Method and apparatus for power grid frequency low frequency oscillation damping suppression

Abstract

The application discloses a power grid frequency low-frequency oscillation damping suppression method and device. The power grid frequency low-frequency oscillation damping suppression method comprises the following steps: acquiring the voltage and output active power of a grid-connected system of a grid-connected energy storage; obtaining first additional damping power through a main additional damping channel according to the voltage of the grid-connected point; obtaining second additional damping power through an auxiliary additional damping channel according to the output active power; superimposing the second additional damping power on the first additional damping power to obtain total additional damping power; and forming a grid-connected phase based on the active-phase loop of the grid-connected energy storage system according to the total additional damping power, so that the oscillation energy flow formed by the fluctuation amount of the output active power of the grid-connected energy storage system and the fluctuation amount of the power grid frequency is a negative value. The low-frequency oscillation caused by the power grid side is quickly suppressed, the transmission efficiency of the power grid is improved, and the risk of system disconnection caused by frequency oscillation and large-area power cut is significantly reduced.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of new energy, and in particular to a method and apparatus for damping and suppressing low-frequency oscillations in power grids. Background Technology

[0002] The application of new energy power generation, transmission, and consumption equipment using power electronic converters as interfaces is becoming increasingly widespread in power systems. Modern power systems are evolving from synchronous generator-dominated grids to converter-dominated grids, and the trend towards power electronics in power systems is irreversible. However, power electronic converters and synchronous generators have several significant differences in their external characteristics when connected to the grid. Compared to synchronous generators, power electronic converters offer advantages such as flexible control and rapid response. However, they also have poor overcurrent capacity, almost no inertia, difficulty in participating in grid regulation, and are unable to provide the necessary voltage and frequency support or damping effect to the grid. This poses a serious challenge to the safe and stable operation of the power grid.

[0003] As the proportion of new energy sources in the system increases, grid stability will be severely threatened. To improve this situation, more and more energy storage batteries are being connected to the grid through grid-connected converters. Grid-connected converters actively establish voltage and frequency by simulating the rotor equation dynamics of synchronous generators and the external characteristics of voltage sources. Because grid-connected converters have the ability to flexibly set control parameters to achieve damping control, they have the potential to suppress low-frequency oscillations in the grid.

[0004] However, the damping power output of a grid-connected converter, which inherently possesses damping capabilities, may not necessarily meet the grid's demands. When the grid frequency experiences low-frequency oscillations, the grid-connected converter still requires additional damping measures to ensure that the output damping power meets the specified amplitude and phase range requirements, thus providing sufficient damping for the grid. Currently, however, there is no solution for designing the additional damping function of a grid-connected converter to ensure that its output damping power meets the specified amplitude and phase range requirements.

[0005] While some studies have proposed calculating additional damping power based on grid frequency, this approach has significant drawbacks in weak grid applications where grid-connected converters (GDCs) best demonstrate their advantages. These studies have failed to address how to accurately obtain the grid frequency for GDCs in weak grid conditions. Although the grid frequency can be indirectly sensed by detecting the frequency of the grid connection point voltage, the oscillation frequency of the grid connection point in weak grids decays as the damping power output of the GDC increases. This means that in certain frequency bands, the damping power output of the GDC reaches a certain level and then essentially stops increasing. Consequently, in some frequency bands, the damping power cannot be adjusted to the upper or lower limits required by certain test specifications or standards, failing to provide sufficient damping power to the grid. Current damping solutions do not solve this problem. Summary of the Invention

[0006] This invention provides a method and apparatus for damping and suppressing low-frequency oscillations in power grids. It effectively solves the problem that the oscillation frequency at the grid connection point decreases as the damping power output of the grid-connected converter increases under weak power grid conditions, resulting in the damping power output of the grid-connected converter basically not increasing after reaching a certain level in certain frequency bands. This ensures that the output damping power can reach the preset upper and lower limits, meet the standard requirements, quickly suppress low-frequency oscillations caused by the grid side, improve the grid transmission efficiency, and significantly reduce the risk of system disconnection and large-scale power outages caused by frequency oscillations.

[0007] In a first aspect, embodiments of the present invention provide a method for damping and suppressing low-frequency oscillations in a power grid, wherein the power grid includes a grid-connected energy storage system; the method for damping and suppressing low-frequency oscillations in a power grid includes:

[0008] Obtain the voltage and output active power at the grid connection point of the grid-connected energy storage system;

[0009] The first additional damping power is obtained through the main additional damping channel based on the voltage of the grid connection point;

[0010] The second additional damping power is obtained by passing the output active power through the auxiliary additional damping channel;

[0011] The second additional damping power is superimposed on the first additional damping power to obtain the total additional damping power;

[0012] Based on the total additional damping power, the active-phase loop of the grid-connected energy storage system is used to form the grid phase, so that the oscillating energy flow formed by the fluctuation of the output active power of the grid-connected energy storage system and the fluctuation of the grid frequency is negative.

[0013] Optionally, the first additional damping power is obtained based on the voltage at the grid connection point via the main additional damping channel, including:

[0014] The real-time angular frequency of the power grid is determined by a phase-locked loop based on the voltage at the grid connection point.

[0015] The real-time angular frequency is filtered by a first low-pass filter to obtain the filtered angular frequency of the power grid.

[0016] The opposite value of the angular frequency fluctuation of the power grid is determined based on the difference between the rated angular frequency of the power grid and the filtered angular frequency of the power grid.

[0017] The first lead-lag unit performs phase compensation on the opposite value of the angular frequency fluctuation, and the first additional damping power is obtained based on the first damping coefficient of low-frequency oscillation.

[0018] Optionally, the real-time angular frequency of the power grid is determined via a phase-locked loop based on the voltage at the grid connection point, including:

[0019] Perform dq transformation on the voltage at the grid connection point to determine the q-axis voltage;

[0020] The phase-locked loop angular frequency change is determined based on the q-axis voltage using a proportional-integral control method.

[0021] The real-time angular frequency of the power grid is determined by the sum of the change in the phase-locked loop angular frequency and the rated angular frequency of the power grid.

[0022] Optionally, the second additional damping power is obtained from the output active power via an auxiliary additional damping channel, including:

[0023] The fluctuation of the output active power is obtained by subtracting the output active power from the active power command.

[0024] The fluctuation of the output active power is filtered by a second low-pass filter to obtain the fluctuation of the filtered output active power.

[0025] The second lead-lag unit performs phase compensation on the fluctuation of the filtered output active power, and the second additional damping power is obtained based on the second damping coefficient of low-frequency oscillation.

[0026] Optionally, before obtaining the voltage at the grid connection point of the grid-connected energy storage system, the method further includes:

[0027] The first phase advance compensation time constant and the first phase lag compensation time constant of the first advance and lag unit are set according to the preset phase delay time corresponding to the preset frequency band. The first phase advance compensation time constant is greater than the first phase lag compensation time constant. The preset frequency band is the frequency band corresponding to low frequency oscillation. The preset phase delay time includes the phase delay time caused by the first low-pass filter and the phase delay time caused by the active phase loop.

[0028] The first damping coefficient of the low-frequency oscillation is determined based on the upper limit of the preset damping power range.

[0029] Optionally, before obtaining the output active power, the method further includes:

[0030] Based on the phase of the first additional damping power in the first frequency band, the second phase advance compensation time constant and the second phase lag compensation time constant of the second advance and lag unit are set so that the difference between the phase of the second additional damping power in the first frequency band and the phase of the first additional damping power in the first frequency band is less than a first preset value; wherein, the first frequency band is the frequency band corresponding to the lower limit of the first additional damping power being less than the preset damping power range.

