A new energy and reactive power compensation collaborative commutation failure resisting method and system

Abstract

The present application relates to the technical field of high-voltage direct-current transmission system stability control, and particularly relates to a new energy and reactive power compensation collaborative commutation failure resisting method and system, comprising: a high-voltage direct-current receiving end system multi-reactive power source dynamic equivalent modeling method, according to the capacity proportion and regulation rate of the inverter of the grid-connected new energy unit and the static synchronous compensator, a coupled fast-slow dynamic subsystem model is established; a multi-time scale layered time sequence collaborative control architecture is designed, and the whole process of power grid fault is divided into a fault transient stage and a voltage recovery stage; based on the coupled fast-slow dynamic subsystem model, a reactive power distribution objective function is constructed, which takes into account the dynamic margin of the static synchronous compensator and the operation safety and voltage quality of the grid-connected new energy unit; in the fault transient stage, the fast dynamic subsystem model is used to execute strong excitation reactive power control on the static synchronous compensator, and the voltage at the point of common coupling is clamped above the critical commutation voltage.

Description

Technical Field

[0001] This invention relates to the technical field of stability control of high-voltage direct current transmission systems, and in particular to a method and system for mitigating commutation failure through the synergy of new energy sources and reactive power compensation. Background Technology

[0002] With the advancement of the "dual-carbon" strategy, a new power system based on new energy sources has become the core direction of energy transformation, and large-scale grid-connected new energy transmission via high-voltage direct current has become the mainstream consumption mode. However, the receiving-end power grid exhibits "strong DC and weak AC" characteristics due to the declining proportion of traditional synchronous power sources. This leads to a decrease in the system's short-circuit ratio and a weakening of voltage disturbance immunity. In the event of an AC fault on the inverter side, commutation failure or even continuous commutation failure can easily be induced, seriously threatening the safe and stable operation of the system.

[0003] Current research on commutation failure mitigation mainly focuses on two directions: single-device optimization and multi-device collaborative control. In single-device optimization, static synchronous compensators (SRCs) have a fast response and can improve transient voltage recovery rates, but due to cost and capacity limitations, they cannot cover the reactive power demand throughout the entire fault cycle. Grid-connected renewable energy units can participate in reactive power support through low-voltage ride-through capabilities, but due to the dynamic characteristics of phase-locked loops (PLLs), they exhibit response lag under severe faults, making it difficult to meet the millisecond-level ultra-fast response requirements. To overcome the limitations of single devices, research on multi-reactive-source collaboration has been initiated. Existing solutions mostly focus on steady-state or slow-dynamic reactive power distribution, or adopt multi-device synchronous triggering modes, without considering the timing coordination design for the differences in response characteristics between the two types of devices. This makes it impossible to balance ultra-fast transient support during faults with margin reserves during the recovery phase, making it difficult to prevent the first wave of commutation failures and easily inducing continuous commutation failures, resulting in poor overall system anti-disturbance performance. Summary of the Invention

[0004] This invention provides a method and system for resisting commutation failures by combining new energy sources and reactive power compensation, which can improve the ability of a high-voltage DC weak receiving-end power grid to resist continuous commutation failures and enhance the transient voltage stability of the system. It can effectively solve the problems in the background art.

[0005] To achieve the above objectives, this invention provides a method and system for mitigating commutation failure through the synergy of new energy sources and reactive power compensation, comprising the following steps: Based on the dynamic equivalent modeling method of multiple reactive power sources in high voltage DC receiving-end system, a coupled fast and slow dynamic subsystem model is established according to the capacity ratio and regulation rate of inverter and static synchronous compensator of grid-connected new energy unit. Design a multi-timescale hierarchical time-series collaborative control architecture to divide the entire power grid fault process into a fault transient stage and a voltage recovery stage; Based on the coupled fast and slow dynamic subsystem model, a reactive power distribution objective function is constructed that takes into account both the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected new energy units. During the fault transient phase, the static synchronous compensator is subjected to forced excitation reactive power control based on the coupled fast and slow dynamic subsystem model, clamping the voltage at the common coupling point above the critical commutation voltage. During the voltage recovery phase, the renewable energy units are controlled to take over reactive power support based on the coupled fast and slow dynamic subsystem model and the reactive power distribution objective function, and the reactive power output of the static synchronous compensator and the grid-connected renewable energy units is smoothly and collaboratively transferred through the voltage at the common coupling point.

[0006] Furthermore, a coupled fast and slow dynamic subsystem model is established, including the following steps: A quasi-steady-state model of the inverter side of the high-voltage DC receiving-end system was established to clarify the evolution mechanism of commutation failure and the voltage constraint boundary. A slow-dynamic subsystem model of a grid-connected new energy unit and a fast-dynamic subsystem model of a static synchronous compensator were established to quantify the differences in multi-timescale response characteristics between the two types of equipment. Based on the Thevenin equivalent circuit of the power grid, the fast dynamic subsystem model and the slow dynamic subsystem model are coupled to obtain a coupled fast and slow dynamic subsystem model, which characterizes the dynamic interaction characteristics of the two types of equipment.

[0007] Furthermore, the establishment of the quasi-steady-state model of the inverter side of the high-voltage DC receiving-end system specifically describes the voltage-current relationship on the inverter side through quasi-steady-state mathematical equations. The expression of the quasi-steady-state mathematical equations is as follows: In the formula, This refers to the no-load DC voltage on the rectifier side and the inverter side; , These are the effective values ​​of the AC bus voltages on the rectifier and inverter sides. This refers to the critical effective value of the AC side line voltage of the converter bus. This refers to the DC line current. The reactive power consumed by the converter; For DC line resistance; , The equivalent leakage reactance of the converter transformers on the rectifier and inverter sides includes the equivalent inductance of the AC system and the leakage reactance of the converter transformers. These are the transformer turns ratio and the number of six-pulse converter bridges connected in series, respectively. The inverter-side delayed firing angle, It is a leading trigger angle. The inverter-side shut-off angle. Its commutation overlap angle; This refers to the active power transmitted by the LCC on the inverter side. Power factor; This is the zero-crossing offset angle of the commutation voltage.

