Method, device and controller for subsynchronous oscillation suppression of photovoltaic power delivery system

Abstract

This invention provides a method, apparatus, and controller for suppressing subsynchronous oscillations in a photovoltaic (PV) power transmission system. The method includes: acquiring the PV array port output voltage, reference PV output voltage, grid-side current dq-axis component, and grid-side voltage dq-axis component of the PV power plant in the LCC-HVDC power transmission system; obtaining the reference grid-side current d-axis component based on the PV array port output voltage and the reference PV output voltage; performing sliding diaphragm control based on the reference grid-side current d-axis component, a preset reference grid-side current q-axis component, and the grid-side current dq-axis component to obtain a grid-side current dq-axis control quantity; and controlling the inverter port voltage of the inverter in the PV power plant based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component to suppress subsynchronous oscillations in the PV power transmission system via LCC-HVDC. This invention can effectively suppress subsynchronous oscillations in PV power transmission systems via LCC-HVDC.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method, apparatus and controller for suppressing subsynchronous oscillations in a photovoltaic power transmission system. Background Technology

[0002] Energy is a crucial resource foundation for human societal development. With population growth and economic development, the demand for sustainable development is rapidly increasing, primarily due to the need to address the growing energy shortage. Solar energy, as an ideal renewable energy source, is becoming an important clean energy alternative due to its widespread distribution and ability to overcome some limitations of traditional energy sources. With the continued growth of photovoltaic power generation in some parts of my country, large-scale photovoltaic power transmission via grid-commutated high-voltage direct current (LCC-HVDC) has become a vital mode of power transmission.

[0003] Because photovoltaic (PV) systems inherently possess a weakly damped subsynchronous oscillation (SSO) mode, in scenarios where PV power plants are electrically close to the LCC-HVDC rectifier station during PV transmission via LCC-HVDC, the dynamic interaction between the two may weaken the SSO mode damping, thereby increasing the risk of SSO and affecting system stability. However, current research on SSO issues in PV transmission systems primarily focuses on PV power plants connected to weak AC grids, with less attention paid to LCC-HVDC. Therefore, to improve the stability of PV transmission systems via LCC-HVDC, it is necessary to study SSO suppression methods for these systems. Summary of the Invention

[0004] This invention provides a method, apparatus, and controller for suppressing subsynchronous oscillations in a photovoltaic power transmission system, in order to address the problem of subsynchronous oscillations affecting the stability of the photovoltaic power transmission system via LCC-HVDC.

[0005] In a first aspect, embodiments of the present invention provide a method for suppressing subsynchronous oscillations in a photovoltaic power transmission system, comprising:

[0006] Acquire the photovoltaic array port output voltage, reference photovoltaic output voltage, grid-side current dq-axis component, and grid-side voltage dq-axis component of the photovoltaic power plant in the photovoltaic power plant transmitted through the LCC-HVDC system;

[0007] The d-axis component of the reference grid-side current is obtained based on the output voltage of the photovoltaic array port and the reference photovoltaic output voltage.

[0008] Sliding control is performed based on the reference grid-side current d-axis component, the preset reference grid-side current q-axis component, and the grid-side current dq-axis component to obtain the grid-side current dq-axis control quantity;

[0009] The inverter port voltage of the inverter in the photovoltaic power station is controlled based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component to suppress the subsynchronous oscillation of the photovoltaic system transmitted through the LCC-HVDC.

[0010] In one possible implementation, the step of performing sliding control based on the reference grid-side current d-axis component, the preset reference grid-side current q-axis component, and the grid-side current dq-axis component to obtain the grid-side current dq-axis control quantity includes:

[0011] Calculate the first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and design the d-axis sliding surface based on the first difference;

[0012] Calculate the second difference between the q-axis component of the preset reference grid-side current and the dq-axis component of the grid-side current, and design the q-axis sliding surface based on the second difference;

[0013] Based on the d-axis sliding surface, the q-axis sliding surface, and a preset approach law, sliding control is performed to obtain the dq-axis control quantity of the grid-side current.

[0014] In one possible implementation, calculating a first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and designing the d-axis sliding surface based on the first difference, includes:

[0015] Design the d-axis sliding surface ;

[0016] in, The d-axis sliding surface, The d-axis component of the reference grid-side current. The d-axis component of the grid-side current;

[0017] The step of calculating the second difference between the q-axis component of the preset reference grid-side current and the dq-axis component of the grid-side current, and designing the q-axis sliding surface based on the second difference, includes:

[0018] Design the q-axis sliding surface ;

[0019] in, The q-axis sliding film surface, The preset reference grid-side current q-axis component, Let q be the q-axis component of the grid-side current.

[0020] In one possible implementation, the preset approach law is an exponential approach law;

[0021] The method of obtaining the grid-side current dq-axis control quantity based on the d-axis sliding surface, the q-axis sliding surface, and a preset reaching law includes:

[0022] based on Perform sliding mode control to obtain the dq-axis control quantity of the grid-side current;

[0023] in, The derivative of the d-axis sliding surface is given. For the first d-axis parameter, For symbolic functions, The d-axis sliding surface, For the second d-axis parameter, Let be the derivative of the q-axis sliding surface. For the first q-axis parameter, The q-axis sliding film surface, This is the parameter for the second q-axis.

