Wide-area safety protection method and system for offshore new energy through direct current delivery system

Abstract

The invention relates to a wide-area safety control method and system for offshore new energy through a direct current delivery system, and belongs to the field of new energy direct current delivery. The method comprises the following steps: collecting steady-state values of a plurality of operation parameters of the direct-current delivery system before a fault occurs and instantaneous values after the fault occurs; simulating the direct-current delivery system based on the steady-state value and the instantaneous value, and determining key parameters influencing the stability of the system; and issuing a corresponding instruction to a control center of the direct current delivery system based on the key parameters. According to the method, by exploring the internal stability mechanism of the offshore new energy through the direct current delivery system in a large disturbance scene, key parameters influencing system stability are determined through simulation, corresponding parameters of the system are adjusted in time when the direct current delivery end system breaks down, and the system stability is kept.

Description

Technical Field

[0001] This invention relates to the field of DC transmission of new energy, and in particular to a wide-area safety protection method for a DC transmission system for marine new energy. Background Technology

[0002] With the completion and implementation of large-scale offshore renewable energy projects integrating wind and solar power, the adoption of wind-thermal bundled DC transmission technology has become an important technical path to improve renewable energy absorption capacity and system stability. The interactions between various control components in the wind-thermal bundled LCC-HVDC system (a high-voltage DC transmission system based on thyristor current source converters) exhibit strong coupling characteristics, which can easily lead to transient energy interaction instability under large disturbances, seriously threatening the safe operation of the power grid.

[0003] Currently, some progress has been made in the stability research of wind-thermal bundled DC transmission systems. However, in-depth research is lacking on the energy interaction mechanism between wind turbines and thermal power units under fault conditions, and the potential for cascading instability risks caused by the control response characteristics of the DC system. The analytical methods for the safety protection of offshore renewable energy transmission systems via DC under large disturbance scenarios mainly rely on time-domain simulation or simplified models to analyze the impact of single control links. These methods suffer from biased analysis results, making it difficult to comprehensively and accurately assess the system's safety protection level under large disturbance scenarios, thus affecting the system's safety protection effectiveness. Therefore, exploring the inherent stability mechanism of offshore renewable energy transmission systems via DC under large disturbance scenarios and studying how to precisely regulate the system to ensure stability during N-2 faults have become urgent problems to be solved. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to disclose a wide-area safety protection method and system for a marine new energy transmission system via DC. By simulating the system, the method accurately establishes and quantitatively analyzes the energy interaction of multiple links, defines the interaction stability factor, and determines the key control parameters that affect stability through quantitative characterization, thereby ensuring that the system remains stable when an N-2 fault occurs.

[0005] On the one hand, the present invention provides a wide-area security protection method for a marine new energy transmission system via DC transmission, specifically including the following steps:

[0006] Collect the steady-state values ​​of multiple operating parameters of the DC transmission system before the fault occurs and the instantaneous values ​​after the fault occurs;

[0007] The DC transmission system is simulated based on the steady-state and instantaneous values ​​to determine the key parameters affecting system stability.

[0008] Based on the key parameters, corresponding instructions are sent to the control center of the DC transmission system.

[0009] Furthermore, the DC transmission system includes a doubly-fed wind turbine subsystem, a thermal power unit subsystem, and a conventional high-voltage DC transmission subsystem; the simulation of the DC transmission system based on the steady-state values ​​and the instantaneous values ​​to determine the key parameters affecting system stability includes:

[0010] The DC transmission system is divided into multiple subsystems.

[0011] Construct dynamic energy models for each subsystem;

[0012] Simulations are performed based on the steady-state values, instantaneous values, and dynamic energy models of each subsystem.

[0013] The rate of change of interactive energy of each subsystem is calculated based on the simulation results.

[0014] The key parameters affecting system stability are determined based on the rate of change of each interaction energy.

[0015] Furthermore, the division of each subsystem of the collected DC transmission system into multiple subsystems includes:

[0016] The doubly fed wind turbine subsystem is divided into a rotor-side subsystem, a stator-side subsystem, and a phase-locked loop subsystem.

[0017] The thermal power unit system is divided into a stator and rotor subsystem that takes armature reaction into account, a primary frequency regulation subsystem that takes DC limiting into account, and a thermal power unit excitation subsystem.

[0018] The traditional high-voltage direct current (HVDC) transmission subsystem is divided into the traditional HVDC rectifier side subsystem, the traditional HVDC inverter side and DC line subsystem, and the traditional HVDC AC filter subsystem.

[0019] Furthermore, the determination of key parameters affecting system stability based on the rate of change of the interaction energy includes:

[0020] The corresponding interaction stability factor is obtained by calculating the derivative of the rate of change of each interaction energy with respect to each control parameter;

[0021] Based on the values ​​of each interaction stability factor, the key parameters affecting system stability are determined:

[0022] When the interaction stability factor is negative, it is beneficial to system stability. The corresponding control parameters are determined as the key parameters that affect the system.

[0023] When the interaction stability factor is zero, it is unrelated to the system stability level, and the corresponding control parameter is not a critical parameter.

[0024] When the interaction stability factor is positive, it is not conducive to system stability, and the corresponding control parameters are not critical parameters.

[0025] Furthermore, the steady-state values ​​of multiple operating parameters of the DC transmission system before the fault and the instantaneous values ​​after the fault include:

[0026] The system collects the steady-state values ​​of the following operating parameters before and after a fault: d-axis and q-axis output current of the doubly-fed induction generator (DFIG) at the grid connection point; d-axis and q-axis output voltage of the DFIG stator; d-axis and q-axis output current of the DFIG stator; d-axis and q-axis output current of the DFIG rotor; d-axis and q-axis output current of the DFIG grid-side converter; magnetomotive force of the synchronous generator; d-axis and q-axis current of the synchronous generator stator; DC current on the rectifier side of the conventional DC transmission system; DC current on the inverter side of the conventional DC transmission system; and DC voltage on the rectifier side of the conventional DC transmission system.

[0027] Furthermore, the formula for calculating the rate of change of interactive energy of the doubly fed wind turbine subsystem is as follows:

[0028]

[0029] in, The rate of change of interactive energy in the doubly fed wind turbine subsystem;

[0030] Δi dpcc and Δi qpcc These are the instantaneous changes in the d-axis output current at the grid connection point of the doubly-fed induction generator (DFIG) and the instantaneous changes in the q-axis output current at the grid connection point of the DFIG, respectively.

[0031] ω s This indicates the synchronous operating angular velocity of the doubly-fed wind turbine unit;

[0032] Δu ds and Δu qs These are the instantaneous changes in the output voltage of the stator d-axis and the instantaneous changes in the output voltage of the stator q-axis of the doubly-fed induction generator, respectively.

[0033] L s The inductance of the equivalent two-phase stator winding in the dq coordinate system of a doubly fed wind turbine;

[0034] L r The inductance of the equivalent two-phase rotor winding in the dq coordinate system of the doubly fed wind turbine;

[0035] L m The equivalent mutual inductance between the stator and rotor windings on the same coordinate axis;

[0036] ω c It is the slip angular velocity;

[0037] Δi qs and Δi ds These are the instantaneous changes in the q-axis output current of the doubly-fed induction generator stator and the instantaneous changes in the d-axis output current of the doubly-fed induction generator stator, respectively.

[0038] R r The resistance of the equivalent two-phase rotor winding in the dq coordinate system of the doubly fed wind turbine;

[0039] Δi dr Δi represents the instantaneous change in the output current of the doubly-fed induction generator rotor along the d-axis. qr This represents the instantaneous change in the output current of the q-axis rotor of the doubly-fed wind turbine.

[0040] ω r This indicates the angular velocity of the rotor of a doubly-fed wind turbine.

[0041] Δu dr This refers to the instantaneous change in DC voltage on the rectifier side of a traditional DC transmission system.

[0042] Δu qr The instantaneous change in the output current of the q-axis of the doubly-fed fan rotor;

[0043] k pll_d and k pll_q These are the proportional coefficients of the phase-locked loop;

[0044] Δθ pll The phase-locked loop subsystem outputs the phase-locked angle change at its port;

[0045] C pll =1 / k pll_i k pll_i These are the integral coefficients of the phase-locked loop;

[0046] Δω pll The change in angular frequency output at the PLL subsystem port;

[0047] K i1_POL The integral coefficient of the d-axis PI controller in the power outer loop control;

[0048] K p1_POL This refers to the proportional coefficient of the d-axis PI controller in the power outer loop control.

[0049] ΔP ref This indicates the change in the active power command value;

[0050] Δx1 is the state variable of the integral link in the outer loop PI controller of the rotor d-axis power of the doubly-fed wind turbine.

