Power control method and photovoltaic power generation system

Abstract

The invention provides a power control method and a photovoltaic power generation system, and the method comprises the steps: recording the maximum value and the minimum value of the working current of each path of photovoltaic input; determining a first current value based on the recorded maximum value of the working current, and determining a second current value based on the recorded minimum value of the working current; determining a first photovoltaic input and a second photovoltaic input; adjusting the output power of the first photovoltaic input and the output power of the second photovoltaic input so as to enable the sum of the output power of each path of photovoltaic input to be smaller than or equal to a preset total power threshold value; updating the first current value based on the maximum value of the current working current, and updating the second current value based on the minimum value of the current working current; and returning to determine the photovoltaic input of which the working current is close to the first current value or the second current value as the first photovoltaic input. Under the condition that the complexity of a control algorithm is not increased, the stability of the limited power of the photovoltaic power generation system can be improved, and the working efficiency of the photovoltaic power generation system tends to be optimal.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic power generation, and in particular to a power control method and a photovoltaic power generation system. Background Art

[0002] In photovoltaic power generation technology, inverters usually need to support multiple photovoltaic inputs and make different photovoltaic inputs work in the optimal state. At present, inverters usually use MPPT algorithms to make each photovoltaic input work at the maximum power point. However, when the inverter is connected to the grid, the energy storage battery is fully charged, or it overheats during operation, the inverter still needs to limit power.

[0003] In the related technologies, one is to make the photovoltaic input maintain the power at the last moment before the power limit, specifically by controlling the voltage of the photovoltaic input to remain unchanged. Another is to control the working point of all photovoltaic inputs to move in the direction of increasing power. Another is to perform PI (proportional-integral) control on the output power of the inverter.

[0004] However, the above technology may have problems such as unstable power limit and suboptimal inverter efficiency when the photovoltaic input fluctuates due to light fluctuations. Summary of the invention

[0005] In view of the above, it is necessary to provide a power control method and a photovoltaic power generation system, which can improve the stability of the power limit of the photovoltaic power generation system and optimize its working efficiency.

[0006] The present application provides a power control method, which is applied to a photovoltaic power generation system. The photovoltaic power generation system includes multiple photovoltaic inputs, wherein the photovoltaic inputs have a limited power state and a non-limited power state. The power control method includes: when each photovoltaic input is in a non-limited power state, recording the maximum value and the minimum value of the working current of each photovoltaic input; when each photovoltaic input is in a limited power state, determining a first current value based on the maximum value of the working current recorded by each photovoltaic input, and determining a second current value based on the minimum value of the working current recorded by each photovoltaic input; determining a photovoltaic input whose working current is close to the first current value or the second current value as a first photovoltaic input, and determining a photovoltaic input other than the first photovoltaic input as a second photovoltaic input; and controlling the working current of the first photovoltaic input to approach The output power of the first photovoltaic input is adjusted by a preset current-sharing current or by controlling the working voltage of the first photovoltaic input based on the working current of the first photovoltaic input, and the output power of the second photovoltaic input is adjusted by controlling the working current of the second photovoltaic input to be close to the current-sharing current or by controlling the working voltage of the second photovoltaic input based on the working current of the second photovoltaic input, so that the sum of the output powers of the photovoltaic inputs is less than or equal to a preset total power threshold; the first current value is updated based on the maximum value of the current working current of each photovoltaic input, and the second current value is updated based on the minimum value of the current working current of each photovoltaic input; when the first current value and the second current value do not meet the current-sharing condition, the photovoltaic input whose working current is close to the first current value or the second current value is determined to be the first photovoltaic input.

[0007] In some embodiments, when a photovoltaic input whose operating current is close to a first current value is a first photovoltaic input, the operating current of the first photovoltaic input is reduced based on a step parameter to approach the current sharing current, and the operating current of the second photovoltaic input is increased based on the step parameter to approach the current sharing current; or, when a photovoltaic input whose operating current is close to a second current value is a first photovoltaic input, the operating current of the first photovoltaic input is increased based on the step parameter to approach the current sharing current, and the operating current of the second photovoltaic input is reduced based on the step parameter to approach the current sharing current.

[0008] In some embodiments, the current sharing condition is: the current operating current of each photovoltaic input is equal to the current sharing current.

[0009] In some embodiments, determining the first current value based on the maximum value of the working current recorded by each photovoltaic input includes: determining the first current value based on the maximum value of the working current recorded by each photovoltaic input and a preset first coefficient. Updating the first current value based on the current maximum value of the working current of each photovoltaic input includes: updating the first current value based on the current maximum value of the working current of each photovoltaic input and a preset first coefficient.

[0010] In some embodiments, determining the second current value based on the minimum value of the working current recorded by each photovoltaic input includes: determining the second current value based on the minimum value of the working current recorded by each photovoltaic input and a preset second coefficient. Updating the second current value based on the minimum value of the current working current of each photovoltaic input includes: updating the second current value based on the minimum value of the current working current of each photovoltaic input and a preset second coefficient.

[0011] In some embodiments, the photovoltaic input includes a boost mode and a bypass mode; adjusting the output power of the first photovoltaic input includes: when the photovoltaic input is in the boost mode, sending a current instruction to control the working current of the first photovoltaic input to be close to the current sharing current; when the photovoltaic input is in the bypass mode, sending a voltage instruction to control the working voltage of the first photovoltaic input. Adjusting the output power of the second photovoltaic input includes: when the photovoltaic input is in the boost mode, sending a current instruction to control the working current of the second photovoltaic input to be close to the current sharing current; when the photovoltaic input is in the bypass mode, sending a voltage instruction to control the working voltage of the second photovoltaic input.

