Power generation system and inverter control method

Abstract

The invention provides a power generation system and a control method of an inverter, and is applied to the technical field of electrics. The power generation system comprises an inverter and a controller, and the controller is used for controlling the inverter to convert direct current into alternating current and output the alternating current to a power grid. The controller is specifically used for adjusting the active power amplitude limit of the inverter when the port voltage of the inverter exceeds a preset voltage range; or when the change rate of the port voltage of the inverter is larger than or equal to the voltage change rate threshold value, the active power amplitude limit of the inverter is adjusted. Thus, the size of the active power output by the inverter is limited, the stability of the power grid voltage is improved, meanwhile, the change rate can reflect the change trend of the port voltage, the active power amplitude limit of the inverter can be timely responded and adjusted under the condition that the port voltage has the large change trend, and the stability of the power grid voltage is further improved.

Description

Technical Field

[0001] The present application relates to the field of electrical technology, and in particular to a control method for a power generation system and an inverter. Background Art

[0002] Power supply equipment is used to supply power to the power grid. As more and more power supply equipment is connected to the power grid, and the lines between the common points of the equipment gradually increase, some regional power grids will eventually show certain weak power grid characteristics. In a weak power grid, it is easy to be affected by various factors. A small disturbance may cause a large fluctuation in the grid voltage. The grid is prone to overvoltage and undervoltage faults, resulting in poor stability of the grid voltage. Summary of the invention

[0003] The embodiment of the present application provides a control method for a power generation system and an inverter, which reduces the large-range fluctuation of the grid voltage and improves the stability of the grid voltage by reasonably adjusting the active power output by the inverter.

[0004] In a first aspect, an embodiment of the present application provides a power generation system, the power generation system includes an inverter and a controller, the controller is used to control the inverter to convert direct current into alternating current and output it to a power grid. The controller is also used to adjust the active power limit of the inverter when the port voltage of the inverter exceeds a preset voltage range; or when the rate of change of the port voltage of the inverter is greater than or equal to a voltage change rate threshold, adjust the active power limit of the inverter.

[0005] Among them, active power refers to the power that the inverter transmits to the grid for work, can be converted into other forms of energy (such as mechanical energy, thermal energy, light energy, etc.) and is actually consumed and utilized by the load. Active power limit refers to the limit of active power output by the inverter, and the active power usually does not exceed the active power limit.

[0006] The active power output by the inverter affects the grid voltage. The active power is transmitted from the inverter to the grid through charge movement in the transmission line. The greater the active power, the more charge movement and the greater the voltage drop at the grid.

[0007] In this embodiment, the port voltage of the inverter exceeds the preset voltage range or the change rate of the port voltage is greater than or equal to the voltage change rate threshold, and the grid voltage is considered to be unstable or in a critical stable state. In this case, if the active power output by the inverter is less than or equal to the original specified active power limit, the active power scheduling can continue to increase, but continuing to increase the active power scheduling will aggravate the instability of the grid voltage. In this application, by adjusting the active power limit of the inverter when the grid voltage is unstable or in a critical stable state, the size of the active power output by the inverter is limited, and the stability of the grid voltage is improved. At the same time, the change rate of the port voltage can reflect the change trend of the port voltage. The condition for adjusting the active power limit of the inverter is set to be that the change rate of the port voltage is greater than or equal to the voltage change rate threshold. When the port voltage has a large change trend (for example, undervoltage or overvoltage trend), the active power limit of the inverter can be adjusted in time (for example, the active power limit of the inverter is adjusted in advance before the voltage change reaches overvoltage or undervoltage), further improving the stability of the grid voltage.

[0008] In an embodiment of the first aspect, when the change rate of the port voltage is greater than or equal to a voltage change rate threshold and the port voltage does not exceed a preset voltage range, the active power limit output by the inverter is controlled to decrease.

[0009] In this embodiment, when the rate of change of the port voltage is greater than or equal to the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the grid voltage is considered to be in a critical stable state. By controlling the active power limit of the inverter output to be reduced, it is avoided that when the grid voltage is in a critical stable state, the active power output of the inverter is too large, resulting in large fluctuations in the grid voltage, thereby improving the stability of the grid voltage.

[0010] In an embodiment of the first aspect, when the change rate of the port voltage is less than the voltage change rate threshold and the port voltage does not exceed a preset voltage range, the active power limit output by the inverter is controlled to increase.

[0011] In this embodiment, when the port voltage change rate is less than the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the grid voltage is considered stable. By controlling the active power limit of the inverter output to increase, the active power output of the inverter is released on the basis of the grid voltage stability, thereby increasing the power generation of the power generation system.

[0012] In an embodiment of the first aspect, the active power limit does not exceed an upper limit of the active power limit; and / or the active power limit is not lower than a lower limit of the active power amplitude.

