Control method and system for realizing maximum generating capacity of photovoltaic inverter

Abstract

The invention discloses a control method and system for realizing the maximum generating capacity of a photovoltaic inverter, and the method comprises the steps: carrying out the maximum power point tracking MPPT optimization of the photovoltaic inverter, detecting the duty ratio in real time, judging whether the optimization is stable or not according to the change of the duty ratio, and recording the current duty ratio and the corresponding output power if the optimization is stable; the method comprises the steps of calculating the output power after the duty ratio is increased, increasing the duty ratio, calculating the output power after the duty ratio is increased, repeatedly increasing or reducing the duty ratio according to the size relation of the output power before and after the duty ratio is increased, and determining the final duty ratio according to the output power before and after the duty ratio is increased or reduced each time. By adjusting the duty ratio and adopting an output power magnitude comparison method, the saved loss power is larger than the advantage-seeking deviation loss power, the maximum output power of the inverter is achieved, and the overall generating capacity is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of photovoltaic power generation control, and more particularly relates to a control method and system for realizing maximum power generation of a photovoltaic inverter. BACKGROUND

[0002] The photovoltaic inverter is an inverter applied in a solar power generation system and is an important component in the photovoltaic power generation system. The size of the output power of the photovoltaic inverter directly affects the amount of power generation. Currently, a group string type photovoltaic inverter is composed of two modules, DCDC and DCAC. The DCDC module is used to realize maximum power point tracking, and the DCAC is used to invert and connect to the grid. The output voltage of the DCDC is the input voltage of the DCAC, and the two can be relatively independently controlled through bus capacitor decoupling. In actual application, the DCDC tracks the maximum power point through the duty cycle, and the bus voltage also changes according to the change of the duty cycle.

[0003] When the light intensity, i.e., the ambient temperature, is different at sunrise, sunset, and cloudy days, the photovoltaic power generation property changes. In order to track the maximum power, the duty cycle of the DCDC changes, the duty cycle causes the bus voltage to change, and the module loss also changes because the bus voltages are different, resulting in a loss of power generation. Based on this, the maximum power output point is found through duty cycle adjustment to improve the power generation of the photovoltaic inverter.

[0004] Patent CN114142526B proposes a bus voltage variable control strategy, i.e., the second stage voltage parameter changes after the duty cycle of the first stage power optimizer changes, in view of the fact that when some photovoltaic components are shaded, the corresponding optimizer needs to step down and step up, and the inverter works in a low duty cycle range, thereby affecting the working efficiency of the system. However, the patent has the following shortcomings: ① The patent is only applicable to the scenario where multiple DCDCs are connected in series to the same bus, and there is a situation where the optimizer voltage and the bus voltage are inconsistent; ② The patent only focuses on the high efficiency of the power optimizer, but not the maximum overall output power.

[0005] Patent CN104158417B proposes to set a corresponding switching carrier frequency value for each output power segment to improve the inductance utilization rate and reduce the switching loss in view of the switching loss problem of a single-stage photovoltaic inverter. However, the patent has the following shortcomings: ① The switching frequency not only affects the switching loss of the switching tube, but also affects the inductance loss and capacitance loss of the circuit. The overall loss is not the lowest when the switching loss is the lowest, and there is a difference between the fixed frequency segment preset frequency and the actual running state; ② The patent is only applicable to single-stage DCAC inversion, and the application range is limited. SUMMARY

[0006] To solve the problems in the prior art, the present application provides a control method and system for realizing maximum power generation of a photovoltaic inverter.

[0007] The application adopts the technical scheme as follows.

[0008] The first aspect of the application provides a control method for realizing maximum power generation of a photovoltaic inverter, and comprises the following contents.

[0009] The photovoltaic inverter is subjected to maximum power point tracking (MPPT) optimization, and the duty cycle is detected in real time; whether the optimization is stable is judged according to the variation of the duty cycle; if the optimization is stable, the current duty cycle d1 is recorded, and the corresponding output power P d1 is calculated.

