A network configuration converter with multiple power branches in parallel and a frequency support control method thereof

Abstract

The application provides a network converter with multiple power branch parallel connection and a frequency support control method thereof, the control method comprising: adjusting a frequency deviation to obtain a frequency deviation action; adjusting the frequency deviation action to obtain a first frequency modulation power instruction and a frequency modulation initial power instruction; determining a first active power instruction according to the initial active power instruction and the first frequency modulation power instruction; determining a second active power instruction according to at least the active power instruction of each network type control power branch and the first actual active power, and the frequency deviation action, the initial active power instruction and the frequency modulation initial power instruction of each follow network type control power branch; and controlling the corresponding power branch according to the first active power instruction and the second active power instruction. The method provided by the application solves the problem of power generation loss caused by small amplitude fluctuation of the power grid frequency of the generator set, and effectively reduces the problem of frequent fluctuation of the output power caused by small amplitude fluctuation of the power grid frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and particularly to a grid-forming converter with multiple parallel power branches and a frequency support control method therefor. Background Art

[0002] Currently, the new energy power generation equipment and the energy storage equipment supporting new energy power generation stations basically use grid-following control converters to connect to the grid. With the continuous increase in the proportion of new energy power generation in the power system and the improvement of the degree of electrification of loads in the system, the system is developing towards a "dual-high" form of "high proportion of new energy" and "high proportion of power electronics". Since the grid-forming control converter has the advantages of effectively improving the voltage support ability of new energy units, while improving its grid connection stability, providing voltage, frequency and damping support for the system, the proportion of grid-forming control converters is increasing continuously.

[0003] However, the grid-forming control has a slow response to the active power command, making it difficult for the unit to respond to the optimal power command in a timely manner, resulting in power generation loss of the unit. In addition, in the grid connection standards for new energy and energy storage, a dead zone setting requirement is proposed for the primary frequency regulation of the unit, that is, when the grid frequency deviation amplitude does not exceed the dead zone boundary, the power system does not want new energy or energy storage to activate the primary frequency regulation function.

[0004] In the grid-forming control, the damping control in the active power synchronization control loop will introduce a primary frequency regulation effect while maintaining the stable operation of the unit in a complex and changeable grid environment, resulting in the frequent start and stop of the primary frequency regulation function of new energy units or energy storage when the grid frequency fluctuates slightly. This will not only reduce the smoothness of the unit output power, but also easily cause the mechanical units of wind turbines to act frequently, affecting their service life, and at the same time, it is also easy to cause power generation loss of new energy units. Summary of the Invention

[0005] The present invention provides a grid-forming converter with multiple parallel power branches and a frequency support control method therefor, which solves the problem of power generation loss caused by small fluctuations in the grid frequency of the generator set, and effectively reduces the problem of frequent fluctuations in the output power caused by small fluctuations in the grid frequency.

[0006] According to the first aspect of the embodiments of the present invention, a frequency support control method for a grid-forming converter with multiple parallel power branches is provided. The converter includes a plurality of parallel power branches, and the plurality of parallel power branches include at least one grid-forming control power branch and at least one grid-following control power branch. The control method includes:

[0007] Obtain the frequency deviation and the initial active power command of each power branch, and the first actual active power of each grid-forming control power branch;

[0008] Adjust the frequency deviation of each power branch to obtain the effect of the frequency deviation of each power branch;

[0009] Adjust the frequency deviation of each power branch to obtain the first frequency modulation power command of each grid-type control power branch and the initial frequency modulation power command of each follow-grid control power branch;

[0010] The first active power command of each network-type control power branch is determined based on the initial active power command and the first frequency modulation power command of each network-type control power branch.

[0011] The frequency modulation correction power command of each grid-type control power branch is determined based at least on the active power command and the first actual active power of each grid-type control power branch, as well as the frequency deviation effect of each grid-type control power branch.

[0012] Based on the initial active power command, initial frequency modulation power command, and frequency modulation correction power command of each grid-type control power branch, determine the second active power command of each grid-type control power branch.

[0013] Control the corresponding grid-type control power branch at least according to the first active power command of each grid-type control power branch; control the corresponding follow-grid type control power branch at least according to the second active power command of each follow-grid type control power branch.

[0014] In one possible implementation, the frequency deviation of each power branch is obtained, including:

[0015] Obtain the rated angular frequency of the converter, as well as the actual angular frequency and initial active power command for each power branch;

[0016] Perform the following steps for each power branch:

[0017] The difference between the rated angular frequency and the actual angular frequency is determined to obtain the angular frequency deviation;

[0018] The frequency deviation is determined based on the angular frequency deviation.

[0019] In one possible implementation, the frequency deviation of each power branch is adjusted to obtain the effect of the frequency deviation of each power branch, including:

[0020] Perform the following steps for each power branch:

[0021] The frequency deviation is adjusted using a frequency dead-zone regulator to obtain the effect of the frequency deviation.