[0013] In this embodiment, by limiting the active power limit to not exceed the upper limit of the active power limit and / or the active power limit to not be lower than the lower limit of the active power amplitude, the safety of the power generation system and the serious fluctuation of the grid voltage due to excessive or insufficient active power limiting are avoided, thereby improving the safety of power generation.

[0014] In an embodiment of the first aspect, when the port voltage of the inverter exceeds a preset voltage range, the reactive power output by the inverter is adjusted and the active power limit of the inverter is adjusted.

[0015] Among them, reactive power refers to the power transmitted by the inverter to the power grid to establish and maintain energy exchanges such as magnetic fields and electric fields, and does not directly participate in doing work.

[0016] The reactive power and active power output by the inverter both affect the grid voltage. The maximum power that the inverter can output is the apparent power, which is composed of active power and reactive power. Active power and reactive power affect each other, and changes in reactive power and active power will cause changes in the grid voltage.

[0017] In this embodiment, when the port voltage of the inverter exceeds the preset voltage range, the grid voltage is considered unstable. By adjusting the reactive power output by the inverter and adjusting the active power limit of the inverter, the reactive power and active power are coordinated and controlled. Compared with stabilizing the voltage by controlling the reactive power or the active power alone, the coordinated control of the reactive power and the active power speeds up the process of stabilizing the voltage and enhances the effect of stabilizing the grid voltage.

[0018] In an embodiment of the first aspect, when the port voltage is less than or equal to a preset undervoltage threshold, the reactive power output by the inverter is controlled to increase; and / or, when the port voltage is greater than or equal to a preset overvoltage threshold, the reactive power output by the inverter is controlled to decrease.

[0019] In this embodiment, when the port voltage is less than or equal to the preset undervoltage threshold, it indicates that the reactive power output by the inverter is insufficient, and the reactive power output by the inverter is controlled to increase to achieve a stable grid voltage. When the port voltage is greater than or equal to the preset overvoltage threshold, it indicates that the reactive power output by the inverter is excessive, and the reactive power output by the inverter is controlled to decrease to achieve a stable grid voltage.

[0020] In an embodiment of the first aspect, when the port voltage is less than or equal to a preset undervoltage threshold, the reactive power output by the inverter is controlled to increase and the active power limit of the inverter is controlled to decrease.

[0021] In this embodiment, when the port voltage is less than or equal to the preset undervoltage threshold, it is considered that the grid has an undervoltage fault. By controlling the reactive power output by the inverter to increase, the grid voltage is increased to solve the grid voltage undervoltage fault, and at the same time controlling the active power limit of the inverter to decrease, the reactive power and active power are controlled in a coordinated manner, the process of stabilizing the voltage is accelerated, and the effect of stabilizing the grid voltage is enhanced.

[0022] In an embodiment of the first aspect, the controller is also used for: when the rate of change of the port voltage of the inverter is greater than or equal to the voltage change rate threshold, and / or when the port voltage exceeds the preset voltage range, controlling the preset adjustment factor to increase, and controlling the inverter to adjust the output active power limit to decrease as the preset adjustment factor and reactive power increase, and the preset adjustment factor is used to adjust the active power limit; and / or, when the rate of change of the port voltage of the inverter is less than the voltage change rate threshold, and the port voltage does not exceed the preset voltage range, controlling the preset adjustment factor to decrease, and controlling the inverter to adjust the output active power limit to increase as the preset adjustment factor decreases.

[0023] In this embodiment, the active power limit of the inverter is dynamically adjusted by setting a preset adjustment factor. When the change rate of the port voltage of the inverter is greater than or equal to the voltage change rate threshold, and / or the port voltage exceeds the preset voltage range, the preset adjustment factor is controlled to increase, and the active power limit of the inverter is controlled to decrease with the increase of the preset adjustment factor and reactive power, so as to avoid the excessive active power output of the inverter causing large fluctuations in the grid voltage, thereby improving the stability of the grid voltage. When the change rate of the port voltage of the inverter is less than the voltage change rate threshold, and the port voltage does not exceed the preset voltage range, the preset adjustment factor is controlled to decrease, and the active power limit of the inverter is controlled to increase with the decrease of the preset adjustment factor, so as to release the active power output of the inverter and increase the power generation of the power generation system.

[0024] In an embodiment of the first aspect, the controller is further configured to: send an active power instruction to the inverter to adjust an active power limit of the inverter.

[0025] In this embodiment, by sending an active power instruction to the inverter to adjust the active power limit of the inverter, the active power output by the inverter is quickly adjusted, which is beneficial to improving the stability of the grid voltage.