[0051] Δx2 is the state variable of the integral link in the outer loop PI controller of the rotor q-axis power of the doubly-fed wind turbine.

[0052] u qs0 This represents the steady-state value of the stator q-axis output voltage of the doubly fed wind turbine before a fault occurs.

[0053] iqs0 This represents the steady-state value of the stator q-axis output current of the doubly fed wind turbine before a fault occurs.

[0054] Δθ s This refers to the change in the phase angle of the stator voltage.

[0055] i ds0 This represents the steady-state value of the stator d-axis output current of the doubly fed wind turbine before a fault occurs.

[0056] u ds0 This represents the steady-state value of the stator d-axis output voltage of the doubly fed wind turbine before a fault occurs.

[0057] K p2_POL and K i2_POL These are the proportional and integral coefficients of the q-axis PI controller in the power outer loop control, respectively.

[0058] ΔQ ref This represents the change in the reactive power command value.

[0059] Furthermore, the formula for calculating the rate of change of interactive energy of the thermal power unit system is as follows:

[0060]

[0061] in, The rate of change of interactive energy in the thermal power unit component system;

[0062] T″ q0 、T′ q0 These represent the subtransient time constant and transient time constant of the q-axis of the thermal power unit, respectively;

[0063] x″ q 、x′ q x q These represent the subtransient reactance, transient reactance, and synchronous reactance of the generator rotor q-axis, respectively.

[0064] ΔI q This represents the instantaneous change in the q-axis value of the stator current of the synchronous generator.

[0065] ΔE′ d , ΔE″ d The changes in port voltage and current of the stator and rotor d-axis subsystems of the thermal power unit, which take into account armature reaction, are determined through simulation.

[0066] T″ d0 、T′ d0 These represent the subtransient time constant and transient time constant of the generator rotor d-axis, respectively.

[0067] ΔE fd x″ represents the change in stator excitation electromotive force. d 、x′d x d These represent the subtransient reactance, transient reactance, and synchronous reactance of the generator rotor d-axis, respectively.

[0068] ΔI d This represents the instantaneous change in the d-axis value of the stator current of the synchronous generator.

[0069] ΔE' q , ΔE” q The changes in port voltage and current of the stator and rotor q-shaft subsystems of the thermal power unit, which take into account armature reaction, are determined through simulation.

[0070] K pr_FES and K ir_FES These are the proportional and integral coefficients of the PI controller in DC limiting control.

[0071] K ir_EXS The integral coefficient of the PI controller in primary frequency modulation control;

[0072] K d These are the control parameters corresponding to the ideal transformer in the excitation subsystem;

[0073] ΔU C This indicates the change in port voltage of the excitation subsystem of a thermal power unit;

[0074] f H This is the dead zone value for DC limiting control;

[0075] Δx F The state variables are obtained from the integral element in the PI element of the primary frequency regulation subsystem of a thermal power unit, taking into account DC limiting.

[0076] u ar The effective value of the AC voltage on the rectifier side was determined through simulation.

[0077] α r0 This refers to the steady-state firing angle of the rectifier side during steady-state operation of the sending-end system.

[0078] Δα r The steady-state firing angle change on the rectifier side during steady-state operation of the sending-end system is determined through simulation;

[0079] x sr This refers to the commutation reactance on the rectifier side;

[0080] Δi dr This represents the instantaneous change in the output current of the d-axis rotor of the doubly-fed wind turbine.

[0081] i dr0 This represents the steady-state value of the d-axis output current of the doubly fed wind turbine rotor before a fault occurs.

[0082] udr0 Steady-state value of DC voltage on the rectifier side of a traditional DC transmission system before a fault occurs;

[0083] Δf represents the frequency change at the port of the primary frequency regulation subsystem of the thermal power unit, taking into account DC limiting, and is determined through simulation.

[0084] Furthermore, the formula for calculating the rate of change of interactive energy in the traditional high-voltage direct current transmission subsystem is as follows:

[0085]

[0086] in, The rate of change of interactive energy in a traditional high-voltage direct current transmission subsystem;

[0087] u ar AC voltage measurement for the rectifier-side converter;

[0088] α r0 The steady-state value of the firing angle of the rectifier-side subsystem in a traditional DC transmission system was determined through simulation.

[0089] K pr_FCC K ir_FCC These are the proportional-integral parameters of the PI controller in the constant current control loop.

[0090] ΔI dcref The change in the current command value of the constant current control loop;

[0091] T mr The time constant of the rectifier-side current measurement module;

[0092] K mr Equivalent gain of the rectifier-side current measurement module;

[0093] ΔI drm This represents the change in the rectified DC current obtained after passing through the acquisition inertial circuit.

[0094] Δα r This represents the change in firing angle of the rectifier-side subsystem in a traditional DC transmission system.

[0095] ΔU d This refers to the DC voltage variation on the inverter side and DC line subsystem of a traditional DC transmission system.

[0096] ΔI dr This refers to the instantaneous change in the DC current on the rectifier side of a traditional DC transmission system.

[0097] u ai This is the effective value of the AC voltage on the inverter side;

[0098] γ0 is the steady-state arc extinction advance angle;

[0099] Δγ is the arc extinction angle of the inverter-side subsystem in a traditional DC transmission system;

[0100] ΔI di This represents the change in DC current in the inverter-side subsystem of a traditional DC transmission system.

[0101] Δi ar2 The change in AC current of the filter is determined through simulation.

[0102] Δu c , Δi ar1 These represent the changes in filter capacitor voltage and AC current in a traditional high-voltage direct current transmission AC filter subsystem, respectively.

[0103] Δu ar The change in AC voltage of the rectifier-side converter is determined through simulation.

[0104] Furthermore, the determination of key parameters affecting system stability based on the rate of change of the interaction energy also includes:

[0105] The key parameters affecting system stability include the active power command value, the proportional coefficient of the rectifier side constant current control loop, the proportional coefficient of the phase-locked loop, the integral coefficient of the excitation system control loop, and the proportional / integral coefficient of the primary frequency regulation system control loop.

[0106] On the other hand, the present invention also provides a wide-area safety protection system for a marine new energy transmission system via DC, characterized in that it includes:

[0107] The data acquisition module is used to collect the steady-state values ​​of multiple operating parameters of the DC transmission system before a fault occurs and the instantaneous values ​​after a fault occurs;

[0108] The system simulation module is used to simulate the DC transmission system based on the steady-state value and the instantaneous value, and to determine the key parameters affecting the system stability;

[0109] The instruction issuing module is used to issue corresponding instructions to the control center of the DC transmission system based on the key parameters.

[0110] The present invention can achieve at least one of the following beneficial effects:

[0111] By dividing the DC transmission system into multiple subsystems and constructing mathematical models for each subsystem, the interaction energy between the subsystems is calculated, thus improving the calculation accuracy. By obtaining the rate of change of interaction energy between the subsystems through simulation and calculation, and analyzing it, the stability of the wind-fire combined DC transmission system can be quickly and effectively evaluated.

[0112] By using the interaction stability factor index provided by the energy change rate calculation module between each subsystem, key system parameters are determined, providing a basis for issuing system commands and ensuring the reliable operation of the system.

[0113] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0114] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0115] Figure 1 This is a flowchart of an embodiment of the method of the present invention;

[0116] Figure 2 This is a schematic diagram of a doubly-fed wind turbine generator.

[0117] Figure 3 This is a schematic diagram of the structure of a traditional high-voltage direct current transmission system;

[0118] Figure 4 A schematic diagram illustrating the impact of key parameters of the outer power loop of a doubly-fed wind turbine on system stability;

[0119] Figure 5 A schematic diagram illustrating the impact of key parameters of the phase-locked loop (PLL) of a doubly-fed wind turbine on system stability;

[0120] Figure 6 This diagram illustrates the impact of key parameters of the excitation system of a thermal power unit on system stability.

[0121] Figure 7 This diagram illustrates the impact of key parameters of the excitation system of a thermal power unit on system stability.

[0122] Figure 8 This diagram illustrates the impact of key parameters of a high-voltage direct current transmission system on system stability. Detailed Implementation

[0123] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0124] Method Implementation Examples

[0125] One embodiment of the present invention discloses a wide-area security protection method for a marine new energy transmission system via DC transmission, specifically including steps S1-S3.

[0126] S1. Collect the steady-state values ​​of multiple operating parameters of the DC transmission system before the fault occurs and the instantaneous values ​​after the fault occurs.

[0127] Specifically, the DC transmission system is a combined wind and thermal power DC transmission system, consisting of doubly-fed wind turbines, thermal power units, and a traditional high-voltage DC transmission system.