[0012] In some embodiments, if the voltage of the photovoltaic input is less than the DC bus voltage of the inverter circuit in the photovoltaic power generation system, it is determined that the photovoltaic input is in a boost mode; if the voltage of the photovoltaic input is not less than the DC bus voltage of the inverter circuit in the photovoltaic power generation system, it is determined that the photovoltaic input is in a bypass mode.

[0013] In some embodiments, when the photovoltaic input is configured with a current limit value, the maximum value of the working current of the photovoltaic input is made equal to the current limit value.

[0014] In some embodiments, if the output power of the inverter circuit in the photovoltaic power generation system is greater than a first preset value, the photovoltaic input is determined to be in a limited power state; if the output power of the inverter circuit in the photovoltaic power generation system is less than a second preset value and the output power of the inverter circuit continues to be less than the second preset value for a period greater than a preset time, the photovoltaic input is determined to be in a non-limited power state; the second preset value is less than the first preset value.

[0015] The present application also provides a photovoltaic power generation system, including: multiple photovoltaic inputs, an inverter circuit and a controller, wherein the multiple photovoltaic inputs are connected to a power grid through the inverter circuit, wherein the photovoltaic inputs have a limited power state and a non-limited power state, and the controller is configured as follows: when each photovoltaic input is in a non-limited power state, recording the maximum value and minimum value of the working current of each photovoltaic input; when each photovoltaic input is in a limited power state, determining a first current value based on the maximum value of the working current recorded by each photovoltaic input, and determining a second current value based on the minimum value of the working current recorded by each photovoltaic input; determining a photovoltaic input whose working current is close to the first current value or the second current value as a first photovoltaic input, and determining a photovoltaic input other than the first photovoltaic input as a second photovoltaic input; by controlling the working current of the first photovoltaic input The output power of the first photovoltaic input is adjusted by approaching a preset current-sharing current or controlling the working voltage of the first photovoltaic input based on the working current of the first photovoltaic input, and the output power of the second photovoltaic input is adjusted by controlling the working current of the second photovoltaic input to approach the current-sharing current or controlling the working voltage of the second photovoltaic input based on the working current of the second photovoltaic input, so that the sum of the output powers of the photovoltaic inputs is less than or equal to a preset total power threshold; the first current value is updated based on the maximum value of the current working current of each photovoltaic input, and the second current value is updated based on the minimum value of the current working current of each photovoltaic input; when the first current value and the second current value do not meet the current-sharing condition, the photovoltaic input whose working current is close to the first current value or the second current value is determined to be the first photovoltaic input.

[0016] Compared with the prior art, this application has at least the following advantages: 1. In this application, when limiting power, the maximum current value and the minimum current value of each photovoltaic input are used to control each photovoltaic input to approach the current sharing current or control the voltage of each photovoltaic input, and finally reach the current sharing state, and the output power of the photovoltaic input will not fluctuate due to fluctuations such as light. In this case, the output power of each photovoltaic input is adjusted first, and then the power limiting of the inverter circuit is realized. The working efficiency of the inverter circuit is better, and the power limiting process of the inverter circuit is smoother and more stable. In addition, since the output power of the photovoltaic input is adjusted by adjusting the current or voltage during the power limiting process, the complexity of the control algorithm is not high.

[0017] 2. In the present application, the output power is adjusted by controlling the working current of each photovoltaic input, and the adjustment response speed is faster. Moreover, when controlling the working current of each photovoltaic input, the working current of each photovoltaic input is approached to the equalizing current in a step-by-step manner and finally reaches the equalizing current state, and the control process is smoother and more stable.

[0018] 3. In the present application, when controlling the working current of each photovoltaic input, by introducing the adjustment coefficient, the control of the working current of each photovoltaic input can be made more precise, thereby improving the accuracy of the power limiting process of the inverter circuit.

[0019] 4. In the present application, in the process of controlling the working current of each photovoltaic input, the inverter circuit of the photovoltaic power generation system may have current limitation, excessive temperature or has reached the maximum power point, etc. The maximum value of the working current of the photovoltaic input can be made equal to the current limit value, thereby reducing the situation of excessive temperature of the photovoltaic power generation system and improving the adaptability of the photovoltaic power generation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure and connection relationship of the photovoltaic power generation system 1 involved in the embodiment of the present application.

[0021] Figure 2 It is a flow chart of the power control method involved in the embodiment of the present application.

[0022] Figure 3 It is a sub-flowchart of step S400 of the power control method involved in the embodiment of the present application.

[0023] Figure 4 It is a characteristic curve diagram of the photovoltaic input involved in the embodiment of the present application.

[0024] Description of main component symbols: 1. Photovoltaic power generation system; 11. Photovoltaic input; 111. Photovoltaic panel; 112. DC conversion circuit; 12. Inverter circuit; 2. Power grid.

[0025] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0026] In the description of the embodiments of the present application, words such as "exemplary", "or", "for example" and the like are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary", "or", "for example" and the like is intended to present related concepts in a concrete manner.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art in the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. "At least one" refers to one or more. "Multiple" refers to two or more than two. For example, at least one of a, b or c can represent: a, b, c, a and b, a and c, b and c, a, b and c, seven situations.

[0028] It should also be noted that the terms "first" and "second" in the specification, claims and drawings of the present application are used to distinguish similar objects rather than to describe a specific order or sequence.

[0029] With the development of photovoltaic power generation technology, photovoltaic panels and other related products are also constantly iterating. Currently, the performance parameters of photovoltaic panels on the market are diverse. In photovoltaic power generation technology, the inverter must be able to support multiple photovoltaic inputs (that is, the DC end of the inverter needs to be connected to multiple photovoltaic panels with different parameters), and at the same time, it must make different photovoltaic inputs work in the optimal state. At present, the inverter usually adopts the MPPT algorithm to make each photovoltaic input work at the maximum power point. However, when the inverter is connected to the grid, the energy storage battery is fully charged, or its own operation is overheated, the inverter also needs to operate with limited power.

