A method and medium for suppressing transient voltage rise during commutation failure of an ac-dc transmission system with meshed equipment

Abstract

The application discloses a method and medium for suppressing transient voltage rise during commutation failure of an AC / DC sending-out system containing grid-forming equipment, and belongs to the technical field of power grid safety, stability and control. The method comprises the following steps: constructing an AC / DC hybrid sending-out system model containing grid-forming equipment and grid-following equipment, determining the dynamic coupling relationship between the transient voltage rise of the DC sending end converter bus during commutation failure and the active power deviation and the reactive power deviation of each power unit, establishing a virtual synchronous control model of the grid-forming equipment, based on the AC / DC hybrid sending-out system model and the virtual synchronous control model, analyzing the transient characteristics during commutation failure, designing the switching timing of the current limiting link according to the active power-frequency control loop and the reactive power-voltage control loop, and making the switching timing of the current limiting link and the switching timing of the DC system control link coordinated. The application solves the problem that the transient voltage rise of the DC sending end converter bus during commutation failure of the AC / DC sending-out system containing grid-forming equipment cannot be effectively suppressed in the prior art.

Description

Technical Field

[0001] This invention relates to a method and medium for suppressing transient voltage rise during commutation failure in AC / DC power transmission systems with grid-type equipment, belonging to the field of power grid safety, stability and control technology. Background Technology

[0002] In recent years, to meet the demand for transmitting electricity from large-scale renewable energy bases, my country has built multiple ultra-high-voltage direct current (UHVDC) transmission lines, creating favorable conditions for renewable energy transmission. However, the AC grid structure at the DC transmission end is relatively weak, and some conventional power generation capacity has been replaced by renewable energy, resulting in insufficient dynamic reactive power and voltage support capacity of the sending-end grid. Faults such as DC commutation failure, single / bipolar blocking, and AC faults near converter stations can all trigger transient overvoltages at the DC transmission end. This not only poses a significant risk to the safe operation of the UHVDC transmission end grid but also easily leads to large-scale disconnection of renewable energy units from the grid, directly limiting DC transmission capacity. Grid-connecting equipment uses virtual synchronous generator (VSG) control to simulate the frequency and voltage regulation process of a synchronous generator. It dynamically adjusts the system frequency through active power control and reduces system voltage deviation through reactive power control, restoring the output characteristics of a synchronous generator to achieve grid-connecting capability.

[0003] In AC / DC power transmission systems with grid-type equipment, the grid-type equipment exhibits significant drawbacks when commutation failure occurs. Its current limiting function cannot be deactivated, severely restricting its ability to suppress transient overvoltages at the transmitting end. More seriously, it may trigger power oscillations, leading to subsequent commutation failures, making it difficult for existing technologies to effectively suppress the transient voltage rise on the DC transmitting end converter bus during commutation failures in AC / DC power transmission systems with grid-type equipment. Summary of the Invention

[0004] The purpose of this invention is to provide a method and medium for suppressing transient voltage rise during commutation failure in AC / DC power transmission systems of grid-type equipment. By determining the transient characteristics during commutation failure and designing a coordinated switching sequence between the current limiting circuit and the DC system control circuit, this invention solves the problem in the prior art where transient voltage rise at the DC sending end converter bus is difficult to effectively suppress during commutation failure in AC / DC power transmission systems of grid-type equipment.

[0005] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution.

[0006] In a first aspect, the present invention provides a method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system containing a grid-type device, comprising:

[0007] Construct a hybrid AC / DC transmission system model for both grid-type and grid-connected equipment;

[0008] Based on the AC / DC hybrid power transmission system model, the dynamic coupling relationship between the transient voltage rise of the DC power transmission end converter bus and the active power deviation and reactive power deviation of each power unit is determined when commutation fails.

[0009] A virtual synchronous control model for the network-type equipment is established based on the dynamic coupling relationship. The virtual synchronous control model includes at least an active-frequency control loop and a reactive-voltage control loop for outputting current commands, as well as a current limiting loop for constraining the current commands.

[0010] Based on the AC / DC hybrid power transmission system model and the virtual synchronous control model, by analyzing the transient characteristics during commutation failure, the current limiting loop is designed according to the active-frequency control loop and the reactive-voltage control loop, so that the activation and deactivation sequence is coordinated with the switching sequence of the DC system control loop. The relationship between the current output of the grid-type equipment and the converter station bus voltage during the fault is obtained, and the transient voltage rise during commutation failure is suppressed.

[0011] The activation and deactivation sequence includes activating the current limiting circuit during the transient low voltage phase at the DC sending end, delaying the deactivation of the current limiting circuit during the transient overvoltage development phase, and deactivating the current limiting circuit before the DC system returns to stable control.

[0012] Furthermore, the AC / DC hybrid power transmission system model includes a DC sending-end converter bus, and an LCC-HVDC rectifier station, a grid-type converter, a grid-connected new energy unit, and a power unit connected in parallel to the DC sending-end converter bus.

[0013] Furthermore, based on the AC / DC hybrid power transmission system model, the dynamic coupling relationship between the transient voltage rise of the DC sending-end converter bus and the active power deviation and reactive power deviation of each power unit when commutation fails is determined, including:

[0014] Establish the steady-state power balance equation for the DC sending-end converter bus;

[0015] Based on the steady-state power balance equation, the voltage deviation equation for commutation failure is derived.