[0128] The steady-state values ​​of multiple operating parameters at the port of the wind-fire combined DC transmission system before and after a fault were collected, with the period of the dominant oscillation mode as the sampling time interval. The period of the dominant oscillation mode was [missing information]. ω is the angular velocity of the dominant oscillation mode of the wind-fire bundled DC transmission system.

[0129] The normal and instantaneous values ​​of these operating parameters are collected by voltage and current sensors installed inside the unit.

[0130] Specifically, the steady-state values ​​of multiple operating parameters at the port of the combined wind and fire DC transmission system before and after a fault include:

[0131] The steady-state values ​​of the d-axis and q-axis output currents at the grid connection point of the doubly fed fan before the fault occurred. dpcco i qpcc0 and the instantaneous value i after the fault occurs dpcc i qpcc ;

[0132] The steady-state values ​​u of the stator d-axis and q-axis output voltages of the doubly fed fan before the failure ds0 u qs0 and the instantaneous value u after the fault occurs ds u qs ;

[0133] Steady-state values ​​of the stator d-axis and q-axis output currents of the doubly fed fan before the failure i ds0 i qs0 and the instantaneous value i after the fault occurs ds i qs ;

[0134] The steady-state values ​​of the output current of the doubly fed fan rotor d-axis and q-axis before the fault i dr0 i qr0 and the instantaneous value i after the fault occurs dr i qr ;

[0135] Steady-state values ​​of the d-axis and q-axis output currents of the doubly fed wind turbine grid-side converter before the fault. dg0 iqg0 and the instantaneous value i after the fault occurs dg i qg ;

[0136] Steady-state value E of synchronous generator excitation potential before failure fd0 and the instantaneous value E after the fault occurs fd ;

[0137] Steady-state values ​​I of the stator current d-axis and q-axis of the synchronous generator before a fault occurs d0 I q0 and the instantaneous value I after the fault occurs d I q ;

[0138] Steady-state value I of the DC current on the rectifier side of a traditional DC transmission system before a fault occurs dr0 and the instantaneous value I after the fault occurs dr ;

[0139] Steady-state value I of DC current on the inverter side of a traditional DC transmission system before a fault occurs di0 and the instantaneous value I after the fault occurs di ;

[0140] The steady-state value u of the DC voltage on the rectifier side of a traditional DC transmission system before a fault occurs. dr0 and the instantaneous value u after the fault occurs dr .

[0141] S2. Simulate the DC transmission system based on the steady-state and instantaneous values ​​to determine the key parameters affecting system stability. This specifically includes S21-S25.

[0142] S21. Divide each subsystem of the DC transmission system into multiple subsystems. Specifically, this includes:

[0143] The doubly-fed induction generator (DFIG) wind turbine subsystem is divided into a rotor-side subsystem (i.e., the d-axis and q-axis subsystem of the DFIG rotor), a stator-side subsystem (i.e., the d-axis and q-axis subsystem of the DFIG stator), and a phase-locked loop (PLL) subsystem. Figure 2 As shown.

[0144] The thermal power unit system is divided into the stator and rotor subsystem that takes into account armature reaction (i.e., the stator and rotor d-axis and q-axis subsystems of the thermal power unit that take into account armature reaction), the primary frequency regulation subsystem that takes into account DC limiting (i.e., the primary frequency regulation subsystem of the thermal power unit that takes into account DC limiting), and the excitation subsystem of the thermal power unit.

[0145] The traditional high-voltage direct current (HVDC) transmission subsystem is divided into the traditional HVDC rectifier side subsystem, the traditional HVDC inverter side and DC line subsystem, and the traditional HVDC AC filter subsystem, such as... Figure 3 As shown.

[0146] S22. Construct dynamic energy models for each subsystem. This includes S221-S222.

[0147] S221. Construct dynamic mathematical models for each subsystem.

[0148] Mathematical model of the stator d-shaft subsystem of a doubly-fed wind turbine:

[0149]

[0150] Where, Δu ds Δi represents the instantaneous change in the stator d-axis output voltage of the doubly-fed induction generator (in practice, this change is equivalent to the change in the port voltage of the GSC current inner loop subsystem); ds H represents the instantaneous change in the output current of the stator d-axis of the doubly-fed induction generator (DFIG). DFIG_X1 H DFIG_Y1 For interaction with other subsystems; L s R s Let L be the inductance and resistance of the equivalent two-phase stator winding in the dq coordinate system, which are known quantities; m The mutual inductance between the coaxial equivalent stator and rotor windings is a known quantity; L r R r The inductance and resistance of the equivalent two-phase rotor winding in the dq coordinate system are known quantities; Δi dpcc ω represents the change in d-axis current at the grid connection point of the doubly-fed wind turbine; s The synchronous operating angular velocity of the doubly-fed wind turbine is a known quantity, obtained by subtracting the synchronous angular velocity from the rotor angular velocity; C t ω represents the stator port filter capacitor, which is a known quantity; c ω is the slip angular velocity, which is a known quantity; r The angular velocity of the rotor of the doubly-fed wind turbine is a known quantity; Δi dr Δi represents the instantaneous change in the output current of the doubly-fed induction generator rotor along the d-axis. qr Δi represents the instantaneous change in the output current of the q-axis rotor of the doubly-fed wind turbine. qs This represents the instantaneous change in the output current of the stator q-axis of the doubly-fed induction generator.

[0151] Mathematical model of the stator q-shaft subsystem of a doubly-fed wind turbine:

[0152]

[0153] Where, Δu qs Δi represents the instantaneous change in the q-axis output voltage of the doubly-fed induction generator stator; qs H represents the instantaneous change in the q-axis output current of the doubly-fed induction generator stator; DFIG_X2H DFIG_Y2 Interaction with other subsystems; L s R s Let L be the inductance and resistance of the equivalent two-phase stator winding in the dq coordinate system, which are known quantities; m The mutual inductance between the coaxial equivalent stator and rotor windings is a known quantity; L r R r Let ω be the inductance and resistance of the equivalent two-phase rotor winding in the dq coordinate system, which are known quantities; s ω represents the synchronous operating angular velocity of the doubly-fed wind turbine, which is a known quantity; c ω is the slip angular velocity, which is a known quantity; r The angular velocity of the rotor of the doubly-fed wind turbine is a known quantity; C t The stator port filter capacitor represents a known quantity; Δi qpcc Δi represents the instantaneous change in the q-axis output current at the grid connection point of the doubly-fed induction generator (DFIG). dr Δi represents the instantaneous change in the output current of the doubly-fed induction generator rotor along the d-axis. qr Δi represents the instantaneous change in the output current of the q-axis rotor of the doubly-fed wind turbine. ds This represents the instantaneous change in the output current of the stator d-axis of the doubly-fed fan.

[0154] Mathematical model of phase-locked loop subsystem:

[0155]

[0156] Where, Δθ pll The change in phase-locked angle (Δω) is the output phase-locked angle of the PLL subsystem port. pll k is the change in angular frequency output from the PLL subsystem port. pll_p ,k pll_i These are the proportional and integral coefficients of the phase-locked loop, respectively, and are known quantities that can be adjusted; Δu qg The change in q-axis voltage at the port of the doubly fed wind turbine is a known quantity, obtained by Parker transformation based on the three-phase voltage at the port of the doubly fed wind turbine.

[0157] Mathematical model of the rotor d-shaft subsystem of a doubly-fed wind turbine:

[0158]

[0159] Where Δx1 is the state variable of the integral link in the outer loop PI controller of the rotor d-axis power of the doubly-fed wind turbine; Δi dr This refers to the instantaneous change in port current of the rotor d-shaft subsystem of a doubly-fed wind turbine; u ds0 The steady-state value of the stator d-axis output voltage of the doubly-fed induction generator before a fault occurs; Δi ds H represents the instantaneous change in the output current of the stator d-axis of the doubly-fed induction generator (DFIG). DFIG_X4H DFIG_Y4 For H DFIG_Y2 Interaction with other subsystems; T d1 The time constant of the inner loop of the current along the d-axis, which is equivalent to a first-order inertial element, is a known quantity; K p1_POL and K i1_POL Let P be the proportional and integral coefficients of the d-axis PI controller in the power outer loop control, and P be a known, adjustable quantity. ref This is the active power command value; ΔP ref Indicates the change in the active power command value; u qs0 i qs0 The steady-state values ​​of the stator q-axis output voltage and output current of the doubly-fed induction generator before a fault occurs; Δθ s The change in stator voltage phase angle; Δθ pll The phase-locked loop (PLL) subsystem outputs the phase-locked angle change at the port; Δu ds i represents the instantaneous change in the output voltage of the stator d-axis of the doubly-fed induction generator (DFIG). ds0 Steady-state value of the stator d-axis output current of the doubly fed fan before a fault occurs.

