A photovoltaic direct-current grid-connected converter control method considering power module current sharing and MPPT

Abstract

The application provides a photovoltaic direct-current grid-connected converter control method which considers power module current sharing and MPPT, encodes power modules in the direct-current grid-connected converter, sets initial values of duty cycle and other control parameters, samples photovoltaic array state information, determines a duty cycle disturbance direction, calculates a photovoltaic array power disturbance increment, determines a duty cycle disturbance increment, determines the number of power modules which are disturbed according to power module current information, updates the duty cycle of the disturbed power modules according to the number of the disturbed modules and the disturbance increment, and controls the turn-on and turn-off of the switch tube according to the power module duty cycle modulation signal. The method controls the maximum power tracking and the power module current sharing simultaneously, omits the current closed-loop control link, and can realize current sharing of any multiple power modules.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation technology, specifically relating to a photovoltaic DC grid-connected converter control method that takes into account both power module current sharing and maximum power point tracking (MPPT). Background Technology

[0002] With the massive consumption of fossil fuels such as coal, oil, and natural gas, a series of problems have emerged, including energy crises, environmental pollution, and climate change. Utilizing new energy sources can effectively improve my country's energy structure while avoiding environmental degradation caused by fossil fuel consumption. Among various new energy sources, solar energy, due to its large total amount and clean, pollution-free operation, is becoming a key focus of research and utilization in various countries.

[0003] Due to the influence of light intensity and ambient temperature, the output of photovoltaic cells exhibits nonlinearity. To improve the system's conversion efficiency, the photovoltaic cells should always operate at their maximum power point (MPP). For high-power photovoltaic DC-DC grid-connected converters, the input is a DC photovoltaic array of several hundred to one thousand volts, and the output is high voltage / high current. To reduce the voltage / current stress on the modules, a modular topology can be adopted, i.e., a topology with parallel inputs and series / parallel outputs. Due to the coupling characteristics of modular systems, the power transmission power of the power modules in the system is directly proportional to the input current. When the power transmission power of the power modules in the system is unbalanced, the power module with the higher output power will experience overcurrent problems. Although limiting the current can ensure the stable operation of the parallel system, it will cause a loss in the power transmission of the converter.

[0004] Chinese invention patent CN202110989159.0 discloses an MPPT control method for an LLC topology photovoltaic power generation system. This method improves the algorithm parameters, enhancing the dynamic tracking performance of MPPT. When the dynamic effect is rapid, it can gradually reduce steady-state oscillations, decrease system losses, and improve control accuracy. However, the control method used in this paper is only applicable to a single module. For multi-module parallel systems, an additional current closed-loop controller is required to ensure current sharing among power modules, increasing the control complexity and reducing the system's robustness.

[0005] Chinese invention patent CN201910604753.6 discloses a current sharing method for a spacecraft solar power regulation module without current detection. When the converter is operating in voltage regulation mode, the output power is balanced by controlling the operating point voltage of the solar cell array, thereby indirectly achieving current sharing of the power module. This method is simple to control, greatly reduces the number of Hall elements in the system, and improves the reliability of the system. However, this method is only applicable to photovoltaic conversion systems with independent inputs and parallel outputs, and is not suitable for large photovoltaic arrays. At the same time, the current sharing effect of the module is limited by the operating state of the photovoltaic array. When the temperature / illuminance difference is large, the current sharing effect is poor.

[0006] Chinese invention patent CN201510629954.3 discloses a grid-connected control method for a photovoltaic high-voltage DC grid-connected converter. This method uses a combination of voltage and current dual closed-loop control and voltage and current sharing loop control to achieve current sharing control of the input parallel and output series photovoltaic conversion system. It can realize current sharing of power modules and the control idea is clear. However, the control process is relatively complex and the parameter adjustment is difficult. Moreover, when the number of operating modules changes, especially when the power module fails, if the converter does not obtain fault information in time, it will generate incorrect current sharing commands, causing the system to fail to operate normally.