[0026] In a second aspect, an embodiment of the present application provides a control method for an inverter, which is applied to a power generation system, wherein the power generation system includes an inverter and a controller, and the controller is used to control the inverter to convert direct current into alternating current and output it to a power grid. When the port voltage of the inverter exceeds a preset voltage range, the active power limit of the inverter is adjusted; or, when the rate of change of the port voltage of the inverter is greater than or equal to a voltage change rate threshold, the active power limit of the inverter is adjusted.

[0027] As for the supplementary and technical effects of the solution provided in the second aspect above, please refer to the corresponding description of the first aspect and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a power generation system 100 provided in an embodiment of the present application is shown;

[0029] Figure 2 A schematic diagram of a controller provided in an embodiment of the present application is shown;

[0030] Figure 3 A schematic diagram of a controller provided in an embodiment of the present application is shown;

[0031] Figure 4 A flowchart of internal control of a controller provided by an embodiment of the present application is shown;

[0032] Figure 5 A flow chart of internal control of a controller provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0034] The prefixes such as "first" and "second" used in the embodiments of the present application are only used to distinguish different description objects, and have no limiting effect on the position, order, priority, quantity or content of the described objects. The use of prefixes such as ordinal numbers used to distinguish description objects in the embodiments of the present application does not constitute a limitation on the described objects. For the statement of the described objects, please refer to the description in the context of the claims or embodiments, and the use of such prefixes should not constitute an unnecessary limitation.

[0035] As more and more power supply equipment is connected to the power grid, and the lines between the common points of the equipment gradually increase, some regional power grids will eventually show certain weak grid characteristics. In a weak grid, it is easy to be affected by various factors. A small disturbance may cause a large fluctuation in the grid voltage. The grid is prone to overvoltage and undervoltage faults, resulting in poor stability of the grid voltage.

[0036] In some cases, the reactive power output by the inverter is adjusted to stabilize the grid voltage. However, this method cannot be applied to equipment power-limited operation scenarios caused by various reasons. In other cases, the grid voltage is used as the control target. When the grid voltage shows a significant deviation, special control is performed, resulting in the grid voltage being in a critical stable state. A slight disturbance may cause the grid voltage to fluctuate.

[0037] In view of this, an embodiment of the present application provides a control method for a power generation system and an inverter. When the port voltage of the inverter exceeds a preset voltage range or the rate of change of the port voltage is greater than or equal to a voltage change rate threshold, it is considered that the grid voltage is unstable or in a critical stable state. In this case, if the active power output by the inverter is less than or equal to the original specified active power limit, the active power scheduling can continue to be increased, but continuing to increase the active power scheduling will aggravate the instability of the grid voltage. In the present application, by adjusting the active power limit of the inverter when the grid voltage is unstable or in a critical stable state, and controlling the active power output by the inverter to be less than or equal to the adjusted active power limit, the size of the active power output by the inverter is limited, and the stability of the grid voltage is improved. At the same time, the change rate of the port voltage can reflect the changing trend of the port voltage. The condition for adjusting the active power limit of the inverter is set to that the change rate of the port voltage is greater than or equal to the voltage change rate threshold. When the port voltage has a large change trend (such as undervoltage or overvoltage trend), the active power limit of the inverter can be adjusted in time (for example, the active power limit of the inverter can be adjusted in advance before the voltage change reaches overvoltage or undervoltage), further improving the stability of the grid voltage.

[0038] See also Figure 1 , Figure 1 1 shows a schematic diagram of a power generation system 100 provided in an embodiment of the present application. The power generation system 100 includes a power supply device 101, an inverter 102, a controller 103 and a power grid 104. The power supply device 101, the inverter 102, the controller 103 and the power grid 104 are electrically connected via a transmission line. The line impedance of the transmission line is as follows: Figure 1 As shown in Figure 105.

[0039] Among them, the power supply device 101 is used to output electric energy to power the inverter 102. The power supply device 101 can be a battery, and the power supply device outputs electric energy by discharging. In addition, the electric energy output by the power supply device 101 can be converted from other energy sources, and there is no restriction on the source of electric energy of the power supply device 101 in the embodiment of the present application. For example, when the power generation system 100 is a photovoltaic power generation system, the power supply device 101 is a photovoltaic (PV) component or a photovoltaic string, and the PV component or the photovoltaic string is used to receive solar energy and convert the solar energy into electric energy; when the power generation system 100 is a wind power generation system, the power supply device 10 can be a wind turbine, and the wind turbine is used to convert wind energy into electric energy, etc.

[0040] The inverter 102 is used to receive the input voltage of the power supply device 101 and convert the input voltage to be incorporated into the power grid. For example, the inverter 102 may include a power conversion system (PCS), a direct current to alternating current (DC / AC) conversion circuit, and the like.