[0010] The duty cycle is increased, the output power P d2 after the increase of the duty cycle is calculated, and is compared with P d1 .

[0011] If P d2 is greater than P d1 , the duty cycle is repeatedly increased and the corresponding output power is calculated until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the last duty cycle, and the duty cycle is restored to the last duty cycle.

[0012] If P d2 is less than or equal to P d1 , the duty cycle is reduced, the output power P d3 after the reduction of the duty cycle is calculated, if P d3 is greater than or equal to P d1 , the duty cycle is restored to d1, if P d3 is less than P d1 , the duty cycle is repeatedly reduced and the corresponding output power is calculated until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the last duty cycle, and the duty cycle is restored to the last duty cycle.

[0013] Preferably, whether the optimization is stable is judged according to the variation of the duty cycle, and specifically:

[0014] whether the average variation difference of the duty cycle in a set first period is less than a duty cycle variation threshold is judged, when the average variation difference is less than the duty cycle variation threshold, it is determined that the optimization is stable, otherwise the optimization is unstable, and the maximum power point tracking (MPPT) optimization is continuously performed.

[0015] Preferably, the steps of increasing and reducing the duty cycle are all the same.

[0016] Preferably, when the duty cycle is adjusted, the photovoltaic input current is detected in real time, when the variation of the photovoltaic input current in a set second period exceeds a set first proportion of the average value of the photovoltaic input current in the first period, the adjustment of the duty cycle is stopped, and the MPPT optimization of the photovoltaic inverter is continuously performed, and the second period is less than the first period.

[0017] Preferably, the output power is calculated after waiting for a set time interval after each increase or decrease of the duty cycle, and the power is taken as the output power corresponding to the duty cycle.

[0018] Preferably, the output power is equal to the photovoltaic power minus the DCDC circuit loss and the DCAC circuit loss.

[0019] Preferably, when the duty cycle is adjusted, the temperature of any module of the photovoltaic inverter is detected in real time, and when the module temperature reaches a set temperature threshold, the adjustment of the duty cycle is stopped until the value of the module temperature decreases to a set second proportion of the temperature threshold, and then the adjustment of the duty cycle is continued.

[0020] The second aspect of the present application proposes a control system for realizing maximum power generation of a photovoltaic inverter based on the control method of the first aspect of the present application, comprising an optimization stability judgment module, a preliminary duty cycle adjustment module, an output power comparison module, a first adjustment module, and a second adjustment module, characterized in that:

[0021] The optimization stability judgment module is used for MPPT optimization of the photovoltaic inverter and real-time detection of the duty cycle, and judges whether the optimization is stable according to the size of the change of the duty cycle.

[0022] The preliminary duty cycle adjustment module is used for recording the current duty cycle d1 when the optimization is stable, calculating the corresponding output power P d1 , increasing the duty cycle, and calculating the output power P d2 after the increase of the duty cycle.

[0023] The output power comparison module is used for comparing the size of P d2 and P d1 .

[0024] The first adjustment module is used for repeating the increase of the duty cycle and the calculation of the corresponding output power if P d2 is greater than P d1 , until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the last duty cycle, and the duty cycle is restored to the last duty cycle.

[0025] The second adjustment module is used for decreasing the duty cycle if P d2 is less than or equal to P d1 , calculating the output power P d3 after the decrease of the duty cycle, restoring the duty cycle to d1 if P d3 is greater than or equal to P d1 , and decreasing the duty cycle if P d3 is less than P d1If the current duty cycle corresponds to an output power greater than the output power corresponding to the previous duty cycle, the duty cycle is reduced and the corresponding output power is calculated again until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the previous duty cycle, and the duty cycle is restored to the previous duty cycle.

[0026] The third aspect of the present application provides a device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the steps of the control method for achieving maximum power generation of a photovoltaic inverter according to the first aspect of the present application.