[0007] Existing MPPT (Multi-Level Testing) and power module current sharing control methods applied to photovoltaic (PV) power generation systems are mostly based on a hierarchical approach. This involves adding an additional current / voltage closed-loop controller on top of the MPPT to achieve current sharing among parallel power modules. This makes the system controller quite complex, and the problem becomes particularly prominent when these methods are applied to large-scale PV power generation systems with a large number of power modules. Although some scholars have proposed sensorless current sharing control strategies, this method is essentially equivalent to single-module operation and ignores the impact of environmental factors on the current sharing effect.

[0008] In summary, existing control methods for HVDC grid-connected converters that balance power module current sharing and MPPT are quite complex and lack the ability to achieve current sharing across any number of power modules. Therefore, it is necessary to improve upon existing MPPT methods and propose a control method for HVDC grid-connected converters that balances power module current sharing and MPPT. Summary of the Invention

[0009] To achieve both MPPT tracking and current balance of power modules in a DC-DC converter, this invention proposes a control method for a photovoltaic DC-DC grid-connected converter that balances current sharing among power modules and MPPT. This method employs an adaptive duty cycle control strategy that eliminates the need for current sharing commands. Based on the concept of duty cycle perturbation, this invention enables a multi-module parallel photovoltaic power generation system to simultaneously track MPPT and achieve current sharing among power modules by adjusting their duty cycles, thus ensuring reliable and stable system operation.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A control method for a photovoltaic DC-DC grid-connected converter that balances power module current sharing and MPPT includes the following specific steps:

[0012] (1) Encode the power modules in the DC-DC grid-connected converter and set the initial values ​​of the control parameters;

[0013] (2) Sample the photovoltaic array status information to determine the direction of duty cycle disturbance;

[0014] (3) Calculate the power disturbance increment of the photovoltaic array and determine the duty cycle disturbance increment;

[0015] (4) Determine the power module number to be subjected to duty cycle disturbance based on the power module current information;

[0016] (5) Update the duty cycle of the disturbance power module according to the module number of the duty cycle disturbance and the duty cycle disturbance increment;

[0017] (6) Control the switching transistor to turn on and off according to the duty cycle modulation signal of the power module.

[0018] Further, the encoding of the power modules in step (1) includes: uniformly encoding the power modules in sequence, where the encoding of the power module is a positive integer, wherein the initial value of the encoding is 1, and the encoding of each power module is incremented by 1 in sequence according to the encoding order, until all power modules in the DC grid-connected converter are encoded. Let the total number of power modules in the grid-connected converter be N, then the encoding form of each power module is: 1, 2, 3, ..., N.

[0019] Furthermore, the control parameters in step (1) include: the initial duty cycle D1, D2, ..., D of each power module. N Duty cycle perturbation direction D dir Duty cycle disturbance increment ΔD, total input power of the power module at time 0 P0, and maximum power transmitted by a single power module P. mod_max Maximum input current I of a single power module mod_max .

[0020] Furthermore, the photovoltaic array status information in step (2) includes the output voltage V of the photovoltaic array. in and the input current I of each power module in_1 I in_2 , ..., I in_N .

[0021] Furthermore, the direction of the duty cycle disturbance in step (2) is the direction of duty cycle adjustment. When adjusting in the direction of increasing duty cycle, D dir =1, when adjusted in the direction of decreasing duty cycle, D dir =-1.

[0022] Furthermore, the method for determining the duty cycle perturbation direction in step (2) includes the following seven steps:

[0023] Step 1: Calculate the input power P of each power module at time k. in_1 P in_2 ..., P in_N ;

[0024] Step 2: Calculate the total input power P of the power module at time k. in =P in_1 +P in_2 +……+P in_N ;

[0025] Step 3: Calculate the total input power increment ΔP of the power module at time k and the previous time.