[0022] In one possible implementation, the frequency deviation action of each power branch is adjusted to obtain the first frequency modulation power command for each grid-type control power branch and the initial frequency modulation power command for each follow-grid-type control power branch, including:

[0023] Perform the following steps for each network-type control power branch:

[0024] The frequency deviation action is adjusted by using a grid frequency regulator to obtain the first frequency modulation power command;

[0025] Perform the following steps for each network-type control power branch:

[0026] The frequency deviation action is adjusted by using a grid frequency regulator to obtain the initial power command for frequency modulation.

[0027] In one possible implementation, the first active power command for each grid-type control power branch is determined based on the initial active power command and the first frequency modulation power command for each branch, including:

[0028] Perform the following steps for each network-type control power branch:

[0029] The sum of the initial active power command and the first frequency modulation power command is determined to obtain the first active power command.

[0030] In one possible implementation, the frequency modulation correction power command for each grid-type control power branch is determined based at least on the active power command and the first actual active power of each grid-type control power branch, and the frequency deviation effect of each grid-type control power branch, including:

[0031] Perform the following steps for each grid-connected control power branch:

[0032] The upper and lower limit values ​​are determined based on the frequency modulation dead zone setting and the effect of the second frequency deviation.

[0033] Based on the actual active power and the first active power command of each grid-type control power branch, determine the active power control deviation of each grid-type control power branch;

[0034] Determine the active power control deviation and value for each grid-type control power branch to obtain the total active power control deviation;

[0035] The initial frequency modulation correction power command is obtained by determining the quotient of the total active power control deviation and the number of grid-type control power branches.

[0036] The frequency modulation correction power command is obtained by using upper and lower limit values ​​to limit the initial frequency modulation correction power command.

[0037] In one possible implementation, based on the initial active power command, the initial frequency modulation power command, and the frequency modulation correction power command of each grid-type control power branch, a second active power command for each grid-type control power branch is determined, including:

[0038] Perform the following steps for each grid-connected control power branch:

[0039] The sum of the initial frequency modulation power command and the frequency modulation correction power command is calculated to obtain the second frequency modulation power command;

[0040] The sum of the initial active power command and the second frequency modulation power command is determined to obtain the second active power command.

[0041] In one possible implementation, at least according to the first active power command of each grid-type control power branch, the corresponding grid-type control power branch is controlled, including:

[0042] Perform the following steps for each network-type control power branch:

[0043] Obtain the grid connection point voltage, the first grid-side current, and the first reactive power command;

[0044] Based on the grid connection point voltage and the first grid-side current, power calculation is performed to obtain the first actual active power and the first actual reactive power.

[0045] The deviations between the first active power command and the first actual active power, as well as the deviations between the first reactive power command and the first actual reactive power, are adjusted to obtain the virtual internal potential phase and the virtual internal potential amplitude, respectively.

[0046] The PWM modulation voltage command is determined based on the virtual internal potential phase and the virtual internal potential amplitude.

[0047] The PWM modulated voltage command is spatially vector modulated to generate the drive signal required to control the power branch of the grid control.

[0048] In one possible implementation, at least according to the second active power command of each grid-connected control power branch, the corresponding grid-connected control power branch is controlled, including:

[0049] Perform the following steps for each grid-connected control power branch:

[0050] Obtain commands for grid connection point voltage, second grid-side current, and second reactive power;

[0051] Based on the grid connection point voltage and the second grid-side current, power calculation is performed to obtain the second actual active power and the second actual reactive power.

[0052] The deviations between the second active power command and the second actual active power, as well as the deviations between the second reactive power command and the second actual reactive power, are adjusted to obtain the active current command and the reactive current command, respectively.

[0053] The active and reactive currents are obtained by using the phase angle of the phase-locked loop output to perform coordinate transformation on the second grid-side current.

[0054] The deviation between the active current command and the active current, as well as the deviation between the reactive current command and the reactive current, are adjusted and transformed by coordinates to obtain the PWM modulated voltage command.

[0055] The PWM modulated voltage command is spatially vector modulated to generate the drive signal required to control the power branch of the grid control.

[0056] According to a second aspect of the present invention, a multi-parallel power branch converter is provided. The converter includes multiple parallel power branches, each power branch including a power module or a sub-converter. The multiple parallel power branches include at least one grid-type control power branch and at least one grid-following control power branch. The converter further includes a processor and a memory storing computer program instructions. When the processor executes the computer program instructions, it implements the frequency support control method for a multi-power branch parallel grid-type converter of the first aspect of the present invention and any possible implementation thereof.