[0041] Among them, the controller 103 is used to control the operation of the inverter 102. For example, the controller 103 generates or receives active power instructions and reactive power instructions to adjust the active power and reactive power output by the inverter 102. The controller 103 can be a general-purpose central processing unit (CPU), a general-purpose processor, a digital signal processing (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. It can implement or execute various exemplary logic blocks, modules and circuits described in conjunction with the disclosure of this application. The above-mentioned processor can also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of DSP and microprocessors, and the like.

[0042] In one embodiment, a sampling point 106 for collecting the port voltage of the inverter is provided at the output end of the inverter 102 , and a sampling device collects the port voltage of the inverter at the sampling point 106 .

[0043] The architecture of the embodiment of the present application is described above. The power generation system 100 provided in the present application will be described below in conjunction with a specific embodiment.

[0044] like Figure 2 As shown, the controller is used to: adjust the active power limit of the inverter when the port voltage of the inverter exceeds a preset voltage range; or adjust the active power limit of the inverter when the change rate of the port voltage of the inverter is greater than or equal to a voltage change rate threshold.

[0045] The port voltage refers to the port voltage at the output end of the inverter, and the port voltage and the change of the port voltage can indicate the voltage of the power grid or the public access point and the change of the voltage.

[0046] Among them, the preset voltage range includes a preset overvoltage threshold and a preset undervoltage threshold. In the embodiment of the present application, the specific values ​​of the preset overvoltage threshold and the preset undervoltage threshold are not limited. If the port voltage is greater than or equal to the preset overvoltage threshold, it is considered that the power grid has an overvoltage fault; if the port voltage is less than or equal to the preset undervoltage threshold, it is considered that the power grid has an undervoltage fault. Both situations will affect the stability of the power grid voltage and even cause the power supply equipment to be disconnected from the grid.

[0047] In the embodiment of the present application, the specific value of the voltage change rate threshold is not limited. If the change rate of the port voltage is greater than or equal to the voltage change rate threshold, it is considered that the grid voltage has a tendency to change to overvoltage or undervoltage; if the change rate of the port voltage is less than the voltage change rate threshold, it is considered that the grid voltage has no tendency to change to overvoltage or undervoltage.

[0048] Among them, active power refers to the power transmitted by the inverter to the power grid for work, which can be converted into other forms of energy (such as mechanical energy, thermal energy, light energy, etc.) and actually consumed and utilized by the load.

[0049] Since the current output by the inverter is alternating current, the active power can be positive or negative. For ease of description, the active power mentioned in the embodiments of the present application refers to the value of the active power, regardless of whether it is positive or negative.

[0050] Active power limit refers to the limit of active power, that is, the maximum value of active power cannot exceed the active power limit. If the active power is greater than the active power limit, it will cause large-scale fluctuations in the grid voltage and affect the stability of the grid voltage.

[0051] The specific value of the active power can be determined by a proportional-integral controller (PI controller) or other control strategies.

[0052] If the port voltage of the inverter exceeds the preset voltage range or the port voltage change rate is greater than or equal to the voltage change rate threshold, the grid voltage is considered unstable or in a critical stable state. At this time, even if the active power output by the inverter is less than or equal to the original specified active power limit, continuing to increase the active power scheduling will also aggravate the instability of the grid voltage. At the same time, in order to ensure the stability of the grid voltage, the active power needs to be reduced in the future, which increases the control cost.

[0053] In this case, the active power limit of the inverter is adjusted so that the active power limit is adapted to the current scenario, thereby limiting the size of the active power output by the inverter.

[0054] In this embodiment, the port voltage of the inverter exceeds the preset voltage range or the change rate of the port voltage is greater than or equal to the voltage change rate threshold, and the grid voltage is considered to be unstable or in a critical stable state. In this case, if the active power output by the inverter is less than or equal to the original specified active power limit, the active power scheduling can continue to increase, but continuing to increase the active power scheduling will aggravate the instability of the grid voltage. In this application, by adjusting the active power limit of the inverter when the grid voltage is unstable or in a critical stable state, and controlling the active power output by the inverter to be less than or equal to the adjusted active power limit, the size of the active power output by the inverter is limited, and the stability of the grid voltage is improved. At the same time, the change rate of the port voltage can reflect the change trend of the port voltage. The condition for adjusting the active power limit of the inverter is set to be that the change rate of the port voltage is greater than or equal to the voltage change rate threshold. When the port voltage has a large change trend (for example, undervoltage or overvoltage trend), the active power limit of the inverter can be adjusted in time (for example, the active power limit of the inverter is adjusted in advance before the voltage change reaches overvoltage or undervoltage), further improving the stability of the grid voltage.