[0026] Step 4: Update the duty cycle perturbation direction based on the duty cycle perturbation direction and power increment ΔP at time k;

[0027] Step 5: Determine the input power P of each power module in_n Is it greater than P? mod_max If so, then the duty cycle is perturbed in the direction of decreasing power, and proceed to step 7;

[0028] Step 6: Determine the input current I of each power module in_n Is it greater than I? mod_max If so, then the duty cycle is perturbed in the direction of decreasing power, and proceed to step 7;

[0029] Step 7: Output duty cycle perturbation direction D dir .

[0030] Furthermore, step 4 comprises the following four steps:

[0031] Step 1: Determine the direction of the duty cycle perturbation at time k. If the perturbation is in the direction of increasing duty cycle, proceed to Step 2; if the perturbation is in the direction of decreasing duty cycle, proceed to Step 3.

[0032] Step 2: Determine whether the power increment ΔP is greater than 0. If yes, the duty cycle disturbance direction remains unchanged, and proceed to step 4; if no, the duty cycle disturbance direction is reversed, and proceed to step 4.

[0033] Step 3: Determine whether the power increment ΔP is greater than 0. If yes, reverse the direction of the duty cycle disturbance and proceed to step 4; otherwise, keep the direction of the duty cycle disturbance unchanged and proceed to step 4.

[0034] Step 4: Output the duty cycle perturbation direction;

[0035] Where N is the number of power modules; P in_n The input power of the power module coded as n, where n = 1, 2, 3, ..., N; I in_n Let n be the input current of the power module with code n, where n = 1, 2, 3, ..., N.

[0036] Furthermore, the calculation method for the duty cycle disturbance increment ΔD in step (5) is as follows:

[0037]

[0038] Where A is a constant; dP / dD is the step size adjustment coefficient; and γ is the adjustment threshold used to limit the duty cycle increment, thereby balancing the speed and stability of the tracking process.

[0039] Furthermore, the method for determining the power module encoding for duty cycle perturbation in step (4) includes the following four steps:

[0040] Step 1: Determine the number of update modules m per cycle based on the required tracking speed, where m∈N + And m <N;

[0041] Step 2: Sort the power module currents;

[0042] Step 3: If the perturbation is directed in the direction of decreasing duty cycle, i.e., D... dir =-1, then the power module encoding for duty cycle perturbation is the encoding of the first m modules with larger power module currents; if the perturbation is performed in the direction of increasing duty cycle, i.e., D dir If = 1, then the power module encoding for duty cycle perturbation is the encoding of the first m modules with smaller power module currents;

[0043] Step 4: Output the power module code with duty cycle perturbation.

[0044] Furthermore, the method for updating the duty cycle of the power module in step (5) is as follows: D i =D i +ΔD×D dir , where i is the code of the power module whose duty cycle needs to be updated.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] First, the method of the present invention achieves maximum power point tracking of the photovoltaic array while simultaneously realizing balanced control among the power modules of the modular system. When the outputs of each DC / DC power module are connected in series or parallel, it can achieve equal voltage / current of each power module, avoiding the phenomenon of damage to the equipment due to excessive voltage / current stress of a certain power module, thereby improving the overall reliability of the photovoltaic DC grid-connected converter.

[0047] Secondly, the method of the present invention directly adjusts the duty cycle of the power module based on the duty cycle perturbation method, omitting the closed-loop controller and avoiding the system oscillation caused by the use of a closed-loop controller in the existing method. This can effectively improve the system response speed and enhance the robustness of the system.

[0048] Third, the method of the present invention achieves balanced control of power modules by comparing the relative values ​​of currents among power modules. It does not require calculating the voltage / current setpoint of the power modules. Without modifying the algorithm, it can achieve current sharing of any number of modules, and can still ensure the stable operation of the system when a power module fails and exits operation. Attached Figure Description

[0049] Figure 1 This is a flowchart illustrating the steps of a photovoltaic DC-DC grid-connected converter control method that combines power module current sharing and MPPT according to the present invention.

