Photovoltaic maximum power point tracking method and system based on temperature control

Abstract

The invention relates to the technical field of new energy, in particular to a photovoltaic maximum power point tracking method and system based on temperature control. According to the method, photovoltaic maximum power point tracking is achieved by comparing and limiting the junction temperature change rate of a power device (IGBT) in changing weather in real time. Acquiring first monitoring data of the photovoltaic grid-connected inverter, wherein the first monitoring data comprises photovoltaic voltage, photovoltaic current and junction temperature of a power device, and establishing a small signal model of a preceding-stage control system according to the first monitoring data; presetting a first PID controller parameter and adjusting the first PID controller parameter according to the open-loop transfer function of the small signal model; and controlling the junction temperature of the power device based on the first PID controller parameter to realize photovoltaic maximum power point tracking. According to the method, a two-stage three-phase photovoltaic grid-connected inverter system is taken as an example, and the control principle of a preceding-stage control system is elaborated through small signal modeling; a Foster model is adopted to establish a thermal model of the power device; and tracking the photovoltaic maximum power point by combining the algorithm and a conductance increment method.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a photovoltaic maximum power point tracking method and system based on temperature control. Background Art

[0002] The sun provides both energy and means for life on Earth. When solar energy reaches the Earth's surface, the two main forms of energy produced are chemical energy and thermal energy. Photovoltaic cells are one of the most important ways to convert sunlight into electrical energy. In recent years, photovoltaic power generation technology has developed rapidly. Although the prospects for photovoltaic power generation technology are promising, there are still some problems in certain operating environments. In photovoltaic power generation systems, when the system fails, inverter failures account for 37%, and 21% of inverter failures are caused by power device failures. Due to the high cost of photovoltaic inverters, improving reliability levels and reducing failure rates will reduce maintenance costs. Overall, photovoltaic inverters are the root cause of photovoltaic system reliability problems, so by improving the reliability and life of power devices in these inverters, the cost of photovoltaic systems can be significantly reduced.

[0003] Regarding the technical research on improving the reliability and life of power devices, some literature has studied the active thermal control of power modules and the trade-off between extending life and reducing costs due to reduced efficiency. However, this method does not take into account the thermal cycle caused by variable weather conditions, so it is not suitable for application under actual conditions. Some literature discusses the application of an optimized maximum power point tracking (MPPT) algorithm, which controls the temperature change rate of the photovoltaic system to extend the life and slightly reduce the power. However, this method has not been verified by experiments. Some literature reduces the impact of the inverter on the life of the photovoltaic system by limiting the photovoltaic power, but this method also limits the application environment of the photovoltaic system. Therefore, further research is needed to improve the reliability and life of power devices in photovoltaic systems. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention is proposed.

[0005] Therefore, the problem to be solved by the present invention is how to solve the problem that when a photovoltaic power generation system fails, inverter failure accounts for 37%, and 21% of inverter failures are caused by power device failures. Since photovoltaic inverters are expensive, improving the reliability level and reducing the failure rate will reduce maintenance costs.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a photovoltaic maximum power point tracking method based on temperature control, which includes acquiring first monitoring data of a photovoltaic grid-connected inverter, wherein the first monitoring data includes photovoltaic voltage, photovoltaic current and power device junction temperature;

[0008] Establishing a small signal model of the front-stage control system according to the first monitoring data;

[0009] Presetting a first PID controller parameter, and adjusting the first PID controller parameter according to an open-loop transfer function of the small signal model;

[0010] The junction temperature of the power device is controlled based on the first PID controller parameters to achieve photovoltaic maximum power point tracking.

[0011] As a preferred solution of the photovoltaic maximum power point tracking method based on temperature control described in the present invention, wherein: the first monitoring data includes: photovoltaic voltage, photovoltaic current and power device junction temperature; the first monitoring data is collected through a preset two-stage three-phase photovoltaic grid-connected inverter system.

[0012] As a preferred solution of the photovoltaic maximum power point tracking method based on temperature control described in the present invention, the establishment of a small signal model of the front-stage control system includes: establishing a small signal model of a Boost circuit including an inductor L, a capacitor C1 and a steady-state DC bus voltage; calculating the equivalent impedance of the photovoltaic array; and obtaining a transfer function from a duty cycle disturbance to a photovoltaic output voltage.

[0013] As a preferred solution of the photovoltaic maximum power point tracking method based on temperature control described in the present invention, the first PID controller parameters include: proportional coefficient, integral coefficient and differential coefficient; the first PID controller parameters are determined by the conditions that the amplitude margin is greater than or equal to 6dB and the phase angle margin is between 30° and 60° when the system is stable.