[0016] Based on the AC / DC hybrid power transmission system model and voltage deviation equation, the dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power unit is determined.

[0017] Furthermore, the steady-state power balance equation is expressed as:

[0018] ;

[0019] In the formula, , These represent the active power and reactive power transmitted by the thermal power unit, respectively. , These refer to the active power and reactive power transmitted by the new energy generating units, respectively. The active power transmitted by a DC system. The reactive power provided to the rectifier-side AC filter system This refers to the reactive power consumed during the rectification process of the rectifier;

[0020] The voltage deviation equation is expressed as:

[0021] ;

[0022] In the formula, This refers to the voltage deviation at the rectifier-side converter bus during steady state. This is the steady-state voltage of the rectifier-side converter bus. and These represent the active power deviation and reactive power deviation of the line where the thermal power unit is located during the commutation failure period, respectively. and These represent the active power deviation and reactive power deviation of the line where the new energy unit is located during the commutation failure period, respectively. >0、 >0、 >0、 >0 represents the reactive power surplus and active power surplus of the lines where thermal power units and new energy units are located, respectively, both of which will lead to Increase , These are the equivalent reactances between thermal power units and new energy units and the DC system, respectively. , Approximately equal to 0.

[0023] Furthermore, based on the AC / DC hybrid power transmission system model and voltage deviation equation, the dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power unit is determined, including:

[0024] When the sending-end system does not contain new energy units, based on the equivalent reactance of the sending-end system, the AC / DC hybrid sending-out system model and voltage deviation equation are used to determine the active power deficit at the sending end caused by the reduction of DC transmission power during the commutation failure period, and obtain the dynamic coupling relationship between transient voltage rise and active power deviation and reactive power deviation of each power unit.

[0025] When the sending-end system contains new energy sources, the power shunting characteristics of the active power deviation of the sending-end converter bus on the AC branch and the new energy grid-connected branch are considered. Based on the dynamic process of the reduction of DC transmission power during the commutation failure, the dynamic coupling relationship between transient voltage rise and active power deviation and reactive power deviation of each power unit is determined based on the AC / DC hybrid sending system model and voltage deviation equation.

[0026] The dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power unit is expressed as follows:

[0027] ;

[0028] In the formula, This refers to the active power of the thermal power unit during the transient period. This refers to the active power of new energy sources during the transient period. It is the sum of the active power of thermal power units and new energy sources during the transient period.

[0029] Furthermore, a virtual synchronization control model for network-type devices is established based on the aforementioned dynamic coupling relationship, including:

[0030] Based on the adjustment characteristics of the active-frequency control loop and the reactive-voltage control loop of the network-type equipment, the basic control equations of the reactive-voltage control loop and the active-frequency control loop are established based on the dynamic coupling relationship.

[0031] Based on the reactive-voltage control loop control equation and the active-frequency control loop control equation, the relationship between reactive power and current of grid-type equipment, as well as the relationship between active power and current, are determined. According to the characteristics of the virtual impedance link, the current command equation for the virtual impedance circuit is obtained.

[0032] Based on the virtual impedance circuit, a current command equation is generated, a current limiting link for the inner loop current of the network-type equipment is set, the control logic of the current limiting link is generated, and a virtual synchronous control model for the network-type equipment is established.

[0033] Furthermore, the basic control equations for the reactive-voltage control loop and the active-frequency control loop are expressed as follows:

[0034] ;

[0035] In the formula, , These represent the active power reference value and the active power of the network-type transmission, respectively. Indicates virtual damping. Represents virtual angular frequency. Represents virtual inertia. Indicates a virtual reference angle. Represents the fundamental value of the virtual internal potential. Represents the integral coefficient. Represents the complex frequency domain operator, This represents the voltage droop factor. Indicates the reference value of the grid connection point voltage. Indicates the actual voltage at the grid connection point. Represents the reactive power coefficient. Indicates the reactive power reference value. This indicates the reactive power exchanged by the sending system. Indicates the magnitude of the virtual internal potential. The time derivative of the virtual reference angle.

[0036] Furthermore, the virtual impedance circuit generates a current command equation, expressed as:

[0037] ;

[0038] In the formula, Indicates converter shaft current, Indicates the actual voltage at the grid connection point. Indicates converter shaft current;

[0039] The active power of the network-type transmission is expressed as:

[0040] ;

[0041] In the formula, Represents the sine function. This represents the phase angle of the virtual internal potential in the network configuration. Indicates the phase angle of the voltage at the grid connection point. Indicates the equivalent reactance of the network-type equipment. Indicates the gain coefficient. Indicates the phase difference;

[0042] The reactive power exchanged by the sending-end system is expressed as:

[0043] ;

[0044] In the formula, Represents the cosine function;

[0045] The control logic of the current limiting circuit is expressed as follows:

[0046] , , ;

[0047] In the formula, This indicates the current reference value provided by the limiter. Indicates the current limiting factor. Indicates the current limiting value. Indicates the converter output current Actual value of the shaft Representing the virtual internal potential Axis component values, Indicates the voltage at the grid connection point Axis component values, Indicates the virtual resistance value. This represents the virtual inductance value.