[0160] Mathematical model of the rotor q-shaft subsystem of a doubly-fed wind turbine:

[0161]

[0162] Where Δx2 is the state variable of the integral link in the outer loop PI controller of the q-axis power of the doubly-fed wind turbine rotor; Δi qr The change in port current of the rotor q-shaft subsystem of a doubly-fed wind turbine; u ds0 The steady-state value of the stator d-axis output voltage of the doubly-fed induction generator before a fault occurs; Δi qs H represents the instantaneous change in the q-axis output current of the doubly-fed induction generator stator; DFIG_X5 H DFIG_Y5 For interaction with other subsystems; T d2 The time constant of the inner loop of the current q-axis is equivalent to a first-order inertial element; K p2_POL and K i2_POL Let Q be the proportional and integral coefficients of the q-axis PI controller in the power outer loop control, and let Q be an adjustable known quantity. ref The reactive power command value is a known quantity; ΔQ ref The change in the reactive power command value; u qs0 i represents the steady-state value of the stator q-axis output voltage of the doubly-fed induction generator before a fault occurs. ds0 i represents the steady-state value of the stator d-axis output current of the doubly-fed induction generator before a fault occurs; qs0 The steady-state value of the stator q-axis output current of the doubly-fed induction generator before a fault occurs; Δθ s The change in stator voltage phase angle; Δθ pllThe phase-locked loop (PLL) subsystem outputs the phase-locked angle change at the port; Δu qs This represents the instantaneous change in the q-axis output voltage of the doubly-fed induction generator (DFIG).

[0163] Mathematical model of the stator and rotor d-shaft subsystem of a thermal power unit considering armature reaction:

[0164]

[0165] Among them, T″ q0 、T′ q0 Let ΔE' represent the subtransient time constant and transient time constant of the generator rotor q-axis, respectively. d , ΔE” d The changes in port voltage and current of the stator and rotor d-axis subsystems of the thermal power unit, considering armature reaction, are determined through simulation; x″ q 、x′ q x q H represents the subtransient reactance, transient reactance, and synchronous reactance of the generator rotor q-axis, respectively, all of which are known quantities; THE_X1 H THE_Y1 Interaction with other subsystems; ΔI q This represents the instantaneous change in the q-axis value of the stator current of the synchronous generator.

[0166] Mathematical model of the stator-rotor q-shaft subsystem of a thermal power unit considering armature reaction:

[0167]

[0168] Among them, T″ d0 、T′ d0 Let ΔE' represent the subtransient time constant and transient time constant of the generator rotor d-axis, respectively. q , ΔE” q The changes in port voltage and current of the stator and rotor q-shaft subsystems of a thermal power unit, considering armature reaction, are determined through simulation; x″ d 、x′ d x d H represents the subtransient reactance, transient reactance, and synchronous reactance of the generator rotor d-axis, respectively, all of which are known quantities; THE_X2 H THE_Y2 For interaction with other subsystems; ΔE fd This represents the change in stator excitation electromotive force.

[0169] Mathematical model of primary frequency regulation subsystem of thermal power unit considering DC limiting:

[0170]

[0171] Where, Δx FThe state variable is obtained from the integral element in the PI circuit of the primary frequency regulation subsystem of the thermal power unit considering DC limiting; Δf represents the port frequency change of the primary frequency regulation subsystem of the thermal power unit considering DC limiting, obtained through simulation; K pr_FES and K ir_FES f represents the proportional and integral coefficients of the PI controller in DC limiting control, both of which are known quantities. H , where is the dead zone value of DC limiting control, and is a known quantity; D is the damping coefficient of the thermal power unit, and is a known quantity; R is the droop coefficient of the thermal power unit speed governor, and is a known quantity; H THE_X3 H THE_Y3 For interaction with other subsystems; u ar The effective value of the AC voltage on the rectifier side is obtained through measurement; α r0 The steady-state firing angle of the rectifier side during steady-state operation of the sending-end system is obtained through simulation; Δα r x is the change in firing angle; sr The commutation reactance on the rectifier side is a known quantity; Δi dr i represents the instantaneous change in the output current of the doubly-fed wind turbine rotor along the d-axis; dr0 The steady-state value of the d-axis output current of the doubly-fed wind turbine rotor before a fault occurs; u dr0 Steady-state value of DC voltage on the rectifier side of a traditional DC transmission system before a fault occurs.

[0172] Mathematical model of the excitation subsystem of thermal power unit:

[0173]

[0174] Wherein, ΔU X The state variable ΔU is obtained from the integral element in the PI circuit of the excitation subsystem of a thermal power unit. C K represents the change in port voltage of the excitation subsystem of a thermal power unit. d These are the control parameters corresponding to the ideal transformer in the excitation subsystem; K pr_EXS and K ir_EXS The proportional and integral coefficients of the PI controller in primary frequency regulation control are known quantities; T A H represents the time constant of the inertial element in primary frequency control, and is a known quantity; THE_X4 H THE_Y4 This is for interaction with other subsystems.

[0175] Mathematical model of the rectifier subsystem of a traditional DC transmission system:

[0176]

[0177] Where, Δα r ΔI drK represents the changes in firing angle and DC current of the rectifier-side subsystem in a traditional DC transmission system, obtained through simulation; pr_FCC K ir_FCC K represents the proportional-integral parameters of the PI controller in the constant current control loop, which are known quantities. mr The equivalent gain of the rectifier-side current measurement module is ΔU, which is a known quantity. d ΔI represents the change in voltage across the equivalent capacitance of a DC line to ground. dcref R is the change in the current command value of the constant current control loop, which is a known quantity. d L d X represents the equivalent resistance and inductance of a DC line to ground, which are known quantities. sr U is the commutation reactance on the rectifier side, which is a known quantity; ar The effective value of the AC voltage on the rectifier side is determined through simulation; T mr H is the time constant of the rectifier-side current measurement module, which is a known quantity; HVDC_X1 H HVDC_Y1 For interaction with other subsystems; ΔI drm ΔI is the change in the rectified DC current obtained after passing through the inertial acquisition element. drm =(k mr / (1+sT mr ))ΔI dr ;k mr To collect the proportional constant of the inertial element; T mr This is the time constant of the inertial element in the measurement module.

[0178] Mathematical model of the inverter side and DC line subsystem of a traditional DC transmission system:

[0179]

[0180] Wherein, ΔU d ΔI di These represent the changes in DC voltage and DC current on the inverter side and DC line subsystem of a traditional DC transmission system, respectively; Δγ and ΔI. di ΔI represents the arc extinction angle and DC current change of the inverter-side subsystem in a traditional DC transmission system, respectively. dr ΔU represents the change in DC current on the rectifier side of a traditional DC transmission system. d R represents the change in voltage across the equivalent capacitance of a DC line to ground. d x is the equivalent resistance of a DC line to ground; si For the inverter side equivalent commutation reactance; u ai γ0 is the effective value of the AC voltage on the inverter side; γ0 is the steady-state arc extinction lead angle; H HVDC_X2 H HVDC_Y2 This is for interaction with other subsystems.

[0181] Mathematical model of traditional high-voltage direct current transmission AC filter subsystem:

[0182]

[0183] Where, Δu c , Δi ar1 The values ​​represent the changes in filter capacitor voltage and AC current in a traditional HVDC transmission AC filter subsystem, respectively, obtained through simulation; C f For filtering capacitors; R1 and L1 are the equivalent resistance and inductance of the rectifier side AC line, respectively; Δu ar The AC voltage change of the rectifier-side converter is obtained from simulation; Δi ar2 H represents the change in AC current of the filter, obtained through simulation. HVDC_X3 H HVDC_Y3 This is for interaction with other subsystems.

[0184] S222. Based on the data models of each subsystem in S221, construct the corresponding dynamic energy model.

[0185] Specifically, the dynamic energy models include: energy models of the stator d-axis and q-axis subsystems of wind turbine generators, energy models of the PLL subsystem, energy models of the rotor d-axis and q-axis subsystems of doubly-fed wind turbine generators, energy models of the stator and rotor d-axis and q-axis subsystems of thermal power generators, energy models of the primary frequency regulation subsystem of thermal power generators considering DC limiting, energy models of the excitation subsystem of thermal power generators, energy models of the rectifier side subsystem of traditional high-voltage direct current transmission, energy models of the inverter side and DC line subsystem of traditional high-voltage direct current transmission, and energy models of the AC filter subsystem of traditional high-voltage direct current transmission.

