A control method of a new energy power plant under a grid sub-synchronous oscillation condition

Abstract

The application discloses a control method of a new energy power station under a sub-super synchronous oscillation of a power grid. When the sub-super synchronous oscillation occurs in the power grid, different equipment resonance suppression modes are switched according to preset characteristic frequencies as thresholds. Different power grid current low-frequency component comparison thresholds are set for equipment in the power station. When the power grid current low-frequency component exceeds the comparison threshold of N power generation equipments in the power station, the operation mode of the N power generation equipments is switched to perform smooth transition. The method utilizes the damping characteristics of different power generation equipments, comprehensively and effectively suppresses the sub-super synchronous oscillation of the power grid in different degrees, prevents the power grid oscillation from further spreading, only part of the power generation equipments perform mode switching or control strategy switching when the power grid oscillates, and the remaining equipments maintain power generation operation, so that the power output level of the new energy power station is basically ensured, the stability of the power grid is ensured, the risk of batch power generation equipment off-grid caused by the power grid oscillation is reduced, and the power generation efficiency of the new energy power station is ensured.

Description

Technical Field

[0001] This invention relates to the field of new energy grid connection technology, and in particular to a control method for new energy power plants under sub-supersynchronous oscillation conditions of the power grid. Background Technology

[0002] With the introduction of national policies on carbon peaking and carbon neutrality, new energy power generation has received widespread attention, and the proportion of new energy power plants in the power grid is constantly increasing. The power generation end faces enormous challenges in dealing with the subsynchronous oscillation problem of the power grid.

[0003] Currently, to address the subsynchronous oscillation problem in power grids, renewable energy power plants mainly rely on improved control strategies for doubly-fed induction generator (DFIG) converters to provide damping for suppression. Chinese invention patent application CN201510315488.1 discloses a blocking filtering method for suppressing subsynchronous resonance in the series compensation transmission system of a DFIG wind farm. This method has a certain suppression effect on power grid oscillations, but when the amplitude of power grid oscillations is too large, the DFIG is prone to runaway. Therefore, improved control strategies for DFIGs alone cannot effectively handle subsynchronous oscillations in the power grid and ensure the stability of the power grid system. There is an urgent need to provide more comprehensive and powerful measures to address the subsynchronous oscillation problem of different degrees in the power grid. Summary of the Invention

[0004] The technical problem this invention aims to solve is to propose a control method for new energy power plants under subsynchronous oscillations of the power grid. This method utilizes the damping characteristics of different power generation equipment to comprehensively and effectively suppress subsynchronous oscillations of varying degrees in the power grid, preventing further spread of grid oscillations. Simultaneously, only some power generation equipment switches modes or control strategies during grid oscillations, while the remaining equipment maintains power generation operation. This essentially ensures the power output level of the new energy power plant, guarantees the stability of the power grid, reduces the risk of mass disconnection of power generation equipment caused by grid oscillations, and to a certain extent reduces power loss, thus ensuring the power generation efficiency of the new energy power plant.

[0005] To solve the above-mentioned technical problems, the present invention provides a control method for a new energy power station under the condition of sub-supersynchronous oscillation of the power grid. When the power grid experiences sub-supersynchronous oscillation, the method switches the resonance suppression mode of different devices according to the oscillation characteristics of the power grid and uses a preset characteristic frequency as a threshold.

[0006] Different comparison thresholds for low-frequency components of the grid current are set for the equipment within the power station. When the low-frequency component of the grid current exceeds the comparison threshold of N power generation devices within the power station, the operating modes of N devices are switched for a smooth transition.

[0007] Alternatively, different comparison thresholds for grid voltage frequency and equipment bus voltage can be set for the equipment in the station. When the grid voltage frequency or equipment bus voltage exceeds the comparison threshold of N equipment in the station, the operating mode of N equipment will be switched for a smooth transition.

[0008] The power grid oscillation characteristics include power grid voltage, power grid current, and equipment bus voltage.

[0009] Preferably, the new energy power station is a doubly-fed new energy power station, or a full-power new energy power station, or a photovoltaic new energy power station, or a hybrid new energy power station of doubly-fed, full-power, and photovoltaic power stations.