[0048] Furthermore, the relationship between the current output by the grid-type equipment and the converter station bus voltage during the fault is expressed as follows:

[0049] ;

[0050] In the formula, This indicates the output current of the network-type equipment. To take the real part of a complex number, " " indicates a ratio.

[0051] In a second aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the transient voltage rise suppression method during commutation failure of a structured network device AC / DC transmission system as described in the first aspect.

[0052] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0053] This invention constructs a hybrid AC / DC power transmission system model containing grid-type and grid-connected equipment. It analyzes the dynamic coupling relationship between the transient voltage rise of the DC-end converter bus and the active and reactive power deviations of each power unit during commutation failure. Based on this, a virtual synchronous control model for the grid-type equipment is established, including an active-frequency control loop and a reactive-voltage control loop for output current commands, as well as a current limiting loop for constraining current commands. Furthermore, the transient characteristics during commutation failure are analyzed, and a scheme is designed to coordinate the switching timing of the current limiting loop with the switching timing of the DC system control loop. The relationship between the current output of the grid-type equipment and the converter station bus voltage during the fault is derived, suppressing the transient voltage rise during commutation failure. This effectively enhances the suppression effect of the grid-type equipment on the transient voltage rise of the DC-end converter bus during commutation failure, reduces the risk of power oscillation and multiple commutation failures, and improves the operational stability of the AC / DC power transmission system.

[0054] This invention constructs a hybrid AC / DC power transmission system model, including an LCC-HVDC rectifier station, a grid-connected converter, grid-connected renewable energy units, and power generation units. Based on this model, it establishes the steady-state power balance equation for the DC sending-end converter bus, and then derives the voltage deviation equation for commutation failure. Furthermore, it analyzes the dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power generation unit, respectively, for cases where the sending-end system contains and does not contain renewable energy units. This allows for targeted measures to suppress transient voltage rise, fundamentally improving the effectiveness and relevance of the suppression method.

[0055] This invention establishes a virtual synchronous control model for grid-type equipment based on dynamic coupling relationships. It includes an active-frequency control loop and a reactive-voltage control loop for outputting current commands, as well as a current limiting loop for constraining current commands. By establishing basic control equations based on the regulation characteristics of the grid-type equipment, analyzing the relationship between reactive power and current, and active power and current, and combining the characteristics of the virtual impedance loop, the current command generation equation of the virtual impedance circuit is obtained. Furthermore, the control logic of the current limiting loop is set, enabling the grid-type equipment to more accurately simulate the output characteristics of a synchronous generator. This allows for better regulation of active and reactive power during commutation failures, effectively enhancing the suppression of transient voltage rise on the DC sending-end converter bus and avoiding power oscillations and multiple commutation failures caused by improper regulation of the grid-type equipment.

[0056] This invention, based on an AC / DC hybrid power transmission system model and a virtual synchronous control model, analyzes the transient characteristics during commutation failure and designs a scheme to coordinate the activation and deactivation timing of the current limiting circuit with the switching timing of the DC system control circuit. It derives the relationship between the output current of the grid-type equipment and the converter station bus voltage during the fault, suppressing transient voltage rise during commutation failure. Specifically, activating the current limiting circuit during the transient low voltage stage at the DC sending end prevents excessive current from damaging the equipment; delaying the deactivation of the current limiting circuit during the transient overvoltage development stage effectively suppresses further increases in transient overvoltage; and deactivating the current limiting circuit before the DC system returns to stable control allows the system to return to normal operation. This invention fully considers various transient characteristics of the system during commutation failure, enabling timely and effective responses to transient voltage rise issues, ensuring the stable operation of the AC / DC power transmission system during commutation failure, and improving the overall system reliability and safety. Attached Figure Description

[0057] Figure 1 This is a flowchart illustrating a method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a structured network device, provided in an embodiment of the present invention.

[0058] Figure 2This is a schematic diagram of a DC transmission system structure that combines grid-connected and grid-connected types according to an embodiment of the present invention.

[0059] Figure 3 This is a simplified topology diagram of a DC transmission system with hybrid grid-connected and grid-connected configurations provided in an embodiment of the present invention.

[0060] Figure 4 This is a schematic diagram of the system phasor relationship provided in an embodiment of the present invention;

[0061] Figure 5 This is a schematic diagram of the power reference decomposition results of the transmitting line provided in an embodiment of the present invention;

[0062] Figure 6 This is a schematic diagram illustrating the voltage and frequency transient characteristics analysis of the entire process of a failed commutation in a network-type limiting circuit, provided in an embodiment of the present invention.

[0063] Figure 7 This is a schematic diagram illustrating the voltage and frequency transient characteristics analysis of the entire process of the failure of the delayed switching on / off phase switching of the network-type limiting circuit provided in the embodiment of the present invention. Detailed Implementation

[0064] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations thereof. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0065] Example 1

[0066] like Figure 1 As shown in the figure, this embodiment introduces a method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-type equipment, including:

[0067] Step 1: Construct a hybrid AC / DC transmission system model that includes both grid-type and grid-connected equipment.