[0031] The second damping coefficient for low-frequency oscillation is determined based on the difference between the lower limit of the preset damping power range and the power value of the first additional damping power in the first frequency band.

[0032] Optionally, based on the total additional damping power, a grid-connected phase is formed according to the active-phase loop of the grid-connected energy storage system, including:

[0033] Based on the output angular frequency of the grid-connected energy storage system at the previous moment and the rated angular frequency of the power grid, the change in the active power command of the grid-connected energy storage system is determined by droop control.

[0034] The input power of the grid-connected energy storage system is determined based on the change in the active power command, the total additional damping power, and the active power command of the grid-connected energy storage system.

[0035] The difference between the input power and the output power and feedback damping power of the grid-connected energy storage system is calculated, and then the quotient is taken with the virtual inertia value. The result is then integrated to obtain the change in the output angular frequency of the grid-connected energy storage system at the current moment.

[0036] The output angular frequency at the current moment is determined based on the change in the output angular frequency at the current moment and the rated angular frequency of the power grid;

[0037] The network phase of the active-phase loop is determined based on the output angular frequency at the current moment using integral calculation.

[0038] Optionally, before subtracting the input power from the output power and feedback damping power of the grid-connected energy storage system, the method further includes:

[0039] The feedback damping power is determined based on the change in output angular frequency and feedback damping coefficient of the grid-connected energy storage system at the previous moment.

[0040] Optionally, after forming the grid-connected phase based on the active-phase loop of the grid-connected energy storage system according to the total additional damping power, the method further includes:

[0041] The fluctuation of the output active power is obtained by subtracting the active power command from the output active power of the grid-connected energy storage system.

[0042] The fluctuation of the grid frequency is obtained by subtracting the rated frequency of the grid from the real-time frequency of the grid connection point.

[0043] The value of the oscillating energy flow is obtained by multiplying the fluctuation of the output active power with the fluctuation of the grid frequency and then integrating the product.

[0044] Secondly, embodiments of the present invention provide a low-frequency oscillation damping and suppression device for power grids, wherein the power grid includes a grid-connected energy storage system; the low-frequency oscillation damping and suppression device for power grids includes:

[0045] The acquisition module is used to acquire the voltage and output active power at the grid connection point of the grid-connected energy storage system.

[0046] The main additional damping channel is used to obtain the first additional damping power based on the voltage of the grid connection point through the main additional damping channel;

[0047] An auxiliary additional damping channel is used to obtain a second additional damping power based on the output active power via the auxiliary additional damping channel;

[0048] The summation module is used to add the second additional damping power to the first additional damping power to obtain the total additional damping power;

[0049] The active-phase loop module is used to form the grid-connected phase based on the active-phase loop of the grid-connected energy storage system according to the total additional damping power, so that the oscillating energy flow formed by the fluctuation of the output active power of the grid-connected energy storage system and the fluctuation of the grid frequency is negative.

[0050] The technical solution of this embodiment uses the first additional damping power obtained by the voltage at the grid connection point through the main additional damping channel and the second additional damping power obtained by the output active power through the auxiliary additional damping channel to form a total additional damping power. This allows the second additional damping power to compensate for the deficiency of the first additional damping power in some frequency bands of the preset oscillation frequency band, so that the total additional damping power in the frequency band corresponding to the low-frequency oscillation of the grid side frequency can reach the preset damping power range. Then, the total additional damping power is added to the active power command to adjust the active power, thereby effectively adjusting the active power output of the grid-type converter and suppressing the low-frequency oscillation of the grid frequency in all frequencies of the preset oscillation frequency band. This effectively solves the problem that the oscillation frequency at the grid connection point in weak power grids decreases as the damping power output of the grid-connected converter increases, causing the output damping power of the grid-connected converter to essentially stop increasing after reaching a certain level in certain frequency bands. This ensures that the output damping power can reach the preset damping power range and meet the standard requirements. Furthermore, it synchronously adjusts the phase according to the active power, quickly suppressing low-frequency oscillations caused by the grid side, improving the transmission efficiency of the power grid, and significantly reducing the risk of system disconnection and large-scale power outages caused by frequency oscillations. Attached Figure Description

[0051] Figure 1 A flowchart of a method for damping and suppressing low-frequency oscillations in power grid frequency provided in an embodiment of the present invention;

[0052] Figure 2 This is a schematic diagram of a structure for obtaining total additional damping power according to an embodiment of the present invention;

[0053] Figure 3 A flowchart of another method for damping and suppressing low-frequency oscillations in power grid frequency provided in an embodiment of the present invention;

[0054] Figure 4 A flowchart of another method for damping and suppressing low-frequency oscillations in power grid frequency provided in an embodiment of the present invention;

[0055] Figure 5 This is a schematic diagram of a phase-locked loop provided in an embodiment of the present invention;

[0056] Figure 6 A flowchart of another method for damping and suppressing low-frequency oscillations in power grid frequency provided in an embodiment of the present invention;

[0057] Figure 7 A flowchart of another method for damping and suppressing low-frequency oscillations in power grid frequency provided in an embodiment of the present invention;

[0058] Figure 8 This is a schematic diagram of an active-phase loop structure provided in an embodiment of the present invention;

[0059] Figure 9 A schematic diagram of a power grid frequency curve provided for related technologies;

[0060] Figure 10 A schematic diagram of the active power output of a grid-connected energy storage system for related technologies;

[0061] Figure 11 A schematic diagram of the power oscillation energy flow curve provided by a grid-connected energy storage system during damping suppression response, for related technologies.

[0062] Figure 12 A schematic diagram of a power grid frequency curve provided for an embodiment of the present invention;

[0063] Figure 13 A schematic diagram of the active power output of a grid-connected energy storage system provided in an embodiment of the present invention;

[0064] Figure 14 A schematic diagram of the power oscillation energy flow provided by a grid-connected energy storage system during damping suppression response, provided for an embodiment of the present invention;

[0065] Figure 15 A schematic diagram of another power grid frequency curve provided for related technologies;

[0066] Figure 16 A schematic diagram of the active power output of another grid-connected energy storage system for related technologies;

[0067] Figure 17 A schematic diagram of the power oscillation energy flow curve provided by a grid-connected energy storage system during another damping suppression response provided for related technologies;

[0068] Figure 18 A schematic diagram of another power grid frequency provided in an embodiment of the present invention;

[0069] Figure 19 A schematic diagram of the active power output curve of another grid-connected energy storage system provided in an embodiment of the present invention;

[0070] Figure 20 A schematic diagram of the power oscillation energy flow curve provided by a grid-connected energy storage system during another damping suppression response, as provided in an embodiment of the present invention;

[0071] Figure 21 This is a schematic diagram of a low-frequency oscillation damping and suppression device for power grid frequencies provided in an embodiment of the present invention. Detailed Implementation

[0072] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0073] Figure 1 This is a flowchart illustrating a method for damping and suppressing low-frequency oscillations in a power grid, provided as an embodiment of the present invention. This embodiment is applicable to situations where the power grid includes a grid-connected energy storage system. Specifically, the grid-connected energy storage system may include a DC power supply, a grid-connected converter, and a grid-connected control system. The DC power supply may include DC power generation components, such as a photovoltaic module array. The DC power supply may also include battery packs for storing the electrical energy generated by the DC power generation components. The grid-connected converter enables bidirectional interaction between DC power and the standard AC power of the power grid. The grid-connected control system coordinates the operation of the DC power supply and the grid-connected converter, ensuring that the grid-connected energy storage system meets the active / reactive power and frequency requirements of the power grid, achieving synchronization with the grid.

