time. When the ratio is lower than a preset value, start the global scan mode, adjust the input voltage bidirectionally with a preset step size, and record the maximum power point. In response to a power rising edge detected in the global sweep mode, the sweep is immediately terminated and restored to the normal tracking mode, while retaining the power extreme point data obtained during the sweep process; By integrating ambient light sensor data, when a sudden change in irradiance is detected, the voltage adjustment direction is temporarily frozen and the current operating point is maintained until the irradiance stabilizes and the tracking parameters are reinitialized.

6. The method for maximum power tracking applied to photovoltaic direct-drive heating according to claim 5, characterized in that: The calculation formula of the load resistance matching range is as follows: ； in, Indicates the load resistance matching range, Indicates internal resistance.

7. The method for maximum power tracking applied to photovoltaic direct-drive heating according to claim 6, characterized in that: The calculation formula of the load voltage matching interval is as follows: ； in, Indicates the load voltage matching range, Indicates the voltage at maximum power.

8. A system for maximum power tracking of photovoltaic direct-drive heating, which is applicable to a method for maximum power tracking of photovoltaic direct-drive heating according to any one of claims 1 to 7, characterized in that: include: A matching determination unit (1), the matching determination unit (1) is used to obtain electrical parameters of the photovoltaic module; wherein the electrical parameters include output power, maximum output power, internal resistance, open circuit voltage, short circuit current and voltage at maximum power; and the matching degree is determined according to the output power and the maximum output power; An interval determination unit (2) is used to determine a load resistance matching coefficient interval of an external circuit of the photovoltaic module according to the matching degree; determine a load resistance matching interval according to the load resistance matching coefficient interval and the internal resistance; determine a load voltage matching coefficient interval of an external circuit of the photovoltaic module according to the matching degree; and determine a load voltage matching interval according to the load voltage matching coefficient interval and the voltage at maximum power.

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