[0068] This invention constructs a hybrid AC / DC power transmission system model that includes grid-connected and grid-linked equipment, enabling a comprehensive and accurate simulation of the complex structure and operating characteristics of actual AC / DC power transmission systems. The model encompasses the DC sending-end converter bus, as well as key components connected in parallel, such as the LCC-HVDC rectifier station, grid-connected converter, grid-linked renewable energy units, and power generation units. This model provides a solid platform for in-depth analysis of the transient voltage rise problem of the DC sending-end converter bus during commutation failure. It allows researchers to simulate and analyze the system under various operating conditions in a highly realistic virtual environment, thereby more accurately grasping the dynamic behavior of the system during commutation failure and laying the foundation for developing effective transient voltage rise suppression strategies.

[0069] Step 2: Based on the AC / DC hybrid power transmission system model, determine the dynamic coupling relationship between the transient voltage rise of the DC power transmission end converter bus and the active power deviation and reactive power deviation of each power unit when commutation fails.

[0070] This invention, based on a constructed AC / DC hybrid power transmission system model, deeply analyzes the dynamic coupling relationship between the transient voltage rise of the DC sending-end converter bus and the active and reactive power deviations of each power unit during commutation failure, which is of crucial significance. This analysis process, by establishing the steady-state power balance equation of the DC sending-end converter bus and deriving the voltage deviation equation during commutation failure, clearly reveals the intrinsic connection between the transient voltage rise and the power deviation of each power unit. Regardless of whether the sending-end system contains renewable energy units, this analysis method can obtain an accurate dynamic coupling relationship. This profound understanding of the system's internal dynamic characteristics provides a crucial theoretical basis for subsequently establishing a virtual synchronous control model for grid-connected equipment, enabling the control model to be designed more precisely to address the transient voltage rise problem, thereby improving the suppression effect.

[0071] Step 3: Establish a virtual synchronous control model for the network-type equipment based on the dynamic coupling relationship. The virtual synchronous control model includes at least an active-frequency control loop and a reactive-voltage control loop for outputting current commands, as well as a current limiting loop for constraining the current commands.

[0072] This invention establishes a virtual synchronous control model for grid-type equipment based on dynamic coupling relationships. It includes an active-frequency control loop and a reactive-voltage control loop for outputting current commands, as well as a current limiting loop for constraining current commands. This enables the grid-type equipment to better simulate the characteristics of a synchronous generator. By establishing basic control equations based on the regulation characteristics of the grid-type equipment, analyzing the relationships between reactive power and current, and active power and current, and combining the characteristics of the virtual impedance loop, the current command equation generated by the virtual impedance circuit is obtained, and then the control logic of the current limiting loop is set. This design allows the grid-type equipment to accurately adjust the output of active and reactive power according to the dynamic changes of the system during commutation failures, effectively suppressing transient voltage rise on the DC sending-end converter bus, avoiding power oscillations and multiple commutation failures, and improving the adaptability and stability of the grid-type equipment under complex operating conditions.

[0073] Step 4: Based on the AC / DC hybrid power transmission system model and the virtual synchronous control model, by analyzing the transient characteristics during commutation failure, the activation and deactivation sequence of the current limiting link is designed according to the active-frequency control loop and the reactive-voltage control loop, so that the activation and deactivation sequence is coordinated with the switching sequence of the DC system control loop, and the relationship between the current output of the grid-type equipment and the converter station bus voltage during the fault is obtained, thereby suppressing the transient voltage rise during commutation failure.

[0074] This invention, based on an AC / DC hybrid power transmission system model and a virtual synchronous control model, deeply analyzes the transient characteristics during commutation failure and designs the activation and deactivation sequence of the current limiting circuit to coordinate with the switching sequence of the DC system control circuit. This is a key measure to ensure stable system operation. By analyzing various transient characteristics of the system during commutation failure, the development process and changing patterns of transient voltage rise can be accurately grasped. Based on this, and according to the characteristics of the active-frequency control loop and the reactive-voltage control loop, a scientifically reasonable activation and deactivation sequence of the current limiting circuit is designed. Activating the current limiting circuit during the transient low-voltage phase at the DC sending end prevents excessive current from damaging the equipment; delaying the deactivation of the current limiting circuit during the transient overvoltage development phase effectively suppresses further increases in transient overvoltage; and deactivating the current limiting circuit before the DC system returns to stable control allows the system to return to normal operation. This coordinated activation and deactivation sequence design can promptly and effectively address the transient voltage rise problem during commutation failure, ensuring that the AC / DC power transmission system can still operate stably and reliably under complex operating conditions.

[0075] In this embodiment, the activation and deactivation sequence includes activating the current limiting circuit during the transient low voltage phase at the DC sending end, delaying the deactivation of the current limiting circuit during the transient overvoltage development phase, and deactivating the current limiting circuit before the DC system returns to stable control.

[0076] Example 2

[0077] Based on the same inventive concept as Embodiment 1, this embodiment introduces the implementation steps of a transient voltage rise suppression method during commutation failure in an AC / DC power transmission system with a grid-like device, including:

[0078] Step 1: Construct a hybrid AC / DC transmission system model that includes both grid-type and grid-connected equipment.