[0074] The grid frequency low-frequency oscillation damping suppression method provided in this embodiment of the invention can be executed by a grid frequency low-frequency oscillation damping suppression device, which can be integrated into the grid-connected control system of the grid-connected energy storage system. For example... Figure 1 As shown, the method for damping and suppressing low-frequency oscillations in the power grid includes:

[0075] S110, Obtain the voltage and output active power at the grid connection point of the grid-connected energy storage system;

[0076] In this context, the grid connection point of a grid-connected energy storage system is the Point of Common Coupling (PCC) between the system and the power grid, i.e., the location where the system connects to the grid. When the grid-connected energy storage system includes a grid-type converter, the DC side of the converter is connected to the DC power supply, and the AC side is connected to the power grid. Therefore, the grid connection point is the location where the AC side of the converter connects to the grid. At the grid connection point, the grid voltage and the AC side voltage of the converter can be synchronized. In this case, the voltage at the grid connection point can characterize the grid voltage. After obtaining the voltage at the grid connection point, the current can also be obtained, and then the output active power of the system can be determined based on instantaneous power theory.

[0077] S120. Obtain the first additional damping power based on the voltage at the grid connection point through the main additional damping channel;

[0078] Voltage fluctuations can characterize frequency fluctuations. The first additional damping power is the active power required for primary damping control when the grid-side frequency exhibits low-frequency oscillations. Figure 2 This is a schematic diagram of a structure for obtaining total additional damping power according to an embodiment of the present invention. Figure 2 As shown, after obtaining the voltage at the grid connection point, the fluctuation of the grid-side frequency can be determined based on the voltage at the grid connection point. Then, based on the fluctuation of the grid-side frequency and the main additional damping channel 210, the first additional damping power P corresponding to the low-frequency oscillation of the grid-side frequency can be determined. f .

[0079] S130. The second additional damping power is obtained from the output active power through the auxiliary additional damping channel;

[0080] Specifically, when the grid-side frequency fluctuates, the output active power of the grid-connected energy storage system will fluctuate accordingly to adjust the phase, thereby suppressing grid frequency oscillations. The second additional damping power is the active power corresponding to the auxiliary damping control when the grid-side frequency has low-frequency oscillations. For example... Figure 2 As shown, after obtaining the output active power P of the grid-connected energy storage system, the second additional damping power P corresponding to the low-frequency oscillation of the grid-side frequency can be determined based on the low-frequency oscillation damping control of the auxiliary additional damping channel 220. p .

[0081] S140. The second additional damping power is superimposed on the first additional damping power to obtain the total additional damping power;

[0082] Among them, such as Figure 2 As shown, the low-frequency oscillation damping suppression device for the power grid also includes a summing module 230, which sums the second additional damping power P. p Superimposed on the first additional damping power P f From this, we can obtain the total additional damping power P. a This allows the second additional damping power P to be made... p The additional damping power P is compensated for by the decrease in the amplitude of the oscillation frequency at the grid connection point as the output damping power of the grid-connected converter increases. f The deficiency in certain frequency bands within the preset oscillation frequency band results in a decrease in the total additional damping power P corresponding to the low-frequency oscillation frequency band on the grid side. a All can reach the preset damping power range, so that the total additional damping power P a When used to regulate active power, it can suppress low-frequency oscillations of the power grid frequency at all frequencies within a preset oscillation band.

[0083] For example, the preset damping power range can be 10% to 30% of the rated active power output of the grid-connected energy storage system. The total additional damping power P...a When the preset damping power range can be achieved within the preset oscillation frequency band, the maximum value of the change in active power output of the grid-connected energy storage system can be guaranteed to meet the rated active power P output of the grid-connected energy storage system. ref 10% to 30%.

[0084] S150. Based on the total additional damping power, form the grid phase of the grid-connected energy storage system using the active-phase loop, so that the oscillating energy flow formed by the fluctuation of the output active power of the grid-connected energy storage system and the fluctuation of the grid frequency is negative.

[0085] In this grid-connected energy storage system, the active-phase loop simulates the rotor characteristics of a prime mover governor and a synchronous motor, enabling synchronous phase adjustment using active power. After determining the total additional damping power, this power can be superimposed on the active power command to adjust the active power, effectively regulating the active power output of the grid-connected converter. Synchronous phase adjustment based on active power rapidly suppresses low-frequency oscillations induced by the grid, improving grid transmission efficiency and significantly reducing the risk of system disconnection and large-scale power outages caused by frequency oscillations. It also facilitates oscillation damping of frequency fluctuations caused by load switching on the grid side.

[0086] The technical solution of this embodiment uses the first additional damping power obtained by the voltage at the grid connection point through the main additional damping channel and the second additional damping power obtained by the output active power through the auxiliary additional damping channel to form a total additional damping power. This allows the second additional damping power to be sufficient to compensate for the deficiency of the first additional damping power in some frequency bands of the preset oscillation frequency band. This ensures that the total additional damping power in the frequency band corresponding to the low-frequency oscillation of the grid side frequency can reach the preset damping power range. Then, the total additional damping power is added to the active power command to adjust the active power, thereby effectively adjusting the active power output of the grid-type converter and suppressing the low-frequency oscillation of the grid frequency in all frequencies of the preset oscillation frequency band. This effectively solves the problem that the oscillation frequency at the grid connection point in weak power grids decreases as the damping power output of the grid-connected converter increases, causing the output damping power of the grid-connected converter to essentially stop increasing after reaching a certain level in certain frequency bands. This ensures that the output damping power can reach the preset damping power range and meet the standard requirements. Furthermore, it synchronously adjusts the phase according to the active power, quickly suppressing low-frequency oscillations caused by the grid side, improving the transmission efficiency of the power grid, and significantly reducing the risk of system disconnection and large-scale power outages caused by frequency oscillations.

[0087] Figure 3 A flowchart illustrating another method for damping and suppressing low-frequency oscillations in power grid frequencies provided in an embodiment of the present invention. Figure 3 As shown, the method includes:

[0088] S210, Obtain the voltage and output active power at the grid connection point of the grid-connected energy storage system;

[0089] S220. Determine the real-time angular frequency of the power grid using a phase-locked loop based on the voltage at the grid connection point.

[0090] Among them, such as Figure 2 As shown, the main additional damping channel 210 may include a phase-locked loop (PLL), which latches the output voltage u at point PCC. pcc Then, based on the output voltage u at point PCC pcc The real-time angular frequency ω of the power grid PLL .

[0091] S230. The real-time angular frequency of the power grid is passed through the first low-pass filter to obtain the filtered angular frequency of the power grid.

[0092] The main additional damping channel 210 also includes a first low-pass filter LPF1. The real-time angular frequency ω of the output power grid of the phase-locked loop (PLL) is... PLL Then, the real-time angular frequency ω of the power grid can be obtained through the first low-pass filter LPF1. PLL Low-pass filtering is performed to remove harmonics in the subsynchronous frequency band and above, thus suppressing subsynchronous oscillations. For example... Figure 2 As shown, the filtered angular frequency ω of the power grid is obtained after passing through the first low-pass filter LPF1. g For example, the transfer function expression of the first low-pass filter LPF1 is:

[0093]

[0094] Where T1 is the time constant of the first low-pass filter LPF1. The cutoff frequency of the first low-pass filter LPF1 can be located in the synchronous oscillation frequency band, used to suppress low-frequency oscillations. The first damping coefficient k df The increase causes subsynchronous oscillations. For example, the cutoff frequency range of the first low-pass filter LPF1 can be set to 20Hz-30Hz according to the low-frequency band to filter out interference signals in other frequency bands outside the low-frequency band.