[0010] Preferably, when the new energy power station is a doubly fed new energy power station, the doubly fed new energy power station switches the equipment's doubly fed / asynchronous operation mode according to the characteristics of the low-frequency components of the grid voltage or current during the sub-supersynchronous oscillation of the grid. Different comparison thresholds for the low-frequency components of the grid current are set for the equipment in the station. When the low-frequency component of the grid current exceeds the comparison threshold of N equipment in the station, it switches to asynchronous mode operation, and the remaining equipment maintains doubly fed mode operation.

[0011] The N devices in the power station that switch to asynchronous mode provide positive damping to suppress the sub-supersynchronous oscillation of the power grid while maintaining power output. The remaining devices in the power station that maintain doubly-fed mode continue to provide power output to maintain power grid stability. Only N devices switch operating modes, and the total power output of the power station remains basically unchanged at the moment of switching, thus completing a smooth switch.

[0012] Preferably, the grid-connected equipment of the doubly fed new energy power station includes a grid-connected contactor and a stator short-circuit contactor. The switching to asynchronous operation is accomplished by disconnecting the grid-connected contactor and closing the stator short-circuit contactor.

[0013] Preferably, when the power grid oscillation characteristics are the power grid voltage and the equipment bus voltage,

[0014] The phrase "setting different comparison thresholds for grid voltage frequency and equipment bus voltage for equipment within the station, and when the grid voltage frequency or equipment bus voltage exceeds the comparison threshold for N pieces of equipment within the station, switching the operating mode of N pieces of equipment for a smooth transition" specifically means:

[0015] The new energy power station performs grid-side control transformation of equipment based on the grid voltage frequency and equipment bus voltage characteristics during subsynchronous oscillation of the power grid. Different grid voltage frequencies and equipment bus voltage comparison thresholds are set for the equipment in the station. When the grid voltage frequency and equipment bus voltage exceed the comparison threshold of N equipment in the station, positive damping is provided by injecting currents of N equipment with the same frequency and phase as the grid resonant voltage to suppress the subsynchronous oscillation of the power grid. The remaining equipment maintains unchanged grid-side control and operates smoothly through the subsynchronous oscillation of the power grid.

[0016] Preferably, when the new energy power station is a doubly-fed, full-power, and photovoltaic hybrid new energy power station, when the power grid experiences sub-supersynchronous oscillation, the doubly-fed, full-power, and photovoltaic hybrid new energy power station will, according to the respective equipment characteristics and damping characteristics of the doubly-fed, full-power, and photovoltaic systems, perform mixed allocation of a certain number of devices by switching operating modes and control strategies, thereby achieving the overall positive damping characteristics of the power station and suppressing the sub-supersynchronous oscillation of the power grid.

[0017] Preferably, when the power grid experiences subsynchronous oscillation, and when the new energy power station is a doubly-fed, full-power, and photovoltaic hybrid new energy power station, the doubly-fed, full-power, and photovoltaic hybrid new energy power station switches the operating mode and control strategy of a certain number of devices according to the power output level of the doubly-fed, full-power, and photovoltaic devices at different stages, so as to complete the overall positive damping characteristics of the power station and suppress the subsynchronous oscillation of the power grid.

[0018] Preferably, the control strategy switching is as follows: the grid-side converter control system of the corresponding photovoltaic generator set / full-power wind turbine injects a current signal with the same frequency and phase as the grid voltage into the current inner loop; or the grid-side converter control system of the corresponding photovoltaic generator set / full-power wind turbine restores the original current inner loop control strategy for power generation operation by removing the current signal injected into the current inner loop.