[0055] In one embodiment, the active power limit does not exceed the upper limit of the active power limit; and / or the active power limit of the inverter is not lower than the lower limit of the active power amplitude.

[0056] In the embodiment of the present application, the specific values ​​of the upper limit of the active power limit and the lower limit of the active power amplitude are not limited. The active power limit is greater than or equal to the lower limit of the active power amplitude, and less than or equal to the upper limit of the active power limit. It is believed that even if the active power output by the inverter reaches the active power limit, it will not affect the safety of the power generation system and the serious fluctuation of the grid voltage.

[0057] In this embodiment, by limiting the active power limit to not exceed the upper limit of the active power limit and / or the active power limit to not be lower than the lower limit of the active power amplitude, the safety of the power generation system and severe fluctuations in the grid voltage caused by excessive or insufficient active power limiting are avoided, thereby improving the safety of power generation.

[0058] In one embodiment, when the change rate of the port voltage is greater than or equal to the voltage change rate threshold and the port voltage does not exceed a preset voltage range, the active power limit output by the inverter is controlled to decrease.

[0059] If the port voltage change rate is greater than or equal to the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the grid voltage is considered to be in a critical stable state, that is, on the edge of stability and instability. A slight increase in the active power output by the inverter will cause grid voltage instability.

[0060] In this case, the active power limit output by the inverter is controlled to be reduced, so that the active power limit is adapted to the current scenario, thereby reducing the large fluctuation of the grid voltage caused by the change of active power.

[0061] In this embodiment, when the rate of change of the port voltage is greater than or equal to the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the grid voltage is considered to be in a critical stable state. By controlling the active power limit of the inverter output to be reduced, it is avoided that when the grid voltage is in a critical stable state, the active power output of the inverter is too large, resulting in large fluctuations in the grid voltage, thereby improving the stability of the grid voltage.

[0062] In one embodiment, when the change rate of the port voltage is less than the voltage change rate threshold and the port voltage does not exceed a preset voltage range, the active power limit of the inverter output is controlled to increase.

[0063] If the port voltage change rate is less than the voltage change rate threshold and the port voltage does not exceed the preset voltage range, it is considered that the grid voltage is stable and there is no trend of the grid voltage changing to overvoltage or undervoltage.

[0064] In this case, the active power output by the inverter is controlled to be limited and increased, and the active power output by the inverter is released to increase the power generation.

[0065] In this embodiment, when the port voltage change rate is less than the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the grid voltage is considered stable. By controlling the active power limit of the inverter output to increase, the active power output of the inverter is released on the basis of the grid voltage stability, thereby increasing the power generation of the power generation system.

[0066] In addition to active power, the inverter also outputs reactive power to the grid, and changes in reactive power will also affect the stability of the grid voltage. Reactive power refers to the power that the inverter delivers to the grid to establish and maintain energy exchanges such as magnetic fields and electric fields, and does not directly participate in work. For ease of description, the reactive power mentioned in the embodiments of the present application refers to the value of reactive power, regardless of whether it is positive or negative.

[0067] Thus, in one embodiment, if Figure 3 As shown, the controller is also used to: when the port voltage of the inverter exceeds a preset voltage range, adjust the reactive power output by the inverter and adjust the active power limit of the inverter.

[0068] The port voltage of the inverter exceeds the preset voltage range, and the grid voltage is considered unstable.

[0069] In this case, by adjusting the reactive power output by the inverter and adjusting the active power limit of the inverter, the reactive power and the active power are controlled in a coordinated manner, and the voltage is stabilized faster than by controlling the reactive power or the active power alone.

[0070] It is known that the maximum power that the inverter can output is the apparent power. Among them, the apparent power refers to the product of the effective value of the voltage and current in the AC circuit, including active power and reactive power. The apparent power is usually represented by S.

[0071] Therefore, when the apparent power of the inverter remains unchanged, the adjusted value of the active power limit is related to the adjusted value of the reactive power.

[0072] In the embodiment of the present application, no limit is set for reactive power.

[0073] If the port voltage of the inverter does not exceed the preset voltage range, the reactive power output by the inverter does not need to be adjusted, and only the active power output by the inverter needs to be adjusted as in the above embodiment.

[0074] In this embodiment, when the port voltage of the inverter exceeds the preset voltage range, the grid voltage is considered unstable. By adjusting the reactive power output by the inverter and adjusting the active power limit of the inverter, the reactive power and active power are coordinated and controlled. Compared with stabilizing the voltage by controlling the reactive power or the active power alone, the coordinated control of the reactive power and the active power speeds up the process of stabilizing the voltage and enhances the effect of stabilizing the grid voltage.

[0075] The controller 103 adjusts the reactive power in different ways in the two situations of undervoltage and overvoltage of the grid voltage, as follows.