[0030] One of the power limiting methods in the related art is: when power limiting is required, the photovoltaic input maintains the output power just before the power limiting, which can be achieved by controlling the working voltage of the photovoltaic input to remain unchanged. However, since the light conditions may fluctuate, the output power of the inverter may also fluctuate randomly, so this method has the problem of unstable power limiting process.

[0031] Another method is to control the working points of all photovoltaic inputs to move in the direction of increasing power. However, when the energy of the photovoltaic input is greater than the energy output of the inverter, the excess energy will be stored in the DC bus, causing the DC bus voltage to increase. At this time, a DC bus overvoltage control loop needs to be set. The higher the DC bus voltage, the smaller the maximum photovoltaic input current needs to be controlled. This method needs to determine whether the photovoltaic input is limited in power by whether the DC bus voltage is raised, and due to the increased coupling of the DC bus voltage, it will affect the complexity of the control algorithm of the entire inverter. In addition, the increase in the DC bus voltage will reduce the working efficiency of the inverter and increase the risk of overvoltage damage to various devices in the inverter.

[0032] Another method is to perform PI control on the output power of the inverter to obtain the working voltage of each photovoltaic input so that it can output the power of the inverter's power limit value. This method can dynamically adjust the output power of the photovoltaic input, has good power limit stability, and does not involve raising the DC bus voltage, and does not increase the coupling of the control quantity. However, in multiple photovoltaic inputs, the inverter's power limit value can be combined from the output power of multiple different photovoltaic inputs. Therefore, when the output power of the photovoltaic input may fluctuate or have random results, such as one photovoltaic input has a large current and one photovoltaic input has a small current, it is difficult to optimize the inverter's working efficiency.

[0033] To this end, the present application provides a power control method and a photovoltaic power generation system, which can improve the stability of the power limit of the photovoltaic power generation system and optimize its working efficiency. The power control method and the photovoltaic power generation system involved in the embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0034] Figure 1 It is a schematic diagram of the structure and connection relationship of the photovoltaic power generation system 1 involved in the embodiment of the present application.

[0035] The present application embodiment first provides a photovoltaic power generation system 1, see Figure 1 The photovoltaic power generation system 1 may include: multiple photovoltaic inputs 11, an inverter circuit 12 and a controller. The multiple photovoltaic inputs 11 (such as photovoltaic inputs 11a to 11n) may be connected to the power grid 2 through the inverter circuit 12. Specifically, the photovoltaic input 11 may include photovoltaic panels 111 and DC conversion circuits 112 that are the same in number and electrically connected to the photovoltaic panels 111. If there are n photovoltaic panels 111 (such as photovoltaic panels 111a to 111n), there are also n DC conversion circuits 112 (such as DC conversion circuits 112a to 112n). Multiple DC conversion circuits 112 are connected to the inverter circuit 12 through a DC bus, and the inverter circuit 12 is connected to the power grid 2.

[0036] In some embodiments, the combination of the DC conversion circuit 112 and the inverter circuit 12 can also be called an inverter, the DC conversion circuit 112 is the DC end of the inverter, and the inverter circuit 12 is the AC end of the inverter. In the photovoltaic power generation system 1, the photovoltaic panel 111 (also called a photovoltaic module) can use the electric energy generated by solar energy to input into the inverter of the photovoltaic power generation system 1, specifically, it can be input into the DC end of the inverter, that is, it can be input into the DC conversion circuit 112. Therefore, the photovoltaic panel 111 to the DC conversion circuit 112 can be called the photovoltaic input 11.

[0037] In some embodiments, the DC conversion circuit 112 may include a BOOST circuit. The DC conversion circuit 112 has a boost mode and a bypass mode. In the boost mode, the DC conversion circuit 112 can increase the voltage of the photovoltaic input 11 to the DC bus voltage after filtering inductance by turning on or off the switch tube. In the bypass mode, the DC conversion circuit 112 can keep the switch tube closed, and the current of the photovoltaic input 11 flows directly to the DC bus through the diode of the DC conversion circuit 112.

[0038] It should be noted that the inverter involved in the embodiment of the present application can be either a single-phase inverter or a three-phase inverter, so there is no limitation on the inverter circuit 12.

[0039] In some embodiments, the photovoltaic power generation system 1 may further include an energy storage battery, which is connected to the DC bus through a bidirectional power conversion circuit, and then connected to the inverter circuit 12 through the DC bus, and can be used to store the electric energy generated by the photovoltaic panel 111 or the electric energy of the power grid 2. Therefore, the inverter involved in the embodiment of the present application may also be an energy storage inverter.

[0040] As described above, when the inverter is connected to the power grid 2, the energy storage battery is fully charged, or its own operation is overheated, the inverter also needs to perform power-limited operation. The photovoltaic input 11 involved in the embodiment of the present application has a limited power state and a non-limited power state. The limited power state may refer to the inverter circuit 12 of the inverter needing to limit the output power according to the aforementioned situation, which is specifically achieved by limiting the input power of the DC conversion circuit 112, that is, by limiting the output power of the photovoltaic input 11. The non-limited power state refers to the state of normal operation of the photovoltaic power generation system 1. Therefore, the photovoltaic input 11 having a limited power state and a non-limited power state may also refer to the inverter or the photovoltaic power generation system 1 having a limited power state and a non-limited power state.

[0041] In some embodiments, if the output power of the inverter circuit 12 is greater than the first preset value, the photovoltaic input 11 is determined to be in a power-limited state. For example, according to grid regulations, when the energy storage battery is fully charged or the inverter is overheated, the output power limit value (i.e., the first preset value) of the inverter circuit 12 is 1000W (watts). When it exceeds 1000W (watts), the photovoltaic input 11 is determined to be in a power-limited state. According to grid regulations, energy storage battery type or inverter type, the first preset value can be adjusted and is not limited here.