[0019] After adopting the above method, the control method for new energy power plants under sub-supersynchronous oscillation of the power grid is as follows: When sub-supersynchronous oscillation occurs in the power grid, the resonance suppression mode of different equipment is switched according to the characteristics of the power grid oscillation and a preset characteristic frequency is used as the threshold. Different comparison thresholds for low-frequency components of the power grid current are set for the equipment in the power plant. When the low-frequency component of the power grid current exceeds the comparison threshold of N power generation equipment in the power plant, the operating mode of N equipment is switched for a smooth transition. Alternatively, different comparison thresholds for the power grid voltage frequency and the equipment bus voltage are set for the equipment in the power plant. When the power grid voltage frequency and the equipment bus voltage exceed the comparison threshold of N equipment in the power plant, the operating mode of N equipment is switched for a smooth transition. This method utilizes the damping characteristics of different power generation equipment to comprehensively and effectively suppress sub-supersynchronous oscillations of the power grid to varying degrees, preventing the further spread of power grid oscillations. At the same time, only some power generation equipment switches modes or control strategies when the power grid oscillates, while the remaining equipment maintains power generation operation. This basically ensures the power output level of the new energy power plant, guarantees the stability of the power grid, reduces the risk of batch disconnection of power generation equipment caused by power grid oscillations, and reduces power loss to a certain extent, thus ensuring the power generation efficiency of the new energy power plant. Attached Figure Description

[0020] Figure 1 This is an overall connection diagram of the power generation equipment of a new energy power plant, which is the control method for a new energy power plant under the sub-supersynchronous oscillation of the power grid according to Embodiment 4 of the present invention.

[0021] Figure 2 This is an overall connection diagram of the power generation equipment of a new energy power plant, which is the control method for a new energy power plant under the sub-supersynchronous oscillation of the power grid according to Embodiment 7 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Example 1

[0024] This embodiment discloses a control method for a new energy power station under the condition of sub-supersynchronous oscillation of the power grid. When the power grid experiences sub-supersynchronous oscillation, the resonance suppression mode of different devices is switched according to the oscillation characteristics of the power grid and with a preset characteristic frequency as the threshold.

[0025] Different comparison thresholds for low-frequency components of the grid current are set for the equipment within the power station. When the low-frequency component of the grid current exceeds the comparison threshold of N power generation devices within the power station, the operating modes of N devices are switched for a smooth transition.

[0026] Alternatively, different comparison thresholds for grid voltage frequency and equipment bus voltage can be set for the equipment in the station. When the grid voltage frequency or equipment bus voltage exceeds the comparison threshold of N equipment in the station, the operating mode of N equipment will be switched for a smooth transition.

[0027] The power grid oscillation characteristics include power grid voltage, power grid current, and equipment bus voltage.

[0028] Example 2

[0029] This embodiment is based on Embodiment 1. In this embodiment, the new energy power station is a doubly-fed new energy power station, or a full-power new energy power station, or a photovoltaic new energy power station, or a doubly-fed, full-power, and photovoltaic hybrid new energy power station.

[0030] Example 3

[0031] This embodiment is based on embodiment two. In this embodiment, when the new energy power station is a doubly fed new energy power station, the doubly fed new energy power station switches the doubly fed / asynchronous operation mode of the equipment according to the characteristics of the low-frequency components of the grid voltage or current during the sub-supersynchronous oscillation of the grid. Different comparison thresholds for the low-frequency components of the grid current are set for the equipment in the station. When the low-frequency component of the grid current exceeds the comparison threshold of N equipment in the station, it switches to asynchronous mode operation, and the remaining equipment maintains doubly fed mode operation.

[0032] The N devices in the power station that switch to asynchronous mode provide positive damping to suppress the sub-supersynchronous oscillation of the power grid while maintaining power output. The remaining devices in the power station that maintain doubly-fed mode continue to provide power output to maintain power grid stability. Only N devices switch operating modes, and the total power output of the power station remains basically unchanged at the moment of switching, thus completing a smooth switch.

[0033] The grid-connected equipment of the doubly fed new energy power station includes a grid-connected contactor and a stator short-circuit contactor. The switching to asynchronous operation is accomplished by disconnecting the grid-connected contactor and closing the stator short-circuit contactor.

[0034] Example 4

[0035] Please see Figure 1 , Figure 1 This is an overall connection diagram of the power generation equipment of a new energy power plant, which is the control method for a new energy power plant under the sub-supersynchronous oscillation of the power grid according to Embodiment 4 of the present invention.

[0036] This embodiment is based on Embodiment 3. In this embodiment, the N devices are 30 doubly-fed wind turbine generator sets; the new energy power station includes 30 doubly-fed wind turbine generator sets, and each wind turbine generator set includes a grid-connected contactor, a stator short-circuit contactor, a grid current transformer, and a generator set converter control system.