[0050] Figure 2 This is a block diagram of the photovoltaic DC grid-connected converter of the present invention;

[0051] Figure 3 This is a control flowchart for a DC-DC grid-connected converter with three power modules connected in parallel input and output, where the number of modules updated in a single operation is 1, according to a specific embodiment of the present invention. Detailed Implementation

[0052] The present invention will now be fully described in conjunction with the accompanying drawings. Figure 3 The present invention describes an application scenario where three power modules are connected in parallel with a single update module count of 1. However, the invention is also applicable to application scenarios with series outputs and combinations of any number of modules. This application scenario is presented to facilitate description and to make the disclosure of the invention more thorough and comprehensive.

[0053] This invention proposes a control method for photovoltaic DC-DC grid-connected converters that balances power module current sharing and MPPT (Maximum Power Point Test). Generally, for topologies with power modules connected in parallel at the output, power module equalization can be achieved through input current sharing control. For topologies with power modules connected in series at the output, output voltage equalization control requires acquiring the output voltage signal as a control feedback signal. However, voltage sampling circuits are complex and have high hardware costs. This invention achieves output voltage equalization control through input current sharing control. The principle is that when power modules are connected in parallel at the input, the output current / voltage is equal when the outputs are connected in series / parallel. According to the principle of energy conservation, equalizing the input current of each power module can achieve output voltage / current equalization, thus realizing balanced control between modules. Figure 1 As shown, a photovoltaic DC-DC grid-connected converter control method of the present invention, which takes into account both power module current sharing and MPPT, includes the following steps:

[0054] Step 101: Encode the power modules in the DC-DC grid-connected converter and set the initial values ​​of control parameters such as duty cycle;

[0055] The method for encoding the power modules is as follows: Power modules are uniformly encoded sequentially, with each module's code being a positive integer. The initial value of the code is 1, and the code for each power module increments by 1 sequentially according to the encoding order, until all power modules in the DC-DC grid-connected converter are encoded. Let the total number of power modules in the grid-connected converter be N, then the encoding format for each power module is: 1, 2, 3, ..., N.

[0056] The control parameters include: the initial duty cycle D1, D2, ..., D of each power module. N Duty cycle perturbation direction D dir Duty cycle disturbance increment ΔD, total input power of the power module at time 0 P0, and maximum power transmitted by a single power module P. mod_max Maximum input current I of a single power module mod_max .

[0057] Step 102: Sample the photovoltaic array status information to determine the direction of duty cycle perturbation;

[0058] The state information of the photovoltaic array includes the output voltage V of the photovoltaic array. in and the input current I of each power module in_1 I in_2 , ..., I in_N .

[0059] The aforementioned duty cycle disturbance direction is the same as the duty cycle adjustment direction. When adjusting in the direction of increasing duty cycle, D dir =1, when adjusted in the direction of decreasing duty cycle, D dir =-1.

[0060] The method for determining the direction of the duty cycle disturbance includes the following seven steps:

[0061] Step 1: Calculate the input power P of each power module at time k. in_1 P in_2 ..., P in_N ;

[0062] Step 2: Calculate the total input power P of the power module at time k. in =P in_1 +P in_2 +……+P in_N ;

[0063] Step 3: Calculate the total input power increment ΔP of the power module at time k and the previous time.

[0064] Step 4: Update the duty cycle perturbation direction based on the duty cycle perturbation direction and power increment ΔP at time k;

[0065] Step 5: Determine the input power P of each power module in_n Is it greater than P? mod_max If so, then the duty cycle is perturbed in the direction of decreasing power, and proceed to step 7;

[0066] Step 6: Determine the input current I of each power module in_n Is it greater than I? mod_max If so, then the duty cycle is perturbed in the direction of decreasing power, and proceed to step 7;

[0067] Step 7: Output duty cycle perturbation direction D dir .

[0068] In step 4 of the method for determining the duty cycle perturbation direction, updating the duty cycle perturbation direction based on the duty cycle perturbation direction at time k and the power increment ΔP includes the following four steps:

[0069] Step 1: Determine the direction of the duty cycle perturbation at time k. If the perturbation is in the direction of increasing duty cycle, proceed to Step 2; if the perturbation is in the direction of decreasing duty cycle, proceed to Step 3.