[0027] The fourth aspect of the present application provides a computer readable storage medium storing a computer program, wherein the computer program is executable by a processor to execute the steps of the control method for achieving maximum power generation of a photovoltaic inverter according to the first aspect of the present application.

[0028] The present application has the beneficial effect that, compared with the prior art, the present application, on the basis of optimization of a photovoltaic string inverter, detects the inverter circuit parameters, and under different environmental temperatures and light conditions, adjusts the DCDC duty cycle by using the output power magnitude ratio, so that the power loss of the photovoltaic inverter is greater than the power loss of the optimization point deviation, the output power of the inverter is maximized, and the overall power generation is improved. The DCDC module of the photovoltaic inverter dominates the bus voltage, and the duty cycle of the DCDC module is controlled to realize the control logic line of the duty cycle-bus voltage-inverter output power, realize maximum power generation output, and there is no need to preset any power gear and frequency gear. The module saves the loss and the power tracking point power loss, etc. are equivalent to a "black box", and the optimization is realized by automatic operation. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The photovoltaic inverter is a two-stage topology architecture;

[0030] Figure 2 The present application is a flowchart of the method;

[0031] Figure 3 The present application is a schematic diagram of the execution process of the method. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. The embodiments described in the present application are only a part of the embodiments of the present application, but not all the embodiments. Based on the spirit of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0033] The photovoltaic inverter mainly comprises a DCDC and a DCAC, as shown inFigure 1 As shown, the conventional MPPT optimization control generates a reference signal by sampling photovoltaic voltage and photovoltaic current to do MPP operation, and generates a control signal after comparison with an operational amplifier, thereby realizing maximum power point tracking. The bus voltage is regulated smoothly by DCAC.

[0034] In a two-stage string inverter, the intermediate bus voltage of DCDC and DCAC can be controlled by DCDC and DCAC at the same time. By changing the duty cycle of DCDC, the bus voltage changes. According to Ohm's law, the bus voltage increases and the current decreases, and the losses of DCDC and DCAC change, and the optimized power point also changes. The losses of DCDC and DCAC and the optimized power point are equivalent to a "black box", and the minimum power loss interval is found by using the maximum power generation logic purpose, and the maximum power generation of the inverter is realized.

[0035] As shown in Figure 2 Embodiment 1 of the present application provides a control method for realizing maximum power generation of a photovoltaic inverter, characterized in that it comprises the following contents:

[0036] The photovoltaic inverter is subjected to maximum power point tracking (MPPT) optimization, and the duty cycle is detected in real time. Whether the optimization is stable is judged according to the change of the duty cycle. If it is stable, the current duty cycle d1 is recorded, and the corresponding output power P d1 is calculated. The duty cycle is increased, and the output power P d2 after the increase of the duty cycle is calculated.

[0037] If P d2 is greater than P d1 , the duty cycle is repeatedly increased and the corresponding output power is calculated until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the last duty cycle, and the duty cycle is restored to the last duty cycle.

[0038] If P d2 is less than or equal to P d1 , the duty cycle is reduced, the output power P d3 after the reduction of the duty cycle is calculated, P d3 is greater than or equal to P d1 , the duty cycle is restored to d1, and P d3 is less than P d1 , the duty cycle is repeatedly reduced and the corresponding output power is calculated until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the last duty cycle, and the duty cycle is restored to the last duty cycle.

[0039] The judgment of whether the optimization is stable according to the change of the duty cycle is specifically:

[0040] The average duty cycle change difference in the first period is determined whether it is less than the duty cycle change threshold value, and when it is less than the duty cycle change threshold value, it is determined that the optimization is stable, otherwise the optimization is unstable, and the maximum power point tracking (MPPT) optimization is continued, and the duty cycle change threshold value is set to 0.02.

[0041] It should be noted that the first period in the embodiment is set to 1 min.

[0042] All the steps of increasing and decreasing the duty cycle are the same, and the embodiment is set to 0.01.