[0024] In one possible implementation, controlling the inverter port voltage of the inverter in the photovoltaic power station based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component includes:

[0025] according to Control the inverter port voltage of the inverter in the photovoltaic power station;

[0026] in, This is the d-axis control quantity of the inverter port voltage. This is the q-axis control quantity of the inverter port voltage. This is the output voltage of the photovoltaic array port. This refers to the grid-side equivalent inductance in the photovoltaic power station. The equivalent rotational angular velocity on the grid side of the photovoltaic power station is given. The q-axis component of the grid-side current. The d-axis component of the grid-side current. The d-axis component of the grid-side voltage is... The grid-side voltage q-axis component is... The grid-side equivalent resistance in the photovoltaic power station is denoted as .

[0027] In one possible implementation, obtaining the d-axis component of the reference grid-side current based on the photovoltaic array port output voltage and the reference photovoltaic output voltage includes:

[0028] Calculate the third difference between the output voltage of the photovoltaic array port and the output voltage of the reference photovoltaic array, and perform a PI operation on the third difference to obtain the d-axis component of the reference grid-side current.

[0029] Secondly, embodiments of the present invention provide a subsynchronous oscillation suppression device for a photovoltaic power transmission system, comprising:

[0030] The acquisition module is used to acquire the photovoltaic array port output voltage, reference photovoltaic output voltage, grid-side current dq-axis component, and grid-side voltage dq-axis component of the photovoltaic power station in the photovoltaic power station transmitted through the LCC-HVDC system;

[0031] The first processing module is used to obtain the d-axis component of the reference grid-side current based on the output voltage of the photovoltaic array port and the reference photovoltaic output voltage.

[0032] The second processing module is used to perform sliding control based on the d-axis component of the reference grid-side current, the preset q-axis component of the reference grid-side current, and the dq-axis component of the grid-side current to obtain the dq-axis control quantity of the grid-side current.

[0033] The third processing module is used to control the inverter port voltage of the inverter in the photovoltaic power station according to the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component, so as to suppress the subsynchronous oscillation of the photovoltaic power transmission system via LCC-HVDC.

[0034] In one possible implementation, the second processing module is used for:

[0035] Calculate the first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and design the d-axis sliding surface based on the first difference;

[0036] Calculate the second difference between the q-axis component of the preset reference grid-side current and the dq-axis component of the grid-side current, and design the q-axis sliding surface based on the second difference;

[0037] Based on the d-axis sliding surface, the q-axis sliding surface, and a preset approach law, sliding control is performed to obtain the dq-axis control quantity of the grid-side current.

[0038] Thirdly, embodiments of the present invention provide a controller, including a memory and a processor, wherein the memory is used to store a computer program, and the processor is used to call and run the computer program stored in the memory to perform the steps of the method as described in the first aspect or any possible implementation thereof.

[0039] Fourthly, embodiments of the present invention provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the method as described in the first aspect or any possible implementation thereof.

[0040] This invention provides a method, apparatus, and controller for suppressing subsynchronous oscillations in a photovoltaic (PV) power transmission system. The method involves acquiring the PV array port output voltage, reference PV output voltage, grid-side current dq-axis component, and grid-side voltage dq-axis component of the PV power plant in the LCC-HVDC power transmission system; obtaining the reference grid-side current d-axis component based on the PV array port output voltage and the reference PV output voltage; performing sliding diaphragm control based on the reference grid-side current d-axis component, a preset reference grid-side current q-axis component, and the grid-side current dq-axis component to obtain the grid-side current dq-axis control quantity; and controlling the inverter port voltage of the inverter in the PV power plant based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component to suppress subsynchronous oscillations in the PV power transmission system via LCC-HVDC. Because the embodiments of the present invention perform sliding diaphragm control based on the d-axis component of the reference grid-side current, the q-axis component of the preset reference grid-side current, and the dq-axis component of the grid-side current to obtain the dq-axis control quantity of the grid-side current, instead of using the current inner loop control of the traditional inverter to obtain the dq-axis control quantity of the grid-side current, the positive feedback loop of the subsynchronous current boosting of the photovoltaic system transmitted through LCC-HVDC can be cut off, reducing the boosting effect of the current inner loop control on the subsynchronous component of the photovoltaic system transmitted through LCC-HVDC, thereby effectively suppressing the subsynchronous oscillation of the photovoltaic system transmitted through LCC-HVDC. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the photovoltaic power transmission system via LCC-HVDC provided in an embodiment of the present invention;

[0043] Figure 2 This is a voltage-oriented vector control strategy diagram for a photovoltaic inverter in a photovoltaic power station subsystem provided in an embodiment of the present invention;

[0044] Figure 3 This is a diagram of the constant current control strategy for the rectifier station in the LCC-HVDC subsystem provided in this embodiment of the invention;

[0045] Figure 4 This is a flowchart illustrating the implementation of the subsynchronous oscillation suppression method for a photovoltaic power transmission system provided in this embodiment of the invention.

[0046] Figure 5 This is a control strategy diagram based on sliding diaphragm control for a photovoltaic inverter in a photovoltaic power station subsystem provided in an embodiment of the present invention;

[0047] Figure 6 These are the active power response curves with and without sliding mode control circuitry under different light intensity conditions provided in the embodiments of the present invention.