[0057] This invention provides a grid-connected converter with multiple power branches in parallel and its frequency support control method. The converter's multiple parallel power branches include at least one grid-connected control power branch and at least one grid-following control power branch. Different control methods are used for the grid-connected and grid-following control power branches. When controlling the grid-following control power branch, not only is its own power branch data used, but also the power data of the grid-connected control power branch is considered. This solves the problem of power generation loss caused by small fluctuations in grid frequency and effectively reduces the resulting frequent fluctuations in output power. While ensuring grid connection stability, it also ensures that the unit can provide the required frequency support capability according to grid connection requirements, improving its response capability to optimal power generation. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0059] Figure 1A schematic diagram of the control structure of a multi-parallel power branch converter provided in an embodiment of the present invention;

[0060] Figure 2 A schematic diagram of a control system structure for another multi-parallel power branch converter provided in an embodiment of the present invention;

[0061] Figure 3 A flowchart illustrating a frequency support control method for a grid converter with multiple power branches connected in parallel, provided in an embodiment of the present invention;

[0062] Figure 4 A schematic diagram of the first frequency modulation power command for generating a network-type control power branch provided in an embodiment of the present invention;

[0063] Figure 5 A schematic diagram of the principle for generating the second frequency modulation power command of the grid-type control power branch provided in an embodiment of the present invention;

[0064] Figure 6-a , Figure 6-b and Figure 6-c A schematic diagram of simulation results comparison provided for an embodiment of the present invention;

[0065] Figure 7-a and Figure 7-b This is another simulation result comparison diagram provided for an embodiment of the present invention;

[0066] Figure 8-a and Figure 8-b And a comparative diagram of another simulation result provided in an embodiment of the present invention;

[0067] Figure 9 This is a schematic diagram of the control structure of a network-type control power branch provided in an embodiment of the present invention;

[0068] Figure 10 This is a schematic diagram of the control structure of the grid-type control power branch provided in an embodiment of the present invention. Detailed Implementation

[0069] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] Converter: An electrical device that changes the voltage, frequency, number of phases, and other electrical quantities or characteristics of a power supply system. It includes rectifiers (AC to DC), inverters (DC to AC), AC converters, and DC converters. New energy generator sets are connected to the grid via converters.

[0071] The method provided in this invention is applied to the converters of generator units in new energy power plants, such as wind power converters in wind power plants and photovoltaic converters in photovoltaic power plants.

[0072] Example 1

[0073] This invention provides a control system for a multi-parallel power branch converter, such as... Figure 1 or Figure 2 As shown, the system includes a power grid, a converter with multiple power branches, a converter control unit, and a feeder side. The power grid and the feeder side are connected via a DC bus. The feeder side consists of an energy storage unit, a photovoltaic generator, and / or a wind turbine generator. Each power branch includes at least a PWM rectifier bridge composed of power devices and DC capacitors. If each power branch includes a sub-converter, such as... Figure 1 As shown, it also includes a filter capacitor. The power branches are connected in parallel and then connected to the grid connection point of the converter; if each power branch includes a power module, such as Figure 2 As shown, the power branches are connected in parallel, and a filter capacitor is also connected between the converter and the grid connection point. .

[0074] in,

[0075] u g : Power grid voltage;

[0076] Z g : Power grid impedance;

[0077] i o : Converter output current;

[0078] u o : Converter grid connection point voltage;

[0079] n: The total number of parallel power branches;

[0080] AC filter capacitors for the sub-converter;

[0081] The AC filter capacitor of the converter, which is composed of power modules connected in parallel in the power branch;

[0082] : Filter inductors for power branch 1, power branch 2... power branch n;

[0083] : Grid-side current of power branch 1, power branch 2... power branch n;

[0084] AC side voltages of power branch 1, power branch 2... power branch n;

[0085] DC side voltages of power branch 1, power branch 2... power branch n;

[0086] : Drive signals for power branch 1, power branch 2... power branch n.

[0087] Each power branch's AC side is connected in parallel to the power grid, and its DC side is connected in parallel to the power feeder side, or the DC side of each power branch is independently connected to the power feeder side. When the DC sides of the power branches are independently connected to the power feeder side, each power branch is connected to one type of power feeder side, such as an energy storage unit, a photovoltaic generator set, or a wind turbine generator set. The power feeders connected to multiple power branches of the converter do not have to be exactly the same; that is, the power feeder side of a converter can be connected to one or more of the following: an energy storage unit, a photovoltaic generator set, or a wind turbine generator set.

[0088] In the aforementioned multi-parallel power branch converter control system, the multiple parallel power branches of the converter include at least one grid-connected control power branch and at least one grid-following control power branch. The same power branch can switch between grid-connected and grid-following control modes based on demand. The number of power branches operating in grid-connected and grid-following control modes is determined according to the grid conditions. Under weak grid conditions, the number of power branches operating in grid-connected control is greater than or equal to the number of power branches operating in grid-following control; under strong grid conditions, the number of power branches operating in grid-following control is greater than or equal to the number of power branches operating in grid-connected control.

[0089] Based on the above-described multi-parallel power branch converter control system, this invention provides a frequency support control method for grid-connected converters with multiple power branches in parallel. The control method is as follows: Figure 3 As shown, it includes the following steps:

[0090] S310, acquires the frequency deviation and initial active power command for each power branch, as well as the first actual active power for each grid-type control power branch.

[0091] Obtain the rated angular frequency of the converter, as well as the actual angular frequency and initial active power command for each power branch; such as Figure 4 or Figure 5 As shown, the following steps are performed for each power branch:

[0092] First, determine the rated angular frequency. and actual angular frequency The difference is used to obtain the angular frequency deviation; then, the frequency deviation is determined based on the angular frequency deviation. ,in, = .