[0095] S240. Determine the opposite value of the angular frequency fluctuation of the power grid based on the difference between the rated angular frequency of the power grid and the filtered angular frequency of the power grid.

[0096] Among them, such as Figure 2 As shown, the rated angular frequency ω of the power grid is... ref The filtered angular frequency ω of the power grid g The difference is used to determine the opposite value of the angular frequency fluctuation of the power grid. ω g The angular frequency fluctuation of the power grid is the filtered angular frequency ω of the power grid. gSubtract the rated angular frequency ω of the power grid ref The value of .

[0097] S250, Phase compensation is performed on the opposite value of the angular frequency fluctuation by the first lead-lag unit, and the first additional damping power is obtained based on the first damping coefficient of low frequency oscillation.

[0098] Among them, such as Figure 2 As shown, the inverse value of the angular frequency fluctuation of the power grid is... ω g After passing through the first lead-lag unit 202, phase lead compensation is applied. Then, after passing through the low-frequency oscillation first damping unit 201, the low-frequency oscillation first damping coefficient k is applied. df The proportional gain is adjusted so that the amplitude of the first additional damping power is within a suitable active power range, thus obtaining the first additional damping power P. f .

[0099] S260. The second additional damping power is obtained from the output active power through the auxiliary additional damping channel;

[0100] S270. The second additional damping power is superimposed on the first additional damping power to obtain the total additional damping power;

[0101] S280. Based on the total additional damping power, form the grid-phase based on the active-phase loop of the grid-connected energy storage system, so that the oscillating energy flow formed by the fluctuation of the output active power of the grid-connected energy storage system and the fluctuation of the grid frequency is negative.

[0102] Figure 4 A flowchart illustrating another method for damping and suppressing low-frequency oscillations in power grid frequencies provided in an embodiment of the present invention. Figure 4 As shown, the method includes:

[0103] S310, Obtain the voltage and output active power at the grid connection point of the grid-connected energy storage system;

[0104] S320. Perform dq transformation on the voltage at the grid connection point to determine the q-axis voltage;

[0105] in, Figure 5 This is a schematic diagram of a phase-locked loop provided in an embodiment of the present invention. Figure 5 As shown, the voltage u at the grid connection point pcc For three-phase voltage, the phase-locked loop can first convert the grid-connected point voltage u through the dq conversion unit 203. pcc Perform a dq transformation to determine the d-axis voltage v. d and q-axis voltage v q .

[0106] S330. Determine the phase-locked loop angular frequency change based on the q-axis voltage using a proportional-integral control method.

[0107] Among them, continue to refer to Figure 5 For the q-axis voltage v q Proportional-integral (PI) controllers are used for proportional-integral (PI) control to determine the change in the phase-locked loop (PLL) angular frequency. ω PLL .

[0108] S340. Determine the real-time angular frequency of the power grid based on the sum of the phase-locked loop angular frequency change and the rated angular frequency of the power grid.

[0109] Among them, continue to refer to Figure 5 The change in phase-locked loop angular frequency ω PLL and the rated angular frequency ω of the power grid s By adding them together, we obtain the real-time angular frequency ω of the power grid. PLL .

[0110] S350, the real-time angular frequency of the power grid is passed through the first low-pass filter to obtain the filtered angular frequency of the power grid.

[0111] S360. Determine the opposite value of the angular frequency fluctuation of the power grid based on the difference between the rated angular frequency of the power grid and the filtered angular frequency of the power grid.

[0112] S370. Phase compensation is performed on the opposite value of the angular frequency fluctuation by the first lead-lag unit, and the first additional damping power is obtained based on the first damping coefficient of the low-frequency oscillation.

[0113] S380. The second additional damping power is obtained from the output active power through the auxiliary additional damping channel;

[0114] S390. The second additional damping power is superimposed on the first additional damping power to obtain the total additional damping power;

[0115] S400. Based on the total additional damping power, the active-phase loop of the grid-connected energy storage system is used to form the grid phase, so that the oscillating energy flow formed by the fluctuation of the output active power of the grid-connected energy storage system and the fluctuation of the grid frequency is negative.

[0116] In some embodiments, performing a dq transformation on the voltage at the grid connection point to determine the q-axis voltage includes:

[0117] The phase during the dq transformation process is determined based on the real-time angular frequency of the power grid at the previous moment.

[0118] Among them, continue to refer to Figure 5 In determining the real-time angular frequency ω of the power grid PLL Then, the real-time angular frequency ω of the power gridPLL Phase θ can be formed by integration. PLL The voltage u at the grid connection point locked by the phase-locked loop is fed back to the dq conversion unit 203. pcc Phase.

[0119] Figure 6 A flowchart illustrating another method for damping and suppressing low-frequency oscillations in power grid frequencies provided in an embodiment of the present invention. Figure 6 As shown, the method includes:

[0120] S410: Obtain the voltage and output active power at the grid connection point of the grid-connected energy storage system;

[0121] S420. Obtain the first additional damping power based on the voltage at the grid connection point through the main additional damping channel;

[0122] S430: The fluctuation of the output active power is obtained by subtracting the output active power from the active power command.

[0123] Among them, such as Figure 2 As shown, the fluctuation of the output active power P of the grid-connected energy storage system is determined by subtracting the active power command from the output active power P. The active power command of the grid-connected energy storage system is the rated active power P of the system. ref .

[0124] S440. The fluctuation of the output active power is filtered by the second low-pass filter to obtain the fluctuation of the output active power after filtering.

[0125] Among them, such as Figure 2 As shown, the auxiliary damping channel 220 may include a second low-pass filter LPF2. The second low-pass filter LPF2 performs low-pass filtering on the obtained fluctuation of the output active power to filter out high-frequency interference signals, obtaining the filtered fluctuation of the output active power. For example, the transfer function expression of the second low-pass filter LPF2 is:

[0126]

[0127] Where T2 is the time constant of the second low-pass filter LPF2. The cutoff frequency of the second low-pass filter LPF2 can be set in the synchronous oscillation frequency band to filter out high-frequency interference in the auxiliary additional damping channel 220, so that the channel shields high-frequency signals and only allows low-frequency signals to pass through.

[0128] S450: The second lead-lag unit performs phase compensation on the fluctuation of the filtered output active power, and the second additional damping power is obtained based on the second damping coefficient of low-frequency oscillation.

[0129] Among them, such as Figure 2As shown, the auxiliary additional damping channel 220 may further include a second lead-lag unit 204, which performs phase lead compensation on the fluctuation of the filtered output active power. Then, it passes through a low-frequency oscillation second damping unit 205, which applies a low-frequency oscillation second damping coefficient k to the fluctuation of the phase-compensated output active power. dp The proportional gain is adjusted so that the amplitude of the second additional damping power is within a suitable active power range, thus obtaining the second additional damping power P. p .

[0130] S460. The second additional damping power is superimposed on the first additional damping power to obtain the total additional damping power;

[0131] S470. Based on the total additional damping power, form the grid phase of the grid-connected energy storage system using the active-phase loop, so that the oscillating energy flow formed by the fluctuation of the output active power of the grid-connected energy storage system and the fluctuation of the grid frequency is negative.

[0132] In the following embodiments, before obtaining the voltage at the grid connection point of the grid-connected energy storage system, the method further includes:

[0133] The first phase advance compensation time constant and the first phase lag compensation time constant of the first advance lag unit are set according to the preset phase delay time corresponding to the preset frequency band. The first phase advance compensation time constant is greater than the first phase lag compensation time constant. The preset frequency band is the frequency band corresponding to the low frequency oscillation. The preset phase delay time includes the phase delay time caused by the first low-pass filter and the phase delay time caused by the active phase loop.