[0048] Figure 7 These are the active power response curves provided by embodiments of the present invention under different grid-connected photovoltaic unit numbers, with and without the use of sliding mode control circuits;

[0049] Figure 8 This is a schematic diagram of the subsynchronous oscillation suppression device of the photovoltaic power transmission system provided in an embodiment of the present invention;

[0050] Figure 9 This is a schematic diagram of the controller provided in an embodiment of the present invention. Detailed Implementation

[0051] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0052] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0053] The "China's Energy Development in the New Era" report released in 2020 proposed that China strive to peak carbon dioxide emissions before 2030 and endeavor to achieve carbon neutrality before 2060. To achieve the "30·60" dual carbon target, accelerate the construction of a new power system, and realize the low-carbon transformation of the energy system, solar energy is becoming an important alternative clean energy source: In 2021, my country's newly installed photovoltaic (PV) capacity reached 54.88 million kilowatts, accounting for 31.1% of the total new installed capacity; by the end of 2021, my country's cumulative installed PV capacity reached 306 million kilowatts, accounting for 12.9% of the total installed power generation capacity. It is projected that by 2025, my country's total installed PV capacity will reach 560 million kilowatts, of which 66% will be centralized PV power plants and 32.1% will be distributed PV power plants. With the annual increase in PV installed capacity, the impact of large-scale PV grid connection on the stable operation of the power system can no longer be ignored.

[0054] The short-circuit oscillation (SSO) problem in new energy sources first appeared in a wind farm in Texas, USA, in 2009. Subsequently, similar SSO phenomena occurred in Buffalo Ridge, Canada, and North my country. In 2015, a photovoltaic power plant in Spain experienced power oscillations at a frequency of 25Hz; in 2018, the interaction between a photovoltaic power plant in Sichuan and a long-chain transmission line triggered several SSOs, severely limiting photovoltaic power transmission capacity; in October 2019, significant low-frequency oscillations occurred in the Taizhou-Wenzhou area; and in November of the same year, due to reduced system short-circuit capacity, a photovoltaic power plant in eastern Inner Mongolia experienced current oscillations at a frequency of 8-9Hz, leading to system voltage fluctuations. Analysis of oscillation recording data from grid-connected photovoltaic power plants in actual engineering projects shows that the interaction between the photovoltaic inverter control system and the grid impedance characteristics can cause SSO accidents, seriously threatening the safe and stable operation of the power grid.

[0055] Therefore, it is necessary to study the SSO suppression method of photovoltaic power transmission systems via LCC-HVDC.

[0056] Figure 1 This is a schematic diagram of the photovoltaic power transmission system via LCC-HVDC provided in an embodiment of the present invention. Figure 1 As shown, for ease of analysis, the entire system is divided into four parts: the sending-end AC system, the receiving-end AC system, the photovoltaic power plant, and the LCC-HVDC. The photovoltaic power plant subsystem includes the photovoltaic power plant and its transmission line connected to the sending-end AC system; the LCC-HVDC subsystem includes the LCC-HVDC transmission system and its associated AC filter bank. The photovoltaic power plant and the sending-end AC system are connected in parallel to the same busbar, and their power is transmitted to the receiving-end AC system via the LCC-HVDC.

[0057] Figure 1 The variables are defined as follows: In the photovoltaic power station subsystem, , , , , These are the output voltage (or DC capacitor voltage) at the photovoltaic array port, the inverter port voltage, the filter capacitor voltage, the grid-side voltage, and the parallel capacitor voltage, respectively. , , , , These are the photovoltaic array port output current, inverter output current, filter capacitor current, grid-side current, and photovoltaic power plant transmission line current, respectively. For the DC-side capacitor of the photovoltaic power station, This refers to the DC-side current of the photovoltaic power station. , , These are the filter capacitor and inductor, respectively. , , , , These are the line resistance, inductance, and capacitance, respectively. For series reactance, , These represent the turns ratios of the first and second step-up transformers. In the LCC-HVDC subsystem, , , , These are the rectifier station bus voltage and DC voltage, and the inverter station bus voltage and DC voltage, respectively. , , , These are the line current and DC current of the rectifier station, and the line current and DC current of the inverter station, respectively. , , These are the resistance, inductance, and capacitance of a DC transmission line. , This refers to the transformer turns ratio at the rectifier station and the transformer turns ratio at the inverter station. In the sending-end AC system, , These represent the voltage and current of the AC system at the sending end, respectively. In the AC system at the receiving end, , These represent the voltage and current of the receiving-end AC system, respectively. Since the photovoltaic power plant is relatively close to the rectifier station in the research scenario, while the sending-end thermal power unit is far from the rectifier station, and the receiving-end AC system is only connected to the inverter station, its impact on the dynamic interaction between the photovoltaic power plant and the LCC-HVDC under study is relatively small. Therefore, according to Thevenin's theorem, the sending-end AC system is equivalent to an equivalent voltage source (…). ) and its equivalent impedance ( The receiving-end AC system is equivalent to an equivalent voltage source. ) and its equivalent impedance ( ).

[0058] for Figure 1 The photovoltaic power plant system shown, which transmits photovoltaic data via LCC-HVDC, typically employs a grid voltage-oriented vector control strategy in its photovoltaic inverter controller. Figure 2 As shown, the outer loop of the photovoltaic inverter controller adopts a constant DC voltage control strategy and a unity power factor control strategy. The control equation is shown in equation (1):

[0059] (1);

[0060] In equation (1), , , For state variables, , These are the proportional and integral coefficients of the DC voltage outer-loop PI regulator. , These are the proportional and integral coefficients of the active current inner-loop PI regulator. , These are the proportional and integral coefficients of the reactive current inner-loop PI regulator. The reference photovoltaic output voltage, The d-axis component of the grid-side current. This represents the q-axis component of the grid-side current. To preset the q-axis component of the reference grid current, The d-axis component of the reference grid current. The grid-side voltage d-axis component, This represents the q-axis component of the grid-side voltage. The equivalent rotational angular velocity, For example, it can be the equivalent inductance. and The sum of.