[0079] In this embodiment, the AC / DC hybrid power transmission system model includes a DC sending-end converter bus, and LCC-HVDC rectifier stations, grid-connected converters, grid-connected renewable energy units, and power generation units connected in parallel to the DC sending-end converter bus, such as... Figure 2 and Figure 3 As shown, where, For grid-connected generator terminal voltage, To match the output current of grid-connected units, For the voltage at the grid connection point of the new energy power station, and These represent the voltage and equivalent current at the converter bus at the sending end, respectively. and This represents the equivalent impedance of the collecting line and the equivalent impedance of the converter transformer.

[0080] Step 2: Based on the AC / DC hybrid power transmission system model, determine the dynamic coupling relationship between the transient voltage rise of the DC power transmission end converter bus and the active power deviation and reactive power deviation of each power unit when commutation fails.

[0081] Step 2.1: Establish the steady-state power balance equation of the DC sending-end converter bus.

[0082] In this embodiment, the steady-state power balance equation is expressed as:

[0083] ;

[0084] In the formula, , These represent the active power and reactive power transmitted by the thermal power unit, respectively. , These refer to the active power and reactive power transmitted by the new energy generating units, respectively. The active power transmitted by a DC system. The reactive power provided to the rectifier-side AC filter system This refers to the reactive power consumed during the rectification process of the rectifier.

[0085] In this embodiment, the voltage deviation equation is expressed as:

[0086] ;

[0087] In the formula, This refers to the voltage deviation at the rectifier-side converter bus during steady state. This is the steady-state voltage of the rectifier-side converter bus. and These represent the active power deviation and reactive power deviation of the line where the thermal power unit is located during the commutation failure period, respectively. and These represent the active power deviation and reactive power deviation of the line where the new energy unit is located during the commutation failure period, respectively. >0、 >0、 >0、 >0 represents the reactive power surplus and active power surplus of the lines where thermal power units and new energy units are located, respectively, both of which will lead to Increase , These are the equivalent reactances between thermal power units and new energy units and the DC system, respectively. , Approximately equal to 0.

[0088] Step 2.2: Based on the steady-state power balance equation, derive the voltage deviation equation when commutation fails.

[0089] Step 2.3: Based on the AC / DC hybrid power transmission system model and voltage deviation equation, determine the dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power unit.

[0090] When the sending-end system does not contain new energy units, based on the equivalent reactance of the sending-end system, the AC / DC hybrid sending-out system model and voltage deviation equation are used to determine the active power deficit at the sending end caused by the reduction of DC transmission power during the commutation failure period, and obtain the dynamic coupling relationship between transient voltage rise and active power deviation and reactive power deviation of each power unit.

[0091] When the sending-end system contains new energy sources, the power shunting characteristics of the active power deviation of the sending-end converter bus on the AC branch and the new energy grid-connected branch are considered. Based on the dynamic process of the reduction of DC transmission power during the commutation failure, the dynamic coupling relationship between transient voltage rise and active power deviation and reactive power deviation of each power unit is determined based on the AC / DC hybrid sending system model and voltage deviation equation.

[0092] In this embodiment, the dynamic coupling relationship between the transient voltage rise and the active power deviation and reactive power deviation of each power unit is expressed as follows:

[0093] ;

[0094] In the formula, This refers to the active power of the thermal power unit during the transient period. This refers to the active power of new energy sources during the transient period. It is the sum of the active power of thermal power units and new energy sources during the transient period.

[0095] Step 3: Establish a virtual synchronous control model for the network-type equipment based on the dynamic coupling relationship. The virtual synchronous control model includes at least an active-frequency control loop and a reactive-voltage control loop for outputting current commands, as well as a current limiting loop for constraining the current commands.

[0096] Step 3.1: Based on the regulation characteristics of the active-frequency control loop and reactive-voltage control loop of the network-type equipment, establish the basic control equations of the reactive-voltage control loop and the active-frequency control loop based on the dynamic coupling relationship.

[0097] In this embodiment, the basic control equations for the reactive-voltage control loop and the active-frequency control loop are expressed as follows:

[0098] ;

[0099] In the formula, , These represent the active power reference value and the active power of the network-type transmission, respectively. Indicates virtual damping. Represents virtual angular frequency. Represents virtual inertia. Indicates a virtual reference angle. Represents the fundamental value of the virtual internal potential. Represents the integral coefficient. Represents the complex frequency domain operator, This represents the voltage droop factor. Indicates the reference value of the grid connection point voltage. Indicates the actual voltage at the grid connection point. Represents the reactive power coefficient. Indicates the reactive power reference value. This indicates the reactive power exchanged by the sending system. Indicates the magnitude of the virtual internal potential. The time derivative of the virtual reference angle.

[0100] Step 3.2: Based on the reactive-voltage control loop control equation and the active-frequency control loop control equation, determine the relationship between reactive power and current of the grid-type equipment, as well as the relationship between active power and current. According to the characteristics of the virtual impedance link, obtain the current command equation generated by the virtual impedance circuit.

[0101] In this embodiment, the virtual impedance circuit generates a current command equation, which is expressed as:

[0102] ;

[0103] In the formula, Indicates converter shaft current, Indicates the actual voltage at the grid connection point. Indicates converter Axis current.