[0042] In some embodiments, if the output power of the inverter circuit 12 is less than the second preset value and the time for which the output power of the inverter circuit 12 continues to be less than the second preset value is greater than the preset time, it is determined that the photovoltaic input 11 is in a non-limited power state. The second preset value is less than the first preset value. Specifically, the second preset value can be the first preset value minus the threshold value, and the threshold value is related to the output power fluctuation amplitude of the inverter circuit 12. The preset time is related to the duration of the output power fluctuation of the photovoltaic input 11 or the inverter circuit 12. In this case, during the power limit adjustment process of the inverter, if there is a fluctuation, the second preset value and the preset time can be used to determine whether the photovoltaic input 11 has exited the power limit state, that is, whether it is in a non-limited power state, thereby reducing the situation where the photovoltaic input 11 abnormally exits the power limit state or is mistakenly determined to be in a non-limited power state. For example, if the first preset value is 1000W, the threshold value can be 100W, and the preset time can be equal to 0.1s, then when the output power of the inverter circuit 12 is less than 900W and lasts for 0.1s, it is determined that the photovoltaic input 11 is in a non-limited power state.

[0043] The controller can be used to control the output power of the photovoltaic input 11 to limit the output power of the inverter, that is, it can be used to control the inverter to operate with limited power. Specifically, it can be implemented by executing the power control method involved in any of the following embodiments of the present application.

[0044] As described above, the embodiment of the present application further provides a power control method, which can be applied to the photovoltaic power generation system 1 involved in any of the above embodiments of the present application.

[0045] Figure 2 It is a flow chart of the power control method involved in the embodiment of the present application.

[0046] See also Figure 2 , the power control method may include: Step S100: when each photovoltaic input is in a non-power-limited state, the maximum value and the minimum value of the working current of each photovoltaic input are recorded.

[0047] When each photovoltaic input is in a non-power-limited state, the maximum and minimum working current values ​​can be obtained by comparing the working currents of all photovoltaic inputs, that is, the maximum and minimum working currents of each photovoltaic input are recorded. All photovoltaic inputs should be in a working state.

[0048] In some embodiments, the working state of the photovoltaic input may be determined before comparing the working currents of all photovoltaic inputs. Whether the photovoltaic input is working may be determined based on the voltage of the photovoltaic input. For example, when the DC conversion circuit is not connected to the photovoltaic panel or the photovoltaic panel is blocked, the voltage of the photovoltaic input is very low and the working current of the photovoltaic input is close to or equal to zero. At this time, the photovoltaic input below the voltage threshold may be determined to be in a non-working state, so the working current of the photovoltaic input when it is in a non-working state may not be recorded as the minimum value.

[0049] The voltage threshold may be set according to the photovoltaic tracking range of the inverter. For example, an inverter with a tracking range of 50V to 450V determines that the DC conversion circuit is not connected to the photovoltaic panel or the photovoltaic panel is blocked when the voltage is lower than 50V.

[0050] Step S200: when each photovoltaic input is in a power-limited state, a first current value is determined based on a maximum value of an operating current recorded by each photovoltaic input, and a second current value is determined based on a minimum value of an operating current recorded by each photovoltaic input.

[0051] In the power limiting state, all photovoltaic inputs may have different working currents. For example, when generating electricity in any combination through photovoltaic panels of different specifications, the working current of each photovoltaic input is different. The first current value is determined from the maximum value of the working current recorded by each photovoltaic input, and the second current value is determined from the minimum value of the working current recorded by each photovoltaic input. Thus, a photovoltaic input close to or equal to the first current value can be used to reduce its current to reduce its output power, and a photovoltaic input close to or equal to the second current value can be used to increase its current to increase its output power, and finally the output power of all photovoltaic inputs is made the same, thereby achieving equilibrium and satisfying the power limiting state. In program design, the first current value can also be called the "maximum current instruction", and the second current value can also be called the "minimum current instruction".

[0052] In some embodiments, since the control precision of the inverter circuits of different inverters is different, such as the inverter circuit of a certain inverter needs more precise control to achieve the optimal output effect, an adjustment coefficient Kn can also be introduced in step S200, representing the adjustment coefficient of the nth photovoltaic input. The adjustment coefficient can be a fixed value or a voltage function of the photovoltaic input. For example, assuming that the rated working voltage Vpve=300V of the photovoltaic input, then let Kn=Vpvn / Vpve, where Vpvn is the working voltage. If the working voltage of the photovoltaic input is higher than the rated voltage, then let Kn increase, and the working current of the corresponding photovoltaic input will also increase accordingly. In addition, the higher the voltage of the photovoltaic input, the shorter the conduction time of the switch tube of the DC conversion circuit will be. By making the current flowing through the DC conversion circuit larger, the heat can be made more uniform to a certain extent, thereby reducing the situation where the inverter temperature is too high.

[0053] Therefore, in step S200, the first current value is determined based on the maximum value of the working current recorded by each photovoltaic input, which can be: the first current value is determined based on the maximum value of the working current recorded by each photovoltaic input and a preset first coefficient. The second current value is determined based on the minimum value of the working current recorded by each photovoltaic input, which can be: the second current value is determined based on the minimum value of the working current recorded by each photovoltaic input and a preset second coefficient. For example, assuming that the working currents of the 4 photovoltaic inputs are 1A, 3A, 5A, and 7A, respectively, after introducing the adjustment coefficient, they are 1*K1A, 3*K2A, 5*K3A, and 7*K4A, respectively, the first coefficient is K4, the first current value is 7*K4A, the second coefficient is K1, and the second current value is 1*K1A. In this way, the control of the working current of each photovoltaic input can be made more precise, and the accuracy of the power limiting process of the inverter circuit can be improved.