[0061] like Figure 3 As shown, the rectifier-side controller of the LCC-HVDC controller adopts constant current control, and the control equation is shown in equation (2):

[0062] (2);

[0063] In equation (1), This refers to the firing angle command value output by the constant current controller. For state variables, , For the proportional and integral coefficients of the constant current controller, , These are the proportional and integral coefficients of the DC current sampling and filtering stage. This refers to the DC current of the rectifier station after sampling and filtering. The reference rectifier station DC current.

[0064] However, when a Subsynchronous State Occurrence (SSO) occurs in the photovoltaic (PV) power transmission system via LCC-HVDC, the PI controller in the inner current loop of the aforementioned PV inverter controller amplifies the subsynchronous component in the PV power transmission system via LCC-HVDC, thus boosting the subsynchronous component in the system. When a large-amplitude subsynchronous current appears in the current, a subsynchronous current error will appear in the control system. This subsynchronous current error is input to the PI current controller, and after passing through proportional and integral stages, the subsynchronous current is further amplified. Since the filtering stage has limited filtering effect on the subsynchronous frequency current component, the subsynchronous current component cannot be completely attenuated on the line. Therefore, the subsynchronous current component will be superimposed on the original subsynchronous current component in the system, further increasing the subsynchronous current content in the PV power transmission system via LCC-HVDC. As this subsynchronous current component derivation process continues to repeat, a positive feedback loop of subsynchronous current boosting will be formed in the system, consisting of the AC system, the PV power plant, and its control system. The subsynchronous component content in the grid-connected current of the PV power transmission system via LCC-HVDC will continuously increase, eventually leading to SSO instability in the system.

[0065] Therefore, it is necessary to study the SSO suppression method of photovoltaic power transmission systems via LCC-HVDC.

[0066] See Figure 4 The document illustrates a flowchart of the implementation of the subsynchronous oscillation suppression method for a photovoltaic power transmission system provided in an embodiment of the present invention, which is described in detail below:

[0067] In step 401, the output voltage of the photovoltaic array port, the reference photovoltaic output voltage, the dq-axis component of the grid-side current, and the dq-axis component of the grid-side voltage of the photovoltaic power station in the photovoltaic power station transmitted through the LCC-HVDC system are obtained.

[0068] Combination Figure 1 and Figure 5 Among them, the reference photovoltaic output voltage The dq-axis components of the grid-side current and the grid-side voltage can be determined based on actual needs, and can be obtained separately by analyzing the grid-side current. and grid-side voltage It is obtained by performing a rotational coordinate transformation.

[0069] In step 402, the d-axis component of the reference grid-side current is obtained based on the output voltage of the photovoltaic array port and the reference photovoltaic output voltage.

[0070] Optionally, obtaining the d-axis component of the reference grid-side current based on the photovoltaic array port output voltage and the reference photovoltaic output voltage may include:

[0071] Calculate the third difference between the output voltage of the photovoltaic array port and the reference photovoltaic output voltage, and perform PI calculation on the third difference to obtain the d-axis component of the reference grid-side current.

[0072] In this embodiment, with Figure 2 The method for obtaining the d-axis component of the reference grid-side current is the same, and the output voltage at the photovoltaic array port can be calculated. and reference photovoltaic output voltage The third difference is then calculated based on the proportional and integral coefficients of the DC voltage outer loop PI regulator. , Perform a PI calculation on the third difference to obtain the d-axis component of the reference grid side current.

[0073] In step 403, sliding control is performed based on the d-axis component of the reference grid-side current, the preset q-axis component of the reference grid-side current, and the dq-axis component of the grid-side current to obtain the dq-axis control quantity of the grid-side current.

[0074] In this embodiment, in order to cut off the positive feedback loop of the subsynchronous current boosting of the photovoltaic system transmitted through LCC-HVDC, a sliding mode controller for the photovoltaic system transmitted through LCC-HVDC was designed. The PI controller of the current inner loop of the photovoltaic inverter in the original photovoltaic power station was replaced by the sliding mode controller, thereby effectively suppressing the SSO of the photovoltaic system transmitted through LCC-HVDC.

[0075] Optionally, sliding control is performed based on the d-axis component of the reference grid-side current, the preset q-axis component of the reference grid-side current, and the dq-axis component of the grid-side current to obtain the dq-axis control quantity of the grid-side current, which may include:

[0076] Calculate the first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and design the d-axis sliding surface based on the first difference.

[0077] Calculate the second difference between the q-axis component of the grid-side current and the dq-axis component of the grid-side current, and design the q-axis sliding surface based on the second difference.

[0078] Sliding control is performed based on the d-axis sliding surface, the q-axis sliding surface, and a preset reaching law to obtain the dq-axis control quantity of the grid-side current.

[0079] Optionally, calculating the first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and designing the d-axis sliding surface based on the first difference, may include:

[0080] Design the d-axis sliding surface (3).

[0081] in, For the d-axis sliding film surface, The d-axis component of the reference grid current. This represents the d-axis component of the grid-side current.