[0037] The control method for doubly-fed renewable energy power plants under sub-supersynchronous oscillations of the power grid is as follows:

[0038] The converter control system of the 30 doubly fed wind turbine generator sets controls the grid-connected contactor to close and the stator short-circuit contactor to open. The generator sets are operating normally in the doubly fed power generation mode. At a certain moment, the power grid experiences a sub-supersynchronous oscillation. All wind turbine generator sets detect low-frequency harmonics in the grid current through the grid current transformer. The harmonic content is THDc.

[0039] The grid current harmonic content thresholds used for switching unit operating modes in the converter control systems of units 1-5 of the power plant are set as follows: THD1 for units 6-10, THD2 for units 11-15, THD4 for units 16-20, THD5 for units 21-25, and THD6 for units 26-30, wherein THD1 < THD2 < THD3 < THD4 < THD5 < THD6.

[0040] If, during subsynchronous oscillation of the power grid, the low-frequency harmonic content (THDc) of the grid current detected by each wind turbine in the power station exceeds the unit's own grid current harmonic content threshold, the converter control system of the corresponding wind turbine will control its grid-connected contactor to open and its stator short-circuit contactor to close, switching from doubly-fed generation mode to asynchronous generation mode. If THDc > THD1, then units 1-5 of the power station will switch to asynchronous generation mode.

[0041] If, during subsynchronous oscillation of the power grid, the low-frequency harmonic content (THDc) of the grid current detected by each wind turbine at the power station is less than or equal to the unit's own grid current harmonic content threshold, the corresponding wind turbine will either maintain doubly-fed generation mode or, through its converter control system, control the stator short-circuit contactor to open and the grid-connected contactor to close, thus reverting from asynchronous generation mode to doubly-fed generation mode. If THDc < THD2, then units 6-30 at the power station will maintain doubly-fed generation mode.

[0042] When units 1-5 in the power station switch from doubly fed generator mode to asynchronous generator mode, they can provide positive damping, suppress the subsynchronous oscillation of the power grid, and reduce the low-frequency harmonics in the power grid current, so that THDc < THD1. Then, units 1-5 can be restored from asynchronous generator mode to doubly fed generator mode.

[0043] Based on the detection of low-frequency harmonics in the grid current during subsynchronous oscillations, the subsynchronous oscillations of the grid were effectively suppressed by switching the operating modes of wind turbines 1-5 at the doubly-fed renewable energy power plant, preventing the wind turbines from disconnecting from the grid in batches. At the same time, during the switching of the operating modes of wind turbines 1-5, wind turbines 6-30 maintained their original doubly-fed power generation mode, which basically ensured the power output level of the doubly-fed renewable energy power plant and reduced the power loss of the power plant when the operating modes of the turbines were switched.

[0044] Example 5

[0045] This embodiment is based on Embodiment 1. In this embodiment, when the power grid oscillation characteristics are the power grid voltage and the equipment bus voltage,

[0046] The phrase "setting different comparison thresholds for grid voltage frequency and equipment bus voltage for equipment within the station, and when the grid voltage frequency or equipment bus voltage exceeds the comparison threshold for N pieces of equipment within the station, switching the operating mode of N pieces of equipment for a smooth transition" specifically means:

[0047] The new energy power station performs grid-side control transformation of equipment based on the grid voltage frequency and equipment bus voltage characteristics during subsynchronous oscillation of the power grid. Different grid voltage frequencies and equipment bus voltage comparison thresholds are set for the equipment in the station. When the grid voltage frequency and equipment bus voltage exceed the comparison threshold of N equipment in the station, positive damping is provided by injecting currents of N equipment with the same frequency and phase as the grid resonant voltage to suppress the subsynchronous oscillation of the power grid. The remaining equipment maintains unchanged grid-side control and operates smoothly through the subsynchronous oscillation of the power grid.

[0048] Example 6

[0049] This embodiment is based on Embodiment 2.