[0043] When the duty cycle adjustment is performed, the photovoltaic input current is detected in real time, and when the change of the photovoltaic input current in the second period exceeds the first proportion of the average value of the photovoltaic input current in the first period, the duty cycle adjustment is stopped, and the MPPT optimization of the photovoltaic inverter is continued. The second period is less than the first period, and the first proportion is set to 10%.

[0044] It should be noted that after the MPPT optimization of the photovoltaic inverter is continued each time, it is repeated whether the optimization is stable according to the size of the duty cycle change, and the duty cycle adjustment is performed after the optimization is stable.

[0045] After the duty cycle is increased or decreased each time, the output power is calculated after a set time interval, and the power is taken as the output power corresponding to the duty cycle, and the set time interval is greater than or equal to 5 seconds.

[0046] The output power is equal to the photovoltaic power minus the DCDC circuit loss and the DCAC circuit loss.

[0047] When the duty cycle adjustment is performed, the temperature of any module of the photovoltaic inverter is detected in real time, and when the module temperature reaches the set temperature threshold value, the duty cycle adjustment is stopped until the value of the module temperature decreases to the second proportion of the temperature threshold value, and then the duty cycle adjustment is continued.

[0048] It should be noted that the second proportion in the embodiment is set to 20%.

[0049] Embodiment 2 of the present application proposes a control system for realizing the maximum power generation of a photovoltaic inverter based on the control method described in Embodiment 1 of the present application, which comprises an optimization stability judgment module, a preliminary duty cycle adjustment module, an output power comparison module, a first adjustment module, and a second adjustment module, characterized in that:

[0050] The optimization stability judgment module is used for performing the maximum power point tracking (MPPT) optimization of the photovoltaic inverter, and detecting the duty cycle in real time, and determining whether the optimization is stable according to the size of the duty cycle change.

[0051] Preliminary duty cycle adjustment module: used to record the current duty cycle d1 and calculate the corresponding output power P when seeking optimal stability d1 ; Increase the duty cycle and calculate the output power P after increasing the duty cycle d2 ;

[0052] Output power comparison module: used to compare P d2 and P d1 size;

[0053] The first adjustment module: used for P d2 Greater than P d1 , then repeatedly increase the duty cycle and calculate its corresponding output power until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the previous duty cycle, and restore the duty cycle to the previous duty cycle;

[0054] The second adjustment module: used for P d2 Less than or equal to P d1 , then reduce the duty cycle and calculate the output power P after reducing the duty cycle d3 , if P d3 Greater than or equal to P d1 , then restore the duty cycle to d1; if P d3 Less than P d1 , then repeatedly reduce the duty cycle and calculate its corresponding output power until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the previous duty cycle, and restore the duty cycle to the previous duty cycle.

[0055] It should be noted that if Figure 3 As described above, when the above module executes the method, sensors are used for measurement when collecting duty cycle and calculating power and loss parameters; and a DSP is used as the microprocessor when performing calculations, comparisons, and controlling the inverter.

[0056] Embodiment 3 of the present invention proposes a device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the steps of the control method for achieving maximum power generation of a photovoltaic inverter as described in embodiment 1 of the present invention.

[0057] Embodiment 4 of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the steps of the control method for achieving maximum power generation of a photovoltaic inverter described in embodiment 1 of the present invention are used.

[0058] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0059] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit it. Although the present application has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the specific embodiments of the present application can be modified or equivalently replaced without departing from the spirit and scope of the present application, and any modification or equivalent replacement should be covered within the protection scope of the claims of the present application.

Claims

1. A control method for achieving maximum power generation of a photovoltaic inverter, characterized in that: Includes the following: Perform maximum power point tracking (MPPT) optimization on the photovoltaic inverter and detect the duty cycle in real time. Determine whether the optimization is stable based on the change in duty cycle. If it is stable, record the current duty cycle d1 and calculate the corresponding output power P. d1 ; Increase the duty cycle and calculate the output power P after increasing the duty cycle d2 and with P d1 Compare; If P d2 Greater than P d1 , then repeatedly increase the duty cycle and calculate its corresponding output power until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the previous duty cycle, and restore the duty cycle to the previous duty cycle; If P d2 Less than or equal to P d1 , then reduce the duty cycle and calculate the output power P after reducing the duty cycle d3 , if P d3 Greater than or equal to P d1 , then restore the duty cycle to d1; if P d3 Less than P d1 , then repeatedly reduce the duty cycle and calculate its corresponding output power until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the previous duty cycle, and restore the duty cycle to the previous duty cycle.