[0008] Furthermore, the establishment of a slow-dynamic subsystem model for the grid-connected new energy unit specifically characterizes the decoupling control relationship between the unit's active and reactive power outputs and the voltage and output current at the point of common coupling through a power equation. The power equation is as follows: In the formula For the voltage at the common coupling point Axial components; The output current component; controlled by Active power can be controlled ,control Reactive power can be controlled ; The phase tracking characteristics of the phase-locked loop of the unit's synchronous rotating coordinate system are characterized by the current inner loop control equation, which is as follows: In the formula , This is the reference voltage command for the converter; The fundamental angular frequency of the power grid; For filtering inductors; , These are the proportional and integral gain coefficients; , These are reference values ​​for the d-axis and q-axis currents. , These are the actual current feedback values ​​for the d and q axes. Rapid current tracking is achieved through inner-loop control. The effective reactive current generation logic injected into the grid by the generating unit is characterized by the reactive response equation, which is: In the formula The phase angle of the phase-locked loop output; The rated angular frequency of the power grid; This represents the q-axis component of the voltage at the common coupling point.

[0009] Furthermore, a fast dynamic subsystem model of the static synchronous compensator is established. Specifically, the current dynamic characteristics of the static synchronous compensator connected to the power grid are characterized by the AC side dynamic equations. The AC side dynamic equations are as follows: In the formula Injecting grid current into the static synchronous compensator Axial components; For the voltage at the access point Axial components; The output voltage component of the static synchronous compensator bridge arm; The inductance value of the connected reactor; The generation logic of inductive reactive power in a static synchronous compensator is characterized by a reactive power output equation, which is: Static synchronous compensator injects reactive current For the converter bus voltage The lifting effect can be achieved using the short-circuit impedance of the receiving-end power grid. Approximate description; The voltage rise characteristic equation characterizes the effect of reactive power injection by the static synchronous compensator on the converter bus voltage. The voltage rise characteristic equation is as follows: In the formula, SCR is the system short-circuit ratio; The reference value for injecting reactive current into the static synchronous compensator.

[0010] Furthermore, the fast-dynamic subsystem model and the slow-dynamic subsystem model are coupled. Specifically, the voltage dynamic sensitivity equation characterizes the correlation between the voltage change at the common coupling point and the total reactive current injection. The voltage dynamic sensitivity equation is as follows: In the formula, The short-circuit reactance of the system characterizes the sensitivity of the weak receiving-end power grid to reactive current. , These refer to the reactive current injection of the static synchronous compensator and the inverter of the grid-connected new energy unit, respectively.

[0011] Furthermore, the proposed multi-timescale hierarchical timing cooperative control architecture divides the entire power grid fault process into a fault transient phase and a voltage recovery phase, specifically including: Based on the evolution mechanism of commutation failure and the characteristics of grid voltage recovery, a two-stage hierarchical timing control architecture is constructed, which combines fault transient rapid support and voltage recovery relay coordination. The time period from 10ms to 50ms after the occurrence of grid fault is divided into the fault transient stage, and the time period of grid fault duration exceeding 50ms is divided into the voltage recovery stage.

[0012] Furthermore, the construction of the two-stage hierarchical timing control architecture specifically uses a state equation with voltage deviation as the core to characterize the dynamic evolution of the voltage at the common coupling point. The state equation is as follows: In the formula, , , This represents the time derivative of the static synchronous compensator, the grid-connected new energy unit inverter, and the load current. The extremely fast response characteristics of the static synchronous compensator to voltage deviation during the fault transient stage are characterized by the fast subsystem convergence characteristic equation. The fast subsystem convergence characteristic equation is as follows: The equivalent time constant of the inner current loop closed loop; , These are the second and first derivatives of the voltage at the grid connection point.

[0013] Furthermore, based on the coupled fast and slow dynamic subsystem model, a reactive power distribution objective function is constructed that takes into account both the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected renewable energy units. Specifically, with the goal of minimizing the overall system operational risk, a weighted objective function is constructed. The weighted objective function includes three weighted terms: a dynamic margin term for penalizing the steady-state output of the static synchronous compensator, a load rate term for penalizing the full-load level of grid-connected renewable energy units, and a voltage deviation term for constraining the grid voltage control accuracy. These terms are then summed using preset weighting coefficients.

[0014] Furthermore, the forced excitation reactive power control of the static synchronous compensator specifically involves: when the voltage drop amplitude at the common coupling point exceeds a preset start-up threshold, the static synchronous compensator is switched from the conventional voltage regulation mode to the variable structure forced excitation mode. The reactive power output target is directly set through the forced excitation mode current command equation, bypassing the voltage outer loop PI control, to achieve millisecond-level full reactive current output. The forced excitation mode current command equation is as follows: In the formula, This is the optimal feedforward instruction. This represents the total steady-state reactive power demand of the system after low-pass filtering. For the amplitude limiting function, its upper bound is... The remaining capacity of the inverter in the grid-connected new energy unit is dynamically determined by the definition.