[0134] in, Figure 2 The example illustrates that the main additional damping channel 210 also includes a first lead-lag unit 202. This is inversely proportional to the angular frequency fluctuation of the power grid. ω g After low-frequency oscillation, the first damping coefficient k df The inverse value of the angular frequency fluctuation of the power grid before proportional gain is applied. ω g Phase adjustment can be performed first through the first lead-lag unit 202 to reverse the angular frequency fluctuation of the power grid. ω g Phase advance compensation can be performed to ensure that the power oscillation energy flow is negative, meeting the relevant standards for grid-connected energy storage systems. Simultaneously, the first damping coefficient k of low-frequency oscillations can be adjusted. df The excessively large subsynchronous oscillations are suppressed to a certain extent, thereby increasing the first damping coefficient k of the low-frequency oscillations. df The adjustment margin is increased, and the first additional damping power is increased, which is conducive to further effective adjustment of active power and suppression of low-frequency oscillation.

[0135] For example, the expression for the power oscillation energy flow is:

[0136]

[0137] Where W is the power oscillation energy flow. P represents the change in active power output of the grid-type converter. f represents the change in the power grid frequency.

[0138] From the above formula, it can be seen that when P and Conversely, when f is reversed, the power oscillation energy flow W can be made less than 0. That is, when the grid frequency oscillates at a low frequency, the grid-type converter also outputs power with sinusoidal fluctuations. When the grid frequency fluctuation reaches its highest point, the active power output of the grid-type converter is at its lowest point. At this time, by reversing the angular frequency fluctuation of the grid... ω g Phase advance compensation can make the power oscillation energy flow negative, which meets the relevant standards for grid connection of grid-connected energy storage systems.

[0139] In some embodiments, when performing phase lead compensation for the opposite value of the grid's angular frequency fluctuation, the goal is to compensate for the total phase delay caused by the active-phase loop and the first low-pass filter LPF1 in the main additional damping channel 210. The phase lead compensation time constant and the phase lag compensation time constant of the first lead-lag unit 202 of the main additional damping channel 210 are determined according to the preset frequency band of the frequency oscillation to be suppressed. The phase delay of the active-phase loop is the difference between the phase of the output angular frequency of the input grid-connected energy storage system at the previous moment and the output grid phase. The first lead-lag unit 202 has a first phase lead compensation time constant and a first phase lag compensation time constant. The first phase lead compensation time constant characterizes the amount of phase lead compensation for the opposite value of the grid's angular frequency fluctuation, and the first phase lag compensation time constant characterizes the amount of phase lag compensation for the opposite value of the grid's angular frequency fluctuation. After determining the structure of the active-phase loop and the preset frequency band of the grid frequency oscillation to be suppressed (i.e., the preset frequency band), the first phase advance compensation time constant and the first phase lag compensation time constant of the opposite value of the angular frequency fluctuation can be determined based on the phase delay of the active-phase loop and the frequency band of the preset oscillation frequency of the grid. Making the first phase advance compensation time constant greater than the first phase lag compensation time constant ensures that the phase of the opposite value of the angular frequency fluctuation is compensated in advance, guaranteeing that the power oscillation energy flow is negative. This not only meets the relevant standards for grid-connected energy storage systems but also allows for adjustments to the first damping coefficient k of low-frequency oscillations. dfThe excessively large subsynchronous oscillations are suppressed to a certain extent, thereby increasing the first damping coefficient k of the low-frequency oscillations. df The adjustment margin is increased, and the first additional damping power is increased, which is conducive to further effective adjustment of active power and suppression of low-frequency oscillation.

[0140] For example, the expression for the transfer function of the first lead-lag unit 202 is:

[0141]

[0142] Among them, T 1Lead T is the time constant for the first phase advance compensation. 1Lag This is the time constant for the first phase lag compensation.

[0143] In some embodiments, when the active-phase loop has a complex structure and a large phase delay, the difference between the first phase lead compensation time constant and the first phase lag compensation time can be increased. This increases the phase lead compensation for the opposite value of the angular frequency fluctuation, ensuring that the power oscillation energy flow is negative. Similarly, when the phase fluctuation of the preset grid oscillation frequency to be suppressed is large, the difference between the first phase lead compensation time constant and the first phase lag compensation time can be increased to increase the phase lead compensation for the opposite value of the angular frequency fluctuation, thus compensating for the phase fluctuation of the preset oscillation frequency and ensuring that the power oscillation energy flow is negative. For example, when the difference between the first phase lead compensation time constant and the first phase lag compensation time increases, the first phase lead compensation time constant can be increased or decreased. Similarly, when the active-phase loop structure is simple, the phase delay of the active-phase loop is relatively small. In this case, the difference between the first phase lead compensation time constant and the first phase lag compensation time can be reduced, thereby reducing the phase lead compensation amount for the opposite value of the angular frequency fluctuation, and avoiding overcompensation while ensuring that the power oscillation energy flow is negative. When the phase fluctuation of the preset grid oscillation frequency to be suppressed is small, the difference between the first phase lead compensation time constant and the first phase lag compensation time can also be reduced, thus reducing the phase lead compensation amount for the opposite value of the angular frequency fluctuation, achieving compensation for the phase fluctuation of the preset oscillation frequency, and ensuring that the power oscillation energy flow is negative. For example, when the difference between the first phase lead compensation time constant and the first phase lag compensation time decreases, the first phase lead compensation time constant can be decreased or the first phase lag compensation time constant can be increased.

[0144] After determining the first phase advance compensation time constant and the first phase lag compensation time constant, the phase advance compensation amount of the opposite value of the angular frequency fluctuation can be determined based on the transfer function of the first advance and lag unit 202, so as to realize the phase compensation of the main additional damping channel 210.

[0145] The first damping coefficient for low-frequency oscillation is determined based on the upper limit of the preset damping power range.

[0146] Specifically, the first damping coefficient for low-frequency oscillation can be taken as the maximum value that ensures the amplitude of the first additional damping power does not exceed the upper limit of the preset damping power range and does not cause oscillations in other frequency bands.

[0147] For example, the relevant standards for grid-connected energy storage systems stipulate that the upper limit of the fluctuation amplitude of the active power output of the grid-connected energy storage converter can be the rated active power P output by the grid-connected energy storage system. ref The first damping coefficient of the low-frequency oscillation of the main additional damping channel 210 is designed with the goal that the amplitude of the first additional damping power does not exceed the upper limit of the preset damping power range and does not cause oscillation in other frequency bands. The maximum value of the first damping coefficient of the low-frequency oscillation that satisfies this goal is taken.

[0148] In some embodiments, before obtaining the output active power, the method further includes:

[0149] Based on the phase of the first additional damping power in the first frequency band, the second phase advance compensation time constant and the second phase lag compensation time constant of the second advance and lag unit are set so that the difference between the phase of the second additional damping power in the first frequency band and the phase of the first additional damping power in the first frequency band is less than a first preset value; wherein, the first frequency band is the frequency band corresponding to the lower limit of the preset damping power range where the first additional damping power is less than the preset damping power range.