[0082] Calculating the second difference between the q-axis component of the pre-defined reference grid-side current and the dq-axis component of the grid-side current, and designing the q-axis sliding surface based on the second difference, may include:

[0083] Design the q-axis sliding surface (4).

[0084] in, For the q-axis sliding film surface, To preset the q-axis component of the reference grid current, This represents the q-axis component of the grid-side current.

[0085] Optionally, the preset reaching law can be an exponential reaching law.

[0086] Sliding control based on the d-axis sliding surface, the q-axis sliding surface, and a preset reaching law is used to obtain the dq-axis control quantity of the grid-side current, which may include:

[0087] based on (5) Perform sliding control to obtain the control quantity of the grid-side current dq axis.

[0088] in, Let be the derivative of the d-axis sliding surface. For the first d-axis parameter, For symbolic functions, For the d-axis sliding film surface, For the second d-axis parameter, Let be the derivative of the q-axis sliding surface. For the first q-axis parameter, For the q-axis sliding film surface, This is the parameter for the second q-axis.

[0089] In this embodiment, in the inner current loop control of the photovoltaic inverter controller, in order to enable... and Effective tracking benchmark value and In the synchronously rotating dq coordinate system, define the current inner loop control sliding surface (i.e., the d-axis sliding surface and the q-axis sliding surface) as shown in equations (3) and (4) above. Let the d-axis sliding surface... and q-axis sliding film surface The derivative is 0, which gives equation (6):

[0090] (6);

[0091] To overcome the system jitter caused by the inherent jump characteristics of the sliding mode controller's control law after the state trajectory reaches the sliding surface, a sliding mode control method is adopted for the inverter's inner current loop. The corresponding d-axis and q-axis exponential reaching law expressions are shown in equation (5) above. Wherein, the first d-axis parameter in equation (5) Second d-axis parameters First q-axis parameters Second q-axis parameters Multiple simulation analyses can be performed during the tuning process. By analyzing the dynamic processes of each system variable, their values ​​are continuously corrected until the system reaches a better operating state. (Sign function) The definition is shown in equation (7):

[0092] (7);

[0093] in, The above-mentioned d-axis sliding film surface or q-axis sliding film surface .

[0094] In step 404, the inverter port voltage of the inverter in the photovoltaic power station is controlled according to the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component, so as to suppress the subsynchronous oscillation of the photovoltaic power transmission system via LCC-HVDC.

[0095] Optional, combined Figure 5 Controlling the inverter port voltage of the inverter in a photovoltaic power plant based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component can include:

[0096] according to The inverter port voltage of the inverter in the photovoltaic power station is controlled.

[0097] in, This is the d-axis control quantity for the inverter port voltage. This is the q-axis control quantity for the inverter port voltage. This is the output voltage at the photovoltaic array port. This refers to the grid-side equivalent inductance in a photovoltaic power plant. This refers to the grid-side equivalent rotational angular velocity in a photovoltaic power plant. This represents the q-axis component of the grid-side current. The d-axis component of the grid-side current. The grid-side voltage d-axis component, This represents the q-axis component of the grid-side voltage. This refers to the grid-side equivalent resistance in a photovoltaic power plant.

[0098] The following specific embodiments further illustrate the subsynchronous oscillation suppression method of the photovoltaic power transmission system.

[0099] Figure 6 This example presents the active power response curves of the circuit with and without sliding mode control under different light intensity conditions. Specific operating conditions are set as follows: Sliding mode control is applied at t=4.0s, and the dynamic response with and without sliding mode control is compared under different operating conditions. Three operating conditions with light intensities of 950W / m², 1000W / m², and 1050W / m² are selected to verify the effectiveness of sliding mode control in suppressing SSO of photovoltaic power transmitted via the LCC-HVDC system.

[0100] Figure 6 In the middle (a), the active power response curves with and without the use of sliding mode control circuit are shown when the light intensity is 950W / m2. Figure 6 (b) shows the active power response curve with and without a sliding mode control circuit when the illuminance is 1000W / m2. Figure 6 In Figure (c), the active power response curves are shown with and without a sliding mode control circuit when the illuminance is 1050 W / m². Figure 6 As shown in (a), (b), and (c), without sliding mode control, the photovoltaic system transmitting the photovoltaic data via the LCC-HVDC transmission system will induce SSO under all three light intensities; after adopting sliding mode control, the oscillation converges rapidly. Therefore, the sliding mode control strategy adopted under different light intensities can effectively suppress SSO of the photovoltaic data transmitted via the LCC-HVDC transmission system.

[0101] Figure 7 This example examines the active power response curves of the circuit with and without sliding mode control under different grid-connected photovoltaic (PV) unit numbers. Specific operating conditions are set as follows: Sliding mode control is applied at t=4.0s, and the dynamic response with and without sliding mode control is compared under different operating conditions. Three operating conditions are selected with 126, 140, and 154 grid-connected PV units to verify the effectiveness of the sliding mode control strategy in suppressing SSO (Single State Operation) of PV power transmitted via the LCC-HVDC system.

[0102] Figure 7 (a) shows the active power response curves with and without a sliding mode control circuit when there are 126 grid-connected photovoltaic units. Figure 7 (b) shows the active power response curves with and without a sliding mode control circuit when there are 140 grid-connected photovoltaic units. Figure 7 (c) shows the active power response curves with and without a sliding mode control circuit when there are 154 grid-connected photovoltaic units. Figure 7As shown in (a), (b), and (c), without sliding mode control, the weakening of the AC system strength will cause SSO under different grid-connected photovoltaic (PV) units. After adopting sliding mode control, the oscillation converges rapidly, and the SSO of the system can be effectively suppressed. Under different grid-connected PV units, the equipped sliding mode control strategy can effectively suppress the SSO of the PV system transmitted via LCC-HVDC.