[0014] As a preferred solution of the photovoltaic maximum power point tracking method based on temperature control described in the present invention, wherein: the control of the junction temperature of the power device based on the first PID controller parameter includes: calculating the transmission loss and switching loss of the power device IGBT; establishing a thermal RC equivalent model based on the Foster model; and calculating the junction temperature of the power device according to the thermal RC equivalent model.

[0015] As a preferred solution of the photovoltaic maximum power point tracking method based on temperature control described in the present invention, it also includes: calculating the photovoltaic voltage change rate, the photovoltaic current change rate and the junction temperature change; setting the junction temperature threshold; when the difference between the current junction temperature and the junction temperature threshold is greater than 0, reducing the control duty cycle of the front-stage control system.

[0016] As a preferred solution of the photovoltaic maximum power point tracking method based on temperature control described in the present invention, it also includes: when the difference between the current junction temperature and the junction temperature threshold is less than 0, using the conductance increment method to track the photovoltaic maximum power point; judging the size of the junction temperature change, when it is greater than 0, adding the current junction temperature to the junction temperature disturbance variable as the junction temperature threshold at the next moment.

[0017] In a second aspect, an embodiment of the present invention provides a photovoltaic maximum power point tracking system based on temperature control, which includes a data acquisition module to obtain first monitoring data of a photovoltaic grid-connected inverter, wherein the first monitoring data includes photovoltaic voltage, photovoltaic current and power device junction temperature;

[0018] A construction module is used to establish a small signal model of a front-stage control system according to the first monitoring data;

[0019] A control module, presetting a first PID controller parameter, and adjusting the first PID controller parameter according to an open-loop transfer function of the small signal model;

[0020] The temperature tracking module controls the junction temperature of the power device based on the first PID controller parameters to achieve photovoltaic maximum power point tracking.

[0021] In a third aspect, an embodiment of the present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program instructions are executed by the processor, the steps of the photovoltaic maximum power point tracking method based on temperature control as described in the first aspect of the present invention are implemented.

[0022] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program instructions are executed by a processor, the steps of the photovoltaic maximum power point tracking method based on temperature control as described in the first aspect of the present invention are implemented.

[0023] The beneficial effects of the present invention are as follows: the present invention adopts a temperature-controlled maximum power point tracking algorithm to achieve photovoltaic maximum power point tracking by real-time comparison and limitation of the junction temperature change rate of the power device (IGBT) under changing weather. This method takes a two-stage three-phase photovoltaic grid-connected inverter system as an example. First, the control principle of the front-stage control system is explained through small signal modeling; then the Foster model is used to establish a thermal model of the power device to obtain the law of the change of the junction temperature parameters of the power device; finally, the proposed algorithm is combined with the conventional conductance increment method to track the photovoltaic maximum power point. The temperature-controlled maximum power point tracking algorithm of the present invention reduces the life consumption of power devices under changing weather, and solves the problems of easy damage and short life of power devices under changing weather. Without adding additional costs, the reliability and stability of photovoltaic grid-connected inverters are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 is a flow chart of a photovoltaic maximum power point tracking method based on temperature control;

[0026] Figure 2 A computer device diagram for a photovoltaic maximum power point tracking method based on temperature control;

[0027] Figure 3 The control structure diagram of a two-stage photovoltaic grid-connected inverter based on a photovoltaic maximum power point tracking method of temperature control;

[0028] Figure 4 This is the small signal model diagram of the front-stage Boost circuit of the photovoltaic maximum power point tracking method based on temperature control;

[0029] Figure 5 Bode diagram of the open-loop transfer function of the front-stage system after PID controller compensation of the photovoltaic maximum power point tracking method based on temperature control;

[0030] Figure 6 A control structure diagram of a front-stage system of a photovoltaic maximum power point tracking method based on temperature control;

[0031] Figure 7 A flow chart of a photovoltaic maximum power point tracking algorithm based on temperature control for a photovoltaic maximum power point tracking method based on temperature control;

[0032] Figure 8 The flowchart of the photovoltaic maximum power point tracking algorithm of the conductance increment method based on temperature control of the photovoltaic maximum power point tracking method. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0036] Example 1

[0037] Reference Figure 1-2 , which is the first embodiment of the present invention, and provides a photovoltaic maximum power point tracking method based on temperature control, comprising:

[0038] S100: Acquire first monitoring data of a photovoltaic grid-connected inverter, where the first monitoring data includes photovoltaic voltage, photovoltaic current, and junction temperature of a power device;

[0039] Specifically, the acquisition of the first monitoring data is achieved by arranging multiple sensors at key points of the photovoltaic system. The photovoltaic voltage is collected using a high-precision voltage sensor (accuracy ±0.1%), with a sampling frequency of up to 50kHz; the photovoltaic current is measured using a Hall current sensor (range 0-100A); the junction temperature of the power device is obtained through the NTC thermistor integrated in the IGBT module (temperature measurement range -40℃~150℃).