[0050] When the new energy power station is a doubly fed, full-power, and photovoltaic hybrid new energy power station, when the power grid experiences sub-supersynchronous oscillation, the doubly fed, full-power, and photovoltaic hybrid new energy power station will, according to the equipment characteristics and damping characteristics of each of the doubly fed, full-power, and photovoltaic equipment, perform mixed allocation of a certain number of equipment by switching operating modes and control strategies, so as to complete the overall positive damping characteristics of the power station and suppress the sub-supersynchronous oscillation of the power grid.

[0051] When the new energy power station is a doubly-fed, full-power, photovoltaic hybrid new energy power station, when the power grid experiences sub-supersynchronous oscillation, the doubly-fed, full-power, photovoltaic hybrid new energy power station will switch the operating mode and control strategy of a certain number of devices according to the power output level of the doubly-fed, full-power, and photovoltaic devices at different stages, so as to complete the overall positive damping characteristics of the power station and suppress the sub-supersynchronous oscillation of the power grid.

[0052] Example 7

[0053] Please see Figure 2 , Figure 2 This is an overall connection diagram of the power generation equipment of a new energy power plant, which is the control method for a new energy power plant under the sub-supersynchronous oscillation of the power grid according to Embodiment 7 of the present invention.

[0054] This embodiment is based on Embodiment Six.

[0055] The new energy power station includes 10 photovoltaic generator sets, 10 full-power wind turbine sets, and 10 doubly-fed wind turbine sets. Each photovoltaic generator set and full-power wind turbine set includes a grid voltage transformer, a DC bus voltage transformer, and a grid-side converter control system. Each doubly-fed wind turbine set includes a grid-connected contactor, a stator short-circuit contactor, a grid voltage transformer, a DC bus voltage transformer, and a converter control system.

[0056] The control method for a full-power doubly-fed hybrid photovoltaic power station under sub-supersynchronous oscillation of the power grid is as follows:

[0057] The grid-side converter control systems of the 10 photovoltaic generator units and 10 full-power wind turbine units in the hybrid new energy power station all use the current inner loop for control and are operating normally. The converter control systems of the 10 doubly-fed wind turbine units control the grid-connected contactor to close and the stator short-circuit contactor to open, operating normally in the doubly-fed power generation mode. At a certain moment, the power grid experiences a sub-supersynchronous oscillation. All units in the power station detect a sudden change in the power grid frequency through the power grid voltage transformer. At this time, the rate of change of the power grid voltage frequency is Δfc. The DC bus voltage transformer detects a sudden rise in the DC bus voltage, and the DC bus voltage at this time is Vdc.

[0058] The grid-side converter control systems for photovoltaic generators 1-5 at the power station are configured with the following thresholds: grid voltage frequency change rate threshold Δf1_PV and DC bus voltage threshold Vdc1_PV, used to determine whether to inject a current with the same frequency and phase as the grid voltage into the inner current loop; and for photovoltaic generators 6-10, the grid voltage frequency change rate threshold Δf2_PV and DC bus voltage threshold Vdc2_PV. Similarly, the grid voltage frequency change rate threshold for the grid-side converter control systems for full-power wind turbines 1-5 at the power station is set to Δf1_PG and DC bus voltage threshold Vdc1_PG, used to determine whether to inject a current with the same frequency and phase as the grid voltage into the inner current loop. The frequency change rate threshold is Δf2_PG, and the DC bus voltage threshold is Vdc2_PG. The grid voltage frequency change rate threshold for switching the operating mode of the units in the converter control systems of the No. 1-5 doubly-fed wind turbines at the power station is set to Δf1_DG, and the DC bus voltage threshold is set to Vdc1_DG. The grid voltage frequency change rate threshold for the No. 6-10 doubly-fed wind turbines is set to Δf2_DG, and the DC bus voltage threshold is set to Vdc2_DG. Wherein, Δf1_PV < Δf2_PV < Δf1_PG < Δf2_PG < Δf1_DG < Δf2_DG, and Vdc1_PV < Vdc2_PV < Vdc1_PG < Vdc2_PG < Vdc1_DG < Vdc2_DG.