[0015] This invention also provides a commutation failure mitigation system that combines new energy sources and reactive power compensation, comprising: The dynamic modeling module is based on the dynamic equivalent modeling method of multiple reactive sources in the high voltage DC receiving-end system. According to the capacity ratio and regulation rate of the inverter and static synchronous compensator of the grid-connected new energy unit, a coupled fast and slow dynamic subsystem model is established. The timing architecture module designs a multi-timescale hierarchical timing collaborative control architecture, dividing the entire power grid fault process into a fault transient phase and a voltage recovery phase. The objective function construction module, based on the coupled fast and slow dynamic subsystem model, constructs a reactive power distribution objective function that takes into account both the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected new energy units. The transient forced excitation control module performs forced excitation reactive power control on the static synchronous compensator based on the coupled fast and slow dynamic subsystem model during the fault transient phase, clamping the voltage at the common coupling point above the critical commutation voltage. In the steady-state relay coordination module, during the voltage recovery phase, the new energy generating units take over the reactive power support based on the coupled fast and slow dynamic subsystem model and the reactive power distribution objective function, and achieve smooth coordinated handover of reactive power output between the static synchronous compensator and the grid-connected new energy generating units through the common coupling point voltage.

[0016] The technical solution of this invention can achieve the following technical effects: This invention establishes a coupled fast-slow dynamic subsystem model that matches the response characteristics of the static synchronous compensator and the grid-connected renewable energy units. It designs a phased time-series coordinated control architecture for the entire fault cycle and constructs a multi-dimensional constrained reactive power allocation objective function. This can accurately match the multi-timescale response differences of the two types of equipment, fill the reactive power output gap of renewable energy in the early stage of a fault, block the first wave of commutation failure, achieve a smooth handover of the main reactive power support, release the dynamic margin of the static synchronous compensator, improve the ability of the weak receiving end of the high-voltage DC grid to resist continuous commutation failure, and enhance the transient voltage stability of the system. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the commutation failure mitigation method of the coordinated new energy source and reactive power compensation in this invention. Figure 2 This is a schematic diagram of the structure of a high-voltage direct current receiving-end system containing multiple reactive power sources; Figure 3 For the control topology diagram of the grid-type fan; Figure 4 Comparison of voltage response waveforms at the common coupling point under different control methods; Figure 5 For collaborative control logic diagram; Figure 6 The transient response results of the grid-connected wind turbine and the static synchronous compensator are shown in the figure. Figure 7 The diagram shows the commutation failure and dynamic response results of a single-device system. Figure 8Figure showing the commutation failure and dynamic response results of a multi-reactive power feeder collaborative control system. Figure 9 This is a schematic diagram of the commutation failure mitigation system that combines new energy sources and reactive power compensation in this invention. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] like Figure 1 As shown, the present invention provides a method for mitigating commutation failure through the coordinated use of new energy sources and reactive power compensation, which specifically includes the following steps: Based on the dynamic equivalent modeling method of multiple reactive power sources in high voltage DC receiving-end system, a coupled fast and slow dynamic subsystem model is established according to the capacity ratio and regulation rate of inverter and static synchronous compensator of grid-connected new energy unit. Design a multi-timescale hierarchical time-series collaborative control architecture to divide the entire power grid fault process into a fault transient stage and a voltage recovery stage; Based on the coupled fast and slow dynamic subsystem model, a reactive power distribution objective function is constructed that takes into account both the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected new energy units. During the fault transient phase, the static synchronous compensator is subjected to forced excitation reactive power control based on the coupled fast and slow dynamic subsystem model, clamping the voltage at the common coupling point above the critical commutation voltage. During the voltage recovery phase, the renewable energy units are controlled to take over reactive power support based on the coupled fast and slow dynamic subsystem model and the reactive power distribution objective function, and the reactive power output of the static synchronous compensator and the grid-connected renewable energy units is smoothly and collaboratively transferred through the voltage at the common coupling point.

[0023] This invention establishes a coupled fast-slow dynamic subsystem model that matches the response characteristics of the static synchronous compensator and the grid-connected renewable energy units. It designs a phased time-series coordinated control architecture for the entire fault cycle and constructs a multi-dimensional constrained reactive power allocation objective function. This can accurately match the multi-timescale response differences of the two types of equipment, fill the reactive power output gap of renewable energy in the early stage of a fault, block the first wave of commutation failure, achieve a smooth handover of the main reactive power support, release the dynamic margin of the static synchronous compensator, improve the ability of the weak receiving end of the high-voltage DC grid to resist continuous commutation failure, and enhance the transient voltage stability of the system.

[0024] Based on the above embodiments, a coupled fast and slow dynamic subsystem model is established, including the following steps: A quasi-steady-state model of the inverter side of the high-voltage DC receiving-end system was established to clarify the evolution mechanism of commutation failure and the voltage constraint boundary. A slow-dynamic subsystem model of a grid-connected new energy unit and a fast-dynamic subsystem model of a static synchronous compensator were established to quantify the differences in multi-timescale response characteristics between the two types of equipment. Based on the Thevenin equivalent circuit of the power grid, the fast dynamic subsystem model and the slow dynamic subsystem model are coupled to obtain a coupled fast and slow dynamic subsystem model, which characterizes the dynamic interaction characteristics of the two types of equipment.

[0025] By establishing a quasi-steady-state model of the inverter side of the high-voltage DC receiving-end system, a slow-dynamic subsystem model of the grid-connected new energy unit and a fast-dynamic subsystem model of the static synchronous compensator are constructed respectively. Based on the Thevenin equivalent circuit of the power grid, the two types of models are coupled, which can clarify the evolution mechanism and critical voltage constraint of commutation failure, accurately quantify the difference in response characteristics between the two types of equipment, clearly characterize the dynamic interaction law between the equipment, provide accurate model support for subsequent coordinated control, and improve the adaptability of commutation failure mitigation strategies.