[0070] Step 2: Determine whether the power increment ΔP is greater than 0. If yes, the duty cycle disturbance direction remains unchanged, and proceed to step 4; if no, the duty cycle disturbance direction is reversed, and proceed to step 4.

[0071] Step 3: Determine whether the power increment ΔP is greater than 0. If yes, reverse the direction of the duty cycle disturbance and proceed to step 4; otherwise, keep the direction of the duty cycle disturbance unchanged and proceed to step 4.

[0072] Step 4: Output the duty cycle perturbation direction.

[0073] Where N is the number of power modules; P in_n The input power of the power module coded as n, where n = 1, 2, 3, ..., N; I in_n Let n be the input current of the power module with code n, where n = 1, 2, 3, ..., N.

[0074] Step 103: Calculate the photovoltaic array power disturbance increment and determine the duty cycle disturbance increment;

[0075] The method for calculating the duty cycle disturbance increment ΔD is as follows:

[0076]

[0077] Where A is a constant; dP / dD is the step size adjustment coefficient; and γ is the adjustment threshold used to limit the duty cycle increment, thereby balancing the speed and stability of the tracking process.

[0078] Step 104: Determine the power module code for duty cycle perturbation based on the power module current information;

[0079] The method for determining the power module encoding for duty cycle perturbation includes the following four steps:

[0080] Step 1: Determine the number of update modules m per cycle based on the required tracking speed, where m∈N + And m <N;

[0081] Step 2: Sort the power module currents;

[0082] Step 3: If the perturbation is directed in the direction of decreasing duty cycle, i.e., D... dir =-1, then the power module encoding for duty cycle perturbation is the encoding of the first m modules with larger power module currents; if the perturbation is performed in the direction of increasing duty cycle, i.e., D dir If = 1, then the power module encoding for duty cycle perturbation is the encoding of the first m modules with smaller power module currents;

[0083] Step 4: Output the power module code with duty cycle perturbation.

[0084] Step 105: Update the duty cycle of the disturbance power module according to the disturbance module code and disturbance increment;

[0085] The method for updating the duty cycle of the power module is as follows: D i =D i +ΔD×D dir , where i is the code of the power module whose duty cycle needs to be updated.

[0086] Step 106: Each power module compares the duty cycle modulation signal with the triangular carrier wave to generate a pulse width modulation (PWM) signal to control the switching transistors of the power module to turn on and off.

[0087] Figure 2 The present invention is a structural block diagram of a photovoltaic DC grid-connected converter, which includes two DC grid-connected forms: input parallel output parallel grid-connected form 201 and input parallel output series grid-connected form 202. Each grid-connected form includes a photovoltaic array 203, a photovoltaic DC grid-connected converter 204 and a DC grid 205.

[0088] Figure 3 This is a control flowchart for a DC-DC grid-connected converter with three power modules connected in parallel input and output, where the number of modules updated in a single operation is one, according to a specific embodiment of the present invention. The control of the DC-DC grid-connected converter with three power modules connected in parallel input and output is achieved through an initialization setting module 301, a duty cycle disturbance direction determination module 302, an adaptive duty cycle module 303, and a duty cycle update module 304.

[0089] The initialization setting module 301 sets the following parameters: the initialization duty cycles D1, D2, and D3 of the three power modules, and the duty cycle disturbance direction D. dir Duty cycle disturbance increment ΔD, total input power of the power module at time 0 P0, and maximum power transmitted by a single power module P. mod_max Maximum input current I of a single power module mod_max .

[0090] The operation flow of the duty cycle disturbance direction determination module 302 is as follows:

[0091] Procedure 1: Calculate the total input power of the power module at time k, and calculate the increase in the total input power of the power module between time k and the previous time.