[0054] Step S300: determining a photovoltaic input whose operating current is close to a first current value or a second current value as a first photovoltaic input, and determining a photovoltaic input other than the first photovoltaic input as a second photovoltaic input.

[0055] It can be understood that the photovoltaic input whose working current is close to the first current value or the second current value is determined as the first photovoltaic input, that is, from all photovoltaic inputs, one or more channels whose working current is close to (or equal to) the maximum current or the minimum current are selected as the first photovoltaic input, and the remaining channels are all used as the second photovoltaic input. For example, assuming that the working currents of the four photovoltaic inputs are 1A, 3A, 5A, and 7A respectively, the first current value is 7A, and the second current value is 1A, then the photovoltaic input corresponding to 1A or 7A is the first photovoltaic input, and the photovoltaic input corresponding to 3A and 5A is the second photovoltaic input; or, assuming that the working currents of the four photovoltaic inputs are 1A, 3A, 5A, and 7A respectively, and after disturbance, they are stabilized at 1.1A, 3.1A, 5.1A, and 7.1A respectively, the first current value is 7A, and the second current value is 1A, then the photovoltaic input corresponding to 1.1A or 7.1A is the first photovoltaic input, and the photovoltaic input corresponding to 3.1A and 5.1A is the second photovoltaic input.

[0056] Figure 3 It is a sub-flowchart of step S400 of the power control method involved in the embodiment of the present application. Figure 4 It is a characteristic curve diagram of the photovoltaic input involved in the embodiment of the present application.

[0057] Step S400: Adjust the output power of the first photovoltaic input and the second photovoltaic input. Figure 3 As shown, step S400 may include step S401 and step S402, specifically including: As described above, the DC conversion circuit has a boost mode and a bypass mode. Since in the bypass mode, the current of the photovoltaic panel flows directly to the DC bus through the DC conversion circuit diode, the current of the photovoltaic input cannot be controlled, and the output power of the photovoltaic input needs to be controlled by controlling the voltage of the photovoltaic input. Therefore, in some embodiments, the photovoltaic input can include a boost mode and a bypass mode.

[0058] In step S400, the output power of the first photovoltaic input is adjusted, and step S401 may also be included: when the photovoltaic input is in a boost mode, a current instruction is sent to control the working current of the first photovoltaic input to be close to the current sharing current; when the photovoltaic input is in a bypass mode, a voltage instruction is sent to control the working voltage of the first photovoltaic input.

[0059] In step S400, adjusting the output power of the second photovoltaic input may further include step S402: when the photovoltaic input is in a boost mode, sending a current instruction to control the working current of the second photovoltaic input to be close to the current sharing current; when the photovoltaic input is in a bypass mode, sending a voltage instruction to control the working voltage of the second photovoltaic input. The current instruction is an instruction for controlling the current, and the voltage instruction is an instruction for controlling the voltage.

[0060] Among them, the current instruction can be: by controlling the working current of the first photovoltaic input to be close to the preset current sharing current, the output power of the first photovoltaic input is adjusted, and by controlling the working current of the second photovoltaic input to be close to the current sharing current, the output power of the second photovoltaic input is adjusted, so that the sum of the output powers of each photovoltaic input is less than or equal to the preset total power threshold. For example, assuming that the working currents of the 4 photovoltaic inputs in the power limiting state are 1A, 3A, 5A, and 7A respectively, the first current value is 7A, the second current value is 1A, and the current sharing current is 4A, then the 4 photovoltaic inputs are adjusted to 4A, 4A, 4A, and 4A in the final power limiting state. Thus, the power limiting process in the boost mode reaches the current sharing state.

[0061] The voltage instruction may be: based on the working current of the first photovoltaic input, the working voltage of the first photovoltaic input is controlled, and the output power of the first photovoltaic input is adjusted; based on the working current of the second photovoltaic input, the working voltage of the second photovoltaic input is controlled, and the output power of the second photovoltaic input is adjusted, so that the sum of the output powers of the photovoltaic inputs is less than or equal to the preset total power threshold. For example, assuming that the working currents of the four photovoltaic inputs in the power-limited state are 1A, 3A, 5A, and 7A respectively, the first current value is 7A, and the second current value is 1A. Figure 4 As shown, according to the characteristic curve of the photovoltaic input, on the right side of the maximum power point (MPP), the operating voltage decreases and the output power increases. Therefore, the output power can be increased by reducing the operating voltage of the photovoltaic input corresponding to 1A and 3A, and the output power can be reduced by increasing the voltage of the photovoltaic input corresponding to 5A and 7A, and finally the power limiting process of the bypass mode is realized.

[0062] In some embodiments, the method for adjusting the working voltage of the photovoltaic input may be to increase or decrease the voltage by a step parameter (such as 0.5 V) at a fixed time (such as 20 ms). The principle of selecting the step parameter is that it should not cause power impact on the adjustment of the maximum current loop.

[0063] In other embodiments, the method for adjusting the working voltage of the photovoltaic input may be through PI control.

[0064] In some embodiments, the photovoltaic input voltage can be used to determine whether the photovoltaic input is in the boost mode or the bypass mode. If the photovoltaic input voltage is less than the DC bus voltage of the inverter circuit in the photovoltaic power generation system, the photovoltaic input is determined to be in the boost mode; if the photovoltaic input voltage is not less than the DC bus voltage of the inverter circuit in the photovoltaic power generation system, the photovoltaic input is determined to be in the bypass mode.