[0026] Based on the above embodiments, the establishment of the quasi-steady-state model of the inverter side of the high-voltage DC receiving-end system specifically describes the voltage-current correlation on the inverter side through quasi-steady-state mathematical equations. The expression of the quasi-steady-state mathematical equations is as follows: In the formula, This refers to the no-load DC voltage on the rectifier side and the inverter side; , These are the effective values ​​of the AC bus voltages on the rectifier and inverter sides. This refers to the critical effective value of the AC side line voltage of the converter bus. This refers to the DC line current. The reactive power consumed by the converter; For DC line resistance; , The equivalent leakage reactance of the converter transformers on the rectifier and inverter sides includes the equivalent inductance of the AC system and the leakage reactance of the converter transformers. These are the transformer turns ratio and the number of six-pulse converter bridges connected in series, respectively. The inverter-side delayed firing angle, It is a leading trigger angle. The inverter-side shut-off angle. Its commutation overlap angle; This refers to the active power transmitted by the LCC on the inverter side. Power factor; This is the zero-crossing offset angle of the commutation voltage.

[0027] By describing the voltage and current relationship on the inverter side of the high-voltage DC receiving-end system using quasi-steady-state mathematical equations, the mapping logic between various electrical parameters and the commutation process is clarified. This enables precise characterization of the commutation electrical characteristics on the inverter side, clarifies the evolution mechanism of commutation failure, quantifies the impact of key parameters on the commutation process, and defines the critical voltage constraint boundary for commutation failure. This provides precise underlying support for subsequent dynamic modeling and coordinated control, and improves the accuracy of judging the critical conditions for commutation failure.

[0028] Based on the above embodiments, the establishment of a slow-dynamic subsystem model for grid-connected new energy generating units specifically characterizes the decoupling control relationship between the unit's active and reactive power outputs and the voltage and output current at the point of common coupling through a power equation. The power equation is as follows: In the formula For the voltage at the common coupling point Axial components; The output current component; controlled by Active power can be controlled ,control Reactive power can be controlled ; The phase tracking characteristics of the phase-locked loop of the unit's synchronous rotating coordinate system are characterized by the current inner loop control equation, which is as follows: In the formula , This is the reference voltage command for the converter; The fundamental angular frequency of the power grid; For filtering inductors; , These are the proportional and integral gain coefficients; , These are reference values ​​for the d-axis and q-axis currents. , These are the actual current feedback values ​​for the d and q axes. Rapid current tracking is achieved through inner-loop control. The effective reactive current generation logic injected into the grid by the generating unit is characterized by the reactive response equation, which is: In the formula The phase angle of the phase-locked loop output; The rated angular frequency of the power grid; This represents the q-axis component of the voltage at the common coupling point.

[0029] By characterizing the decoupling control relationship between the active and reactive power outputs of the generator unit and the voltage and output current at the common coupling point through the power equation, characterizing the phase tracking characteristics of the generator unit's phase-locked loop through the current inner loop control equation, and characterizing the effective reactive current generation logic injected into the grid by the generator unit through the reactive response equation, it is possible to accurately quantify the slow dynamic response characteristics of grid-connected new energy generator units, clarify the coupling effect of phase-locked loop dynamics on reactive power output, clarify the underlying control logic of generator unit reactive power regulation, and improve the control accuracy of reactive power support strategy.

[0030] Based on the above embodiments, a fast dynamic subsystem model of the static synchronous compensator is established. Specifically, the current dynamic characteristics of the static synchronous compensator connected to the power grid are characterized by the AC side dynamic equations. The AC side dynamic equations are as follows: In the formula Injecting grid current into the static synchronous compensator Axial components; For the voltage at the access point Axial components; The output voltage component of the static synchronous compensator bridge arm; The inductance value of the connected reactor; The generation logic of inductive reactive power in a static synchronous compensator is characterized by a reactive power output equation, which is: Static synchronous compensator injects reactive current For the converter bus voltage The lifting effect can be achieved using the short-circuit impedance of the receiving-end power grid. Approximate description; The voltage rise characteristic equation characterizes the effect of reactive power injection by the static synchronous compensator on the converter bus voltage. The voltage rise characteristic equation is as follows: In the formula, SCR is the system short-circuit ratio; The reference value for injecting reactive current into the static synchronous compensator.

[0031] By characterizing the current dynamic characteristics of the static synchronous compensator connected to the grid through the AC side dynamic equation, the reactive power output equation characterizes its inductive reactive power generation logic, and the voltage rise characteristic equation characterizes the regulation effect of reactive power injection on the converter bus voltage, the fast dynamic response characteristics of the static synchronous compensator can be accurately quantified, the mapping relationship between reactive power injection and bus voltage regulation can be clarified, and the underlying logic of its fast reactive power support can be defined. This provides accurate model support for fault transient excitation control and improves the response speed of commutation failure prevention and control strategies.

[0032] Based on the above embodiments, the fast dynamic subsystem model and the slow dynamic subsystem model are coupled. Specifically, the voltage dynamic sensitivity equation characterizes the correlation between the voltage change at the common coupling point and the total reactive current injection. The voltage dynamic sensitivity equation is as follows: In the formula, The short-circuit reactance of the system characterizes the sensitivity of the weak receiving-end power grid to reactive current. , These refer to the reactive current injection of the static synchronous compensator and the inverter of the grid-connected new energy unit, respectively.

[0033] By establishing the correlation between the voltage change at the common coupling point and the total reactive current injection through the voltage dynamic sensitivity equation, the fast and slow dynamic subsystem models are coupled, which can accurately reflect the sensitivity of the weak receiving end grid voltage to reactive current injection, fully characterize the dynamic interaction characteristics of the two types of equipment, unify the collaborative interface of fast and slow dynamic responses, provide a reliable theoretical basis for phased collaborative control, and improve the rationality of the overall control strategy.