[0093] Obtain the grid connection point voltage of the converter and the grid-side current of each grid-type control power branch; based on the grid connection point voltage... The grid-side current of each grid-type control power branch is used to calculate the power of each grid-type control power branch, thereby obtaining the first actual active power of each grid-type control power branch.

[0094] S320 adjusts the frequency deviation of each power branch to obtain the effect of the frequency deviation of each power branch.

[0095] like Figure 4 or Figure 5 As shown, a frequency dead-time regulator is used to adjust the frequency deviation of each power branch, and the effect of the frequency deviation of each power branch is obtained. The transfer function of the frequency dead-time regulator is expressed by the following formula:

[0096]

[0097] In the formula, Indicates the effect of frequency deviation. Indicates frequency deviation. This indicates the dead time setting value for a single frequency modulation. .

[0098] S330 adjusts the frequency deviation of each power branch to obtain the first frequency modulation power command of each grid-type control power branch and the initial frequency modulation power command of each follow-grid control power branch.

[0099] Perform the following steps for each network-type control power branch:

[0100] A grid-connected frequency regulator is used to adjust the frequency deviation to obtain the first frequency modulation power command. Specifically, the grid-connected frequency regulator adjusts the frequency deviation based on the primary modulation coefficient, damping coefficient, and rated angular frequency to obtain the first frequency modulation power command, such as... Figure 4 As shown, the transfer function of the network frequency regulator is expressed by the following formula:

[0101]

[0102] in, This indicates the first frequency modulation power command. This represents the primary frequency modulation coefficient. This represents the damping coefficient of the control power branch in a grid-type configuration.

[0103] Perform the following steps for each network-type control power branch:

[0104] The frequency deviation action is adjusted using a grid-following frequency regulator to obtain the initial frequency modulation power command. Specifically, the frequency deviation action is adjusted based on the primary frequency modulation coefficient using the grid-following frequency regulator to obtain the initial frequency modulation power command, such as... Figure 4 As shown, the transfer function of the grid frequency regulator is expressed by the following formula:

[0105]

[0106] in, This indicates the initial power command for frequency modulation. This represents the primary frequency modulation coefficient.

[0107] S340 determines the first active power command for each network-type control power branch based on the initial active power command and the first frequency modulation power command for each network-type control power branch.

[0108] For each grid-type control power branch, the sum of the initial active power command and the first frequency modulation power command is calculated to obtain the first active power command for each grid-type control power branch.

[0109] S350 determines the frequency modulation correction power command for each grid-type control power branch based at least on the active power command and the first actual active power of each grid-type control power branch, as well as the frequency deviation effect of each grid-type control power branch.

[0110] S360 determines the second active power command for each grid-type control power branch based on the initial active power command, the initial frequency modulation power command, and the frequency modulation correction power command for each grid-type control power branch.

[0111] Perform the following steps for each grid-connected control power branch:

[0112] The sum of the initial frequency modulation power command and the frequency modulation correction power command is calculated to obtain the second frequency modulation power command;

[0113] The sum of the initial active power command and the second frequency modulation power command is determined to obtain the second active power command.

[0114] S370 controls the corresponding grid-type control power branch at least according to the first active power command of each grid-type control power branch; and controls the corresponding follow-grid control power branch at least according to the second active power command of each follow-grid control power branch.

[0115] For each grid-type control power branch, the first active power command generated in the above steps is used as the active power command to generate the virtual internal potential phase and virtual internal potential amplitude; based on the virtual internal potential phase and virtual internal potential amplitude, the PWM modulation voltage command is determined; the PWM modulation voltage command is space vector modulated to generate the drive signal required for controlling the grid-type control power branch.

[0116] For each grid-type control power branch, the second active power command generated in the above steps is used as the active power command to generate the PWM modulation voltage command.

[0117] The following simulation demonstrates the effectiveness of the technique used in this method by simulating the change of the power grid frequency within the frequency dead zone. The rated frequency of the power grid is 50Hz, and the primary frequency regulation dead zone is set to 0.05Hz.

[0118] Figure 6-a , Figure 6-b , Figure 6-c Simulation results are presented for three scenarios: using the control method provided in this embodiment, not using the control method provided in this embodiment, and not using the control method provided in this embodiment but reducing the active power synchronous control loop damping coefficient at 5s. The total power command Pref represents the target value of the converter's output active power, and the total power feedback Pfb represents the actual output active power of the converter. Before 4s, the grid frequency is 50Hz; at 4s, the grid frequency begins to rise, increasing to 50.03Hz, and the grid frequency deviation does not exceed the dead zone boundary. Figure 6-a It can be seen that after a slight fluctuation in the grid frequency, the total power feedback Pfb remains at 1, with no loss of power generation; from Figure 6-b It can be seen that the total power feedback Pfb decreased from 1.000 at 3.496s to 0.9606 at 4.844s, resulting in a power generation loss; from Figure 6-c It can be seen that the total power feedback Pfb decreased from 1.000 at 3.496s to 0.9899 at 6.029s, indicating a significant oscillation in the unit's output power and a loss of power generation. Comparison shows that the control method provided in this embodiment eliminates the power generation loss caused by the unit's output power deviating from the command when the grid frequency fluctuates slightly, and it does not weaken the unit's grid connection stability compared to the control method that reduces the active power loop damping coefficient.