[0186] Furthermore, the dynamic energy models of the above twelve subsystems all consist of three parts: stored energy, dissipated energy, and interactive energy, as shown in formula (13):

[0187]

[0188] Where, ΔV s The change in energy stored in each subsystem, ΔV d Let ΔV be the change in energy dissipated by the subsystem. t K represents the change in energy interaction between subsystems. a K b All coefficients are greater than 0; R k L k C k These represent the equivalent resistance, equivalent inductance, and equivalent capacitance in the subsystem, respectively; ΔU and ΔI represent the instantaneous changes in the output voltage and current at the subsystem ports, respectively. Where K... a K bFor setting values, they are generally set to values ​​greater than 0 and not exceeding 10. ΔU and ΔI represent the changes in output voltage and output current of each subsystem. For example, when calculating the interactive energy flowing from the stator d-axis subsystem of a doubly-fed wind turbine to the stator q-axis subsystem, ΔU and ΔI are the changes in output voltage and current of the d-axis system, Δu. ds , Δi ds .

[0189] S23. Simulation is performed based on the steady-state value, instantaneous value, and dynamic energy model of each subsystem.

[0190] Specifically, the real-time simulation environment RT-LAB was used to simulate the offshore new energy transmission system via DC.

[0191] During simulation, known parameters of the system are set, and the system's operating status before and after the fault is simulated based on the instantaneous changes in the values ​​of each operating parameter.

[0192] Furthermore, the instantaneous changes in the values ​​of each operating parameter are calculated based on their steady-state values ​​before the fault and their instantaneous values ​​after the fault. See formula (14):

[0193]

[0194] Where, Δi dpcc Δi represents the instantaneous change in the d-axis output current at the grid connection point of the doubly-fed induction generator (DFIG). qpcc Δu represents the instantaneous change in the q-axis output current at the grid connection point of the doubly-fed induction generator (DFIG). ds Δu represents the instantaneous change in the output voltage of the stator d-axis of the doubly-fed induction generator (DFIG). qs Δi represents the instantaneous change in the q-axis output voltage of the doubly-fed induction generator stator; ds Δi represents the instantaneous change in the output current of the stator d-axis of the doubly-fed induction generator (DFIG). qs Δi represents the instantaneous change in the q-axis output current of the doubly-fed induction generator stator; dr Δi represents the instantaneous change in the output current of the doubly-fed induction generator rotor along the d-axis. qr Δi represents the instantaneous change in the output current of the q-axis rotor of the doubly-fed wind turbine. dg Δi represents the instantaneous change in the d-axis output current of the doubly-fed induction generator (DFIG) grid-side converter. qg ΔE represents the instantaneous change in the q-axis output current of the doubly-fed induction generator (DFIG) grid-side converter. fd ΔI is the instantaneous change in the excitation electromotive force of the synchronous generator. d ΔI represents the instantaneous change in the d-axis value of the stator current of the synchronous generator. q ΔI represents the instantaneous change in the q-axis value of the stator current of the synchronous generator. dr ΔI represents the instantaneous change in DC current on the rectifier side of a traditional DC transmission system. diΔu represents the instantaneous change in DC current on the inverter side of a traditional DC transmission system. dr This refers to the instantaneous change in DC voltage on the rectifier side of a traditional DC transmission system.

[0195] S24. Calculate the rate of change of interactive energy of each subsystem based on the simulation results.

[0196] Specifically, the calculation formulas for the interaction energy change rate of the doubly fed wind turbine, thermal power unit and traditional high voltage DC transmission system are derived according to formulas (1)-(13). The instantaneous value change of each operating parameter calculated by formula (14) and the relevant operating parameter values ​​obtained by simulation are substituted into each calculation formula to obtain the interaction energy change rate of each subsystem.

[0197] The formula for calculating the rate of change of interactive energy in the doubly fed wind turbine subsystem is as follows:

[0198]

[0199] in, The rate of change of interactive energy in the doubly fed wind turbine subsystem;

[0200] Δi dpcc and Δi qpcc These are the instantaneous changes in the d-axis output current at the grid connection point of the doubly-fed induction generator (DFIG) and the instantaneous changes in the q-axis output current at the grid connection point of the DFIG, respectively.

[0201] ω s This indicates the synchronous operating angular velocity of the doubly-fed wind turbine unit;

[0202] Δu ds and Δu qs These are the instantaneous changes in the output voltage of the stator d-axis and the instantaneous changes in the output voltage of the stator q-axis of the doubly-fed induction generator, respectively.

[0203] L s The inductance of the equivalent two-phase stator winding in the dq coordinate system of a doubly fed wind turbine;

[0204] L r The inductance of the equivalent two-phase rotor winding in the dq coordinate system of the doubly fed wind turbine;

[0205] L m The equivalent mutual inductance between the stator and rotor windings on the same coordinate axis;

[0206] ω c It is the slip angular velocity;

[0207] Δi qs and Δi ds These are the instantaneous changes in the q-axis output current of the doubly-fed induction generator stator and the instantaneous changes in the d-axis output current of the doubly-fed induction generator stator, respectively.

[0208] R r The resistance of the equivalent two-phase rotor winding in the dq coordinate system of the doubly fed wind turbine;

[0209] Δi dr Δi represents the instantaneous change in the output current of the doubly-fed induction generator rotor along the d-axis. qr This represents the instantaneous change in the output current of the q-axis rotor of the doubly-fed wind turbine.

[0210] ω r This indicates the angular velocity of the rotor of a doubly-fed wind turbine.

[0211] Δu dr This refers to the instantaneous change in DC voltage on the rectifier side of a traditional DC transmission system.

[0212] Δu qr The instantaneous change in the output current of the q-axis of the doubly-fed fan rotor;

[0213] k pll_d and k pll_q These are the proportional coefficients of the phase-locked loop;

[0214] Δθ pll The phase-locked loop subsystem outputs the phase-locked angle change at its port;

[0215] C pll =1 / k pll_i k pll_i These are the integral coefficients of the phase-locked loop;

[0216] Δω pll The change in angular frequency output at the PLL subsystem port;

[0217] K i1_POL The integral coefficient of the d-axis PI controller in the power outer loop control;

[0218] K p1_POL This refers to the proportional coefficient of the d-axis PI controller in the power outer loop control.

[0219] ΔP ref This indicates the change in the active power command value;

[0220] Δx1 is the instantaneous change in the port voltage of the rotor d-axis subsystem of the doubly-fed wind turbine.

[0221] Δx2 is the change in port voltage of the rotor q-shaft subsystem of the doubly-fed wind turbine.

[0222] u qs0 This represents the steady-state value of the stator q-axis output voltage of the doubly fed wind turbine before a fault occurs.

[0223] i qs0This represents the steady-state value of the stator q-axis output current of the doubly fed wind turbine before a fault occurs.

[0224] Δθ s This refers to the change in the phase angle of the stator voltage.

[0225] i ds0 This represents the steady-state value of the stator d-axis output current of the doubly fed wind turbine before a fault occurs.

[0226] u ds0 This represents the steady-state value of the stator d-axis output voltage of the doubly fed wind turbine before a fault occurs.

[0227] K p2_POL and K i2_POL These are the proportional and integral coefficients of the q-axis PI controller in the power outer loop control, respectively.

[0228] ΔQ ref This represents the change in the reactive power command value.

[0229] The formula for calculating the rate of change of interactive energy of the thermal power component system is as follows:

[0230]

[0231] in, The rate of change of interactive energy in the thermal power unit component system;

[0232] T″ q0 、T′ q0 These represent the subtransient time constant and transient time constant of the q-axis of the thermal power unit, respectively;

[0233] x″ q 、x′ q x q These represent the subtransient reactance, transient reactance, and synchronous reactance of the generator rotor q-axis, respectively.

[0234] ΔI q This represents the instantaneous change in the q-axis value of the stator current of the synchronous generator.

[0235] ΔE′ d , ΔE″ d The changes in port voltage and current of the stator and rotor d-axis subsystems of the thermal power unit, which take into account armature reaction, are determined through simulation.

[0236] T″ d0 、T′ d0 These represent the subtransient time constant and transient time constant of the generator rotor d-axis, respectively.

[0237] ΔE fd x″ represents the change in stator excitation electromotive force. d 、x′ d xd These represent the subtransient reactance, transient reactance, and synchronous reactance of the generator rotor d-axis, respectively.

[0238] ΔI d This represents the instantaneous change in the d-axis value of the stator current of the synchronous generator.

[0239] ΔE' q , ΔE” q The changes in port voltage and current of the stator and rotor q-shaft subsystems of the thermal power unit, which take into account armature reaction, are determined through simulation.

[0240] K pr_FES and K ir_FES These are the proportional and integral coefficients of the PI controller in DC limiting control.