[0065] In some embodiments, when the output power is adjusted by controlling the working voltage of the photovoltaic input, if the photovoltaic input adopts the parallel connection method, that is, one photovoltaic panel is connected to two DC conversion circuits at the same time. At this time, the voltage of the photovoltaic input is consistent, and the current is different due to hardware differences. At this time, the sum of the working currents is the output current of the photovoltaic input. Therefore, assuming that there are n photovoltaic inputs all working in bypass mode, the working currents of the n photovoltaic inputs can be added and then compared with the first current value *n and the second current value *n. In other words, all photovoltaic inputs in bypass mode can be regarded as a whole for control.

[0066] When the photovoltaic input whose operating current is close to the first current value is the first photovoltaic input, the operating current of the first photovoltaic input is reduced based on the step parameter to approach the current sharing current, and the operating current of the second photovoltaic input is increased based on the step parameter to approach the current sharing current.

[0067] It can be understood that when the photovoltaic input whose working current is close to the first current value is the first photovoltaic input, the working current of the first photovoltaic input is reduced based on the step parameter to approach the current sharing current, and the goal is to make the working current of each photovoltaic input less than the first current value. In order to achieve this goal, when the working current of the first photovoltaic input is reduced based on the step parameter to approach the current sharing current, it is necessary to compare each photovoltaic input with the first current value. For example, assuming that the working currents of the 4 photovoltaic inputs are 1A, 3A, 5A, and 7A respectively when they are in the power limiting state, the first current value is 7A, and the current sharing current is 4A, then the photovoltaic input corresponding to 7A is the first photovoltaic input, and the step parameter can be 0.1A. Therefore, after comparing with the first current value, the first photovoltaic input can be reduced to 6.9A with a step parameter of 0.1A.

[0068] It can also be understood that when the photovoltaic input whose working current is close to the first current value is the first photovoltaic input, the working current of the second photovoltaic input is increased based on the step parameter to approach the current sharing current, and the goal is to make the working current of each photovoltaic input greater than the second current value. In order to achieve this goal, when the working current of the second photovoltaic input is increased based on the step parameter to approach the current sharing current, it is necessary to compare each photovoltaic input with the second current value. For example, assuming that the working currents of the 4 photovoltaic inputs are 1A, 3A, 5A, and 7A respectively when they are in the power limiting state, the second current value is 1A, and the current sharing current is 4A, then the photovoltaic input corresponding to 1A is the second photovoltaic input, and the step parameter can be 0.1A. Therefore, after comparing with the second current value, the photovoltaic input corresponding to 1A can be increased to 1.1A with a step parameter of 0.1A. Although 3A and 5A are also the second photovoltaic inputs, they are larger than the second current value, so they can be temporarily unchanged.

[0069] Alternatively, when the photovoltaic input whose operating current is close to the second current value is the first photovoltaic input, the operating current of the first photovoltaic input is increased based on the step parameter to approach the current sharing current, and the operating current of the second photovoltaic input is reduced based on the step parameter to approach the current sharing current.

[0070] It can also be understood that when the photovoltaic input whose working current is close to the second current value is the first photovoltaic input, the working current of the first photovoltaic input is increased based on the step parameter to approach the current sharing current, and the goal is to make the working current of each photovoltaic input greater than the second current value. In order to achieve this goal, when the working current of the first photovoltaic input is increased based on the step parameter to approach the current sharing current, it is necessary to compare each photovoltaic input with the second current value. For example, assuming that the working currents of the 4 photovoltaic inputs are 1A, 3A, 5A, and 7A respectively when they are in the power limiting state, the second current value is 1A, and the current sharing current is 4A, then the photovoltaic input corresponding to 1A is the first photovoltaic input, and the step parameter can be 0.1A. Therefore, after comparing with the second current value, the first photovoltaic input can be increased to 1.1A with a step parameter of 0.1A.

[0071] It can also be understood that when the photovoltaic input whose working current is close to the second current value is the first photovoltaic input, the working current of the second photovoltaic input is reduced based on the step parameter to approach the current sharing current, and the goal is to make the working current of each photovoltaic input less than the first current value. In order to achieve this goal, when the working current of the second photovoltaic input is increased based on the step parameter to approach the current sharing current, it is necessary to compare each photovoltaic input with the first current value. For example, assuming that the working currents of the four photovoltaic inputs are 1A, 3A, 5A, and 7A respectively when they are in the power limiting state, the first current value is 7A, and the current sharing current is 4A, then the photovoltaic input corresponding to 7A is the second photovoltaic input, and the step parameter can be 0.1A. Therefore, after comparing with the first current value, the photovoltaic input corresponding to 7A can be reduced to 6.9A with a step parameter of 0.1A. Although 3A and 5A are also the second photovoltaic inputs, they are smaller than the first current value, so they can be temporarily unchanged.

[0072] In some embodiments, the step parameters may be set according to the specifications of the inverter.

[0073] Step S500: updating the first current value based on the maximum value of the current working current of each photovoltaic input, and updating the second current value based on the minimum value of the current working current of each photovoltaic input.

[0074] It can be understood that the current working current of each photovoltaic input may refer to the working current of the photovoltaic input after executing step S100 to step S400. For example, assuming that the working currents of the four photovoltaic inputs in the power limiting state are 1A, 3A, 5A, and 7A respectively, the first current value is 7A, the second current value is 1A, and the current sharing current is 4A, after executing step S100 to step S400, the working currents are 1.1A, 3A, 5A, and 6.9A respectively, the first current value is 6.9A, the second current value is 1.1A, and the current sharing current is 4A.