[0119] Figure 7-a , Figure 7-bSimulation results are presented for using the control method provided in this embodiment and for not using the control method provided in this embodiment. The total power command Pref represents the target value of the converter's output active power, and the total power feedback Pfb represents the actual output active power of the converter. Before 4 seconds, the grid frequency was 50Hz. After 4 seconds, the grid frequency began to rise, reaching 50.2Hz. The grid frequency deviated from the rated value and entered the primary frequency regulation range. Using the method of this invention, while ensuring the grid connection stability of the unit, it ensures that it can provide the required frequency support capability according to the grid connection requirements, thus improving its response capability to optimal power generation.

[0120] Figure 8-a , Figure 8-b The simulation results are shown for using the control method provided in the embodiments of the present invention and not using the control method provided in the embodiments of the present invention. The grid frequency fluctuates slightly around the rated frequency. When the control method provided in the embodiments of the present invention is not used, the output active power fluctuates significantly. When the control method provided in the embodiments of the present invention is used, the output active power fluctuation is significantly reduced. The comparison shows that the control method provided in the embodiments of the present invention can effectively reduce the frequent fluctuations in active power caused by the slight fluctuations in grid frequency.

[0121] This invention provides a frequency support control method for a grid-connected converter with multiple power branches in parallel. The converter's multiple parallel power branches include at least one grid-connected control power branch and at least one grid-following control power branch. Different control methods are employed for the grid-connected and grid-following control power branches. When controlling the grid-following control power branch, not only is its own data used, but also the power data from the grid-connected control power branch is considered. This method solves the problem of power generation loss caused by small fluctuations in grid frequency and effectively reduces the resulting frequent fluctuations in output power. While ensuring grid connection stability, it also ensures that the unit can provide the required frequency support capability according to grid connection requirements, improving its response capability to optimal power generation.

[0122] Example 2

[0123] In one embodiment, such as Figure 5 As shown, S350: Based at least on the active power command and the first actual active power of each grid-type control power branch, and the frequency deviation effect of each grid-type control power branch, determine the frequency modulation correction power command for each grid-type control power branch, including:

[0124] Perform the following steps for each grid-connected control power branch:

[0125] S351, determine the upper limit amplitude limit and the lower limit amplitude limit based on the frequency modulation dead zone setting value and the second frequency deviation effect.

[0126] Specifically, when the second frequency deviation action amount Less than the frequency dead zone setting value When the opposite number is reached, the upper limit value is set to 0, and the second frequency deviation action is... Greater than or equal to the FM dead zone setting value When the opposite number is obtained, the upper limit value is determined based on the sum of the frequency modulation dead zone setting and the effect of the second frequency deviation, as well as the damping coefficient of the power branch.

[0127] Second frequency deviation effect Greater than the frequency dead zone setting value When the lower limit amplitude is set to 0, the second frequency deviation action amount... Less than or equal to the FM dead zone setting value The lower limit amplitude is determined based on the sum of the frequency dead zone setting and the effect of the second frequency deviation, as well as the damping coefficient of the power branch.

[0128] It can be expressed by the following formula:

[0129]

[0130]

[0131] in, The upper limit represents the amplitude limit, and the lower limit represents the amplitude limit value. D represents the damping coefficient of the power branch when operating under network control.

[0132] S352, based on the actual active power and the first active power command of each grid-type control power branch, determine the active power control deviation of each grid-type control power branch.

[0133] For each grid-type control power branch, the difference between the actual active power and the first active power command is calculated to obtain the active power control deviation of each grid-type control power branch.

[0134] S353, determine the active power control deviation and value of each network-type control power branch, and obtain the total active power control deviation.

[0135] S354 determines the quotient of the total active power control deviation and the number of grid-type control power branches, and obtains the initial frequency modulation correction power command.

[0136] like Figure 5 As shown, it can be expressed by the following formula:

[0137]

[0138] in, This indicates the initial frequency modulation correction power command. Indicates the number of control power branches in a network configuration. , This represents the active power control deviation of the i-th grid-type controlled power branch, 1≤i≤ , This indicates the total deviation in active power control. Indicates the number of control power branches in the network topology. .

[0139] S355 uses upper and lower limit values ​​to limit the initial frequency modulation correction power command, resulting in the frequency modulation correction power command.

[0140] like Figure 5 As shown, the upper limit value is used. and lower limit amplitude value Initial frequency modulation correction power command Limiting, resulting in frequency modulation correction power command It can be expressed by the following formula:

[0141]

[0142] The control method provided in this invention uses not only the data of the current power branch but also the power data of the grid-connected control power branch when controlling the grid-connected control power branch. This solves the problem of power generation loss caused by small fluctuations in grid frequency and effectively reduces the problem of frequent fluctuations in output power. While ensuring the grid connection stability of the unit, it also ensures that the unit can provide the required frequency support capability according to the grid connection requirements and improves its response capability to optimal power generation.