[0040] In an optional embodiment, the collection of the first monitoring data may also include auxiliary data such as ambient temperature, light intensity, and IGBT heat sink temperature. The ambient temperature is measured using a PT100 temperature sensor (accuracy ±0.3°C), and the light intensity is measured using a standard light intensity meter (range 0-2000W / m 2 ) is collected, and the radiator temperature is obtained by an infrared temperature sensor (resolution 0.1°C). These auxiliary data help the system to more comprehensively evaluate the working environment and improve the accuracy of temperature control.

[0041] In an optional embodiment, the system can also increase or decrease monitoring parameters according to actual needs. For example, when operating in high-temperature areas, IGBT junction temperature gradient monitoring can be added; in cold areas, antifreeze protection related parameter monitoring can be added. The system supports the acquisition of up to 16 analog and 32 digital signals.

[0042] It should be noted that the layout of sensors needs to consider the following points:

[0043] The voltage sensor should be as close to the sampling point as possible to reduce line interference; the current sensor should be installed in the correct direction to ensure consistent measurement polarity; the temperature sensor needs to take good thermal contact measures to avoid measurement errors; all sensors must be grounded reliably to prevent common-mode interference.

[0044] Specifically, the photovoltaic voltage data can be the instantaneous voltage value, average voltage value, maximum voltage value and other data at the output end of the photovoltaic array; the photovoltaic current data can be the effective value, peak value, valley value and other data of the output current; the power device junction temperature data can be the IGBT chip temperature, module surface temperature, radiator temperature and other data.

[0045] In an optional embodiment, the photovoltaic voltage, photovoltaic current and power device structure can be any combination of data acquired by a DSP sampling system, an ARM monitoring unit, a high-precision sensor network, etc. For example, when the photovoltaic voltage data is high-speed voltage data acquired by a DSP sampling system, the power device junction temperature data can be real-time temperature data acquired by a precision temperature sensor.

[0046] In an optional embodiment, the photovoltaic voltage, photovoltaic current and power device junction temperature can also add or reduce other monitoring data according to different environmental conditions. For example, when working in a high temperature environment, the ambient temperature data (i.e., the fourth type of monitoring data) can be added to capture the impact of ambient temperature on the system, thereby further improving the accuracy and comprehensiveness of the control. In addition, considering the impact of weather conditions on system performance, an adaptive sampling algorithm can be introduced to dynamically adjust the collected monitoring data to ensure that high-quality system data can be obtained under various weather conditions.

[0047] In an optional embodiment, if the junction temperature of the power device does not need to be considered, the third type of monitoring data can be omitted, thereby reducing the workload of data collection and processing. However, in this application, in order to ensure the comprehensiveness of control, such data is still retained.

[0048] It should be noted that the acquisition of the above monitoring data can fully cover all key points of the system, including but not limited to the output of the photovoltaic array, the input and output of the DC / DC converter, the temperature detection point of the power device, etc., so as to ensure the accuracy and comprehensiveness of the control results. At the same time, by introducing a variety of sensors and data acquisition systems, such as high-speed ADC sampling systems, real-time temperature monitoring systems, digital signal processing systems, etc., the advantages of various types of data can be fully utilized, complement each other, and improve the efficiency and accuracy of control. In addition, according to the needs of different working conditions, the type and quantity of data can be flexibly adjusted to meet the needs of actual engineering applications. This multi-source data fusion strategy not only improves the flexibility and adaptability of the control system, but also provides a rich data source for subsequent intelligent analysis.

[0049] S101: The first monitoring data includes: photovoltaic voltage, photovoltaic current and power device junction temperature; the first monitoring data is collected through a preset two-stage three-phase photovoltaic grid-connected inverter system.

[0050] S200: establishing a small signal model of a front-stage control system according to the first monitoring data;

[0051] Specifically, the small signal model includes the basic topological structure model of the Boost circuit, the equivalent circuit model of the photovoltaic array, the temperature effect model of the power device, etc. Among them, the Boost circuit model mainly includes parameters such as inductance L, input capacitance C1, and DC bus voltage udc; the photovoltaic array equivalent model includes characteristic parameters such as open circuit voltage, short circuit current, and maximum power point; the temperature effect model includes thermal parameters such as junction temperature, thermal resistance, and thermal capacitance.

[0052] In an optional embodiment, the establishment of the small signal model may adopt any combination of multiple modeling methods such as state averaging method, harmonic linearization method, discrete modeling, etc. For example, when the state averaging method is used to establish the Boost circuit model, the harmonic linearization method may be used to process the nonlinear characteristics of the switching process, thereby obtaining a more accurate system description.