[0076] When the port voltage is less than or equal to a preset undervoltage threshold, the reactive power output by the inverter is controlled to increase; and / or when the port voltage is greater than or equal to a preset overvoltage threshold, the reactive power output by the inverter is controlled to decrease.

[0077] Among them, the port voltage is proportional to the reactive power.

[0078] In both overvoltage and undervoltage situations, the specific value of the reactive power output by the inverter can also be determined by a proportional-integral controller (PI controller) or other control strategies.

[0079] In this embodiment, when the port voltage is less than or equal to the preset undervoltage threshold, it indicates that the reactive power output by the inverter is insufficient, and the reactive power output by the inverter is controlled to increase to achieve a stable grid voltage. When the port voltage is greater than or equal to the preset overvoltage threshold, it indicates that the reactive power output by the inverter is excessive, and the reactive power output by the inverter is controlled to decrease to achieve a stable grid voltage.

[0080] In one embodiment, when the port voltage is less than or equal to a preset undervoltage threshold, the reactive power output by the inverter is controlled to increase and the active power limit of the inverter is controlled to decrease.

[0081] The value of the active power limit of the inverter after the reduction is related to the value of the reactive power output of the inverter after the increase, and the value of the active power limit of the inverter after the increase decreases as the value of the reactive power limit of the inverter after the reduction increases.

[0082] In this embodiment, when the port voltage is less than or equal to the preset undervoltage threshold, it is considered that the grid has an undervoltage fault. By controlling the reactive power output by the inverter to increase, the grid voltage is increased to solve the grid voltage undervoltage fault, and at the same time controlling the active power limit of the inverter to decrease, the reactive power and active power are controlled in a coordinated manner, the process of stabilizing the voltage is accelerated, and the effect of stabilizing the grid voltage is enhanced.

[0083] It can be known that the value of the active power limit is related to the value of the reactive power. In addition, the embodiment of the present application is also provided with a preset adjustment factor for adjusting the active power limit. The sum of the square of the product of the preset adjustment factor and the reactive power and the square of the active power limit is equal to the square of the maximum value of the apparent power. When the reactive power remains unchanged, the value of the active power limit is only related to the preset adjustment factor.

[0084] In one embodiment, the calculation method of the active power limit includes: calculating the square of the maximum value of the apparent power as the first value; calculating the square of the product of the preset adjustment factor and the reactive power as the second value; calculating the arithmetic square root of the difference between the first value and the second value as the active power limit. The calculation formula is as follows:

[0085]

[0086] Among them, Plmt(k) represents the active power limit of the kth beat, Smax represents the maximum value of the apparent power, Qref(k) represents the reactive power of the kth beat, m(k) represents the preset adjustment factor of the kth beat, and m(k)≥1 means that the lower limit value of m(k) is 1. The beat here represents a moment or a stage.

[0087] In the embodiment of the present application, the upper limit value of m(k) is not limited, and the control efficiency of active power limiting is improved by setting a preset adjustment factor greater than or equal to 1. The specific value of m(k) is related to whether the change rate of the port voltage of the inverter is greater than or equal to the voltage change rate threshold, and / or whether the port voltage exceeds the preset voltage range.

[0088] In one embodiment, when the rate of change of the port voltage of the inverter is greater than or equal to a voltage change rate threshold, and / or the port voltage exceeds a preset voltage range, the preset adjustment factor is controlled to increase, and the active power limit of the inverter output is controlled to decrease as the preset adjustment factor and reactive power increase; or, in response to the rate of change of the port voltage of the inverter being less than the voltage change rate threshold, and the port voltage does not exceed the preset voltage range, the preset adjustment factor is controlled to decrease, and the active power limit of the inverter output is controlled to increase as the preset adjustment factor decreases.

[0089] When the change rate of the port voltage of the inverter is greater than or equal to the voltage change rate threshold, and / or the port voltage exceeds a preset voltage range, the preset adjustment factor is controlled to increase.

[0090] In one embodiment, a first adjustment step can be set, and in response to the change rate of the port voltage of the inverter being greater than or equal to the voltage change rate threshold, and / or the port voltage exceeding the preset voltage range, the sum of the preset adjustment factor of the previous beat and the first adjustment step is obtained as the preset adjustment factor of the current beat. The symbol is expressed as m(k)=m(k-1)+step1, where step1 represents the first adjustment step, which is a smaller value.

[0091] When the preset adjustment factor increases, if the port voltage is less than or equal to the preset undervoltage threshold, the reactive power is controlled to increase. At this time, the inverter adjusts the output active power limit to decrease.

[0092] If the port voltage is greater than or equal to the preset overvoltage threshold, the reactive power is controlled to decrease. In this case, the value of the active power limit is calculated according to the above calculation formula, and the active power limit is adjusted accordingly.