[0103] Figure 6 , Figure 7 The results of the numerical examples verify the effectiveness and feasibility of the subsynchronous oscillation suppression method for photovoltaic power transmission systems using sliding mode control strategy provided in this invention.

[0104] This invention provides an embodiment of the photovoltaic power plant that transmits photovoltaic data via an LCC-HVDC transmission system. It acquires the photovoltaic array port output voltage, reference photovoltaic output voltage, grid-side current dq-axis component, and grid-side voltage dq-axis component from the photovoltaic array port output voltage and the reference photovoltaic output voltage. Based on these values, it obtains the reference grid-side current d-axis component. Using the reference grid-side current d-axis component, a preset reference grid-side current q-axis component, and the grid-side current dq-axis component, it performs sliding diaphragm control to obtain the grid-side current dq-axis control quantity. Finally, based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component, it controls the inverter port voltage of the inverter in the photovoltaic power plant to suppress subsynchronous oscillations in the LCC-HVDC transmission system. Because this invention uses sliding diaphragm control based on the d-axis component of the reference grid-side current, the q-axis component of the preset reference grid-side current, and the dq-axis component of the grid-side current to obtain the dq-axis control quantity of the grid-side current, instead of using the current inner loop control of a traditional inverter, it can cut off the positive feedback loop of the subsynchronous current boosting function of the photovoltaic system transmitted via LCC-HVDC, reducing the boosting effect of the current inner loop control on the subsynchronous component of the photovoltaic system transmitted via LCC-HVDC, thereby effectively suppressing the subsynchronous oscillation of the photovoltaic system transmitted via LCC-HVDC. This is beneficial for promoting the integrated development of power systems and power electronic converters, improving the flexibility and economy of the power grid.

[0105] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0106] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0107] Figure 8 A schematic diagram of the subsynchronous oscillation suppression device for a photovoltaic power transmission system provided in an embodiment of the present invention is shown. For ease of explanation, only the parts relevant to the embodiment of the present invention are shown, and are described in detail below:

[0108] like Figure 8 As shown, the subsynchronous oscillation suppression device of the photovoltaic transmission system includes: an acquisition module 81, a first processing module 82, a second processing module 83, and a third processing module 84.

[0109] The acquisition module 81 is used to acquire the photovoltaic array port output voltage, reference photovoltaic output voltage, grid-side current dq-axis component and grid-side voltage dq-axis component of the photovoltaic power station in the photovoltaic power station transmitted through the LCC-HVDC system;

[0110] The first processing module 82 is used to obtain the d-axis component of the reference grid-side current based on the output voltage of the photovoltaic array port and the reference photovoltaic output voltage.

[0111] The second processing module 83 is used to perform sliding control based on the reference grid-side current d-axis component, the preset reference grid-side current q-axis component and the grid-side current dq-axis component to obtain the grid-side current dq-axis control quantity.

[0112] The third processing module 84 is used to control the inverter port voltage of the inverter in the photovoltaic power station according to the grid-side current dq-axis control quantity, the grid-side current dq-axis component and the grid-side voltage dq-axis component, so as to suppress the subsynchronous oscillation of the photovoltaic power transmission system via LCC-HVDC.

[0113] This invention provides an embodiment of the photovoltaic power plant that transmits photovoltaic data via an LCC-HVDC transmission system. It acquires the photovoltaic array port output voltage, reference photovoltaic output voltage, grid-side current dq-axis component, and grid-side voltage dq-axis component from the photovoltaic array port output voltage and the reference photovoltaic output voltage. Based on these values, it obtains the reference grid-side current d-axis component. Using the reference grid-side current d-axis component, a preset reference grid-side current q-axis component, and the grid-side current dq-axis component, it performs sliding diaphragm control to obtain the grid-side current dq-axis control quantity. Finally, based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component, it controls the inverter port voltage of the inverter in the photovoltaic power plant to suppress subsynchronous oscillations in the LCC-HVDC transmission system. Because the embodiments of the present invention perform sliding diaphragm control based on the d-axis component of the reference grid-side current, the q-axis component of the preset reference grid-side current, and the dq-axis component of the grid-side current to obtain the dq-axis control quantity of the grid-side current, instead of using the current inner loop control of the traditional inverter to obtain the dq-axis control quantity of the grid-side current, the positive feedback loop of the subsynchronous current boosting of the photovoltaic system transmitted through LCC-HVDC can be cut off, reducing the boosting effect of the current inner loop control on the subsynchronous component of the photovoltaic system transmitted through LCC-HVDC, thereby effectively suppressing the subsynchronous oscillation of the photovoltaic system transmitted through LCC-HVDC.

[0114] In one possible implementation, the second processing module 83 can be used for:

[0115] Calculate the first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and design the d-axis sliding surface based on the first difference;

[0116] Calculate the second difference between the q-axis component of the preset reference grid-side current and the dq-axis component of the grid-side current, and design the q-axis sliding surface based on the second difference;

[0117] Based on the d-axis sliding surface, the q-axis sliding surface, and a preset approach law, sliding control is performed to obtain the dq-axis control quantity of the grid-side current.