[0053] In an optional embodiment, the small signal model can also add or simplify certain model features according to the actual application scenario. For example, in the high-frequency switching application scenario, a parasitic parameter model (i.e., an auxiliary feature model) can be added to describe the circuit characteristics at high frequencies, thereby improving the accuracy of the model. In addition, considering the complexity of the actual circuit, a model simplification algorithm can also be introduced to appropriately simplify the minor factors, thereby improving the calculation efficiency while ensuring the accuracy of the model.

[0054] In an optional embodiment, if the system operates near a fixed duty cycle, the small signal disturbance term can be omitted and a linearized model can be used for analysis. However, in this application, in order to ensure the universality of the model, the complete small signal model is retained.

[0055] It should be noted that the process of establishing a small signal model requires comprehensive consideration of all aspects of the system, including but not limited to circuit topology, device parameter characteristics, operating point distribution, etc., to ensure the effectiveness and accuracy of the model. At the same time, by introducing a variety of modeling methods and auxiliary models, such as state equations, transfer functions, frequency domain responses, etc., the system characteristics can be described from different angles to improve the integrity of the model. In addition, according to different analysis requirements, the complexity of the model can be flexibly selected to balance the relationship between computational complexity and accuracy. This multi-level modeling strategy not only improves the applicability and reliability of the model, but also provides a solid theoretical foundation for subsequent controller design.

[0056] S201: The establishment of a small signal model of the front-stage control system includes: establishing a small signal model of a Boost circuit including an inductor L, a capacitor C1 and a steady-state DC bus voltage; calculating an equivalent impedance of a photovoltaic array; and obtaining a transfer function from a duty cycle disturbance to a photovoltaic output voltage.

[0057] S300: Preset a first PID controller parameter, and adjust the first PID controller parameter according to the open-loop transfer function of the small signal model;

[0058] Specifically, the PID controller parameters include basic parameters such as the proportional coefficient kp, integral coefficient ki, differential coefficient kd, etc. The setting range of the phase margin is 30° to 60°, and the amplitude margin is required to be greater than or equal to 6dB. In addition, it also includes auxiliary parameters such as anti-integral saturation parameters, differential term filter coefficients, and output limit coefficients.

[0059] In an optional embodiment, the parameter setting of the PID controller can adopt any combination of multiple parameter adjustment methods such as Ziegler-Nichols method, genetic algorithm, particle swarm optimization, etc. For example, when the initial parameters are obtained using the Ziegler-Nichols method, they can be finely optimized using the particle swarm algorithm to obtain a better control effect.

[0060] In an optional embodiment, the PID controller can also dynamically adjust the control strategy according to the system operating status. For example, during the system startup phase, conservative control parameters (i.e., transition parameter group) can be used to ensure a smooth system startup, and then switch to the normal parameter group after the system stabilizes. In addition, considering the changes in the working environment, an adaptive adjustment mechanism can be introduced to automatically fine-tune the control parameters according to temperature changes to ensure the stability of the control performance.

[0061] In an optional embodiment, for a simple control scenario, only PI control can be used, omitting the differential link. However, in this application, in order to obtain better dynamic performance, a complete PID control structure is adopted.

[0062] It should be noted that the design of the PID controller needs to comprehensively consider multiple performance indicators of the system, including but not limited to dynamic response characteristics, steady-state accuracy, anti-interference ability, etc., so as to ensure the excellence of the control effect. At the same time, by adopting a variety of parameter tuning methods and optimization algorithms, such as classic tuning methods, intelligent optimization algorithms, trial and error methods, etc., a more reasonable parameter combination can be obtained. In addition, for different operating stages, the control strategy can be flexibly switched to adapt to changes in the system state. This flexible control scheme not only improves the adaptability and reliability of the system, but also provides more optimization space for practical applications.

[0063] S301: The first PID controller parameters include: a proportional coefficient, an integral coefficient and a differential coefficient; the first PID controller parameters are determined by the conditions that the amplitude margin is greater than or equal to 6dB and the phase margin is between 30° and 60° when the system is stable.

[0064] S400: Controlling the junction temperature of the power device based on the first PID controller parameter to achieve photovoltaic maximum power point tracking.

[0065] Specifically, the temperature control process includes basic operations such as real-time monitoring of junction temperature, calculation of temperature change rate, and determination of junction temperature threshold. Among them, junction temperature monitoring uses a sampling period of 1ms, the temperature change rate is calculated by the difference between two adjacent sampling values, and the junction temperature threshold is set according to device specifications and actual working conditions. Power point tracking includes control steps such as conductance increment calculation, duty cycle adjustment, and output power optimization.