[0104] In this embodiment, under a synchronously rotating coordinate system, such as Figure 4 and Figure 5 As shown, the active power transmitted in the network configuration is expressed as:

[0105] ;

[0106] In the formula, Represents the sine function. This represents the phase angle of the virtual internal potential in the network configuration. Indicates the phase angle of the voltage at the grid connection point. Indicates the equivalent reactance of the network-type equipment. Indicates the gain coefficient. This indicates the phase difference.

[0107] In this embodiment, the sending-end system exchanges reactive power, which is represented as:

[0108] ;

[0109] In the formula, This represents the cosine function.

[0110] Step 3.3: Generate current command equations based on virtual impedance circuits, set current limiting links for the inner loop current of the network-type equipment, generate control logic for the current limiting links, and establish a virtual synchronous control model for the network-type equipment.

[0111] In this embodiment, the control logic of the current limiting circuit is expressed as follows:

[0112] , , ;

[0113] In the formula, This indicates the current reference value provided by the limiter. Indicates the current limiting factor. Indicates the current limiting value. Indicates the converter output current Actual value of the shaft Representing the virtual internal potential Axis component values, Indicates the voltage at the grid connection point Axis component values, Indicates the virtual resistance value. This represents the virtual inductance value.

[0114] Step 4: Based on the AC / DC hybrid power transmission system model and the virtual synchronous control model, by analyzing the transient characteristics during commutation failure, the activation and deactivation sequence of the current limiting link is designed according to the active-frequency control loop and the reactive-voltage control loop, so that the activation and deactivation sequence is coordinated with the switching sequence of the DC system control loop, and the relationship between the current output of the grid-type equipment and the converter station bus voltage during the fault is obtained, thereby suppressing the transient voltage rise during commutation failure.

[0115] In this embodiment, the activation and deactivation sequence includes activating the current limiting circuit during the transient low voltage phase at the DC sending end, delaying the deactivation of the current limiting circuit during the transient overvoltage development phase, and deactivating the current limiting circuit before the DC system returns to stable control.

[0116] In this embodiment, the relationship between the current output by the grid-type equipment during the fault and the converter station bus voltage is expressed as follows:

[0117] ;

[0118] In the formula, This indicates the output current of the network-type equipment. To take the real part of a complex number, " " indicates a ratio.

[0119] In this embodiment, the active power of the network transmission is given by the formula. Direction is Figure 4 The pink dashed arrow indicates the magnitude of the active power transmitted by the AC system. This indicates that its changing trend is consistent with the changing trend of the DC system's transmitted power. Shifting this phasor to the origin, as shown... Figure 5 As shown, using this phasor as a reference, the phasor of the sending system can be... Figure 5 With power characterization DC system Figure 2 When the reactive power of the sending system is obtained, the reactive power consumption of the rectifier increases significantly. At the same time, due to the control logic of the reactive current limiting circuit of the grid-type equipment, the voltage of the rectifier-side converter bus drops sharply.

[0120] In this embodiment, Figure 6 and Figure 7 The diagram shows the transient voltage and frequency characteristics of the system throughout the entire commutation failure process, where:

[0121] In the first stage, when the inverter side of the AC / DC hybrid power transmission system experiences three consecutive commutation failures, the DC current on the rectifier side increases instantaneously, the reactive power absorbed by the rectifier increases, and a transient voltage drop occurs on the sending-end converter bus. The DC power transmission drops sharply, and the sending-end system generates an active power surplus, causing the system frequency to rise. At this time, the grid-type equipment increases the virtual power angle based on the active-frequency control loop, injecting active power into the system. At the same time, the current limiting circuit is activated to limit the current command and support the temporary recovery of the voltage on the sending-end converter bus.

[0122] In the second stage, the current limiting circuit is deactivated later. At the same time, as the DC fault is cleared, the reactive power absorbed by the rectifier decreases, and a transient overvoltage occurs on the sending-end converter bus. Due to the delayed deactivation of the current limiting circuit, the rise of the transient overvoltage is suppressed.

[0123] In the third stage, after the low-voltage current limiting link of the DC system exits, the DC system control switches to constant current control mode; at this time, the current limiting link has completed its delayed exit, and the grid-type equipment has no power oscillation.

[0124] In the fourth stage, the DC system control switches to the current deviation control mode. The current limiting value of the current limiting circuit is first increased to the preset value and then restored to the normal operating limit. The system does not experience commutation failure again afterward.

[0125] Example 3

[0126] Based on the same inventive concept as other embodiments, this embodiment describes a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the steps of the methods of Embodiment 1 or 2 described above.

[0127] In summary, this invention constructs a hybrid AC / DC power transmission system model containing grid-type and grid-connected equipment. It analyzes the dynamic coupling relationship between the transient voltage rise of the DC-end converter bus and the active and reactive power deviations of each power unit during commutation failure. Based on this, a virtual synchronous control model for the grid-type equipment is established, including an active-frequency control loop and a reactive-voltage control loop for output current commands, as well as a current limiting loop for constraining current commands. Furthermore, the transient characteristics during commutation failure are analyzed, and a scheme is designed to coordinate the switching timing of the current limiting loop with the switching timing of the DC system control loop. The relationship between the current output by the grid-type equipment and the converter station bus voltage during the fault is obtained, suppressing the transient voltage rise during commutation failure. This effectively enhances the suppression effect of the grid-type equipment on the transient voltage rise of the DC-end converter bus during commutation failure, reduces the risk of power oscillation and multiple commutation failures, and improves the operational stability of the AC / DC power transmission system.