[0059] If, during subsynchronous grid oscillation, the rate of change of grid voltage frequency Δfc detected by each unit in the power station is greater than the unit's own grid voltage frequency change threshold and the DC bus voltage Vdc is greater than the unit's own DC bus voltage threshold, the grid-side converter control system of the corresponding photovoltaic generator / full-power wind turbine will inject a current signal with the same frequency and phase as the grid voltage into the current inner loop, changing the control strategy. Alternatively, the converter control system of the corresponding doubly-fed wind turbine will control the stator short-circuit contactor to open and the grid-connected contactor to close, switching from doubly-fed generation mode to asynchronous generation mode. If Δfc > Δf1_PG and Vdc > Vdc1_PG, the grid-side converter control system of photovoltaic generators No. 1-10 and full-power wind turbines No. 1-5 in the power station will change the control strategy.

[0060] If, during subsynchronous grid oscillation, the grid voltage frequency change rate Δfc detected by each unit at the power station is less than or equal to the unit's own grid voltage frequency change rate threshold or the DC bus voltage Vdc is less than or equal to the unit's own DC bus voltage threshold, the grid-side converter control system of the corresponding photovoltaic generator / full-power wind turbine will restore the original current inner loop control strategy for power generation operation by removing the current signal injected into the current inner loop. The corresponding doubly-fed wind turbine will control its stator short-circuit contactor to open and the grid-connected contactor to close through its converter control system, restoring the operation from asynchronous power generation mode to doubly-fed power generation mode. If Δfc < Δfc1_PG or Vdc < Vdc1_PG, then the grid-side converters of photovoltaic generators No. 1-10 and full-power wind turbines No. 1-5 at the power station will restore the original current inner loop control strategy for power generation operation.

[0061] When the grid-side converters of photovoltaic generators No. 1-10 and full-power wind turbines No. 1-5 in the power station change their control strategies, positive damping can be provided to suppress the sub-supersynchronous oscillation of the power grid, reduce the rate of change of the power grid voltage frequency, and reduce the bus voltage fluctuation caused by the sub-supersynchronous oscillation of the power grid. As a result, Δfc < Δf1_PV and Vdc < Vdc1_PV, the grid-side converters of photovoltaic generators No. 1-10 and full-power wind turbines No. 1-5 will resume the original current inner loop control strategy for power generation operation.

[0062] Based on the rate of change of grid voltage frequency and the DC bus voltage of the power station units during the subsynchronous oscillation of the power grid, the grid-side converter control strategies of photovoltaic generator units 1-10 and full-power wind turbine units 1-5 in the hybrid renewable energy power station were changed. This effectively suppressed the subsynchronous oscillation of the power grid and prevented its further spread. At the same time, during the switching of the grid-side converter control strategies of photovoltaic generator units 1-10 and full-power wind turbine units 1-5 in the hybrid renewable energy power station, the grid-side converters of full-power wind turbine units 6-10 in the power station maintained the original control strategy, and the doubly-fed wind turbine units 1-10 maintained the original doubly-fed power generation mode. This basically ensured the power output level of the hybrid renewable energy power station, reduced the power loss of the hybrid renewable energy power station, and prevented the possibility of batch disconnection of units during the switching period, thus effectively guaranteeing the stability of the power grid.

[0063] It should be understood that the above are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A control method for a new energy power station under sub-supersynchronous oscillation conditions of the power grid, characterized in that: When the power grid experiences subsynchronous oscillation, the resonance suppression mode of different devices is switched according to the oscillation characteristics of the power grid, with a preset characteristic frequency as the threshold. Different comparison thresholds for low-frequency components of the grid current are set for the equipment within the power station. When the low-frequency component of the grid current exceeds the comparison threshold of N power generation devices within the power station, the operating modes of N devices are switched for a smooth transition. Alternatively, different comparison thresholds for grid voltage frequency and equipment bus voltage can be set for the equipment in the station. When the grid voltage frequency or equipment bus voltage exceeds the comparison threshold of N equipment in the station, the operating mode of N equipment will be switched for a smooth transition. The grid oscillation characteristics include grid voltage, grid current, or equipment bus voltage.

2. The control method for new energy power stations under sub-supersynchronous oscillation conditions of the power grid according to claim 1, characterized in that, The new energy power station is a doubly-fed new energy power station, or a full-power new energy power station, or a photovoltaic new energy power station, or a hybrid new energy power station of doubly-fed, full-power, and photovoltaic.