[0150] Specifically, the second phase lead compensation time constant and the second phase lag compensation time constant of the second lead-lag unit 204 in the auxiliary additional damping channel 220 are designed to ensure that the phase difference between the second additional damping power at the frequency where the first additional damping power does not reach the lower limit of the preset damping power range and the phase of the first additional damping power is less than a first preset value. For example, the range of the first preset value can be less than or equal to 45°, so that the phases of the first additional damping power and the second additional damping power in the first frequency band are as close as possible. This allows the first additional damping power and the second additional damping power to increase in the same direction in the first frequency band, enabling the second additional damping power to compensate for the deficiency of the first additional damping power in the first frequency band.

[0151] For example, Figure 2 The example illustrates an auxiliary additional damping channel 220 in a low-frequency oscillation damping control module, including a second lead-lag unit 204. The fluctuation in the filtered output active power is controlled by a second damping coefficient k in the low-frequency oscillation. dpBefore proportional gain is applied, the fluctuation of the filtered output active power can be phase-adjusted by the second lead-lag unit 204 to compensate for the phase of the fluctuation of the filtered output active power. This ensures that the phase of the second additional damping power in the frequency band where the first additional damping power does not reach the lower limit of the preset damping power range is as close as possible to the phase of the first additional damping power. Based on this objective, the phase to be compensated by the second lead-lag unit 204 of the auxiliary additional damping channel 220 is determined.

[0152] For example, the expression for the transfer function of the second lead-lag unit 204 is:

[0153]

[0154] Among them, T 2Lead T is the time constant for the second phase advance compensation. 2Lag This is the time constant for the second phase lag compensation.

[0155] The second phase lead compensation time constant and the second phase lag compensation time constant of the second lead-lag unit 204 are determined based on the phase to be compensated by the second lead-lag unit 204 of the auxiliary additional damping channel 220. After determining the second phase lead compensation time constant and the second phase lag compensation time constant, the phase lead compensation amount of the fluctuation of the filtered output active power can be determined based on the transfer function of the second lead-lag unit 204, thereby achieving phase compensation for the auxiliary additional damping channel 220.

[0156] The second damping coefficient for low-frequency oscillation is determined based on the difference between the lower limit of the preset damping power range and the power value of the first additional damping power in the first frequency band.

[0157] When setting the second damping coefficient for low-frequency oscillation of the auxiliary additional damping channel 220, it can be determined based on the difference between the lower limit of the preset damping power range and the power value of the first additional damping power in the first frequency band, so that the second additional damping power makes up for the difference between the first additional power and the lower limit of the preset damping power range.

[0158] For example, the relevant standards for grid-connected energy storage systems stipulate that the lower limit of the fluctuation amplitude of the active power output of the grid-connected energy storage converter is the rated active power P output by the grid-connected energy storage system. ref When designing the second damping coefficient for the low-frequency oscillation of the auxiliary additional damping channel 220, the second additional damping power is made up to compensate for the difference between the first additional power and the lower limit of the preset damping power range in the frequency band where the first additional damping power does not reach the lower limit of the preset damping power range.

[0159] Figure 7A flowchart illustrating another method for damping and suppressing low-frequency oscillations in power grid frequencies provided in an embodiment of the present invention. Figure 7 As shown, the method includes:

[0160] S510, Obtain the voltage and output active power at the grid connection point of the grid-connected energy storage system;

[0161] S520. Obtain the first additional damping power based on the voltage at the grid connection point through the main additional damping channel;

[0162] S530: The second additional damping power is obtained from the output active power through the auxiliary additional damping channel;

[0163] S540. The second additional damping power is superimposed on the first additional damping power to obtain the total additional damping power;

[0164] S550. Based on the output angular frequency of the grid-connected energy storage system at the previous moment and the rated angular frequency of the power grid, the change in the active power command of the grid-connected energy storage system is determined by droop control.

[0165] The grid frequency low-frequency oscillation damping and suppression device may also include an active-phase loop module, which is used to form a grid phase based on the active-phase loop of the grid-connected energy storage system according to the total additional damping power, so as to suppress the low-frequency oscillation of the grid frequency. Figure 8 This is a schematic diagram of an active-phase loop provided in an embodiment of the present invention. Figure 8 As shown, the active-phase loop module 300 includes a droop control unit 301, an inertial damping control unit 302, and an integrator unit 303. During the operation of the active-phase loop module 300, the output angular frequency ω and rated angular frequency ω of the grid-connected energy storage system at the previous moment are... ref Droop control is achieved through the droop control unit 301. Specifically, the output angular frequency ω of the grid-connected energy storage system at the previous moment is reduced by the rated angular frequency ω. ref Then the difference between the two is compared with the droop coefficient k. p The product determines the change in active power command of the grid-connected energy storage system. P ref Among them, the active power command of the grid-connected energy storage system is the rated active power P of the grid-connected energy storage system. ref .

[0166] S560. Determine the input power of the grid-connected energy storage system based on the change in active power command, total additional damping power, and active power command of the grid-connected energy storage system.

[0167] Among them, continue to refer to Figure 8 In determining the change in active power command of the grid-connected energy storage system Pref Subsequently, the change in active power command of the grid-connected energy storage system can be monitored. P ref After taking the negative value, it is compared with the active power command of the grid-connected energy storage system (that is, the rated active power P of the grid-connected energy storage system). ref and total additional damping power P a After addition, the input power P of the grid-connected energy storage system is obtained. m This makes the total additional damping power P a The input power P of the grid-connected energy storage system can be adjusted. m This enables the suppression of low-frequency oscillations in the power grid.

[0168] S570. The difference between the input power and the output power and feedback damping power of the grid-connected energy storage system is calculated, and the quotient is given with the virtual inertia value. The result is then integrated to obtain the change in the output angular frequency of the grid-connected energy storage system at the current moment.

[0169] Among them, continue to refer to Figure 8 In determining the input power P of the grid-connected energy storage system m Then, the input power P of the grid-connected energy storage system can be used. m Subtract the output power P of the grid-connected energy storage system at the previous moment and the feedback damping power P of the grid-connected energy storage system at the previous moment. D Then the difference among the three is passed through the inertial element 1 / Jω in the inertial damping control unit 302. s Control is performed by dividing by the virtual inertia value and then controlling it through the integral element 1 / s in the inertial damping control unit 302 to determine the change in the output angular frequency of the grid-connected energy storage system at the current moment. ω. Where J is the inertial coefficient of the inertial element.

[0170] S580. Determine the current output angular frequency based on the change in output angular frequency at the current moment and the rated angular frequency of the power grid;

[0171] Among them, continue to refer to Figure 8 The change in the output angular frequency of the grid-connected energy storage system at the current moment. ω and the rated angular frequency ω of the power grid ref Add them together to determine the current output angular frequency ω.

[0172] S590. Determine the network phase of the active-phase loop based on integral calculation according to the output angular frequency at the current moment.

[0173] Among them, continue to refer to Figure 8After determining the current output angular frequency ω, the current output angular frequency ω can be integrated through the integrator 1 / s to determine the network phase θ of the active-phase loop.

[0174] Continue to refer to Figure 8 Before subtracting the input power from the output power and feedback damping power of the grid-connected energy storage system, the following steps are also included:

[0175] The feedback damping power is determined based on the change in output angular frequency and feedback damping coefficient of the grid-connected energy storage system at the previous moment.

[0176] Among them, such as Figure 8 As shown, the change in output angular frequency at the previous moment is determined. After ω, the change in the output angular frequency at the previous moment can be... ω is multiplied by the feedback damping coefficient D in the feedback damping control module of the inertial damping control unit 302 to form the feedback damping power P at the previous moment. D And it is superimposed on the input power P of the grid-connected energy storage system in the form of negative feedback. m The system completes closed-loop control to regulate active power and provide support for damping.