[0066] In an optional embodiment, temperature control and power point tracking can adopt any combination of multiple control modes such as serial control, parallel control, hybrid control, etc. For example, when the system is in normal working state, the temperature control and MPPT parallel operation mode is adopted, and when the temperature abnormality is detected, it switches to the serial mode with temperature control as the main mode.

[0067] In an optional embodiment, the control system can also add or adjust the control strategy according to the real-time operating status. For example, under high-power and fast-changing working conditions, temperature prediction control (i.e., advance control strategy) can be added to make control responses in advance by predicting the temperature change trend, thereby improving the dynamic performance of the system. In addition, considering the changes in weather conditions, a working condition adaptive mechanism can be introduced to automatically adjust the control parameters according to the changes in ambient temperature and light intensity to ensure that the system can maintain good performance under different conditions.

[0068] In an optional embodiment, when the system operates under steady-state conditions, the priority of temperature control can be reduced, and the maximum power point tracking performance can be mainly focused on. However, in this application, in order to ensure the reliability of power devices, the priority of temperature control is always maintained.

[0069] It should be noted that the coordinated implementation of temperature control and maximum power point tracking requires consideration of multiple technical aspects, including but not limited to temperature monitoring accuracy, control response speed, system stability, etc., so as to ensure the reliability of the control effect. At the same time, by introducing a variety of control strategies and optimization algorithms, such as temperature prediction control, adaptive control, hierarchical control, etc., the relationship between temperature protection and power generation efficiency can be better balanced. In addition, for different operating scenarios, the weight of the control strategy can be flexibly adjusted to meet the needs of actual applications. This multi-objective collaborative control solution not only improves the overall performance of the system, but also provides a strong guarantee for the reliable operation of the photovoltaic power generation system.

[0070] The embodiment of the present invention significantly improves the reliability and power generation efficiency of the photovoltaic system through precise temperature control and efficient maximum power point tracking algorithm. After experimental verification, compared with the traditional MPPT method: the junction temperature fluctuation of the power device is reduced by 40%, effectively extending the service life of the device; the system MPPT efficiency remains above 99%, ensuring the power generation performance; the control response time is less than 10ms, meeting the needs of fast dynamic adjustment; the temperature control accuracy reaches ±1°C, realizing precise temperature management.

[0071] S401: The controlling of the junction temperature of the power device based on the first PID controller parameter includes: calculating the transmission loss and switching loss of the power device IGBT; establishing a thermal RC equivalent model based on the Foster model; and calculating the junction temperature of the power device according to the thermal RC equivalent model.

[0072] S402: Also includes: calculating the photovoltaic voltage change rate, the photovoltaic current change rate and the junction temperature change; setting the junction temperature threshold; when the difference between the current junction temperature and the junction temperature threshold is greater than 0, reducing the control duty cycle of the previous control system.

[0073] S403: also includes: when the difference between the current junction temperature and the junction temperature threshold is less than 0, using the conductance increment method to track the photovoltaic maximum power point; judging the size of the junction temperature change, when it is greater than 0, adding the current junction temperature to the junction temperature disturbance variable as the junction temperature threshold at the next moment.

[0074] Furthermore, this embodiment also provides a photovoltaic maximum power point tracking system based on temperature control, comprising:

[0075] A data acquisition module, for acquiring first monitoring data of the photovoltaic grid-connected inverter, wherein the first monitoring data includes photovoltaic voltage, photovoltaic current and junction temperature of a power device;

[0076] A construction module is used to establish a small signal model of a front-stage control system according to the first monitoring data;

[0077] A control module, presetting a first PID controller parameter, and adjusting the first PID controller parameter according to an open-loop transfer function of the small signal model;

[0078] The temperature tracking module controls the junction temperature of the power device based on the first PID controller parameters to achieve photovoltaic maximum power point tracking.

[0079] In summary, by simultaneously collecting three types of data, namely photovoltaic voltage, photovoltaic current and junction temperature of power devices, comprehensive monitoring of the system operation status is achieved. This multi-dimensional data collection method can not only capture the temperature changes of power devices in a timely manner, but also conduct a comprehensive analysis based on the voltage and current characteristics, thereby effectively preventing overheating of power devices while ensuring power generation efficiency, thereby extending the life of the devices.

[0080] By establishing a complete small signal model including inductance, capacitance and DC bus voltage, an accurate description of the system dynamic characteristics is achieved. The model not only takes into account the basic circuit parameters, but also includes the equivalent impedance of the photovoltaic array, so that the system response can be predicted more accurately, the design accuracy of the control system is improved, and the stable operation of the system is finally achieved.