[0118] In one possible implementation, the second processing module 83 can be used for:

[0119] Design the d-axis sliding surface ;

[0120] in, The d-axis sliding surface, The d-axis component of the reference grid-side current. The d-axis component of the grid-side current;

[0121] Design the q-axis sliding surface ;

[0122] in, The q-axis sliding film surface, The preset reference grid-side current q-axis component, Let q be the q-axis component of the grid-side current.

[0123] In one possible implementation, the preset reaching law is an exponential reaching law; the second processing module 83 can be used for:

[0124] based on Perform sliding mode control to obtain the dq-axis control quantity of the grid-side current;

[0125] in, The derivative of the d-axis sliding surface is given. For the first d-axis parameter, For symbolic functions, The d-axis sliding surface, For the second d-axis parameter, Let be the derivative of the q-axis sliding surface. For the first q-axis parameter, The q-axis sliding film surface, This is the parameter for the second q-axis.

[0126] In one possible implementation, the third processing module 84 can be used for:

[0127] according to Control the inverter port voltage of the inverter in the photovoltaic power station;

[0128] in, This is the d-axis control quantity of the inverter port voltage. This is the q-axis control quantity of the inverter port voltage. This is the output voltage of the photovoltaic array port. This refers to the grid-side equivalent inductance in the photovoltaic power station. The equivalent rotational angular velocity on the grid side of the photovoltaic power station is given. The q-axis component of the grid-side current. The d-axis component of the grid-side current. The d-axis component of the grid-side voltage is... The grid-side voltage q-axis component is... The grid-side equivalent resistance in the photovoltaic power station is given.

[0129] In one possible implementation, the first processing module 81 can be used to calculate a third difference between the output voltage of the photovoltaic array port and the reference photovoltaic output voltage, and perform a PI operation on the third difference to obtain the d-axis component of the reference grid-side current.

[0130] Figure 9 This is a schematic diagram of the controller provided in an embodiment of the present invention. Figure 9 As shown, the controller 9 in this embodiment includes a processor 90, a memory 91, and a computer program 92 stored in the memory 91 and executable on the processor 90. When the processor 90 executes the computer program 92, it implements the steps in the embodiments of the subsynchronous oscillation suppression methods for the various photovoltaic power transmission systems described above, for example... Figure 4 Steps 401 to 404 are shown. Alternatively, when processor 90 executes computer program 92, it implements the functions of each module / unit in the above-described device embodiments, for example... Figure 8 The functions of modules / units 81 to 84 shown.

[0131] For example, computer program 92 can be divided into one or more modules / units, one or more of which are stored in memory 91 and executed by processor 90 to complete the present invention. One or more modules / units can be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 92 in controller 9. For example, computer program 92 can be divided into... Figure 8 Modules / units 81 to 84 are shown.

[0132] Controller 9 can be the controller of the photovoltaic inverter in a photovoltaic power plant within a photovoltaic power plant system that transmits photovoltaic power via LCC-HVDC. Controller 9 may include, but is not limited to, a processor 90 and a memory 91. Those skilled in the art will understand that... Figure 9 This is merely an example of controller 9 and does not constitute a limitation on controller 9. It may include more or fewer components than shown, or combine certain components, or different components. For example, the controller may also include input / output devices, network access devices, buses, etc.

[0133] The processor 90 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0134] The memory 91 can be an internal storage unit of the controller 9, such as a hard disk or RAM of the controller 9. The memory 91 can also be an external storage device of the controller 9, such as a plug-in hard disk, SmartMedia Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the controller 9. Furthermore, the memory 91 can include both internal and external storage units of the controller 9. The memory 91 is used to store computer programs and other programs and data required by the controller. The memory 91 can also be used to temporarily store data that has been output or will be output.

[0135] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0136] As another embodiment of the present invention, the present invention may also include a photovoltaic LCC-HVDC transmission system, which includes the controller of any of the above embodiments and has the same beneficial effects as the controller described above, and will not be described again here.

[0137] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0138] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0139] In the embodiments provided by this invention, it should be understood that the disclosed devices / controllers and methods can be implemented in other ways. For example, the device / controller embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0140] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0141] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0142] If integrated modules / units are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the subsynchronous oscillation suppression method embodiments of the various photovoltaic power transmission systems described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals.