[0034] Based on the above embodiments, the design of the multi-timescale hierarchical timing cooperative control architecture divides the entire power grid fault process into a fault transient stage and a voltage recovery stage, specifically including: Based on the evolution mechanism of commutation failure and the characteristics of grid voltage recovery, a two-stage hierarchical timing control architecture is constructed, which combines fault transient rapid support and voltage recovery relay coordination. The time period from 10ms to 50ms after the occurrence of grid fault is divided into the fault transient stage, and the time period of grid fault duration exceeding 50ms is divided into the voltage recovery stage.

[0035] By constructing a two-stage hierarchical timing control architecture that coordinates fault transient rapid support and voltage recovery relay, and precisely dividing the control stages according to the fault timing, it can fully match the dynamic response differences between static synchronous compensators and grid-connected new energy units, rationally allocate reactive power support tasks at different fault stages, avoid control timing misalignment, effectively fill the voltage support gap caused by the lag in new energy response, and improve the pertinence of commutation failure mitigation strategies and the effect of transient voltage stability control.

[0036] Based on the above embodiments, the construction of a two-stage hierarchical timing control architecture specifically uses a state equation with voltage deviation as the core to characterize the dynamic evolution of the voltage at the common coupling point. The state equation is as follows: In the formula, , , This represents the time derivative of the static synchronous compensator, the grid-connected new energy unit inverter, and the load current. The extremely fast response characteristics of the static synchronous compensator to voltage deviation during the fault transient stage are characterized by the fast subsystem convergence characteristic equation. The fast subsystem convergence characteristic equation is as follows: The equivalent time constant of the inner current loop closed loop; , These are the second and first derivatives of the voltage at the grid connection point.

[0037] By characterizing the dynamic evolution of the voltage at the common coupling point through the voltage deviation state equation and the convergence characteristic equation of the fast subsystem to depict the ultra-fast response characteristics of the static synchronous compensator, we can accurately describe the intrinsic relationship between voltage changes and equipment response throughout the fault process, clearly define the control boundaries of transient rapid support and steady-state smooth recovery, provide a precise theoretical basis for phased collaborative control, and improve the reliability and voltage recovery efficiency of the overall control strategy.

[0038] Based on the above embodiments, and based on the coupled fast and slow dynamic subsystem model, a reactive power distribution objective function is constructed that takes into account the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected new energy units. Specifically, with the goal of minimizing the overall system operational risk, a weighted objective function is constructed. The weighted objective function includes three weighted terms: a dynamic margin term for penalizing the steady-state output of the static synchronous compensator, a load rate term for penalizing the full-load level of grid-connected new energy units, and a voltage deviation term for constraining the grid voltage control accuracy. These terms are then summed using preset weighting coefficients.

[0039] By constructing a weighted reactive power allocation objective function that takes into account dynamic margin, unit safety, and voltage quality, and rationally allocating the weights of the three types of constraint terms, it is possible to ensure that the static synchronous compensator retains sufficient dynamic reserve while constraining the unit to operate within a safe range, accurately suppressing voltage deviations, achieving optimal allocation of reactive power resources, and improving the overall system's ability to withstand commutation failures and its voltage stability level.

[0040] Based on the above embodiments, the forced excitation reactive power control of the static synchronous compensator specifically involves: when the voltage drop amplitude at the common coupling point exceeds a preset start-up threshold, the static synchronous compensator is switched from the conventional voltage regulation mode to the variable structure forced excitation mode. The reactive power output target is directly set through the forced excitation mode current command equation, bypassing the voltage outer loop PI control link, to achieve millisecond-level full reactive current output. The forced excitation mode current command equation is as follows: In the formula, This is the optimal feedforward instruction. This represents the total steady-state reactive power demand of the system after low-pass filtering. For the amplitude limiting function, its upper bound is... The remaining capacity of the inverter in the grid-connected new energy unit is dynamically determined by the definition.

[0041] By switching to the variable structure forced excitation mode when the voltage drops below the threshold, and directly setting the reactive power output using the forced excitation mode current command equation, the conventional control loop can be bypassed to achieve millisecond-level full reactive power output, quickly raising the common coupling point voltage to a safe level, blocking the first wave of commutation failure, and improving the fault transient voltage support speed and the reliability of commutation failure resistance.

[0042] like Figures 2 to 8 As shown, based on the above embodiments, a receiving-end simulation model including grid-connected wind turbines and static synchronous compensators is built based on the standard CIGRE high-voltage direct current transmission system to verify the cooperative control method. DC side rated transmission power 1000MW, rated DC voltage 500kV; Inverter-side smoothing reactor The value is 0.5968H, which is the rated turn-off angle of the inverter during steady-state operation. Maintain at .

[0043] The rated effective voltage of the receiving-end AC system is 230kV. To simulate the typical weak receiving-end grid characteristics under high-proportion renewable energy feed-in, the system short-circuit ratio is set to 2.0, and the equivalent impedance angle is [missing value]. .

[0044] In terms of new energy and reactive power compensation equipment, the wind farm adopts a converged grid-connected direct-drive wind turbine model, with a total rated capacity of [missing information]. The converter is configured with a capacity of 600 MVA, a maximum allowable overcurrent capacity of 1.2 pu, and a phase-locked loop bandwidth of 20 Hz. The rated capacity is configured at the point of common coupling. This is a ±200Mvar static synchronous compensator device with a short-time forced excitation overload capacity of 1.5 times and an output response time of less than 10ms. The key parameters for the coordinated control strategy are set as follows: voltage thresholds for forced excitation start-up and shutdown. , The rapid coordination time windows in the initial stage of a fault are set to 0.85 pu and 0.9 pu respectively. Take 50ms as the safety shut-off angle threshold for commutation failure defense. Set as .