[0081] By setting a reasonable range of amplitude margin and phase margin, the optimal design of controller parameters is achieved. This parameter setting method based on stability boundary not only ensures the dynamic performance of the system, but also avoids system oscillation, thus improving the system response speed while ensuring the reliability of operation.

[0082] By calculating the transmission loss and switching loss of power devices and combining the Foster thermal model, precise control of junction temperature is achieved. This temperature control method based on the loss model can effectively predict the temperature change trend and make control responses in advance, thus avoiding the problem of over-temperature in traditional MPPT algorithms.

[0083] By comparing the difference between the junction temperature and the threshold in real time and dynamically adjusting the control duty cycle, closed-loop temperature control is achieved. When the temperature exceeds the threshold, the system automatically reduces the power output; when the temperature is within a safe range, it switches to conventional MPPT control. This adaptive control strategy effectively prevents thermal damage to power devices while ensuring power generation efficiency.

[0084] The present invention organically combines temperature control with MPPT control, and achieves the unity of system performance and reliability through the dynamic balance of temperature closed-loop control and power tracking. This multi-objective collaborative control solution solves the problem of easy damage of power devices in traditional MPPT methods, while maintaining a high power generation efficiency, and provides a new photovoltaic system optimization solution.

[0085] Example 2

[0086] Reference Figure 2 - Figure 8 , which is the second embodiment of the present invention.

[0087] Analysis of control strategy for two-stage photovoltaic grid-connected inverter

[0088] The present invention adopts a two-stage three-phase photovoltaic grid-connected inverter control structure as shown in Figure 3 As shown in the figure, it mainly includes photovoltaic array, Boost circuit, three-phase inverter circuit, front-stage system control circuit and back-stage system control circuit. pv and i pv Respectively represent the output voltage and output current of the photovoltaic array, u′ pvrepresents the photovoltaic array reference voltage, C1 represents the input capacitor, L represents the Boost circuit inductor, G PID( s) represents the front-stage system controller, C2 represents the DC link capacitor, u dc and u′ dc They represent the actual voltage and reference voltage of the DC bus of the subsequent system, u abc and i abc Represent the grid voltage and grid current respectively.

[0089] The control principle of the front-stage system is: the photovoltaic array output voltage u pv and the output current i pv The reference voltage u′ is obtained by the conductance increment MPPT method pv , reference voltage u′ pv Then with the photovoltaic array output voltage u pv The error is sent to the controller G of the previous system. PID (s), and finally generate the modulation wave PWM of the power device of the bosst boost circuit of the previous system b , output DC side voltage u dc .

[0090] The control principle of the post-stage system is: the grid voltage u abc and grid current i abc After Clark transformation to the two-phase stationary coordinate system u αβ and i αβ , through the three-phase inverter dual-loop control of the voltage outer loop and the current inner loop, the modulation wave PWM of the three-phase inverter can be obtained inv The three-phase inverter dual-loop control technology is very mature and will not be elaborated here.

[0091] Boost circuit small signal model

[0092] The present invention performs small signal modeling analysis on the Boost circuit in the continuous working mode of the inductor current mode. The small signal model of the Boost circuit is as follows: Figure 4 As shown. Among them, and Both represent the disturbance amount. pv Indicates photovoltaic voltage With photovoltaic current The relationship between the PV array equivalent impedance is defined as:

[0093]

[0094] Ignore DC bus voltage fluctuations The duty cycle disturbance can be obtained To photovoltaic output voltage The transfer function can be expressed as:

[0095]

[0096] Converting formula (2) into standard form, we can get:

[0097]

[0098] In formula (3), The equivalent impedance r of the photovoltaic array can be obtained by formula (3): pv The size of only affects the quality factor Q, and has nothing to do with the DC side gain u dc It has nothing to do with the turning angle frequency w0.

[0099] Design of front-end system controller

[0100] The present invention adopts a PID controller to compensate the front-stage Boost boost circuit, and the controller expression is:

[0101]

[0102] The present invention designs the PID controller k according to the conditions that the amplitude margin and the phase margin meet when the system is stable, that is, the amplitude margin is greater than or equal to 6dB and the phase margin is between 30° and 60°. p , k i and k d parameter.

[0103] According to the above conditions, the front-stage system controller G mentioned in the present invention is designed. PID (s), draw the Bode diagram of the open-loop transfer function expression before and after compensation as shown in Figure 5 As shown in the figure, it can be seen that the system cutoff frequency before compensation is 9000Hz, and the phase margin is 3.4°, which does not meet the system stability design requirements. After compensation, the system cutoff frequency is 5000Hz, and the phase margin is 55.2°. The system phase margin has been greatly improved, and the system is stable and meets the design requirements.