[0177] As can be seen from the above process, by adding the total additional damping power provided by the frequency oscillation suppression module to the active power command in the active-phase loop, the active-phase loop can achieve active frequency droop control and inertial damping support for the grid-connected energy storage system through droop control, inertial control, feedback damping control, and additional low-frequency oscillation damping control.

[0178] For example, Figure 9 This is a schematic diagram of a power grid frequency curve provided for related technologies, where the horizontal axis represents time and the vertical axis represents frequency. Figure 10 This diagram illustrates the active power output of a grid-connected energy storage system, where the horizontal axis represents time and the vertical axis represents the active power output of the grid-connected energy storage system. Figure 11 This diagram illustrates the power oscillation energy flow curve of a grid-connected energy storage system during damping suppression response, providing insights into related technologies. The horizontal axis represents time, and the vertical axis represents the power oscillation energy flow. Figures 9 to 11 As shown, at this time, the grid-connected energy storage system does not have additional low-frequency oscillation damping suppression, that is, the input power P of the grid-connected energy storage system is... m Uncompensated total additional damping power P a When the grid frequency f oscillates at a frequency of 0.2Hz and an amplitude of 0.02Hz at 2s, the maximum change in the active power P output by the grid-connected energy storage system is less than the rated active power P output by the grid-connected energy storage system.ref 10% of the samples do not meet the standard DL / T 2246.7-2021.

[0179] Figure 12 This is a schematic diagram of a power grid frequency curve provided in an embodiment of the present invention, wherein the horizontal axis represents time and the vertical axis represents frequency. Figure 13 This is a schematic diagram of the active power output of a grid-connected energy storage system provided in an embodiment of the present invention, wherein the horizontal axis represents time and the vertical axis represents the active power output of the grid-connected energy storage system. Figure 14 This is a schematic diagram of the power oscillation energy flow curve provided by a grid-connected energy storage system during damping suppression response, as provided in an embodiment of the present invention. The horizontal axis represents time, and the vertical axis represents the power oscillation energy flow. Figures 12 to 14 As shown, at this time, the grid-connected energy storage system is equipped with low-frequency oscillation damping suppression, that is, the input power P of the grid-connected energy storage system is reduced. m The total additional damping power P is superimposed. a When the grid frequency f oscillates at a frequency of 0.2Hz and an amplitude of 0.02Hz at 2s, the maximum value of the change in the active power P output by the grid-connected energy storage system is greater than the rated active power P output by the grid-connected energy storage system. ref It is 10% of the rated active power P output by the grid-connected energy storage system. ref The power oscillation energy flow W is less than 0, which meets the standard DL / T 2246.7-2021. Therefore, it can be seen that the total additional damping power P... a Regulate the input power P of the grid-connected energy storage system m This can suppress low-frequency oscillations in the power grid.

[0180] Figure 15 Another schematic diagram of power grid frequency provided for related technologies, where the horizontal axis represents time and the vertical axis represents frequency. Figure 16 This is a schematic diagram of the active power output of another grid-connected energy storage system for related technologies, where the horizontal axis represents time and the vertical axis represents the active power output of the grid-connected energy storage system. Figure 17 This is a schematic diagram of the power oscillation energy flow curve provided by a grid-connected energy storage system during another damping suppression response, provided for related technologies. The horizontal axis represents time, and the vertical axis represents the power oscillation energy flow. For example... Figures 15 to 17 As shown, at this time, the grid-connected energy storage system does not have additional low-frequency oscillation damping suppression, that is, the input power P of the grid-connected energy storage system is... m Uncompensated total additional damping power P aWhen the grid frequency f oscillates at a frequency of 1Hz and an amplitude of 0.02Hz at 2s, the maximum change in the active power P output by the grid-connected energy storage system is less than the rated active power P output by the grid-connected energy storage system. ref 10% of the samples do not meet the standard DL / T 2246.7-2021.

[0181] Figure 18 This is another schematic diagram of the power grid frequency provided in an embodiment of the present invention, wherein the horizontal axis represents time and the vertical axis represents frequency. Figure 19 This is a schematic diagram of the active power output of another grid-connected energy storage system provided in an embodiment of the present invention, wherein the horizontal axis represents time and the vertical axis represents the active power output of the grid-connected energy storage system. Figure 20 This is a schematic diagram of the power oscillation energy flow provided by a grid-connected energy storage system during another damping suppression response, as provided in an embodiment of the present invention. The horizontal axis represents time, and the vertical axis represents the power oscillation energy flow. Figures 18 to 20 As shown, at this time, the grid-connected energy storage system is equipped with low-frequency oscillation damping suppression, that is, the input power P of the grid-connected energy storage system is reduced. m The total additional damping power P is superimposed. a When the grid frequency f oscillates at a frequency of 1Hz and an amplitude of 0.02Hz at 2s, the maximum value of the change in the active power P output by the grid-connected energy storage system is greater than the rated active power P output by the grid-connected energy storage system. ref It is 10% of the rated active power P output by the grid-connected energy storage system. ref 30% of the power oscillation energy flow W is less than 0, satisfying standard DL / T 2246.7-2021. Similarly, by adding damping power P... a Regulate the input power P of the grid-connected energy storage system m This can suppress low-frequency oscillations in the power grid.

[0182] This invention also provides a low-frequency oscillation damping and suppression device for power grids, wherein the power grid includes a grid-connected energy storage system. Figure 21 This is a schematic diagram of a low-frequency oscillation damping and suppression device for power grid frequencies provided in an embodiment of the present invention. Figure 21 As shown, the low-frequency oscillation damping and suppression device for this network includes:

[0183] The acquisition module 100 is used to acquire the voltage and output active power at the grid connection point of the grid-connected energy storage system.

[0184] The main additional damping channel 210 is used to obtain the first additional damping power based on the voltage at the grid connection point through the main additional damping channel;

[0185] The auxiliary additional damping channel 220 is used to obtain the second additional damping power based on the output active power through the auxiliary additional damping channel;

[0186] The summation module 230 is used to add the second additional damping power to the first additional damping power to obtain the total additional damping power;

[0187] The active-phase loop module 300 is used to form the grid-connected phase based on the active-phase loop of the grid-connected energy storage system according to the total additional damping power, so that the oscillating energy flow formed by the fluctuation of the output active power of the grid-connected energy storage system and the fluctuation of the grid frequency is negative. When the main additional damping channel 210 includes a phase-locked loop (PLL), the PLL can be used as an acquisition module 100 to lock the voltage at the grid connection point of the grid-connected energy storage system.

[0188] The technical solution of this embodiment uses a low-frequency oscillation damping control module to superimpose a first additional damping power obtained from the grid connection point voltage via the main additional damping channel and a second additional damping power obtained from the output active power via the auxiliary additional damping channel to form a total additional damping power. This allows the second additional damping power to compensate for the deficiency of the first additional damping power in some frequency bands of the preset oscillation frequency band, ensuring that the total additional damping power for the corresponding frequency bands of the low-frequency oscillation of the grid side frequency reaches the preset damping power range. Then, the total additional damping power is added to the active power command to adjust the active power, thereby effectively regulating the active power output of the grid-type converter and suppressing low-frequency oscillations of the grid frequency in all frequencies of the preset oscillation frequency band. This effectively solves the problem that the oscillation frequency at the grid connection point in weak power grids decreases as the damping power output of the grid-connected converter increases, causing the output damping power of the grid-connected converter to essentially stop increasing after reaching a certain level in certain frequency bands. This ensures that the output damping power can reach the preset damping power range and meet the standard requirements. Furthermore, it synchronously adjusts the phase according to the active power, quickly suppressing low-frequency oscillations caused by the grid side, improving the transmission efficiency of the power grid, and significantly reducing the risk of system disconnection and large-scale power outages caused by frequency oscillations.