[0143] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for suppressing subsynchronous oscillations in a photovoltaic power transmission system, characterized in that, include: Acquire the photovoltaic array port output voltage, reference photovoltaic output voltage, grid-side current dq-axis component, and grid-side voltage dq-axis component of the photovoltaic power plant in the photovoltaic power plant transmitted through the LCC-HVDC system; The d-axis component of the reference grid-side current is obtained based on the output voltage of the photovoltaic array port and the reference photovoltaic output voltage. Sliding control is performed based on the reference grid-side current d-axis component, the preset reference grid-side current q-axis component, and the grid-side current dq-axis component to obtain the grid-side current dq-axis control quantity; Based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component, the inverter port voltage of the inverter in the photovoltaic power station is controlled to suppress the subsynchronous oscillation of the photovoltaic power transmission system via LCC-HVDC. The step of performing sliding control based on the reference grid-side current d-axis component, the preset reference grid-side current q-axis component, and the grid-side current dq-axis component to obtain the grid-side current dq-axis control quantity includes: Calculate the first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and design the d-axis sliding surface based on the first difference; Calculate the second difference between the q-axis component of the preset reference grid-side current and the dq-axis component of the grid-side current, and design the q-axis sliding surface based on the second difference; Sliding control is performed based on the d-axis sliding surface, the q-axis sliding surface, and a preset approach law to obtain the dq-axis control quantity of the grid-side current. The preset approach law is an exponential approach law; The method of obtaining the grid-side current dq-axis control quantity based on the d-axis sliding surface, the q-axis sliding surface, and a preset reaching law includes: based on Perform sliding mode control to obtain the dq-axis control quantity of the grid-side current; in, The derivative of the d-axis sliding surface is given. For the first d-axis parameter, For symbolic functions, The d-axis sliding surface, For the second d-axis parameter, Let be the derivative of the q-axis sliding surface. For the first q-axis parameter, The q-axis sliding film surface, This is the second q-axis parameter; The step of controlling the inverter port voltage of the inverter in the photovoltaic power station based on the grid-side current dq-axis control quantity, the grid-side current dq-axis component, and the grid-side voltage dq-axis component includes: according to Control the inverter port voltage of the inverter in the photovoltaic power station; in, This is the d-axis control quantity of the inverter port voltage. This is the q-axis control quantity of the inverter port voltage. This is the output voltage of the photovoltaic array port. This refers to the grid-side equivalent inductance in the photovoltaic power station. The equivalent rotational angular velocity on the grid side of the photovoltaic power station is given. The q-axis component of the grid-side current. The d-axis component of the grid-side current. The d-axis component of the grid-side voltage is... The grid-side voltage q-axis component is... The grid-side equivalent resistance in the photovoltaic power station is given.

2. The method for suppressing subsynchronous oscillations in a photovoltaic power transmission system according to claim 1, characterized in that, The step of calculating the first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and designing the d-axis sliding surface based on the first difference, includes: Design the d-axis sliding surface ; in, The d-axis sliding surface, The d-axis component of the reference grid-side current. The d-axis component of the grid-side current; The step of calculating the second difference between the q-axis component of the preset reference grid-side current and the dq-axis component of the grid-side current, and designing the q-axis sliding surface based on the second difference, includes: Design the q-axis sliding surface ; in, The q-axis sliding film surface, The preset reference grid-side current q-axis component, Let q be the q-axis component of the grid-side current.

3. The method for suppressing subsynchronous oscillations in a photovoltaic power transmission system according to claim 1 or 2, characterized in that, The step of obtaining the d-axis component of the reference grid-side current based on the output voltage of the photovoltaic array port and the reference photovoltaic output voltage includes: Calculate the third difference between the output voltage of the photovoltaic array port and the output voltage of the reference photovoltaic array, and perform a PI operation on the third difference to obtain the d-axis component of the reference grid-side current.

4. A subsynchronous oscillation suppression device for a photovoltaic power transmission system, characterized in that, include: The acquisition module is used to acquire the photovoltaic array port output voltage, reference photovoltaic output voltage, grid-side current dq-axis component, and grid-side voltage dq-axis component of the photovoltaic power station in the photovoltaic power station transmitted through the LCC-HVDC system; The first processing module is used to obtain the d-axis component of the reference grid-side current based on the output voltage of the photovoltaic array port and the reference photovoltaic output voltage. The second processing module is used to perform sliding control based on the d-axis component of the reference grid-side current, the preset q-axis component of the reference grid-side current, and the dq-axis component of the grid-side current to obtain the dq-axis control quantity of the grid-side current. The third processing module is used to control the inverter port voltage of the inverter in the photovoltaic power station according to the grid-side current dq-axis control quantity, the grid-side current dq-axis component and the grid-side voltage dq-axis component, so as to suppress the subsynchronous oscillation of the photovoltaic power transmission system via LCC-HVDC. The second processing module is specifically used for: Calculate the first difference between the d-axis component of the reference grid-side current and the dq-axis component of the grid-side current, and design the d-axis sliding surface based on the first difference; Calculate the second difference between the q-axis component of the preset reference grid-side current and the dq-axis component of the grid-side current, and design the q-axis sliding surface based on the second difference; Sliding control is performed based on the d-axis sliding surface, the q-axis sliding surface, and a preset approach law to obtain the dq-axis control quantity of the grid-side current. The preset approach law is an exponential approach law; The second processing module is specifically used for: based on Perform sliding mode control to obtain the dq-axis control quantity of the grid-side current; in, The derivative of the d-axis sliding surface is given. For the first d-axis parameter, For symbolic functions, The d-axis sliding surface, For the second d-axis parameter, Let be the derivative of the q-axis sliding surface. For the first q-axis parameter, The q-axis sliding film surface, This is the second q-axis parameter; The third processing module is specifically used for: according to Control the inverter port voltage of the inverter in the photovoltaic power station; in, This is the d-axis control quantity of the inverter port voltage. This is the q-axis control quantity of the inverter port voltage. This is the output voltage of the photovoltaic array port. This refers to the grid-side equivalent inductance in the photovoltaic power station. The equivalent rotational angular velocity on the grid side of the photovoltaic power station is given. The q-axis component of the grid-side current. The d-axis component of the grid-side current. The d-axis component of the grid-side voltage is... The grid-side voltage q-axis component is... The grid-side equivalent resistance in the photovoltaic power station is denoted as .

5. A controller, characterized in that, It includes a memory and a processor, the memory being used to store a computer program, and the processor being used to call and run the computer program stored in the memory to perform the method as described in any one of claims 1 to 3.

6. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 3 above.

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