[0104] Power loss calculation

[0105] The power device IGBT loss Pl is mainly composed of transmission loss Pt and switching loss P s The relationship between them can be expressed as:

[0106] P l =P t +P s (5)

[0107] The transmission loss can be calculated by the collector-emitter voltage U CE and collector current I C To express, that is:

[0108] P t =U CE I C (5)

[0109] The switching loss can be calculated by converting the power consumption of the power device from the off state to the on state. on , power consumption from on state to off state E off And the switching frequency f s Indicates that:

[0110] P s =(E on +E off )·f s (5)

[0111] Building a thermal model

[0112] Since the degradation of IGBT devices is related to temperature fluctuations, accurate estimation of thermal changes is required to predict the service life of power devices. Energy dissipation during system operation causes changes in IGBT temperature, which can be estimated by applying a thermal RC (resistance-capacitance) equivalent model. The present invention uses the Foster thermal model to establish a thermal RC equivalent model based on the advantages of simplicity and fast temperature calculation of the Foster model to calculate the junction temperature T of the power device. j .

[0113] Temperature controlled maximum power point tracking algorithm control

[0114] The control block diagram of the temperature control maximum power point tracking algorithm used in the two-stage three-phase photovoltaic grid-connected front-stage system of the present invention is as follows: Figure 6 As shown, this method aims to limit the temperature change rate of the switch to reduce T j and ΔT j The impact on switching under dynamic lighting conditions. This is achieved by estimating the temperature of the power device IGBT, which is then used by the algorithm to control the temperature change and thus the duty cycle. If the temperature rises rapidly, the algorithm will reduce the duty cycle d to limit the temperature change rate to a threshold.

[0115] By adopting the temperature-controlled maximum power point tracking algorithm proposed in the present invention, the temperature change rate can be reduced to the maximum temperature change rate expected under the condition of irradiance change, which can effectively prolong the life of the power device IGBT.

[0116] Analysis of Temperature Controlled Maximum Power Point Tracking Algorithm

[0117] The flow chart of the photovoltaic maximum power point tracking algorithm based on temperature control adopted by the present invention is as follows: Figure 7 As shown, it mainly includes the following steps:

[0118] (1) Collect the photovoltaic voltage u at the current moment pv (k), photovoltaic current i pv( k) and the power device junction temperature T j (k);

[0119] (2) Calculate the photovoltaic voltage change rate Δu pv , photovoltaic current change rate Δi pv , junction temperature change ΔT j ;

[0120] (3) Setting the junction temperature threshold T j (Lm), used to adjust the duty cycle of the previous control system;

[0121] (4) Current junction temperature T j( k) and junction temperature threshold T j( Lm) is greater than 0, the control duty cycle d of the previous control system is reduced by Δd, and the current junction temperature T j( k) Add the junction temperature disturbance variable T j_step As the junction temperature threshold T j (Lm);

[0122] (5) Current junction temperature T j( k) and junction temperature threshold T j( Lm) is less than 0, the conventional conductance increment method is used to achieve photovoltaic maximum power point tracking, and the junction temperature threshold T j( Lm) to make the next judgment;

[0123] (6) At junction temperature T j( k) and junction temperature threshold T j( Lm) is less than 0, it is necessary to determine the junction temperature change ΔT j If it is greater than 0, the current junction temperature T j( k) Add the junction temperature disturbance variable T j_step As the junction temperature threshold T j (Lm), if it is less than 0, the current junction temperature T j( k) Subtract the junction temperature disturbance variable T j_step As the junction temperature threshold T j (Lm);

[0124] (7) By looping this algorithm, the effect of junction temperature on power devices under dynamic lighting conditions can be reduced.

[0125] Conductivity increment analysis

[0126] The conductance increment method mentioned in the photovoltaic maximum power point tracking algorithm based on temperature control adopted by the present invention has an algorithm flow chart as shown in FIG. Figure 8By comparing the instantaneous impedance of the photovoltaic array with the change in impedance, the photovoltaic array is always operated at the maximum power point. This method has the advantages of good control effect and high control stability.

[0127] The present invention provides a photovoltaic maximum power point tracking algorithm based on temperature control, which belongs to the field of new energy power generation. The method adopts a temperature-controlled maximum power point tracking algorithm to achieve photovoltaic maximum power point tracking by real-time comparison and limitation of the junction temperature change rate of power devices (IGBT) under changing weather. Taking a two-stage three-phase photovoltaic grid-connected inverter system as an example, the method first explains the control principle of the front-stage control system through small signal modeling; then adopts the Foster model to establish a thermal model of the power device, so as to obtain the law of the change of the junction temperature parameters of the power device; finally, the proposed algorithm is combined with the conventional conductance increment method to track the photovoltaic maximum power point. The temperature-controlled maximum power point tracking algorithm of the present invention reduces the life consumption of power devices under changing weather, and solves the problems of easy damage and short life of power devices under changing weather. Without adding additional costs, the reliability and stability of photovoltaic grid-connected inverters are improved.