2. A control method for achieving maximum power generation of a photovoltaic inverter according to claim 1, characterized in that: The determination of whether the optimization is stable according to the change in duty cycle is specifically as follows: It is determined whether the average change difference of the duty cycle in the set first period is less than the duty cycle change threshold. If it is less than the duty cycle change threshold, the optimization is determined to be stable. Otherwise, the optimization is unstable and the maximum power point tracking MPPT optimization continues.

3. A control method for achieving maximum power generation of a photovoltaic inverter according to claim 1 or 2, characterized in that: All steps for increasing and decreasing the duty cycle are the same size.

4. The control method for achieving maximum power generation of a photovoltaic inverter according to claim 2, characterized in that: When the duty cycle is adjusted, the photovoltaic input current is detected in real time. When the change of the photovoltaic input current in the set second period exceeds the set first proportion of the average value of the photovoltaic input current in the first period, the duty cycle adjustment is stopped and the MPPT optimization of the photovoltaic inverter is continued. The second period is smaller than the first period.

5. A control method for achieving maximum power generation of a photovoltaic inverter according to claim 1, 2 or 4, characterized in that: Each time the duty cycle is increased or decreased, the output power is calculated after a set time interval, and the power is used as the output power corresponding to the duty cycle.

6. A control method for achieving maximum power generation of a photovoltaic inverter according to any one of claim 5, characterized in that: The output power is equal to the photovoltaic power minus the DCDC circuit loss and the DCAC circuit loss.

7. The control method for achieving maximum power generation of a photovoltaic inverter according to claim 1, characterized in that: When performing duty cycle adjustment, the temperature of any module of the photovoltaic inverter is detected in real time. When the module temperature reaches the set temperature threshold, the duty cycle adjustment is stopped until the module temperature drops to a set second proportion of the temperature threshold, and then the duty cycle adjustment is continued.

8. A control system for achieving maximum power generation of a photovoltaic inverter based on the control method according to any one of claims 1 to 7, comprising an optimal stability judgment module, a preliminary duty cycle adjustment module, an output power comparison module, a first adjustment module, and a second adjustment module, characterized in that: Optimization and stability judgment module: used to perform maximum power point tracking (MPPT) optimization on photovoltaic inverters, detect duty cycle in real time, and judge whether the optimization is stable based on the change in duty cycle; Preliminary duty cycle adjustment module: used to record the current duty cycle d1 and calculate the corresponding output power P when seeking optimal stability d1 ; Increase the duty cycle and calculate the output power P after increasing the duty cycle d2 ; Output power comparison module: used to compare P d2 and P d1 size; The first adjustment module: used for P d2 Greater than P d1 , then repeatedly increase the duty cycle and calculate its corresponding output power until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the previous duty cycle, and restore the duty cycle to the previous duty cycle; The second adjustment module: used for P d2 Less than or equal to P d1 , then reduce the duty cycle and calculate the output power P after reducing the duty cycle d3 , if P d3 Greater than or equal to P d1 , then restore the duty cycle to d1; if P d3 Less than P d1 , then repeatedly reduce the duty cycle and calculate its corresponding output power until the output power corresponding to the current duty cycle is less than or equal to the output power corresponding to the previous duty cycle, and restore the duty cycle to the previous duty cycle.

9. A device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the steps of the control method for achieving maximum power generation of a photovoltaic inverter according to any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the steps of the method for controlling the maximum power generation of a photovoltaic inverter according to any one of claims 1 to 7 are used.

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