[0128] This invention constructs a hybrid AC / DC power transmission system model, including an LCC-HVDC rectifier station, a grid-connected converter, grid-connected renewable energy units, and power generation units. Based on this model, it establishes the steady-state power balance equation for the DC sending-end converter bus, and then derives the voltage deviation equation for commutation failure. Furthermore, it analyzes the dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power generation unit, respectively, for cases where the sending-end system contains and does not contain renewable energy units. This allows for targeted measures to suppress transient voltage rise, fundamentally improving the effectiveness and relevance of the suppression method.

[0129] This invention establishes a virtual synchronous control model for grid-type equipment based on dynamic coupling relationships. It includes an active-frequency control loop and a reactive-voltage control loop for outputting current commands, as well as a current limiting loop for constraining current commands. By establishing basic control equations based on the regulation characteristics of the grid-type equipment, analyzing the relationship between reactive power and current, and active power and current, and combining the characteristics of the virtual impedance loop, the current command generation equation of the virtual impedance circuit is obtained. Furthermore, the control logic of the current limiting loop is set, enabling the grid-type equipment to more accurately simulate the output characteristics of a synchronous generator. This allows for better regulation of active and reactive power during commutation failures, effectively enhancing the suppression of transient voltage rise on the DC sending-end converter bus and avoiding power oscillations and multiple commutation failures caused by improper regulation of the grid-type equipment.

[0130] This invention, based on an AC / DC hybrid power transmission system model and a virtual synchronous control model, analyzes the transient characteristics during commutation failure and designs a scheme to coordinate the activation and deactivation timing of the current limiting circuit with the switching timing of the DC system control circuit. It derives the relationship between the output current of the grid-type equipment and the converter station bus voltage during the fault, suppressing transient voltage rise during commutation failure. Specifically, activating the current limiting circuit during the transient low voltage stage at the DC sending end prevents excessive current from damaging the equipment; delaying the deactivation of the current limiting circuit during the transient overvoltage development stage effectively suppresses further increases in transient overvoltage; and deactivating the current limiting circuit before the DC system returns to stable control allows the system to return to normal operation. This invention fully considers various transient characteristics of the system during commutation failure, enabling timely and effective responses to transient voltage rise issues, ensuring the stable operation of the AC / DC power transmission system during commutation failure, and improving the overall system reliability and safety.

[0131] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0132] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0133] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0134] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0135] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system containing a grid-type equipment, characterized in that, include: Construct a hybrid AC / DC transmission system model for both grid-type and grid-connected equipment; Based on the AC / DC hybrid power transmission system model, the dynamic coupling relationship between the transient voltage rise of the DC power transmission end converter bus and the active power deviation and reactive power deviation of each power unit is determined when commutation fails. A virtual synchronous control model for the network-type equipment is established based on the dynamic coupling relationship. The virtual synchronous control model includes at least an active-frequency control loop and a reactive-voltage control loop for outputting current commands, as well as a current limiting loop for constraining the current commands. Based on the AC / DC hybrid power transmission system model and the virtual synchronous control model, by analyzing the transient characteristics during commutation failure, the current limiting loop is designed according to the active-frequency control loop and the reactive-voltage control loop, so that the activation and deactivation sequence is coordinated with the switching sequence of the DC system control loop. The relationship between the current output of the grid-type equipment and the converter station bus voltage during the fault is obtained, and the transient voltage rise during commutation failure is suppressed. The activation and deactivation sequence includes activating the current limiting circuit during the transient low voltage phase at the DC sending end, delaying the deactivation of the current limiting circuit during the transient overvoltage development phase, and deactivating the current limiting circuit before the DC system returns to stable control.

2. The method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-like structure as described in claim 1, characterized in that, The AC / DC hybrid power transmission system model includes a DC sending-end converter bus, and LCC-HVDC rectifier stations, grid-type converters, grid-connected new energy units and power units connected in parallel to the DC sending-end converter bus.

3. The method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-like structure as described in claim 1, characterized in that, Based on the AC / DC hybrid power transmission system model, the dynamic coupling relationship between the transient voltage rise of the DC sending-end converter bus and the active power deviation and reactive power deviation of each power unit during commutation failure is determined, including: Establish the steady-state power balance equation for the DC sending-end converter bus; Based on the steady-state power balance equation, the voltage deviation equation for commutation failure is derived. Based on the AC / DC hybrid power transmission system model and voltage deviation equation, the dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power unit is determined.