[0143] Example 3

[0144] In one embodiment, the control structure of the network-type control power branch is as follows: Figure 9 As shown, S370: Controlling the corresponding grid-type control power branch according to at least the first active power command of each grid-type control power branch may include the following steps:

[0145] Perform the following steps for each network-type control power branch:

[0146] S11, obtain the grid connection point voltage, the first grid-side current, and the first reactive power command.

[0147] Collect the grid connection point voltage of the converter The first grid-side current of the grid-controlled power branch and the first reactive power command Let i represent the i-th network-type control power branch, 1 ≤ i ≤ 1. .

[0148] S12, based on the grid connection point voltage and the first grid-side current, perform power calculation to obtain the first actual active power and the first actual reactive power.

[0149] S13, adjust the deviation between the first active power command and the first actual active power, and the deviation between the first reactive power command and the first actual reactive power, to obtain the virtual internal potential phase and the virtual internal potential amplitude, respectively.

[0150] Calculate the first active power command Deviation from the first actual active power The difference is the deviation between the first active power command and the first actual active power. ,right Adjustments are made to obtain the virtual internal potential phase. It can be expressed by the following formula:

[0151]

[0152]

[0153] in, Indicates the amount of angular frequency adjustment. Indicates the angular frequency of the mesh. Represents the virtual moment of inertia. This represents the damping coefficient.

[0154] Calculate the first reactive power command Deviation from the first actual reactive power The difference is the deviation between the first reactive power command and the first actual reactive power. ,right Adjustments are made to obtain the virtual internal potential amplitude. It can be expressed by the following formula:

[0155]

[0156] in, The transfer function of the reactive power regulator in a grid-type controlled power branch is given. This indicates the voltage reference value at the converter's grid connection point.

[0157] S14: Determine the PWM modulation voltage command based on the virtual internal potential phase and the virtual internal potential amplitude.

[0158] The PWM modulation voltage command is determined using conventional methods in existing technologies, which will not be elaborated here.

[0159] S15 performs space vector modulation on the PWM modulated voltage command to generate the drive signal required for controlling the power branch of the grid control.

[0160] The conventional method in the existing technology is used to perform space vector modulation on the PWM modulation voltage command to generate the drive signal required for controlling the power branch of the grid control, which will not be elaborated here.

[0161] The control structure of the power branch with the network control is as follows: Figure 10 As shown, S370: Controlling the corresponding grid-type control power branch at least according to the second active power command of each grid-type control power branch includes the following steps:

[0162] Perform the following steps for each grid-connected control power branch:

[0163] S21, obtain the grid connection point voltage, the second grid-side current, and the second reactive power command.

[0164] Collect the grid connection point voltage of the converter The second grid-side current of the grid-controlled power branch Second reactive power command j represents the j-th root-type controlled power branch, 1≤j≤ .

[0165] S22. Based on the grid connection point voltage and the second grid-side current, power calculation is performed to obtain the second actual active power and the second actual reactive power.

[0166] S23, adjust the deviation between the second active power command and the second actual active power, and the deviation between the second reactive power command and the second actual reactive power, to obtain the active current command and the reactive current command respectively.

[0167] Calculate the second active power command Deviation from the second actual active power The difference is the deviation between the second active power command and the second actual active power. Adjusting this deviation yields the active current command. It can be expressed by the following formula:

[0168]

[0169] in, This represents the transfer function of the active power regulator in the grid-controlled power branch.

[0170] Calculate the second active power command Deviation from the second actual active power The difference is the deviation between the second reactive power command and the second actual reactive power. Adjusting this deviation yields the reactive current command. It can be expressed by the following formula:

[0171]

[0172] in, This represents the transfer function of the reactive power regulator in the grid-controlled power branch.

[0173] S24 uses the phase angle of the phase-locked loop output to perform coordinate transformation on the second grid-side current to obtain the active current and reactive current.

[0174] Phase-locked loop (PLL) is used for phase locking to obtain the phase angle with the grid operation. ,use For the second grid side current Transform from abc coordinates to dq coordinates to obtain the active current. and reactive current .

[0175] S25 adjusts and transforms the active current command and the deviation between active current and reactive current, as well as the reactive current command and the deviation between reactive current, to obtain the PWM modulated voltage command.

[0176] Calculate active current command and active current The difference between the active current command and the active current is used to obtain the deviation between the active current command and the active current. Adjusting this deviation yields the d-axis command of the transmitted voltage, which can be expressed by the following formula:

[0177]

[0178] in, The d-axis component represents the voltage at the grid connection point. This represents the transfer function of the current regulator in grid-connected mode.

[0179] Calculate reactive current command and reactive current The difference between the reactive current command and the reactive current is used to obtain the deviation between the reactive current command and the reactive current. Adjusting this deviation yields the q-axis command of the generated voltage, which can be expressed by the following formula:

[0180]

[0181] in, The q-axis component represents the voltage at the grid connection point. This represents the transfer function of the current regulator in grid-connected mode.