3. The control method for new energy power stations under sub-supersynchronous oscillation conditions of the power grid according to claim 2, characterized in that, When the new energy power station is a doubly fed new energy power station, the doubly fed new energy power station switches the equipment's doubly fed / asynchronous operation mode according to the characteristics of the low-frequency components of the grid voltage or current during the sub-supersynchronous oscillation of the grid. Different comparison thresholds for the low-frequency components of the grid current are set for the equipment in the station. When the low-frequency component of the grid current exceeds the comparison threshold of N equipment in the station, it switches to asynchronous mode operation, and the remaining equipment maintains doubly fed mode operation. The N devices in the power station that switch to asynchronous mode provide positive damping to suppress the sub-supersynchronous oscillation of the power grid while maintaining power output. The remaining devices in the power station that maintain doubly-fed mode continue to provide power output to maintain power grid stability. Only N devices switch operating modes, and the total power output of the power station remains basically unchanged at the moment of switching, thus completing a smooth switch.

4. The control method for new energy power stations under sub-supersynchronous oscillation conditions of the power grid according to claim 3, characterized in that, The grid-connected equipment of the doubly fed new energy power station includes a grid-connected contactor and a stator short-circuit contactor. The switching to asynchronous operation is accomplished by disconnecting the grid-connected contactor and closing the stator short-circuit contactor.

5. The control method for new energy power stations under sub-supersynchronous oscillation conditions of the power grid according to claim 1, characterized in that, When the power grid oscillation characteristics are the power grid voltage and the equipment bus voltage... The phrase "setting different comparison thresholds for grid voltage frequency and equipment bus voltage for equipment within the station, and when the grid voltage frequency or equipment bus voltage exceeds the comparison threshold of N devices within the station, switching the operating mode of N devices for a smooth transition" specifically means: The new energy power station performs grid-side control transformation of equipment based on the grid voltage frequency and equipment bus voltage characteristics during subsynchronous oscillation of the power grid. Different grid voltage frequencies and equipment bus voltage comparison thresholds are set for the equipment in the station. When the grid voltage frequency and equipment bus voltage exceed the comparison threshold of N equipment in the station, positive damping is provided by injecting currents of N equipment with the same frequency and phase as the grid resonant voltage to suppress the subsynchronous oscillation of the power grid. The remaining equipment maintains unchanged grid-side control and operates smoothly through the subsynchronous oscillation of the power grid.

6. The control method for new energy power stations under sub-supersynchronous oscillation conditions of the power grid according to claim 2, characterized in that, When the new energy power station is a doubly-fed, full-power, and photovoltaic hybrid new energy power station, when the power grid experiences sub-supersynchronous oscillation, the doubly-fed, full-power, and photovoltaic hybrid new energy power station will, according to the respective equipment characteristics and damping characteristics of the doubly-fed, full-power, and photovoltaic systems, perform mixed allocation of a certain number of devices by switching operating modes and control strategies, thereby completing the overall positive damping characteristics of the power station and suppressing the sub-supersynchronous oscillation of the power grid.

7. The control method for new energy power stations under sub-supersynchronous oscillation conditions of the power grid according to claim 2, characterized in that, When the power grid experiences subsynchronous oscillation, if the new energy power station is a doubly-fed, full-power, and photovoltaic hybrid new energy power station, the doubly-fed, full-power, and photovoltaic hybrid new energy power station will switch the operating mode and control strategy of a certain number of devices according to the power output level of the doubly-fed, full-power, and photovoltaic devices at different stages, so as to complete the overall positive damping characteristics of the power station and suppress the subsynchronous oscillation of the power grid.

8. The control method for new energy power stations under sub-supersynchronous oscillation conditions of the power grid according to claim 6 or 7, characterized in that, The control strategy is switched as follows: the grid-side converter control system of the corresponding photovoltaic generator set / full-power wind turbine injects a current signal with the same frequency and phase as the grid voltage into the current inner loop; or the grid-side converter control system of the corresponding photovoltaic generator set / full-power wind turbine restores the original current inner loop control strategy for power generation operation by removing the current signal injected into the current inner loop.

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