[0075] It can also be understood that after the adjustment coefficient Kn is introduced into the working current of the photovoltaic input, the first current value is updated based on the maximum value of the current working current of each photovoltaic input, or the first current value is updated based on the maximum value of the current working current of each photovoltaic input and the preset first coefficient. The second current value is updated based on the minimum value of the current working current of each photovoltaic input, or the second current value is updated based on the minimum value of the current working current of each photovoltaic input and the preset second coefficient. For example, assuming that the working currents of the four photovoltaic inputs are 1A, 3A, 5A, and 7A respectively, after the adjustment coefficients are introduced, they are 1*K1A, 3*K2A, 5*K3A, and 7*K4A respectively, the first coefficient is K4, the first current value is 7*K4A, the second coefficient is K1, and the second current value is 1*K1A. After executing steps S100 to S400, the currents are 1.1*K1A, 3*K2A, 5*K3A, and 6.9*K4A respectively, the first coefficient is K4, the first current value is 6.9*K4A, the second coefficient is K1, and the second current value is 1.1*K1A.

[0076] In some embodiments, the method for updating the first current value may be to reduce it by a fixed time (such as 20ms) with a step parameter (such as 0.05A), or by PI control. The method for updating the second current value may be to increase it by a fixed time (such as 20ms) with a step parameter (such as 0.05A), or by PI control. Among them, the selection of fixed time and step parameter is mainly affected by the maximum current control loop, and it is necessary to ensure that the power increase caused by the increase of the minimum current (i.e., the second current value) can be adjusted by the maximum current control loop, and the output power fluctuation is within an acceptable range. When controlled by PI, the minimum current is larger than the maximum current control loop. For example, the maximum current control loop controls the output of 2000W, and the minimum current loop controls the output of 2010W. The minimum current control loop can be gradually increased according to a power conversion of about 10W until it is the same as the maximum current (i.e., the first current value). In other words, the maximum current loop control target is 2000W, and the output power is greater than 2000W, so that the maximum current is reduced, for example, 7A changes to 6.9A. The minimum current loop control target is 2010W. If the output power is less than 2010W, the minimum current is increased. Assuming the current power is 2000W, the minimum current loop increases the output power, for example, from 1A photovoltaic input to 1.1A, the output power is 2001W. The maximum current loop determines that the output power limit is exceeded, so the 7A photovoltaic input is reduced to 6.9A.

[0077] Step S600: when the first current value and the second current value do not satisfy the current sharing condition, returning to determine that the photovoltaic input whose operating current is close to the first current value or the second current value is the first photovoltaic input.

[0078] The current sharing condition is: the current working current of each photovoltaic input is equal to the current sharing current. For example, assuming that the working currents of the four photovoltaic inputs are 1A, 3A, 5A, and 7A respectively, and the current sharing current is 4A, the current sharing condition is: after executing S100 to S600, the working currents of the four photovoltaic inputs are all 4A.

[0079] Combining steps S100 to S600, it can be obtained that: if the current working current of the photovoltaic input is greater than the first current value, it is reduced to the first current value, which is expressed by the formula: IpvRef=MIN(IpvRef, IpvMaxRef), where IpvRef represents the working current of the photovoltaic input, and IpvMaxRef represents the first current value; if the current working current of the photovoltaic input is less than the second current value, it is increased to the second current value, which is expressed by the formula: IpvRef=MAX(IpvRef, IpvMinRef), where IpvRef represents the working current of the photovoltaic input, and IpvMinRef represents the second current value. If the adjustment coefficient is introduced, IpvRef=MIN(IpvRef, IpvMaxRef) is updated to IpvRef=MIN(IpvRef, IpvMaxRef*Kn), and IpvRef=MAX(IpvRef, IpvMinRef) is updated to IpvRef=MAX(IpvRef, IpvMinRef*Kn). In this way, the working current of each photovoltaic input is close to the current sharing current.

[0080] In some embodiments, when the photovoltaic input is configured with a current limit value, the maximum value of the working current of the photovoltaic input is equal to the current limit value. Since the DC conversion circuit itself has a maximum current limit, or the load needs to be reduced due to overtemperature, or the maximum power point is reached, the maximum current limit needs to be set. When the photovoltaic input is configured with a current limit value, the maximum value of the working current of the photovoltaic input is equal to the current limit value, which is expressed by the formula: IpvRef=MIN(IpvRef, IpvLim), where IpvRef represents the working current of the photovoltaic input, and IpvLim represents the current limit value.

[0081] In summary, when the power is limited, the present application controls each photovoltaic input to approach the equalizing current or controls the voltage of each photovoltaic input based on the maximum current value and the minimum current value of each photovoltaic input, and finally reaches the equalizing state, and the output power of the photovoltaic input will not fluctuate due to fluctuations such as light. In this case, the output power of each photovoltaic input is adjusted first, and then the power limiting of the inverter circuit is realized. The working efficiency of the inverter circuit is better, and the power limiting process of the inverter circuit is smoother and more stable. In addition, since the output power of the photovoltaic input is adjusted by adjusting the current or voltage during the power limiting process, the complexity of the control algorithm is not high. Moreover, by controlling the working current of each photovoltaic input to adjust the output power, the adjustment response speed is faster, and when controlling the working current of each photovoltaic input, the working current of each photovoltaic input is approached to the equalizing current by stepping, and finally reaches the equalizing state, and the control process is smoother and more stable. Moreover, when controlling the working current of each photovoltaic input, by introducing the adjustment coefficient, the control of the working current of each photovoltaic input can be made more precise, thereby improving the accuracy of the power limiting process of the inverter circuit.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A power control method, characterized in that: The power control method is applied to a photovoltaic power generation system, wherein the photovoltaic power generation system includes multiple photovoltaic inputs, wherein the photovoltaic inputs have a limited power state and a non-limited power state, and the power control method includes: when each photovoltaic input is in the non-limited power state, recording the maximum value and the minimum value of the working current of each photovoltaic input; when each photovoltaic input is in the limited power state, determining a first current value based on the maximum value of the working current recorded by each photovoltaic input, and determining a second current value based on the minimum value of the working current recorded by each photovoltaic input; determining the photovoltaic input whose working current is close to the first current value or the second current value as the first photovoltaic input, and determining the photovoltaic input other than the first photovoltaic input as the second photovoltaic input; and controlling the working current of the first photovoltaic input to be close to a preset current sharing current or a base current. The output power of the first photovoltaic input is adjusted by controlling the working voltage of the first photovoltaic input based on the working current of the first photovoltaic input, and the output power of the second photovoltaic input is adjusted by controlling the working current of the second photovoltaic input to be close to the current sharing current or controlling the working voltage of the second photovoltaic input based on the working current of the second photovoltaic input, so that the sum of the output powers of the photovoltaic inputs of each channel is less than or equal to a preset total power threshold; the first current value is updated based on the maximum value of the current working current of each photovoltaic input, and the second current value is updated based on the minimum value of the current working current of each photovoltaic input; when the first current value and the second current value do not meet the current sharing condition, the photovoltaic input whose working current is close to the first current value or the second current value is returned to be the first photovoltaic input.