4. The method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-like structure as described in claim 3, characterized in that, The steady-state power balance equation is expressed as: ； In the formula, , These represent the active power and reactive power transmitted by the thermal power unit, respectively. , These refer to the active power and reactive power transmitted by the new energy generating units, respectively. The active power transmitted by a DC system. The reactive power provided to the rectifier-side AC filter system This refers to the reactive power consumed during the rectification process of the rectifier; The voltage deviation equation is expressed as: ； In the formula, This refers to the voltage deviation at the rectifier-side converter bus during steady state. This is the steady-state voltage of the rectifier-side converter bus. and These represent the active power deviation and reactive power deviation of the line where the thermal power unit is located during the commutation failure period, respectively. and These represent the active power deviation and reactive power deviation of the line where the new energy unit is located during the commutation failure period, respectively. >0、 >0、 >0、 >0 represents the reactive power surplus and active power surplus of the lines where thermal power units and new energy units are located, respectively, both of which will lead to Increase , These are the equivalent reactances between thermal power units and new energy units and the DC system, respectively. , Approximately equal to 0.

5. The method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-like structure as described in claim 4, characterized in that, Based on the AC / DC hybrid power transmission system model and voltage deviation equation, the dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power unit is determined, including: When the sending-end system does not contain new energy units, based on the equivalent reactance of the sending-end system, the AC / DC hybrid sending-out system model and voltage deviation equation are used to determine the active power deficit at the sending end caused by the reduction of DC transmission power during the commutation failure period, and obtain the dynamic coupling relationship between transient voltage rise and active power deviation and reactive power deviation of each power unit. When the sending-end system contains new energy sources, the power shunting characteristics of the active power deviation of the sending-end converter bus on the AC branch and the new energy grid-connected branch are considered. Based on the dynamic process of the reduction of DC transmission power during the commutation failure, the dynamic coupling relationship between transient voltage rise and active power deviation and reactive power deviation of each power unit is determined based on the AC / DC hybrid sending system model and voltage deviation equation. The dynamic coupling relationship between transient voltage rise and the active and reactive power deviations of each power unit is expressed as follows: ； In the formula, This refers to the active power of the thermal power unit during the transient period. This refers to the active power of new energy sources during the transient period. It is the sum of the active power of thermal power units and new energy sources during the transient period.

6. The method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-like structure as described in claim 1, characterized in that, A virtual synchronization control model for network-type devices is established based on the aforementioned dynamic coupling relationship, including: Based on the adjustment characteristics of the active-frequency control loop and the reactive-voltage control loop of the network-type equipment, the basic control equations of the reactive-voltage control loop and the active-frequency control loop are established based on the dynamic coupling relationship. Based on the reactive-voltage control loop control equation and the active-frequency control loop control equation, the relationship between reactive power and current of grid-type equipment, as well as the relationship between active power and current, are determined. According to the characteristics of the virtual impedance link, the current command equation for the virtual impedance circuit is obtained. Based on the virtual impedance circuit, a current command equation is generated, a current limiting link for the inner loop current of the network-type equipment is set, the control logic of the current limiting link is generated, and a virtual synchronous control model for the network-type equipment is established.

7. The method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-like structure as described in claim 6, characterized in that, The basic control equations for the reactive-voltage control loop and the active-frequency control loop are expressed as follows: ； In the formula, , These represent the active power reference value and the active power of the network-type transmission, respectively. Indicates virtual damping. Represents virtual angular frequency. Represents virtual inertia. Indicates a virtual reference angle. Represents the fundamental value of the virtual internal potential. Represents the integral coefficient. Represents the complex frequency domain operator, This represents the voltage droop factor. Indicates the reference value of the grid connection point voltage. Indicates the actual voltage at the grid connection point. Represents the reactive power coefficient. Indicates the reactive power reference value. This indicates the reactive power exchanged by the sending system. Indicates the magnitude of the virtual internal potential. The time derivative of the virtual reference angle.

8. The method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-like structure, as described in claim 7, is characterized in that... The virtual impedance circuit generates the current command equation, which is expressed as: The virtual impedance circuit generates the current command equation, which is expressed as: ； In the formula, Indicates converter shaft current, Indicates the actual voltage at the grid connection point. Indicates converter shaft current; The active power of the network-type transmission is expressed as: ； In the formula, Represents the sine function. This represents the phase angle of the virtual internal potential in the network configuration. Indicates the phase angle of the voltage at the grid connection point. Indicates the equivalent reactance of the network-type equipment. Indicates the gain coefficient. Indicates the phase difference; The reactive power exchanged by the sending-end system is expressed as: ； In the formula, Represents the cosine function; The control logic of the current limiting circuit is expressed as follows: ， ， ； In the formula, This indicates the current reference value provided by the limiter. Indicates the current limiting factor. Indicates the current limiting value. Indicates the converter output current Actual value of the shaft Representing the virtual internal potential Axis component values, Indicates the voltage at the grid connection point Axis component values, Indicates the virtual resistance value. This represents the virtual inductance value.

9. The method for suppressing transient voltage rise during commutation failure in an AC / DC power transmission system with a grid-like structure as described in claim 8, characterized in that, The relationship between the current output by the grid-type equipment and the converter station bus voltage during the fault is expressed as follows: ； In the formula, This indicates the output current of the network-type equipment. To take the real part of a complex number, " " indicates a ratio.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the transient voltage rise suppression method during commutation failure of the AC / DC power transmission system of the structured network equipment as described in any one of claims 1-9.

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