[0241] K ir_EXS The integral coefficient of the PI controller in primary frequency modulation control;

[0242] K d These are the control parameters corresponding to the ideal transformer in the excitation subsystem;

[0243] ΔU C This indicates the change in port voltage of the excitation subsystem of a thermal power unit;

[0244] f H This is the dead zone value for DC limiting control;

[0245] Δx F The state variables are obtained from the integral element in the PI element of the primary frequency regulation subsystem of a thermal power unit, taking into account DC limiting.

[0246] u ar The effective value of the AC voltage on the rectifier side was determined through simulation.

[0247] α r0 This refers to the steady-state firing angle of the rectifier side during steady-state operation of the sending-end system.

[0248] Δα r The steady-state firing angle change on the rectifier side during steady-state operation of the sending-end system is determined through simulation;

[0249] x sr This refers to the commutation reactance on the rectifier side;

[0250] Δi dr This represents the instantaneous change in the output current of the d-axis rotor of the doubly-fed wind turbine.

[0251] i dr0 This represents the steady-state value of the d-axis output current of the doubly fed wind turbine rotor before a fault occurs.

[0252] u dr0Steady-state value of DC voltage on the rectifier side of a traditional DC transmission system before a fault occurs;

[0253] Δf represents the frequency change at the port of the primary frequency regulation subsystem of the thermal power unit, taking into account DC limiting, and is determined through simulation.

[0254] The formula for calculating the rate of change of interactive energy in the traditional high-voltage direct current transmission subsystem is as follows:

[0255]

[0256] in, The rate of change of interactive energy in a traditional high-voltage direct current transmission subsystem;

[0257] u ar AC voltage measurement for the rectifier-side converter;

[0258] α r0 The steady-state value of the firing angle of the rectifier-side subsystem in a traditional DC transmission system was determined through simulation.

[0259] K pr_FCC K ir_FCC These are the proportional-integral parameters of the PI controller in the constant current control loop.

[0260] ΔI dcref The change in the current command value of the constant current control loop;

[0261] T mr The time constant of the rectifier-side current measurement module;

[0262] K mr Equivalent gain of the rectifier-side current measurement module;

[0263] ΔI drm This represents the change in the rectified DC current obtained after passing through the acquisition inertial circuit.

[0264] Δα r This represents the change in firing angle of the rectifier-side subsystem in a traditional DC transmission system.

[0265] ΔU d This refers to the DC voltage variation on the inverter side and DC line subsystem of a traditional DC transmission system.

[0266] ΔI dr This refers to the instantaneous change in the DC current on the rectifier side of a traditional DC transmission system.

[0267] u ai This is the effective value of the AC voltage on the inverter side;

[0268] γ0 is the steady-state arc extinction advance angle;

[0269] Δγ is the arc extinction angle of the inverter-side subsystem in a traditional DC transmission system;

[0270] ΔI di This represents the change in DC current in the inverter-side subsystem of a traditional DC transmission system.

[0271] Δi ar2 The change in AC current of the filter is determined through simulation.

[0272] Δu c , Δi ar1 These represent the changes in filter capacitor voltage and AC current in a traditional high-voltage direct current transmission AC filter subsystem, respectively.

[0273] Δu ar The change in AC voltage of the rectifier-side converter is determined through simulation.

[0274] S25. Determine the key parameters affecting system stability based on the rate of change of each interaction energy.

[0275] The corresponding interaction stability factor is obtained by calculating the derivative of the rate of change of interaction energy with respect to each control parameter; the derivative λ of the rate of change of interaction energy with respect to the control parameters is then used as the basis for the stability factor. i j Defined as the interaction stability factor, as follows:

[0276]

[0277] The sign of the interaction stability factor is used as a criterion for judging the impact of key control elements on system stability. Here, i represents the subsystem number. denoted as , where is the rate of change of the interaction energy of the corresponding subsystem; and j is the corresponding control parameter.

[0278] Furthermore, based on the values ​​of each interaction stability factor, the key parameters affecting system stability are determined:

[0279] When the interaction stability factor is negative, that is This is beneficial to system stability, and the corresponding control parameters are determined to be the key parameters that affect the system.

[0280] When the interaction stability factor is zero, The control parameters are not critical parameters and are independent of the system stability level.

[0281] When the interaction stability factor is positive This is detrimental to system stability, and the corresponding control parameters are not critical parameters.

[0282] In the combined wind and thermal power DC transmission system, doubly-fed wind turbines, thermal power units, and high-voltage DC transmission systems all have key control links that play an important role in stability. These links will be analyzed one by one below.

[0283] Impact of key parameters of the outer power loop of doubly-fed wind turbine on system stability:

[0284] During fault ride-through, considering the regulating effect of the power outer loop in the unsaturated state, we have:

[0285]

[0286] i qr_ref and i dr_ref These are the reference values ​​for the rotor current along the q-axis and d-axis, respectively; U s P is the stator voltage; s0_ref k represents the active power command value of the first-order lag element in the power outer loop control. ds_POL P is the proportional coefficient of the first-order lag element in the power outer loop control; select P s0_ref and k ds_POL The key parameters for the power outer loop are:

[0287]

[0288] Analyzing the above equation, after the N-2 fault occurs, we have cosΔθ pll >0, Δu qr <0, Δi qr <0, then we have Explanation of k ds_POL Increase As it increases, it becomes detrimental to system stability; sinΔθ pll Δu dr >0, Δi dr <0, and |k p_CIL sinΔθ pll Δu dr |<<|Δi dr |, then we have Explanation P s0_ref Increase This reduction is beneficial to system stability.

[0289] The impact of key parameters of the phase-locked loop (PLL) of a doubly-fed wind turbine on system stability:

[0290] Key parameters for phase-locked loop (PLL) control: proportional coefficient k pll_p and integral coefficient k pll_i ,have:

[0291]

[0292]

[0293] Analyzing the above formula, after the N-2 fault occurs, Explanation of k pll_p The change is independent of system stability; Δi pll <0,k pll_d Δu dr +k pll_q Δu qr <0, then we have Explanation of k pll_i Increase This reduction is beneficial to system stability.

[0294] The impact of key parameters of the excitation system of thermal power units on system stability:

[0295] Selection of key parameters for the excitation system: Integral coefficient K of the excitation system control loop ir_EXS ,have:

[0296]

[0297] Analyzing the above formula, after the N-2 fault occurs, it is obvious that... Explanation K ir_EXS Increase This reduction is beneficial to system stability.

[0298] The impact of key parameters of the primary frequency regulation system of thermal power units on system stability:

[0299] Key parameter selection for primary frequency regulation system: Proportional coefficient K in the control loop of the primary frequency regulation system pr_FES and integral coefficient K ir_FES ,have:

[0300]

[0301] Analyzing the above formula, after the N-2 fault occurs, Δx F If > 0, then we have Explanation K ir_FES Increase As the value decreases, it improves system stability; if Δf < 0, then... Explanation K pr_FES Increase This increase is detrimental to system stability.

[0302] The impact of key parameters of high-voltage direct current transmission systems on system stability:

[0303] Selection of key parameters for high-voltage direct current transmission systems: Proportional coefficient K of the rectifier-side constant current control circuit. pr_FCC and integral coefficient K ir_FCC ,have:

[0304]

[0305] Analyzing the above formula, after the N-2 fault occurs, Δi drm <0, Δα r <0, ΔU d <0, Δi dr <0, then we have Explanation K pr_FCC Increase This decrease is beneficial to system stability; ΔI dcref If ≈0, then we have Explanation K ir_FCC It has little impact on system stability.

[0306] In summary, after a fault occurs, the active power command value P of the first-order lagging element in the outer loop control of the doubly-fed induction generator (DFIG) should be increased. s0_ref Increase the proportional coefficient k of the phase-locked loop pll_p Increase the integral coefficient K of the excitation system control link. ir_EXS Increase the proportional coefficient K of the primary frequency regulation system control link. ir_FES and reduce the integral coefficient K ir_FES Increase the proportional coefficient K of the rectifier side constant current control circuit. pr_FCC It is beneficial to system stability.

[0307] The key parameters to be determined include the active power command value of the first-order lagging element in the power outer loop control of the doubly fed wind turbine, the proportional coefficient of the phase-locked loop, the integral coefficient of the excitation system control element, the proportional / integral coefficient of the primary frequency regulation system control element, and the proportional coefficient of the rectifier side constant current control element.

[0308] S3. Based on the key parameters, issue the corresponding instructions to the control center of the DC transmission system.

[0309] Specifically, based on the key parameters determined in step S25, the values ​​of each parameter are adjusted sequentially according to the order of active power command value, proportional coefficient of rectifier side constant current control loop, proportional coefficient of phase-locked loop, integral coefficient of excitation system control loop, and proportional / integral coefficient of primary frequency regulation system control loop. The corresponding command is set according to the parameter values ​​obtained from simulation to keep the system stable, and the command is sent to the control center of the DC transmission system.