[0182] Perform coordinate transformation on the d-axis and q-axis commands of the transmitted voltage, transforming from the dq-axis coordinates to... The axis is used to obtain the generated voltage. Axis commands and Axis commands , and This refers to the PWM modulation voltage command.

[0183] S26 performs space vector modulation on the PWM modulated voltage command to generate the drive signal required for controlling the power branch of the grid control.

[0184] The conventional method in the existing technology is used to perform space vector modulation on the PWM modulation voltage command to generate the drive signal PWMDrvj required to control the power branch of the grid control, which will not be elaborated here.

[0185] In the control method provided by this invention, the first power command of the grid-type control power branch and the second power command of the grid-connected control power branch are generated using different control methods. When controlling the grid-connected control power branch, not only the data of this power branch is used, but also the power data of the grid-type control power branch is considered. This solves the problem of power generation loss caused by small fluctuations in grid frequency and effectively reduces the problem of frequent fluctuations in output power. While ensuring the grid connection stability of the unit, it ensures that it can provide the required frequency support capability according to grid connection requirements and improves its response capability to optimal power generation.

[0186] Example 3

[0187] This embodiment provides a multi-parallel power branch converter, which includes multiple parallel power branches. Each power branch includes a power module or a sub-converter. The multiple parallel power branches include at least one grid-type control power branch and at least one grid-following control power branch. The converter also includes a processor and a memory storing computer program instructions. When the processor executes the computer program instructions, it implements the frequency support control method for the multi-power branch parallel grid-type converter described in the above embodiment of the present invention.

[0188] The multi-parallel power branch converter provided in this embodiment belongs to the same inventive concept as the frequency support control method for multi-power branch parallel grid converters provided in the above embodiments of the present invention. It can execute the frequency support control method for multi-power branch parallel grid converters provided in any of the above embodiments of the present invention, and possesses the corresponding functional modules and beneficial effects of the frequency support control method for multi-power branch parallel grid converters. Technical details not described in detail in this embodiment can be found in the specific processing content of the frequency support control method for multi-power branch parallel grid converters provided in the above embodiments of the present invention, and will not be repeated here.

[0189] For the foregoing method embodiments, in order to simplify the description, they are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0190] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For apparatus embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0191] The steps in the methods of the various embodiments of the present invention can be adjusted, merged, or deleted in order according to actual needs, and the technical features described in the various embodiments can be replaced or combined.

[0192] The modules and sub-modules in the various embodiments of the present invention can be merged, divided, and deleted according to actual needs.

[0193] In the embodiments provided by this invention, it should be understood that the disclosed terminals, devices, and methods can be implemented in other ways. For example, the terminal embodiments described above are merely illustrative. For instance, the division of modules or sub-modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple sub-modules or modules may be combined or integrated into another module, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interfaces, devices, or modules, and may be electrical, mechanical, or other forms.

[0194] The modules or submodules described as separate components may or may not be physically separate. The components that constitute a module or submodule may or may not be physical modules or submodules; that is, they may be located in one place or distributed across multiple network modules or submodules. Some or all of the modules or submodules can be selected to achieve the purpose of this embodiment's solution, depending on actual needs.

[0195] Furthermore, the functional modules or sub-modules in the various embodiments of the present invention can be integrated into one processing module, or each module or sub-module can exist physically separately, or two or more modules or sub-modules can be integrated into one module. The integrated modules or sub-modules described above can be implemented in hardware or in the form of software functional modules or sub-modules.

[0196] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0197] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software unit executed by a processor, or a combination of both. The software unit can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0198] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0199] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A frequency support control method for a grid-connected converter with multiple power branches in parallel. The converter comprises multiple parallel power branches, each power branch including a power module or a sub-converter, characterized in that... The plurality of parallel power branches include at least one grid-type control power branch and at least one grid-following control power branch, and the control method includes: Obtain the frequency deviation and initial active power command for each power branch, as well as the first actual active power for each grid-type control power branch; Adjust the frequency deviation of each power branch to obtain the frequency deviation effect of each power branch; Adjust the frequency deviation of each power branch to obtain the first frequency modulation power command of each grid-type control power branch and the initial frequency modulation power command of each follow-grid-type control power branch; The first active power command of each network-type control power branch is determined based on the initial active power command and the first frequency modulation power command of each network-type control power branch. The frequency modulation correction power command of each grid-type control power branch is determined based at least on the active power command and the first actual active power of each grid-type control power branch, as well as the frequency deviation effect of each grid-type control power branch. Based on the initial active power command, initial frequency modulation power command, and frequency modulation correction power command of each grid-type control power branch, determine the second active power command of each grid-type control power branch. Control the corresponding grid-type control power branch at least according to the first active power command of each grid-type control power branch; control the corresponding follow-grid control power branch at least according to the second active power command of each follow-grid control power branch.

2. The frequency support control method for a grid converter with multiple power branches in parallel according to claim 1, characterized in that, Obtain the frequency deviation for each power branch, including: Obtain the rated angular frequency of the converter, as well as the actual angular frequency and initial active power command of each power branch; Perform the following steps for each power branch: The difference between the rated angular frequency and the actual angular frequency is determined to obtain the angular frequency deviation; The frequency deviation is determined based on the angular frequency deviation.