[0045] In the simulation experiment, at t=0.1s, a three-phase symmetrical fault was introduced. The wind farm adopted equivalent converged grid-following control, and the static synchronous compensator adopted variable structure strong excitation control. Due to the reactive power coordination control strategy, a significant reactive power relay and capacity allocation process occurred between the two devices under this condition.

[0046] Based on a comparison of the transient responses of grid-connected wind turbines and static synchronous compensators (SSRs), grid-connected wind turbine units exhibit a response dead zone of approximately 20ms due to the limitations of phase-locked loop (PLL) dynamic adjustment and low-voltage ride-through logic detection time. During this critical window period, SSRs, with their faster response speed, exhibit significantly lower reactive current. After a startup overshoot of approximately 3ms, it quickly stabilized at a limit value of 1.2 pu.

[0047] With the activation of the fault ride-through logic, the grid-connected wind turbine unit is unblocked and begins linear ramp-up. As the total reactive power support received by the system increases, the voltage at the point of common coupling... A steady recovery ensued. At this point, the implicit coordination mechanism based on voltage sensing, designed in this strategy, took effect. The voltage closed-loop controller of the static synchronous compensator detected the gradually decreasing voltage deviation and automatically reduced the current command. The system entered the dynamic reactive power handover zone, during which the main source of reactive power support smoothly shifted from the static synchronous compensator to the grid-connected wind turbines. The power curve of the static synchronous compensator exhibited a natural downward trend, while the grid-connected wind turbines gradually assumed the main task of reactive power support. Throughout the entire process, no power oscillations caused by controller conflicts occurred.

[0048] After the voltage recovers to a steady state, the grid-connected wind turbines assume the main reactive power support task, while the reactive power output of the static synchronizing compensator (SRC) automatically converges. This coordinated control mechanism not only ensures the quality of voltage recovery but also enables dynamic capacity release of the SRC. By transferring the steady-state support task to large-capacity renewable energy units, the SRC quickly returns to hot standby mode, thus providing sufficient capacity reserves to cope with potential continuous commutation failures or subsequent voltage surges.

[0049] To verify the adaptability of the proposed control strategy under different numbers and types of reactive power equipment, two scenarios were set up: one involving only grid-connected wind turbines and the other involving coordinated control of static synchronizing compensators. Based on the dynamic response waveform of the system electrical quantities under the scenario involving only grid-connected wind turbines, simulation results show that in the event of a fault... Inside the window, close the corner The price fell below the critical threshold three times in a row. The situation is as follows. The first drop occurred at t=0.013ms, caused by a voltage surge at the moment of the fault. The angle drops sharply to 0.5°, approaching the physical limit for commutation failure. After the first commutation failure, the DC current... A severe short-circuit impact occurred, with a peak value as high as 1.9 pu. Due to the lack of rapid reactive power support and the deterioration of the dynamic performance of the grid-connected wind turbine phase-locked loop at low voltage (approximately 0.45 pu), the system reactive power deficit expanded sharply. This resulted in the voltage failing to recover, instead inducing a second, more severe voltage drop with a wider amplitude and greater difficulty in recovery, indicating that the system had completely lost its self-recovery capability.

[0050] The dynamic response waveform of the electrical quantities of the system based on the coordinated control of the grid-connected wind turbine and the static synchronous compensator is shown in the simulation results. Simulation results indicate that under the same fault impact, thanks to the millisecond-level strong excitation support of the static synchronous compensator in the initial stage of the fault, the voltage at the common coupling point is forcibly supported above 0.75 pu. With this support, the turn-off angle... A single fluctuation occurs only at the moment of the fault, and the lowest value remains at 11.0°, consistently higher than [previous value]. The safety threshold was reached, and the number of commutation failures decreased from 3 to 0. Due to the successful avoidance of short circuits on the inverter side, the DC current... The maximum transient peak value was only 1.25 pu, a 34.2% reduction compared to the uncontrolled scenario. This not only significantly reduced the electrical stress on the converter valve but also avoided the reactive power avalanche effect caused by current surges. During the fault duration, the system did not exhibit subsequent voltage or angle oscillations, indicating that the cooperative control method presented in this paper can effectively resist both the initial and subsequent commutation failures.

[0051] Analysis shows that, compared to traditional grid-connected wind turbine control, the coordinated control of grid-connected wind turbines and static synchronous compensators can effectively resist commutation failure. The coordinated control algorithm presented in this paper utilizes the response characteristics of reactive power compensation devices under different time sequences, enabling the renewable energy unit and the reactive power compensation device to share the reactive power support task in different time sequences. This coordinated mechanism based on the dynamic response characteristics and capacity differences of multiple reactive power sources allows the system to effectively resist commutation failure. Simultaneously, through capacity allocation, the system's economy and subsequent commutation failure resistance capabilities are simultaneously improved.