[0310] In this embodiment, the DC transmission system is divided into multiple subsystems, and mathematical models are constructed for each subsystem to calculate the interaction energy between them, thus improving the calculation accuracy. The rate of change of interaction energy between each subsystem is obtained through simulation and calculation, and analyzed to quickly and effectively assess the stability of the combined wind and fire DC transmission system. The interaction stability factor index provided by the interaction energy change rate calculation module determines the key system parameters, providing a basis for issuing system commands and ensuring reliable system operation.

[0311] Simulation Examples

[0312] In one specific embodiment of the present invention, a simulation process of a wide-area security protection method for a marine new energy transmission system via DC is disclosed.

[0313] Specifically, a simulation environment was built to simulate the operation of a marine renewable energy transmission system via DC. The rated power of the DC end of the system is 8000MW, and the voltage level is ±800kV. When an N-2 fault occurs in the DC transmission system, the DC transmission loses electrical connection with the AC power grid, and the local power plant and the DC transmission system enter a state of operation supported by the main power grid. The main system parameters are shown in Table 1.

[0314] Table 1 Key parameters of the simulation system

[0315]

[0316]

[0317] The simulation scenario involves cutting off the electrical connection between the AC power grid and the converter station at a specific moment to simulate an N-2 fault in the DC transmission system. Furthermore, the energy distribution of the offshore renewable energy DC transmission system under this fault scenario is analyzed.

[0318] The stability of key control components of the offshore renewable energy DC transmission system under fault scenarios is analyzed separately, such as... Figures 4-8 As shown.

[0319] Figure 4 This indicates the impact of key parameters of the outer power loop of a doubly-fed wind turbine on system stability. Figure 5 This indicates the impact of key parameters of the phase-locked loop (PLL) of a doubly-fed wind turbine on system stability. Figure 6 This indicates the impact of key parameters of the excitation system of thermal power units on system stability; Figure 7 This indicates the impact of key parameters of the primary frequency regulation system of a thermal power unit on system stability; Figure 8 This indicates the impact of key parameters of a high-voltage direct current transmission system on system stability;

[0320] Depend on Figure 4 It can be seen that after the N-2 fault occurs, the rate of change of the interactive energy in the outer loop of the doubly-fed wind turbine is greater than zero and fluctuates significantly, indicating that this control element has a significant impact on system stability. The rate of change of this energy varies with the proportional coefficient k of the first-order lag element in the outer loop of the power turbine. ds_POL It increases with the increase of the active power command value P. s0_ref It decreases as it increases.

[0321] Depend on Figure 5It can be seen that after the N-2 fault occurs, the energy change rate of the doubly-fed wind turbine's phase-locked loop is greater than zero and the amplitude is small, indicating that this control loop has little impact on system stability. This energy change rate varies with the proportional coefficient k. pll_p The value remains constant as the integral coefficient k increases. pll_i It decreases as it increases.

[0322] Depend on Figure 6 It can be seen that after the N-2 fault occurs, the rate of change of interactive energy in the thermal power unit's excitation system is less than zero and the amplitude is small, indicating that this control element has little impact on system stability. This energy change rate varies with the integral coefficient K. ir_EXS It decreases as it increases.

[0323] Depend on Figure 7 It can be seen that after the N-2 fault occurred, the rate of change of interactive energy in the primary frequency regulation system of the thermal power unit was less than zero and the amplitude was large, indicating that this control link had a significant impact on system stability. This energy change rate varies with the integral coefficient K. ir_FES It decreases as the proportionality coefficient K increases. pr_FES It increases as it increases.

[0324] Depend on Figure 8 It can be seen that after the N-2 fault occurs, the rate of change of interactive energy in the HVDC transmission system is less than zero and has a large amplitude, indicating that this control element has a significant impact on system stability. This rate of change of energy varies with the proportional coefficient K of the constant current control element. pr_FCC It decreases as the integral coefficient K increases. ir_FCC The value increases but remains unchanged.

[0325] In this embodiment, based on the interaction stability factor, it is determined that increasing k... p_CIL k ds_POL and K ir_FES Increasing P is detrimental to system stability. s0_ref and K pr_FCC This is beneficial for system stability. When an N-2 fault occurs at the system's sending end, control commands are issued to the system based on the parameter values ​​determined through simulation, and the parameters are adjusted in real time to ensure stable system operation.

[0326] System Implementation Examples

[0327] Another specific embodiment of the present invention discloses a wide-area safety protection system for a marine new energy transmission system via DC, including a data acquisition module, a system simulation module, and a command issuance module.

[0328] The data acquisition module is used to collect the steady-state values ​​of multiple operating parameters of the DC transmission system before a fault occurs and the instantaneous values ​​after a fault occurs;

[0329] The system simulation module is used to simulate the DC transmission system based on the steady-state value and the instantaneous value, and to determine the key parameters affecting the system stability;

[0330] The instruction issuing module is used to issue corresponding instructions to the control center of the DC transmission system based on the key parameters.

[0331] Compared with the prior art, the beneficial effects of the wide-area safety protection system for marine new energy transmission via DC transmission provided in this embodiment are basically the same as those provided in the method embodiment, and will not be described in detail here.

[0332] It should be noted that the above embodiments are based on the same inventive concept, and any parts not described repeatedly can be referenced from each other.

[0333] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A wide-area safety control method for a marine new energy transmission system via DC, characterized in that, Includes the following steps: Collect the steady-state values ​​of multiple operating parameters of the DC transmission system before the fault occurs and the instantaneous values ​​after the fault occurs; The DC transmission system is simulated based on the steady-state and instantaneous values ​​to determine the key parameters affecting system stability. Based on the key parameters, corresponding instructions are sent to the control center of the DC transmission system.

2. The method for wide-area security protection of a marine new energy transmission system via DC as described in claim 1, characterized in that, The DC transmission system includes a doubly-fed wind turbine subsystem, a thermal power unit subsystem, and a traditional high-voltage DC transmission subsystem; the simulation of the DC transmission system based on the steady-state values ​​and the instantaneous values ​​determines the key parameters affecting system stability, including: The DC transmission system is divided into multiple subsystems. Construct dynamic energy models for each subsystem; Simulations are performed based on the steady-state values, instantaneous values, and dynamic energy models of each subsystem. The rate of change of interactive energy of each subsystem is calculated based on the simulation results. The key parameters affecting system stability are determined based on the rate of change of each interaction energy.

3. The method for wide-area security protection of marine new energy transmission systems via DC transmission according to claim 2, characterized in that, The process of dividing the collected DC transmission system into multiple subsystems includes: The doubly fed wind turbine subsystem is divided into a rotor-side subsystem, a stator-side subsystem, and a phase-locked loop subsystem. The thermal power unit system is divided into a stator and rotor subsystem that takes armature reaction into account, a primary frequency regulation subsystem that takes DC limiting into account, and a thermal power unit excitation subsystem. The traditional high-voltage direct current (HVDC) transmission subsystem is divided into the traditional HVDC rectifier side subsystem, the traditional HVDC inverter side and DC line subsystem, and the traditional HVDC AC filter subsystem.

4. The wide-area security protection method for a marine new energy transmission system via DC as described in claim 3, characterized in that, The key parameters affecting system stability determined based on the rate of change of interactive energy include: The corresponding interaction stability factor is obtained by calculating the derivative of the rate of change of each interaction energy with respect to each control parameter; Based on the values ​​of each interaction stability factor, the key parameters affecting system stability are determined: When the interaction stability factor is negative, it is beneficial to system stability. The corresponding control parameters are determined as the key parameters that affect the system. When the interaction stability factor is zero, it is unrelated to the system stability level, and the corresponding control parameter is not a critical parameter. When the interaction stability factor is positive, it is not conducive to system stability, and the corresponding control parameters are not critical parameters.

5. The method for wide-area security protection of a marine new energy transmission system via DC as described in claim 4, characterized in that, The steady-state values ​​of multiple operating parameters of the DC transmission system before the fault occurred and the instantaneous values ​​after the fault occurred include: The system collects the steady-state values ​​of the following operating parameters before and after a fault: d-axis and q-axis output current of the doubly-fed induction generator (DFIG) at the grid connection point; d-axis and q-axis output voltage of the DFIG stator; d-axis and q-axis output current of the DFIG stator; d-axis and q-axis output current of the DFIG rotor; d-axis and q-axis output current of the DFIG grid-side converter; magnetomotive force of the synchronous generator; d-axis and q-axis current of the synchronous generator stator; DC current on the rectifier side of the conventional DC transmission system; DC current on the inverter side of the conventional DC transmission system; and DC voltage on the rectifier side of the conventional DC transmission system.