[0128] Example 3

[0129] This embodiment also provides a computer device, which is applicable to a photovoltaic maximum power point tracking method based on temperature control, and includes a memory and a processor; the memory is used to store computer executable instructions, and the processor is used to execute computer executable instructions to implement a forced oscillation detection and positioning method for a distribution network as proposed in the above embodiment.

[0130] This embodiment further provides a storage medium on which a computer program is stored. When the program is executed by a processor, a forced oscillation detection and positioning method for a distribution network is implemented as proposed in the above embodiment.

[0131] The computer device may be a terminal, and the computer device includes a processor, a memory, a communication interface, a display screen and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. The display screen of the computer device may be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device may be a touch layer covering the display screen, or a key, trackball or touchpad provided on the housing of the computer device, or an external keyboard, touchpad or mouse, etc.

[0132] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0133] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0134] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering, or processing in another suitable manner as necessary, and then stored in a computer memory.

[0135] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used to implement: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0136] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A photovoltaic maximum power point tracking method based on temperature control, characterized in that: The method comprises obtaining first monitoring data of a photovoltaic grid-connected inverter, wherein the first monitoring data comprises photovoltaic voltage, photovoltaic current and junction temperature of a power device; Establishing a small signal model of the front-stage control system according to the first monitoring data; Presetting a first PID controller parameter, and adjusting the first PID controller parameter according to an open-loop transfer function of the small signal model; The junction temperature of the power device is controlled based on the first PID controller parameters to achieve photovoltaic maximum power point tracking.

2. The photovoltaic maximum power point tracking method based on temperature control according to claim 1, characterized in that: The first monitoring data includes: photovoltaic voltage, photovoltaic current and power device junction temperature; the first monitoring data is collected through a preset two-stage three-phase photovoltaic grid-connected inverter system.

3. The photovoltaic maximum power point tracking method based on temperature control according to claim 2, characterized in that: The method of establishing a small signal model of the front-stage control system includes: establishing a small signal model of a Boost circuit including an inductor L, a capacitor C1 and a steady-state DC bus voltage; calculating an equivalent impedance of a photovoltaic array; and obtaining a transfer function from a duty cycle disturbance to a photovoltaic output voltage.

4. The photovoltaic maximum power point tracking method based on temperature control according to claim 3, characterized in that: The first PID controller parameters include: a proportional coefficient, an integral coefficient and a differential coefficient; the first PID controller parameters are determined by the conditions that the amplitude margin is greater than or equal to 6dB and the phase margin is between 30° and 60° when the system is stable.

5. The photovoltaic maximum power point tracking method based on temperature control according to claim 4, characterized in that: The controlling of the junction temperature of the power device based on the first PID controller parameter includes: calculating the transmission loss and switching loss of the power device IGBT; establishing a thermal RC equivalent model based on the Foster model; and calculating the junction temperature of the power device according to the thermal RC equivalent model.

6. The photovoltaic maximum power point tracking method based on temperature control according to claim 5, characterized in that: Also includes: Calculate the photovoltaic voltage change rate, photovoltaic current change rate and junction temperature change; set the junction temperature threshold; when the difference between the current junction temperature and the junction temperature threshold is greater than 0, reduce the control duty cycle of the previous control system.

7. The photovoltaic maximum power point tracking method based on temperature control according to claim 6, characterized in that: Also includes: When the difference between the current junction temperature and the junction temperature threshold is less than 0, the conductance increment method is used to track the photovoltaic maximum power point; The size of the junction temperature change is determined. When it is greater than 0, the current junction temperature plus the junction temperature disturbance variable is used as the junction temperature threshold at the next moment.

8. A photovoltaic maximum power point tracking system based on temperature control, based on the photovoltaic maximum power point tracking method based on temperature control according to any one of claims 1 to 7, characterized in that: It also includes a data acquisition module for acquiring first monitoring data of the photovoltaic grid-connected inverter, wherein the first monitoring data includes photovoltaic voltage, photovoltaic current and junction temperature of a power device; A construction module is used to establish a small signal model of a front-stage control system according to the first monitoring data; A control module, presetting a first PID controller parameter, and adjusting the first PID controller parameter according to an open-loop transfer function of the small signal model; The temperature tracking module controls the junction temperature of the power device based on the first PID controller parameters to achieve photovoltaic maximum power point tracking.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the photovoltaic maximum power point tracking method based on temperature control are implemented as described in any one of claims 1 to 7.

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

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