[0189] In some embodiments, such as Figure 2 As shown, the low-frequency oscillation damping control module includes a main additional damping channel 210 and an auxiliary additional damping channel 220. The main additional damping channel 210 includes a phase-locked loop (PLL), a first low-pass filter (LPF1), a subtractor, a first lead-lag unit 202, and a low-frequency oscillation first damping unit 201. The auxiliary additional damping channel 220 includes a subtractor, a second low-pass filter (LPF2), a second lead-lag unit 204, and a low-frequency oscillation second damping unit 205. The low-frequency oscillation damping control module also includes a summing module 230, used to sum the first additional damping power and the second additional damping power to obtain the total additional damping power.

[0190] In some embodiments, such as Figure 5 As shown, the phase-locked loop (PLL) includes a dq converter unit 203, a proportional-integral controller (PI), and an adder.

[0191] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method of power grid frequency low frequency oscillation damping suppression, characterized in that, The power grid comprises a grid-forming energy storage grid-connected system; The power grid frequency low-frequency oscillation damping suppression method comprises: obtaining the voltage and output active power of the grid-forming energy storage grid-connected system at a grid-connected point; obtaining first additional damping power through a main additional damping channel according to the voltage at the grid-connected point; obtaining second additional damping power through an auxiliary additional damping channel according to the output active power; superimposing the second additional damping power on the first additional damping power to obtain total additional damping power; forming a grid-forming phase based on an active-phase loop of the grid-forming energy storage grid-connected system according to the total additional damping power, so that the oscillation energy flow formed by the fluctuation amount of the output active power of the grid-forming energy storage grid-connected system and the fluctuation amount of the power grid frequency is a negative value; obtaining second additional damping power through an auxiliary additional damping channel according to the output active power, comprising: obtaining the fluctuation amount of the output active power by subtracting the output active power from an active power instruction; filtering the fluctuation amount of the output active power through a second low-pass filter to obtain the fluctuation amount of the filtered output active power; phase compensating the fluctuation amount of the filtered output active power through a second lead-lag unit and obtaining the second additional damping power based on a low-frequency oscillation second damping coefficient; before obtaining the output active power, further comprising: setting a second phase lead compensation time constant and a second phase lag compensation time constant of the second lead-lag unit according to the phase of the first additional damping power in a first frequency band, so that the difference between the phase of the second additional damping power in the first frequency band and the phase of the first additional damping power in the first frequency band is less than a first preset value; wherein the first frequency band is a frequency band corresponding to a lower limit value of a preset damping power range in which the first additional damping power is less than the lower limit value; determining the low-frequency oscillation second damping coefficient according to the difference between the lower limit value of the preset damping power range and the power value of the first additional damping power in the first frequency band.

2. The power grid frequency low frequency oscillation damping mitigation method of claim 1, wherein, obtaining first additional damping power through a main additional damping channel according to the voltage at the grid-connected point, comprising: determining the real-time angular frequency of the power grid through a phase-locked loop according to the voltage at the grid-connected point; filtering the real-time angular frequency through a first low-pass filter to obtain the filtered angular frequency of the power grid; determining the opposite value of the angular frequency fluctuation amount according to the difference between the rated angular frequency of the power grid and the filtered angular frequency of the power grid; phase compensating the opposite value of the angular frequency fluctuation amount through a first lead-lag unit and obtaining the first additional damping power based on a low-frequency oscillation first damping coefficient.

3. The power grid frequency low frequency oscillation damping mitigation method of claim 2, wherein, determining the real-time angular frequency of the power grid through a phase-locked loop according to the voltage at the grid-connected point, comprising: performing dq transformation on the voltage at the grid-connected point to determine the q-axis voltage; determining the phase-locked loop angular frequency change amount based on a proportional-integral control method according to the q-axis voltage; determining the real-time angular frequency of the power grid according to the sum of the phase-locked loop angular frequency change amount and the rated angular frequency of the power grid.

4. The power grid frequency low frequency oscillation damping mitigation method of claim 2, wherein, before obtaining the voltage at the grid-connected point of the grid-forming energy storage grid-connected system, further comprising: The first phase lead compensation time constant and the first phase lag compensation time constant of the first lead-lag unit are set according to a preset phase delay time corresponding to a preset frequency band, wherein the first phase lead compensation time constant is greater than the first phase lag compensation time constant, the preset frequency band is a frequency band corresponding to a low-frequency oscillation, and the preset phase delay time includes a phase delay time caused by the first low-pass filter and a phase delay time caused by the active-phase loop; The first damping coefficient of the low-frequency oscillation is determined according to an upper limit value of a preset damping power range.

5. The method of grid frequency low frequency oscillation damping mitigation of claim 1, wherein, The total additional damping power is used to form a network phase based on the active-phase loop of the network-connected energy storage system. The change amount of the active power instruction of the network-connected energy storage system is determined by droop control according to the output angular frequency of the network-connected energy storage system at the previous moment and the rated angular frequency of the power grid. The input power of the network-connected energy storage system is determined according to the change amount of the active power instruction, the total additional damping power and the active power instruction of the network-connected energy storage system. The output angular frequency change amount of the network-connected energy storage system at the current moment is obtained by integral calculation after the input power is subtracted from the output power and the feedback damping power of the network-connected energy storage system and multiplied by a virtual inertia value. The output angular frequency at the current moment is determined according to the output angular frequency change amount at the current moment and the rated angular frequency of the power grid. The network phase of the active-phase loop is determined based on integral calculation according to the output angular frequency at the current moment.

6. The power grid frequency low frequency oscillation damping mitigation method of claim 5, wherein, Before the input power is subtracted from the output power and the feedback damping power of the network-connected energy storage system, the following steps are further included: The feedback damping power is determined according to the output angular frequency change amount of the network-connected energy storage system at the previous moment and the feedback damping coefficient.

7. The method of grid frequency low frequency oscillation damping suppression of claim 1, wherein, After the total additional damping power is used to form a network phase based on the active-phase loop of the network-connected energy storage system, the following steps are further included: The fluctuation amount of the output active power is obtained by subtracting the active instruction from the output active power of the network-connected energy storage system. The fluctuation amount of the power grid frequency is obtained by subtracting the rated frequency of the power grid from the real-time frequency of the point of common coupling. The value of the oscillation energy flow is obtained by multiplying the fluctuation amount of the output active power by the fluctuation amount of the power grid frequency and then performing integral operation.

8. A power grid frequency low frequency oscillation damping suppression device, characterized in that, The power grid frequency low-frequency oscillation damping suppression method of any one of claims 1-7 is used to perform the power grid frequency low-frequency oscillation damping suppression method. The power grid frequency low-frequency oscillation damping suppression device includes: The acquisition module is used to acquire the voltage and output active power of the point of common coupling of the network-connected energy storage system. The main additional damping channel is used to obtain the first additional damping power through the main additional damping channel according to the voltage of the point of common coupling. The auxiliary additional damping channel is used to obtain the second additional damping power through the auxiliary additional damping channel according to the output active power. The summation module is used to superimpose the second additional damping power on the first additional damping power to obtain the total additional damping power. An active-phase loop module is configured to form a grid phase based on an active-phase loop of a grid-connected energy storage system according to the total additional damping power, so that an oscillation energy flow formed by a fluctuation amount of an output active power of the grid-connected energy storage system and a fluctuation amount of a grid frequency is a negative value.

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