2. The power control method according to claim 1, characterized in that: When the photovoltaic input whose operating current is close to the first current value is the first photovoltaic input, the operating current of the first photovoltaic input is reduced based on the step parameter to approach the current sharing current, and the operating current of the second photovoltaic input is increased based on the step parameter to approach the current sharing current; or, when the photovoltaic input whose operating current is close to the second current value is the first photovoltaic input, the operating current of the first photovoltaic input is increased based on the step parameter to approach the current sharing current, and the operating current of the second photovoltaic input is reduced based on the step parameter to approach the current sharing current.

3. The power control method according to claim 1, characterized in that: The current sharing condition is: the current operating current of each photovoltaic input is equal to the current sharing current.

4. The power control method according to claim 1, characterized in that: The determining of the first current value based on the maximum value of the working current recorded by each photovoltaic input includes: determining the first current value based on the maximum value of the working current recorded by each photovoltaic input and a preset first coefficient; the updating of the first current value based on the current maximum value of the working current of each photovoltaic input includes: updating the first current value based on the current maximum value of the working current of each photovoltaic input and a preset first coefficient.

5. The power control method according to claim 1, characterized in that: The determining of the second current value based on the minimum value of the working current recorded by each photovoltaic input includes: determining the second current value based on the minimum value of the working current recorded by each photovoltaic input and a preset second coefficient; the updating of the second current value based on the minimum value of the current working current of each photovoltaic input includes: updating the second current value based on the minimum value of the current working current of each photovoltaic input and a preset second coefficient.

6. The power control method according to claim 1, characterized in that: The photovoltaic input includes a boost mode and a bypass mode; the adjusting the output power of the first photovoltaic input includes: when the photovoltaic input is in the boost mode, sending a current instruction to control the working current of the first photovoltaic input to be close to the current sharing current; when the photovoltaic input is in the bypass mode, sending a voltage instruction to control the working voltage of the first photovoltaic input; the adjusting the output power of the second photovoltaic input includes: when the photovoltaic input is in the boost mode, sending a current instruction to control the working current of the second photovoltaic input to be close to the current sharing current; when the photovoltaic input is in the bypass mode, sending a voltage instruction to control the working voltage of the second photovoltaic input.

7. The power control method according to claim 6, characterized in that: If the voltage of the photovoltaic input is less than the DC bus voltage of the inverter circuit in the photovoltaic power generation system, it is determined that the photovoltaic input is in the boost mode; if the voltage of the photovoltaic input is not less than the DC bus voltage of the inverter circuit in the photovoltaic power generation system, it is determined that the photovoltaic input is in the bypass mode.

8. The power control method according to claim 1, characterized in that: When the photovoltaic input is configured with a current limit value, the maximum value of the working current of the photovoltaic input is made equal to the current limit value.

9. The power control method according to claim 1, characterized in that: If the output power of the inverter circuit in the photovoltaic power generation system is greater than a first preset value, it is determined that the photovoltaic input is in the limited power state; if the output power of the inverter circuit in the photovoltaic power generation system is less than a second preset value and the output power of the inverter circuit continues to be less than the second preset value for a time greater than a preset time, it is determined that the photovoltaic input is in the non-limited power state; the second preset value is less than the first preset value.

10. A photovoltaic power generation system, characterized in that: include: Multiple photovoltaic inputs, an inverter circuit and a controller, wherein the multiple photovoltaic inputs are connected to a power grid through the inverter circuit, wherein the photovoltaic inputs have a power-limited state and a non-power-limited state, and the controller is configured to: when each photovoltaic input is in the non-power-limited state, record the maximum value and the minimum value of the working current of each photovoltaic input; when each photovoltaic input is in the power-limited state, determine a first current value based on the maximum value of the working current recorded by each photovoltaic input, and determine a second current value based on the minimum value of the working current recorded by each photovoltaic input; Determine that the photovoltaic input whose working current is close to the first current value or the second current value is the first photovoltaic input, and determine that the photovoltaic input other than the first photovoltaic input is the second photovoltaic input; adjust the output power of the first photovoltaic input by controlling the working current of the first photovoltaic input to be close to the preset current sharing current or controlling the working voltage of the first photovoltaic input based on the working current of the first photovoltaic input, and adjust the output power of the second photovoltaic input by controlling the working current of the second photovoltaic input to be close to the current sharing current or controlling the working voltage of the second photovoltaic input based on the working current of the second photovoltaic input, so that the sum of the output powers of the photovoltaic inputs of each channel is less than or equal to a preset total power threshold; update the first current value based on the maximum value of the current working current of each channel of the photovoltaic input, and update the second current value based on the minimum value of the current working current of each channel of the photovoltaic input; when the first current value and the second current value do not meet the current sharing condition, return to the step of determining that the photovoltaic input whose working current is close to the first current value or the second current value is the first photovoltaic input.

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