6. The method for wide-area security protection of a marine new energy transmission system via DC as described in claim 5, characterized in that, The formula for calculating the rate of change of interactive energy in the doubly fed wind turbine subsystem is as follows: in, The rate of change of interactive energy in the doubly fed wind turbine subsystem; Δi dpcc and Δi qpcc These are the instantaneous changes in the d-axis output current at the grid connection point of the doubly-fed induction generator (DFIG) and the instantaneous changes in the q-axis output current at the grid connection point of the DFIG, respectively. ω s This indicates the synchronous operating angular velocity of the doubly-fed wind turbine unit; Δu ds and Δu qs These are the instantaneous changes in the output voltage of the stator d-axis and the instantaneous changes in the output voltage of the stator q-axis of the doubly-fed induction generator, respectively. L s The inductance of the equivalent two-phase stator winding in the dq coordinate system of a doubly fed wind turbine; L r The inductance of the equivalent two-phase rotor winding in the dq coordinate system of the doubly fed wind turbine; L m The equivalent mutual inductance between the stator and rotor windings on the same coordinate axis; ω c It is the slip angular velocity; Δi qs and Δi ds These are the instantaneous changes in the q-axis output current of the doubly-fed induction generator stator and the instantaneous changes in the d-axis output current of the doubly-fed induction generator stator, respectively. R r The resistance of the equivalent two-phase rotor winding in the dq coordinate system of the doubly fed wind turbine; Δi dr Δi represents the instantaneous change in the output current of the doubly-fed induction generator rotor along the d-axis. qr This represents the instantaneous change in the output current of the q-axis rotor of the doubly-fed wind turbine. ω r This indicates the angular velocity of the rotor of a doubly-fed wind turbine. Δu dr This refers to the instantaneous change in DC voltage on the rectifier side of a traditional DC transmission system. Δu qr The instantaneous change in the output current of the q-axis of the doubly-fed fan rotor; k pll_d and k pll_q These are the proportional coefficients of the phase-locked loop; Δθ pll The phase-locked loop subsystem outputs the phase-locked angle change at its port; C pll =1 / k pll_i k pll_i These are the integral coefficients of the phase-locked loop; Δω pll The change in angular frequency output at the PLL subsystem port; K i1_POL The integral coefficient of the d-axis PI controller in the power outer loop control; K p1_POL This refers to the proportional coefficient of the d-axis PI controller in the power outer loop control. ΔP ref This indicates the change in the active power command value; Δx1 is the state variable of the integral link in the outer loop PI controller of the rotor d-axis power of the doubly-fed wind turbine. Δx2 is the state variable of the integral link in the outer loop PI controller of the rotor q-axis power of the doubly-fed wind turbine. u qs0 This represents the steady-state value of the stator q-axis output voltage of the doubly fed wind turbine before a fault occurs. i qs0 This represents the steady-state value of the stator q-axis output current of the doubly fed wind turbine before a fault occurs. Δθ s This refers to the change in the phase angle of the stator voltage. i ds0 This represents the steady-state value of the stator d-axis output current of the doubly fed wind turbine before a fault occurs. u ds0 This represents the steady-state value of the stator d-axis output voltage of the doubly fed wind turbine before a fault occurs. K p2_POL and K i2_POL These are the proportional and integral coefficients of the q-axis PI controller in the power outer loop control, respectively. ΔQ ref This represents the change in the reactive power command value.

7. The method for wide-area security protection of a marine new energy transmission system via DC as described in claim 5, characterized in that, The formula for calculating the rate of change of interactive energy of the thermal power component system is as follows: in, The rate of change of interactive energy in the thermal power unit component system; T″ q0 、T′ q0 These represent the subtransient time constant and transient time constant of the q-axis of the thermal power unit, respectively; x″ q 、x′ q x q These represent the subtransient reactance, transient reactance, and synchronous reactance of the generator rotor q-axis, respectively. ΔI q This represents the instantaneous change in the q-axis value of the stator current of the synchronous generator. ΔE′ d , ΔE″ d The changes in port voltage and current of the stator and rotor d-axis subsystems of the thermal power unit, which take into account armature reaction, are determined through simulation. T″ d0 、T′ d0 These represent the subtransient time constant and transient time constant of the generator rotor d-axis, respectively. ΔE fd x″ represents the change in stator excitation electromotive force. d 、x′ d x d These represent the subtransient reactance, transient reactance, and synchronous reactance of the generator rotor d-axis, respectively. ΔI d This represents the instantaneous change in the d-axis value of the stator current of the synchronous generator. ΔE' q , ΔE″ q The changes in port voltage and current of the stator and rotor q-shaft subsystems of the thermal power unit, which take into account armature reaction, are determined through simulation. K pr_FES and K ir_FES These are the proportional and integral coefficients of the PI controller in DC limiting control. K ir_EXS The integral coefficient of the PI controller in primary frequency modulation control; K d These are the control parameters corresponding to the ideal transformer in the excitation subsystem; ΔU C This indicates the change in port voltage of the excitation subsystem of a thermal power unit; f H This is the dead zone value for DC limiting control; Δx F The state variables are obtained from the integral element in the PI element of the primary frequency regulation subsystem of a thermal power unit, taking into account DC limiting. u ar The effective value of the AC voltage on the rectifier side was determined through simulation. α r0 This refers to the steady-state firing angle of the rectifier side during steady-state operation of the sending-end system. Δα r The steady-state firing angle change on the rectifier side during steady-state operation of the sending-end system is determined through simulation; x sr This refers to the commutation reactance on the rectifier side. Δi dr This represents the instantaneous change in the output current of the d-axis rotor of the doubly-fed wind turbine. i dr0 This represents the steady-state value of the d-axis output current of the doubly fed wind turbine rotor before a fault occurs. u dr0 Steady-state value of DC voltage on the rectifier side of a traditional DC transmission system before a fault occurs; Δf represents the frequency change at the port of the primary frequency regulation subsystem of the thermal power unit, taking into account DC limiting, and is determined through simulation.

8. The method for wide-area security protection of a marine new energy transmission system via DC as described in claim 5, characterized in that, The formula for calculating the rate of change of interactive energy in the traditional high-voltage direct current transmission subsystem is as follows: in, The rate of change of interactive energy in a traditional high-voltage direct current transmission subsystem; u ar AC voltage measurement for the rectifier-side converter; α r0 The steady-state value of the firing angle of the rectifier-side subsystem in a traditional DC transmission system was determined through simulation. K pr_FCC K ir_FCC These are the proportional-integral parameters of the PI controller in the constant current control loop. ΔI dcref The change in the current command value of the constant current control loop; T mr The time constant of the rectifier-side current measurement module; K mr Equivalent gain of the rectifier-side current measurement module; ΔI drm This represents the change in the rectified DC current obtained after passing through the acquisition inertial circuit. Δα r This represents the change in firing angle of the rectifier-side subsystem in a traditional DC transmission system. ΔU d This refers to the DC voltage variation on the inverter side and DC line subsystem of a traditional DC transmission system. ΔI dr This refers to the instantaneous change in the DC current on the rectifier side of a traditional DC transmission system. u ai This is the effective value of the AC voltage on the inverter side; γ0 is the steady-state arc extinction advance angle; Δγ is the arc extinction angle of the inverter-side subsystem in a traditional DC transmission system; ΔI di This represents the change in DC current in the inverter-side subsystem of a traditional DC transmission system. Δi ar2 The change in AC current of the filter is determined through simulation. Δu c , Δi ar1 These represent the changes in filter capacitor voltage and AC current in a traditional high-voltage direct current transmission AC filter subsystem, respectively. Δu ar The change in AC voltage of the rectifier-side converter is determined through simulation.

9. The method for wide-area security protection of a marine new energy transmission system via DC as described in claim 5, characterized in that, The determination of key parameters affecting system stability based on the rate of change of interactive energy also includes: The key parameters affecting system stability include the active power command value, the proportional coefficient of the rectifier side constant current control loop, the proportional coefficient of the phase-locked loop, the integral coefficient of the excitation system control loop, and the proportional / integral coefficient of the primary frequency regulation system control loop.

10. A wide-area safety protection system for a marine new energy transmission system via DC, characterized in that, include: The data acquisition module is used to collect the steady-state values ​​of multiple operating parameters of the DC transmission system before a fault occurs and the instantaneous values ​​after a fault occurs; The system simulation module is used to simulate the DC transmission system based on the steady-state value and the instantaneous value, and to determine the key parameters affecting the system stability; The instruction issuing module is used to issue corresponding instructions to the control center of the DC transmission system based on the key parameters.

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