3. The frequency support control method for a grid converter with multiple power branches in parallel according to claim 1, characterized in that, Adjusting the frequency deviation of each power branch to obtain the frequency deviation effect of each power branch includes: Perform the following steps for each power branch: The frequency deviation is adjusted using a frequency dead-zone regulator to obtain the effect amount of the frequency deviation.

4. The frequency support control method for a grid converter with multiple power branches in parallel according to claim 1, characterized in that, The adjustment of the frequency deviation of each power branch to obtain the first frequency modulation power command for each grid-type control power branch and the initial frequency modulation power command for each follow-grid control power branch includes: Perform the following steps for each network-type control power branch: The frequency deviation action is adjusted by using a grid frequency regulator to obtain the first frequency modulation power command; Perform the following steps for each network-type control power branch: The frequency deviation action is adjusted by using a grid frequency regulator to obtain the initial power command for frequency modulation.

5. The frequency support control method for a grid converter with multiple power branches in parallel according to claim 1, characterized in that, The step of determining the first active power command for each grid-type control power branch based on the initial active power command and the first frequency modulation power command includes: Perform the following steps for each network-type control power branch: The sum of the initial active power command and the first frequency modulation power command is determined to obtain the first active power command.

6. The frequency support control method for a grid converter with multiple power branches in parallel according to claim 1, characterized in that, Based at least on the active power command and the first actual active power of each grid-type control power branch, and the frequency deviation effect of each grid-type control power branch, determine the frequency modulation correction power command for each grid-type control power branch, including: Perform the following steps for each grid-connected control power branch: The upper and lower limit values ​​are determined based on the frequency modulation dead zone setting and the effect of the second frequency deviation. Based on the actual active power and the first active power command of each grid-type control power branch, determine the active power control deviation of each grid-type control power branch; The active power control deviation and value of each grid-type control power branch are determined to obtain the total active power control deviation; The initial frequency modulation correction power command is obtained by determining the quotient of the total active power control deviation and the number of grid-type control power branches. The frequency modulation correction power command is obtained by using upper and lower limit values ​​to limit the initial frequency modulation correction power command.

7. The frequency support control method for a grid converter with multiple power branches in parallel according to claim 1, characterized in that, The step of determining the second active power command for each grid-connected control power branch based on the initial active power command, the initial frequency modulation power command, and the frequency modulation correction power command for each grid-connected control power branch includes: Perform the following steps for each grid-connected control power branch: The sum of the initial frequency modulation power command and the frequency modulation correction power command is calculated to obtain the second frequency modulation power command; The sum of the initial active power command and the second frequency modulation power command is determined to obtain the second active power command.

8. The frequency support control method for a grid converter with multiple power branches in parallel according to claim 1, characterized in that, The step of controlling the corresponding grid-type control power branch according to at least the first active power command of each grid-type control power branch includes: Perform the following steps for each network-type control power branch: Obtain the grid connection point voltage, the first grid-side current, and the first reactive power command; Based on the grid connection point voltage and the first grid-side current, power calculation is performed to obtain the first actual active power and the first actual reactive power. The deviations between the first active power command and the first actual active power, and the deviations between the first reactive power command and the first actual reactive power are adjusted to obtain the virtual internal potential phase and the virtual internal potential amplitude, respectively. The PWM modulation voltage command is determined based on the virtual internal potential phase and the virtual internal potential amplitude. The PWM modulation voltage command is spatially vector modulated to generate the drive signal required to control the power branch of the grid control.

9. The frequency support control method for a grid converter with multiple power branches in parallel according to claim 1, characterized in that, The step of controlling the corresponding grid-connected control power branch according to at least the second active power command of each grid-connected control power branch includes: Perform the following steps for each grid-connected control power branch: Obtain commands for grid connection point voltage, second grid-side current, and second reactive power; Based on the grid connection point voltage and the second grid-side current, power calculation is performed to obtain the second actual active power and the second actual reactive power. The deviations between the second active power command and the second actual active power, and the deviations between the second reactive power command and the second actual reactive power are adjusted to obtain active current command and reactive current command respectively. The active current and reactive current are obtained by using the phase angle of the phase-locked loop output to perform coordinate transformation on the second grid-side current. The deviation between the active current command and the active current, and the deviation between the reactive current command and the reactive current are adjusted and transformed by coordinates to obtain the PWM modulation voltage command. The PWM modulation voltage command is spatially vector modulated to generate the drive signal required to control the power branch of the grid control.

10. A multi-parallel power branch converter, the converter comprising multiple parallel power branches, each power branch comprising a power module or a sub-converter, characterized in that, The plurality of parallel power branches include at least one grid-type control power branch and at least one grid-following control power branch. The converter further includes a processor and a memory storing computer program instructions. When the processor executes the computer program instructions, it implements the frequency support control method for a grid-type converter with multiple power branches in parallel as described in any one of claims 1-9.

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