[0093] Step 1 is a smaller value, that is, the change of m(k) relative to m(k-1) is small. When the port voltage is greater than or equal to the preset overvoltage threshold, if the reduction of reactive power is large, the active power limit is controlled to increase.

[0094] When the change rate of the port voltage of the inverter is less than the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the preset adjustment factor is controlled to decrease.

[0095] In one embodiment, a second adjustment step can be set, and in response to the change rate of the port voltage of the inverter being less than the voltage change rate threshold, and the port voltage not exceeding the preset voltage range, the sum of the preset adjustment factor of the previous beat and the second adjustment step is obtained as the preset adjustment factor of the current beat. The symbol is expressed as m(k)=m(k-1)-step2, where step2 represents the second adjustment step, which is a smaller value.

[0096] Among them, step1 and step2 can be the same or different.

[0097] When the preset adjustment factor decreases, the port voltage does not exceed the preset voltage range, the reactive power output by the inverter is not adjusted, and the active power limit of the inverter output is controlled to increase as the preset adjustment factor decreases.

[0098] In this embodiment, the active power limit of the inverter is dynamically adjusted by setting a preset adjustment factor. When the change rate of the port voltage of the inverter is greater than or equal to the voltage change rate threshold, and / or the port voltage exceeds the preset voltage range, the preset adjustment factor is controlled to increase, and the active power limit of the inverter is controlled to decrease with the increase of the preset adjustment factor and reactive power, so as to avoid the excessive active power output of the inverter causing large fluctuations in the grid voltage, thereby improving the stability of the grid voltage. When the change rate of the port voltage of the inverter is less than the voltage change rate threshold, and the port voltage does not exceed the preset voltage range, the preset adjustment factor is controlled to decrease, and the active power limit of the inverter is controlled to increase with the decrease of the preset adjustment factor, so as to release the active power output of the inverter and increase the power generation.

[0099] In one embodiment, the controller 103 is further configured to send an active power instruction to the inverter to adjust the active power limit of the inverter.

[0100] The active power instruction indicates the value of the active power.

[0101] In one implementation, the active power instruction may be generated by a controller or other device, and the controller adjusts the value of the active power indicated by the active power instruction according to the adjusted active power limit.

[0102] In this embodiment, by sending an active power instruction to the inverter to adjust the active power limit of the inverter, the active power output by the inverter is quickly adjusted, which is beneficial to improving the stability of the grid voltage.

[0103] Similarly, the controller 103 is also used to adjust the reactive power output by the inverter by sending a reactive power instruction to the inverter.

[0104] For easier understanding, see Figure 4 , Figure 4 A flow chart of the internal control of the controller is shown. The reactive power value of the reactive power indication generated by the controller is controlled.

[0105] like Figure 4 As shown, first, it is determined whether U(k) is greater than a preset undervoltage threshold and less than a preset overvoltage threshold. Wherein, U(k) represents the port voltage of the kth beat.

[0106] If so, obtain Qref(k)=Qref(k-1).

[0107] If not, Qref(k) is generated by a PI controller.

[0108] Finally, the reactive power command is generated according to Qref(k).

[0109] See also Figure 5 , Figure 5 A flow chart of the internal control of the controller is shown. The value of reactive power for controlling the active power indication generated by the controller.

[0110] First, S301 is executed to determine whether the change rate of the port voltage is less than a voltage change rate threshold.

[0111] If the change rate of the port voltage is less than the voltage change rate threshold, execute S302 to determine whether U(k) is greater than a preset undervoltage threshold and less than a preset overvoltage threshold.

[0112] If U(k) is greater than the preset undervoltage threshold and less than the preset overvoltage threshold, execute S303 to obtain m(k)=m(k-1)-step 2.

[0113] If the change rate of the port voltage is not less than the voltage change rate threshold, execute S304 to obtain m(k)=m(k-1)+step1.

[0114] If U(k) is not greater than the preset undervoltage threshold or not less than the preset overvoltage threshold, execute S304.

[0115] After m(k) is obtained, S305 is executed to determine whether m(k) is greater than an upper limit value.

[0116] If m(k) is greater than the upper limit, execute S306 to obtain m(k) = the upper limit, then execute S307 to obtain Plmt(k) = sqrt(Smax 2 -(Qref(k)×m(k)) 2 ).

[0117] If m(k) is not greater than the upper limit, execute S308 to determine whether m(k) is less than the lower limit.

[0118] If m(k) is less than the lower limit, execute S309, obtain m(k)=lower limit, and then execute S307.

[0119] If m(k) is not less than the lower limit, execute S307.