[0052] like Figure 9As shown, the present invention also provides a commutation failure mitigation system that combines new energy sources and reactive power compensation, specifically including the following modules; The dynamic modeling module is based on the dynamic equivalent modeling method of multiple reactive sources in the high voltage DC receiving-end system. According to the capacity ratio and regulation rate of the inverter and static synchronous compensator of the grid-connected new energy unit, a coupled fast and slow dynamic subsystem model is established. The timing architecture module designs a multi-timescale hierarchical timing collaborative control architecture, dividing the entire power grid fault process into a fault transient phase and a voltage recovery phase. The objective function construction module, based on the coupled fast and slow dynamic subsystem model, constructs a reactive power distribution objective function that takes into account both the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected new energy units. The transient forced excitation control module performs forced excitation reactive power control on the static synchronous compensator based on the coupled fast and slow dynamic subsystem model during the fault transient phase, clamping the voltage at the common coupling point above the critical commutation voltage. In the steady-state relay coordination module, during the voltage recovery phase, the new energy generating units take over the reactive power support based on the coupled fast and slow dynamic subsystem model and the reactive power distribution objective function, and achieve smooth coordinated handover of reactive power output between the static synchronous compensator and the grid-connected new energy generating units through the common coupling point voltage.

[0053] This system establishes a coupled fast-slow dynamic subsystem model that matches the response characteristics of the static synchronous compensator and the grid-connected renewable energy units. It designs a phased time-series collaborative control architecture for the entire fault cycle and constructs a multi-dimensional constrained reactive power allocation objective function. This system can accurately match the multi-timescale response differences between the two types of equipment, fill the reactive power output gap of renewable energy in the early stage of a fault, block the first wave of commutation failure, achieve a smooth handover of the main reactive power support, release the dynamic margin of the static synchronous compensator, improve the ability of the HVDC weak receiving end grid to resist continuous commutation failure, and enhance the transient voltage stability of the system.

[0054] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for mitigating commutation failure through synergy between new energy sources and reactive power compensation, characterized in that, Includes the following steps: Based on the dynamic equivalent modeling method of multiple reactive power sources in high voltage DC receiving-end system, a coupled fast and slow dynamic subsystem model is established according to the capacity ratio and regulation rate of inverter and static synchronous compensator of grid-connected new energy unit. Design a multi-timescale hierarchical time-series collaborative control architecture to divide the entire power grid fault process into a fault transient stage and a voltage recovery stage; Based on the coupled fast and slow dynamic subsystem model, a reactive power distribution objective function is constructed that takes into account both the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected new energy units. During the fault transient phase, the static synchronous compensator is subjected to forced excitation reactive power control based on the coupled fast and slow dynamic subsystem model to clamp the voltage at the common coupling point above the critical commutation voltage. During the voltage recovery phase, based on the coupled fast and slow dynamic subsystem model and the reactive power distribution objective function, the new energy generating units take over the reactive power support, and the static synchronous compensator and the grid-connected new energy generating units achieve a smooth and coordinated handover of reactive power output through the common coupling point voltage.

2. The method for mitigating commutation failure through the synergy of new energy and reactive power compensation as described in claim 1, characterized in that, Establishing a coupled fast and slow dynamic subsystem model includes the following steps: A quasi-steady-state model of the inverter side of the high-voltage DC receiving-end system was established to clarify the evolution mechanism of commutation failure and the voltage constraint boundary. A slow-dynamic subsystem model of a grid-connected new energy unit and a fast-dynamic subsystem model of a static synchronous compensator were established to quantify the differences in multi-timescale response characteristics between the two types of equipment. Based on the Thevenin equivalent circuit of the power grid, the fast dynamic subsystem model and the slow dynamic subsystem model are coupled to obtain a coupled fast and slow dynamic subsystem model, which characterizes the dynamic interaction characteristics of the two types of equipment.

3. The method for mitigating commutation failure through the synergy of new energy and reactive power compensation as described in claim 2, characterized in that, The establishment of the quasi-steady-state model of the inverter side of the high-voltage DC receiving-end system specifically describes the voltage-current relationship on the inverter side through quasi-steady-state mathematical equations. The expression of the quasi-steady-state mathematical equations is as follows: In the formula, This refers to the no-load DC voltage on the rectifier side and the inverter side; , These are the effective values ​​of the AC bus voltages on the rectifier and inverter sides. This refers to the critical effective value of the AC side line voltage of the converter bus. This refers to the DC line current. The reactive power consumed by the converter; For DC line resistance; , The equivalent leakage reactance of the converter transformers on the rectifier and inverter sides includes the equivalent inductance of the AC system and the leakage reactance of the converter transformers. These are the transformer turns ratio and the number of six-pulse converter bridges connected in series, respectively. The inverter-side delayed firing angle, It is a leading trigger angle. The inverter-side shut-off angle. Its commutation overlap angle; This refers to the active power transmitted by the LCC on the inverter side. Power factor; This is the zero-crossing offset angle of the commutation voltage.

4. The method for mitigating commutation failure through the synergy of new energy and reactive power compensation as described in claim 2, characterized in that, The establishment of a slow-dynamic subsystem model for the grid-connected new energy generating unit specifically characterizes the decoupling control relationship between the unit's active and reactive power outputs and the voltage and output current at the point of common coupling through a power equation. The power equation is as follows: In the formula For the voltage at the common coupling point Axial components; This refers to the output current component; By controlling Active power can be controlled ,control Reactive power can be controlled ; The phase tracking characteristics of the phase-locked loop of the unit's synchronous rotating coordinate system are characterized by the current inner loop control equation, which is as follows: In the formula , This is the reference voltage command for the converter; The fundamental angular frequency of the power grid; For filtering inductors; , These are the proportional and integral gain coefficients; , These are reference values ​​for the d-axis and q-axis currents. , The actual current feedback values ​​for the d and q axes are used; rapid current tracking is achieved through inner-loop control. The effective reactive current generation logic injected into the grid by the generating unit is characterized by the reactive response equation, which is: In the formula The phase angle of the phase-locked loop output; The rated angular frequency of the power grid; This represents the q-axis component of the voltage at the common coupling point.