[0092] Step 2: Determine the direction of the duty cycle perturbation at time k. If the perturbation is in the direction of increasing duty cycle, proceed to Step 3; if the perturbation is in the direction of decreasing duty cycle, proceed to Step 4.

[0093] Step 3: Determine if the power increment ΔP is greater than 0. If yes, the duty cycle disturbance direction remains unchanged, and proceed to Step 5; if no, the duty cycle disturbance direction is reversed, and proceed to Step 5.

[0094] Step 4: Determine if the power increment ΔP is greater than 0. If yes, reverse the direction of the duty cycle disturbance and proceed to Step 5; otherwise, keep the direction of the duty cycle disturbance unchanged and proceed to Step 5.

[0095] Step 5: Determine the input power P of each power module in_n Is it greater than P? mod_maxIf so, then the duty cycle is perturbed in the direction of decreasing power, and process step seven is initiated.

[0096] Step 6: Determine the input current I of each power module in_n Is it greater than I? mod_max If so, then the duty cycle is perturbed in the direction of decreasing power, and process step seven is initiated.

[0097] Step 7: Output duty cycle perturbation direction D dir .

[0098] The operation flow of the adaptive duty cycle module 303 is as follows:

[0099] Procedure 1: Determine whether the absolute value of the step size adjustment coefficient dP / dD is greater than the adjustment threshold γ. If so, set dP / dD = γ.

[0100] Step 2: Duty Cycle Disturbance Increment

[0101] The duty cycle update module 304 includes the following process:

[0102] Step 1: Determine I1×D dir Is it less than or equal to I²×D? dir And I1×D dir Is it less than or equal to I3×D? dir That is, when the duty cycle disturbance direction is increasing, it is determined whether the current I1 of the power module with code 1 is less than the current I2 of the power module with code 2 and whether the current I1 of the power module with code 1 is less than the current I3 of the power module with code 3. When the duty cycle disturbance direction is decreasing, it is determined whether the current I1 of the power module with code 1 is greater than the current I2 of the power module with code 2 and whether the current I1 of the power module with code 1 is greater than the current I3 of the power module with code 3. If so, the duty cycle of the power module with code 1 is updated and the process proceeds to step four.

[0103] Step 2: Determine I²×D dir Is it less than or equal to I1×D? dir And I2×D dir Is it less than or equal to I3×D? dir If so, update the duty cycle of the power module with code 2 and proceed to process four;

[0104] Step 3: Determine I3×D dir Is it less than or equal to I1×D? dir And I3×D dir Is it less than or equal to I²×D? dir If so, update the duty cycle of the power module with code 3 and proceed to process four;

[0105] Step 4: Output the updated duty cycles D1, D2, and D3 for each power module.