[0120] After obtaining Plmt(k), S310 is executed to determine whether Pref(k) is greater than Plmt(k), where Pref(k) represents the active power of the kth beat.

[0121] If Pref(k) is greater than Plmt(k), execute S311 to obtain Pref(k)=Plmt(k), and then execute S312 to generate an active power instruction according to Pref(k).

[0122] If Pref(k) is not greater than Plmt(k), execute S313 to determine whether Pref(k) is less than -Plmt(k).

[0123] If Pref(k) is less than -Plmt(k), execute S314 to obtain Pref(k)=-Plmt(k), and then execute S312.

[0124] If Pref(k) is not less than -Plmt(k), execute S312.

[0125] The embodiment of the present application provides a control method for an inverter. The control method is applied to a power generation system and includes the following steps.

[0126] When the port voltage of the inverter exceeds a preset voltage range, the active power limit of the inverter is adjusted; or when the change rate of the port voltage of the inverter is greater than or equal to the voltage change rate threshold, the active power limit of the inverter is adjusted.

[0127] In one embodiment, when the port voltage of the inverter exceeds a preset voltage range, the reactive power output by the inverter is adjusted and the active power limit of the inverter is adjusted.

[0128] It can be understood that all relevant contents involved in the above-mentioned power generation system embodiment can be referred to the embodiment of the control method, and the embodiment of the present application will not be repeated here.

[0129] Finally, it should be noted that the above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A power generation system, characterized in that: The power generation system includes an inverter and a controller, wherein the controller is used to control the inverter to convert direct current into alternating current and output the alternating current to the power grid; The controller is specifically used for: When the port voltage of the inverter exceeds a preset voltage range, adjusting the active power limit of the inverter; or, When the change rate of the port voltage of the inverter is greater than or equal to a voltage change rate threshold, the active power limit of the inverter is adjusted.

2. The power generation system according to claim 1, characterized in that: When the port voltage of the inverter exceeds a preset voltage range, adjusting the active power limit of the inverter includes: When the port voltage of the inverter exceeds a preset voltage range, the reactive power output by the inverter and the active power limit of the inverter are adjusted.

3. The power generation system according to claim 1, characterized in that: When the change rate of the port voltage of the inverter is greater than or equal to the voltage change rate threshold, adjusting the active power limit of the inverter includes: When the change rate of the port voltage is greater than or equal to the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the active power limit of the inverter is controlled to decrease.

4. The power generation system according to claim 1, characterized in that: The controller is also used for: When the change rate of the port voltage is less than the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the active power limit of the inverter is controlled to increase.

5. The power generation system according to claim 2, characterized in that: When the port voltage of the inverter exceeds a preset voltage range, adjusting the reactive power output by the inverter comprises: When the port voltage is less than or equal to a preset undervoltage threshold, controlling the reactive power output by the inverter to increase; and / or, When the port voltage is greater than or equal to a preset overvoltage threshold, the reactive power output by the inverter is controlled to decrease.

6. The power generation system according to claim 2 or 5, characterized in that: When the port voltage of the inverter exceeds a preset voltage range, adjusting the reactive power output by the inverter and the active power limit of the inverter includes: When the port voltage is less than or equal to a preset undervoltage threshold, the reactive power output by the inverter is controlled to increase and the active power limit of the inverter is controlled to decrease.

7. The power generation system according to claim 2, characterized in that: The controller is specifically used for: When the change rate of the port voltage of the inverter is greater than or equal to the voltage change rate threshold, and / or when the port voltage exceeds the preset voltage range, the preset adjustment factor is controlled to increase, and the active power limit of the inverter adjusted output is controlled to decrease as the preset adjustment factor and the reactive power increase, and the preset adjustment factor is used to adjust the active power limit; and / or, When the change rate of the port voltage of the inverter is less than the voltage change rate threshold and the port voltage does not exceed the preset voltage range, the preset adjustment factor is controlled to decrease, and the active power limit of the inverter output is controlled to increase as the preset adjustment factor decreases.

8. The power generation system according to any one of claims 1 to 7, characterized in that: The active power limit does not exceed the upper limit of the active power limit; and / or the active power limit is not lower than the lower limit of the active power amplitude.

9. The power generation system according to any one of claims 1 to 8, characterized in that: The controller is specifically used for: An active power instruction is sent to the inverter to adjust the active power limit of the inverter.

10. A method for controlling an inverter, characterized in that: Applied to a power generation system, the power generation system includes an inverter and a controller, the controller is used to control the inverter to convert direct current into alternating current and output it to a power grid, including: When the port voltage of the inverter exceeds a preset voltage range, adjusting the active power limit of the inverter; or, When the change rate of the port voltage of the inverter is greater than or equal to a voltage change rate threshold, the active power limit of the inverter is adjusted.

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