5. The method for mitigating commutation failure through the coordinated use of new energy and reactive power compensation as described in claim 2, characterized in that, A fast dynamic subsystem model of the static synchronous compensator is established. Specifically, the current dynamic characteristics of the static synchronous compensator connected to the power grid are characterized by the AC side dynamic equations. The AC side dynamic equations are as follows: In the formula Injecting grid current into the static synchronous compensator Axial components; For the voltage at the access point Axial components; The output voltage component of the static synchronous compensator bridge arm; The inductance value of the connected reactor; The generation logic of inductive reactive power in a static synchronous compensator is characterized by a reactive power output equation, which is: Static synchronous compensator injects reactive current For the converter bus voltage The lifting effect can be achieved using the short-circuit impedance of the receiving-end power grid. Approximate description; The voltage rise characteristic equation characterizes the effect of reactive power injection by the static synchronous compensator on the converter bus voltage. The voltage rise characteristic equation is as follows: In the formula, SCR is the system short-circuit ratio; The reference value for injecting reactive current into the static synchronous compensator.

6. The method for mitigating commutation failure through the coordinated use of new energy and reactive power compensation according to claim 2, characterized in that, The fast-dynamic subsystem model and the slow-dynamic subsystem model are coupled. Specifically, the voltage dynamic sensitivity equation characterizes the relationship between the voltage change at the common coupling point and the total reactive current injection. The voltage dynamic sensitivity equation is as follows: In the formula, The short-circuit reactance of the system characterizes the sensitivity of the weak receiving-end power grid to reactive current. , These refer to the reactive current injection of the static synchronous compensator and the inverter of the grid-connected new energy unit, respectively.

7. The method for mitigating commutation failure through the coordinated use of new energy sources and reactive power compensation as described in claim 1, characterized in that, The proposed multi-timescale hierarchical time-series collaborative control architecture divides the entire power grid fault process into a fault transient phase and a voltage recovery phase, specifically including: Based on the evolution mechanism of commutation failure and the characteristics of grid voltage recovery, a two-stage hierarchical timing control architecture is constructed, which combines fault transient rapid support and voltage recovery relay coordination. The time period from 10ms to 50ms after the occurrence of grid fault is divided into the fault transient stage, and the time period of grid fault duration exceeding 50ms is divided into the voltage recovery stage.

8. The method for mitigating commutation failure through the coordinated use of new energy and reactive power compensation as described in claim 7, characterized in that, The proposed two-stage hierarchical timing control architecture specifically uses a state equation centered on voltage deviation to characterize the dynamic evolution of the voltage at the common coupling point. The state equation is as follows: In the formula, , , This represents the time derivative of the static synchronous compensator, the grid-connected new energy unit inverter, and the load current. The extremely fast response characteristics of the static synchronous compensator to voltage deviation during the fault transient stage are characterized by the fast subsystem convergence characteristic equation. The fast subsystem convergence characteristic equation is as follows: The equivalent time constant of the inner current loop closed loop; , These are the second and first derivatives of the voltage at the grid connection point.

9. The method for mitigating commutation failure through the coordinated use of new energy and reactive power compensation according to claim 1, characterized in that, Based on the coupled fast and slow dynamic subsystem model, a reactive power distribution objective function is constructed that takes into account the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected renewable energy units. Specifically, with the goal of minimizing the overall system operational risk, a weighted objective function is constructed. The weighted objective function includes three weighted terms: a dynamic margin term for penalizing the steady-state output of the static synchronous compensator, a load rate term for penalizing the full-load level of grid-connected renewable energy units, and a voltage deviation term for constraining the grid voltage control accuracy. These terms are weighted and summed using preset weighting coefficients.

10. The method for mitigating commutation failure through the coordinated use of new energy and reactive power compensation according to claim 1, characterized in that, The forced excitation reactive power control of the static synchronous compensator specifically involves: when the voltage drop amplitude at the common coupling point exceeds a preset start-up threshold, the static synchronous compensator is switched from the conventional voltage regulation mode to the variable structure forced excitation mode. The reactive power output target is directly set through the forced excitation mode current command equation, bypassing the voltage outer loop PI control link to achieve millisecond-level full reactive current output. The forced excitation mode current command equation is as follows: In the formula, This is the optimal feedforward instruction. This represents the total steady-state reactive power demand of the system after low-pass filtering. For the amplitude limiting function, its upper bound is... The remaining capacity of the inverter in the grid-connected new energy unit is dynamically determined by the definition.

11. A commutation failure mitigation system that integrates new energy sources and reactive power compensation, characterized in that, include: The dynamic modeling module is based on the dynamic equivalent modeling method of multiple reactive sources in the high voltage DC receiving-end system. According to the capacity ratio and regulation rate of the inverter and static synchronous compensator of the grid-connected new energy unit, a coupled fast and slow dynamic subsystem model is established. The timing architecture module designs a multi-timescale hierarchical timing collaborative control architecture, dividing the entire power grid fault process into a fault transient phase and a voltage recovery phase. The objective function construction module, based on the coupled fast and slow dynamic subsystem model, constructs a reactive power distribution objective function that takes into account both the dynamic margin of the static synchronous compensator and the operational safety and voltage quality of grid-connected new energy units. The transient forced excitation control module performs forced excitation reactive power control on the static synchronous compensator based on the coupled fast and slow dynamic subsystem model during the fault transient phase, clamping the voltage at the common coupling point above the critical commutation voltage. In the steady-state relay coordination module, during the voltage recovery phase, the new energy generating units take over the reactive power support based on the coupled fast and slow dynamic subsystem model and the reactive power distribution objective function, and achieve smooth coordinated handover of reactive power output between the static synchronous compensator and the grid-connected new energy generating units through the common coupling point voltage.

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