[0106] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control method for a photovoltaic DC-DC grid-connected converter that balances power module current sharing and MPPT, characterized in that, Includes the following steps: (1) Encode the power modules in the DC-DC grid-connected converter and set the initial values ​​of the control parameters; (2) Sample the photovoltaic array status information to determine the direction of duty cycle disturbance; Photovoltaic array status information includes the output voltage of the photovoltaic array. V in and the input current of each power module I in_1 , I in_2 , ..., I in_N ; The direction of the duty cycle disturbance is the direction of duty cycle adjustment. When adjusting in the direction of increasing duty cycle, D dir = 1, when adjusting in the direction of decreasing duty cycle, D dir = -1; The method for determining the direction of duty cycle perturbation includes the following seven steps: Step 1, Calculation k Input power of each power module at any time P in_1 , P in_2 , ..., P in_N ; Step 2, Calculation k Total input power of the time power module P in = P in_1 + P in_2 + …… + P in_N ; Step 3, Calculation k Increment of total input power of the power module between time step and the previous time step ΔP ; Step 4, according to k Duty cycle perturbation direction and power increment at time t ΔP Update the duty cycle perturbation direction; Step 5: Determine the input power of each power module P in_n Is it greater than P mod_max If so, then the duty cycle is perturbed in the direction of decreasing power, and proceed to step 7; Step 6: Determine the input current of each power module I in_n Is it greater than I mod_max If so, then the duty cycle is perturbed in the direction of decreasing power, and proceed to step 7; Step 7: Output duty cycle perturbation direction D dir ; (3) Calculate the power disturbance increment of the photovoltaic array and determine the duty cycle disturbance increment; (4) Based on the power module current information, determine the power module number for duty cycle disturbance, which includes the following four steps: Step 1, Judgment k The direction of the duty cycle perturbation is determined at all times. If the perturbation is directed towards increasing the duty cycle, proceed to step 2; if the perturbation is directed towards decreasing the duty cycle, proceed to step 3. Step 2: Determine the power increment ΔP If the value is greater than 0, the duty cycle perturbation direction remains unchanged, and proceed to step 4; otherwise, the duty cycle perturbation direction is reversed, and proceed to step 4. Step 3: Determine the power increment ΔP If the value is greater than 0, the duty cycle perturbation direction is reversed, and the process proceeds to step 4; otherwise, the duty cycle perturbation direction remains unchanged, and the process proceeds to step 4. Step 4: Output the duty cycle perturbation direction; in, N This represents the number of power modules; P in_n For encoding n The input power of the power module, n =1,2,3,……, N ; I in_n For encoding n The input current of the power module, n =1,2,3,……, N； (5) Update the duty cycle of the disturbance power module according to the module number of the duty cycle disturbance and the duty cycle disturbance increment; (6) Control the switching transistor to turn on and off according to the duty cycle modulation signal of the power module.

2. The photovoltaic DC-DC grid-connected converter control method according to claim 1, which takes into account both power module current sharing and MPPT, is characterized in that: The encoding of the power modules in step (1) includes: uniformly encoding the power modules in sequence, where each power module's code is a positive integer. The initial value of the code is 1, and the code of each power module increments by 1 sequentially according to the encoding order, until all power modules in the DC-DC grid-connected converter are encoded, resulting in a total number of power modules in the grid-connected converter. N The encoding format of each power module is: 1, 2, 3, ... N .

3. The photovoltaic DC-DC grid-connected converter control method according to claim 2, which takes into account both power module current sharing and MPPT, is characterized in that: The control parameters in step (1) include: the initial duty cycle of each power module. D 1. D 2, ..., D N Duty cycle perturbation direction D dir Duty cycle disturbance increment ΔD The total input power of the power module at time 0 P 0, Maximum power transmitted by a single power module P mod_max Maximum input current of a single power module I mod_max .

4. The photovoltaic DC-DC grid-connected converter control method according to claim 1, which takes into account both power module current sharing and MPPT, is characterized in that: The duty cycle disturbance increment in step (5) ΔD The calculation method is as follows: in, A It is a constant; dP / dD This is the step size adjustment coefficient; γ The threshold is adjusted to limit the duty cycle increment, thereby balancing the speed and stability of the tracking process.

5. A photovoltaic DC-DC grid-connected converter control method that takes into account both power module current sharing and MPPT as described in claim 4, characterized in that; The method for determining the power module encoding for duty cycle perturbation in step (4) includes the following four steps: Step 1: Determine the number of modules per update based on the required tracking speed. m ,in m ∈ N + and m < N ; Step 2: Sort the power module currents; Step 3: If the perturbation is directed in the direction of decreasing duty cycle, that is... D dir = -1, then the power module that performs duty cycle perturbation is coded as the one with the larger power module current. m The encoding of each module; If the perturbation is directed in the direction of increasing duty cycle, that is... D dir = 1, then the power module that performs duty cycle perturbation is coded as the one with the smaller power module current. m The encoding of each module; Step 4: Output the power module code with duty cycle perturbation.

6. A photovoltaic DC-DC grid-connected converter control method that takes into account both power module current sharing and MPPT as described in claim 5, characterized in that: The method for updating the duty cycle of the power module in step (5) is as follows: D i = D i +ΔD × D dir ,in, i This is the coding for power modules that require duty cycle updates.

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